Proximity proteomics identifies PAK4 as a component of Afadin–Nectin junctions.

ABSTRACT: Human PAK4 is an ubiquitously expressed p21-activated kinase which acts downstream of Cdc42. Since PAK4 is demonstrably enriched in cell-cell junctions, we probed the local protein environment around the kinase with a view to understanding its location and substrates. In U2OS cells expressing PAK4-BirA-GFP the resultant SILAC proximity analyses revealed a subset of 28 proteins that are primarily cell-cell junction components. The protein with highest relative biotin labelling was Afadin/AF6, which associates with the nectin family of homophilic junctional proteins. Reciprocally >50% of the PAK4-proximal proteins were identified by Afadin BioID. Pull-down experiments failed to identify junctional proteins, emphasizing the advantage of the BioID method. Mechanistically PAK4 depended on Afadin for its junctional localization, which is similar to the situation in Drosophila. A highly ranked PAK4-proximal protein LZTS2 was immuno-localized with Afadin at cell-cell junctions. Though PAK4 and Cdc42 are junctional, BioID analysis did not yield conventional cadherins, indicating their spatial segregation. To identify cellular PAK4 substrates we then assessed changes in phospho-proteome after 12 min PF-3758309 treatment. Among the PAK4-proximal junctional proteins 17 PAK4 sites were identified. Thus we show PAK4 is selective for the mammalian Afadin/nectin sub-compartment, with a demonstrably distinct localization from tight and cadherin junctions.

INSTRUMENT(S): LTQ Orbitrap

ORGANISM(S): Homo Sapiens (human)

TISSUE(S): Epithelial Cell

SUBMITTER: Sheena Wee  

LAB HEAD: Jayantha Gunaratne

PROVIDER: PXD024464 | Pride | 2021-11-30

REPOSITORIES: Pride