Membrane depolarization induces calcium-dependent upregulation of Hsp70 and Hmox-1 in skeletal muscle cells.

Jorquera G, Juretic N, Jaimovich E, Riveros N. Membrane depolarization induces calcium-dependent upregulation of Hsp70 and Hmox-1 in skeletal muscle cells. Am J Physiol Cell Physiol 297: C581-C590, 2009. First published July 1, 2009; doi:10.1152/ajpcell.00167.2009.-Heat shock proteins (HSPs) are a conserved family of cytoprotective polypeptides, synthesized by cells in response to stress. Hsp70 and heme oxygenase 1 (Hmox-1) are induced by a variety of cellular stressors in skeletal muscle, playing a role in long-term adaptations and muscle fibers regeneration. Though HSPs expression after exercise has been intensely investigated, the molecular mechanisms concerning Hsp70 and Hmox-1 induction are poorly understood. The aim of this work was to investigate the involvement of calcium in Hsp70 and Hmox-1 expression upon depolarization of skeletal muscle cells. We observed that depolarization of myotubes increased both mRNA levels and protein expression for Hsp70 and Hmox-1. Stimulation in the presence of intracellular calcium chelator BAPTA-AM resulted in a complete inhibition of Hsp70-induced expression. It is known that inositol-1,4,5-trisphophate (IP3)-mediated slow Ca2+ transients, evoked by membrane depolarization, are involved in the regulation of gene expression. Here we demonstrated that inhibition of IP3-dependent calcium signals decreased both Hsp70 mRNA induction and Hsp70 and Hmox-1 protein expression. Inhibitors of calcium-dependent protein kinase C also abolished Hsp70 mRNA induction. Our results provide evidence that membrane depolarization increases Hsp70 and Hmox-1 expression in cultured skeletal muscle cells, which the effect is critically dependent on Ca2+ released from IP3-sensitive intracellular stores and that it involves PKC as an upstream effector in Hsp70 mRNA-induced expression.