Human colorectal carcinoma cells HCT116 (CCL-247), SW480 (CCL-228), DLD-1 (CCL-221) and HT-29 (HTB-38) as well as human embryonic kidney 293T cells (CRL-3216; all American Type Culture Collection, Manassas, VA, USA) were grown in a humidified, 5% CO2-containing atmosphere in Dulbecco's modified Eagle's medium (10-013-CV; Mediatech; Corning Inc., Corning, NY, USA) that was supplemented with 10% fetal bovine serum (S11150; Atlanta Biologicals, Flowery Branch, GA, USA) as previously described (24 (link),25 (link)). Transfection of 293T cells was done by the calcium phosphate coprecipitation method (26 (link),27 (link)), the precipitate washed off with phosphate-buffered saline (28 (link)), retrovirus collected from the supernatant over the next 48 h (29 (link)) and in some cases concentrated by precipitation with poly (ethylene glycol)-8000 (30 (link)). HCT116 cells were infected with retrovirus three times (31 (link)) and then selected with 1.5 µg/ml puromycin for 3–4 days (32 (link)). To measure growth, 2,000 or 2,500 cells were seeded in 96-wells and growth determined essentially as described (33 (link),34 (link)). For clonogenic assays, 1,000 or 3,750 cells were seeded into 6-wells and colony formation assayed as described (30 (link)).