To determine whether blockade of Rb or Trp53 function would overcome senescence resulting from abrogation of ROCK function, we stably infected Rock1f/f;Rock2f/fMEFs with simian virus 40 large T-antigen (SV40 Large T), which is known to inactivate the tumor suppressors Trp53 and Rb (DeCaprio et al., 1988; Kierstead and Tevethia, 1993). Here, RB1 is linked to neoplasm.