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* Department of Biochemistry and Molecular Biology, The George Washington University, Washington, DC, 20037; and Western blotting studies revealed that
connexin43 (Cx43), one of the major gap junction proteins in human vascular endothelial cells, is posttranslationally modified during mitosis. This mitosis-specific modification results in a Cx43 species that migrates as a
single protein band and was designated Cx43m. Cx43m
was shown to be the result of additional Ser/Thr phosphorylation as indicated by: (a) the increased gel mobility induced by both alkaline phosphatase and the Ser/
Thr-specific protein phosphatase-2A (PP2A) and (b) the removal of virtually all 32Pi from Cx43m by PP2A.
Immunofluorescent confocal microscopy of mitotic
cells revealed that Cx43 is intracellularly located, while in nonmitotic cells Cx43 is located at regions of cell-cell
contact. Dye coupling studies revealed that mitotic endothelial cells were uncoupled from each other and
from nonmitotic cells. After cytokinesis, sister cells resumed cell coupling independent of de novo protein synthesis. The mitosis-specific phosphorylation of Cx43
correlates with the transient loss of gap junction intercellular communication and redistribution of Cx43, suggesting that a protein kinase that regulates gap junctions is active in M-phase.
Department of Anatomy and Cell Biology, McGill University, Montreal, Canada H3A-2B2
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