Comparative interactomics analysis reveals potential regulators of α6β4 distribution in keratinocytes

The integrin alpha 6 beta 4 and cytoskeletal adaptor plectin are essential components of type I and type II hemidesmosomes (HDs). We recently identified an alternative type II HD adhesion complex that also contains CD151 and the integrin alpha 3 beta 1. Here, we have taken a BioID proximity labeling approach to define the proximity protein environment for alpha 6 beta 4 in keratinocytes. We identified 37 proteins that interacted with both alpha 6 and beta 4, while 20 and 78 proteins specifically interacted with the alpha 6 and beta 4 subunits, respectively. Many of the proximity interactors of alpha 6 beta 4 are components of focal adhesions (FAs) and the cortical microtubule stabilizing complex (CMSC). Though the close association of CMSCs with alpha 6 beta 4 in HDs was confirmed by immunofluorescence analysis, CMSCs have no role in the assembly of HDs. Analysis of the beta 4 interactome in the presence or absence of CD151 revealed that they are strikingly similar; only 11 different interactors were identified. One of these was the integrin alpha 3 beta 1, which interacted with alpha 6 beta 4 more strongly in the presence of CD151 than in its absence. These findings indicate that CD151 does not significantly contribute to the interactome of alpha 6 beta 4, but suggest a role of CD151 in linking alpha 3 beta 1 and alpha 6 beta 4 together in tetraspanin adhesion structures.