Karyotype analysis of carcinogen-treated Chinese hamster cells in vitro evolving from a normal to a malignant phenotype

Abstract

Summary The relationship of cytogenetic changes with the acquisition of an indefinite life span in vitro, the ability of cells to grow in soft agar and their tumourigenicity in syngeneic animals has been studied in control, trans-7,8-dihydrodiolbenzo(a)pyrene and 7fl,8a-dihydroxy-9a,10a-epoxy-7,8,9,10-tetrahydrobenzo(a)-pyrenetreated secondary cultures derived from Chinese hamster embryonic lung. Karyotype analysis revealed a sequence of chromosome changes as the cells progressed through culture. Aneuploidy, namely trisomy of chromosome 4, the long arm in particular, was an early dominant change. The possible association of this trisomy with the acquisition of immortality in vitro is implicated, although the involvement of other nonrandom chromosome changes cannot be eliminated, implying that there may be several genomic sites in the Chinese hamster which may potentially be involved with the acquisition of unlimited growth potential. Neither the ability of cells to grow in soft agar nor as tumours could be associated with any specific chromosome(s). Double minutes were observed in metaphases from the cell lines, agar colonies and tumours; their possible relationship with growth advantage is discussed.Karotype abnormalities characterise the majority of metaphases recovered from malignant cells. Indeed, cytogenetic analysis of neoplastic golden hamster cells, revertants with a suppressed malignant phenotype and segregants from these revertants which were again malignant, have led to the identification of chromosomes which control the expression and suppression of malignancy (Hitotsumachi et al., 1971(Hitotsumachi et al., ,1972Benedict et al., 1975;Bloch-Shtacher & Sachs, 1976). It has also been reported that more than one chromosome may carry genes which control malignancy in this species (Hitotsumachi et al., 1971(Hitotsumachi et al., ,1972 Yamamoto et al., 1973a, b;Bloch-Shtacher & Sachs, 1976). Some of the factors which control malignancy have also been assigned to specific chromosomes in the rat (Levan & Levan, 1975), mouse (Codish & Paul, 1974;Klein, 1979) and the Chinese hamster (BlochShtacher & Sachs, 1977).The evolution of the malignant phenotype as a progressive multi-step process has been demonstrated both in vivo (Foulds, 1969(Foulds, ,1975 and in vitro (Barrett & Ts'o, 1978a, b;Barrett et al., 1980). In vitro studies have indicated that as the neoplastic phenotype evolves, the unknown series of genetic and/or epigenetic events underlying this evolutionary process are reflected through various abnormal phenotypes, i.e. the acquisition of immortality (Newbold et al., 1982) and loss of anchorage dependency for growth (Connell & Ockey, 1977;Barrett, 1979 7,B,8,9,

Specific aneusomies in Chinese hamster cells at different stages of neoplastic transformation, initiated by nitrosomethylurea

“…The most particular case was made by Sachs et al (52,53), who have distinguished ''E'' chromosomes for expression and ''S'' chromosomes for suppression of neoplastic transformation. Indeed, 11 studies on karyotypes of spontaneously, chemically, or simian virus 40 virus-transformed CH cells have identified one or both of the two most prominent transformation-specific aneusomies that we have identified here, i.e., trisomies 3 and 5, regardless of the carcinogen or strain of the animal used (47,48,(53)(54)(55)(56)(57)(58)(59)(60)(61). Three of these studies also reported prominent trisomies of chromosomes 8 (61), 9 (55), and 10 (48).…”

“…For example, Deaven et al (56) remained uncertain about ''the specific chromosome change hypothesis,'' because different ''nonrandom'' karyotypes were found in CH tumors in their lab and in others. Likewise, others remained undecided or unconfirmed, because no unique transformationspecific aneusomies were found (47,48,54,59,61). As a result some began to interpret transformation-specific aneuploidies as evidence for oncogenes (58,60,62).…”

“…1). Therefore, typically millions of in vitro transformed cells are injected into animals to improve the odds for the missing ''steps'' from transformation in vitro to tumorigenesis to occur in one of these cells (40,(47)(48)(49).…”

Aneuploidy correlated 100% with chemical transformation of Chinese hamster cells

“…In addition, many more primary transformants can be generated and analyzed per cost in vitro than in animals. Several studies have documented that stable, morphological transformation of CHE cells in vitro by chemical carcinogens correlates well with tumorigenicity (20,66,68,69).…”

“…To meet these criteria we studied the chromosomes of Chinese hamster embryo (CHE) cells transformed in vitro, because transformation in vitro can be detected early, within 2 months after treatment (20,66) and thus about 5 months sooner than chemical carcinogenesis (67). In addition, many more primary transformants can be generated and analyzed per cost in vitro than in animals.…”