Partial Down-Regulation of Protein Kinase C in C3H 10T1/2 Mouse Fibroblasts Transfected with the Human Ha-ras Oncogene

Crystal M. Weyman, Elizabeth J. Taparowsky, Marina Wolfson, Curtis L. Ashendel

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63 Scopus citations


Biochemical and immunological comparison of mouse C3H 10T1/2 fibroblasts and C3H 10T1/2 fibroblasts transfected with human activated Ha-ras oncogene indicated significantly lower levels of protein kinase C (PKC) activity and protein in the ras-transfected cells. This effect was observed in three clonal cell lines transfected with an activated ras oncogene. Cytosolic extracts of the ras-transfected cells contained calcium-activated, phospholipid-dependent protein kinase (PKC) activity at 61% of the level of activity present in G3H 10T1/2 cells. A similarly decreased level of phorbol ester-binding activity was observed in these cells. Analysis of the subcellular distribution of PKC activity in cells failed to indicate significant differences between these cell lines. Immu-noblots showed a lower abundance of the Mr 80,000 PKC in ras-transfected cell homogenates and extracts compared to C3H 10T1/2 cells. Both C3H IOT1/2 cells and cells transfected with ras expressed only one of the PKC isozymes as resolved by hydroxylapatite chromatography demonstrating that ras transfection of cells did not induce expression of alternative PKC isozymes. These observations indicate that PKC was partially down-regulated in ras-transfected cells, perhaps resulting from constitutively elevated levels of products of phosphatidylinositol-4,5-bisphos-phate hydrolysis. Although C3H 10T1/2 cells were previously shown to be distinct from NIH 3T3 cells in their sensitivity to transformation by the T24-ras oncogene, ras transformation appears to partially down-regulate PKC in C3H 10T1/2 cells in a manner identical to that for ras-transformed NIH 3T3 cells. This indicates that down-regulation of PKC directly results from the expression of an activated ras oncogene independently of cellular sensitivity to transformation by expression of ras The common action of ras transformation and phorbol esters to down-regulate PKC provides a possible mechanism for synergism during multistage carcinogenesis.

Original languageEnglish
Pages (from-to)6535-6541
Number of pages7
JournalCancer Research
Issue number22
StatePublished - 1 Jan 1988
Externally publishedYes

ASJC Scopus subject areas

  • Oncology
  • Cancer Research


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