Rab2 requires PKCi/λ to recruit β-COP for vesicle formation

Abstract

The small GTPase Rab2 initiates the recruitment of soluble components necessary for protein sorting and recycling from pre-Golgi intermediates. Our previous studies showed that Rab2 required protein kinase C (PKC) or a PKC-like protein to recruit β-COP to membrane (Tisdale EJ, Jackson M. Rab2 protein enhances coatomer recruitment to pre-Golgi intermediates. J Biol Chem 1998;273: 17269-17277). We investigated the role of PKC in Rab2 function by first determining the active isoform that associates with membranes used in our assay. Western blot analysis detected three isoforms: PKCα, γ and i/λ. A quantitative binding assay was used to measure recruitment of these kinases when incubated with Rab2. Only PKCi/λ translocated to membrane in a dose-dependent manner. Microsomes treated with anti-PKCi/λ. lost the ability to bind β-COP, suggesting that Rab2 requires PKCi/λ. for β-COP recruitment. The recruitment of β-COP to membranes is not regulated by PKCi/λ kinase activity. However, PKCi/λ. kinase activity was necessary for Rab2-mediated vesicle budding. We found that the addition of either a kinase-deficient PKCi/λ. mutant or atypical PKC pseudosubstrate peptide to the binding assay drastically reduced vesicle formation. These data suggest that Rab2 causes translocation of PKCi/λ. to vesicular tubular clusters (VTCs), which promotes the recruitment of COPI to generate retrograde-transport vesicles. Copyright © Munksgaard 2000.