Localization of Atypical Protein Kinase C Isoforms into Lysosome-Targeted Endosomes through Interaction with p62

Abstract

An increasing number of independent studies indicate that the atypical protein kinase C (PKC) isoforms (aPKCs) are critically involved in the control of cell proliferation and survival. The aPKCs are targets of important lipid mediators such as ceramide and the products of the PI 3-kinase. In addition, the aPKCs have been shown to interact with Ras and with two novel proteins, LIP (lambda-interacting protein; a selective activator of /PKC) and the product of par-4 (a gene induced during apoptosis), which is an inhibitor of both /PKC and PKC. LIP and Par-4 interact with the zinc finger domain of the aPKCs where the lipid mediators have been shown to bind. Here we report the identification of p62, a previously described phosphotyrosineindependent p56 lck SH2-interacting protein, as a molecule that interacts potently with the V1 domain of /PKC and, albeit with lower affinity, with PKC. We also show in this study that ectopically expressed p62 colocalizes perfectly with both /PKC and PKC. Interestingly, the endogenous p62, like the ectopically expressed protein, displays a punctate vesicular pattern and clearly colocalizes with endogenous /PKC and endogenous PKC. P62 colocalizes with Rab7 and partially with lamp-1 and limp-II as well as with the epidermal growth factor (EGF) receptor in activated cells, but not with Rab5 or the transferrin receptor. Of functional relevance, expression of dominant negative /PKC, but not of the wild-type enzyme, severely impairs the endocytic membrane transport of the EGF receptor with no effect on the transferrin receptor. These findings strongly suggest that the aPKCs are anchored by p62 in the lysosome-targeted endosomal compartment, which seems critical for the control of the growth factor receptor trafficking. This is particularly relevant in light of the role played by the aPKCs in mitogenic cell signaling events.

The Drosophila Atypical Protein Kinase C-Ref(2)P Complex Constitutes a Conserved Module for Signaling in the Toll Pathway

“…Of note, the down-regulation of Ref (2)P by RNAi promotes the release of DaPKC from a Triton-soluble membrane fraction (Fig. 8B), consistent with previously published evidence on the localization of p62 in mammalian cells (28).…”

“…Proteins were transferred onto poly(vinylidene fluoride) membranes by electroblotting and then probed with the corresponding antibody. The membrane localization of PKC in Ref(2)P RNAi-treated cells was determined as described previously (28).…”

“…However, the existence of scaffold proteins may explain how a single PKC subtype can be involved in different signaling cascades. Thus, through their interaction with p62, the aPKCs are located in the NF-B pathway (28)(29)(30), while their binding to MEK5 (7) may serve to place the aPKCs in the BMK1/ ERK5 mitogenic signaling cascade that likely regulates c-Jun expression. In addition, the interaction with Par-6/ASIP involves the aPKCs in the control of cell polarity.…”

p62/SQSTM1 at the interface of aging, autophagy, and disease

“…Through the PB1 domain, p62/ SQSTM1 associates with several kinases, like atypical protein kinase C (aPKC) and p56 lck , and participates in signal transduction cascades (Joung et al 1996;Sanchez et al 1998). Furthermore, the PB1 domain allows p62/ SQSTM1 to oligomerize, a process that helps clearing selective autophagy substrates (Kirkin et al 2009;Itakura and Mizushima 2011;Pankiv et al 2007).…”

Identification of a consensus site for TRAF6/p62 polyubiquitination

“…Cytoplasmic protein p62 was identified as an interacting partner of atypical protein kinase C (PKC) [2] and has been shown to contain several protein-protein interacting modules that enable the protein to serve as a scaffold for activation of the transcription factor NF-κB [3]. The multidomain protein structure of p62 is suggestive of diverse protein-protein interactions and its link in cellular functions.…”