Androgens down-regulate the expression of the human homologue of Paternally expressed gene-3 in the prostatic adenocarcinoma cell line LNCaP

mRNA differential display polymerase chain reaction analysis was used to sc reen systematically for novel androgen-regulated genes in the human prostat ic adenocarcinoma cell line LNCaP. A 232 bp PCR fragment was found to be co nsistently down-regulated by the synthetic androgen R1881. Sequencing revea led complete identity with the human homologue of mouse Paternally expresse d gene 3 (Peg3), an imprinted gene that plays an important role as a downst ream mediator of the effects of tumor necrosis factor (TNF). The down-regul ation of Peg3 mRNA by androgens was confirmed by Northern blot hybridizatio n. The effect proved time and dose dependent with maximal repression (3.5-f old) after 24 h of treatment with 10(-8) M R1881. The steroid specificity o f Peg3 mRNA regulation reflected the aberrant ligand specificity of the mut ated androgen receptor in LNCaP cells, supporting the involvement of the an drogen receptor in the repression process. Basal expression of Peg3 mRNA wa s almost completely abolished by the protein synthesis inhibitor cyclohexim ide. Experiments with Actinomycin D suggested that androgens act at a trans criptional level rather than by changing the stability of Peg3 mRNA. Compar ison of the expression of Peg3 mRNA in 50 different human tissues revealed ubiquitous expression, but low levels in the prostate. The highest levels w ere observed in endocrine tissues such as ovary, placenta, adrenal and pitu itary. High levels were also noted in various parts of the brain. No detect able levels of Peg3 mRNA were observed in two other androgen receptor-posit ive prostate tumor cell lines (MDA PCa-2a and -2b), and in the poorly diffe rentiated and androgen receptor-negative prostate tumor lines PC-3 and DU-1 45. It is concluded that both androgens and loss of differentiation may aff ect the expression of Peg3, a mediator of the effects of TNF. Further exper iments will be required to explore whether these changes affect the respons iveness of prostate tumor cells to TNF. (C) 1999 Elsevier Science Ireland L td. All rights reserved.