MOUSE P53 REPRESSES THE RAT-BRAIN CREATINE-KINASE GENE BUT ACTIVATES THE RAT MUSCLE CREATINE-KINASE GENE

The creatine kinases (CK) regenerate ATP for cellular reactions with a high energy expenditure. While muscle CK (CKM) is expressed almost ex clusively in adult skeletal and cardiac muscle, brain CK (CKB) express ion is more,widespread and is highest in brain glial cells. CKB expres sion is also high in human lung tumor cells, many of which contain mut ations in p53 alleles. We have recently detected high levels of CKB mR NA in HeLa cells and, in this study, have tested whether this may be d ue to the extremely low amounts of p53 protein present in HeLa cells. Transient transfection experiments showed that wild-type mouse p53 sev erely repressed the rat CKB promoter in HeLa but not CV-1 monkey kidne y cells, suggesting that, in HeLa but not CV-1 cells, p53 either assoc iates with a required corepressor or undergoes a posttranslational mod ification necessary for CKB repression. Conversely, mouse wild-type p5 3 strongly activated the rat CKM promoter in CV-1 cells but not in HeL a cells, suggesting that, in CV-1 cells, p53 may associate with a requ ired coactivator or is modified in a manner necessary for CKM activati on. The DNA sequences required for p53-mediated modulations were found to be within bp -195 to +5 of the CKB promoter and within bp -168 to -97 of the CKM promoter. Moreover, a 112-bp fragment from the proximal rat CKM promoter (bp -168 to -57), which contained five degenerate p5 3-binding elements, was capable of conferring p53-mediated activation on a heterologous promoter in CV-1 cells. Also, this novel p53 sequenc e, when situated in the native 168-bp rat CKM promoter, conferred p53- mediated activation equal to or greater than that of the originally ch aracterized far-upstream (bp -3160) mouse CKM p53 element. Therefore, CKB and CKM may be among the few cellular genes which could be targets of p53 in vivo. In addition, we analyzed a series of missense mutants with alterations in conserved region II of p53. Mutations affected p5 3 transrepression and transactivation activities differently, indicati ng that these activities in p53 are separable. The ability of p53 muta nts to transactivate correlated well with their ability to inhibit tra nsformation of rat embryonic fibroblasts by adenovirus Ela and activat ed Ras.