A NEW MEMBER OF THE 3RD CLASS IN THE PROTEIN-KINASE-C FAMILY, PKC-LAMBDA, EXPRESSED DOMINANTLY IN AN UNDIFFERENTIATED MOUSE EMBRYONAL CARCINOMA CELL-LINE AND ALSO IN MANY TISSUES AND CELLS

Protein kinase C (PHC)-related cDNA clones isolated from cDNA librarie s of mouse P19 embryonal carcinoma cells and mouse brain encoded a 67- kDa protein, PKC lambda. PKC lambda shows the highest amino acid seque nce identity with PKC zeta (72%), the third class of the PKC family. N orthern blot analysis showed that the mRNA for PKC lambda is expressed in a wide variety of cells and tissues, including P19 and MH 3T3 cell s, as well as brain, kidney, testis, and ovary. In undifferentiated P1 9 cells, the mRNA for PKC lambda is the most abundant among all the PK C family members. The differentiation of P19 cells results in an incre ase in PKC alpha and epsilon, and a decrease in PKC lambda. Antiserum raised against a peptide of PKC lambda identified a 74-kDa protein in P19 cell extracts as well as in extracts from COS cells transfected wi th the PKC lambda expression plasmid. Autophosphorylation of the PKC l ambda that immunoprecipitated with the specific antiserum was observed , indicating that PKC lambda possesses protein kinase activity. A phor bol ester binding assay using intact COS cells expressing PKC lambda f ailed to detect binding activity specific to PKC lambda at phorbol dib utylate concentrations up to 300 nM, suggesting that PKC lambda does n ot possess phorbol ester binding activity. These results, in conjuncti on with the results obtained in parallel experiments with PKC zeta and other PKC members, suggest a biochemical similarity between PKC lambd a and zeta and their clear difference from other PKC members.