trichostatin-a and 5--azacytidine-5--monophosphate

PCDH10 (protocadherin-10), a novel tumour suppressor gene, is down-regulated in several human cancers due to hypermethylation of promoter CGIs (CpG islands). Here, we investigated the expression of PCDH10 in different normal adult tissues and in a panel of prostate cancer cell lines. PCDH10 was widely expressed in normal tissues with higher levels in the prostate. The expression of PCDH10 was markedly reduced or silenced in prostate cancer cell lines compared with normal adult prostate tissue. Decreased PCDH10 expression was correlated with the methylation status of the PCDH10 promoter. Furthermore, the DNA demethylating agent 5'-azacytidin restored PCDH10 expression by suppressing PCDH10 promoter methylation in prostate cancer cell lines. Treatment with Trichostatin A alone had no significant effect on the expression of PCDH10 but enhanced the effect of 5'-azacytidin. In conclusion, we found that the decreased PCDH10 expression in prostate cancer cells was associated with the aberrant methylation of PCDH10 promoter CGI. Our results may contribute to the understanding of the role of PCDH10 inactivation in the progression of prostate cancers.

Topics: Adult; Blotting, Western; Cadherins; Cell Line, Tumor; CpG Islands; Cytidine Monophosphate; DNA Methylation; Drug Synergism; Epigenesis, Genetic; Gene Expression Regulation, Neoplastic; Humans; Hydroxamic Acids; Male; Polymerase Chain Reaction; Promoter Regions, Genetic; Prostatic Neoplasms; Protocadherins

In breast cancer, approximately one-third of tumors express neither the estrogen receptor (ERalpha) nor estrogen-regulated genes such as the progesterone receptor gene (PR). Our study provides new insights into the mechanism allowing hormone-activated expression of ERalpha target genes silenced in ERalpha-negative mammary tumor cells. In cell lines derived from ERalpha-negative MDA-MB231 cells, stable expression of different levels of ERalpha from a transgene did not result in transcription of PR. A quantitative comparative analysis demonstrates that inhibiting DNA methyltransferases using 5-aza-2'-deoxycytidine or specific disruption of DNMT1 by small interfering RNAs and treatment with the histone-deacetylase inhibitor trichostatin A enabled ERalpha-mediated hormone-dependent expression of endogenous PR. We show that demethylation of a CpG island located in the first exon of PR was a prerequisite for ERalpha binding to these regulatory sequences. Although not a general requirement, DNA demethylation is also necessary for derepression of a subset of ERalpha target genes involved in tumorigenesis. PR transcription did not subsist 4 days after removal of the DNA methyltransferase blocking agents, suggesting that hormone-induced expression of ERalpha target genes in ERalpha-negative tumor cells is transient. Our observations support a model where an epigenetic mark confers stable silencing by precluding ERalpha access to promoters.

Topics: Breast Neoplasms; Cell Line, Tumor; CpG Islands; Cytidine Monophosphate; DNA (Cytosine-5-)-Methyltransferase 1; DNA (Cytosine-5-)-Methyltransferases; DNA Methylation; Enzyme Inhibitors; Epigenesis, Genetic; Estradiol; Estrogen Receptor alpha; Estrogens; Female; Gene Expression Regulation, Neoplastic; Humans; Hydroxamic Acids; Receptors, Progesterone; RNA, Small Interfering