Molecular Regulation and Physiological/Pathophysiological Role of Chloride Channel 5 (Clc-5) and Na/H Exchanger 3 (NHE3)
Xuhang Li, Ph.D.
Douglas Adler, M.S.
Jin Shi, Ph.D.
Angela Yang, M.D./Ph.D.
Xiaoou Yang, M.D.
Xuhang Li, Ph.D.
Assistant Professor of Medicine
Johns Hopkins University School of Medicine
Department of Medicine
746 Ross Research Bldg, 720 Rutland Ave.
Baltimore, M.D. 21205
Phone: 443-287-4804 (Office)
Both NHE3 and Clc-5 are most abundantly expressed in the kidney and small intestine. NHE3 is an epithelial plasma membrane transporter responsible for intestinal and renal neutral Na absorption. Clc-5, an intracellular Cl-/H+ exchanger, is thought to play an important role in regulating vesicular luminal pH and the apical trafficking of intestinal and renal neutral epithelial cells. Mutations in CLC-5 in human or Clc-5 knockout (KO) mice develop a kidney disease called Dent’s disease.
We have shown recently that in patients with active IBD, both NHE3 and ClC-5 are down regulated, implying a potential mechanism of diarrheal mechanism in IBD. We have also demonstrated that Clc-5 KO mice are more susceptible to DSS-induced colitis. In the small intestine, NHE3 inhibition is a major mechanism for most diarrheal diseases. Preliminary data indicate that Clc-5 may directly or indirectly regulate NHE3 trafficking. Therefore understanding the regulatory mechanisms of Clc-5 and NHE3 is of great significance in gastrointestinal and renal physiology.
Nearly all known acute regulations of NHE3 are mediated by its cytosolic C-terminus, which we have demonstrated to form large dynamic multi-protein complexes, ranging from 300 kDa to 1000 kDa. We postulated that a dynamic interaction of the NHE3 C-terminus with different regulatory proteins regulate NHE3 activity. By proteomic approach, we recently identified a new NHE3-associated regulatory protein, casein kinase 2 (CK2) that is involved in the controlling NHE3 activity.
Current research aims to:
- Determine how NHE3 C-terminus plays a role in NHE3 regulation and dictates NHE3 trafficking
- Investigate the role of Clc-5 in regulating membrane trafficking, mucosal inflammation and nutrient absorption in the intestine
- Identify novel regulatory factors that dynamically interact with the NHE3 and Clc-5 using proteomic approach
- Investigate molecular and functional relationship between Clc-5 and NHE3 in the intestine
- Lin, R., Murtazina, R., Cha, B., Chakraborty, M., Sarker, R., Chen, T., Lin, Z., Hogema, B. M., deJonge, Seidler, U., Turner, J. R., Li, X., Kovbasnjuk, O., Donowitz, M. 2011. D-Glucose Acts via SGLTI to Increase NHE3 in Mouse Jejunal Brush Border by a NHERF2-Dependent Process. Gastroenterology. 140 (2): 560-71
- Donowitz, M., Singh, S., Singh, P., Chakraborty, M., Chen, Y., Murtazina, R., Gucek, M., Zachos, N.C., Salahuddin, F.F., Kavbasnjuk, O., Broere, N., Smalley-Freed, W.G., Reynolds, A.B., Hubbard, A.L., Seidler, U., Weinman, E., de Jonge H.R., Li, X. 2011. Alternations in the proteome of the NHERF2 knockout mice jejunal brush border membrane vesicles. Physiol Genomics. 43 (11): 674-84
- Donowitz, M, Singh, S, Singh, P., Salahuddin, FF, Chen, Y, Chakraborty, M., Gucek, M., Cole, R.N., Ham, A., Zachos, N.C., Kovbasnjuk, O., Lapierre, L.A., Broere, N., Smalley, W.G., Reynolds, A.B., Hubbard, A.L., Goldenring, J., Seidler, U., de Jonge, H., R. Murtazina, Hogema, B.M., and Li, X. 2010. Alterations in the Proteome of the NHERF1 Knockout Mouse Jejunal Brush Border Membrane Vesicles. Physiol Genomics. 42A (3): 200-10
- Alex, P., Ye, M., Sipes, J., Nguyen, T., Gonzales, L., Saksonov-Suhodrev, M., Zhang, T., Arora, Z., Centola, M., Guggino, S.E., Li, X. 2010. Clc-5 Knockout Mice Are More Susceptible to Dextran Sulphate Sodium Induced Colitis. Journal of Immunology. 187, 3988-3996
- Sullivan, S., Alex P., Dassopoulos, T., Zachos, N.C., Iacobuzio-Donahue, C., Donowitz, M., Brant, S.R., Cuffari, C., Harris, M.L., Datta L.W., Conklin, L., Chen, Y., and Li, X. 2009. Down-Regulation of Sodium Transporters and NHERF Proteins in IBD Patients and Mouse Colitis Models: Potential Contributors to IBD-associated Diarrhea. Inflammatory Bowel Disease. 15(2), 261-274
- Sarker, R., Grønborg, M., Cha, B., Chen, Y., Mohan, S., Pandey, A., Litchfield, D., Donowitz, M. and Li, X. 2008. CK2 Binds to the C-Terminus of NHE3 and Stimulates NHE3 Basal Activity by Phosphorylating a Separate Site. Mol. Biol. Cell. 19(9), 3859-3870
- Donowitz, M., Singh, S., Salahuddin, F. F., Hogema, B. M., Gucek, M., Cole, R. N., Chen, Y., Zachos, N., Kovbasnjuk, O., Lapierre, L., Broere, N., Goldenring, J., deJonge, H. Li, X. 2007. Proteome of the Murine Jejunal Brush Border. Journal of Proteome Research. 6 (10), 4068-4079
- Donowitz, M and Li, X. 2007. Regulatory binding partner and complexes of NHE3. Physiological Review. 87 (3), 825-72
- Murtazina, R., Kovbasnjuk, O., Donowitz, M., and Li, X. 2006. Na+/H+ exchanger 3 activity and trafficking are lipid raft dependent. J. Biol. Chem. 281, 17845-17855
- Li, X., Leu, S., Birnbaum, M. J., Baibakov, B., Zhang, H., Shih, C. and Donowitz, M. 2004. Akt, PI-3 Kinase and PTEN are in lipid rafts in brush border of intestinal epithelial cells: potential involvement of Akt2 in stimulated Na absorption and differentiation. Gastroenterology. 126, 122-35