alpha-Actinin and vinculin are PIP2-binding proteins involved in signaling by tyrosine kinase.

Western blot analysis of Balb/c 3T3 cell lysates by an antibody specific to phosphatidylinositol 4,5-bisphosphate (PIP2) showed that several proteins exist in a PIP2-bound form. Among them, two proteins, 100 and 115 kDa in molecular mass, were detected as PIP2 abundant proteins. These were identified as alpha-actinin and vinculin by their antibodies. In Balb/c 3T3 cells, alpha-actinin in the cytoskeleton contains PIP2, while alpha-actinin in cytosol does not. The levels of PIP2 bound to alpha-actinin decrease in response to platelet-derived growth factor (PDGF). Similarly, PIP2 bound to vinculin is decreased upon stimulation with PDGF. By immunofluorescent staining, PIP2 was found to be present densely in the central areas around nuclei, microfilament bundles, and focal contacts, where alpha-actinin and vinculin are distributed. PDGF stimulation decreases the intensity of PIP2 staining in these areas. In this paper we suggest that tyrosine kinase-activated phospholipase C hydrolyzes PIP2 bound to alpha-actinin and vinculin, leading to the simultaneous generation of second messengers and reorganization of the cytoskeleton.