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The crucial role of pituitary GnRH receptors (GnRH-R) in the control of reproductive functions is well established. These receptors are the target of GnRH agonists (through receptor desensitization) and antagonists (through receptor blockade) for the treatment of steroid-dependent pathologies, including hormone-dependent tumors. It has also become increasingly clear that GnRH-R are expressed in cancer tissues, either related (i.e. prostate, breast, endometrial, and ovarian cancers) or unrelated (i.e. melanoma, glioblastoma, lung, and pancreatic cancers) to the reproductive system. In hormone-related tumors, GnRH-R appear to be expressed even when the tumor has escaped steroid dependence (such as castration-resistant prostate cancer). These receptors are coupled to a G(αi)-mediated intracellular signaling pathway. Activation of tumor GnRH-R by means of GnRH agonists elicits a strong antiproliferative, antimetastatic, and antiangiogenic (more recently demonstrated) activity. Interestingly, GnRH antagonists have also been shown to elicit a direct antitumor effect; thus, these compounds behave as antagonists of GnRH-R at the pituitary level and as agonists of the same receptors expressed in tumors. According to the ligand-induced selective-signaling theory, GnRH-R might assume various conformations, endowed with different activities for GnRH analogs and with different intracellular signaling pathways, according to the cell context. Based on these consistent experimental observations, tumor GnRH-R are now considered a very interesting candidate for novel molecular, GnRH analog-based, targeted strategies for the treatment of tumors expressing these receptors. These agents include GnRH agonists and antagonists, GnRH analog-based cytotoxic (i.e. doxorubicin) or nutraceutic (i.e. curcumin) hybrids, and GnRH-R-targeted nanoparticles delivering anticancer compounds.

The androgen receptor (AR), a ligand-activated transcription factor, has been found mutated in several human diseases. While some mutations reduce, others potentiate AR functions generating different endocrine dysfunctions. A peculiar AR mutation, the CAG-repeat expansion encoding the AR-polyglutamine (polyQ) tract, generates a neurotoxic gain-of-function(s) in this mutant AR (ARpolyQ). This leads to the motor neuronal disease Spinal and Bulbar Muscular Atrophy (SBMA), in which the transcriptional AR down-regulation might have beneficial impacts. We thus analysed the AR-promoter/5'-UTR activation and androgenic regulation, demonstrating that its constitutive activity is considerably high in motor neurons (NSC34). Testosterone, dihydrotestosterone (DHT), but not estradiol, inhibited AR promoter activation. Thus AR establishes a negative control on its own functions, in opposition to that described on classical androgen-responsive elements (ARE) of the AR gene. The AR/DNA interaction is required for this action, since DHT does not inhibit AR expression in presence of an AR (AR_DeltaPhe581) lacking DNA binding activity. The minimal inhibitory region spans from -740/+570 bp, where "in silico" analysis showed a putative AR binding site; deletion studies excluded that this ARE may be involved in this inhibition. A similar effect of DHT has also been observed in AR negative prostate cancer DU145 cell line transfected with the AR. Moreover, androgens down-regulate the expression of the endogenous AR gene in an AR positive prostate cancer LNCaP cell line. Interestingly, in immortalized motor neurons, ARpolyQ was much less effective than wtAR on the positive androgenic control on classical AREs, while ARpolyQ and wtAR had similar inhibitory properties on the AR promoter/5'-UTR activation. This strongly suggests that, in motor neurons, the two types of AR gene androgenic regulation involve different mechanisms. Thus, by acting on the AR promoter it would be possible to reduce AR levels in motor neurons, providing novel approaches to treat SBMA.

Aggregates, a hallmark of most neurodegenerative diseases, may have different properties, and possibly different roles in neurodegeneration. We analysed ubiquitin-proteasome pathway functions during cytoplasmic aggregation in polyglutamine (polyQ) diseases, using a unique model of motor neuron disease, the SpinoBulbar Muscular Atrophy. The disease, which is linked to a polyQ tract elongation in the androgen receptor (ARpolyQ), has the interesting feature that ARpolyQ aggregation is triggered by the AR ligand, testosterone. Using immortalized motor neurons expressing ARpolyQ, we found that a proteasome reporter, YFPu, accumulated in absence of aggregates; testosterone treatment, which induced ARpolyQ aggregation, allowed the normal clearance of YFPu, suggesting that aggregation contributed to proteasome de-saturation, an effect not related to AR nuclear translocation. Using AR antagonists to modulate the kinetic of ARpolyQ aggregation, we demonstrated that aggregation, by removing the neurotoxic protein from the soluble compartment, protected the proteasome from an excess of misfolded protein to be processed.

This review summarizes the most recent information on two pathologies linked to mutations of the androgen receptor, namely, the complete androgen insensitivity syndrome (CAIS) and the spinal and bulbar muscular atrophy (SBMA or Kennedy's disease). Data on the clinical manifestations of the two diseases are presented, together with the most relevant findings on their physiopathology and genetics.

