Homeostasis of Endocytic and Autophagic Systems: Insights from the Host-Pathogen Interaction
Year: 2010
Type: article
Abstract: The host-pathogen interaction provides a unique system offering insight into both the mechanisms by which pathogens subvert host cellular processes, and the biological processes themselves.The aim of this study was to understand the molecular basis of action of the adenovirus protein RIDα, which was originally identified by its ability to divert constitutively recycling EGF receptors to lysosomes during an adenovirus infection, and also when expressed in cells devoid of other adenovirus proteins.We report that RIDα usurps host cell machinery to exit the trans-Golgi network by an AP-1dependent mechanism.A tyrosine motif located in the carboxyl tail of RIDα mediates this interaction, and mutation to alanine blocks biosynthetic export and inhibits RIDa function.We also found that RIDα mimics GTP-Rab7 by binding two Rab7 effector proteins, RILP and ORP1L, which coordinately recruit the motor proteins necessary for movement of late endosomes along microtubules.As RIDα shares no sequence homology with Rab7 and has no intrinsic enzymatic activity, we asked how RIDα is regulated to mimic Rab7.It was discovered that RIDα is post-translationally modified by the addition of the lipid palmitate to the lone cysteine residue in the carboxyl tail.xx Mutation of this site did not affect the localization of RIDα, as both wild-type and mutant proteins localized to a unique perinuclear "autophagy-like" compartment.However, palmitoylation does affect protein function, as expression of the RIDα palmitoylationdeficient mutant altered the morphology of LAMP1-positive late endosomes.These enlarged compartments were loaded with cholesterol and other lipids, similar to the phenotype observed in the cholesterol storage disease Niemann-Pick type C (NPC).While mutant RIDα disrupted sterol regulated gene regulation, wild-type RIDα was found to rescue the defects created by the mutations that cause NPC disease.This novel function of RIDα was found to be dependent on the class III phosphatidylinositol 3kinase that regulates the expansion of autophagosomal membranes.We conclude that RIDα activates an autonomous cholesterol egress mechanism that is independent of the NPC disease gene products.As a model system, RIDα provides insight into the coordination and homeostasis of endocytic and autophagic systems, and the role of cholesterol in these pathways.
Author: Nicholas L. Cianciola
Institution: Case Western Reserve University
Language: English
Subfield: Cell Biology
Domain: Life Sciences
Open Access status: green
Funder: National Institutes of Health
OpenAlex ID: W2242774247