title: 1alpha,25-Dihydroxyvitamin D(3) antiproliferative actions involve vitamin D receptor-mediated activation of MAPK pathways and AP-1/p21(waf1) upregulation in human osteosarcoma.
abstract: The molecular mechanisms underlying antiproliferative actions of the steroid 1alpha,25-dihydroxy vitamin D(3) (1,25D) in human osteosarcoma cells are known only partially. To better understand the signaling involved in 1,25D anti-tumorigenic properties in bone, we stably silenced vitamin D receptor (VDR) expression in the human osteosarcoma SaOS-2 cell line. We found that 1,25D treatment reduced cell proliferation by approximately 25% after 3 days only in SaOS-2 cells expressing native levels of VDR protein, and involved activation of MAPK/AP-1/p21(waf1) pathways. Both sustained (3 days) and transient (15min) 1,25D treatment activated JNK and ERK1/2 MAPK signaling in a nongenomic VDR-dependent manner. However, only sustained exposure to hormone led to upregulation of p21 and subsequent genomic control of the cell cycle. Specific blockade of MEK1/MEK2 cascade upstream from ERK1/2 abrogated 1,25D activation of AP-1 and p21, and subsequent antiproliferative effects, even in the presence of a nuclear VDR. We conclude that 1,25D-induced inhibition of human osteosarcoma cell proliferation occurs via sustained activation of JNK and MEK1/MEK2 pathways downstream of nongenomic VDR signaling that leads to upregulation of a c-Jun/c-Fos (AP-1) complex, which in turn modulates p21(waf1) gene expression. Our results demonstrate a cross-talk between 1,25D/VDR nongenomic and genomic signaling at the level of MAP kinase activation that leads to reduction of cell proliferation in human osteosarcoma cells.
authors.affiliation: Department of Biochemistry, University of California, 5436 Boyce Hall, Riverside, CA 92521, USA.
authors.forename: Wei
authors.initials: W
authors.lastname: Wu
authors.forename: Xiaoyu
authors.initials: X
authors.lastname: Zhang
authors.forename: Laura P
authors.initials: LP
authors.lastname: Zanello
mesh_terms: D015153:Blotting, Western; D002070:Butadienes / Q000494:pharmacology; D045744:Cell Line, Tumor; D049109:Cell Proliferation / Q000187:drug effects*; D050759:Cyclin-Dependent Kinase Inhibitor p21 / Q000235:genetics / Q000378:metabolism*; D004789:Enzyme Activation / Q000187:drug effects; D004791:Enzyme Inhibitors / Q000494:pharmacology; D006801:Humans; D048031:JNK Mitogen-Activated Protein Kinases / Q000378:metabolism; D020935:MAP Kinase Signaling System / Q000187:drug effects; D020928:Mitogen-Activated Protein Kinases / Q000037:antagonists & inhibitors / Q000378:metabolism*; D008954:Models, Biological; D009570:Nitriles / Q000494:pharmacology; D016760:Proto-Oncogene Proteins c-fos / Q000378:metabolism; D034741:RNA, Small Interfering / Q000235:genetics; D018167:Receptors, Calcitriol / Q000235:genetics / Q000378:metabolism*; D013997:Time Factors; D018808:Transcription Factor AP-1 / Q000235:genetics / Q000378:metabolism*; D014162:Transfection; D015854:Up-Regulation / Q000187:drug effects; D014807:Vitamin D / Q000031:analogs & derivatives / Q000494:pharmacology*
chemical_list: D002070:Butadienes; C493956:CDKN1A protein, human; D050759:Cyclin-Dependent Kinase Inhibitor p21; D004791:Enzyme Inhibitors; D009570:Nitriles; D016760:Proto-Oncogene Proteins c-fos; D034741:RNA, Small Interfering; D018167:Receptors, Calcitriol; D018808:Transcription Factor AP-1; C113580:U 0126; C118756:dihydroxy-vitamin D3; D014807:Vitamin D; D048031:JNK Mitogen-Activated Protein Kinases; D020928:Mitogen-Activated Protein Kinases