Cellular Response to Tissue Hypoxia and Its Involvenment in Progression

8/17/2019 Cellular Response to Tissue Hypoxia and Its Involvenment in Progression

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Pathology International 2005; 55: 603–610

Blackwell Science, LtdOxford, UKPINPathology International1320-54632005 Japanese Society of PathologyOctober 200555106036 10Review ArticlePhysiology and pathology of hypoxiaE. Ikeda

Correspondence: Eiji Ikeda, MD, PhD, Department of Pathology,

Keio University School of Medicine, 35 Shinanomachi, Shinjuku-ku,

Tokyo 160-8582, Japan. Email: [email protected]

Received 18 April 2005. Accepted for publication 20 April 2005.

Review Article

Cellular response to tissue hypoxia and its involvement indisease progression

Eiji Ikeda

Department of Pathology, Keio University School of Medicine, Shinjuku-ku, Tokyo, Japan

Multicellular organisms show adaptive reactions for their

survival when they are exposed to an atmosphere with

reduced oxygen concentration. These reactions include

increase in respiratory volume, switch from aerobic to

anaerobic metabolism, erythropoiesis and angiogenesis.

For these reactions, cells must change the expression ofseveral hypoxia-responsive molecules such as erythropoi-

etin and vascular endothelial growth factor. Hypoxia-

responsible element (HRE) was delineated in the genes of

hypoxia-responsive molecules as the sequence indispens-

able for their hypoxia-induced transcriptional activation,

and hypoxia-inducible factor 1 (HIF-1) was identified as

a transcriptional factor that binds to HRE and regulates

the expression of various hypoxia-responsive molecules.

Increasing evidence has revealed that HIF-1 is a key mole-

cule regulating the cellular response to tissue hypoxia. HIF-

1 is composed of two subunits, HIF-1αααα and HIF-1ββββ, and

HIF-1 activity depends mainly on the intracellular level of

HIF-1αααα protein, which is regulated to be in inverse relationto the oxygen concentration by an oxygen-dependent

enzyme, prolyl hydroxylase 2 (PHD2). Thus, cells respond

to tissue hypoxia by sensing the oxygen concentration as

the enzyme activity of PHD2, regulating the HIF-1 activity

and consequently changing the expression of various

hypoxia-responsive molecules. Cellular response con-

trolled by hypoxia-HIF-1 cascade is also involved in patho-

logical situations such as solid tumor growth, diabetic

retinopathy and rheumatoid arthritis. Under these patholog-

ical situations, the activation of hypoxia-HIF-1 cascade

often leads to the acceleration of disease progression.

Understanding an aspect of disease progression triggered

by tissue hypoxia might provide a clue to new therapeutic

strategies for intractable diseases.

Key words: angiogenesis, diabetic retinopathy, disease pro-

gression, erythropoietin, HIF-1, hypoxia, rheumatoid arthritis,

tumor, ubiquitin, VEGF

Under physiological conditions, cells in multicellular organ-

isms utilize oxygen as the source of energy. Oxygen in the

air is taken into the body from lungs, and transported to

peripheral tissues by red blood cells. Oxygen supply insuffi-

cient for the need of tissues makes it difficult for the cells toperform adequate aerobic metabolism, resulting in the

impairment of their physiological functions. Severe hypoxia

causes necrosis of tissues, which might lead to the death of

an organism. Under hypoxic situations, organisms have sev-

eral reactions. For example, in the acute phase of hypoxic

stress, the cells change their metabolism from aerobic to

anaerobic states, and the organisms increase the respiratory

volume to take in a greater amount of oxygen from the atmo-

sphere. As chronic reactions, erythropoiesis as well as angio-

genesis into ischemic tissues are promoted. Both the

erythropoiesis and angiogenesis can improve the efficiency

of oxygen transportation to peripheral tissues. These reac-tions under hypoxia are thought to be acquired by organisms

during evolution in order to survive even if the oxygen con-

centration of the atmosphere is reduced due to unexpected

causes. However, it should be noted that these adaptive

reactions would be the cause of disease progression and

determine the prognosis of patients with solid tumors, dia-

betic retinopathy and rheumatoid arthritis. In this review, how

cells, tissues or organisms respond to hypoxic stimuli, and

how those hypoxia-induced reactions would lead to the accel-

eration of disease progression, are summarized, with refer-

ence to the remodeling of the vascular system under hypoxic

situations.

CELLULAR RESPONSE TO TISSUE HYPOXIA

The gene expression profile of cells under hypoxia differs

from that under normoxia, and the production of certain

growth factors, cytokines and enzymes is known to be con-

trolled by oxygen concentration in tissues.1 These molecules,

which can be called ‘hypoxia-responsive molecules’, include

erythropoietin (EPO),2 vascular endothelial growth factor

mailto:[email protected]:[email protected]


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604 E. Ikeda

(VEGF),3 tyrosine hydroxylase,4 phosphoglycerate kinase 1

and lactate dehydrogenase A,5 most of which are implicated

in adaptive processes of organisms to hypoxic circum-

stances, for example, erythropoiesis, angiogenesis, increase

in respiratory volume and switch of metabolism to an anaer-

obic state. Among these molecules, EPO and VEGF have

been intensively studied with regard to the molecular mech-anisms of their hypoxic induction, and the results have pro-

vided a valuable clue to the molecular background of cellular

response to hypoxia.

