Constitutive activation of the mitogen-activated protein kinase pathway impairs vitamin D signaling in human prostate epithelial cells.
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 RXRalpha 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 RXRalpha that was reduced by MAPK activation and was restored in RWPE2 cells by mutating S32 and T82 in the RXRalpha 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 RXRalpha AF-1 domain and impaired co-activator recruitment.
Zhang
Zhentao
Z
Department of Foods and Nutrition, Purdue University, West Lafayette, Indiana 47907-2059, USA.
Kovalenko
Pavlo
P
Cui
Min
M
Desmet
Marsha
M
Clinton
Steven K
SK
Fleet
James C
JC
D000595:Amino Acid Sequence; D002117:Calcitriol / Q000494:pharmacology*; D002460:Cell Line; D002461:Cell Line, Transformed; D049109:Cell Proliferation / Q000187:drug effects; D004789:Enzyme Activation / Q000187:drug effects; D004847:Epithelial Cells / Q000166:cytology / Q000187:drug effects* / Q000201:enzymology*; D006801:Humans; D020935:MAP Kinase Signaling System / Q000187:drug effects*; D008297:Male; D020928:Mitogen-Activated Protein Kinases / Q000378:metabolism*; D008954:Models, Biological; D008969:Molecular Sequence Data; D056920:Nuclear Receptor Coactivator 1 / Q000378:metabolism; D015689:Oncogene Protein p21(ras) / Q000378:metabolism; D010766:Phosphorylation / Q000187:drug effects; D011401:Promoter Regions, Genetic / Q000235:genetics; D011467:Prostate / Q000166:cytology*; D011485:Protein Binding / Q000187:drug effects; D018167:Receptors, Calcitriol / Q000378:metabolism; D047490:Retinoid X Receptor alpha / Q000737:chemistry / Q000378:metabolism; D015533:Transcriptional Activation / Q000187:drug effects / Q000235:genetics
D018167:Receptors, Calcitriol; D047490:Retinoid X Receptor alpha; D056920:Nuclear Receptor Coactivator 1; D020928:Mitogen-Activated Protein Kinases; D015689:Oncogene Protein p21(ras); D002117:Calcitriol