Absence of the hybrid bcr‐abl mRNA in Ph1‐positive B lymphoblastoid cell lines established from a patient with chronic myelogenous leukemia

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Abstract
The expression of c‐abl, c‐sis, c‐myc and N‐ras oncogenes was examined in 2 lymphoblastoid cell lines, one with Ph1 (PB‐1049) and the other without Ph1 (LN‐1049), both established from a patient with chronic myelogenous leukemia (CML), and in a Ph1‐positive cell line (PB‐1049‐T) derived from a tumor formed after transplantation of PB‐1049 cells in a nude mouse with reference to their tumorigenic potential in nude mice. The normal transcripts of c‐abl were detected in all 3 lymphoblastoid cell lines. Although in situ hybridization of v‐abl proved, and restriction endonuclease analyses of the bcr region strongly indicated the occurrence of bcr‐abl rearrangement in PB‐1049 and PB‐1049‐T, we could not obtain any evidence for the expression of the hybrid bcr‐abl mRNA. These results indicate that the Ph1 translocation does not ensure the production of the hybrid bcr‐abl mRNA, and that the expression of hybrid bcr‐abl gene is not essential for the maintenance of tumorigenicity of these cell lines. Expression of c‐sis was not detected in any of the cell lines examined, whereas the expression of c‐myc was uniformly higher in the 3 cell lines than in normal control cells. The levels of N‐ras expression varied considerably, probably in parallel with the changes in tumorigenicity of the cell lines. N‐ras expression in the PB‐1049 and PB‐1049‐T cell lines was higher than that in the LN‐1049 line when they retained tumorigenic potential, but it fell to the level of LN‐1049 with loss or decline of tumorigenicity.