1974 Chapters (Layout Features)

[55] Basic methodology for cell culture-cell transformation

Sambrook, Joseph; Pollack, Robert

The word "transformation" is used to describe the permanent acquisition of new characters by cultured cells. Of the many different types of transformation that are known, the best studied is neoplastic transformation. Here, cells that have been exposed to certain viruses, chemicals (or X-rays) change their social behavior and take on many of the attributes of tumor cells (see reviews of Eckhart, Dulbecco, Green, Temin and Sambrook.

All mammalian cells are maintained in culture by the periodic replacement of medium and serum. Populations of untransformed cells divide while they remain sparse, but as the culture becomes more crowded, the growth rate decreases dramatically; in fact the cells of some lines stop dividing altogether once they have formed a confluent monolayer. It is not understood how this growth control is mediated. At one time it was thought that the growth of cells in tissue culture is controlled entirely by "contact inhibition"--the individual cells in a culture responding to the close proximity of other cells by ceasing to multiply.6 It is now clear, however, that although cell with cell contact plays a role in inhibiting cell division, some as yet undefined factors in serum also have an effect in regulating the extent to which cells multiply in culture.7 In any case, after untransformed cells are infected with one of a variety of tumor viruses, or exposed to X-rays or carcinogens, some of the cells may be transformed and will no longer respond to all the controls which regulate the multiplication of untransformed cells in culture: the transformants continue to divide in conditions of high cell density and/or low serum concentration, which severely limits the growth of untransformed cells, and it is this differential multiplication which provides the basis for the commonly used transformation assays.