The receptor for tumor-promoting phorbol esters has been shown to be the Ca+2/phospholipid dependent enzyme protein kinase C (PKC). There are two major groups of PKC, the conventional PKC isotypes (α, βI, βII, γ) and the novel Ca+2-independent PKC (δ, ε, ζ, η). Phorbol esters previously have been demonstrated to increase human IFN-γ gene expression after treatment of a murine T cell line (Cl 9) that has been transfected with human IFN-γ genomic DNA. In contrast, treatment with Ca+2 ionophore alone or in combination with phorbol ester did not enhance IFN-γ production in a synergistic manner above the level obtained with phorbol ester treatment alone. To determine whether the lack of effect of Ca+2 ionophore is due to a defect in PKC, we compared the level of PKC autophosphorylation in the mouse T cell line (Cl 9), a mouse epidermal cell line (JB6), and purified rat brain PKC by in vitro kinase assays. The results demonstrate that instead of the expected 80-kDa autophosphorylated PKC band seen in purified rat brain PKC or mouse JB6 cell lysates, only a novel 97-kDa Ca+2-independent phosphoprotein was observed in Cl 9 cells. To ascertain if there was any nucleic acid sequence similarity to PKCε, we hybridized Cl 9 poly(A+) RNA with a cloned fragment of the PKCε gene and observed two hybridizing RNA bands (4.4 and 4.0 kb). Our results suggest that the 97-kDa phosphoprotein is similar to, but not identical with, PKCε and is the major PKC expressed in the Cl 9 murine T cell line. These data suggested that the 97-kDa PKC may be responsible for the induction of both the transfected human IFN-γ gene and the endogenous murine IL-2R α-chain.
|Original language||English (US)|
|Number of pages||8|
|Journal||Journal of Immunology|
|State||Published - 1992|
ASJC Scopus subject areas
- Immunology and Allergy