Nontransformed cells can normalize gap junctional communication with transformed cells Virginijus Valiunas a, * , John F. Bechberger b , Christian C.G. Naus b , Peter R. Brink a , Gary S. Goldberg a,c a Department of Physiology and Biophysics, School of Medicine, Basic Science Tower L6, Health Science Complex, State University of New York at Stony Brook, Stony Brook, NY 11794-8661, USA b Department of Cellular and Physiological Sciences, University of British Columbia, Faculty of Medicine, 313-2177 Wesbrook Mall, Vancouver, BC, Canada V6T 1Z3 c Department of Molecular Biology, University of Medicine and Dentistry of New Jersey, 2 Medical Center Dr., Stratford, NJ 08083, USA Received 11 May 2005 Available online 31 May 2005 Abstract We demonstrate that the Src kinase can augment gap junctional communication between cells derived from homozygous null Cx43 knockout mice. The total conductance between Src transformed cells was nearly twice that of nontransformed cells. In addi- tion, the unitary conductance of the majority of single channel events between transformed cells was about 35% greater than that of nontransformed cells. Analysis showed that both nontransformed and transformed cells expressed at least two populations of chan- nels, suggesting that Src increased junctional conductance by up-regulating one population and/or by increasing the unitary con- ductance of another population of channels. Interestingly, the conductance displayed by heterologous pairs of transformed and nontransformed cells resembled that of nontransformed cells. The majority of single channel events between heterologous pairs shifted back to lower conductances that were exhibited by nontransformed cells. Thus, nontransformed cells can effectively ‘‘nor- malize’’ the conductance of gap junction channels expressed by adjacent tumor cells. Ó 2005 Elsevier Inc. All rights reserved. Keywords: Gap junctions; Intercellular communication; Connexin; Src kinase; Cell junctions; Transformation; Heterologous; Growth control Gap junctions form channels between adjacent cells exclusive of the extracellular space. Each gap junction channel is formed by 12 connexin subunits with each cell of a pair contributing six subunits. Connexins are an an- cient protein family that has evolved into over 20 mem- bers in humans and mice [1,2]. Gap junction channels are permeable to a host of cytoplasmic solutes from monovalent cations and an- ions to second messengers and metabolites. The perme- ability of these molecules is governed by size and charge of a solute and the specific connexins comprising the gap junction channel [3–7]. This form of communication allows cells within a syncytium to function properly in a coordinated fashion [8–10]. At the organism level the critical role of connexins is evidenced by deleterious phenotypes in connexin knock- out mice. For example, both Cx43 and Cx45 are re- quired for proper development and function of the heart [11]. The importance of connexins to human health is further underscored by many diseases that are associated with mutations that affect connexin func- tion or protein expression [1,12]. Evidence indicates that connexins play important roles in cell growth control. In particular, experiments have identified Cx43 as a tumor suppressor gene [13– 15]. It is of pivotal interest that Cx43 can be phosphor- ylated by the Src tyrosine kinase. Moreover, this event 0006-291X/$ - see front matter Ó 2005 Elsevier Inc. All rights reserved. doi:10.1016/j.bbrc.2005.05.104 * Corresponding author. Fax: +1 631 444 3432. E-mail address: vvaliunas@notes.cc.sunysb.edu (V. Valiunas). www.elsevier.com/locate/ybbrc Biochemical and Biophysical Research Communications 333 (2005) 174–179 BBRC