Genetic analysis of Raf1, Mdm2, c-Myc, Cdc25a and Cdc25b proto-oncogenes in 2 ',3 '-dideoxycytidine- and 1,3-butadiene-induced lymphomas in B6C3F1 mice

We have previously identified activation of ras proto-oncogenes and inactiv ation of tumor suppressor genes including p53, p16(INK4a) and p15(INK4b) in 2',3'-dideoxycytidine (ddC)- and/or 1,3-butadiene (BD)-induced lymphomas d erived from B6C3F1 (C57BL/6xC3H/He) mice, indicating that alterations of ra s signaling pathway, p53 and pRb growth control pathways are important in t he development of these chemically induced lymphomas. However, there is sti ll a subset of tumors that displayed no changes in these genes. Thus, we in vestigated whether the Raf1, Mdm2, c-Myc, Cdc25a and Cdc25b proto-oncogenes , which are implicated in the ras or p53 or pRb pathways, are alternative o ncogenic target genes. Analyses of gross genomic alterations by Southern bl ots failed to reveal rearrangement or amplification in any of the tumors ex amined. Frequent point mutations on the substrate binding domain of the Raf 1 gene has been reported in 1-ethyl-1-nitrosourea (ENU)-induced murine lymp homas and lung tumors, along with a conspicuous lack of ras mutations [U. N aumann, I. Eisenmann-Tappe. U.R. Rapp, The role of raf kinases in developme nt and growth of tumors, Recent Results Cancer Res., 143 (1997) 237-244]. T o investigate whether Raf1 mutation is involved in our set of tumor especia lly those without ras mutations, the PCR-based single-strand conformation a nalyses (SSCA) and diner DNA sequencing were employed. No mutations but fou r genetic polymorphisms between C57BL/6 and C3H/He were found, with two of them reported as point mutations previously (op. cit.). The polymorphisms w ere utilized for allelic loss study of Raf1 locus. Losses of heterozygosity were found in six of 31 ED-induced lymphomas. These results indicate that genetic alterations of c-Myc, Cdc25, Raf1 and Mdm2 proto-oncogenes may not be involved in the development of ddC- and ED-induced lymphomas and the ina ctivation of tumor suppressor gene(s) located close to Raf1 gene might be i mportant in the development of a subset of BD-induced lymphomas. (C) 2000 P ublished by Elsevier Science B.V.