Investigation of the Reciprocal Relationship between the Expression of Two Gap Junction Connexin Proteins, Connexin46 and Connexin43

• Published in: The Journal of biological chemistry 2011-07, Vol.286 (27), p.24519-24533
• Main Authors: Banerjee, Debarshi, Das, Satyabrata, Molina, Samuel A., Madgwick, Dan, Katz, Melanie R., Jena, Snehalata, Bossmann, Leonie K., Pal, Debjani, Takemoto, Dolores J.
• Format: Article
• Language: English
• Subjects: Animals; Carcinogens - pharmacology; Cell Biology; Cells, Cultured; Connexin; Connexin 43 - biosynthesis; Connexin 43 - genetics; connexin43; connexin46; connexin50; Connexins - biosynthesis; Connexins - genetics; Epithelial Cells - cytology; Epithelial Cells - metabolism; Gap Junctions; Gap Junctions - genetics; Gap Junctions - metabolism; Gene Expression Regulation - drug effects; Gene Expression Regulation - physiology; Humans; Lens, Crystalline - cytology; Lens, Crystalline - metabolism; Proteasome; Protein Degradation; Protein Turnover; Rabbits; Rats; Tetradecanoylphorbol Acetate - pharmacology
• ISSN: 0021-9258; 1083-351X
• DOI: 10.1074/jbc.M110.217208

Connexins are the transmembrane proteins that form gap junctions between adjacent cells. The function of the diverse connexin molecules is related to their tissue-specific expression and highly dynamic turnover. Although multiple connexins have been previously reported to compensate for each other's functions, little is known about how connexins influence their own expression or intracellular regulation. Of the three vertebrate lens connexins, two connexins, connexin43 (Cx43) and connexin46 (Cx46), show reciprocal expression and subsequent function in the lens and in lens cell culture. In this study, we investigate the reciprocal relationship between the expression of Cx43 and Cx46. Forced depletion of Cx43, by tumor-promoting phorbol ester 12-O-tetradecanoylphorbol-13-acetate, is associated with an up-regulation of Cx46 at both the protein and message level in human lens epithelial cells. An siRNA-mediated down-regulation of Cx43 results in an increase in the level of Cx46 protein, suggesting endogenous Cx43 is involved in the regulation of endogenous Cx46 turnover. Overexpression of Cx46, in turn, induces the depletion of Cx43 in rabbit lens epithelial cells. Cx46-induced Cx43 degradation is likely mediated by the ubiquitin-proteasome pathway, as (i) treatment with proteasome inhibitors restores the Cx43 protein level and (ii) there is an increase in Cx43 ubiquitin conjugation in Cx46-overexpressing cells. We also present data that shows that the C-terminal intracellular tail domain of Cx46 is essential to induce degradation of Cx43. Therefore, our study shows that Cx43 and Cx46 have novel functions in regulating each other's expression and turnover in a reciprocal manner in addition to their conventional roles as gap junction proteins in lens cells.