Analysis of type 5 adenovirus transformation with a cloned rat embryo cell line (CREF)

A recently isolated cloned cell line of Fischer rat embryo fibroblasts (CREF) can be transformed at high frequency by adenovirus serotype 5 (Ad5). The CREF cells display a near diploid karyotype, do not crisscross at confluency, can be maintained at confluency for greater than 7 wk at 36 degrees C, and do not form macroscopic colonies when seeded in agar. Transformed cells are identified by their altered morphology and the presence of adenovirus DNA sequences in the transformants, which can be demonstrated by lysing cells directly on nitrocellulose filters and hybridizing with 32P-labeled Ad5 DNA (spot hybridization). The frequency of transformation at 36 degrees C is approximately equal to 2 x 10(-4) with wild-type Ad5 and approximately equal to 2 x 10(-3) with the temperature-sensitive mutant H5ts125. Southern blot hybridization analysis indicates that five out of six wild-type Ad5- and six out of six H5ts125-transformed CREF clones isolated at 36 degrees C contain the complete integrated Ad5 genome. Preliminary characterization of four transformed clones (two wild-type and two H5ts125) indicates that, even though transformation was done in CREF cells (a clonal cell line), they differ in their biological properties, such as saturation density and anchorage dependence.