1,25-dihydroxyvitamin D-3 stimulates transforming growth factor-beta 1 synthesis by mouse renal proximal tubular cells

1,25-Dihydroxyvitamin D-3 [1,25-(OH)(2) D-3] is a secosteroid hormone with effects on cell growth, differentiation and immunoregulatory functions in a number of tissues not primarily involved in mineral metabolism. We recentl y demonstrated growth-regulating effects of 1,25-(OH)(2) D-3 on human mesan gial cells and proximal tubular cells. To investigate whether 1,25-(OH)(2) D-3 might a Iso affect the synthesis of cytokines a nd growth facto rs in p roximal tubular cells, we assessed in the present study the expression and secretion of transforming growth factor-beta 1 (TGF-beta 1) in a mouse prox imal tubular cell line (MCT) in vitro. TGF-beta 1 synthesis was measured by a monospecific ELISA in culture supernatant. The secreted TGF-beta 1 was p roven to be biologically active by means of a bioassay system (CCL-64 mink lung epithelial cell proliferation assay). TGF-beta 1 gene expression was a ssessed by RT-PCR. To analyze whether TGF-beta 1 expression mediates the 1, 25-(OH)(2) D-3-induced antiproliferative actions in MCT, proliferation stud ies in the absence or presence of a blocking monoclonal anti TGF-beta 1-3 a ntibody were performed. 1,25-(OH)(2) D-3 (10(-11) to 10(-7) M) specifically increased the TGF-beta 1 protein secretion in MCT with a maximum at 10(-8) M. No detectable effect was found with 25 D-3 at 10 times higher concentra tions. A synthetic 20-epi analogue, MC 1288, increased TGF-beta 1 secretion up to similar amounts at equimolar concentrations as the natural hormone 1 ,25(OH)(2) D-3 Steady-state TGF-beta 1 mRNA concentration in MCT was transi ently increased by 1,25-(OH)(2) D-3 between 12 and 24 h, returning to contr ol values at 48 h. Blocking TGF-beta 1 did not reduce or abrogate the antip roliferative effect of 1,25-(OH)(2) D-3 In conclusion, 1,25(OH)(2) D-3 stim ulates TGF-beta 1 expression in renal proximal tubular cells, a growth fact or with anti-inflammatory and profibrotic actions which plays an important role in the development and progression of nephrosclerosis.