Analysis of karyotype variation following carcinogen treatment of chinese hamster primary cell lines

Abstract

Chinese hamster primary fibroblasts derived from several embryos were treated with the carcinogens benzo(a)pyrene, 7,12-dimethylbenz(a)anthracene or N-methyl-N'-nitro-N-nitrosoguanidine. Karyotype analysis, sister chromatid exchange frequency, evidence of transformation by growth in agar, cell morphology and reaction to cytocholasin B were tested at regular intervals over many culture passages. Carcinogen treatment was found to shorten the time period before onset of permanent karyotypically changed stem and side lines and in vitro transformation. Chromosomes X, 6 and 10 were more frequently involved in all cultures in these karyotype changes which were usually preceded by a period of chromosome variation. Spontaneous chromatid aberrations and aneuploidy increased in frequency with time in culture and generally appeared prior to the expression of transformation. No specific chromosomes were involved with the different carcinogens. There was no correlation between in vitro transformation and karyotype evolution and the criteria for transformation were present independently of one another. It is suggested that the lack of correlation between the parameters tested indicates that the expression of in vitro transformation is a result of selection for growth advantage from a cell population expressing an increasing degree of genetic instability and variation with time in culture.

Changes in surface morphology associated with ageing and carcinogen treatment of Chinese hamster lung cells

“…At this stage, a karyotypic alteration was also observed, the culture becoming dominated by cells trisomic for chromosome 6 (Connell & Ockey, 1977). The above morphology was maintained throughout the next 50 passages.…”

“…The escape of cells from in vitro senescence may be an initial step in the chain of events leading to transformation, since transformation is a continuous process leading from weakly to highly transformed cells (Risser & Pollack, 1974 (Connell, 1976). A serial parallel study of surface morphological changes by Scanning Electron Microscopy (SEM), karyotypic alterations and in vitro criteria for transformation (Connell & Ockey, 1977) (Connell, 1976;Connell & Ockey, 1977 cultures w%ere treated with a single dose of either 10 ,ug BP/ml, 01 ,ug DMBA/ml or 0-01 jug MNNG/ml to produce 50% survival, as predetermined (Connell & Ockey, 1977).…”

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

“…Trisomy for chromosome 4, described here as an early and dominant change, may therefore relate to the acquisition of immortality. Similarly, trisomies of chromosomes 6, 10 and 11 and the loss of an X chromosome are all chromosome anomalies which have been observed early on in the development of a transformed cell line (Tables IV-VI; Connell & Ockey, 1977), as well as being associated with other virally (Kato, 1968;Lehman & Trevor, 1979) and chemically (Trewyn et al, 1979) transformed lines. These chromosomes also may be associated with the acquisition of unlimited growth potential.…”

“…The finding that these cell lines all had chromosome changes associated with chromosome 4 (Table VII) is consistent with previous reports concerning growth characteristics, namely growth in agar, and chromosome abnormalities in both virally and chemicallyinduced Chinese hamster cell lines (Kirkland & Venitt, 1976;Bloch-Shtacher & Sachs, 1977;Trewyn et al, 1979) Bloch-Shtacher & Sachs (1977), in that addition of a long arm of chromosome 4 (3 in their terminology) is insufficient to confer the ability to grow in soft agar. Also, previous work describing a spontaneous Chinese hamster transformed cell line (Connell & Ockey, 1977) (Newbold et al, 1982). One has to consider however that two different in vivo systems have been employed.…”

“…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, …”