No abstract

bAutophagy is a conserved process that enables catabolic and degradative pathways. Rab family proteins, which are active in the GTP-bound form, regulate the transport and fusion of autophagosomes. However, it remains unclear how each cycle of Rab activation and inactivation is precisely regulated. Here, we show that leucine-rich repeat kinase 1 (LRRK1) regulates autophagic flux by controlling Rab7 activity in autolysosome formation. Upon induction of autophagy, LRRK1 was recruited via an association with VAMP7 to the autolysosome, where it activated the Rab7 GTPase-activating protein (GAP) TBC1D2, thereby switching off Rab7 signaling. Consistent with this model, LRRK1 deletion caused mice to be vulnerable to starvation and disrupted autolysosome formation, as evidenced by the accumulation of enlarged autolysosomes with undegraded LC3-II and persistently high levels of Rab7-GTP. This defect in autophagic flux was partially rescued by a mutant form of TBC1D2 with elevated Rab7-GAP activity. Thus, the spatiotemporal regulation of Rab7 activity during tunicamycin-induced autophagy is regulated by LRRK1.

Mutations in the leucine-rich repeat kinase 2 (LRRK2) gene are the most common cause of familial Parkinson's disease (PD). Impaired mitochondrial function is suspected to play a major role in PD. Nonetheless, the underlying mechanism by which impaired LRRK2 activity contributes to PD pathology remains unclear. Here, we identified the role of LRRK2 in endoplasmic reticulum (ER)mitochondrial tethering, which is essential for mitochondrial bioenergetics. LRRK2 regulated the activities of E3 ubiquitin ligases MARCH5, MULAN, and Parkin via kinase-dependent protein-protein interactions. Kinase-active LRRK2(G2019S) dissociated from these ligases, leading to their PERK-mediated phosphorylation and activation, thereby increasing ubiquitin-mediated degradation of ER-mitochondrial tethering proteins. By contrast, kinase-dead LRRK2(D1994A)-bound ligases blocked PERK-mediated phosphorylation and activation of E3 ligases, thereby increasing the levels of ER-mitochondrial tethering proteins. Thus, the role of LRRK2 in the ER-mitochondrial interaction represents an important control point for cell fate and pathogenesis in PD.

Neutrophils rapidly undergo polarization and directional movement to infiltrate the sites of infection and inflammation. Here, we show that an inhibitory MHC I receptor, Ly49Q, was crucial for the swift polarization of and tissue infiltration by neutrophils. During the steady state, Ly49Q inhibited neutrophil adhesion by preventing focal-complex formation, likely by inhibiting Src and PI3 kinases. However, in the presence of inflammatory stimuli, Ly49Q mediated rapid neutrophil polarization and tissue infiltration in an ITIM-domain-dependent manner. These opposite functions appeared to be mediated by distinct use of effector phosphatase SHP-1 and SHP-2. Ly49Q-dependent polarization and migration were affected by Ly49Q regulation of membrane raft functions. We propose that Ly49Q is pivotal in switching neutrophils to their polarized morphology and rapid migration upon inflammation, through its spatiotemporal regulation of membrane rafts and raft-associated signaling molecules.

Tumors or embryonic stem cells bearing foreign mitochondrial DNA are rejected by the innate immune system via a mechanism that depends on MyD88.