INPP4B regulates AR activity

Activation and transcriptional reprograming of AR in advanced prostate cancer frequently overlaps with the loss of two tumor suppressors, INPP4B and PTEN, which are highly expressed in human and mouse prostate epithelium. While regulation of AR signaling by PTEN has been described by multiple groups, it is not known whether the loss of INPP4B affects AR activity. Using prostate cancer cell lines we showed that INPP4B regulates AR transcriptional activity and oncogenic signaling pathways Akt and PKC. Analysis of gene expression in prostate cancer patient cohorts showed a positive correlation between INPP4B expression and both AR mRNA levels and AR transcriptional output. Using an Inpp4b-/- mouse model, we demonstrated that INPP4B suppresses Akt and PKC signaling pathways and modulates AR transcriptional activity in normal mouse prostate. It has been previously shown that the high fat diet activates Akt pathway in mouse prostate. We showed that the loss of INPP4B further increases Akt phosphorylation in dorsolateral and ventral lobes of mice fed with the high fat diet. Remarkably, PTEN protein levels and phosphorylation of S380 were the same in Inpp4b-/- and WT males, suggesting that observed changes were due exclusively to the loss of INPP4B. Our data show that INPP4B modulates AR activity in normal prostate and its loss contributes to the AR-dependent transcriptional profile in prostate cancer. Two groups were analyzed: control and INPP4B knockdown. Each group had 3 biological variables. Control: LNCAP-Cont2, LNCAP-Cont3, LNCAP-Cont4. INPP4B knockdown: LNCAP-INPP4B-2, LNCAP-INPP4B-3, LNCAP-INPP4B-4.