Acquisition of responsiveness to chemical carcinogens by rodent embryo fibroblasts expressing high levels of the c‐myc proto‐oncogene

Abstract

We investigated the ability of overexpression of the c-myc proto-oncogene to potentiate in vitro transformation by model chemical carcinogens. A mouse c-myc gene was introduced to C3H 10T1/2 and Rat 6 embryo fibroblast cell lines via a retroviral vector containing the gene for neomycin resistance. Our present work extends previous findings by showing that individual vectored C3H 10T1/2 clones have enhanced (two-fold to sevenfold) sensitivity to benzo[a]pyrene (BP) and N-methyl-N-nitro-N'-nitrosoguanidine (MNNG). Rat 6 clones acquiring the c-myc gene display various degrees of altered morphology. They form orderly but densely packed cells, grow to higher saturation density, and yield microcolonies in soft agar. The degree of altered growth properties is directly correlated with the level of c-myc expression. Transient exposure of c-myc-expressing clones to BP and MNNG induced the formation of distinct, large colonies in soft agar, whereas the untreated cells formed microcolonies and the parental Rat 6 cells remained single cells in soft agar. We also demonstrated that the degree of responsiveness to chemical carcinogens of the clones correlates with their ability to form microcolonies in soft agar. These cells overexpressing c-myc may be used as a model system to study the interaction between oncogenes and chemical carcinogens in the process of multistage carcinogenesis.

Direct transformation of rodent fibroblasts by jaagsiekte sheep retrovirus DNA

“…Cultures of JSRV-transformed NIH 3T3 cells that had been serially passaged were seeded in agar suspension (10 4 cells per 6cm dish) as described (16). NIH 3T3 nontransformed cells were seeded in parallel.…”

Suppression of the tumorigenicity of mutant p53-transformed rat embryo fibroblasts through expression of a newly cloned rat nonmuscle myosin heavy chain-B

“…Clone T2 is one of the spontaneous transformants isolated from R6#13-8 cells (Yam et al, 1999). The R6#8-2 cell line, a Rat 6 derivative expressing a retroviral backbone vector (Hsiao et al, 1992), was included in the experiment as a control cell line. Both Rat 6 and R6#8-2 are anchorage independent and negative in nude mice assay (Hsiao et al, 1986;Housey et al, 1988).…”