Reversible phenotype and lack of direct link to immortalization of Syrian hamster embryonic cells obtained from so-called transformed colonies

Abstract

The short-term colony transformation assay employing Syrian hamster embryonic (SHE) cells has been widely used as a simple method for detection of chemical and physical carcinogens. However, little investigation has been done on the biological properties of the early transformed colony (ETC: colony characterized by piling up and criss-cross pattern of growth) itself. This study was performed to examine the properties of these colonies. Secondary or tertiary cultures of SHE cells were treated with benzo[a]pyrene or N-methyl-N’-nitro-N-nitrosoguanidine. In total, 37 ETCs and 17 normal colonies (NCs) were cloned and analyzed. Obtained results were as follows: (1) Stability of transformed morphology; immediately after cloning, the cells from 3/37 of the ETCs maintained their transformed phenotype, but all cells from other ETCs (34/37) showed flat or well-oriented morphology. Thus, the “transformed” morphology of more than 90% of the ETCs was reversible. (2) Chromosome abnormality; 3/15 of the clones from ETCs were hypo diploid or tetraploid, while the others (12/15) were normal diploid immediately after cloning. (3) Immortalization; up to about one month after cloning, most of the clones (from transformed or normal colonies) could be subcultured at 1:2 or 1:4 split ratio per week, but thereafter all the clones ceased growing. After about a one month or longer latency, 6/37 of the clones from ETCs and 4/17 of the clones from NCs restarted growing and acquired immortality. That is, there was no significant difference in the frequency of immortalization between ETCs and NCs. Thus, from the present experiment, there was no direct evidence that ETC correlates to acquisition of immortality or tumorigenesis. Further experiments (e.g. comparison of gene expression profiles between cells from transformed and normal colonies using microarray) would be required to give a logical meaning to this short-term transformation assay.