Synergism of the Schmidt-Ruppin strain of the Rous sarcoma virus and cytidine triphosphate in the induction of chromosome breaks in human cultured leukocytes

c-Myc, genome instability, and tumorigenesis: the devil is in the details

The c-myc oncogene acts as a pluripotent modulator of transcription during normal cell growth and proliferation. Deregulated c-myc activity in cancer can lead to excessive activation of its downstream pathways, and may also stimulate changes in gene expression and cellular signaling that are not observed under non-pathological conditions. Under certain conditions, aberrant c-myc activity is associated with the appearance of DNA damage-associated markers and karyotypic abnormalities. In this chapter, we discuss mechanisms by which c-myc may be directly or indirectly associated with the induction of genomic instability. The degree to which c-myc-induced genomic instability influences the initiation or progression of cancer is likely to depend on other factors, which are discussed herein.

Induction of sister-chromatid exchanges (SCEs) by thymidine and the potentiation of mutagen-induced SCEs in Chinese hamster ovary cells

The effect of nucleosides, a group of naturally occurring cell constituents, on the frequency of sister-chromatid exchange (SCE) in Chinese hamster ovary (CHO) cells has been studied. Addition of thymidine (TdR) to the culture medium causes a dose-dependent increase and at 100 microM concentration, the SCE frequency is approximately doubled. This effect is totally reversed by 200 microM deoxycytidine (dCdR) suggesting that deoxycytidine starvation is responsible for this enhancing effect. Neither dCdR by itself nor deoxyadenosine (dAdR) or deoxyguanosine (dGdR) up to 300 microM concentrations had any effect on the incidence of SCE. The frequency of SCE induced by 10(-7) M N-methyl-N-nitro-nitrosoguanine (MNNG) is increased 2-fold by the addition of 100 microM TdR and this effect is also cancelled by 200 microM dCdR. These results point to the importance of the balance in DNA-precursor pools for normal DNA synthesis, infidelity of replication and errors in the replication of alkylated DNA increasing when the precursor pools become unbalanced.

Reticulum cell sarcoma: demonstration of chromosomal changes analogous to those in SV40-transformed cells

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