The growth effects of the G(0) protein.

Title

Identifier

AAI9304687

identifier

9304687

Creator

Kroll, Spencer Daniel.

Contributor

Adviser: Ravi Iyengar

Date

1992

Language

English

Publisher

City University of New York.

Subject

Biology, Genetics | Biology, Molecular | Biology, Cell

Abstract

G proteins are cell surface GTP binding proteins that transduce extracellular signals. G proteins are activated by receptors and in turn, modulate intracellular effectors. G{dollar}\sb{lcub}\rm o{rcub},{dollar} a member of the G protein family, is especially abundant in brain. G{dollar}\sb{lcub}\rm o{rcub}{dollar} specifically enhances muscarinic stimulation of phospholipase C-mediated Cl{dollar}\sp-{dollar} current in Xenopus laevis oocytes. Hence, G{dollar}\sb{lcub}\rm o{rcub}{dollar} may promote release of intracellular calcium and stimulate protein kinase C (PKC).;Mitogenic signals are transduced by many receptors that stimulate phospholipase C through G proteins. Continuous stimulation of these receptors leads to desensitization and subsequent down-regulation of receptors. In contrast, G proteins do not appear to be subject to the same form of regulation. Persistent activation of G proteins may have important effects on cellular growth. Continuous cellular growth may be a contributory factor to the development of cellular transformation. For G{dollar}\sb{lcub}\rm o{rcub},{dollar} its involvement in signal transduction and, in particular, its ability to stimulate phospholipase C could be important in stimulating mitogenesis.;Maturation of Xenopus oocytes is a model system used to assess the capability of many substances (proteins, hormones, drugs) to trigger growth resumption. Experiments described herein show that persistently activated G{dollar}\sb{lcub}\rm o{rcub}{dollar} protein induces cell cycle resumption in oocytes through the activation of PKC. The pathway by which maturation occurs is divergent from the presumed physiological activator progesterone, in that progesterone does not require PKC activation to induce oocyte maturation. Maturation induced by progesterone as well as G{dollar}\sb{lcub}\rm o{rcub}{dollar} appears to converge at the requirement for the translation of the proto-oncogene c-mos, a ser/thr protein kinase. Synthesis of c-mos (p39) is necessary for maturation. Induction of c-mos by G{dollar}\sb{lcub}\rm o{rcub}{dollar} is PKC dependent.;To assess whether activated G{dollar}\sb{lcub}\rm o{rcub}{dollar} induced cell cycle resumption was specific to Xenopus oocytes, I studied the effect of activated G{dollar}\sb{lcub}\rm o{rcub}{dollar}-{dollar}\alpha{dollar} expression on the growth of mammalian cell lines. A plasmid expressed mutant G{dollar}\sb{lcub}\rm o{rcub}{dollar}-{dollar}\alpha{dollar} that could be persistently active was constructed. NIH-3T3 fibroblasts were transfected with vector containing WT {dollar}\alpha\sb{lcub}\rm o{rcub}{dollar} or mutant {dollar}\alpha\sb{lcub}\rm o{rcub}.{dollar} It was found that mutant G{dollar}\sb{lcub}\rm o{rcub}{dollar}-{dollar}\alpha{dollar} stimulated mitogenesis and subsequently induced transformation of NIH-3T3 cells. However, mutant G{dollar}\sb{lcub}\rm o{rcub}{dollar}-{dollar}\alpha{dollar} could not transform RAT-1 fibroblasts.;Hence, it appears that persistent activation of G{dollar}\sb{lcub}\rm o{rcub}{dollar} protein can induce neoplasia when transfected into NIH-3T3 fibroblasts. Previous findings that G{dollar}\sb{lcub}\rm o{rcub}{dollar} protein is linked to stimulation of phosphoinositide hydrolysis and my finding that G{dollar}\sb{lcub}\rm o{rcub}{dollar} induces oocyte maturation through activation of PKC in Xenopus oocytes suggests that G{dollar}\sb{lcub}\rm o{rcub}{dollar} can be an important intracellular growth control regulator.

Type

dissertation

Source

PQT Legacy CUNY.xlsx

degree

Ph.D.

Item