A Regulatory Feedback Loop Between Ca2+/Calmodulin-dependent Protein Kinase Kinase 2 (CaMKK2) and the Androgen Receptor in Prostate Cancer Progression

• Published in: The Journal of biological chemistry Vol. 287; no. 29; pp. 24832 - 24843
• Main Authors: Karacosta, Loukia G., Foster, Barbara A., Azabdaftari, Gissou, Feliciano, David M., Edelman, Arthur M.
• Format: Journal Article
• Language: English
• Published: United States Elsevier Inc 13-07-2012; American Society for Biochemistry and Molecular Biology
• Subjects: Androgen Receptor; Animals; Blotting, Western; Calcium; Calcium Calmodulin-dependent Protein Kinase (CaMK); Calcium-Calmodulin-Dependent Protein Kinase Kinase - genetics; Calcium-Calmodulin-Dependent Protein Kinase Kinase - metabolism; Calmodulin; Cell Cycle - genetics; Cell Cycle - physiology; Cell Line, Tumor; Cell Proliferation; Cell Survival - genetics; Cell Survival - physiology; Humans; Immunohistochemistry; In Vitro Techniques; Male; Mice; Molecular Bases of Disease; Prostate Cancer; Prostatic Neoplasms - enzymology; Prostatic Neoplasms - genetics; Prostatic Neoplasms - metabolism; Prostatic Neoplasms - pathology; Receptors, Androgen - genetics; Receptors, Androgen - metabolism; Reverse Transcriptase Polymerase Chain Reaction; RNA Interference; Calcium Calmodulin-dependent Protein Kinase (CaMK); Androgen Receptor; Prostate Cancer; Calcium; Calmodulin
• ISSN: 0021-9258; 1083-351X
• DOI: 10.1074/jbc.M112.370783

The androgen receptor (AR) plays a critical role in prostate cancer (PCa) progression, however, the molecular mechanisms by which the AR regulates cell proliferation in androgen-dependent and castration-resistant PCa are incompletely understood. We report that Ca2+/calmodulin-dependent kinase kinase 2 (CaMKK2) expression increases and becomes nuclear or perinuclear in advanced PCa. In the TRAMP (transgenic adenocarcinoma of mouse prostate) model of PCa, CaMKK2 expression increases with PCa progression with many cells exhibiting nuclear staining. CaMKK2 expression is higher in human castration-resistant tumor xenografts compared with androgen-responsive xenografts and is markedly higher in the AR-expressing, tumorigenic cell line LNCaP compared with cell lines that are AR-nonexpressing and/or nontumorigenic. In LNCaP cells, dihydrotestosterone induced CaMKK2 mRNA and protein expression and translocation of CaMKK2 to the nucleus. Conversely, androgen withdrawal suppressed CaMKK2 expression. Knockdown of CaMKK2 expression by RNAi reduced LNCaP cell proliferation and increased percentages of cells in G1 phase, whereas correspondingly reducing percentages in S phase, of the cell cycle. CaMKK2 knockdown reduced expression of the AR target gene prostate-specific antigen at both mRNA and protein levels, AR transcriptional activity driven by androgen responsive elements from the prostate-specific probasin gene promoter and levels of the AR-regulated cell cycle proteins, cyclin D1 and hyperphosphorylated Rb. Our results suggest that in PCa progression, CaMKK2 and the AR are in a feedback loop in which CaMKK2 is induced by the AR to maintain AR activity, AR-dependent cell cycle control, and continued cell proliferation.
Background: Defining molecular mechanisms that regulate AR activity is critical for understanding prostate cancer progression.
Results: CaMKK2 increases during disease progression, is transcriptionally regulated by the AR, promotes proliferation, and is required for optimal AR transcriptional activity.
Conclusion: CaMKK2 is in a feedback circuit to maintain AR activity.
Significance: The CaMKK2 pathway is a promising target for prostate cancer therapy.