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 Ca2+- and Mg2+-permeable transient receptor potential melastatin 7 (TRPM7) channel underlies the constitutive Ca2+ influx in some cells. Since autophagy is regulated by cytosolic Ca2+ level, we set out to determine whether Ca2+ 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 Ca2+/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 Ca2+concentration, suggesting that Ca2+ influx through TRPM7 channel directly links to basal autophagy. Thus, our studies demonstrate the new role of TRPM7 channel-mediated Ca2+ entry in the regulation of basal autophagy.