Regulation of requirements for anchorage-independent growth of Syrian hamster fibroblasts by somatic mutation

Abstract

THE ability of mammalian cells to form colonies following suspension in semisolid agar, termed ‘anchorage independence’, is a phenotypic characteristic associated with cells transformed by oncogenic viruses and chemical carcinogens^1–5. Because this phenotypic characteristic has been correlated with tumorigenicity^2–5, colony formation in semisolid agar is used frequently as a quantitative in vitro assay for neoplastic transformation, especially in studies in Syrian hamster cell systems^4,5. It is therefore important to understand the molecular and physiological basis of this phenotype. If the expression of this phenotype can be altered by somatic mutation of identifiable genes, information can be gained concerning the mechanism of anchorage-independent growth in vitro and its exact relationship to tumorigenicity and malignancy in vivo. We have investigated the ability of cells of the highly tumorigenic Syrian hamster fibroblast line, BP6T (ref. 9) to form colonies when suspended in semisolid agar. Cells of this line produce fibrosarcomas in 100% of newborn Syrian hamster inoculated with ten cells. In addition to anchorage-independent growth, BP6T cells also exhibit other in vitro characteristics of neoplastic transformed cell lines, such as increased plating efficiency in liquid medium at low cell densities, and enhanced fibrinolytic activity⁹. In this communication, we report that the ability of this Syrian hamster line to form colonies in semisolid agar is dependent on its utilisation of exogenous purines by way of the hypoxanthine phosphoribosyltransferase (HPRT, E.C.2.4.2.8.)- and adenine phos-phoribosyltransferase (APRT, E.C.2.4.2.7.)-mediated salvage pathways. Furthermore, this anchorage-independent property can be inhibited by a somatic mutation at the HPRT locus.