Identification and characterization of genes whose expressions are alteredin rat 6 fibroblasts transformed by mutant p53(val135)

The wild-type tumor suppressor gene p53 is known as a transcription factor in activating or suppressing target genes that encode proteins in regulatin g genome stability, DNA damage, cell arrest, and apoptosis. However, the ro le of mutant p53 in the process of cell transformation is still unclear. Ou r recent work indicated that overexpression of mutant p53(val135) induced h igh incidence of spontaneous transformation in prolonged cultures of Rat 6 fibroblasts. In order to identify genes related to neoplastic transformatio n induced by the mutant p53, the p53(val135)-overexpressor R6#13-8 and its derived spontaneously transformed cell line T2 were analyzed by mRNA differ ential display. In a systematic screening with 80 primer sets of RT-PCR rea ctions, three genes were found to be differentially expressed between R6#13 -8 and T2 cells. Two genes, identified as homologues of the growth factor i nducible immediate-early gene Cyr61 and the human nonmuscle myosin heavy ch ain-B, were down-regulated in T2 cells. Interestingly, both genes were also suppressed in Rat 6 cells transformed by c-H-ras and v-myc, but not by v-s rc genes. The third gene is a homologue of the frizzled related protein, a gene family that acts, in some cases, as an antagonist to the Wnt signaling pathway. It is intriguing that the rat homologue of the frizzled related p rotein was only expressed in p53(val135)-overexpressing cells, but not in t he parental Rat 6 cells. However, the same gene was also highly expressed i n ras-transformed Rat 6 cells, and moderately expressed in v-src-transforme d Rat 6 cells. This is the first study in which the association of mutant p 53 to these three genes is revealed. Our current report may provide new clu es to the role of mutant p53 in the process of cell transformation. (C) 199 9 Academic Press.