Affiliation: University of California, San Diego La Jolla, CA
Keywords: g. autophagy; c. endocytosis
Macroautophagy (autophagy) is a trafficking pathway that relies on delivery of membrane-bound cytoplasmic contents for degradation by the lysosome, referred to as the autolysosome. The lysosome is a very important component in autophagy regulation as it must be able to accommodate the convergence of cargos from both autophagy and endocytosis pathways, as well as coordinate autolysosome maturation with changing levels of basal versus stress-induced autophagy. In order for to replenish the lysosomes during prolonged starvation-induced autophagy, one-way new lysosomes can be made is through the autophagic lysosome reformation (ALR) pathway. Tubule-like projections from lysosomes pinch-off to form proto-lysosomes, eventually maturing into new functional lysosomes. We identified two phosphoinositide lipid regulators, class II PI3-kinase (PI3KC2) and Myotubularin PI3-phosphatase (Mtm), that act in a shared autolysosome inhibitory pathway to maintain basal levels of autophagy in the fat body of fed Drosophila larvae. Strikingly, we discovered that wildtype flies also co-express a truncated, noncatalytic PI3KC2 splice variant (PI3KC2-short) that, converse to PI3KC2 and Mtm, is required for autolysosome maturation through repression of their catalytic activities. We have shown that defects in autolysosome maturation correlate with aspects of (ALR). Our work addresses the importance of coordinated activity between specific phosphoinositide kinase and phosphatase activities. In addition, this study reveals a novel role for their joint regulation by a noncatalytic splice variant to respond to changing homeostatic demands in membrane flux.