C‐myc expression and transformed phenotypes in hybrid clones between mouse plasmacytoma S194 cells and normal spleen cells or fibroblasts

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Abstract
Expression of the rearranged c‐myc oncogene and transformed phenotypes was investigated in 2 different types of somatic cell hybrid clones between a BALB/c mouse plasmacytoma line (S194) and normal allogeneic spleen cells or fibroblasts. In the parental S194 cells, one allele of the c‐myc was rearranged and its 5′ flanking region was partially deleted by recombination with the immunoglobulin C α gene. Due to this recombination, S194 cells expressed approximately 20‐fold higher than normal spleen or fibroblast levels of c‐myc transcripts from the rearranged allele, which are smaller than normal germ‐line 2.4‐kb c‐myc transcripts, but they expressed the same low levels of 2.4‐kb c‐myc transcripts from the nonrearranged allele as compared with normal spleen cells or fibroblasts. All the hybrid clones retained both the rearranged and the non‐rearranged c‐myc. The hybrid clones between S194 and normal spleen cells showed transformed phenotypes and expressed the same high levels of rearranged c‐myc transcripts and low levels of the non‐rearranged c‐myc transcripts as the parental S194 cells. On the other hand, the hybrid clones between S194 cells and normal fibroblasts showing nontransformed phenotypes inhibited expression of the rearranged c‐myc to undetectable levels but expressed the nonrearranged c‐myc transcripts at low levels. A hybrid clone between S194 cells and normal fibroblasts showing transformed phenotypes also exhibited the same pattern of c‐myc expression as the non‐transformed hybrid clones. These results indicate that expression of the rearranged c‐myc in S194 mouse plasmacytoma cells is modulated in different ways in different components of cell lineages, although the correlation between the levels of rearranged c‐myc transcripts and the transformed phenotypes in the hybrid clones was not absolute.