Human diploid fibroblasts are refractory to oncogene-mediated transformation

It has long been known that human cells are more refractory than rodent cells against oncogenic transformation in vitro. Recent success to make normal human cells susceptible to oncogene-mediated transformation by the ectopic expression of the telomerase catalytic subunit (hTERT) introduces the possibility that the difference in the regulation of telomerase expression can explain the different susceptibility to transformation between human and rodent cells. In a recent study, however, we demonstrated that normal human fibroblasts are still more resistant than normal rodent fibroblasts to oncogenic transformation even with the ectopic expression of hTERT. Our results clearly indicate that a difference in telomere biology can not fully account for the species difference in transformability, and that normal human cells have still undefined intrinsic mechanisms rendering them resistant to oncogenic transformation.