Methylation and silencing of the retinoic acid receptor-beta 2 gene in cervical cancer.
BACKGROUND
Expression of the retinoic acid receptor beta2 (RAR-beta2), a putative tumor suppressor gene, is reduced in various human cancers, including squamous cell carcinomas (SCC) of the uterine cervix. The mechanism of the inhibition of RAR-beta2 expression remains obscure. We examined whether methylation of RAR-beta2 gene could be responsible for this silencing in cervical SCC.


METHODS
Expression of RAR-beta2 mRNA and methylation status of the 5' region of RAR-beta2 gene were examined in 20 matched specimens from patients with cervical SCC and in three cervical cancer cell lines by Northern blot analysis and methylation-specific PCR (MSP) assay or Southern blot analysis respectively.


RESULTS
In 8 out 20 cervical SCC (40%) the levels of RAR-beta2 mRNA were decreased or undetectable in comparison with non-neoplastic cervix tissues. All 8 tumors with reduced levels of RAR-beta2 mRNA expression showed methylation of the promoter and the first exon expressed in the RAR-beta2 transcript. The RAR-beta2 gene from non-neoplastic cervical tissues was mostly unmethylated and expressed, but methylated alleles of the gene were found in three samples of the morphologically normal tissues adjacent to the tumors. Three cervical cancer cell lines with extremely low level of RAR-beta2 mRNA expression, SiHA, HeLA and CaSki, also showed methylation of this region of the RAR-beta2 gene.


CONCLUSIONS
These findings suggest that methylation of the 5' region of RAR-beta2 gene may contribute to gene silencing and that methylation of this region may be an important and early event in cervical carcinogenesis. These findings may be useful to make retinoids more effective as preventive and therapeutic agents in combination with inhibitors of DNA methylation.
Ivanova
Tatyana
T
Institute of Carcinogenesis, Cancer Research Center, Kashirskoye shosse 24, Moscow 115478, Russia. tan_ivanova@mail.ru
Petrenko
Anatolii
A
Gritsko
Tatyana
T
Vinokourova
Svetlana
S
Eshilev
Ernest
E
Kobzeva
Vera
V
Kisseljov
Fjodor
F
Kisseljova
Natalia
N
D020121:5' Untranslated Regions / Q000235:genetics; D002294:Carcinoma, Squamous Cell / Q000235:genetics* / Q000473:pathology; D019175:DNA Methylation; D005260:Female; D015972:Gene Expression Regulation, Neoplastic / Q000235:genetics; D020868:Gene Silencing; D016147:Genes, Tumor Suppressor; D006367:HeLa Cells; D006801:Humans; D009361:Neoplasm Invasiveness; D009367:Neoplasm Staging; D012333:RNA, Messenger / Q000096:biosynthesis; D012334:RNA, Neoplasm / Q000096:biosynthesis; D018168:Receptors, Retinoic Acid / Q000096:biosynthesis / Q000235:genetics*; D015183:Restriction Mapping; D014407:Tumor Cells, Cultured; D002583:Uterine Cervical Neoplasms / Q000235:genetics* / Q000473:pathology
D020121:5' Untranslated Regions; D012333:RNA, Messenger; D012334:RNA, Neoplasm; D018168:Receptors, Retinoic Acid; C082925:retinoic acid receptor beta