Loss of density‐dependent regulation of multiplication of BALB/3T3 cells chemically transformed in vitro

Balb/3T3 cells show density‐dependent regulation of multiplication with the final cell density depending on serum concentration in the media. Chemically transformed Balb/3T3 cells (Balb/3T3‐D) pile up on each other, multiply to a high cell density, but have decreased DNA synthesis at very high cell densities. Balb/3T3‐D cells require less serum for multiplication compared with original Balb/3T3 cells. A rat serum fraction and a bovine β‐globulin fraction stimulate the multiplication of Balb/3T3 cells but only slightly stimulate Balb/3T3‐D cells indicating different serum factors stimulate growth of these two cell types. The multiplication properties of Balb/3T3‐D cells are very similar to those of SV‐40 transformed 3T3 cells, however, these properties were brought about by a single treatment by a chemical carcinogen, without an exogenous virus. The transformation altered the contact of cells to one another, indicating a permanent chemical change in the membrane structure.