The Heterochromatin Protein 1 Family is Regulated in Prostate Development and Cancer

Purpose: The HP1 family of evolutionarily conserved proteins regulates heterochromatin packaging, in addition to a less defined role in the regulation of euchromatic genes. To examine the possible role of HP1 proteins in fetal prostate development and prostate cancer the protein expression of HP1α, β and γ was evaluated in human archival tissue. Materials and Methods: Tissue sections from human prostate cancer and fetal prostate were examined using antibodies against HP1 isoforms to evaluate HP1 modulation in cancer and development. Western blot analysis of HP1 proteins was also performed in extracts of cultured prostate cancer cells. Results: HP1α, β and γ are differentially regulated in various cellular compartments in prostate development. HP1α is not expressed at 14 or 24 weeks of prostate development but it is expressed in adult prostate tissue. HP1β is highly expressed at 14 and 24 weeks, and it appears predominantly in epithelial cells compared to HP1γ, which is expressed at equal levels in epithelial and stromal cells. All 3 HP1 isoforms show altered expression in prostate cancer compared to that in normal adult prostate tissue. Conclusions: HP1 proteins are tightly regulated during prostate development. In the adult prostate HP1α, β and γ antibodies detect high levels of HP1 antigen in a contiguous layer of epithelial cells. However, the detection of HP1 in prostate cancer ranges from undetectable to inconsistent staining of noncontiguous epithelial cells.