Profilin and gelsolin stimulate phosphatidylinositol 3-kinase activity.
Actin-binding proteins such as profilin and gelsolin bind to phosphatidylinositol (PI) 4,5-bisphosphate (PI 4,5-P2) and regulate the concentration of monomeric actin. We report here that profilin and gelsolin stimulate PI 3-kinase-mediated phosphorylation of PI 4,5-P2 (lipid kinase activity) in a concentration-dependent manner. This effect is specific to profilin and gelsolin because other cytoskeletal proteins such as tau or actin do not affect PI 3-kinase activity. In addition to lipid kinase activity, PI 3-kinase also has protein kinase activity: it phosphorylates proteins (p85 subunit of PI 3-kinase). However, the protein kinase activity of PI 3-kinase was not affected in the presence of profilin. Kinetic analysis, as a function of varying concentrations of ATP and PI 4,5-P2, showed that profilin affects the Vmax of PI 3-kinase without affecting k(m). Profilin may also affect PI 3-kinase activity by its direct association to the enzyme because dot-blot analysis using antibody to glutathione S-transferase (GST) suggested that GST-85 kDa, a fusion protein of PI 3-kinase, binds to profilin. However, PI 3-kinase did not affect the actin-sequestering ability of profilin (determined by pyrene-labeled actin), which indicates that actin and p85 do not share a common binding site on profilin. These studies suggest that profilin and gelsolin may control the generation of 3-OH phosphorylated phosphoinositides, which in turn may regulate the actin polymerization.
Singh
S S
SS
NYS Institute For Basic Research in Developmental Disabilities, Staten Island, New York 10314, USA.
Chauhan
A
A
Murakami
N
N
Chauhan
V P
VP
D000199:Actins / Q000378:metabolism; D000255:Adenosine Triphosphate / Q000494:pharmacology; D000818:Animals; D001665:Binding Sites; D002118:Calcium / Q000494:pharmacology; D003285:Contractile Proteins; D003598:Cytoskeletal Proteins / Q000494:pharmacology; D018260:Gelsolin / Q000494:pharmacology*; D066298:In Vitro Techniques; D007700:Kinetics; D008081:Liposomes; D008840:Microfilament Proteins / Q000494:pharmacology*; D019869:Phosphatidylinositol 3-Kinases; D019269:Phosphatidylinositol 4,5-Diphosphate / Q000494:pharmacology; D010716:Phosphatidylinositols / Q000378:metabolism; D010766:Phosphorylation; D017853:Phosphotransferases (Alcohol Group Acceptor) / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D051304:Profilins; D011487:Protein Conformation; D011994:Recombinant Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism
D000199:Actins; D003285:Contractile Proteins; D003598:Cytoskeletal Proteins; D018260:Gelsolin; D008081:Liposomes; D008840:Microfilament Proteins; D019269:Phosphatidylinositol 4,5-Diphosphate; D010716:Phosphatidylinositols; D051304:Profilins; D011994:Recombinant Proteins; D000255:Adenosine Triphosphate; D019869:Phosphatidylinositol 3-Kinases; D017853:Phosphotransferases (Alcohol Group Acceptor); D002118:Calcium