“Involvement of Caveolae in 1,25(OH)2D3 –dependent Activation of MAPKs in Skeletal Muscle Cells”

BUITRAGO C; BOLAND R

Canadá

Congreso; 30th Annual Meeting of the American Society for Bone and Mineral Research (ASBMR); 2008

<!-- /* Style Definitions */ p.MsoNormal, li.MsoNormal, div.MsoNormal {mso-style-parent:""; margin:0cm; margin-bottom:.0001pt; mso-pagination:widow-orphan; font-size:12.0pt; font-family:"Times New Roman"; mso-fareast-font-family:"Times New Roman"; mso-ansi-language:ES; mso-fareast-language:ES;} @page Section1 {size:612.0pt 792.0pt; margin:70.85pt 3.0cm 70.85pt 3.0cm; mso-header-margin:35.4pt; mso-footer-margin:35.4pt; mso-paper-source:0;} div.Section1 {page:Section1;} --> 1a,25(OH)2D3 is a steroid hormone that induces non-transcriptional events modulating components of signal transduction pathways in various cell types. The ERK1/2 and p38 members of the MAPK family are signaling pathways which mediate rapid responses to extracellular stimuli. Although there are data indicating that 1a,25(OH)2D3 regulates MAPK cascades in skeletal muscle cells, the role of plasma membrane components in the fast effects of the hormone in this tissue have not been investigated. In the present work, using the skeletal muscle cell line C2C12 as experimental model, we demonstrate by Western blot analysis with phosphospecific antibodies that 1a,25(OH)2D3 –dependent ERK1/2 and p38 MAPK phosphorylation are suppressed by disassembling caveolae with methyl-beta cyclodextrin (MbCD). Moreover, c-Src activation by the hormone was abolished by exposure of C2C12 cells to MbCD. One of the main molecules of caveolae expressed in this cellular type is caveolin-1 (cav-1). Therefore, we investigated the relationship between cav-1 and     c-Src. Confocal microscopy images of immunocytochemical assays of control C2C12 cells showed that cav-1 and c-Src colocalize at the plasma membrane. Cell treatment with 1a,25(OH)2D3 abolished colocalization of cav-1 and c-Src. These results were corroborated by experiments showing that 1a,25(OH)2D3 blocks coimmunoprecipation of cav-1 and c-Src observed under control conditions. Localization of the vitamin D receptor (VDR) in C2C12 cells was investigated. Congruent with previous results, translocation of the VDR to the plasma membrane occurs in cells treated with 1a,25(OH)2D3. In cells exposed to MbCD the VDR is present only in the nucleus. These data suggest that caveolae are involved in c-Src–dependent MAPK activation by 1a,25(OH)2D3 through the VDR in skeletal muscle cells.