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Interaction of Membrane Skeletal Protein, Protein 4.1B and p55, and Sodium Bicarbonate Cotransporter1 in Mouse Renal S1-S2 Proximal Tubules

Nobuo Terada, Nobuhiko Ohno, Sei Saitoh, George Seki, Masayuki Komada, Tatsuo Suzuki, Hisashi Yamakawa, Manoocher Soleimani and Shinichi Ohno

Department of Anatomy and Molecular Histology, Interdisciplinary Graduate School of Medicine and Engineering, University of Yamanashi, Yamanashi, Japan (NT,NO,SS,SO); Department of Internal Medicine, Faculty of Medicine, Tokyo University, Tokyo, Japan (GS); Department of Biological Sciences, Tokyo Institute of Technology, Kanagawa, Japan (MK); Department of Neuroplasticity, Institute on Aging and Adaptation, Shinshu University Graduate School of Medicine, Nagano, Japan (TS); Department of Human Gene Research, Kazusa DNA Research Institute, Chiba, Japan (HY); and Division of Nephrology and Hypertension, University of Cincinnati, Cincinnati, Ohio (MS)

Correspondence to: Nobuo Terada, MD, PhD, Department of Anatomy and Molecular Histology, Interdisciplinary Graduate School of Medicine and Engineering, University of Yamanashi, 1110 Shimokato, Chuo City, Yamanashi 409-3898, Japan. E-mail: nobuot{at}yamanashi.ac.jp

Our recent studies demonstrated the localization of protein 4.1B, a member of the 4.1 skeletal membrane proteins, to the basolateral membranes of the S1-S2 renal proximal tubules. In the present studies, we investigated the presence of binding partners that could form a molecular complex with the 4.1B protein. Immunohistochemistry revealed the localization of p55, a membrane-associated guanylate kinase, and the sodium bicarbonate cotransporter1 (NBC1), to the basolateral membrane domain of S1-S2 in mouse renal proximal tubules. Using immunoprecipitation of kidney lysates with anti-p55 antibody, a positive band was blotted with anti-4.1B antibody. GST fusion proteins including the NBC1 and 4.1B regions were confirmed to bind with each other by electrophoresis after mixing. Both NBC1- and 4.1B-specific bands were detected in renal protein mixtures immunoprecipated by either anti-4.1B- or NBC1-specific antibodies. It is likely that NBC1, 4.1B, and p55 form a molecular complex in the basolateral membrane of the kidney S1-S2 proximal tubules. We propose that the 4.1B-containing membrane skeleton may play a role in regulating the Na⁺ and HCO₃^– reabsorption in S1-S2 proximal tubules. (J Histochem Cytochem 55:1199–1206, 2007)

Key Words: protein 4.1 • sodium bicarbonate transporter • membrane skeleton • MAGUK • renal proximal tubule

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