CALCITRIOL INDUCES PKC/PTP/c-SRC ACTIVATION UPSTREAM TO ERK 1/2 AND p38 MAPK PHOSPHORYLATION IN SKELETAL MUSCLE CELLS?,

BUITRAGO C; BOLAND R

Buenos Aires

Congreso; XXV Reunion Annual Asociación Argentina de Osteología y Metabolismo Mineral (AAOMM).; 2008

1α,25(OH)2D3 (calcitriol) modulates gene expression via an intracellular receptor (VDR) and also induces fast non-transcriptional responses through transmembrane signal transduction pathways. The existence of the VDR in skeletal muscle cells is well documented but the specific actions of 1α,25(OH)2D3 in these target cells are unclear. In different tissues, calcitriol promotes responses through ERK 1/2 and p38 MAPK. c-Src is a member of a tyrosine kinase family involved in ERK 1/2 and p38 MAPK activation. Dephosphorylation of c-Src in Tyr 527 results in its activation, so c-Src has been reported as a substrate for protein tyrosine phosphatase alpha (PTPalpha) which is in turn activated by PKC. We have previously shown in C2C12 skeletal muscle cells that 1α,25(OH)2D3-dependent ERK 1/2 and p38 MAPK upregulation involves the participation of c-Src. Now, we investigated metabolic steps upstream of c-Src stimulation by calcitriol in these cells. calcitriol stimulates c-Src in a PKC-dependent manner. Therefore the role of PTPalpha in c-Src activation was evaluated. Our results demonstrate that 1α,25(OH)2D3promotes Tyr 789 phosphorylation of PTPalpha, which is necessary to activate c-Src by tyrosine dephosphorylation. An acute increase in PTPalpha phosphatase activity is observed 60 min after calcitriol treatment. Moreover, there is co-localization of PTPalpha and c-Src promoted by 1α,25(OH)2D3that is blocked with the PKC inhibitor Ro 318220. We corroborated the physical association PTPalpha-c-Src by co-immunoprecipitation assays after 1α,25(OH)2D3 and TPA treatments.We conclude that calcitriol activates PKC which induces c-Src kinase activity via stimulation of PTPalpha, events occurring upstream to ERK 1/2 and p38 MAPK upregulation.