Effects of wortmannin upon the late stages of the secretory pathway of AtT-20 cells.
Heterotrimeric GTP-binding (G) proteins, termed Ge, have a role in the late stages of the adrenocorticotrophin (ACTH) secretory pathway in the mouse AtT-20/D16-16 anterior pituitary tumour cell line. The wortmannin sensitivity of Ge-controlled mechanisms in AtT-20 cells was investigated to provide information on the possible mechanisms linking Ge with secretion. Permeabilised cells exposed to calcium ions (10(-9) to 10(-3) M), guanosine 5'-O-(3-thiotriphosphate) (GTP-gamma-S) (10(-8) to 10(-4) M) and mastoparan (10(-8) to 10(-5) M) demonstrated a significant and concentration-dependent stimulation of ACTH secretion from non-stimulated levels for all three agents. Coincubation with wortmannin (10(-5) M) significantly inhibited both calcium-independent and -stimulated secretion. The effect of wortmannin was concentration-dependent being maximal at 10(-6) M. The study shows that wortmannin inhibits both calcium-independent and -stimulated secretion from permeabilised AtT-20 cells indicating a role for phosphatidylinositol-3 kinase in determining the size of the readily releasable pool of ACTH and/or in mediating calcium/Ge-evoked secretion from this pool.
Wilson
M L
ML
Molecular Endocrinology Group, School of Biological and Medical Science, University of St. Andrews, Bute Medical Building, St. Andrews KY16 9TS, UK.
Guild
S B
SB
D000324:Adrenocorticotropic Hormone / Q000378:metabolism*; D000730:Androstadienes / Q000008:administration & dosage / Q000494:pharmacology*; D000818:Animals; D002118:Calcium / Q000494:pharmacology; D004305:Dose-Response Relationship, Drug; D004791:Enzyme Inhibitors / Q000494:pharmacology; D016244:Guanosine 5'-O-(3-Thiotriphosphate) / Q000494:pharmacology; D020962:Heterotrimeric GTP-Binding Proteins / Q000378:metabolism; D036341:Intercellular Signaling Peptides and Proteins; D051379:Mice; D010455:Peptides; D019869:Phosphatidylinositol 3-Kinases / Q000378:metabolism; D000081082:Phosphoinositide-3 Kinase Inhibitors; D010903:Pituitary Gland, Anterior / Q000187:drug effects* / Q000378:metabolism*; D011863:Radioimmunoassay; D014407:Tumor Cells, Cultured; D014862:Wasp Venoms / Q000494:pharmacology; D000077191:Wortmannin
D000324:Adrenocorticotropic Hormone; D000730:Androstadienes; D002118:Calcium; D004791:Enzyme Inhibitors; D016244:Guanosine 5'-O-(3-Thiotriphosphate); D020962:Heterotrimeric GTP-Binding Proteins; D036341:Intercellular Signaling Peptides and Proteins; D010455:Peptides; D019869:Phosphatidylinositol 3-Kinases; D000081082:Phosphoinositide-3 Kinase Inhibitors; D014862:Wasp Venoms; D000077191:Wortmannin; C037500:mastoparan