SV40 transformation of Swiss 3T3 cells can cause a stable reduction in the calcium requirement for growth.

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Abstract
A well-characterized SV40-transformed Swiss 3T3 line, SV101, and its revertant were tested for the ability to grow in reduced Ca2+ (0.01 mM). Transformants and revertants did not differ from the parent 3T3 line in their Ca2+ requirement. all 3 classes of cells grew less well in low Ca2+ than in regular Ca2+ (2.0 mM). SV40 transformants were then selected for the ability to grow in reduced Ca2+. This new class of transformants was found to grow in 1% serum, grow in soft agarose, have a reorganized actin cytoskeleton, and express viral T antigens, as well as grow well in low Ca2+. One of the selected clones was T antigen-negative, yet was transformed in the serum, anchorage, actin and Ca2+ assays. Possibly this clone was a spontaneous transformant. Southern blot analysis revealed the presence of intergrated SV40 DNA. In addition, this analysis revealed the absence of an intact early region fragment, which codes for the viral T antigens. The mechanism of viral transformation for growth in low Ca++ may involve viral-host DNA interactions that may not require a fully functional T antigen. In this case SV40 integration may be acting as a nonspecific cellular mutagen. [This study may be applicable to research on neoplastic transformation.].