The VDR is REQUIRED FOR 1alpha,25(OH)2-vitamin D3 ?regulation of the cellular cycle in skeletal muscle cells

A. PAULA IRAZOQUI; BOLAND R; BUITRAGO C

Congreso; Reunión Anual de la AAOMM; 2013

We previously reported that the VDR participates in non-transcriptional events triggered by 1alpha,25(OH)2-vitamin D3 [1,25D] in skeletal muscle cells. Furthermore, in separate studies we demonstrated that 1,25D promotes muscle cell proliferation and differentiation, but we did not study in depth the hormone actions on these processes. In this work we present data indicating that the VDR also plays a role in the mechanism by which 1,25D stimulates myogenesis. To investigate VDR involvement in hormone regulation of muscle cell cycle, we significantly reduced its expression by infection of C2C12 murine myoblasts with lentiviral particles containing the pLKO.1 plasmid encoding a shRNA against mouse VDR. The vitamin D receptor was knocked down (80%) in these cells [C2C12 (-VDR)]. Cell cycle studies by flow cytometry using propidium iodide staining evidenced that hormone treatment induced an S-phase peak followed by an arrest in G0/G1 phase, events which were dependent on VDR expression. Investigation of changes in cellular cycle regulating proteins by immunoblotting showed that 1,25D augments cyclin D3 protein levels while cyclin D1 was not modified during G0/G1 arrest of cells. The up-regulation of cyclin D3 by 1,25D was abolished in C2C12 (-VDR). We detected in parallel a 1,25D -dependent acute increase in myogenin expression, implying that the G0/G1 arrest was a pro-differentiating event. In agreement with these observations, the hormone increased the cyclin inhibitors p21Waf1/Cip1 and p27Kip1 in C2C12 wild type cells. The results indicate that the VDR is involved in the control of the cellular cycle by 1,25D in skeletal muscle cells, sustaining the operation of a VDR ?dependent mechanism in hormone modulation of myogenesis.