Date of Award

1998

Degree Name

Biomedical Sciences

College

Joan C. Edwards School of Medicine

Type of Degree

Ph.D.

Document Type

Dissertation

First Advisor

Richard M. Niles

Second Advisor

Vernon E. Reichenbecher

Third Advisor

William D. McCumbee

Fourth Advisor

Susan H. Jackman

Fifth Advisor

Michael R. Moore

Sixth Advisor

Leonard J. Deutsch

Abstract

Moore and co-workers have previously demonstrated that progestins stimulate the growth of T47D human breast cancer cells. We now investigate the possibility that progestins might transactivate the protooncogcne c-myc as part of the mechanism for growth stimulation. Treatment of T47D cells with the synthetic progestin R5020 results in a rapid, dose-dependent increase in c-myc mRNA. This stimulation is evident as early as 5 minutes, increases up to 4-fold at 1 hour, and then returns toward basal levels. The optimal concentration of R5020 for induction of c-myc gene expression is 10 nM, which is within the physiologically relevant range of hormone exposure. Co-treatment of T47D cells with R5020 and the anti-progesterone RU486 results ii abrogation of R5020-induced increases in c-myc mRNA levels. These results suggest that R5020 is operating through the progesterone receptor in transactivating the c-myc gene. Stimulation of c-myc expression is specific for progestins and estrogen. Treatment with 10 nM androgens, glucocorticoids, and mineralocorticoids has little or no affect c-myc mRNA levels. An increase in c-myc mRNA levels upon exposure to progestins occurs even in the presence of the protein synthesis inhibitor cycloheximide. Treatment with cycloheximide itself, however, also results in significant elevation of this mRNA. Experiments utilizing actinomycin D demonstrate that R5020 does not alter c-myc message half-life. The half-life of c-myc mRNA in T47D cells grown under our culture conditions is 23 minutes, which is consistent with values reported by other investigators. Together the data suggest that progestins stimulate c-myc expression as a primary response, that is, by direct enhancement of transcription of the c-myc gene via classical steroid hormone receptor pathways. This conclusion will have to be confirmed by nuclear run-on assays. Increased expression of the c-myc gene may be part of the mechanism by which progestins stimulate growth of T47D human breast cancer cells and impact on the progression of cancerous lesions of the breast.

Subject(s)

Cancer cells – Growth.

Breast – Cancer – Research.

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