Variant (6 ; 15) translocation in a murine plasmacytoma occurs near an immunoglobulin κ gene but far from the myc oncogene

Abstract

Chromosome translocations in B-lymphoid tumours are providing intriguing insights and puzzles regarding the role of immunoglobulin genes in the activation of the myc oncogene (reviewed in refs 1, 2). The 15 ; 12 translocations found in most murine plasmacytomas and the analogous 8 ; 14 translocation in human Burkitt's lymphomas involve scissions of murine chromosome 15 (human chromosome 8) near the 5′ end of the c-myc gene and subsequent fusion near an immunoglobulin heavy-chain gene. The less well characterized ‘variant’ translocations found in about 15% of such tumours also involve the myc-bearing chromosome band, but exchange occurs with a chromosome bearing an immunoglobulin light-chain locus—in mice, the κ-chain locus bearing chromosome 6 (refs 3–5) and, in man, chromosome 2 (or 22), at the same band at which the κ (or λ) locus lies (reviewed in ref. 1). The Burkitt variant translocations involve scissions 3′ of c-myc^6–10; one 8 ; 22 translocation placed the C_λ locus just 3′ of c-myc¹⁰, but usually the chromosome 8 breakpoint is a greater, but unknown, distance away from c-myc, more than 20 kilobases (kb) in one 8; 2 translocation involving the C_κ gene⁹. Little is known about the murine 6 ; 15 translocations, although a C_κ gene cloned from one plasmacytoma (PC7183) is linked, via chromosome 12 sequences, to an unidentified region of chromosome 15 (ref. 11). We describe here the chromosome fusion region from plasmacytoma ABPC4, which displays the typical reciprocal 6 ; 15 translocations⁵. We find that the chromosome 6 breakpoint is near C_κ but, unlike those in the heavy-chain locus, not at a position where immunoglobulin genes normally recombine. Moreover, the chromosome 15 sequences involved in the ABPC4 translocation are not derived from the vicinity of c-myc.