Mechanisms of hypoxia-induced expression of EPO

EPO was originally recognized as a hormone to stimulate

erythroid progenitor cells to promote erythropoiesis.2 Recent

studies have revealed a broad range of EPO functions, which

are not confined to erythropoiesis, and it is now accepted

that EPO is also involved in the proliferation, differentiationand anti-apoptosis of non-erythroid cells such as endothelial

cells, vascular smooth muscle cells, neurons and neuronal

progenitor cells.6 EPO is generated by the fetal liver during

development and the kidney after birth. Hep3B cells from

hepatocellular carcinoma, which can produce EPO in vitro ,

have been used to analyze the molecular mechanisms of

EPO expression.2,7 Expression of EPO is known to be con-

trolled by the oxygen concentration in the atmosphere, and

hypoxia stimulates the production of EPO through upregula-

tion of the transcription of the EPO gene. Through analyses

of the EPO gene, Wang and Semenza delineated a

sequence of the hypoxia-responsible element (HRE) in the3′-flanking region of the EPO gene that is essential for

hypoxia-induced transcriptional activation, and further identi-

fied the existence of a binding factor to the HRE, which is

designated hypoxia-inducible factor 1 (HIF-1).7 Binding of

HIF-1 to the HRE was shown to be inversely related to the

oxygen concentration around the cells. It was further demon-

strated that the binding of HIF-1 to the HRE sequence is also

enhanced in cells that do not produce EPO, implying the

general involvement of HRE and HIF-1 in the cellular

response to hypoxia that is not confined to the change in the

transcriptional rate of EPO gene.8

Involvement of HIF-1 in the hypoxia-induced expression

of VEGF

Angiogenesis is one of the important adaptive reactions to

restore the oxygen transport to ischemic tissues. It is true

that angiogenesis improves blood supply to focal tissues, but

the angiogenesis itself often becomes a trigger of disease

progression, which is later discussed in the present article.

Proliferation of blood vessels is determined by the balance

between angiogenic and antiangiogenic activities in the focal

tissues. Accumulated evidence has demonstrated that,

among the vasoactive molecules, VEGF is the central growth

factor controlling various physiological and pathological

angiogenesis, and therefore the formation of new blood

vessels depends mainly on the protein level of VEGF in

tissues.

9–11

The VEGF gene contains eight exons (exons 1–8), which

enables VEGF to have several isoforms by alternative splic-

ing, i.e. VEGF121, VEGF145, VEGF165, VEGF189 and VEGF206

in the human.10,11 Among these isoforms, major isoforms

expressed in various pathological situations such as solid

tumor growth, diabetic retinopathy and rheumatoid arthritis

are VEGF121, VEGF165 and VEGF189.10–13 The sequences

encoded by exons 6 and 7 are rich in basic amino acids, and

therefore confer high binding affinity to the extracellular

matrices as well as low diffusibility to VEGF189, which con-

tains the amino acids from both exons 6 and 7. In contrast

to VEGF189, VEGF121, which lacks the amino acids encodedby both exons 6 and 7, is highly diffusible in tissues.

VEGF165, which contains the amino acids encoded by exon

7 but not those by exon 6, has intermediate biochemical

properties between VEGF121 and VEGF189 in the context of

diffusibility in tissues.10,11 The difference in biochemical prop-

erties leads to the difference in biological properties between

the isoforms, and the involvement of VEGF in the progres-

sion of certain diseases is shown to be dependent on the

expression pattern of isoforms.12,13 As concerns the recep-

tors for VEGF, two high-affinity receptors, VEGFR-1 (Flt1)

and VEGFR-2 (KDR/Flk1), have been identified.10,11 In addi-

tion to these high-affinity receptors, neuropilin-1, which isoriginally known to be a factor regulating the formation of

synapses between neurons, was found to associate with

VEGFR-2 to form the isoform-specific receptor complex for

VEGF165.14

Similarly to EPO, the expression of VEGF is controlled by

oxygen concentration, and angiogenesis into hypoxic tissues

can be triggered by hypoxia-induced expression of

VEGF.9,15,16 Various types of in vitro cultured cells can pro-

duce VEGF in response to hypoxia. Analyses of the human

VEGF gene have revealed that the consensus binding site

for HIF-1 exists in the 5′-flanking region, and that the binding

of HIF-1 to the VEGF gene is indispensable for the transcrip-tional activation of VEGF by hypoxia.3,17 Thus, hypoxia-

induced expression of both EPO and VEGF is under the

control of HIF-1. Subsequently, the expression of various

hypoxia-responsive molecules other than EPO and VEGF is

also shown to be controlled by HIF-1, demonstrating that

HIF-1 is a key molecule to regulate the cellular response to

hypoxia.18–21

Through analyses of hypoxia-induced expression of VEGF,

it was also demonstrated that hypoxia can increase the

VEGF mRNA level by inhibiting the degradation of mRNA.3,22


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Physiology and pathology of hypoxia 605

As regards the mechanisms of VEGF mRNA stabilization,

the destabilizing sequences, together with the factors that

bind to those sequences in hypoxic cells to stabilize the

mRNA, have been reported in 5′-untranslated, coding and

3′-untranslated regions.23,24

Among the isoforms of VEGF, a difference in the contribu-

tion to disease progression is noted. A crucial role forVEGF165 in the angiogenesis of diabetic retinopathy and

rheumatoid arthritis was suggested through analyses of sur-

gically resected samples.12,13 However, until now, there have

been no definitive data concerning the mechanisms of

isoform-specific expression of VEGF.

