Ras Is Involved in Gap Junction Closure in Proliferating Fibroblasts or Preadipocytes but Not in Differentiated Adipocytes

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Abstract
A decrease in gap junctional, intercellular communication (GJIC) has been associated with cells neoplastically transformed by a variety of factors. To investigate the role of the Ras oncogene product in gap junction function, a panel of murine C3H10T½ (10T½) fibroblasts was constructed in which the levels of ras gene expression could be effectively up- or down-regulated. Intercellular communication was measured using a novel technique of in situ electroporation of adherent cells on a partly conductive slide. The introduction of increasing amounts of activated Rasleu61 in mouse 10T½ fibroblasts proportionally reduced GJIC, while the downregulation of endogenous c-ras gene expression increased junctional permeability. These results indicate that Ras plays an important role in the junction closure pathway leading to the proliferation of normal cells. However, differentiation of c-Ras-deficient preadipocytes entirely abolished their initially extensive GJIC, indicating that junction closure in response to adipocytic differentiation is independent of Ras.