p85/p110-type phosphatidylinositol kinase phosphorylates not only the D-3, but also the D-4 position of the inositol ring.
Activation of p85/p110-type phosphatidylinositol (PI) kinase has been implicated in various cellular activities. This PI kinase phosphorylates the D-4 position with a similar or higher efficiency than the D-3 position when trichloroacetic acid-treated cell membrane is used as a substrate, although it phosphorylates almost exclusively the D-3 position of the inositol ring in phosphoinositides when purified PI is used as a substrate. Furthermore, the lipid kinase activities of p110 for both the D-3 and D-4 positions were completely abolished by introducing kinase-dead point mutations in their lipid kinase domains (DeltaKinalpha and DeltaKinbeta, respectively). In addition, both PI 3- and PI 4-kinase activities of p110alpha and p110beta immunoprecipitates were similarly inhibited by either wortmannin or LY294002, specific inhibitors of p110. Insulin induced phosphorylation of not only the D-3 position, but also the D-4 position. Indeed, overexpression of p110 in Sf9 or 3T3-L1 cells induced marked phosphorylation of the D-4 position to a level comparable to or much greater than that of D-3, whereas inhibition of endogenous p85/p110-type PI kinase via overexpression of dominant-negative p85alpha (Deltap85alpha) in 3T3-L1 adipocytes abolished insulin-induced synthesis of both. Thus, p85/p110-type PI kinase phosphorylates the D-4 position of phosphoinositides more efficiently than the D-3 position in vivo, and each of the D-3- or D-4-phosphorylated phosphoinositides may transmit signals downstream.
Institute for Adult Disease, Asahi Life Foundation, 1-9-14, Nishishinjuku, Shinjuku-ku, Tokyo 160, Japan.
M
M
Funaki
H
H
Katagiri
A
A
Kanda
M
M
Anai
M
M
Nawano
T
T
Ogihara
K
K
Inukai
Y
Y
Fukushima
H
H
Ono
Y
Y
Yazaki
M
M
Kikuchi
Y
Y
Oka
T
T
Asano
D019870:1-Phosphatidylinositol 4-Kinase / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D016475:3T3 Cells; D000730:Androstadienes / Q000494:pharmacology; D000818:Animals; D002460:Cell Line; D002867:Chromones / Q000494:pharmacology; D004789:Enzyme Activation; D004791:Enzyme Inhibitors / Q000494:pharmacology; D051379:Mice; D009025:Morpholines / Q000494:pharmacology; D016297:Mutagenesis, Site-Directed; D019869:Phosphatidylinositol 3-Kinases / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D010716:Phosphatidylinositols / Q000378:metabolism*; D010761:Phosphorus Radioisotopes; D010766:Phosphorylation; D017354:Point Mutation; D011994:Recombinant Proteins / Q000737:chemistry / Q000378:metabolism; D018411:Spodoptera; D013379:Substrate Specificity; D014162:Transfection; D000077191:Wortmannin
D000730:Androstadienes; D002867:Chromones; D004791:Enzyme Inhibitors; D009025:Morpholines; D010716:Phosphatidylinositols; D010761:Phosphorus Radioisotopes; D011994:Recombinant Proteins; C085911:2-(4-morpholinyl)-8-phenyl-4H-1-benzopyran-4-one; D019869:Phosphatidylinositol 3-Kinases; D019870:1-Phosphatidylinositol 4-Kinase; D000077191:Wortmannin