As concerns the expression of VEGF receptors, VEGFR-

1 expression is upregulated in hypoxic endothelial cells, and

promoter analysis delineated the sequence responsible for

hypoxia-induced transcriptional activation of VEGFR-1,

which contains the consensus binding site for HIF-1.

Hypoxic induction of VEGFR-2 is somewhat controversial,

although VEGFR-2 expression by hypoxia was reported withan in vivo experimental system. This hypoxic induction of

VEGFR-2 is thought to be indirect and mediated by other

molecules that are induced by hypoxia, because the consen-

sus binding site for HIF-1 was not found in the VEGFR-2

gene.10

HIF-1 and HIF family

As aforementioned, HIF-1 is a factor controlling the tran-

scriptional rates of various hypoxia-responsive molecules in

response to the oxygen concentration around cells.20

ActiveHIF-1 is a heterodimer composed of two subunits, HIF-1α

and HIF-1β, both of which belong to a protein superfamily

containing the basic helix–loop–helix (bHLH) and the Per–

Arnt–Sim (PAS) domains.25 In general, members of the

bHLH-PAS protein superfamily are involved in cellular func-

tions that are activated in response to the changes of envi-

ronment.21,26 They include arylhydrocarbon receptor (AhR)

and arylhydrocarbon receptor nuclear translocator (Arnt) for

the pollution of the environment, period (Per) for the circa-

dian rhythm, single-minded (Sim) for the development of

central nervous system and trachealess (Trh) for the devel-

opment of salivary glands and trachea. HIF-1β, which waslater found to be identical to Arnt, is constitutively expressed

independent of environmental oxygen concentration, while

the expression of HIF-1α is negligible under normoxia and

induced under hypoxia. Up to now, HIF-1α, HIF-2α and HIF-

3α have been identified and cloned as the members of HIFα

family that can dimerize with HIF-1β and bind to HRE in the

genes of hypoxia-responsive molecules. HIF-2α is also

known as endothelial PAS domain protein 1 (EPAS 1), HIF-

1-like factor (HLF) or HIF-1-related factor (HRF). HIF-3α

appears not to activate the transcription of target genes due

to the lack of the transcription activation domain.21 Among

HIFα family members, HIF-1α is thought to be the key mol-

ecule regulating the cellular response to various physiologi-

cal and pathological hypoxia, although the critical role of

HIF-2α, not HIF-1α, is noted in certain pathological

situations.21,27

Regulation of the intracellular level of HIF-1αααα and the

cellular sensor for oxygen concentration

Mechanisms of hypoxia-induced expression of HIF-1α have

been intensively studied, and the intracellular level of HIF-1α

protein under reduced oxygen concentration was found

to be increased mainly through stabilization of the protein.

Turnover of HIF-1α protein is regulated by the ubiquitin–

proteasome system, in which target proteins are degraded

by proteasome depending on the ubiquitylation of pro-

teins.28,29

Ubiquitylation of the target proteins is catalyzed bythe enzyme complex composed of E1 (ubiquitin-activating

enzyme), E2 (ubiquitin-conjugating enzyme) and E3 (ubiq-

uitin ligase). Under normoxia, the level of HIF-1α protein is

kept low through rapid ubiquitylation and subsequent protea-

somal degradation. HIF-1α protein becomes susceptible to

rapid ubiquitylation through hydroxylation of proline residues

at Pro-402 and Pro-564 by prolyl hydroxylase 2 (PHD2),

which requires oxygen for its enzyme activity.30–32 In cells

under hypoxia, the ubiquitylation and subsequent degrada-

tion of HIF-1α protein is suppressed due to the decrease in

PHD2 activity, and therefore the level of HIF-1α protein

increases. In addition, the activity of HIF-1 as a transcriptionfactor is also controlled by hydroxylation of HIF-1α protein.

Hydroxylation of asparagine residue at Asn-803 inhibits the

interaction between HIF-1α protein and p300, which is

essential for the transcriptional activity of HIF-1.33 Because

the factor inhibiting HIF (FIH) that hydroxylates Asn-803 of

HIF-1α protein is also an oxygen-dependent enzyme, the

transcriptional activity of HIF-1 increases under hypoxia due

to the suppressed hydroxylation at Asn-803.34,35 Namely, cells

can control the transcription of HIF-1-regulated genes by

sensing the oxygen concentration as the activities of oxygen-

dependent enzymes PHD2 and FIH, and consequently reg-

ulating the intracellular level as well as the transcriptionalactivity of HIF-1 (Fig. 1).36

The ubiquitin–proteasome system degrades the proteins

with target specificity. This target specificity is attributed to

the E3 component of the enzyme complex, and the E3 com-

ponent responsible for ubiquitylation of HIF-1α protein was

found to be identical to the product of the von Hippel–Lindau

tumor suppressor gene (pVHL; Fig. 1).37,38 This finding shed

light on the tumorigenesis of renal cell carcinoma, pheochro-

mocytoma and hemangioblastoma because pVHL is often

mutated in these tumors.


