M. Sasaki et al., Progesterone receptor B gene inactivation and CpG hypermethylation in human uterine endometrial cancer, CANCER RES, 61(1), 2001, pp. 97-102
The expressions of two isoforms of human progesterone receptor (PR) are und
er the control of the two different promoters. Recent studies revealed diff
erences between these isoforms, PRA and PRB, in their expression and functi
on in endometrial cells. Aberrant methylation of normally unmethylated CpG
islands has been associated with inactivation of several genes in human can
cers. In this study, we investigated the methylation status and the express
ion of the two different PR isoforms, PRA and PRB, in uterine endometrial c
arcinoma (UEC) using methylation-specific PCR (MSP), reverse transcription-
PCR (RT-PCR), the 5' rapid amplification of cDNA ends method (5'RACE), and
immunohistochemical staining, The results of RT-PCR and 5'RACE suggest that
only PRB is inactivated, although PRA is activated in all UEC cell lines.
Treatment with a demethylating agent, 5-aza-2'-deoxycytidine, restored PRB
expression in all cell lines, suggesting that inactivation of this gene is
through methylation. By MSP and direct DNA sequencing, PRB was methylated,
whereas PRA was unmethylated in all of the cell lines. To determine the met
hylation status of PRB in UEC patients, we investigated 83 cancerous and 33
normal samples. Sixty-two of 83 cancer samples had only methylated alleles
of PRB, although all cancer samples had only unmethylated PRB alleles. Sev
enty-one of 83 cancer samples were negative for PRB expression. All 62 canc
er samples that had only methylated PRB alleles were negative for PRB expre
ssion. No significant changes were observed in PRA methylation status or im
munohistochemistry positivity in normal and cancer samples. To determine wh
ether de novo methylation of PRB occurred in UEC patients, we studied 32 pa
irs of cancer and normal samples from the same patient. Twenty of 32 cancer
samples had only methylated PRB alleles, although all 32 normal samples ha
d only unmethylated PRB alleles. The loss of unmethylated alleles was well
correlated with negativity in immunohistochemical staining for PRB. This is
the first report of the selective methylation and the subsequent silencing
of PRB in uterine endometrial cancer.