Summary of Research Focus

P.I.:  Thomas D. DuBose, M.D.
Co-Investigator:  Juan Codina, Ph.D.
Professor and Chair, Internal Medicine
Professor of Physiology and Pharmacology

The goal of studies in my laboratory is to elucidate factors involved in the molecular regulation of tubule transporters involved in urinary acidification and potassium conservation.  Many of these transporters have been implicated in monogenic diseases associated with renal tubular acidosis, or abnormalities in potassium homeostasis and blood pressure regulation. Our studies highlight correlation between regulation of transport protein abundance and function at the cellular level.  Current studies are designed to investigate the contribution of Na⁺,K⁺-ATPases and H⁺,K⁺-ATPases in the kidney and distal colon.  Our laboratory was the first to show that while both gastric and colonic a-subunits of the H⁺,K⁺-ATPase are expressed in kidney, the colonic a H⁺,K⁺-ATPase is selectively and site-specifically up-regulated in the outer medullary collecting duct by potassium deprivation in an animal model of chronic hypokalemia (2, 4).  We have also shown that, while, unlike the gastric a H⁺,K⁺-ATPase there is no unique b-subunit for the colonic a H⁺,K⁺-ATPase (HKa₂),  b₁-Na⁺,K⁺-ATPase (NKb₁) functions as the physiologic b-subunit in kidney and distal colon (1).  Both subunits are translocated to the apical membrane in distal colon, and in transiently transfected HEK 293 cells (5).  Moreover, the carboxy terminus of the colonic a H⁺,K⁺-ATPase is critical for b subunit protection of the a-subunit and translocation of the heterodimer to the apical membrane (5, 6).  Recently, we have demonstrated that HKa₂ - NKb₁ translocation and function is critically dependent on interaction with the tetraspanin protein CD63 (3).  CD63 appears to function as a negative regulatory interacting protein that is responsible for the internalization of HKa₂ - Nab₁ and thereby, regulation of function (manuscript under review).  The techniques employed in these studies include cell culture, Northern and Western blot analysis, transient transfection, site-directed mutagenesis, immunofluorescence, imaging, and siRNA. 

Selected References:

1. Codina J, Delmas Mata JT, and DuBose TD, Jr. The a-subunit of the colonic H⁺,K⁺-ATPase assembles with b₁-Na⁺,K⁺-ATPase in kidney and distal colon. J Biol Chem 273: 7894-7899, 1998.

2. Codina J, Delmas-Mata JT, and DuBose TD, Jr. Expression of HKa₂ protein is increased selectively in renal medulla by chronic hypokalemia. Am J Physiol 275: F433-440, 1998.

3. Codina J, Li J, and DuBose TDJ. A carboxy terminus motif of HKa₂ is necessary for assembly and function. Kidney Int, 2004 (in press).

4. Codina J, Li J, Hong Y, Tulleuda A, and DuBose TD, Jr. The tetraspanin CD63 associates with the carboxy-terminus of HKa₂. J Am Soc Nephrol 13: 269A, 2002.

5. DuBose TD, Jr., Codina J, Burges A, and Pressley TA. Regulation of H⁺,K⁺-ATPase expression in kidney. Am J Physiol 269: F500-507, 1995.

6. Li J, Codina J, Petroske E, Werle MJ, and DuBose TD, Jr.. The carboxy-terminus of the colonic H⁺,K⁺-ATPase a-subunit is required for stable b-subunit assembly and function. Kidney Int 65: 1301-1310, 2004.

7. Li J, Codina J, Petroske E, Werle MJ, Willingham MC, and DuBose TD, Jr.. The effect of b-subunit assembly on function and localization of the colonic H⁺,K⁺-ATPase a-subunit. Kidney Int 66: 1068-1075, 2004.