THE TUMOR SUPPRESSOR MERLIN REGULATES AUTOPHAGY

University Of California-Irvine, Irvine CA

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Abstract

This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. Primary support for the subproject and the subproject's principal investigator may have been provided by other sources, including other NIH sources. The Total Cost listed for the subproject likely represents the estimated amount of Center infrastructure utilized by the subproject, not direct funding provided by the NCRR grant to the subproject or subproject staff. Autophagy is a cellular catabolic process in which long-lived proteins and damaged organelles are enclosed by autophagosomes and delivered to lysosomes for degradation. However, the regulatory mechanisms governing initial autophagy induction remain poorly understood. Here we show that Merlin, a tumor suppressor that causes neurofibromatosis type 2 (NF2) when mutated, binds Unc-51/Atg1, an autophagy regulator, and that loss of Merlin leads to attenuated autophagy and autophagic membrane trafficking induced by nutrient starvation. Upon autophagy induction, Merlin forms a complex with the autophagic membrane protein LC3 and the motor protein dynein in an Unc-51/Atg1-dependent manner. MerlinK79E, a point mutation found in NF2, abolishes formation of the complex between LC3 and dynein, demonstrating a role of Merlin as an adaptor that links autophagic membranes and motors. In addition, in a 3-dimensional (3D) culture system, attenuated autophagy caused by loss of Merlin leads to enhanced metabolic stress, a phenotype typically seen in autophagy-deficient 3D culture conditions. Rapamycin, an mTOR inhibitor and autophagy inducer, restores autophagy in the absence of Merlin, suggesting that Merlin's role in autophagy is mediated upstream of mTOR. Thus, Merlin functions in autophagy by coordinating the assembly of proteins essential for autophagy induction and autophagic membrane trafficking. Detecting FRET signal in autophagy would enable us to further ascertain the mechanism and kinetics of