Association of the tensin N-terminal protein-tyrosine phosphatase domain with the α isoform of protein phosphatase-1 in focal adhesions

Focal adhesions attach cultured cells to the extracellular matrix, and we found endogenous protein phosphatase-1 alpha-isoform (PP1 alpha) localized in adhesions across the entire area of adherent fibroblasts. However, in fibroblasts migrating into a scrape wound or spreading after replating PP1 alpha did not appear in adhesions near the leading edge but was recruited into other adhesions coincident in time and space with incorporation of tensin. Endogenous tensin and PP1 alpha co-precipitated from cell lysates with isoform-specific PP1 antibodies. Chemical cross-linking of focal adhesion preparations with Lomant's reagent demonstrated molecular proximity of endogenous PP1 alpha and tensin, whereas neither focal adhesion kinase nor vinculin was cross-linked and co-precipitated with PP1 alpha, suggesting distinct spatial subdomains within adhesions. Transient expression of truncated tensin showed the N-terminal 360 residues, which comprise a protein-tyrosine phosphatase domain, alone were sufficient for isoform-selective co-precipitation of co-expressed PP1 alpha. Human prostate cancer PC3 cells are deficient in tensin relative to fibroblasts and have fewer, mostly peripheral adhesions. Transient expression of green fluorescent protein tensin in these cancer cells induced formation of adhesions and recruited endogenous PP1 alpha into those adhesions. Thus, the protein-tyrosine phosphatase domain of tensin exhibits isoform-specific association with PP1 alpha in a restricted spatial region of adhesions that are formed during cell migration.