Date of Award

1997

Degree Name

Biomedical Sciences

College

Joan C. Edwards School of Medicine

Type of Degree

M.S.

Document Type

Thesis

First Advisor

Beverly C. Delidow

Second Advisor

Michael Moore

Third Advisor

Vernon Reichenbecher

Fourth Advisor

Sheldon Finver

Fifth Advisor

William McCumbee

Abstract

Physical contacts between cells are known to influence a broad range of biological activities. Investigations into the regulation of prolactin gene expression have shown that cell behavior within the pituitary may also be affected by adhesive contacts. To better understand the mechanisms that regulate cell-cell adhesive contacts in these endocrine cells, we developed a procedure that quantitatively assays homotypic aggregation in the rat pituitary tumor cell line, 235-1. We observed that treatment of 235-1 cells with dexamethasone (Dex), a synthetic glucocorticoid, not only reduces prolactin production but also decreases the reformation of cell-cell contacts. In two independent experiments, control cells showed 90% aggregation, while homotypic binding decreased steadily in Dex-treated cells over a four-day time course: to 78% on day one, 68% on d 2, and 58% on d 4. Comparing assays of serial dilutions of Dex-treated and control cells showed that the effects observed were not due to decreased cell numbers in Dex-treated samples. Since the assay measures calcium-dependent cell-cell adhesion, the observed decrease in homotypic binding may be due to a change in the function of calcium-dependent cell adhesion molecules. These molecules are linked intracellularly to catenins which form structures that physically connect cadherins to the cytoskeleton. The cadherins are a family of membrane-spanning proteins that mediate calcium-dependent, homotypic cell-to-cell adhesion in diverse tissue types. Northern blots probed for cadherins showed a weak signal for cadherin-related mRNA that was not changed by Dex treatment. Westem blots showed decreases in alpha and beta catenin levels in Dex-treated cells. Our results show that Dex decreases prolactin production in 235-1 cells, and reduces cell-cell adhesion from a control level of 90% to 58%. Although the levels of cadherin-related mRNAs were unchanged in response to Dex, catenin levels showed a decrease in response to Dex-treatment. Since the changes in cell-cell adhesion parallel the changes observed in prolactin gene expression, both may be part of a coordinated shift in cell function initiated by glucocorticoids.

Subject(s)

Cell adhesion -- Molecular aspects

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