NON-GENOMIC MECHANISM INVOLVED IN THE ANTIAPOPTOTIC ACTION OF 17beta-ESTRADIOL IN SKELETAL MUSCLE CELLS

RICARDO BOLAND; LORENA MILANESI; ANA RONDA; ANDREA VASCONSUELO

CONCEPCIÓN, CHILE

Workshop; SECOND WORKSHOP OF SIGNAL TRANSDUCTION MECHANISM MEDIATING STEROID NON-GENOMIC ACTION; 2008

In this study we report that 17beta-estradiol, through estrogen receptors with non-nuclear localization, e.g. mitochondria, endoplasmic reticulum and Golgi, can regulate apoptosis in mouse skeletal muscle C2C12 cells. 17beta-estradiol, at physiological concentrations, abrogates DNA damage, PARP cleavage and cytochrome c release induced by H2O2 or etoposide. This protective action of the steroid involves fast activation of the PI3K/Akt/Bad pathway. Within the same short time interval 17beta-estradiol increases phosphorylation of ERK 1/2 and p38 MAPK. Interestingly the main localization of phosphorylated ERK 1/2 is mitochondrial. In addition the effect of the hormone on cytochrome c release was blocked in presence of inhibitors of MAPKs. Evidence was obtained suggesting that the ERK 1/2 and PI3K/Akt/Bad pathways play a role in the antiapoptotic effects of 17beta-estradiol at the level of mitochondria. Blocking experiments with specific antibodies and siRNAs against the estrogen receptors alpha (ER alpha) and beta (ER beta) isoforms, revealed that ER beta mediates to a greater extent than ER alpha the antiapoptotic effects of 17beta-estradiol in mitochondria. Furthermore, it was shown that the protective role of the hormone requires the participation of heat shock protein 27 (HSP27). 17beta-estradiol rapidly induced phosphorylation of HSP27. Immunocytochemistry and co-immunoprecipitation assays demonstrated co-localization and interaction of the chaperone with ER beta in mitochondria. Altogether, these results suggest that the antiapoptotic signal triggered by 17beta-estradiol in muscle cells involves a non-genomic mechanism mediated by ER beta and rapid activation of Akt and MAPKs, and the participation of HSP27.