Transport proteins NHA1 and NHA2 are essential for survival, but have distinct transport modalities

Abstract

The cation/proton antiporter (CPA) family includes the well-known sodium/proton exchanger (NHE; SLC9A) family of Na + /H + exchangers, and the more recently discovered and less well understood CPA2s (SLC9B), found widely in living organisms. In Drosophila, as in humans, they are represented by two genes, Nha1 (Slc9b1) and Nha2 (Slc9b2), which are enriched and functionally significant in renal tubules. The importance of their role in organismal survival has not been investigated in animals, however. Here we show that single RNAi knockdowns of either Nha1 or Nha2 reduce survival and in combination are lethal. Knockdown of either gene alone results in up-regulation of the other, suggesting functional complementation of the two genes. Under salt stress, knockdown of either gene decreases survival, demonstrating a key role for the CPA2 family in ion homeostasis. This is specific to Na + stress; survival on K + intoxication is not affected by sodium/hydrogen antiporter (NHA) knockdown. A direct functional assay in Xenopus oocytes shows that Nha2 acts as a Na + /H + exchanger. In contrast, Nha1 expressed in Xenopus oocytes shows strong Cl − conductance and acts as a H + -Cl − cotransporter. The activity of Nha1 is inhibited by chloride-binding competitors 4,4′-diiso-thiocyano-2,2′-disulfonic acid stilbene and 4,4′-dibenzamido-2,2′-stilbenedisulphonate. Salt stress induces a massive up-regulation of NHA gene expression not in the major osmoregulatory tissues of the alimentary canal, but in the crop, cuticle, and associated tissues. Thus, it is necessary to revise the classical view of the coordination of different tissues in the coordination of the response to osmoregulatory stress.The NHA Gene Family Ionic homeostasis is essential for life and requires a significant fraction of an organism's total energy budget. Primary ion-motive ATPases provide electrochemical ion gradients to drive an array of channels, cotransporters, and antiporters. The cation/proton antiporter (CPA) family is ubiquitous and best known for the NHE, or CPA1, branch exemplified by the classical Na + /H + exchanger NHE1 (1, 2), which is a target for the potassium-sparing diuretic amiloride in the treatment of hypertension and congestive heart failure. More recently discovered are the sodium/hydrogen antiporters (NHAs), a subbranch of the CPA2 family, which is much less well understood (3, 4). Originally studied in bacteria, yeast, and plants (5, 6), this subbranch in humans includes two NHA genes in tandem: NHA1 (SLC9B1), which is testis-specific, and NHA2 (SLC9B2), which is ubiquitous (7,8).In osteoclasts, NHA2 colocalizes with the V-ATPase a3 subunit and the lysosomal marker LAMP2 (9), and resides in the plasma membrane of Madin-Darby canine kidney (MDCK) cells (7). In the pancreas, NHA2 is necessary for insulin secretion but localizes not to insulin-containing vesicles, but rather to transferrin-positive endocytic vesicles (4, 10). NHA2 also has been linked to hypertension (8). Thus, NHAs are multifunctional proteins expressed in a wide range of ...

NHA2 is expressed in distal nephron and regulated by dietary sodium

“…Taken together, we show that NHA2 expression responds to high salt diet. Similarly, the orthologous Nha antiporters in Drosophila were induced by a high salt (Na + but not K + ) diet [5]. …”

Dissecting the proton transport pathway in electrogenic Na + /H + antiporters

“…Consistent with this idea, NHA2 is found to localize to late endosomes, where it further colocalizes with the vacuolar ATPase (V-ATPase) (25), which establishes a low pH on the inside of endosomes. Because of the two conserved aspartates and the similarity to the bacterial homologues, NHA2 was thought to be electrogenic, but experiments in whole cells have not supported this assumption (2,(22)(23)(24)26). We therefore aimed to clarify the energetics of human NHA2 in an isolated system using purified components.…”

Improved detection of genetic loci in estimated glomerular filtration rate and type 2 diabetes using a pleiotropic cFDR method

“…Another study found that the distribution and expression of NHA2 are especially limited to individual organs, such as in the bone or distal tubules of the kidney (Deisl et al 2016). NHA2 resides in the plasma membrane of Madin–Darby canine kidney (MDCK) cells, which are highly enriched and functionally significant in renal tubules (Chintapalli et al 2015). To sum up, gene SLC9B2 had been reported to be associated with T2D and kidney functions, but there was no earlier study which illustrated its relationship with both two traits.…”