Quiescent mammary epithelial cells have reduced connexin43 but maintain a high level of gap junction intercellular communication

✍ Scribed by Sia, Michael A. ;Woodward, Terry L. ;Turner, Jeffrey D. ;Laird, Dale W.

• Publisher: John Wiley and Sons
• Year: 1999
• Tongue: English
• Weight: 703 KB
• Volume: 24
• Category: Article
• ISSN: 0192-253X
• DOI: 10.1002/(sici)1520-6408(1999)24:1/2<111::aid-dvg11>3.0.co;2-p

✦ Synopsis

Gap junctions have been implicated in growth control, but it remains unclear whether cells that enter a quiescent state continue to express connexins and maintain a high level of gap junction intercellular communication (GJIC). To this end, MAC-T cells, a bovine mammary epithelial cell line, were serum starved for 48 h to induce a quiescent (G 0 ) state. In quiescent cells, [ 3 H]thymidine incorporation was reduced by 97.3% from serum-fed controls. Western blotting in conjunction with PhosphorImager analysis revealed up to a 20-fold decrease in the expression of the gap junction protein connexin43 (Cx43 or ␣ 1 ) and a shift toward the unphosphorylated form in quiescent cells. However, cell-to-cell transfer of the gap junction-permeable fluorescent tracer, Lucifer yellow, was only moderately reduced in quiescent cells. In control cells, Cx43 was predominantly perinuclear, although it was also present at sites of cell-cell apposition. In quiescent cells, intracellular labeling for Cx43 decreased without a corresponding reduction at areas of cell-cell contact. Recovery from serum deprivation resulted in increased thymidine incorporation that corresponded with an elevation in Cx43 protein expression and phosphorylation. In parallel studies, MAC-T cells were also induced to enter a quiescent state through contact inhibition. Despite a 20-fold reduction in 5-bromo-2Ј-deoxyuridine and a substantial reduction in intracellular Cx43, contact inhibited MAC-T cells also maintained gap junctions and GJIC. These experiments demonstrate that the maintenance of dye coupling in quiescent mammary cells is correlated with a redistribution of intracellular stores of Cx43.