title: Cell-cycle-dependent association of protein phosphatase 1 and focal adhesion kinase.
abstract: Immunofluorescence studies with protein phosphatase-1 (PP1) isoforms-specific antibodies detected PP1delta, but not alpha or gamma1, at focal adhesions. PP1delta also co-immunoprecipitated with the focal adhesion kinase (FAK) and the alphav-integrin. In the present study glutathione S-transferase (GST)-PP1delta pulled-down FAK from fibroblasts extract and the interaction domain localized between residues 159 and 295 of delta. The association was confirmed by the ability to GST-FAK-related non-kinase (FRNK) to pull-down PP1delta from fibroblasts extract. GST-FRNK also pulled-down purified muscle PP1 catalytic subunit, thus indicating direct interaction between FAK and PP1. FAK displays consensus sequences for phosphorylation by cell division cycle kinase-2-cyclin B, and might be a PP1 substrate. In fact, FAK immunoprecipitated from metabolically-labelled mitotic HeLa cells without tyrosine phosphatase inhibitors was phosphorylated on Ser only and was dephosphorylated in vitro by purified muscle PP1, with loss of phospho-Ser. No PP1 was associated with FAK immunoprecipitated from mitotic HeLa cells. However, progressively more PP1 activity was assayed in FAK-immunoprecipitates obtained from cells released from mitosis. The associated activity was maximal at 2 h from the mitotic release (when 85-90% of the cells remained round) and decreased to basal level by 8 h (when cells were all polygonal). At the same time FAK underwent dephosphorylation, which was completed by 4 h. FAK obtained from cells at 1.5 h was Ser-phosphorylated, and underwent dephosphorylation during in vitro incubation, with loss of phospho-Ser, indicating the presence of active FAK-bound phosphatase. The only FAK-associated PP1 isoform between 1 and 8 h was PP1delta. The results suggest that FAK dephosphorylation by PP1delta occurs in cells released from mitosis, and confirmed the specific association of PP1delta, as detected previously in adherent cells.
authors.affiliation: Department of Experimental Pathology, University of Pisa, Via Roma 55 56126 Pisa, Italy.
authors.forename: M
authors.initials: M
authors.lastname: Fresu
authors.forename: M
authors.initials: M
authors.lastname: Bianchi
authors.forename: J T
authors.initials: JT
authors.lastname: Parsons
authors.forename: E
authors.initials: E
authors.lastname: Villa-Moruzzi
mesh_terms: D000818:Animals; D002453:Cell Cycle; D002478:Cells, Cultured; D051417:Focal Adhesion Kinase 1; D051416:Focal Adhesion Protein-Tyrosine Kinases; D005982:Glutathione Transferase / Q000235:genetics; D006367:HeLa Cells; D006801:Humans; D008938:Mitosis; D018482:Muscle, Skeletal / Q000201:enzymology; D010749:Phosphoprotein Phosphatases / Q000235:genetics / Q000378:metabolism*; D010766:Phosphorylation; D054645:Protein Phosphatase 1; D011505:Protein-Tyrosine Kinases / Q000235:genetics / Q000378:metabolism*; D011817:Rabbits; D051381:Rats; D011916:Rats, Inbred F344; D011993:Recombinant Fusion Proteins / Q000378:metabolism
chemical_list: D011993:Recombinant Fusion Proteins; D005982:Glutathione Transferase; C113183:FAK-related nonkinase; D011505:Protein-Tyrosine Kinases; D051417:Focal Adhesion Kinase 1; D051416:Focal Adhesion Protein-Tyrosine Kinases; C496050:PTK2 protein, human; C496052:Ptk2 protein, rat; D010749:Phosphoprotein Phosphatases; D054645:Protein Phosphatase 1