Aberrant activation of the androgen receptor through signaling pathways independent of androgen may be responsible for the progression of prostate tumors to the rapidly proliferating androgen-independent state. In this study, the effects of protein kinase A modulators on human androgen receptor activity were tested. Using an adenoviral DNA delivery system, we demonstrate that the androgen receptor can be activated by a protein kinase A activator, forskolin, in the absence of androgen when androgen receptor is co-transfected into monkey kidney CV1 cells or human prostate PC-3 cells with androgen-responsive reporters. Immunoblotting reveals that there is no significant change in androgen receptor protein level following forskolin treatment, suggesting that the enhanced activity is due to activation of the receptor. This activation can be blocked by a protein kinase A inhibitor peptide. Two potent anti-androgens, casodex and flutamide, can significantly reduce this activation, confirming that the ligand-independent pathway is an androgen receptor-mediated phenomenon. An intact DNA binding domain of the receptor is critical for this alternate signaling pathway since mutants with reduced DNA binding ability are inactive. The phosphorylation status of the androgen receptor or associated proteins may critically modulate receptor activity and should be considered when designing improved approaches to prostate cancer therapy.Androgens, acting via their receptors, regulate the development and maintenance of the differentiated function of the male reproductive system (1-3). The androgen receptor (AR) 1 is a member of a large family of transcription factors known as the steroid/thyroid receptor superfamily. This superfamily includes receptors for steroid and thyroid hormones and the retinoids, as well as orphan receptors for which the ligands are not known. The receptors are ligand-dependent transcription factors and have distinct functional domains involved in transcriptional activation and repression, DNA binding, and steroid binding. In the presence of ligand (steroid hormone), the receptor is activated, resulting in stimulation or repression of transcription of genes that are under steroid hormone control (4). Hormone antagonists (either natural or synthetic molecules) compete with the agonist for binding to the receptor and block transcriptional activation by the receptor (5, 6).The activity of many transcription factors, including steroid receptors, is regulated by their phosphorylation status. In the case of these steroid receptors, there is an enhanced phosphorylation of the receptor and/or associated proteins with a concomitant increase in transcriptional activity of the receptor upon binding of the hormone to the receptor (7). This occurs predominantly at serine and threonine residues of the receptor and has been well documented for the progesterone receptor (PR) (8), the glucocorticoid receptor (9), and the AR (10, 11). Phosphorylation of the estrogen receptor (12) and the retinoic acid receptor ␤ (13) also occ...

No abstract

No abstract

Steroidogenic factor 1 (SF-1) is an orphan nuclear receptor that serves as an essential regulator of many hormone-induced genes in the vertebrate endocrine system. The apparent absence of a SF-1 ligand prompted speculation that this receptor is regulated by alternative mechanisms involving signal transduction pathways. Here we show that maximal SF-1-mediated transcription and interaction with general nuclear receptor cofactors depends on phosphorylation of a single serine residue (Ser-203) located in a major activation domain (AF-1) of the protein. Moreover, phosphorylation-dependent SF-1 activation is likely mediated by the mitogen-activated protein kinase (MAPK) signaling pathway. We propose that this single modification of SF-1 and the subsequent recruitment of nuclear receptor cofactors couple extracellular signals to steroid and peptide hormone synthesis, thereby maintaining dynamic homeostatic responses in stress and reproduction.

No abstract