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Journal of Tongji Medical University 16 (1): 58-60, 1996 58 ~ i~ ~ ~ ~c ~ ~ ~ ( ~ b ~ ) C-Ha-ras Oncogene in Oral Leukoplakia Tissues CHENG Peng (~ ~) Department of Stomatology, Tongji Hospital, Tongji Medical University, Wuhan 430030 LI Huifeng (~t~) Stomatology Hospital, Hubei Medqcal University, Wuhan 430070 YANG Ping (~ "~), TAN Yun ('~t -L-) Institute of Virology, Hubei Medical Universt'ty, Wuhan 430071 Summary: The amplification and the G-T mutation at eodon l~-of the C-Ha-ras oncogene in oral leuk0ptakia tissues were analyzed by using polymerase chain reac- tion (PCR) and molecular biologic technique. The results showed that these tis- sues had no amplification of Ha-ras oncogene. Only one case harbored G-T muta- tion in 11 oral leukoplakias, but this mhtation Was absent in 10 normal oral mu- cosal tissues. The possible role and significance of C-Ha-ras oncogene in oral pre- Cancerous lesions were also discussed. Key words: oral leukoplakia; ras oncogene; mutation; amplification Oral leukoplakia (OLK) is a common oral mucosal disease, which has tendency of carcinogenesis. It has been taken as a pre- cancerous lesion by World Health Organiza- tion (WHO), but the mechanism of its car- cinogenesis remains uncertain. During the last decade, oncogene have been demon- strated to play a significant role in the stages of generation and development of hu- man tumors. Ras gene family has involved in the progression of various human tu- mors, and point mutation and gene amplifi- cation are its important mechanisms of acti- vation ~13. To date, there have been many reports on oncogene in oral cancers, but they did not cover such oral pre-cancerous diseases as OLK. By application of a sensi- tive method of oligonucleot;de hybridization and polymerase chain reaction (PCR), we, for the first time, investigated both quality and quantity of c;Ha-ras oncogene in OLK tissues, and provided a new way of elucidat- ing the mechanism of oral carcinogenesis at molecular level. 1 MATERIALS AND METHODS 1.1 Preparation of Tissues DNA Biopsy specimens used in this study were obtained from patients in Hospital of Stomatology, Hubei Medical University. CHENG Peng,male, born in 1965, Chief Resident The patients included 11 cases of OLK and 10 subjects with normal oral mucosal (NOM) tissues, all specimens were patho- logically examined, and DNA wasextracted by the phenolehloroform method.. Density of DNA was detected by ultraviolet spec- trophotometry. DNA from Ha-ras gene plasmid and normal white blood cells was extracted ac- cording, to the standard method of Maniatis et al. 1.2 C-Ha-ras Oncogene Amplification Detected by Nucleic Acid Hybridization Tissues DNA 5 /.tg were doted on Hy- bond nylon membrane, after being dena- tured with 1 mol/L NaOH and neutralized with 1. 5 mol/L NaCl Tfis-HC1 . Dotted membrane was prehyhridized in 5 X SSC, 5 XDenhardt's, 0. 5 ~ SDS and 0. 1 mg/ml salmon sperm DNA for 4 h at 42 ~ Selec- tive hybridization was performed in .the same solution with Ha-ras gene probe la- belled by 3ZP-dATP for 24 h. Finally, the membrane was autoradiographed at -30 ~ Quantitative analysis of dot blots were per- formed by densitometry. 1.3 Detection of C-Ha-ras Oneogene Mu- tation by PCR and Oligonucleotide Probe The amplifying primers and mutated oligonucleotide probe were designed by the Department of Molecular Biology of Hubei Medical University, and synthesized by Shanghai Institute of Cell Biology. The se-

C-Ha-ras oncogene in oral leukoplakia tissues

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Page 1: C-Ha-ras oncogene in oral leukoplakia tissues

Journal of Tongji Medical University 16 (1): 58-60, 1996 58 ~ i~ ~ ~ ~c ~ ~ ~ ( ~ b ~ )

C-Ha-ras Oncogene in Oral Leukoplakia Tissues CHENG Peng ( ~ ~ ) Department of Stomatology, Tongji Hospital, Tongji Medical University, Wuhan 430030 LI Huifeng ( ~ t ~ ) Stomatology Hospital, Hubei Medqcal University, Wuhan 430070 YANG Ping ( ~ "~), TAN Yun ('~t -L-) Institute of Virology, Hubei Medical Universt'ty, Wuhan 430071

Summary: The amplification and the G-T mutation at eodon l~-of the C-Ha-ras oncogene in oral leuk0ptakia tissues were analyzed by using polymerase chain reac- tion (PCR) and molecular biologic technique. The results showed that these tis- sues had no amplification of Ha-ras oncogene. Only one case harbored G-T muta- tion in 11 oral leukoplakias, but this mhtation Was absent in 10 normal oral mu- cosal tissues. The possible role and significance of C-Ha-ras oncogene in oral pre- Cancerous lesions were also discussed. Key words: oral leukoplakia; ras oncogene; mutation; amplification

