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Deborah A Steplock M.S.

Academic Title: Faculty Research Assistant
Primary Appointment: Medicine
Location: BRB Room 8-027
Phone: (410) 706-1556
Fax: (410) 706-4669

Research Interests:

Our research efforts have focused on the regulation of renal electrolyte transport. Our specific interest has been in the regulation of the renal apical membrane sodium-hydrogen exchanger (NHE3) by cAMP. We have isolated and cloned two members of a protein family called the Sodium-Hydrogen Exchanger Regulatory Factor (NHERF-1 and NHERF-2). These proteins contain two tandem PDZ domains and a C-terminal ezrin-radixin-moesin-merlin binding domain. They link NHE3 to the actin cytoskeleton thereby facilitating the phosphorylation and down regulation of NHE3 by forming a signal-complex with ezrin and protein kinase A. Recent studies have indicated that NHERF interacts with other epithelial transporters such as the sodium-bicarbonate co-transporter, type IIa sodium-phosphate co-transporter, renal outer medullary potassium channel, H+-ATP’ase, and the cystic fibrosis transmembrane regulator. In addition, NHERF-1 and NHERF2 interact with selected receptors (a2-adrenergic receptor, P2Y purinergic receptor, and the Platelet Derived Growth Factor Receptor), scaffolding proteins (ezrin, radixin, moesin, merlin), and signaling proteins (PKC, C-Yes associated protein). Other experiments defined a role for the NHERF family of proteins in testicular differentiation and in the effect of estrogen in estrogen-receptor positive breast cancer cell lines. We are currently characterizing the biologic role of NHERF using knock-out mice and heterologous expression systems. The biochemistry and cellular trafficking of the NHERF proteins are being studied using expression systems, yeast 2-hybrid analyses, and by confocal microcroscopy. The potential role of NHERF in clinical renal diseases is being studied using archived renal biopsy material and immunocytochemistry.


Weinman EJ, Mohanlal V, Stoycheff N, Wang F, Steplock D, Shenolikar S, Cunningham R.  Longitudinal study of urinary excretion of phosphate, calcium, and uric acid in mutant NHERF-1 null mice. Am J Physiol Renal Physiol. 2006 Apr;290(4):F838-43.


Khundmiri SJ, Weinman EJ, Steplock D, Cole J, Ahmad A, Baumann PD, Barati M, Rane MJ, Lederer E.   Parathyroid hormone regulation of NA+,K+-ATPase requires the PDZ 1 domain of sodium hydrogen exchanger regulatory factor-1 in opossum kidney cells. J Am Soc Nephrol. 2005 Sep;16(9):2598-607.


Cunningham R, E X, Steplock D, Shenolikar S, Weinman EJ. Defective PTH regulation of sodium-dependent phosphate transport in NHERF-1-/- renal proximal tubule cells and wild-type cells adapted to low-phosphate media. Am J Physiol Renal Physiol. 2005 Oct;289(4):F933-8.


Cunningham R, Steplock D, Wang F, Huang H, E X, Shenolikar S, Weinman EJ.   Defective parathyroid hormone regulation of NHE3 activity and phosphate adaptation in cultured NHERF-1-/- renal proximal tubule cells. J Biol Chem. 2004 Sep 3;279(36):37815-21.


Weinman EJ, Wang Y, Wang F, Greer C, Steplock D, Shenolikar S.   A C-terminal PDZ motif in NHE3 binds NHERF-1 and enhances cAMP inhibition of sodium-hydrogen exchange. Biochemistry. 2003 Nov 4;42(43):12662-8.


Weinman EJ, Boddeti A, Cunningham R, Akom M, Wang F, Wang Y, Liu J, Steplock D, Shenolikar S, Wade JB.   NHERF-1 is required for renal adaptation to a low-phosphate diet. Am J Physiol Renal Physiol. 2003 Dec;285(6):F1225-32.


Wade JB, Liu J, Coleman RA, Cunningham R, Steplock DA, Lee-Kwon W, Pallone TL, Shenolikar S, Weinman EJ.   Localization and interaction of NHERF isoforms in the renal proximal tubule of the mouse. Am J Physiol Cell Physiol. 2003 Dec;285(6):C1494-503.


Weinman EJ, Steplock D, Shenolikar S.   NHERF-1 uniquely transduces the cAMP signals that inhibit sodium-hydrogen exchange in mouse renal apical membranes. FEBS Lett. 2003 Feb 11;536(1-3):141-4.


Weinman EJ, Evangelista CM, Steplock D, Liu MZ, Shenolikar S, Bernardo A.   Essential role for NHERF in cAMP-mediated inhibition of the Na+-HCO3- co-transporter in BSC-1 cells. J Biol Chem. 2001 Nov 9;276(45):42339-46.


Weinman EJ, Steplock D, Shenolikar S. Acute regulation of NHE3 by protein kinase A requires a multiprotein signal complex. Kidney Int. 2001 Aug;60(2):450-4. Review.


Weinman EJ, Steplock D, Wade JB, Shenolikar S.   Ezrin binding domain-deficient NHERF attenuates cAMP-mediated inhibition of Na(+)/H(+) exchange in OK cells. Am J Physiol Renal Physiol. 2001 Aug;281(2):F374-80.


Shenolikar S, Minkoff CM, Steplock DA, Evangelista C, Liu M, Weinman EJ. N-terminal PDZ domain is required for NHERF dimerization. FEBS Lett. 2001 Feb 2;489(2-3):233-6.