Phosphatidylinositol 4,5-bisphosphate phosphatase regulates the rearrangement of actin filaments.
Phosphatidylinositol 4,5-bisphosphate (PIP2) reorganizes actin filaments by modulating the functions of a variety of actin-regulatory proteins. Until now, it was thought that bound PIP2 is hydrolyzed only by tyrosine-phosphorylated phospholipase Cgamma (PLCgamma) after the activation of tyrosine kinases. Here, we show a new mechanism for the hydrolysis of bound PIP2 and the regulation of actin filaments by PIP2 phosphatase (synaptojanin). We isolated a 150-kDa protein (p150) from brains that binds the SH3 domains of Ash/Grb2. The sequence of this protein was found to be homologous to that of synaptojanin. The expression of p150 in COS 7 cells produces a decrease in the number of actin stress fibers in the center of the cells and causes the cells to become multinuclear. On the other hand, the expression of a PIP2 phosphatase-negative mutant does not disrupt actin stress fibers or produce the multinuclear phenotype. We have also shown that p150 forms the complexes with Ash/Grb2 and epidermal growth factor (EGF) receptors only when the cells are treated with EGF and that it reorganizes actin filaments in an EGF-dependent manner. Moreover, the PIP2 phosphatase activity of native p150 purified from bovine brains is not inhibited by profilin, cofilin, or alpha-actinin, although PLCdelta1 activity is markedly inhibited by these proteins. Furthermore, p150 suppresses actin gelation, which is induced by smooth muscle alpha-actinin. All these data suggest that p150 (synaptojanin) hydrolyzes PIP2 bound to actin regulatory proteins, resulting in the rearrangement of actin filaments downstream of tyrosine kinase and Ash/Grb2.
Sakisaka
T
T
Department of Biochemistry, Institute of Medical Science, University of Tokyo, Minato-ku, Japan.
Itoh
T
T
Miura
K
K
Takenawa
T
T
D008841:Actin Cytoskeleton / Q000648:ultrastructure*; D051339:Actin Depolymerizing Factors; D000185:Actinin / Q000378:metabolism; D000199:Actins / Q000648:ultrastructure*; D048868:Adaptor Proteins, Signal Transducing; D000595:Amino Acid Sequence; D000818:Animals; D019556:COS Cells; D002417:Cattle; D003001:Cloning, Molecular; D003285:Contractile Proteins; D066246:ErbB Receptors / Q000378:metabolism; D051380:GRB2 Adaptor Protein; D008840:Microfilament Proteins / Q000378:metabolism; D008969:Molecular Sequence Data; D009419:Nerve Tissue Proteins / Q000378:metabolism* / Q000502:physiology*; D019269:Phosphatidylinositol 4,5-Diphosphate / Q000502:physiology*; D010744:Phosphoric Monoester Hydrolases / Q000378:metabolism* / Q000502:physiology*; D051304:Profilins; D011506:Proteins / Q000378:metabolism
D051339:Actin Depolymerizing Factors; D000199:Actins; D048868:Adaptor Proteins, Signal Transducing; D003285:Contractile Proteins; D051380:GRB2 Adaptor Protein; D008840:Microfilament Proteins; D009419:Nerve Tissue Proteins; D019269:Phosphatidylinositol 4,5-Diphosphate; D051304:Profilins; D011506:Proteins; D000185:Actinin; D066246:ErbB Receptors; C097702:synaptojanin; D010744:Phosphoric Monoester Hydrolases