title: Polycystin-1 regulates skeletogenesis through stimulation of the osteoblast-specific transcription factor RUNX2-II.
abstract: Polycystin-1 (PC1) may play an important role in skeletogenesis through regulation of the bone-specific transcription factor Runx2-II. In the current study we found that PC1 co-localizes with the calcium channel polycystin-2 (PC2) in primary cilia of MC3T3-E1 osteoblasts. To establish the role of Runx2-II in mediating PC1 effects on bone, we crossed heterozygous Pkd1(m1Bei) and Runx2-II mice to create double heterozygous mice (Pkd1(+/m1Bei)/Runx2-II(+/-)) deficient in both PC1 and Runx2-II. Pkd1(+/m1Bei)/Runx2-II(+/-) mice exhibited additive reductions in Runx2-II expression that was associated with impaired endochondral bone development, defective osteoblast-mediated bone formation, and osteopenia. In addition, we found that basal intracellular calcium levels were reduced in homozygous Pkd1(m1Bei) osteoblasts. In contrast, overexpression of a PC1 C-tail construct increased intracellular calcium and selectively stimulated Runx2-II P1 promoter activity in osteoblasts through a calcium-dependent mechanism. Site-directed mutagenesis of critical amino acids in the coiled-coil domain of PC1 required for coupling to PC2 abolished PC1-mediated Runx2-II P1 promoter activity. Additional promoter analysis mapped the PC1-responsive region to the "osteoblast-specific" enhancer element between -420 and -350 bp that contains NFI and AP-1 binding sites. Chromatin immunoprecipitation assays confirmed the calcium-dependent binding of NFI to this region. These findings indicate that PC1 regulates osteoblast function through intracellular calcium-dependent control of Runx2-II expression. The overall function of the primary cilium-polycystin complex may be to sense and transduce environmental clues into signals regulating osteoblast differentiation and bone development.
authors.affiliation: Kidney Institute, University of Kansas Medical Center, Kansas City, Kansas 66160, USA.
authors.forename: Zhousheng
authors.initials: Z
authors.lastname: Xiao
authors.forename: Shiqin
authors.initials: S
authors.lastname: Zhang
authors.forename: Brenda S
authors.initials: BS
authors.lastname: Magenheimer
authors.forename: Junming
authors.initials: J
authors.lastname: Luo
authors.forename: L Darryl
authors.initials: LD
authors.lastname: Quarles
mesh_terms: D000818:Animals; D000831:Animals, Newborn; D001483:Base Sequence; D001846:Bone Development; D001842:Bone and Bones / Q000002:abnormalities / Q000196:embryology; D002118:Calcium / Q000378:metabolism; D002460:Cell Line; D002923:Cilia / Q000378:metabolism; D050659:Core Binding Factor Alpha 1 Subunit / Q000172:deficiency / Q000235:genetics / Q000378:metabolism*; D020869:Gene Expression Profiling; D018507:Gene Expression Regulation, Developmental; D042541:Intracellular Space / Q000378:metabolism; D051379:Mice; D008969:Molecular Sequence Data; D009929:Organ Size; D009928:Organ Specificity; D010006:Osteoblasts / Q000378:metabolism* / Q000473:pathology; D011401:Promoter Regions, Genetic / Q000235:genetics; D021381:Protein Transport; D015398:Signal Transduction; D050396:TRPP Cation Channels / Q000378:metabolism*; D014157:Transcription Factors / Q000235:genetics / Q000378:metabolism*
chemical_list: D002118:Calcium; D050659:Core Binding Factor Alpha 1 Subunit; D050396:TRPP Cation Channels; D014157:Transcription Factors; C493716:Runx2 protein, mouse