ROMK (Kir 1.1, product of the KCNJ1 gene) channels in the kidney are exquisitely regulated to adjust renal potassium excretion and maintain potassium balance. Clathrin-dependent endocytosis plays a critical role, limiting urinary potassium loss in potassium deficiency. In renal disease, aberrant ROMK endocytosis may contribute to potassium retention and life-threatening hyperkalemia. Available evidence indicates ROMK endocytosis is stimulated by WNKs, kinases that are mutated in Familial Hyperkalemic and Hypertension (FHHt). This application builds on our recent discoveries that: 1) Low potassium directly stimulates ROMK endocytosis in the distal nephron, 2) WNK stimulates ROMK endocytosis by phosphorylating the clathrin-adaptor, ARH, 3) NEDD4 Family of Interacting Proteins, NDFIP1 and 2, interact with ROMK to control post-endocytic processing of the channel. To carry these breakthrough observations toward a completely new understanding of how potassium balance is achieved, we outline plans to: 1) Define the mechanism by which potassium directly regulates ROMK endocytosis; 2) Explore the involvement of this pathway in a mouse model of FHHt, 3) Elucidate the molecular mechanism by which NDFIP1 and NDFIP2 control post-endocytic routing of ROMK to the lysosome. The studies should provide novel insights into the molecular basis of renal K handling and K homeostasis in health and disease while illuminating fundamental mechanisms of membrane protein targeting in the kidney.

Public Health Relevance

ROMK potassium channels are tightly regulated in the kidney by membrane trafficking mechanisms, ensuring that potassium is precisely excreted in accord with the demands of potassium balance. Disruption of ROMK channel trafficking and surface expression can, in fact, have devastating consequences on salt and mineral balance. Despite its importance, a long-standing and fundamental question in cell biology and physiology has been how the number and location of these membrane proteins are precisely controlled. In the present proposal, we elucidate the molecular mechanisms driving membrane trafficking of these channels in health and study what may happen when these processes go awry in disease. Thus, the studies should provide novel insights into the molecular basis of renal K handling and K homeostasis in health and disease while illuminating fundamental mechanisms of membrane protein targeting in the kidney.

Agency
National Institute of Health (NIH)
Institute
National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK)
Type
Research Project (R01)
Project #
5R01DK054231-17
Application #
9502271
Study Section
Kidney Molecular Biology and Genitourinary Organ Development (KMBD)
Program Officer
Ketchum, Christian J
Project Start
2017-06-07
Project End
2021-03-31
Budget Start
2018-04-01
Budget End
2019-03-31
Support Year
17
Fiscal Year
2018
Total Cost
Indirect Cost
Name
University of Maryland Baltimore
Department
Physiology
Type
Schools of Medicine
DUNS #
188435911
City
Baltimore
State
MD
Country
United States
Zip Code
21201
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