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Depolarization-induced slow calcium transients activate early genes in skeletal muscle cells
Maria Angélica Carrasco1, Nora Riveros, Juan Ríos
1Instituto de Ciencias Biomédicas, Facultad de Medicina, Universidad de Chile, Santiago 6530499, Chile. mcarras@machi.med.uchile.cl
Abstract:
The signaling mechanisms by which skeletal muscle electrical activity leads to changes in gene expression remain largely undefined. We have reported that myotube depolarization induces calcium signals in the cytosol and nucleus via inositol 1,4,5-trisphosphate (IP(3)) and phosphorylation of both ERK1/2 and cAMP-response element-binding protein (CREB). We now describe the calcium dependence of P-CREB and P-ERK induction and of the increases in mRNA of the early genes c-fos, c-jun, and egr-1. Increased phosphorylation and early gene activation were maintained in the absence of extracellular calcium, while the increase in intracellular calcium induced by caffeine could mimic the depolarization stimulus. Depolarization performed either in the presence of the IP(3) inhibitors 2-aminoethoxydiphenyl borate or xestospongin C or on cells loaded with BAPTA-AM, in which slow calcium signals were abolished, resulted in decreased activation of the early genes examined. Both early gene activation and CREB phosphorylation were inhibited by ERK phosphorylation blockade. These data suggest a role for calcium in the transcription-related events that follow membrane depolarization in muscle cells.
Insights
Skeletal muscle electrical activity triggers gene expression changes through calcium signaling. This study reveals calcium
Area of Science:
- Molecular Biology
- Cell Signaling
- Exercise Physiology
Background:
- Skeletal muscle electrical activity influences gene expression.
- The precise signaling pathways linking muscle depolarization to gene expression changes are not fully understood.
- Previous work identified roles for calcium, inositol 1,4,5-trisphosphate (IP3), ERK1/2, and cAMP-response element-binding protein (CREB).
Purpose of the Study:
- To investigate the calcium dependence of signaling events following skeletal muscle membrane depolarization.
- To elucidate the role of intracellular calcium in the induction of early gene expression.
- To determine the interplay between calcium, IP3, ERK, and CREB pathways in response to depolarization.
Main Methods:
- Myotube depolarization was induced.
- Calcium signals were measured using fluorescent indicators.
- Inhibitors of IP3 signaling (2-aminoethoxydiphenyl borate, xestospongin C) and calcium chelators (BAPTA-AM) were used.
- Phosphorylation of ERK1/2 and CREB was assessed.
- mRNA levels of early genes (c-fos, c-jun, egr-1) were quantified.
Main Results:
- Depolarization-induced phosphorylation of CREB (P-CREB) and ERK1/2 (P-ERK), and early gene mRNA increases were calcium-dependent.
- Intracellular calcium increases mimicked depolarization effects.
- Inhibition of IP3 signaling or depletion of intracellular calcium reduced early gene activation.
- ERK phosphorylation blockade inhibited both early gene activation and CREB phosphorylation.
Conclusions:
- Calcium signaling plays a crucial role in mediating the effects of skeletal muscle membrane depolarization on gene expression.
- The findings highlight a signaling cascade involving calcium, IP3, ERK, and CREB in muscle adaptation.
- These insights contribute to understanding the molecular basis of exercise-induced gene regulation.