RESUMO
The expression of the androgen receptor (AR) gene is regulated by androgens. Although androgens down-regulate AR mRNA in most cell lines and tissues, including the prostate, up-regulation occurs in some tissues. Androgen-mediated reduction in AR mRNA is reproduced in COS1 cells and in the androgen-sensitive human prostate cancer cell line LNCaP when each expresses the AR cDNA. We have previously established that the AR cDNA contains the requisite sequences for this down-regulation. Here we shown that androgen promoted up-regulation of AR mRNA in two androgen-independent human prostate cancer cell lines, PC3 and DU145, when each was transfected with a human AR cDNA. This effect was due to the AR cDNA and not to the heterologous promoter driving AR expression. In addition to up-regulation of AR mRNA, androgen induced comparable increases in AR protein levels in PC3 cells stably expressing an AR cDNA (PC3/AR). Up-regulation of AR in PC3/AR cells was accompanied by failure of these cells to undergo desensitization or inactivation of AR following prolonged (96 h) androgen administration, whereas the same conditions resulted in desensitization of AR transactivation in LNCaP cells and in CVl cells that stably express the AR cDNA. Androgen treatment of PC3/AR cells resulted in induction of an androgen-regulated reporter gene (MMTV-CAT) as well as the native prostate-specific antigen gene, which is silent in untransfected PC3 but is androgen up-regulated in LNCaP and in the prostate. These results suggest that ectopic expression of AR in androgen-independent prostate cancer cell lines establishes both typical and atypical androgenic responses in a target gene-specific manner. Androgenic up-regulation of AR cDNA expression may be due to distinct signaling mechanisms that influence androgen action in androgen-independent prostate cancer cells.
Assuntos
Adenocarcinoma/genética , Androgênios/farmacologia , Neoplasias da Próstata/genética , Receptores Androgênicos/genética , Regulação para Cima/genética , Adenocarcinoma/tratamento farmacológico , Adenocarcinoma/patologia , Animais , Células Cultivadas , Cloranfenicol O-Acetiltransferase/efeitos dos fármacos , Cloranfenicol O-Acetiltransferase/genética , Cloranfenicol O-Acetiltransferase/metabolismo , Citomegalovirus/genética , DNA Complementar/biossíntese , Regulação Neoplásica da Expressão Gênica/efeitos dos fármacos , Genes Reporter , Vetores Genéticos/genética , Haplorrinos , Homeostase , Humanos , Rim/citologia , Rim/efeitos dos fármacos , Rim/metabolismo , Masculino , Vírus do Tumor Mamário do Camundongo/genética , Regiões Promotoras Genéticas , Antígeno Prostático Específico/efeitos dos fármacos , Antígeno Prostático Específico/genética , Antígeno Prostático Específico/metabolismo , Neoplasias da Próstata/tratamento farmacológico , Neoplasias da Próstata/patologia , RNA Mensageiro/biossíntese , Receptores Androgênicos/metabolismo , Transfecção , Células Tumorais CultivadasRESUMO
Androgen receptor (AR) levels are regulated by androgens, other steroids and non-steroidal hormones via complex, tissue-specific processes. Since alterations in receptor levels may influence cellular sensitivity to androgens, understanding AR regulation is of fundamental and potentially therapeutic significance. In most target tissues and AR-containing cell lines, AR mRNA is down-regulated in response to androgens. We have reconstituted this androgen-mediated down-regulation of AR mRNA in COS 1 cells transfected with a human AR cDNA under the control of the cytomegalovirus (CMV) promoter. The sequences mediating receptor mRNA down-regulation are represented within the AR cDNA and not within the CMV promoter. Androgenic down-regulation of AR cDNA expression was time- and dose-dependent, resembling native AR mRNA down-regulation. In addition, androgenic regulation of the receptor cDNA was not dependent on protein synthesis suggesting that AR and/or another pre-existing protein(s) is involved in this process. In COS 1 cells co-transfected with androgen and glucocorticoid receptor cDNAs, dexamethasone mimicked the action of androgen in down-regulating AR mRNA. This response depended on glucocorticoid receptors. Androgen had little effect on steady-state levels of AR protein consistent with reports that androgen down-regulates AR mRNA but increases AR protein half-life (Kemppainen et al. (1992) J. Biol. Chem. 267, 968-974; Zhou et al. (1995) Mol. Endocrinol. 9, 208-218). However, glucocorticoids decreased AR protein levels in cells that co-expressed androgen and glucocorticoid receptors. These results indicate that sequences represented in the AR cDNA mediate AR mRNA down-regulation by both androgens and glucocorticoids. Inhibition of AR mRNA and protein by glucocorticoids suggests that these steroids may modulate androgen action in tissues, such as mammary gland and prostate, which express both androgen and glucocorticoid receptors.
