This brief review of the human Na/H exchanger gene family introduces a new classification with three subgroups to the SLC9 gene family. Progress in the structure and function of this gene family is reviewed with structure based on homology to the bacterial Na/H exchanger NhaA. Human diseases which result from genetic abnormalities of the SLC9 family are discussed although the exact role of these transporters in causing any disease is not established, other than poorly functioning NHE3 in congenital Na diarrhea

Rabbit NHE2 and NHE3 are two epithelial isoform Na+/H+ exchangers (NHE), the messages for which are found predominantly and entirely, respectively, in renal, intestinal, and gastric mucosa. The current studies used Western analysis and immunohistochemistry to identify and characterize the apical vs. basolateral membrane distribution of NHE2 and NHE3 in intestinal epithelial cells. Based on Western analysis, NHE2 and NHE3 both are present in brush-border but not basolateral membranes of small intestine. Both NHE2 and NHE3 are 85-kDa proteins. Consistent with Western analysis, NHE2 and NHE3 are immunolocalired to the brush-border but not basolateral membranes of villus epithelial cells, but not goblet cells, in human jejunum and ileum and in surface epithelial cells in the ascending and descending colon and rectum. In addition, NHE2 and NHE3 are present in small amounts in the crypt cell brush border of human jejunum, ileum, ascending and descending colon, and rectum. In rabbit jejunum, ileum, and ascending colon, NHE2 and NHE3 are present in the brush border of epithelial and not goblet cells, again much more in the villus (small intestine)/ surface cells (colon) than the crypt. NHE2 but not NHE3 is present in the brush border of rabbit descending colon surface cells and in small amounts in crypt cells. NHE2 and NHE3 are both human and rabbit small intestinal and colonic epithelial cell brush-border Na+/H+ exchanger isoforms that colocalize in all intestinal segments except rabbit descending colon, which lacks NHE3.

Regulation of gene expression by intranuclear transduction of macromolecules such as transcription factors is an alternative to gene therapy for the treatment of numerous diseases. The identification of an effective intranuclear delivery vehicle and pathway for the transport of therapeutic macromolecules across plasma and nuclear membranes, however, has posed a significant challenge. The anti-DNA antibody fragment 3E10 Fv has received attention as a novel molecular delivery vehicle due to its penetration into living cells with specific nuclear localization, absence of toxicity, and successful delivery of therapeutic cargo proteins in vitro and in vivo. Elucidation of the pathway that allows 3E10 Fv to cross cell membranes is critical to the development of new molecular therapies. Here we show that 3E10 Fv penetrates cells through a nucleoside salvage transporter. 3E10 Fv is unable to penetrate into cells deficient in the equilibrative nucleoside transporter ENT2, and reconstitution of ENT2 into ENT2-deficient cells restores 3E10 Fv transport into cell nuclei. Our results represent the first demonstration of protein transport through a nucleoside salvage pathway. We expect that our finding will facilitate a variety of methods of gene regulation in the treatment of human diseases, open up new avenues of research in nucleoside salvage pathways, and enhance our understanding of the pathophysiology of autoimmune diseases.The ability to regulate gene expression through intranuclear delivery of macromolecules would significantly impact the treatment of a multitude of human diseases. Effective macromolecular therapy is dependent upon molecular delivery vehicles to circumvent the plasma membrane barrier and facilitate intracellular transport of cargo molecules. The single chain Fv fragment of the 3E10 anti-DNA autoantibody (3E10 Fv) has recently been harnessed as a novel molecular delivery vehicle due to its specific nuclear localization and apparent lack of toxicity (1). 3E10 Fv and Fv fusion proteins readily transduce across cell membranes and penetrate into cell nuclei, and 3E10 Fv has successfully delivered biologically active proteins such as Hsp70 (2) and p53 (3) into living cells in vitro. Moreover, 3E10 Fv mediated full-length p53 protein therapy in vivo (4). The pathway that carries 3E10 Fv across cell membranes and into cell nuclei, however, has not been identified.Previous studies implicated DNA binding as important in 3E10 Fv transduction into cell nuclei. Specifically, mutations that abrogate DNA binding by the antibody render it incapable of cellular penetration (5). The association between cellular penetration and DNA binding distinguished 3E10 Fv from other protein transduction domains and implied that nucleoside salvage pathways might be involved in 3E10 Fv transport. Both concentrative (CNT) 3 and equilibrative (ENT) nucleoside salvage transporters mediate the uptake of nucleobases and nucleosides by mammalian cells (6). Since any major role of CNTs in 3E10 Fv transport was excluded by previous studie...