SIP/SHIP inhibits Xenopus oocyte maturation induced by insulin and phosphatidylinositol 3-kinase.
SIP (signaling inositol phosphatase) or SHIP (SH2-containing inositol phosphatase) is a recently identified SH2 domain-containing protein which has been implicated as an important signaling molecule. SIP/SHIP becomes tyrosine phosphorylated and binds the phosphotyrosine-binding domain of SHC in response to activation of hematopoietic cells. The signaling pathways and biological responses that may be regulated by SIP have not been demonstrated. SIP is a phosphatidylinositol- and inositol-polyphosphate 5-phosphatase with specificity in vitro for substrates phosphorylated at the 3' position. Phosphatidylinositol 3'-kinase (PI 3-kinase) is an enzyme which is involved in mitogenic signaling and whose phosphorylated lipid products are predicted to be substrates for SIP. We tested the hypothesis that SIP can modulate signaling by PI 3-kinase in vivo by injecting SIP cRNAs into Xenopus oocytes. SIP inhibited germinal vesicle breakdown (GVBD) induced by expression of a constitutively activated form of PI 3-kinase (p110*) and blocked GVBD induced by insulin. SIP had no effect on progesterone-induced GVBD. Catalytically inactive SIP had little effect on insulin- or PI 3-kinase-induced GVBD. Expression of SIP, but not catalytically inactive SIP, also blocked insulin-induced mitogen-activated protein kinase phosphorylation in oocytes. SIP specifically and markedly reduced the level of phosphatidylinositol (3,4,5) triphosphate [PtdIns(3,4,5)P3] generated in oocytes in response to insulin. These results demonstrate that a member of the phosphatidylinositol polyphosphate 5-phosphatase family can inhibit signaling in vivo. Further, our data suggest that the generation of PtdIns(3,4,5)P3 by PI 3-kinase is necessary for insulin-induced GVBD in Xenopus oocytes.
Deuter-Reinhard
M
M
Chiron Corporation, Emeryville, California 94608, USA.
Apell
G
G
Pot
D
D
Klippel
A
A
Williams
L T
LT
Kavanaugh
W M
WM
D000818:Animals; D019556:COS Cells; D017871:Calcium-Calmodulin-Dependent Protein Kinases / Q000378:metabolism; D002454:Cell Differentiation / Q000187:drug effects; D007328:Insulin / Q000494:pharmacology*; D008969:Molecular Sequence Data; D009865:Oocytes / Q000166:cytology* / Q000187:drug effects; D019869:Phosphatidylinositol 3-Kinases; D000072183:Phosphatidylinositol-3,4,5-Trisphosphate 5-Phosphatases; D010744:Phosphoric Monoester Hydrolases / Q000494:pharmacology*; D010766:Phosphorylation; D017853:Phosphotransferases (Alcohol Group Acceptor) / Q000378:metabolism*; D017346:Protein Serine-Threonine Kinases / Q000378:metabolism; D011518:Proto-Oncogene Proteins / Q000378:metabolism; D019908:Proto-Oncogene Proteins c-raf; D014981:Xenopus; D018909:src Homology Domains
D017871:Calcium-Calmodulin-Dependent Protein Kinases; D007328:Insulin; D019869:Phosphatidylinositol 3-Kinases; D000072183:Phosphatidylinositol-3,4,5-Trisphosphate 5-Phosphatases; D010744:Phosphoric Monoester Hydrolases; D017853:Phosphotransferases (Alcohol Group Acceptor); D017346:Protein Serine-Threonine Kinases; D011518:Proto-Oncogene Proteins; D019908:Proto-Oncogene Proteins c-raf; C098706:INPPL1 protein, human