RESUMO
The gene expression of both the mouse plasmocytoma (SP2/0) and the hybrid cells crossed with rat nucleated erythroblasts were detected by in situ hybridization technique using the probes of mouse ?-globin gene and 7 oncogenes (v-Ki-ras, v-H-ras, v-sis, erb-B, v-abl, v-fos, c-myc). After plasmic amplification, DNA was isolated by alkali lysis, purified and recovered, the DNA containing gene fragments were labelled with ~(32)P to become high activity ~(32)P-cDNA probes through nick translation, and the labelled probes were used to detect the gene transcripts in cellular level. The results indicated that: (1) no mouse ?-globin gene transcripts could be detected in the cytoplasm of SP2/0 cells, as well as in hybrid cells within 72 hours after cell fusion, but transcript signals could be observed in hybrid cells from 4th to 26th passages. (2) Active expression of multioncogenes in SP2/0 cells was demonstrated, all the 7 oneogenes tested, except v-sis, were expressed more strongly. On the other hand, the expression of oncogenes in hybrid cells was found to be dramatically decreased, among them, the oncogenes of c-myc and Ki-ras been suppressed completely. After long term of passages (26th subcultures), the expression of c-myc and Ki-ras was still lower than that of SP2/o ceils although in some cases other oncogenes increased in their expression levels. These results confirmed that the multistep carcinogenesis involved multi-oncogenes expression and that the decancerization of tumor cells may be due to the suppression of multi-oncogenes activity as well as to activate the expression of differentiation genes.