Tat1, a Novel Sulfate Transporter Specifically Expressed in Human Male Germ Cells and Potentially Linked to RhoGTPase Signaling

Abstract

RhoGTPases (Rho, Rac, and Cdc42) are known to regulate multiple functions, including cell motility, adhesion, and proliferation; however, the signaling pathways underlying these pleiotropic effects are far from fully understood. We have recently described a new RhoGAP (GTPase activating protein for RhoGTPases) gene, MgcRacGAP, primarily expressed in male germ cells, at the spermatocyte stage. We report here the isolation, through two-hybrid cloning, of a new partner of MgcRacGAP, very specifically expressed in the male germ line and showing structural features of anion transporters. This large protein (970 amino acids and a predicted size of 109 kDa), we provisionally designated Tat1 (for testis anion transporter 1), is closely related to a sulfate permease family comprising three proteins in human (DRA, Pendrin, and DTD); it is predicted to be an integral membrane protein with 14 transmembrane helices and intracytoplasmic NH 2 and COOH termini. In situ hybridization studies demonstrate that Tat1 and MgcRacGAP genes are coexpressed in male germ cells at the spermatocyte stage. On testis sections, Tat1 protein can be immunodetected in spermatocytes and spermatids associated with plasma membrane. Two-hybrid and in vitro binding assays demonstrate that MgcRacGAP stably interacts through its NH 2 -terminal domain with the Tat1 COOH-terminal region. Expression of Tat1 protein in COS7 cells generates a 4,4-diisothiocyano-2,2-disulfonic acid stilbene and chloride-sensitive sulfate transport. Therefore we conclude that Tat1 is a novel sulfate transporter specifically expressed in spermatocytes and spermatids and interacts with MgcRacGAP in these cells. These observations raise the possibility of a new regulatory pathway linking sulfate transport to Rho signaling in male germ cells.

Expression of ion transport-associated proteins in human efferent and epididymal ducts

“…The specificity of the anti-A8 serum was tested by western blot made of adult rat testis, known to express this protein (Toure et al 2001). The anti-A8 serum detected a strong specific band of approximately 100 kDa on the western blot made of adult rat testis (Fig.…”

“…During passage through the epididymal ducts, the composition of the luminal fluid is further gradually changed by sequential absorption and secretion processes (Turner 2002, Wong et al 2002. Water absorption in efferent ducts is allowed by interdependent transport of Cl K and Na C , which may be mediated by an apical anion Cl hereditary diseases when mutated (Hastbacka et al 1994, Hoglund et al 1996, Everett et al 1997, Toure et al 2001, Liu et al 2003 OMIM database which can be viewed online at www. ncbi.nlm.nih.gov/entrez/query.fcgi?db=OMIM).…”

N-glycosylation and topology of the human SLC26 family of anion transport membrane proteins

“…SLC26A7 is a basolateral protein in gastric parietal cells and in renal type A intercalated cells (18,31) and acts as a chloride channel (26). SLC26A8 is expressed in sperm, and mutations result in male infertility (15,31,64). SLC26A9 has a widespread distribution but is abundant in the apical membrane of epithelial cells in the lung, brain, and stomach where it mediates chloride/bicarbonate exchange or acts as a chloride and bicarbonate channel in concert with cystic fibrosis transmembrane regulator (CFTR) (17,31).…”

Un transporteur d’anions est essentiel à la mobilité des spermatozoïdes

“…De manière analogue, les mutations du gène SLC26A4 dont l'expression est restreinte à l'oreille interne (cochlée) et à la thyroïde, sont à l'origine du syndrome de Pendred ; dans ce cas, les patients présentent une surdité bilatérale liée à une malformation de la cochlée et un goitre thyroïdien consécutif à un défaut d'organification de l'iodure au niveau thyroïdien [6,7]. Notre équipe a précédemment isolé la protéine TAT1 (testis anion transporteur 1) comme un nouveau membre de la famille SLC26 [8]. TAT1/SLC26A8 s'exprime de façon exclusive au niveau du testicule et spécifiquement dans la lignée germinale mâle, dès le stade spermatocyte.…”

“…La protéine TAT1 est présente à la surface des spermatocytes et des spermatides ; dans les spermatozoïdes, elle est localisée spécifiquement dans la région de l'annulus, une structure fibrillaire sous-membranaire située à Figure 1). In vitro, la protéine TAT1 transporte les anions sulfate, chlorure et oxalate [8,9]. Afin d'élucider la fonction physiologique du transporteur TAT1 dans la lignée germinale mâle, notre équipe a créé puis caractérisé un modèle d'inactivation du gène Tat1 par recombinaison homologue chez la souris.…”