The Greatwall kinase Rim15 promotes microautophagy and microlipophagy under the control of TORC1

Atg1/ULK1 protein kinase induces macroautophagy, but not microautophagy, after nutrient starvation and inactivation of target of rapamycin complex 1 (TORC1) protein kinase. Microautophagy is also induced by TORC1 inactivation, but a TORC1-downstream protein kinase responsible for microautophagy induction remains obscure. Here, we show that the Greatwall kinase Rim15, a downstream protein kinase of TORC1, promotes bulk microautophagy induction after TORC1 inactivation. In addition, Rim15 was required for proper induction of microlipophagy (microautophagic degradation of lipid droplet). Endosomal sorting complex required for transport (ESCRT) machinery is recruited onto the vacuolar membrane after TORC1 inactivation for microautophagy. Loss of Rim15 reduced protein levels of subunits (Vps27 and Hse1) of ESCRT-0, a primary ESCRT subcomplex. Consistently, the recruitment of ESCRT-0 onto the vacuolar membrane after rapamycin was reduced in rim15Δ cells. On the other hand, Rim15 was dispensable for ESCRT function in multivesicular body formation. This study reveals that Rim15 specifically regulates function of ESCRT-0 in microautophagy under the control of TORC1 and provides a new insight into lipophagy-related human diseases.