UV BUT NOT GAMMA-IRRADIATION INDUCES SPECIFIC TRANSCRIPTIONAL ACTIVITY OF P53 IN PRIMARY HEPATOCYTES

The mechanisms are poorly understood by which p53 can stimulate differ ent downstream events, including growth arrest, DNA repair, and apopto sis, after DNA damage, Changes in protein levels do not predict a part icular p53 response, but it is possible that differences in functional activities such as transactivation are important, The present report describes the successful use of a specific p53 reporter plasmid transf ected into primary murine hepatocytes to evaluate p53 transactivation activity over time after two different genotoxic injuries (gamma-irrad iation, 15 Gy and UV-c irradiation, 10 J/m(2)) known to produce p53-de pendent growth arrest in this cell type, The results show that UV inju ry to hepatocytes was followed by a transient increase in transcriptio nal activation of the reporter plasmid by p53 and that this response p receded changes in p53 protein levels,:ls assessed by immunocytochemis try. By contrast, gamma-irradiation injury failed to induce detectable changes in either transactivation activity or hepatocyte p53 protein levels, The data show that p53 responses to DNA damage are dependent o n both cell and injury type and suggest that in hepatocytes they can b e independent of protein concentration and specific transcriptional ac tivity, The results have implications for how particular dysfunctional p53 mutations in carcinogenesis could alter hepatocyte responses to d ifferent DNA injuries, (C) 1997 John Wiley & Sons, Ltd.