Prostate cancer growth depends, in its earlier stages, on androgens and is usually pharmacologically modulated with androgen blockade. However, androgen-ablation therapy may generate androgen-independent prostate cancer, often characterized by an increased invasiveness. We have found that the 5alpha-reduced testosterone derivative, dihydrotestosterone (the most potent natural androgen) inhibits cell migration with an androgen receptor-independent mechanism. We have shown that the dihydrotestosterone metabolite 5alpha-androstane-3beta,17beta-diol (3beta-Adiol), a steroid which does not bind androgen receptors, but efficiently binds the estrogen receptor beta (ERbeta), exerts a potent inhibition of prostate cancer cell migration through the activation of the ERbeta signaling. Very surprisingly, estradiol is not active, suggesting the existence of different pathways for ERbeta activation in prostate cancer cells. Moreover, 3beta-Adiol, through ERbeta, induces the expression of E-cadherin, a protein known to be capable of blocking metastasis formation in breast and prostate cancer cells. The inhibitory effects of 3beta-Adiol on prostate cancer cell migration is counteracted by short interfering RNA against E-cadherin. Altogether, the data showed that (a) circulating testosterone may act with estrogenic effects downstream in the catabolic process present in the prostate, and (b) that the estrogenic effect of testosterone derivatives (ERbeta-dependent) results in the inhibition of cell migration, although it is apparently different from that linked to estradiol on the same receptor and may be protective against prostate cancer invasion and metastasis. These results also shed some light on clinical observations suggesting that alterations in genes coding for 3beta-hydroxysteroid dehydrogenases (the enzymes responsible for 3beta-Adiol formation) are strongly correlated with hereditary prostate cancer.

Steroid receptor coactivator-1 (SRC-1) has a crucial role in many different biological effects mediated by nuclear receptors. However, in spite of its ubiquitous expression, there are no data regarding its possible involvement in nuclear receptor transcriptional activity at the level of the peripheral nervous system. We investigated whether this coactivator might have a role in the control of glycoprotein Po gene expression. This myelin protein is a specific product of Schwann cells, with a fundamental role in the maintenance and functionality of peripheral myelin. Po is known to be stimulated by progesterone and by its 5alpha-reduced metabolite, dihydroprogesterone (DHP), through the corresponding steroid receptor. To determine whether the effect exerted by DHP on Po mRNA levels could be affected by and therefore associated with altered levels of SRC-1, a mouse Schwann cell line was stably transfected to over- or underexpress this coactivator. We found that SRC-1 overexpressing cells are more responsive to Po mRNA induction by DHP, whereas the effect of the steroid is completely lost in SRC-1-deficient cells. Interestingly, SRC-1 levels are also positively correlated with Po gene expression independently of DHP exposure. Finally, DHP treatment increases not only Po but also SRC-1 mRNA levels. Altogether, these data indicate for the first time that in rat Schwann cells, SRC-1 plays a role in the regulation of one of the most typical proteins of peripheral myelin.

The sciatic nerve, and the Schwann cells in particular, are able to synthesize progesterone and possess the enzymes forming the 5alpha-reduced and the 3alpha-5alpha-reduced derivatives of progesterone: dihydroprogesterone and tetrahydroprogesterone. Moreover, the progesterone receptor (PR) is present in the sciatic nerve and in Schwann cell cultures. These facts suggest that progesterone and its derivatives might play a role in the control of the synthesis of the two major proteins of the peripheral nervous system (PNS): the glycoprotein Po (Po) and peripheral myelin protein 22 (PMP22). We have shown that: (a) dihydroprogesterone enhances the low mRNA levels of Po in the sciatic nerve of aged male rats; (b) progesterone and its derivatives stimulate the gene expression of Po in the sciatic nerve of adult rats and in Schwann cell cultures; (c) tetrahydroprogesterone increases PMP22 gene expression in the sciatic nerve of adult rats and in Schwann cell cultures. In additional experiments, utilizing agonists and antagonists of PR and GABAA receptor, we have observed that progesterone and its derivatives control Po gene expression via the PR, while tetrahydroprogesterone modulates the expression of PMP22 through the GABAA receptor.

The CAG/polyglutamine (polyGln)-related diseases include nine different members that together form the most common class of inherited neurodegenerative disorders; neurodegeneration is linked to the same type of mutation, found in unrelated genes, consisting of an abnormal expansion of a polyGln tract normally present in the wild-type proteins. Nuclear, cytoplasmic, or neuropil aggregates are detectable in CAG/polyGln-related diseases, but their role is still debated. Alteration of the androgen receptor (AR), one of these proteins, has been linked to spinal and bulbar muscular atrophy, an X-linked recessive disease characterized by motoneuronal death. By using immortalized motoneuronal cells (the neuroblastoma-spinal cord cell line NSC34), we analyzed neuropil aggregate formation and toxicity: green fluorescent protein-tagged wild-type or mutated ARs were cotransfected into NSC34 cells with a blue fluorescent protein tagged to mitochondria. Altered mitochondrial distribution was observed in neuronal processes containing aggregates; occasionally, neuropil aggregates and mitochondrial concentration corresponded to axonal swelling. Neuropil aggregates also impaired the distribution of the motor protein kinesin. These data suggest that neuropil aggregates may physically alter neurite transport and thus deprive neuronal processes of factors or components that are important for axonal and dendritic functions. The soma may then be affected, leading to neuronal dysfunctions and possibly to cell death.

The mechanisms through which LHRH-secreting neurons are controlled still represent a crucial and debated field of research in the neuroendocrine control of reproduction. In the present review, we have specifically considered two potential signals reaching these hypothalamic neurons: steroid hormones and growth factors. Examples of the relevant physiological role of the interactions between these two families of biologically acting molecules have been provided. In many cases, these interactions occur at the level of hypothalamic astrocytes, which are presently accepted as functional partners of the LHRH-secreting neurons. On the basis of the observations here summarized, we have formulated the hypothesis that a functional co-operation of steroid hormones and growth factors occurring in the hypothalamic astrocytic compartment represents a key factor in the neuroendocrine control of reproductive functions.