Maik Obendorf

PRMT2, a member of the protein arginine methyltransferase family, is a coactivator of the androgen receptor

The basal transcriptional activity of nuclear receptors (NRs) is regulated by interactions with additional comodulator proteins (coactivator/corepressor). Here, we describe a new androgen receptor (AR)-associated coactivator, PRMT2, which belongs to the arginine methyltransferase protein family. To search for AR-interacting proteins a fragment of the AR was used in a library screen exploiting the yeast two-hybrid technique and identifying the C-terminal region of PRMT2. We demonstrated that PRMT2 acts as a strong coactivator of the AR, had modest or none influence on transcriptional activation mediated by other NRs. Interestingly, PRMT2 interaction with the estrogen receptor (ER) was strongly dependent on the cellular background, thus, suggesting the involvement of additional, differentially expressed coregulators. We also demonstrated synergistic interaction of PRMT2 with other known nuclear receptor coactivators, such as GRIP1/TIF-2. Potentiation of AR-mediated transactivation by PRMT2 alone and in synergism with GRIP1 was prevented by a competitive inhibitor of methyltransferase activity. The PRMT2 expression profile overlaps with the distribution of AR, with strongest PRMT2 abundance in androgen target tissues. Immunofluorescence experiments showed that the intracellular localization of PRMT2 depends on the presence of the cognate receptor ligand. Under androgen-free conditions, both AR and PRMT2 are confined to the cytoplasm, whereas in the presence of androgens both proteins colocalize and translocate into the nucleus. Treatment with the AR antagonist hydroxyflutamide results in nuclear translocation of the AR, but not the coactivator PRMT2. Thus, it appears that the ligand-dependent AR conformation is essential for the recruitment and nuclear translocation of PMRT2 which acts as AR-coactivator, presumably by arginine methylation.

FoxG1, a member of the forkhead family, is a corepressor of the androgen receptor ☆

The androgen receptor (AR) is a ligand-dependent transcriptional regulator which belongs to the nuclear receptor superfamily. The basal transcriptional activity of the androgen receptor is regulated by interaction with coactivator or corepressor proteins. The exact mechanism whereby comodulators influence target gene transcription is only partially understood, especially for corepressors. Whereas several coactivators are described for the AR, only a few corepressors are known. Here, we describe the discovery of a new androgen receptor corepressor, FoxG1, which belongs to the forkhead family. By using a fragment of the AR (aa 325-919) as bait in a yeast two hybrid screen, the C-terminal region (aa 175-489) of FoxG1 (also known as BF1), was identified as AR-interacting protein. Binding of AR to the FoxG1 fragment was verified by one- and two-hybrid assays, and pull-down experiments. In addition, we show that the full-length form of FoxG1 functions as a strong corepressor in the AR-mediated transactivation. The FoxG1 expression profile in adult individuals is restricted to brain and testis in human and decreases during aging in the rodent brain. Both AR and FoxG1 expression are developmentally regulated. Besides its reported role in neurogenesis, the strong expression of FoxG1 in AR-abundant areas of the adult brain suggests possible involvement in neuroendocrine regulation. Taken together, the data presented suggest that, in addition to repression of transcription by direct binding to DNA, FoxG1 may interact with AR in vivo, thereby targeting its repressor function specifically to sex hormone signaling.

Interactions of Sex Steroids with Mechanisms of Inflammation

Differential sex-specific liability to inflammatory and autoimmune diseases, and changes in symptom severity in association with physiological fluctuations in gonadal secretions are indicative of significant contribution of sex hormones to the regulation of immune responsiveness. Apart from a postulated role in sex-specific organization of the immune system during ontogeny, gonadal steroids may influence the immune response in numerous ways. This review analyzes existing concepts, experimental and clinical data, aiming at the definition of cellular and molecular mechanisms which may serve as suitable targets for discovery of immunomodulatory drugs whose principal feature is specific interaction with sex hormone receptors. Separation of immunomodulatory effects of sex steroids from those which are exerted by glucocorticoids, and subsequent identification of sex-hormone-specific molecular targets appear to be crucial for the justification of drug discovery on the basis of sex steroid receptor ligands.

Endpoints of drug discovery for menopausal vasomotor symptoms: interpretation of data from a proxy of disease.

ObjectiveEstrogen supplementation is considered a reliable therapeutic approach to symptoms of vasomotor dysregulation (hot flashes) associated with the menopausal transition and sex hormone deprivation. Implication of changes in central neurotransmission in the pathogenesis of hot flashes has prompted the off-label use of serotonergic and &ggr;-aminobutyric acid-ergic drugs as a therapeutic alternative, claiming similarity of outcomes to those of estrogen treatment. MethodsUsing telemetric recordings in a rat model of estrogen deficit–induced vasomotor dysregulation, we compared the long- and short-term effects of estrogen supplementation and treatment with neuropharmaceuticals (venlafaxine, desvenlafaxine, fluoxetine, agomelatine, gabapentin) on endpoints of thermoregulation. ResultsAmong the tested drugs, only fluoxetine was capable to emulate the restorative action of estradiol on the diurnal oscillations in skin temperature and control of heat dissipation. Unlike estradiol, several of the tested compounds produced marked transient decreases in skin temperature within the first 2 hours of application while being unable to restore physiological diurnal patterns of thermoregulation. ConclusionsOur findings suggest that in this animal model of impaired thermoregulation, neuropharmaceuticals may simulate therapeutic effects by eliciting immediate but transient hypothermia, which is not associated with the recovery of physiological control of heat dissipation. Therefore, short-term monitoring of drug actions in this disease model may considerably bias readouts of drug discovery for menopausal vasomotor symptoms.