Down-regulation of Androgen Receptor Expression and Inhibition of Lacrimal Gland Cell Proliferation by Retinoic Acid

Abstract

Androgens and retinoids are known to be involved in control of lacrimal gland function. Because retinoids generally antagonize androgen function it was the purpose of this study to investigate interactions of retinoic acid and androgens in rabbit lacrimal acinar cells in culture by determining effects of retinoic acid on androgen receptor (AR) mRNA expression, AR protein levels and androgen-stimulated cell proliferation. Experiments were conducted using primary rabbit lacrimal acinar cells and a transformed rabbit lacrimal acinar cell line. Exposure of primary lacrimal acinar cells in culture to 10−10–10−6M all-trans retinoic acid for 4–24hr causes an approximately 50% decrease in AR mRNA expression. Expression of AR protein in primary and transformed rabbit lacrimal acinar cells was confirmed by immunohistochemistry. Exposure of the primary cells to 10−6M retinoic acid for 24hr caused a 40% decrease in AR protein levels as determined by measurement of binding of3 [H]-dihydrotestosterone (DHT) to cells in culture and Scatchard analysis. Exposure to 10−9–10−6M DHT stimulates proliferation of transformed rabbit lacrimal acinar cells. This effect is receptor mediated since it is blocked by the AR antagonist, flutamide. Proliferation of the lacrimal acinar cells is inhibited by retinoic acid, as compared to control, and retinoic acid also completely inhibits androgen stimulation of cell proliferation. This study supports the hypothesis that androgens play a supportive role in lacrimal gland function. The antagonistic influences of androgens and retinoic acid suggests that, under physiologic conditions there is a balance between the effects of androgens and retinoids in the lacrimal gland. A decrease in androgen levels in a dry eye patient may alter the balance between the effects of these important controllers of gene expression. The antagonistic effect of retinoids on androgens in the lacrimal gland must also be considered when devising pharmaceutical treatments for dye eye.