Application of differential display to the comparison of androgen-stimulated and unstimulated human prostate carcinoma cell line LNCaP identified androgen induction of the L-plastin gene, which encodes an actin-binding protein isoform. Further investigation demonstrated that L-plastin expression in LNCaP cells is up-regulated by both dihydrotestosterone and estradiol. This induction of expression is detected as early as 2 hours after addition of steroids to the cell culture. L-plastin expression is also detected in other prostate carcinoma cell lines by reverse transcriptase polymerase chain reaction and immunohistochemistry but not in the single normal adult prostate epithelial cell line that is available to us. Analysis of multiple primary prostatic tumor tissues as well as normal and tumor tissues of the same prostate gland showed that tumor tissues exhibit a higher level of expression as compared with the normal tissues. Immunohistochemical study using anti-L-plastin antiserum on normal and carcinomatous prostate tissues showed a very striking difference in the staining patterns. Positive staining was seen in the fibromuscular stroma in normal prostates but not in the glandular epithelial cells. In contrast, strong staining was seen predominantly within the carcinomatous glandular epithelial cells. Taken together, these results suggest that the expression of L-plastin in prostatic epithelial cells is linked to the malignant state and that, once expressed in carcinomas, its expression is regulated by steroid hormone receptors