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606 E. Ikeda

TISSUE HYPOXIA AND DISEASE PROGRESSION

Pathological tissues often become hypoxic as the result of

vascular obstruction with thrombi, vascular compression by

increased tissue hydrostatic pressure, increased tissue cell

density and so forth. Tissue hypoxia plays an important role

in determining the clinical course of certain diseases, for

example solid tumor growth, diabetic retinopathy and rheu-

matoid arthritis, and the contribution of tissue hypoxia to

disease progression is often mediated by the remodeling of

vasculature such as angiogenesis and loss of tissue-specific

vascular structures (Fig. 2).

Figure 1 Cellular response to hypoxia. Cells sense the oxygen concentration as the activities of oxygen-dependent enzymes, prolyl

hydroxylase 2 (PHD2) and factor inhibiting hypoxia-inducible factor (FIH), which determine the hypoxia-inducible factor-1 (HIF-1) function and

consequently the transcriptional rates of HIF-1-regulated genes. Under normoxia (blue arrows), the intracellular level of HIF-1α is kept low

by rapid ubiquitylation and subsequent proteasomal degradation, which depend on the hydroxylation of proline residues by PHD2; the activity

of HIF-1α as a transcription factor is also inhibited by the hydroxylation of asparagine residue by FIH. In contrast, under hypoxia (red arrows),

both the intracellular level and the transcriptional activity of HIF-1α increase as a result of suppressed PHD2 and FIH activities, respectively.

Consequently, HIF-1α forms a heterodimer with HIF-1β and changes the transcriptional rates of HIF-1-regulated genes under hypoxia. pVHL,

product of the von Hippel–Lindau tumor suppressor gene.

p V H L

HIF-1

AsnPro

p300

p300OH OH

pVHL

HIF-1

AsnPro

HIF-1

HIF-1

HIF-1

AsnPro

p300

PHD2, FIH

Normoxia

Hypoxia

Proteasomal degradationUbiquitylation

Inhibition of transcriptional activity

[Nucleus]

Changes in transcriptional rates

HIF-1-regulated genes

Suppression of proteasomal degradation

Increased transcriptional activity

[Oxygen-dependent enzymes]

Figure 2 Physiological and patholog-

ical reactions to tissue hypoxia. Physi-

ological reactions of a multicellularorganism under hypoxia share com-

mon pathways with pathological reac-

tions causing the disease progression.

Hypoxia

Disease progressionRemodeling of vascular system

Angiogenesis Solid tumor growth

Diabetic retinopathyRheumatoid arthritis

of HIF-1 regulated genes

Erythropoietin

VEGF

Tyrosine hydroxylase

Phosphoglycerokinase 1

Lactate dehydrogenase A

VEGFR-1

Physiological reactions

Pathological reactions

Erythropoiesis

Angiogenesis

Metabolic changes

Loss of tissue-specific properties

Vascular occlusion

Anti-apoptosis

Changes in the expression

Survival of cells, tissues

and organisms


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Solid tumor

Oxygen concentration inside solid tumors is reduced, and

there are studies to show the contribution of intratumoral

hypoxia to the tumor aggressiveness and poor prognosis of

patients.39,40 Resistance to chemotherapy and radiation ther-

apy can be attributed, at least in part, to the hypoxic conditionof tumor cells.41 Hypoxia confers these aggressive properties

on the tumors through either the remodeling of tumor vascu-

lature or the direct phenotypic changes of tumor cells

themselves.

Growth of solid tumors is angiogenesis dependent. As the

tumor mass becomes larger, tumor cells, especially at the

center of the mass, are exposed to the more hypoxic condi-

tion, and tumor cells cannot proliferate to form a mass beyond

a few millimeters in diameter without angiogenesis. Occur-

rence of angiogenesis confers the properties of continuous

growth as well as metastasis on the tumor, and therefore it

can be said that the angiogenic switch is a critical checkpointduring tumor progression.42 It has been demonstrated that

among angiogenic or antiangiogenic factors, the level of

VEGF is most highly correlated with the degree of angiogen-

esis in various kinds of tumors.43,44 A critical role for HIF-1α

in tumor progression has also been noted through analyses

of various tumors, although there are tumors in which HIF-

2α, not HIF-1α, is essential for tumorigenesis.27,45 Overex-

pression of HIF-1α in tumor tissues and its correlation with

degree of tumor angiogenesis as well as poor prognosis have

been demonstrated in patients with tumors such as brain

tumors, endometrial carcinomas, ovarian carcinomas, breast

carcinomas and head and neck tumors.46–51

Although studieswith mouse xenograft transplantation models have yielded

contradictory results regarding the role of HIF-1α in tumori-

genesis,52–54 a study focusing on the transition from avascular

to vascular tumors demonstrated that nuclear localization of

HIF-1α and subsequent VEGF upregulation in tumor cells are

important for initiating tumor angiogenesis.42 The question is

raised regarding the trigger of nuclear accumulation of HIF-

1α in tumor cells during the course of tumor progression.

Although HIF-1 can be activated by non-hypoxic pathways,

hypoxia inside the growing tumor mass is the most probable

candidate for the activation of HIF-1α cascade in tumor cells,

and this hypothesis is supported by the data that both HIF-1α and VEGF expression are upregulated predominantly in

tumor cells around the necrotic areas of highly vascularized

tumor mass in glioblastoma.15,16,46 Therefore, it can be true

that angiogenesis triggered by the hypoxia-HIF-1α-VEGF

cascade plays an important, even if not essential, role in

tumor progression to the more aggressive phenotypes.

