Repression of Rearranged μ Gene and Translocated c- myc in Mouse 3T3 Cells × Burkitt Lymphoma Cell Hybrids

Abstract

The productively rearranged immunoglobulin mu chain gene and the translocated cellular oncogene c-myc are transcribed at high levels both in human Burkitt lymphoma cells carrying the t(8;14) chromosome translocation and in mouse plasmacytoma X Burkitt lymphoma cell hybrids. In the experiments reported here these genes were found to be repressed in mouse 3T3 fibroblast X Burkitt lymphoma cell hybrids. Such repression probably occurs at the transcriptional level since no human mu- and c-myc messenger RNA's are detectable in hybrid clones carrying the corresponding genes. It is therefore concluded that the ability to express these genes requires a differential B cell environment. The results suggest that the 3T3 cell assay may not be suitable to detect oncogenes directly involved in human B cell oncogenesis, since 3T3 cells apparently are incapable of transcribing an oncogene that is highly active in malignant B cells with specific chromosomal translocations.

"Retroposon" insertion into the cellular oncogene c-myc in canine transmissible venereal tumor.

“…The inserted sequence shows 62% homology to a region of the Kpn I element beginning approximately 900 bp from the 3' end of the Kpn I element. This is similar to the homology between mouse MIF repetitive element and monkey Kpn I element (39). It is of interest that the homology is in the 3' to 5' orientation of the Kpn I element, suggesting a possibility of inversion of the inserted element.…”

Trans-acting elements modulate expression of the human c-myc gene in Burkitt lymphoma cells.

“…However, it is likely that sequences in the immunoglobulin loci to which the c-myc gene is translocated also play a role in c-myc activation. Cell hybrid studies have shown that the translocated c-myc gene is activated only in the B-cell background (36). In rare instances of Burkitt lymphoma (37) and murine plasmacytoma (38), the c-myc gene translocates to the immunoglobulin Ig heavy chain enhancer sequence.…”

An active chromatin structure acquired by translocated c-myc genes.

“…In addition, somatic cell hybrid studies demonstrate that the cryptic promoters of truncated c-myc genes adjacent to immunoglobulin switch, and constant regions are active, in a B-cell background but not in lymphoblastoid or nonlymphoid cell backgrounds (10,31,32). This demonstrates a requirement for B-cell-specific factors and suggests that B-cell factors normally involved in immunoglobulin gene transcription may also activate the cryptic c-myc promoters translocated adjacent to immunoglobulin genes.…”

“…6,1986 on May 10, 2018 by guest http://mcb.asm.org/ Downloaded from did not cause the altered chromatin structure since the reciprocally translocated 5' c-myc region did not acquire the same structure. Furthermore, since activation of translocated c-myc genes requires a mature B-cell environment (10,31,32), adjacent Ca sequences are causally implicated in this altered chromatin structure.…”