The testis anion transporter TAT1 (SLC26A8) physically and functionally interacts with the cystic fibrosis transmembrane conductance regulator channel: a potential role during sperm capacitation

Abstract

The Slc26 gene family encodes several conserved anion transporters implicated in human genetic disorders, including Pendred syndrome, diastrophic dysplasia and congenital chloride diarrhea. We previously characterized the TAT1 (testis anion transporter 1; SLC26A8) protein specifically expressed in male germ cells and mature sperm and showed that in the mouse, deletion of Tat1 caused male sterility due to a lack of sperm motility, impaired sperm capacitation and structural defects of the flagella. Ca(2+), Cl(-) and HCO(3)(-) influxes trigger sperm capacitation events required for oocyte fertilization; these events include the intracellular rise of cyclic adenosine monophosphate (cAMP) and protein kinase A (PKA)-dependent protein phosphorylation. The cystic fibrosis transmembrane conductance regulator (CFTR) is expressed in mature sperm and has been shown to contribute to Cl(-) and HCO(3)(-) movements during capacitation. Furthermore, several members of the SLC26 family have been described to form complexes with CFTR, resulting in the reciprocal regulation of their activities. We show here that TAT1 and CFTR physically interact and that in Xenopus laevis oocytes and in CHO-K1 cells, TAT1 expression strongly stimulates CFTR activity. Consistent with this, we show that Tat1 inactivation in mouse sperm results in deregulation of the intracellular cAMP content, preventing the activation of PKA-dependent downstream phosphorylation cascades essential for sperm activation. These various results suggest that TAT1 and CFTR may form a molecular complex involved in the regulation of Cl(-) and HCO(3)(-) fluxes during sperm capacitation. In humans, mutations in CFTR and/or TAT1 may therefore be causes of asthenozoospermia and low fertilizing capacity of sperm.

Mechanism and synergism in epithelial fluid and electrolyte secretion

“…The isolated STAS domain was sufficient to fully activate CFTR (66) and when the R domain is targeted to the plasma membrane it activated the SLC26 transporters (127). Similar interaction between CFTR was demonstrated for Slc26a4 (38, 129), Slc26a5 (50), Slc26a8 (118) and Slc26a9 (8, 11). These findings indicate that in the resting state the unphosphorylated CFTR R domain interacts with NBD1 to inhibit CFTR and at the same time to sequester the R domain away from the STAS domain, thus maintain the SLC26 transporters n the inactive state by their STAS domain.…”

Mouse Sperm Membrane Potential Hyperpolarization Is Necessary and Sufficient to Prepare Sperm for the Acrosome Reaction

“…In this respect, several lines of evidence suggest that regulation of the sperm Em during capacitation occurs mainly in the flagella. First, functional and/or immunofluorescence experiments suggest that Slo3 (20,49), ENaC (7), and CFTR (21,50), three channels postulated to mediate the capacitation-associated hyperpolarization, are present in the sperm flagellum. Second, sustained hyperpolarization appears to be downstream of the activation of the HCO 3 Ϫ /SACY/PKA pathway.…”

Intracellular pH in sperm physiology

“…On the other hand, mutations in human SLC26A3 produce congenital chloride diarrhea (CLD) and patients with CLD are subfertile, suggesting this transporter is important for sperm physiology [56]. In fact, SLC26A8, SLC26A3, as well as SLC26A6 and CFTR, have been identified in the midpiece of mouse/guinea pig spermatozoa [18], [21], [57]–[59]. These transporters physically interact and participate in the pHi increase that takes place during capacitation [21].…”