AGI August 40/2

Malakooti, Jaleh, Refka Y. Dahdal, Larry Schmidt, Thomas J. Layden, Pradeep K. Dudeja, and Krishnamurthy Ramaswamy. Molecular cloning, tissue distribution, and functional expression of the human Na1/H1 exchanger NHE2. Am. J. Physiol. 277 (Gastrointest. Liver Physiol. 40): G383–G390, 1999.—In the present report, we describe the cloning of a human colonic cDNA that describes the full-length Na1/H1 exchanger (NHE) 2 coding region. The human NHE2 (hNHE2) cDNA encodes for a polypeptide of 812 amino acids with a 90% overall identity to both rabbit and rat NHE2 isoforms. In comparison with SLC9A2, recently reported as the human NHE2, the hNHE2 polypeptide is 115 amino acids longer in the NH2-terminal end and shows only an 84% DNA nucleotide sequence identity. Northern blot analysis revealed that hNHE2 message has an uneven tissue distribution, with high levels in the skeletal muscle, colon, and kidney and lower levels in the testis, prostate, ovary, and small intestine. Protein expression studies with hNHE2 clone showed that a 75-kDa protein was expressed. Stable expression of transfected full-length hNHE2 cDNA in Na1/H1 exchange-deficient LAP1 cells exhibited Na1-dependent pH recovery after an acid prepulse that was inhibited by 0.1 mM amiloride. These data indicate that this cDNA is the true human NHE2 cDNA and that the encoded protein is capable of catalyzing Na1/H1 exchange activity.