Thrombin receptors modulate insulin-stimulated phosphatidylinositol 3,4,5-trisphosphate accumulation in 1321N1 astrocytoma cells.
Thrombin and insulin receptor signaling via phosphoinositide (PI)-specific phospholipase C (PLC) and PI 3-kinase was studied in [3H]inositol-labelled 1321N1 cells. Thrombin stimulated a dramatic, transient activation of PLC which is probably mediated via receptors of the 'tethered-ligand' type, since it was both reproduced by, and abolished following, pretreatment of cells with a synthetic peptide (SFLLRN) corresponding to the ligand domain of the human thrombin receptor. However, neither thrombin nor SFLLRN stimulated PI 3-kinase. By contrast, insulin did not influence [3H]InsP3 concentration but stimulated accumulation of [3H]PtdIns(3,4,5)P3 and [3H]PtdIns(3,4)P2, the relative steady-state concentrations of which may indicate degradation of [3H]PtdIns(3,4,5)P3 by 5- and 3-phosphatases. The independent coupling of thrombin and insulin receptors to PLC and PI 3-kinase respectively in 1321N1 cells allowed interactions between these systems to be examined. Thus insulin-stimulated [3H]PtdIns(3,4,5)P3 accumulation was attenuated on co-stimulation of the thrombin receptor, whereas concentrations of [3H]PtdIns(3,4)P2 were transiently enhanced but then reduced. These results indicate that thrombin receptors in 1321N1 cells do not activate PI 3-kinase, but can modulate signalling by this enzyme.
Batty
I H
IH
Department of Biochemistry, University of Dundee, Scotland, UK.
Downes
C P
CP
D000595:Amino Acid Sequence; D001254:Astrocytoma; D004789:Enzyme Activation / Q000187:drug effects; D006801:Humans; D007328:Insulin / Q000494:pharmacology*; D008969:Molecular Sequence Data; D010446:Peptide Fragments / Q000494:pharmacology; D019869:Phosphatidylinositol 3-Kinases; D018129:Phosphatidylinositol Phosphates / Q000096:biosynthesis*; D017853:Phosphotransferases (Alcohol Group Acceptor) / Q000378:metabolism; D018179:Receptors, Thrombin / Q000378:metabolism*; D015398:Signal Transduction / Q000187:drug effects; D013917:Thrombin / Q000494:pharmacology*; D014407:Tumor Cells, Cultured; D010738:Type C Phospholipases / Q000378:metabolism
D007328:Insulin; D010446:Peptide Fragments; D018129:Phosphatidylinositol Phosphates; D018179:Receptors, Thrombin; C060974:phosphatidylinositol 3,4,5-triphosphate; C060980:phosphatidylinositol 3,4-diphosphate; C082835:thrombin receptor peptide (42-47); D019869:Phosphatidylinositol 3-Kinases; D017853:Phosphotransferases (Alcohol Group Acceptor); D010738:Type C Phospholipases; D013917:Thrombin