Suman Barua

Defense Date

1-8-2007

Graduation Date

Fall 1-1-2007

Availability

Worldwide Access

Submission Type

thesis

Degree Name

MS

Department

Biological Sciences

Committee Chair

Kyle W. Selcer

Committee Member

John A. Pollock

Committee Member

Vicki L. Davis

Keywords

cell culture, glucocorticoids, MDA-MB-231, MG-63, osteoblasts, sulfated estrogens

Abstract

Steroid sulfatase is an enzyme involved in the conversion of active estrogens and androgens from inactive systemic precursors such as estrone sulfate (E1S) and dehydropiandrosterone sulfate (DHEAS). This protein is known to play a role in the fetal-adrenal endocrine axis during pregnancy and it is suspected to have additional physiological functions. Steroid sulfatase has also been implicated in stimulation of hormone-dependent cancers; consequently, a substantial amount of research has been undertaken to develop inhibitors of this enzyme. By comparison, relatively little is known about the regulation of steroid sulfatase. Previous work in our lab had suggested that glucocorticoids may affect steroid sulfatase activity in human breast and bone cells. The purpose of my research was to study the regulation of steroid sulfatase by glucocorticoids in two human cell lines, MDA-MB-231 hormone-independent breast cancer cells, and MG-63 osteosarcoma cells. MDA-MB-231 cells treated for 72 hours with 10 or 1.0µM cortisol showed a decrease in steroid sulfatase activity, as determined by a whole cell radiolabeled steroid conversion assay. Similarly, intact MDA-MB-231 cells treated with 10, 1.0 or 0.1µM dexamethasone showed significantly decreased steroid sulfatase activity. This reduction of steroid sulfatase activity was dose responsive. MDA-MB-231 cell lysates prepared after exposure to dexamethasone provided mixed results with regard to steroid sulfatase activity. The observed decrease in steroid sulfatase activity was not due to competitive inhibition by the glucocorticoids, as neither cortisol nor dexamethasone was found to be competitive inhibitors of steroid sulfatase activity in MDA-MB-231 microsomes. Qualitative analysis of steroid sulfatase mRNA using RT-PCR suggests levels are not affected by dexamethasone. However, quantitative assays must be performed to determine anything conclusive. In contrast to the MDA-MB-231 results, MG-63 bone precursor cells showed no change in steroid sulfatase activity after exposure to dexamethasone for 24 or 96 hours. However, MG-63 cell lysates demonstrated an upregulation in steroid sulfatase activity at the 96h time period. Data from this study indicate that glucocorticoids can influence steroid sulfatase activity in human breast and bone cells.

Format

PDF

Language

English

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