IDENTIFICATION OF THE PRIMARY GROWTH-RESPONSE GENE, ST2 T1, AS A GENEWHOSE EXPRESSION IS DIFFERENTIALLY REGULATED BY DIFFERENT PROTEIN-KINASE-C ISOZYMES/

Individual protein kinase C isozymes have been shown to play different roles in mediating proliferation, differentiation and transformation, but it is not known to what extent these effects involve induction of expression of particular genes. To explore the differential gene expr ession that might be induced by activation of different PKC isozymes, we stably transfected NIH 3T3 cells with expression vectors that encod e the isozymes PKC-alpha, -beta II, -gamma -delta, -epsilon, -zeta and -eta. Using differential display-reverse transcription-polymerase cha in reaction we isolated a small cDNA that encodes a portion of the pri mary response gene, ST2 (also referred to as T1 or DER4), and we confi rmed by RNA blot studies that ST2/T1 expression is differentially regu lated by PKC isozymes. ST2/T1 mRNA is undetectable in the unstimulated parental NIH 3T3 cells that express only the alpha isozyme of PKC, bu t it can be induced by phorbol ester treatment. Clones that overexpres s PKC-alpha, -delta or -epsilon similarly do not express ST2/T1 until they are stimulated with phorbol esters, which induces expression of S T2/T1 with kinetics similar to wild-type NM 3T3 but to different exten ts. In contrast, ST2/T1 mRNA is already present in unstimulated cells that overexpress PKC-beta II, -gamma, -zeta and -eta, but phorbol este r greatly enhances ST2/T1 expression in these cells. These results sug gest a differential role for PKC isozymes in mediating the ST2/T1 expr ession that is induced by growth stimuli.