Androgen induction of the SVS family related protein MSVSP99: identification of a functional androgen response element

Transgelin: an androgen-dependent protein identified in the seminal vesicles of three Saharan rodents

During the breeding season, a major androgen-dependent protein with an apparent molecular weight of 21 kDa was isolated and purified from the seminal vesicles of three Saharan rodents (MLVSP21 from Meriones libycus, MSVSP21 from Meriones shawi, and MCVSP21 from Meriones crassus). The 21-kDa protein was isolated and purified from soluble seminal vesicle proteins of homogenate by one-dimensional polyacrylamide gel electrophoresis (SDS-PAGE). Using polyclonal antibodies directed against POSVP21 (Psammomys obesus seminal vesicles protein of 21 kDa), a major androgen-dependent secretory protein from sand rat seminal vesicles, identified previously as transgelin, we showed an immunological homology with POSVP21 by immunoblotting. These three major androgen-dependent proteins with a same apparent molecular weight of 21 kDa designated as MLVSP21 (Meriones libycus seminal vesicles protein of 21 kDa), MSVSP21 (Meriones shawi seminal vesicles protein of 21 kDa), and MCVSP21 (Meriones crassus seminal vesicles protein of 21 kDa) were localized by immunohistochemistry and identified by applying a proteomic approach. Our results indicated that the isolated proteins MLSVP21, MSSVP21, and MCSVP21 seem to correspond to the same protein: the transgelin. So that transgelin can be used as a specific marker of these rodent physiological reproduction mechanisms.

Androgen-receptor-specific DNA binding to an element in the first exon of the human secretory component gene

Androgens and glucocorticoids are steroid hormones, which exert their effects in vivo by binding and activating their cognate receptors. These intracellular receptors are transcription factors that can bind specific DNA sequences, called hormone response elements, located near the target genes. Although the androgen receptor (AR) and the glucocorticoid receptor (GR) bind the same consensus DNA sequence, androgen-specific responses can be achieved by non-conventional androgen response elements (AREs). Here we determine the specificity mechanism of such a selective element recently identified in the first exon of the human gene for secretory component (sc ARE). This sc ARE consists of two receptor-binding hexamers separated by three nucleotides. The DNA-binding domains of the AR and GR both bind the sc ARE, but, although the AR fragment dimerizes on the element, the GR fragment does not. Comparing the affinities of the DNA-binding domains for mutant forms of the sc ARE revealed that dimeric GR binding is actively excluded by the left hexamer and more precisely by the presence of a G residue at position -3, relative to the central spacer nucleotide. Inserting a G at this position changed a non-selective element into an androgen-selective one. We postulate that the AR recognizes the sc ARE as a direct repeat of two 5'-TGTTCT-3'-like core sequences instead of the classical inverted repeat. Direct repeat binding is not possible for the GR, thus explaining the selectivity of the sc ARE. This alternative dimerization by the AR on the sc ARE is also indicated by the DNA-binding characteristics of receptor fragments in which the dimerization interfaces were swapped. In addition, the flanking and spacer sequences seem to affect the functionality of the sc ARE.

The first exon of the human sc gene contains an androgen responsive unit and an interferon regulatory factor element

Secretory component (SC) plays a key role in the transport of IgA and IgM to the lumina of many glands. The gene is constitutively expressed, but can be modulated by hormonal and immunological stimuli. Recently, the promoter and the first exon of the human sc gene have been cloned. The first exon contains a putative androgen/glucocorticoid response element (ARE/GRE) and an Interferon Regulatory Factor Element (IRF-E). Here we show that the ARE/GRE can bind the DNA-binding domain (DBD) of both the androgen (AR) and glucocorticoid receptor (GR) with a preference for the AR-DBD. In transient transfection experiments, this element confers higher responsiveness to androgens than to glucocorticoids. The IRF-E can function as an IRF-2, but surprisingly not as an IRF-I responsive element. We postulate that these two regulatory elements play a key role in the complex regulation of the sc gene in vivo.

Po gene expression is modulated by androgens in the sciatic nerve of adult male rats

The present results show that androgens are able to modulate the Po gene expression in different models. In particular, we have shown that: (1) the messenger for the androgen receptor (AR) is present in the rat sciatic nerve but not in cultured Schwann cells; (2) castration induces a decrease of Po mRNA levels in the sciatic nerve of male rats, which is counteract by the subsequent treatment with dihydrotestosterone (DHT), the 5alpha-reduced metabolite of testosterone; (3) castration is also able to significantly decrease in the sciatic nerve the activity of the enzyme 5alpha-reductase (which converts testosterone into DHT); and (4) DHT is able to stimulate Po gene expression in cultured Schwann cells. These observations seem to indicate that androgens may exert their effect on Po gene expression via indirect mechanisms; modulation of neuronal influences reaching the Schwann cells through the binding of the androgen to the AR present in neurons may be postulated. However, alternative mechanisms may also be taken in consideration. The data presented suggest indeed that androgens might act on Schwann cells via the progesterone receptor (PR) rather than the AR. It has been observed that: (1) the messenger for PR is present in Schwann cells; (2) DHT may activate the transcriptional activity of a PR-responsive gene by binding to the PR; and (3) putative steroid responsive elements have been described in this paper to be present in the Po promoter region.