1,25-Dihydroxyvitamin D-3 upregulates natriuretic peptide receptor-C expression in mouse osteoblasts

1,25-Dihydroxyvitamin DQ [1,25(OH)(2)D-3], a key regulator of mineral metab olism, regulates expression of several genes related to bone formation. The present study examined the 1,25(OH)(2)D-3-mediated regulation of natriuret ic peptide receptor-C (NPR-C) expression in osteoblasts. 1,25(OH)(2)D-3 tre atment significantly increased NPR-C-dependent atrial natriuretic peptide-b inding activity and synthesis of the NPR-C protein in mouse osteoblastic ce lls in a cell-specific manner. Western blot analysis also demonstrated that 1,25(OH)(2)D-3 upregulated expression of NPR-C protein in slow kinetics. N ext, Northern blot analysis revealed a significant increase in the steady-s tate NPR-C mRNA level by 1,25(OK)(2)D-3. Sequence analysis of the 9 kb of t he 5'-flanking region of the mouse NPR-C gene revealed an absence of consen sus vitamin D-response elements, and promoter analysis using osteoblastic c ells stably transfected with mouse NPR-C promoter-reporter constructs showe d a slight increase of promoter activity with 1,25(OH)(2)D-3 treatment. In addition, a nuclear run-on assay exhibited that the transcriptional rate of the NPR-C gene was unchanged by 1,25(OH)(2)D-3, whereas that of the osteop ontin gene was increased. Evaluation of NPR-C mRNA half-life demonstrated t hat 1,25(OH)(2)D-3 significantly increased the NPR-C mRNA stability in oste oblastic cells. 1,25(OH)(2)D-3 attenuated intracellular cGMP production in osteoblastic cells stimulated by C-type natriuretic peptide (CNP) without a significant change of the natriuretic peptide receptor-B mRNA level, sugge sting enhancement of the clearance of exogenously added CNP via NPR-C. Furt hermore, NPR-C and osteopontin mRNAs in mouse calvariae were significantly increased by administration of 1,25(OH)(2)D-3, and immunohistological analy sis demonstrated that NPR-C is actually and strongly expressed in mouse per iosteal fibroblasts. These findings suggest that 1,25(OH)(2)D-3 can play a critical role for determination of the natriuretic peptide availability in bones by regulation of NPR-C expression through stabilizing its mRNA.