Hypoxia accelerates tumor growth and metastasis by act-

ing directly on tumor cells themselves.41 Tumor cells under

hypoxia can acquire anti-apoptotic and chemoresistant prop-

erties through changes in the expression of apoptosis-related

molecules, and the involvement of HIF-1α in the tumor

progression to anti-apoptotic phenotype was reported.55

Genomes of tumor cells become unstable under hypoxic

conditions,56 and hypoxia can be the selective pressure for

the expansion of clones with anti-apoptotic, treatment-

resistant or highly metastatic potential.57 Hypoxia itself can

be a cause of tumor resistance to therapy because somedrugs and radiation require oxygen for their toxicity.58

It is interesting to note that pVHL is identical to the E3

component of the enzyme complex responsible for the ubiq-

uitylation and subsequent degradation of HIF-1α.37,38 In

tumor cells that have mutations in pVHL, HIF-1α-mediated

transcription of VEGF is constitutively activated due to the

impaired ubiquitylation of HIF-1α. Thus, independent of the

intratumoral oxygen concentration, the tumor growth can be

accelerated by continuous angiogenesis. However, involve-

ment of mechanisms other than that mediated by over-

production of VEGF are suggested in pVHL-related

tumorigenesis.27,59,60

Diabetic retinopathy

Retinopathy is one of the major complications of diabetes

mellitus and an important cause of adult blindness.61,62 The

clinical course of diabetic retinopathy is divided into three

stages: background, preproliferative and proliferative diabetic

retinopathies. The site attacked primarily in diabetic retinop-

athy is the blood vessel, and the visual acuity of patients is

impaired as a result of the vascular remodeling of retinal

vasculature by, for example, vascular occlusion, breakdownof the blood–retinal barrier (BRB) and angiogenesis. In par-

ticular, retinal angiogenesis that appears in the stage of pro-

liferative retinopathy leads to serious outcomes such as

vitreous hemorrhage and tractional retinal detachment.

Breakdown of BRB impairs the visual acuity of patients by

causing retinal edema.

Retinal angiogenesis in proliferative retinopathy results in

the formation of fibrovascular tissue that extends from the

retina to the vitreous body and generates adhesion between

them. Through analyses of the vitreous fluid and fibrovascu-

lar tissue from the diabetic retinopathy patients, the degree

of retinal angiogenesis is shown to be correlated with thelevel of VEGF protein in the eye.12 Production of VEGF in the

eye of diabetic retinopathy patients can be enhanced by

tissue hypoxia that is thought to be present in the retina from

a relatively early stage of diabetic retinopathy. Correlation

between the HIF-1α-mediated VEGF induction in the retina

and the breakdown of BRB is also demonstrated in diabetic

animal models.63 Thus, in addition to the increased retinal

glucose concentration and the accumulation of advanced

glycation end-products in retinal tissues, tissue hypoxia is

believed to be an important trigger of disease progression


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608 E. Ikeda

in diabetic retinopathy through the remodeling of retinal

vasculature.

Rheumatoid arthritis

Rheumatoid arthritis is a systemic inflammatory disease of

unknown etiology that mainly involves the joints in the form

of proliferative synovitis. In the affected joints, synovial tis-

sues proliferate into the joint spaces, exhibiting hyperplasia

of synovial lining cells as well as inflammatory cell infiltration

and angiogenesis in sublining layers. As the disesase

progresses, extracellular matrices, especially those of artic-

ular cartilage, are degraded by proteinases produced by the

proliferating synovial tissues, resulting in the deformation of

affected joints. Synovial angiogenesis that is initiated at the

relatively early stage of rheumatoid arthritis enables inflam-

matory cells to access the synovial tissues, and the inflam-

matory cells in turn promote the angiogenesis by producing

various vaso-active cytokines such as interleukin-8. Thus, the

angiogenesis and inflammatory cell infiltration interact to

accelerate disease progression, and the critical role of syn-

ovial angiogenesis in the establishment of proliferative syno-

vitis has been demonstrated with arthritic animal models.64,65

Analysis of the surgical specimens of rheumatoid arthritis has

revealed that synovial angiogenesis depends on the induc-

tion of VEGF synthesis in synovial tissues.13 Together with

the findings that inflamed synovial tissues are under hypoxia66

and that the level of HIF-1α protein is elevated in rheumatoid

synovial tissues,66–68 tissue hypoxia and HIF-1α-mediated

expression of VEGF are thought to be essential for disease

progression of rheumatoid arthritis by promoting angiogene-

sis. The role of tissue hypoxia in the prolongation of the

synovial inflammatory process of rheumatoid arthritis has

been also highlighted by the finding that hypoxia represses

activation-induced cell death of lymphocytes by supporting

their survival through the hypoxia–HIF-1α cascade.68

CONCLUSION

Progression of certain diseases shares mechanisms with the

physiological cellular response to tissue hypoxia, which are

originally thought to be acquired by multicellular organisms

for their survival under unexpected hypoxic stress. Under-

standing of disease progression from the aspect of tissue

hypoxia is expected to provide targets of new therapeutic

strategies for intractable diseases.

