Constitutive activation of the mitogen-activated protein kinase pathway impairs vitamin D signaling in human prostate epithelial cells

✍ Scribed by Zhentao Zhang; Pavlo Kovalenko; Min Cui; Marsha DeSmet; Steven K. Clinton; James C. Fleet

• Publisher: John Wiley and Sons
• Year: 2010
• Tongue: English
• Weight: 341 KB
• Volume: 224
• Category: Article
• ISSN: 0021-9541
• DOI: 10.1002/jcp.22139

✦ Synopsis

Abstract

We studied the effect of prolonged activation of mitogen‐activated protein kinase (MAPK) signaling on 1,25 dihydroxyvitamin D (1,25(OH)~2~D~3~) action in the immortalized human prostate epithelial cell line RWPE1 and its Ki‐Ras transformed clone RWPE2. 1,25(OH)~2~D~3~‐treatment caused growth arrest and induced gene expression in both cell lines but the response was blunted in RWPE2 cells. Vitamin D receptor (VDR) levels were lower in RWPE2 cells but VDR over‐expression did not increase vitamin‐D‐mediated gene transcription in either cell line. In contrast, MAPK inhibition restored normal vitamin D transcriptional responses in RWPE2 cells and MAPK activation with constitutively active MEK1R4F reduced vitamin‐D‐regulated transcription in RWPE1 cells. 1,25(OH)~2~D~3~‐mediated transcription depends upon the VDR and its heterodimeric partner the retinoid X receptor (RXR) so we studied whether changes in the VDR–RXR transcription complex occur in response to MAPK activation. Mutation of putative phosphorylation sites in the activation function 1 (AF‐1) domain (S32A, T82A) of RXRα restored 1,25(OH)~2~D~3~‐mediated transactivation in RWPE2 cells. Mammalian two‐hybrid and co‐immunoprecipitation assays revealed a vitamin‐D‐independent interaction between steroid receptor co‐activator‐1 (SRC‐1) and RXRα that was reduced by MAPK activation and was restored in RWPE2 cells by mutating S32 and T82 in the RXRα AF‐1 domain. Our data show that a common contributor to cancer development, prolonged activation of MAPK signaling, impairs 1,25(OH)~2~D~3~‐mediated transcription in prostate epithelial cells. This is due in part to the phosphorylation of critical amino acids in the RXRα AF‐1 domain and impaired co‐activator recruitment. J. Cell. Physiol. 224: 433–442, 2010. © 2010 Wiley‐Liss, Inc.