Title

Hormonal influences on gene expression: Gonadotropin and growth factor control of oncogenes

Date of Award

1990

Availability

Article

Degree Name

Doctor of Philosophy (Ph.D.)

First Committee Member

J. David Puett, Committee Chair

Abstract

The study of hormone and growth factor signalling systems within responsive cells provides insight into the basic mechanisms whereby intercellular communication and cellular response occur. Cultures of MA-10 murine Leydig tumor cells were exposed to various concentrations of human chorionic gonadotropin (hCG), insulin, insulin-like growth factor-1 (IGF-1), epidermal growth factor (EGF), transforming growth factor $\beta$ (TGF$\beta$), dibutyryl cyclic adenosine monophosphate ((Bu)$\sb2$cAMP), tetradecanoyl phorbol acetate (TPA) or its inactive 4$\alpha$ isomer. Analysis of resultant cellular responses, including the production of cAMP and steroids, alterations in morphology, production of growth and elevations of certain specific mRNA levels, were made for many of these factors either individually or in combinations.Elevations of c-fos and c-myc oncogene mRNA levels occurred after addition of hCG, insulin, EGF, (Bu)$\sb2$ cAMP or TPA, but not in control, TGF$\beta$ or 4$\alpha$-TPA treated cells. Correlations of the quantitative and temporal characteristics of oncogene expression with morphological changes, cAMP accumulation and steroid production were made. Dose-dependent elevation of these mRNAs by hCG were found and are consistent with receptor-mediated events. Several signalling mechanisms, including activation of protein kinases were assessed and found to be effective in production of this elevation. Combinations of insulin and hCG produced an additive increment of these mRNAs. Ornithine decarboxylase (ODC) mRNA was amplified after hCG and (Bu)$\sb2$ cAMP treatment in a temporal pattern coincident with other events in cellular proliferation. Other mRNA's evaluated included those for the c-abl oncogene, TGF$\beta$ and the EGF receptor.Analysis of MA-10 growth in the absence of serum-supplementation was complicated by apparent toxic effects of prolonged hCG and cAMP treatment. These were partially blocked by the addition of serum or exogenous lipoprotein, suggesting a role for cholesterol depletion in this phenomenon. A defined medium whereby MA-10 cell proliferation could be induced by a high dose of insulin (5 $\mu$g/ml), without significantly affecting the steroidogenic response to hCG was established. A role for gonadotropins in MA-10 cell proliferation is presented which, in combination with the oncogene data, suggests that hCG may act in a manner analogous to growth factors.

Keywords

Biology, Molecular; Chemistry, Biochemistry; Health Sciences, Medicine and Surgery

Link to Full Text

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