Degradation of gap junction connexins is regulated by the interaction with Cx43-interacting protein of 75 kDa (CIP75)

• Type of Material: Article
• Authors: Jennifer L. Kopanic, University of Nebraska Medical Center; Barbara Schlingmann, Emory University; Michael Koval, Emory University; Alan F. Lau, University of Hawai’i; Paul L. Sorgen, University of Nebraska Medical Center; Vivian F. Su, University of Hawai’i
• Language: English
• Date: 2015-03-15
• Publisher: Portland Press
• Publication Version: Author Accepted Manuscript (After Peer Review)
• Copyright Statement: © The Authors. Journal compilation © 2015 Biochemical Society.
• Final Published Version (URL): http://dx.doi.org/10.1042/BJ20141042
• Title of Journal or Parent Work: Biochemical Journal
• ISSN: 0264-6021
• Volume: 466
• Issue: 3
• Start Page: 571
• End Page: 585
• Grant/Funding Information: This work was supported in part by Graduate Assistance in Areas of National Need Fellowships from the U.S. Department of Education [grant number P200A070554 (to J.L.K.)], the United States Public Health Service Grant [grant number GM072631 (to P.L.S.)], the National Heart, Lung, and Blood Institute, National Institutes of Health [grant number HL116958 (to M.K.)], the American Heart Association [grant number 11POST5460028 (to V.S.)], the Hawaii Community Foundation [grant number 11ADVC-49235 (to V.S. and A.F.L.)], the National Cancer Institute, National Institutes of Health [grant number CA052098 (to A.F.L.)], the National Center for Research Resources [grant number 2G12RR003061-26 (to A.F.L.)], the National Institute on Minority Health and Health Disparities [grant number 8G12MD7601-27 (to A.F.L.)], and support from the Pacific Biosciences Research Center (to V.S. and A.F.L.).
• Keywords: CIP75; CARBOXYL-TERMINAL DOMAIN; CYTOSOLIC STRESS; ATRIAL-FIBRILLATION; PROTEASOMAL DEGRADATION; ENDOPLASMIC-RETICULUM; connexin; CONNEXIN43-INTERACTING PROTEIN; ZONULA OCCLUDENS-1; INTERCELLULAR COMMUNICATION; STRUCTURAL-CHANGES; protein degradation; proteasome; Life Sciences & Biomedicine; Science & Technology; LIFE-CYCLE; Biochemistry & Molecular Biology; ERAD
• Research Categories: Chemistry, Biochemistry; Biology, Molecular

Abstract

Connexins are a family of transmembrane proteins that form gap junction channels. These proteins undergo both proteasomal and lysosomal degradation, mechanisms that serve to regulate connexin levels. Our previous work described CIP75 [connexin43 (Cx43)-interacting protein of 75 kDa], a protein involved in proteasomal degradation, as a novel Cx43-interacting protein. We have discovered two additional connexins, connexin40 (Cx40) and connexin45 (Cx45), that interact with CIP75. Nuclear magnetic resonance (NMR) analyses identified the direct interaction of the CIP75 UBA domain with the carboxyl-terminal (CT) domains of Cx40 and Cx45. Reduction in CIP75 by shRNA in HeLa cells expressing Cx40 or Cx45 resulted in increased levels of the connexins. Furthermore, treatment with trafficking inhibitors confirmed that both connexins undergo endoplasmic reticulum-associated degradation (ERAD), and that CIP75 preferentially interacts with the connexin proteins bound for proteasomal degradation from the ER. In addition, we have also discovered that CIP75 interacts with ER-localized Cx32 in a process that is likely mediated by Cx32 ubiquitination. Thus, we have identified novel interacting connexin proteins of CIP75, indicating a role for CIP75 in regulating the levels of connexins in general, through proteasomal degradation.