REFERENCES

1 Scheurer SB, Rybak JN, Rosli C, Neri D, Elia G. Modulation

of gene expression by hypoxia in human umbilical cord vein

endothelial cells: A transcriptomic and proteomic study. Pro-

teomics 2004; 4: 1737–60.

2 Krantz SB. Erythropoietin. Blood 1991; 77: 419–34.

3 Ikeda E, Achen MG, Breier G, Risau W. Hypoxia-induced tran-

scriptional activation and increased mRNA stability of vascular

endothelial growth factor in C6 glioma cells. J Biol Chem 1995;

270: 19 761–66.

4 Czyzyk-Krzeska MF, Furnari BA, Lawson EE, Millhorn DE.

Hypoxia increases rate of transcription and stability of tyrosinehydroxylase mRNA in pheochromocytoma (PC12) cells. J Biol

Chem 1994; 269: 760–64.

5 Firth JD, Ebert BL, Pugh CW, Ratcliffe PJ. Oxygen-regulated

control elements in the phosphoglycerate kinase 1 and lactate

dehydrogenase A genes: Similarities with the erythropoietin 3′

enhancer. Proc Natl Acad Sci USA 1994; 91: 6496–500.

6 Li F, Chong ZZ, Maiese K. Erythropoietin on a tightrope: Bal-

ancing neuronal and vascular protection between intrinsic and

extrinsic pathways. Neurosignals 2004; 13: 265–89.

7 Semenza GL, Wang GL. A nuclear factor induced by hypoxia

via de novo protein synthesis binds to the human erythropoietin

gene enhancer at a site required for transcriptional activation.

Mol Cell Biol 1992; 12: 5447–54.

8 Wang GL, Semenza GL. General involvement of hypoxia-

inducible factor 1 in transcriptional response to hypoxia. Proc Natl Acad Sci USA 1993; 90: 4304–8.

9 Risau W. Mechanisms of angiogenesis. Nature 1997; 386:

671–74.

10 Ferrara N. Molecular and biological properties of vascular

endothelial growth factor. J Mol Med 1999; 77: 527–43.

11 Ferrara N, Gerber HP, LeCouter J. The biology of VEGF and

its receptors. Nat Med 2003; 9: 669–76.

12 Ishida S, Shinoda K, Kawashima S, Oguchi Y, Okada Y, Ikeda

E. Coexpression of VEGF receptors VEGF-R2 and neuropilin-

1 in proliferative diabetic retinopathy. Invest Ophthalmol Vis Sci

2000; 41: 1649–56.

13 Ikeda M, Hosoda Y, Hirose S, Okada Y, Ikeda E. Expression

of vascular endothelial growth factor isoforms and their recep-

tors Flt-1, KDR, and neuropilin-1 in synovial tissues of rheuma-

toid ar thritis. J Pathol 2000; 191: 426–33.

14 Soker S, Takashima S, Miao HQ, Neufeld G, Klagsbrun M.

Neuropilin-1 is expressed by endothelial and tumor cells as an

isoform-specific receptor for vascular endothelial growth factor.

Cell 1998; 92: 735–45.

15 Plate KH, Breier G, Weich HA, Risau W. Vascular endothelial

growth factor is a potential tumour angiogenesis factor in

human gliomas in vivo . Nature 1992; 359: 845–48.

16 Shweiki D, Itin A, Soffer D, Keshet E. Vascular endothelial

growth factor induced by hypoxia may mediate hypoxia-initiated

angiogenesis. Nature 1992; 359: 843–45.

17 Damert A, Ikeda E, Risau W. Activator-protein-1 binding poten-

tiates the hypoxia-inducible factor-1-mediated hypoxia-induced

transcriptional activation of vascular-endothelial growth factor

expression in C6 glioma cells. Biochem J 1997; 327 (Pt 2):

419–23.

18 Semenza GL. Hypoxia-inducible factor 1: Control of oxygen

homeostasis in health and disease. Pediatr Res 2001; 49: 614–

17.

19 Semenza GL. Hypoxia-inducible factor 1: Oxygen homeostasis

and disease pathophysiology. Trends Mol Med 2001; 7: 345–

50.

20 Semenza G. Signal transduction to hypoxia-inducible factor 1.

Biochem Pharmacol 2002; 64: 993–98.

21 Covello KL, Simon MC. HIFs, hypoxia, and vascular develop-

ment. Curr Top Dev Biol 2004; 62: 37–54.

22 Ikeda E, Damert A, Risau W. Molecular mechanisms of

hypoxia-induced angiogenesis. In: Ishimura Y, Shimada M,


7/8


Suematsu M, eds. Oxygen Homeostasis and its Dynamics .

Tokyo: Springer, 1998; 388–99.

23 Levy NS, Chung S, Furneaux H, Levy AP. Hypoxic stabilization

of vascular endothelial growth factor mRNA by the RNA-binding

protein HuR. J Biol Chem 1998; 273: 6417–23.

24 Dibbens JA, Miller DL, Damert A, Risau W, Vadas MA, Goodall

GJ. Hypoxic regulation of vascular endothelial growth factor

mRNA stability requires the cooperation of multiple RNA

elements. Mol Biol Cell 1999; 10: 907–19.25 Wang GL, Jiang BH, Rue EA, Semenza GL. Hypoxia-inducible

factor 1 is a basic-helix-loop-helix-PAS heterodimer regulated

by cellular O2 tension. Proc Natl Acad Sci USA 1995; 92: 5510–

14.

