Ubiquitin-regulated sorting of Caveolin-1 in the endosomal system

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Caveolin-1 (CAV1) and its isoforms are the major constituents of caveolae, which play important roles in cellular mechano-protection, endocytosis, and signalling. Mono-ubiquitination of CAV1 governs CAV1 trafficking along the endocytic pathway and sorting into endolysosomes for degradation. One effector of ubiquitinated CAV1 (Ub-CAV1) is an endosomal complex of the VCP/p97 AAA-ATPase. Crucially, disease-associated mutations in VCP/p97, which cause muscle and neuronal degeneration in humans, affect Ub-CAV1 binding and endosomal sorting. However, key regulators of the process such as the CAV1-specific ubiquitin ligase and additional downstream effectors of Ub-CAV1 are unknown. Using a microscopy-based ubiquitination assay, we wish to carry out an siRNA-mediated screen to identify the relevant E3 ubiquitin ligase. In parallel, we wish to perform CAV1 affinity purification coupled with mass spectrometry to identify additional effector proteins that mediate transport of Ub-CAV1. Using established transport assays in tissue culture cells, we will study how these factors mediate different steps in Ub-CAV1 sorting in endosomal pathways and CAV1 turnover in the lysosome. The expected results will help understand a novel layer of regulation of CAV1, and provide further insights into the complex pathogenesis of degenerative diseases caused by mutations in p97 and related defects in the endolysosomal system.