Psoriasin (S100A7) associates with integrin β6 subunit and is required for αvβ6-dependent carcinoma cell invasion

Expression of the integrin αvβ6 is upregulated in a variety of carcinomas where it appears to be involved in malignant progression, although the biology of this integrin is not fully explored. We have generated oral carcinoma cells that express αvβ6 composed of wild-type αv and a mutant β6 that lacks the unique C-terminal 11 amino acids (aa). We found that these residues, although not required for αvβ6-dependent adhesion or migration, are essential for αvβ6-dependent invasive activity. We have used a proteomic approach to identify novel binding partners for the β6 subunit cytoplasmic tail and report that psoriasin (Psor) (S100A7) bound preferentially to the recombinant β6 cytoplasmic domain, though not in the absence of the unique C-terminal 11aa. Endogenous cellular Psor co-precipitated with endogenous β6 and colocalised with αvβ6 at the cell membrane and intracellular vesicles. Knockdown of Psor, with small interfering RNA, had no effect on αvβ6-dependent adhesion or migration but abrogated αvβ6-mediated oral carcinoma cell invasion both in Transwell and, the more physiologically relevant, organotypic invasion assays, recapitulating the behaviour of the β6-mutant cell line. Membrane-permeant Tat-peptides encoding the unique C-terminal residues of β6, bound directly to recombinant Psor and inhibited cellular Psor binding to β6; this blocked αvβ6-dependent, but not αvβ6-independent, invasion. These data identify a novel interaction between Psor and β6 and demonstrate that it is required for αvβ6-dependent invasion by carcinoma cells. Inhibition of this interaction may represent a novel therapeutic strategy to target carcinoma invasion.