MKP-1 is essential for canonical vitamin D-induced signaling through nuclear import and regulates RANKL expression and function.
Vitamin D(3,) and its most active form, 1,25(OH)(2)D(3), are well known to stimulate osteoclastogenesis through stromal cell induction of the receptor activator of nuclear factor-κB ligand (RANKL). MAPK phosphatase-1 (MKP-1) is a phosphatase classically known to negatively regulate the innate immune response through dephosphorylation of p38, ERK, and c-Jun N-terminal kinase activity. This paper describes a new function of MKP-1 in permitting genomic 1,25(OH)(2)D(3) signaling and downstream osteoclastogenesis through RANKL. Initially, quantitative RT-PCR (qRT-PCR) and immunoblot analysis comparing bone marrow stromal cells (BMSC) revealed that 1,25(OH)(2)D(3)-induced vitamin D receptor (VDR), cytochrome P 45024a1, and RANKL mRNA expression and protein were significantly attenuated or absent in MKP-1(-/-) BMSC. Immunoblot analysis from cellular fractions of wild type and MKP-1(-/-) BMSC stimulated with 10(-7) m 1,25(OH)(2)D(3) revealed retinoid X receptor (RXR)α nuclear import was impaired in MKP-1(-/-) BMSC, whereas VDR import was not. Proximity ligation assays revealed that baseline VDR-RXRα heterodimer translocation was unchanged, yet 1,25(OH)(2)D(3)-induced nuclear translocation of VDR-RXRα heterodimers was reduced in MKP-1(-/-) BMSC. A functional consequence was observed as BMSC from MKP-1(-/-) mice treated with 1,25(OH)(2)D(3) and cocultured with RAW 264.7 cells had a 91% decrease in osteoclastogenesis and a 94.5% decrease in mineralized matrix resorption compared with wild-type cocultures (P < 0.01). These results reveal an unexpected, permissive role for MKP-1 in canonical 1,25(OH)(2)D(3) signaling via VDR-RXRα heterodimer nuclear import and downstream osteoclastogenesis through stromal cell RANKL expression.
Department of Craniofacial Biology, Medical University of South Carolina, Charleston, 173 Ashley Avenue, BSB 449, Charleston, South Carolina 29425, USA.
Alfred C
AC
Griffin
Michael J
MJ
Kern
Keith L
KL
Kirkwood
D021581:Active Transport, Cell Nucleus; D000818:Animals; D001483:Base Sequence; D001854:Bone Marrow Cells / Q000378:metabolism / Q000502:physiology; D002454:Cell Differentiation; D002467:Cell Nucleus / Q000378:metabolism*; D002478:Cells, Cultured; D018920:Coculture Techniques; D054638:Dual Specificity Phosphatase 1 / Q000235:genetics / Q000378:metabolism / Q000502:physiology*; D051379:Mice; D057507:Mice, 129 Strain; D008810:Mice, Inbred C57BL; D018345:Mice, Knockout; D010010:Osteoclasts / Q000378:metabolism; D011401:Promoter Regions, Genetic; D053245:RANK Ligand / Q000235:genetics / Q000378:metabolism*; D018167:Receptors, Calcitriol / Q000378:metabolism; D047490:Retinoid X Receptor alpha / Q000378:metabolism; D015398:Signal Transduction; D013250:Steroid Hydroxylases / Q000235:genetics / Q000378:metabolism; D014158:Transcription, Genetic; D015533:Transcriptional Activation; D014807:Vitamin D / Q000502:physiology*; D030181:Vitamin D Response Element; D065668:Vitamin D3 24-Hydroxylase
D053245:RANK Ligand; D018167:Receptors, Calcitriol; D047490:Retinoid X Receptor alpha; C505689:Tnfsf11 protein, mouse; D014807:Vitamin D; D013250:Steroid Hydroxylases; D065668:Vitamin D3 24-Hydroxylase; D054638:Dual Specificity Phosphatase 1; C517020:Dusp1 protein, mouse