Multi-step neoplastic transformation of normal human fibroblasts by Co-60 gamma rays and Ha-ras oncogenes

Mutation inp53 and de-regulation ofp53-related gene expression in three human cell lines immortalized with 4-nitroquinoline 1-oxide or60Co gamma rays

“…Immortalization of human fibroblasts is a critical step in the in vitro multi-step carcinogenesis of human cells (Namba et al, 1988), but it is an extremely rare event. Although the rate of immortalization is very low, the SV40 large-T antigen can enable normal human cells to escape from cellular senescence by a 2-step process, consisting of stages M1 and M2 (Shay et al, 1991).…”

“…The resulting immortalized cell lines were designated SUSM-1, KMST-6 and OUMS-24F respectively (Namba et al, 1985(Namba et al, , 1988Bai et al, 1993). The culture medium used was Eagle's minimum essential medium (MEM) (Nissui, Tokyo, Japan) supplemented with 10% fetal bovine serum (FBS).…”

Transformation of normal human fibroblasts into immortalized cells with the mutant p53 gene and X‐rays

“…In vitro cell transformation is a valuable model for studying the mechanisms of multistep carcinogenesis. The human cell system is useful for studying the various stages of in vitro transformation, because events in the transformation process, from normal to neoplastic phenotypes, are clearly defined by the successive stages of aging, immortalization, and neoplastic transformation (Namba et al, 1988). For normal human cells to undergo neoplastic transformation, they must first be immortalized.…”

“…However, senescent cells have lost the ability to express c-fos and cdc2-cyclin A kinase activity and to phosphorylate Rb protein (Seshadri and Campisi, 1990;Stein et al, 1990Stein et al, , 1991. p53 regulates the cell-cycle machinery partially through the expression of p21, because p21 inhibits the action of multiple cyclin-dependent kinase (cdk) complexes and arrests growth (Noda et al, 1994).We obtained 3 human cell lines immortalized with either 4-nitroquinoline 1-oxide (4-NQO) or 60 Co gamma-rays (Namba et al, 1988;Bai et al, 1993) and found that all 3 cell lines had mutations in the p53 gene. Furthermore, a relationship between the loss of p53 functions and immortalization of human cells has been implied in several human cell systems: mammary cells immortalized with gamma-rays (Wazer et al, 1994), with HPV 16 E6 gene (Wazer et al, 1995), and with mutant p53 (Gao et al, 1996) spontaneously immortalized mammary cells (Moyret et al, 1994) and keratinocytes (HaCaT line, Lehman et al, 1993), and LiFraumeni fibroblasts (Bischoff et al, 1990;Rogan et al, 1995) and its mammary cells (Shay et al, 1995).…”

Malignant transformation of human fibroblasts caused by expression of a transfected T24 HRAS oncogene.

“…Although the MSU- (19,21), who utilized KMST-6 cells. In their studies, introduction of ras oncogenes by either virus infection (18,19) or by transfection (21) resulted in cells able to form tumors in athymic mice, although, in contrast to our results with the SV40-immortalized GM0637B cells, the tumors produced with the Va2 cells did not grow progressively (18)-an important criterion for malignant transformation, along with the ability to invade.…”