A major challenge in treating advanced prostate cancer (PCa) resides in the inevitable progression of PCa cells from an androgen-sensitive (AS) to an androgen-insensitive (AI) state. Although multiple molecular pathways have been identified as the underlying mechanisms controlling this switch, chromatin remodeling remains as one that is largely understudied. We recently identified Peroxisomal Membrane Protein 24KDa (PMP24) gene as a candidate whose transcription is under cytosine methylation regulation during prostate cancer progression. Two LNCaP sublines: 1) AS-LNCaP maintained in full serum and 2) AI-LNCaP kept in charcoal-stripped serum for over 50 passages were used in this study. A regulatory CpG island located in the 5’ end of PMP24 was found to be heavily methylated in both AS-LNCaP and AI-LNCaP using bisulfite genomic sequencing. PMP24 expression was silenced in both lines. However, re-expression of PMP24 was readily achieved in AS-LNCaP by treatment with a histone deacetylase inhibitor, trichostatin A (TSA), but not by exposure to the demethylating agent, 5-aza-2’-deoxycytidine (5-AZAdC). In contrast, PMP24 transcription was reactivated by treatment with 5-AZAdC but not by TSA in AI-LNCaP. To elucidate the apparent paradoxical behavior between the two cell lines we used a novel real-time PCR-based chromatin accessibility assay (CHART-PCR) to measure accessibility at the PMP24 CpG island in these two cell lines. Our results showed that PMP24 CpG island of AS-LNCaP was highly compact while that of AI-LNCaP was readily assessable. These findings would explain the ability of TSA, known to relax chromatin structure, to activate PMP24 expression in AS-LNCaP cells whereas demethylation alone would have no effect on transcription. On the contrary, since PMP24 CpG island in AI-LNCaP cells is easily accessible, demethylation with 5-AZAdC alone was able to reactivate transcription. In conclusion, our data was first to demonstrate chromatin remodeling is involved in the progression of PCa cells from the AS to the AI state. (Research supported in part by the NIH award ES012281-R21).
[Proc Amer Assoc Cancer Res, Volume 45, 2004]