ABSTRACT
Activation and transcriptional reprogramming of AR in advanced prostate cancer frequently coincides 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 the 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. Remarkably, PTEN protein levels and phosphorylation of S380 were the same in Inpp4b-/- and WT males, suggesting that the 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.
Subject(s)
Phosphoric Monoester Hydrolases/metabolism , Prostate/metabolism , Prostatic Neoplasms/metabolism , Proto-Oncogene Proteins c-akt/metabolism , Signal Transduction , Animals , Cell Line, Tumor , Humans , Male , Mice , Mice, Knockout , Phosphoric Monoester Hydrolases/genetics , Prostate/pathology , Prostatic Neoplasms/genetics , Protein Kinase C/genetics , Protein Kinase C/metabolism , Proto-Oncogene Proteins c-akt/genetics , Receptors, Androgen/genetics , Receptors, Androgen/metabolismABSTRACT
PURPOSE: Castration therapy in advanced prostate cancer eventually fails and leads to the development of castration-resistant prostate cancer (CRPC), which has no cure. Characteristic features of CRPC can be increased androgen receptor (AR) expression and altered transcriptional output. We investigated the expression of nuclear receptor corepressor 1 (NCOR1) in human prostate and prostate cancer and the role of NCOR1 in response to antiandrogens. EXPERIMENTAL DESIGN: NCOR1 protein levels were compared between matched normal prostate and prostate cancer in 409 patient samples. NCOR1 knockdown was used to investigate its effect on bicalutamide response in androgen-dependent prostate cancer cell lines and transcriptional changes associated with the loss of NCOR1. NCOR1 transcriptional signature was also examined in prostate cancer gene expression datasets. RESULTS: NCOR1 protein was detected in cytoplasm and nuclei of secretory epithelial cells in normal prostate. Both cytoplasmic and nuclear NCOR1 protein levels were lower in prostate cancer than in normal prostate. Prostate cancer metastases show significant decrease in NCOR1 transcriptional output. Inhibition of LNCaP cellular proliferation by bicalutamide requires NCOR1. NCOR1-regulated genes suppress cellular proliferation and mediate bicalutamide resistance. In the mouse, NCOR1 is required for bicalutamide-dependent regulation of a subset of the AR target genes. CONCLUSIONS: In summary, we demonstrated that NCOR1 function declines with prostate cancer progression. Reduction in NCOR1 levels causes bicalutamide resistance in LNCaP cells and compromises response to bicalutamide in mouse prostate in vivo Clin Cancer Res; 22(15); 3937-49. ©2016 AACR.
Subject(s)
Gene Expression , Nuclear Receptor Co-Repressor 1/genetics , Prostatic Neoplasms/genetics , Prostatic Neoplasms/pathology , Androgen Antagonists/pharmacology , Androgen Antagonists/therapeutic use , Androgens/metabolism , Androgens/pharmacology , Anilides/pharmacology , Anilides/therapeutic use , Animals , Cell Line, Tumor , Disease Models, Animal , Disease Progression , Gene Knockdown Techniques , Gene Silencing , Humans , Male , Mice , Mice, Transgenic , Neoplasm Metastasis , Nitriles/pharmacology , Nitriles/therapeutic use , Nuclear Receptor Co-Repressor 1/metabolism , Prostatic Neoplasms/therapy , RNA Interference , Tosyl Compounds/pharmacology , Tosyl Compounds/therapeutic use , TranscriptomeABSTRACT
BACKGROUND: INPP4B and PTEN dual specificity phosphatases are frequently lost during progression of prostate cancer to metastatic disease. We and others have previously shown that loss of INPP4B expression correlates with poor prognosis in multiple malignancies and with metastatic spread in prostate cancer. RESULTS: We demonstrate that de novo expression of INPP4B in highly invasive human prostate carcinoma PC-3 cells suppresses their invasion both in vitro and in vivo. Using global gene expression analysis, we found that INPP4B regulates a number of genes associated with cell adhesion, the extracellular matrix, and the cytoskeleton. Importantly, de novo expressed INPP4B suppressed the proinflammatory chemokine IL-8 and induced PAK6. These genes were regulated in a reciprocal manner following downregulation of INPP4B in the independently derived INPP4B-positive LNCaP prostate cancer cell line. Inhibition of PI3K/Akt pathway, which is highly active in both PC-3 and LNCaP cells, did not reproduce INPP4B mediated suppression of IL-8 mRNA expression in either cell type. In contrast, inhibition of PKC signaling phenocopied INPP4B-mediated inhibitory effect on IL-8 in either prostate cancer cell line. In PC-3 cells, INPP4B overexpression caused a decline in the level of metastases associated BIRC5 protein, phosphorylation of PKC, and expression of the common PKC and IL-8 downstream target, COX-2. Reciprocally, COX-2 expression was increased in LNCaP cells following depletion of endogenous INPP4B. CONCLUSION: Taken together, we discovered that INPP4B is a novel suppressor of oncogenic PKC signaling, further emphasizing the role of INPP4B in maintaining normal physiology of the prostate epithelium and suppressing metastatic potential of prostate tumors.