26 Kewley RJ, Whitelaw ML, Chapman-Smith A. The mammalian

basic helix-loop-helix/PAS family of transcriptional regulators.

Int J Biochem Cell Biol 2004; 36: 189–204.

27 Kondo K, Klco J, Nakamura E, Lechpammer M, Kaelin WG Jr.

Inhibition of HIF is necessary for tumor suppression by the von

Hippel-Lindau protein. Cancer Cell 2002; 1: 237–46.

28 Semenza GL. HIF-1 and tumor progression: Pathophysiology

and therapeutics. Trends Mol Med 2002; 8: S62–7.

29 Mazure NM, Brahimi-Horn MC, Berta MA et al. HIF-1: Master

and commander of the hypoxic world. A pharmacological

approach to its regulation by siRNAs. Biochem Pharmacol 2004; 68: 971–80.

30 Berra E, Benizri E, Ginouves A, Volmat V, Roux D, Pouyssegur

J. HIF prolyl-hydroxylase 2 is the key oxygen sensor setting low

steady-state levels of HIF-1alpha in normoxia. EMBO J 2003;

22: 4082–90.

31 Ivan M, Haberberger T, Gervasi DC et al. Biochemical purifica-

tion and pharmacological inhibition of a mammalian prolyl

hydroxylase acting on hypoxia-inducible factor. Proc Natl Acad

Sci USA 2002; 99: 13 459–64.

32 Pereira T, Zheng X, Ruas JL, Tanimoto K, Poellinger L. Identi-

fication of residues critical for regulation of protein stability and

the transactivation function of the hypoxia-inducible factor-

1alpha by the von Hippel-Lindau tumor suppressor gene prod-

uct. J Biol Chem 2003; 278: 6816–23.

33 Lando D, Peet DJ, Whelan DA, Gorman JJ, Whitelaw ML.

Asparagine hydroxylation of the HIF transactivation domain a

hypoxic switch. Science 2002; 295: 858–61.

34 Lando D, Peet DJ, Gorman JJ, Whelan DA, Whitelaw ML,

Bruick RK. FIH-1 is an asparaginyl hydroxylase enzyme that

regulates the transcriptional activity of hypoxia-inducible factor.

Genes Dev 2002; 16: 1466–71.

35 Hewitson KS, McNeill LA, Riordan MV et al. Hypoxia-inducible

factor (HIF) asparagine hydroxylase is identical to factor inhib-

iting HIF (FIH) and is related to the cupin structural family. J

Biol Chem 2002; 277: 26 351–55.

36 Haddad JJ. Oxygen-sensing mechanisms and the regulation of

redox-responsive transcription factors in development and

pathophysiology. Respir Res 2002; 3: 26.

37 Maxwell PH, Wiesener MS, Chang GW et al. The tumour sup-

pressor protein VHL targets hypoxia-inducible factors for oxy-

gen-dependent proteolysis. Nature 1999; 399: 271–75.

38 Cockman ME, Masson N, Mole DR et al. Hypoxia inducible

factor-alpha binding and ubiquitylation by the von Hippel-

Lindau tumor suppressor protein. J Biol Chem 2000; 275: 25

733–41.

39 Hockel M, Schlenger K, Hockel S, Aral B, Schaffer U, Vaupel

P. Tumor hypoxia in pelvic recurrences of cervical cancer. Int

J Cancer 1998; 79: 365–69.

40 Stadler P, Becker A, Feldmann HJ et al. Influence of the

hypoxic subvolume on the survival of patients with head and

neck cancer. Int J Radiat Oncol Biol Phys 1999; 44: 749–

54.

41 Williams KJ, Cowen RL, Brown LM, Chinje EC, Jaffar M,

Stratford IJ. Hypoxia in tumors: Molecular targets for anti-

cancer therapeutics. Adv Enzyme Regul 2004; 44: 93–108.

42 Fang J, Yan L, Shing Y, Moses MA. HIF-1alpha-mediated up-

regulation of vascular endothelial growth factor, independent of

basic fibroblast growth factor, is important in the switch to the

angiogenic phenotype during early tumorigenesis. Cancer Res

2001; 61: 5731–5.

43 Hasan J, Byers R, Jayson GC. Intra-tumoural microvessel den-sity in human solid tumours. Br J Cancer 2002; 86: 1566–77.

44 Loureiro RM, D’Amore PA. Transcriptional regulation of vascu-

lar endothelial growth factor in cancer. Cytokine Growth Factor

Rev 2005; 16: 77–89.

45 Talks KL, Turley H, Gatter KC et al. The expression and

distribution of the hypoxia-inducible factors HIF-1alpha and

HIF-2alpha in normal human tissues, cancers, and tumor-

associated macrophages. Am J Pathol 2000; 157: 411–21.

46 Zagzag D, Zhong H, Scalzitti JM, Laughner E, Simons JW,

Semenza GL. Expression of hypoxia-inducible factor 1alpha in

brain tumors: Association with angiogenesis, invasion, and pro-

gression. Cancer 2000; 88: 2606–18.

