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Heterotrimeric G-protein candidates for Ge in the ACTH secretory pathway
R Erlich1, B W McFerran, D M Felstead
1Molecular Endocrinology Group, School of Biological and Medical Sciences, University of St Andrews, UK.
Abstract:
The mouse AtT-20/D16-16 anterior pituitary tumour cell line was used to identify candidate heterotrimeric G-proteins for G-exocytosis (Ge) which mediates calcium ion-stimulated adrenocorticotrophin (ACTH) secretion in this cell line. AtT-20 cells express several heterotrimeric G-protein alpha subunits; Gs alpha, Gt alpha, Gq alpha, G11alpha, G12alpha, G13alpha, G14alpha, G15alpha, Gz alpha, Gi2alpha, Gi3alpha, and Go alpha and so heterotrimeric G-protein selective agents were used to differentiate between these candidates. Agents which stimulate ACTH secretion via Ge were not pertussis toxin (PTX)-sensitive nor was cholera toxin (CTX) able to stimulate ACTH secretion from permeabilised cells in the absence of calcium. G-protein antagonists which inhibit activation of Gs, Gi, and Gq subfamilies did not attenuate Ge-stimulated ACTH secretion from permeabilised AtT-20 cells. In AtT-20 cells the stimulatory G-protein involved in the late stages of the ACTH secretory pathway does not belong to the Gs, Gi (with the exception of Gz) or Gq subfamilies of heterotrimeric G-proteins leaving Gz, G12 or G13 as the strongest candidates for Ge.
Insights
Researchers identified potential G-proteins involved in adrenocorticotrophin (ACTH) secretion. The study suggests Gz, G12, or G13 G-proteins mediate calcium-stimulated ACTH release in AtT-20 cells.
Area of Science:
- Endocrinology
- Cell Biology
- Molecular Pharmacology
Background:
- The AtT-20/D16-16 anterior pituitary tumor cell line is a model for studying adrenocorticotrophin (ACTH) secretion.
- Heterotrimeric G-proteins play crucial roles in cellular signaling pathways, including hormone secretion.
Purpose of the Study:
- To identify the specific heterotrimeric G-proteins responsible for G-exocytosis (Ge), which mediates calcium-stimulated ACTH secretion in AtT-20 cells.
Main Methods:
- Utilized heterotrimeric G-protein selective agents to differentiate between candidate G-proteins expressed in AtT-20 cells.
- Assessed the sensitivity of ACTH secretion to pertussis toxin (PTX) and cholera toxin (CTX).
- Examined the effect of G-protein subfamily antagonists on Ge-stimulated ACTH secretion.
Main Results:
- Ge-mediated ACTH secretion was not sensitive to pertussis toxin (PTX).
- Cholera toxin (CTX) did not stimulate ACTH secretion from permeabilized cells without calcium.
- Antagonists for Gs, Gi, and Gq subfamilies did not inhibit Ge-stimulated ACTH secretion.
Conclusions:
- The stimulatory G-protein in the late stages of ACTH secretion in AtT-20 cells is not from the Gs, Gi (except Gz), or Gq subfamilies.
- Gz, G12, or G13 G-proteins are the strongest candidates for mediating G-exocytosis and ACTH secretion.