Title: Novel Functions for Dynein Adaptor RILP in Neuronal Autophagy
Description: Cytoplasmic dynein is a highly conserved multi-subunit motor protein that transports a variety of cellular cargoes, including proteins and organelles, towards minus ends of microtubules. Dynein is recruited to specific subclasses of cellular organelles via a specialized class of adaptor proteins, that serve as physical scaffolds for dynein recruitment to cargoes. Recent work shows that these adaptor proteins are also capable of altering biophysical properties of dynein in vitro and in vivo. This work now finds that a dynein adaptor protein, RILP, through multiple interactors, coordinates the progression of a complex biological pathway. Autophagy is a multi-step, highly conserved pathway that involves de novo formation of a double-membraned autophagosome around ubiquitinated cellular cargoes including long-lived proteins and damaged organelles for subsequent degradation by the lysosome. My work finds a dynein adaptor protein, RILP, to control not only retrograde microtubule-based autophagosome transport but their formation as well.

RILP achieves these functions by sequentially interacting with the isolation membrane protein, ATG5, and the autophagosome membrane protein, LC3. During autophagosome formation, ATG5 competes with dynein to bind to a common site within the RILP N-terminus to prevent premature initiation of autophagosome motility. Depletion or LC3-interacting site mutations in RILP prevent formation of autophagosomes as well as impede their retrograde transport. This in turn results in an accumulation of ubiquitinated cargoes, including p62/ Sequestosome-1 in cells, showing that RILP is essential for autophagic clearance in cells, a finding that has broad implications for aggregate-prone neurodegenerative diseases. Finally, this work characterizes the molecular composition of the RILP-dynein supercomplex, and identifies Lis1 (implicated in lissencephaly) as an obligate component of the RILP supercomplex. Interestingly, another dynein regulator, NudE (implicated in microcephaly) is absent. Lis1 depletion results in RILP vesicle dispersion, suggesting that it is needed for RILP-mediated dynein driven transport.

Altogether, these findings show for the first time that dynein adaptor RILP controls a complex multi-step biological pathway. The unique composition of RILP supercomplex holds new possibilities for dynein regulation in vivo.