Growth Inhibitor of Hamster Fibroblast Cells

Abstract

THE hamster fibroblast cell line BHK21/13 (ref. 1) has been used extensively in investigations of transformation by polyoma virus². This report describes a difference in a possible aspect of the regulation of growth in BHK21/13 and a polyoma-transformed derivative, PyY (ref. 3). Normally BHK21/13 cells grow with a doubling time of about 12 h in a medium consisting of 8 parts Eagle's medium supplemented with 1 part of autoclaved tryptose phosphate broth (‘Difco’) and 1 part of calf serum. When the calf serum is reduced to 0.25 per cent final concentration the cells attach and spread but do not increase in number. Cell growth occurs if more serum is added to the medium (Fig. 1). In contrast, our polyoma-transformed derivative, PyY, grew rapidly (Fig. 1) even in the presence of the trace amount of serum used for attachment (expressible as 0.25 per cent final concentration, 0.025 ml./million cells, or 1.25 µd./cm² of the dish). In order to investigate whether a particular substance in serum stimulates the growth of BHK21/13, calf serum was fractionated on ‘Sephadex G-75’ and ‘G-200’. The fractions stimulated growth in proportion to the absorption at 280 mµ. This indicates a non-specific serum–protein requirement. Foetal calf serum showed a similar non-specific effect.