47 Birner P, Gatterbauer B, Oberhuber G et al. Expression of

hypoxia-inducible factor-1 alpha in oligodendrogliomas: Its

impact on prognosis and on neoangiogenesis. Cancer 2001;92: 165–71.

48 Sivridis E, Giatromanolaki A, Gatter KC, Harris AL, Koukourakis

MI. Association of hypoxia-inducible factors 1alpha and 2alpha

with activated angiogenic pathways and prognosis in patients

with endometrial carcinoma. Cancer 2002; 95: 1055–63.

49 Birner P, Schindl M, Obermair A, Breitenecker G, Oberhuber

G. Expression of hypoxia-inducible factor 1alpha in epithelial

ovarian tumors: Its impact on prognosis and on response to

chemotherapy. Clin Cancer Res 2001; 7: 1661–8.

50 Bos R, Zhong H, Hanrahan CF et al. Levels of hypoxia-inducible

factor-1 alpha during breast carcinogenesis. J Natl Cancer Inst

2001; 93: 309–14.

51 Koukourakis MI, Giatromanolaki A, Sivridis E et al. Hypoxia-

inducible factor (HIF1A and HIF2A), angiogenesis, and chemo-

radiotherapy outcome of squamous cell head-and-neck cancer.

Int J Radiat Oncol Biol Phys 2002; 53: 1192–202.

52 Carmeliet P, Dor Y, Herbert JM et al. Role of HIF-1alpha

in hypoxia-mediated apoptosis, cell proliferation and tumour

angiogenesis. Nature 1998; 394: 485–90.

53 Hopfl G, Wenger RH, Ziegler U et al. Rescue of hypoxia-

inducible factor-1alpha-deficient tumor growth by wild-type cells

is independent of vascular endothelial growth factor. Cancer

Res 2002; 62: 2962–70.

54 Maltepe E, Keith B, Arsham AM, Brorson JR, Simon MC. The

role of ARNT2 in tumor angiogenesis and the neural response

to hypoxia. Biochem Biophys Res Commun 2000; 273: 231–38.

55 Erler JT, Cawthorne CJ, Williams KJ et al. Hypoxia-mediated

down-regulation of Bid and Bax in tumors occurs via hypoxia-

inducible factor 1-dependent and -independent mechanisms

and contributes to drug resistance. Mol Cell Biol 2004; 24:

2875–89.

56 Young SD, Marshall RS, Hill RP. Hypoxia induces DNA over-

replication and enhances metastatic potential of murine tumor

cells. Proc Natl Acad Sci USA 1988; 85: 9533–37.

57 Graeber TG, Osmanian C, Jacks T et al. Hypoxia-mediated

selection of cells with diminished apoptotic potential in solid

tumours. Nature 1996; 379: 88–91.

58 Teicher BA. Hypoxia and drug resistance. Cancer Metastasis

Rev 1994; 13: 139–68.

59 Pugh CW, Ratcliffe PJ. The von Hippel-Lindau tumor suppres-

sor, hypoxia-inducible factor-1 (HIF-1) degradation, and cancer

pathogenesis. Semin Cancer Biol 2003; 13: 83–89.


8/8

610 E. Ikeda

60 Maranchie JK, Vasselli JR, Riss J, Bonifacino JS, Linehan WM,

Klausner RD. The contribution of VHL substrate binding and

HIF1-alpha to the phenotype of VHL loss in renal cell carci-

noma. Cancer Cell 2002; 1: 247–55.

61 Frank RN. Diabetic retinopathy. N Engl J Med 2004; 350: 48–

58.

62 Cunha-Vaz J, Bernardes R. Nonproliferative retinopathy in dia-

betes type 2. Initial stages and characterization of phenotypes.

Prog Retin Eye Res 2005; 24: 355–77.63 Poulaki V, Qin W, Joussen AM et al. Acute intensive insulin

therapy exacerbates diabetic blood–retinal barrier breakdown

via hypoxia-inducible factor-1alpha and VEGF. J Clin Invest

2002; 109: 805–15.

64 Oliver SJ, Cheng TP, Banquerigo ML, Brahn E. Suppression

of collagen-induced arthritis by an angiogenesis inhibitor, AGM-

1470, in combination with cyclosporin: Reduction of vascular

endothelial growth factor (VEGF). Cell Immunol 1995; 166:

196–206.

65 Storgard CM, Stupack DG, Jonczyk A, Goodman SL, Fox RI,

Cheresh DA. Decreased angiogenesis and arthritic disease in

rabbits treated with an alphavbeta3 antagonist. J Clin Invest

1999; 103: 47–54.

66 Distler JH, Wenger RH, Gassmann M et al. Physiologic

responses to hypoxia and implications for hypoxia-inducible

factors in the pathogenesis of rheumatoid arthritis. Arthritis

Rheum 2004; 50: 10–23.

67 Hollander AP, Corke KP, Freemont AJ, Lewis CE. Expressionof hypoxia-inducible factor 1alpha by macrophages in the rheu-

matoid synovium: Implications for targeting of therapeutic

genes to the inflamed joint. Arthritis Rheum 2001; 44: 1540–

44.

68 Makino Y, Nakamura H, Ikeda E et al. Hypoxia-inducible factor

regulates survival of antigen receptor-driven T cells. J Immunol

2003; 171: 6534–40.

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Cellular Response to Tissue Hypoxia and Its Involvenment in Progression