Oral leukoplakia ( O L K ) is a common oral mucosal disease, which has tendency of carcinogenesis. It has been taken as a pre- cancerous lesion by World Heal th Organiza- tion ( W H O ) , but the mechanism of its car- cinogenesis remains uncertain. During the last decade, oncogene have been demon- s t rated to play a significant role in the stages of generation and development of hu- man tumors . Ras gene family has involved in the progression of various human tu- m o r s , and point muta t ion and gene amplifi- cation are its important mechanisms of acti- vation ~13. To date , there h a v e been many reports on oncogene in oral cancers , but they did not cover such oral pre-cancerous diseases as OLK. By application of a sensi- tive method of oligonucleot;de hybridization and polymerase chain reaction ( P C R ) , we, for the first t ime , invest igated both quality and quant i ty of c ;Ha- ras oncogene in O L K t issues , and provided a new way of elucidat- ing the mechanism of oral carcinogenesis at molecular level.

1 MATERIALS AND METHODS

1.1 Preparation of Tissues DNA Biopsy specimens used in this s tudy

were obtained f rom pat ients in Hospital of S tomato logy , Hubei Medical Universi ty .

CHENG Peng,male, born in 1965, Chief Resident

The patients included 11 cases of O L K and 10 subjects with normal oral mucosal ( N O M ) tissues, all specimens were patho- logically examined, and DNA w a s e x t r a c t e d by the phenolehloroform m e t h o d . . Density of DNA was detected by ul t raviole t spec- t rophotometry .

DNA from Ha- ras gene plasmid and normal white blood cells was extracted ac- cording, to the s tandard method of Maniatis et al. 1.2 C-Ha-ras Oncogene Amplification Detected by Nucleic Acid Hybridization

Tissues DNA 5 /.tg were doted on H y - bond nylon m e m b r a n e , af ter being dena- t u r e d with 1 m o l / L N a O H and neutralized with 1. 5 m o l / L NaCl Tfis-HC1 . Dotted membrane was prehyhridized in 5 X SSC, 5 X D e n h a r d t ' s , 0. 5 ~ SDS and 0. 1 m g / m l salmon sperm DNA for 4 h at 42 ~ Selec- tive hybridization was performed in .the same solution with Ha- ras gene probe la- belled by 3ZP-dATP for 24 h. Final ly , the membrane was autoradiographed at -30 ~ Quanti ta t ive analysis of dot blots were per- formed by densi tometry. 1.3 Detection of C-Ha-ras Oneogene Mu- tat ion by PCR and Oligonucleotide Probe

The amplifying pr imers and muta ted oligonucleotide probe were designed by the Depar tment of Molecular Biology of Hubei Medical Univers i ty , and synthesized by Shanghai Inst i tute of Cell Biology. The se-

Page 2: C-Ha-ras oncogene in oral leukoplakia tissues

CHEN Peng et al. C-Ha-ras Oncogene in Oral Tissues 59

quences were as fol lows: Pr imer 1: 5'- A C G G A A T A T A A G C T G G T G G - 3 ' ; Pr imer 2: 5 ' -CGGCGGCAGGTCCACGGTC- 3 ' ; Probe : 5 ' - T G G G C G C C G T C G G T G T G G G - 3'. 5 '-end of the primers were located at the no. 1673 and the no. 1810 of nucleic acid . GTC in probe sequence was the mutated 12th codon of c-Ha-ras oncogene. The probe was 5 '-end-labeled by phosphoryla- tion with 35 p_ ( T ) ATP . PCR was per- formed as described by Saiki et a l c~]. Ampli-

�9 fled DAN was dotted on nitrocellulose mem- brane, which was prehybridized for 4 h at 42 "C. The labeled oligonucleotide probe with specific mutated was then added and hybridization was con t inued at the same temperature for 24 h. T h e n , the membrane was washed twice in 2 X SSC, 0. 1 ~ SDS for 15 rain at room tempera ture , and in 0. 1 • 0. 1 ~ SDS for 10 rain at 55 "C, fi- nally in 0. 1Xssc , 0. 1 0~ SDS for 10 rain at 68 "C. The membrane was autoradio- graphed at -30 "C.

2 RESULTS

2. 1 Amplification of C-Ha-ras Oncogene in OLK Tissues

Both OLK and NOM tissues showed positive signal by being hybridized with the probe of c-Ha-ras. Quanti tat ive analysis of dots were performed by densi tometry. The mean values of density-dimension were 4580 + 2425 in OLK group and 4584-+-2186 in normal control group. The data were ana- lyzed by t- test ( P ~ 0 . 05). There was no significant difference between two groups. This finding indicated no c-Ha-ras gene am- plification in OLK. 2. 2 Point Mutation of C-Ha-ras Onco- gene in OLK Tissues

DNA from t issues, Ha-ras plasmid (positive cont ro l ) and normal white blood cells (negative control) was subjected to 35 cycles of in v i t r o amplification using two primers, 2 ~ agarose gel electrophoresis showed obvious 138 bp amplified bands (fig. 1).

