Retinoic Acid Receptor AlphaRetinoic Acid Receptor Alpha(RARα)(RARα)

Acute Promyelocytic Acute Promyelocytic LeukemiaLeukemia

(APL)(APL)

APL OverviewAPL Overview

Subtype of AML (5-8% of AML adults)Subtype of AML (5-8% of AML adults) Abnormal accumulation of Abnormal accumulation of

promyelocytes resulting in decreased promyelocytes resulting in decreased production of RBCsproduction of RBCs

Median age is 40 yearsMedian age is 40 years Increased incidence in patients from Increased incidence in patients from

Latin AmericaLatin America Anemia and thrombocytopeniaAnemia and thrombocytopenia

RARα is a transcription factorRARα is a transcription factor

Nuclear receptorNuclear receptor Ligand-inducible Ligand-inducible

transcriptional transcriptional regulatorregulator

Ligand is retinoic Ligand is retinoic acid (RA)acid (RA)

Cyberlipid Center; www.cyberlipid.org

RARα

Active transcription factor is a Active transcription factor is a heterodimerheterodimer

RARα forms RARα forms heterodimer with heterodimer with RXRs RXRs

Heterodimer binds Heterodimer binds DNA sequence DNA sequence called RA-response called RA-response element (RARE)element (RARE)

Marlétaz F, et al. Int J Biol Sci 2006; 2:38-47.

Retinoic Acid AbsentRetinoic Acid Absent

RAR-RXR heterodimer is a repressorRAR-RXR heterodimer is a repressor Co-repressors modify histonesCo-repressors modify histones

SMRT, N-CoRSMRT, N-CoR mSin3mSin3 HDACsHDACs

Marlétaz F, et al. Int J Biol Sci 2006; 2:38-47.

Retinoic Acid PresentRetinoic Acid Present

Repression complex dissociates and Repression complex dissociates and a co-activator complex assemblesa co-activator complex assembles

Co-activator complex modifies Co-activator complex modifies histones to induce transcriptional histones to induce transcriptional activationactivation

Marlétaz F, et al. Int J Biol Sci 2006; 2:38-47.

Scientists knocked outScientists knocked out RARα RARα Gene in MiceGene in Mice

Homologous Homologous recombinationrecombination

Disrupt exon 8, Disrupt exon 8, which prevents which prevents synthesis of all synthesis of all RARRARα α isoformsisoforms

Lufkin, Thomas, et al. Proc. Natl. Acad. Sci. USA. Vol. 90, pp. 7225-7229

RARαRARα-null mutants viable but -null mutants viable but generally die before 2 generally die before 2

monthsmonths Intercross Intercross RARα RARα

heterozygotes to heterozygotes to give give RARαRARα-null -null homozygoteshomozygotes

RARα RARα gene gene disruption is not disruption is not embryonic lethalembryonic lethal

RARα, RARβ and RARα, RARβ and RARγ are highly RARγ are highly redundantredundant

Lufkin, Thomas, et al. Proc. Natl. Acad. Sci. USA. Vol. 90, pp. 7225-7229

Testis Degeneration in Testis Degeneration in RARαRARα Mutant MiceMutant Mice

MaleMale RARα RARα-null homozygotes that survived -null homozygotes that survived for > 2 months were sterilefor > 2 months were sterile

Severe degeneration of germinal epithelium Severe degeneration of germinal epithelium in testesin testes

Lufkin, Thomas, et al. Proc. Natl. Acad. Sci. USA. Vol. 90, pp. 7225-7229

Chromosomal Translocation Chromosomal Translocation causes mutationcauses mutation

Chromosome 17Chromosome 17 Fusion proteins Fusion proteins

created with 5 created with 5 common partnerscommon partners PMLPML PLZFPLZF NPMNPM NuMANuMA Stat5bStat5b

Medicine OnLine. www.meds.com

Fusion proteins can form Fusion proteins can form homodimershomodimers

Homodimer Homodimer associates with associates with multiple units of multiple units of the co-repressor the co-repressor complexcomplex

Enhanced Enhanced transcriptional transcriptional repressionrepression

Lin, Richard, et. al. “Transcriptional regulation in APL”

Fusion proteins react Fusion proteins react strongly with co-repressors strongly with co-repressors

to recruit HDACsto recruit HDACs Physiological [RA] will not dissociate Physiological [RA] will not dissociate

repression complexrepression complex

Lin, Richard, et. al. “Transcriptional regulation in APL”

High [RA] dissociates High [RA] dissociates repression complex formed by repression complex formed by

some fusion proteinssome fusion proteins PML-RARα but not PLZF-RARαPML-RARα but not PLZF-RARα

Lin, Richard, et. al. “Transcriptional regulation in APL”

Target genes involved in Target genes involved in myeloid proliferation and myeloid proliferation and

differentiationdifferentiation p21WAF, C/EBP, HoxA1, etc.p21WAF, C/EBP, HoxA1, etc. Inhibition blocks differentiationInhibition blocks differentiation

Lin, Richard, et. al. “Transcriptional regulation in APL”

TreatmentTreatment

Pharmacological [RA] with Pharmacological [RA] with chemotherapychemotherapy

Possibly HDAC inhibitorsPossibly HDAC inhibitors

Lin, Richard, et. al. “Transcriptional regulation in APL”