Regulation of basal autophagy by transient receptor potential melastatin 7 (TRPM7) channel

Macroautophagy (hereafter referred to as autophagy) is a catabolic process for the degradation and recycling of cellular components. Autophagy digests intracellular components, recycling material subsequently used for new protein synthesis. The Ca(2+)- and Mg(2+)-permeable transient receptor potential melastatin 7 (TRPM7) channel underlies the constitutive Ca(2+) influx in some cells. Since autophagy is regulated by cytosolic Ca(2+) level, we set out to determine whether Ca(2+) influx through the TRPM7 channel regulates basal autophagy. When TRPM7 channel expression was induced from HEK293 cells in a nutrient-rich condition, LC3-II level increased indicating the increased level of basal autophagy. The effect of TRPM7 channel on basal autophagy was via Ca(2+)/calmodulin-dependent protein kinase kinase β, and AMP-activated protein kinase pathway. In contrast, the level of basal autophagy was decreased when the endogenous TRPM7 channel in SH-SY5Y cells was down-regulated using short hairpin RNA. Similarly, an inhibitor for TRPM7 channel decreased the level of basal autophagy. In addition, the inhibitory effect of channel inhibitor on basal autophagy was reversed by increasing extracellular Ca(2+)concentration, suggesting that Ca(2+) influx through TRPM7 channel directly links to basal autophagy. Thus, our studies demonstrate the new role of TRPM7 channel-mediated Ca(2+) entry in the regulation of basal autophagy.