Eric Beyer, M.D., Ph.D.

Studies of Gap Junction-Mediated Intercellular Communication

Research Summary

My laboratory is currently investigating the process of intercellular communication; our specific goal is a molecular understanding of the structure and function of gap junctions. Gap junctions are the specialized plasma membrane structures which contain low resistance channels linking adjacent cells. In excitable tissues, they permit electrical coupling; in non-excitable tissues, they permit passage of small molecules involved in metabolic support, growth control, and embryogenesis. They may also facilitate drug metabolite delivery between cells. In migratory cells (such as macrophages), which also express these proteins, they may facilitate more transient interactions.

We have cloned cDNAs corresponding to gap junction proteins from a number of different tissues and species. These sequences demonstrate that there is a family of gap junction proteins (connexins) which are related in their transmembrane and extracellular regions, but which have unique cytoplasmic domains. Connexin-specific sequences confer different physiologic channel properties or regulation. We have also raised antibodies directed against specific domains within the connexin sequences. The cDNA and antibody regents are being used in a number of whole animal, tissue culture, and expression systems to investigate the structure and function of gap junctions and the regulation of intercellular communication. Our studies have demonstrated that different connexins have different expression patterns (eg. one isoform is specifically expressed in conducting tissue). We have found evidence of regulation of connexin proteins by phosphorylation and turnover/degradation.

A major current effort is underway to elucidate the mechanisms of degradation of gap junctions and the importance of this process in the remodeling of cardiac cellular connections. The transfection of communication-deficient cells with connexin sequences has demonstrated connexin-specific channel properties, permeabilities, and regulation. Site-directed mutagenesis is being used to identify sites within the connexins important in determining gating and permeability properties.

Several aspects of these studies are of particular importance to cancer biology. Several connexins have been identified in screens for tumor supressor genes. Explaining their functions may elucidate a novel mechanism of tumor supression. We have shown that gap junctional intercellular communication is regulated by protein kinase C as stimulated by tumor promoting phorbol esters.

We have ongoing studies of the role of gap junctions in the "bystander effect" in gene therapy approaches to cancer treatment.

Selected Papers

Reed KE, Westphale EM, Larson DM, Wang H-Z, Veenstra RD, Beyer EC. (1993) Molecular cloning and functional expression of human connexin37, anendothelial cell gap junction protein. J Clin Invest, 91: 997-1004.

Steinberg TH, Civitelli R, Geist ST, Robertson AJ, Veenstra RD, Wang H-Z, Warlow PM, Hick E, Laing JG, Beyer EC. (1994). Connexin43 and connexin45 form gap junctions with different molecular permeabilities in osteoblastic cells. EMBO J., 13: 744-750.

Gupta VK, Berthoud VM, Atal N, Jarillo JA, Barrio LC, Beyer EC. (1994). Bovine connexin44, a lens gap junction protein: molecular cloning, immunological characterization, and functional expression. Invest. Ophthalmol. Vis. Sci., 35: 3747-3758.

Davis LM, Kanter HL, Beyer EC, Saffitz JE. (1994). Distinct gap junction phenotypes in cardiac tissues with disparate conduction properties. J. Am. Coll. Cardiol., 24: 1124-1132.

Fick J, Dazin P, Westphale EM, Beyer EC, Israel MA. (1995). The extent of heterocellular communication is predictive of bystander cytotoxicity in vitro. Proc. Natl. Acad. Sci. U.S.A. , 92: 11071-11075.

Laing JG, Beyer EC. (1995). The gap junction protein connexin43 is degraded by the ubiquitin-proteasome pathway. J. Biol. Chem., 270: 26399-26403.

Veenstra RD, Wang H-Z, Beblo DA, Chilton M.G., Harris AL, Beyer EC, Brink PR. (1995). Selectivity of connexin-specific gap junction channels does not correlate with channel conductance. Circ. Res., 77: 1156-1165.

Larson DM, Wrobleski MJ, Sagar GDV, Westphale EM, Beyer EC. (1997). Connexin43 and connexin37 are differentially regulated in endothelial cells by cell density, growth, and TGF-B1. Am. J. Physiol. (Cell Physiol. 41), 272: C405-C415.

Berthoud VM, Beyer EC, Kurata WE, Lau AF, Lampe PD. (1997). Connexin56 is phosphorylated within both the cytoplasmic loop and tail domains. Eur. J. Biochem., 244: 89-97.

Guerrero PA, Schuessler RB, Davis LM, Beyer EC, Johnson CM, Yamada KA, Saffitz JE. (1997). Slow ventricular conduction in mice heterozygous for a connexin43 null mutation. J. Clin. Invest., 99: 1991-1998.

Brink PR, Cronin K, Banach K, Peterson E., Westphale EM, Seul KH, Ramanan SV, Beyer EC. (1997). Evidence for heteromeric gap junction channels formed by rat connexin43 and human connexin37. Am. J. Physiol. (Cell Physiol. 42), 273: C1386-C1396.

Laing JG, Tadros PN, Westphale EM, Beyer EC. (1997). Degradation of connexin43 gap junctions involves both the proteasome and the lysosome. Exp. Cell Res., 236: 482-492.

Seul K-H, Tadros PN, Beyer EC. (1997). Mouse connexin40: gene structure and promoter analysis. Genomics, 46: 120-126.