Dot hybridization with specific mutated oligonucleotide probe for Ha-ras gene re- vealed that 1 of 11 cases of OLK had posi- tive signal but none in 10 cases of normal o-

Fig. 1 PCR products analyzed by 2 ~ a- garose gel electrophoresis 1 DNA marker, ).DNA-Hind | / o X 174-Hae | 2 PCR product from Ha-ras plasmid DNA 3 PCR product from tissues DNA 4 PCR product form normal white blood cells DNA

ra| mucosal tissues had such signal. This indicated that the signal-positive OLK con- tained the G-T mutat ion at codon 12 of C- Ha-ras oncogene (fig. 2).

Fig. 2 Dot hybridization of PCR products with specific oligonucleotide probe for c-Ha-ras A1-A5: positive controls (PCR products from mutated Ha-ras); A6-A8: negative controls ( PCR products from normal white biood cells DNA) ; A9-A10, B1-BS: PCR products from NOM tissues DNA; B9-B10, C1-C9: PCR products from 11 cases of OLKtissues DNA.

Page 3: C-Ha-ras oncogene in oral leukoplakia tissues

60 Journal of T0ngji Medical University 16 (1): 58-60, 1996

3 DISCUSSION

Normal ly , oncogene plays an impor tant role in regulation of cell g rowth and differ- entiation. It causes neoplastic t ransforma- tion only under the conditions of abnormal s t ruc tures or function. Over the last decade, quality and quanti ta t ive al terat ions of ras oncogene were believed to be one of the molecular mechanisms involved in can- cer development and progression. Point mu- tat ion and amplification are Its ma in way of activation cs3. One of the characteris t ics in progression of many human tumors reveled benign pre-cancerous lesions. Some pre- cancerous lesions may fur ther progress into cancer. O L K is an oral pre-cancerous lesion and its mechanism of carcinogenesis remains uncertain. Balmain C4J first reported that be- nign tumors harbored activated Ha-ras oncogene and demonst ra ted that activation was an early initiating event in tumor-gene- sis. It was more significant in many cases that corresponding relat ions were observed between point muta t ion of ras gene and car- cinogenesis of pre-cancerous les ions, i. e . , once benign tumors developed ras gene mu- tat ion may have priori ty to progress into carcinomas . This had an impor tant value for evaluation of susceptibi l i ty and early di- agnosis of cancers. Many researchers stud- ied ras muta t ion at different clinical s tages in various types of human tumo/ ' s , and ob- tained a lot of significant results .

In order to elucidate the relat ions be- tween actions of c -Ha-ras oncogene and O L K , we have detected muta t ion pa t te rns of c -Ha- ras oncogene by PCR and dot hy- bridization technique. The resul ts showed that O L K tissues had no amplif ication of c- Ha- ra s oncogene, only one case harbored G- T muta t ion in 11 cases of OLK. At pre-

sen t , only few studies dealt with point mu- tat ion of ras gene in cells of non-cancerous s i te , a l though the carcinogenesis mech- anism of ras oncogene is not fully under- s tood , many repor ts have showed tha t mu- tated Ha- ras gene may affect cellular prolif- erat ion and different iat ion, and has capabili- ty of t ransforming cells. The ras p21 pro- tein possesses intrinsic G T P a s e activity and appears to directly involve in the regulation of cellular growth and differentiation. Mu- tat ion of ras oncogene will lead t o alter- at ions of its p ro te ins , thereby fur ther re- sult ing in uncontrolled conditions of cellular g rowth thereby forming mal ignant tumors . Our resul ts suggested that point mutat ion of c - H a - r a s oncogene may be one of the car- cinogenesis mechanism of pre-cancerous le- s ions , and provided a new way of elucidat- ing the mechanism of development and pro- gression of oral tumors .

R E F E R E N C E S

1 Bos J L. Ras oncogene in human cancer. A re- view. Cancer Res, 1984, 49:4862

2 Saiki R K, Scharf S, Faloona F et al. Enzymat- ic amplification of ~-globin genomic sequences and restriction site analysis for diagnosis of sickle cell anemia. Science, 1985, 230. 1350

3 Friedman W H. Oneogenes.. their presence and significance in squamous cell cancer of head and neck. Laryngoscope, 1985, 95-. 313

4 Balmain A, Ramsden M. Activating of the mouse cellular Harvey-ras gene in chemically induce benign skin papillomas. Nature, 1984, 307 = 658

5 Burmer G C, Loeb L A. Mutation in the K- ras-2 oncogene during progressive stages of hu- man colon carcinoma. Proc Natl Acad Sci USA, 1989, 86= 2403

6 Field J K, Spandidos D A, Stell P Met al. Ex- pression of oncogenes in human tumors with special reference to the head and neck region. J Oral Pathol, 1987, 16:97

(Received Sept. 1, 1995)