Developmental Cell 5 (2003) 539-545. doi:10.1016/S1534-5807(03)00296-XReceived by publisher: 0000-01-01Harvest Date: 2016-01-04 12:23:40DOI: 10.1016/S1534-5807(03)00296-XPage Range: 539-54

Among the various coats involved in vesicular transport, the clathrin associated coats that contain the adaptor complexes AP-1 and AP-2 are the most extensively characterized. The function of the recently described adaptor complex AP-3, which is similar to AP-1 and AP-2 in protein composition but does not associate with clathrin, is not known. By monitoring surface plasmon resonance we observed that AP-3 is able to interact with the tail of the lysosomal integral membrane protein LIMP-II and that this binding depends on a DEXXXLI sequence in the LIMP-II tail. Furthermore, AP-3 bound to the cytoplasmic tail of the melanosome-associated protein tyrosinase which contains a related EEXXXLL sequence. The tails of LIMP-II and tyrosinase either did not interact, or only interacted poorly, with AP-1 or AP-2. In contrast, the cytoplasmic tails of other membrane proteins containing di-leucine and/or tyrosine-based sorting signals did not bind AP-3, but AP-1 and/or AP-2. This points to a function of AP-3 in intracellular sorting to lysosomes and melanosomes of a subset of cargo proteins via di-leucine-based sorting motifs.

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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.