PLZF regulates pbxl transcription and Pbx1-HoxC8 complex leads to androgen-independent prostate cancer proliferation

BACKGROUND. Promyelocytic leukemia zinc finger (PLZF) protein, a transcriptional repressor and negative regulator of the cell cycle, has been characterized as a prostatic androgen-responsive gene. DU145 cells show androgen-independent growth and lack PLZF gene expression. METHODS. We analyzed PLZF-regulating genes by DNA microarray using DU145 cells infected with LacZ- or PLZF-carrying adenoviruses. RESULTS. DNA microarray revealed that Pbx1 is a prominent suppressed gene in PLZF-overexpressing DU145 cells. Androgen receptor (AR)-expressing DU145 cells recovered androgen-dependent PLZF expression and subsequent repression of Pbx1 expression. Immunoprecipitation of Pbx1 in DU145 cells revealed a Pbx1-HoxC8 heterocomplex. siRNAs for Pbx1 and HoxC8 knocked downexpression of each, and this suppressed androgenin-dependent cell growth. Double knockdown of both Pbx1 and HoxC8 suppressed cell growth much more significantly. CONCLUSIONS. Androgen-independent cell line DU145 cells lack PLZF gene expression, resulting in the upregulation of Pbx1 and HoxC8 expression. The Pbx1-HoxC8 heterocomplex may lead to androgen-independent growth in prostate cancer.