HYPERSOMY OF CHROMOSOME-15 WITH RETROVIRALLY REARRANGED C-MYC, LOSS OF GERMLINE C-MYC AND IGK C-MYC JUXTAPOSITION IN A MACROPHAGE-MONOCYTICTUMOR LINE/

From a lymphoid tumour induced by 7,12 -dimethylbenz-[a]-anthracene (D MBA) + methyl-N-nitrose-N-urea (MNU) in an [AKR Rb(6.15) x CBAT6T6]F1 mouse, a macrophage- monocyte line (KT-10) was isolated. Following eth yl methanesulfonate (EMS) treatment, a bromodeoxyuridine (BUdR) resist ant subline was selected. Serial propagation of this line in vitro in the presence of BUdR (28 months) with periodic cytogenetic and molecul ar examinations, has led to the definition of four successive stages. During stage I, the cells were trisomic for chromosome 15. They contai ned Rb(6.15) and Rb(del6.15) of AKR and T(14;15) of CBA origin. Southe rn blotting showed the presence of both germline (G) and rearranged (R ) c-myc. At stage II, Rb(del6.15) has duplicated. Both Rb(6.15) and T( 14;15) persisted together with G-myc and R-myc. In stage III, the CBA- derived T(14;15) was lost, in parallel with G-myc. At this stage, a Di c.In(6.15) was detected. One of its arms was cytogenetically identical with the long arm of In(6.15) in the variant IgK/myc translocations. This chromosome carried R-myc and IgK in juxtaposition, as indicated b y comigration on pulsed field electrophoresis (PFGE). At stage IV, the R-myc carrying AKR-derived chromsome 15s were present in six copies. Possible relationships between the increasing R/G mgc ratio and change d growth characteristics in vivo and in vitro are discussed.