Figure 1.

Full-length and truncated forms of APC proteins. (A) Detection of full-length and truncated forms of APC proteins. Cell lysates from normal fibroblasts (6 mg of protein) and cancer cells (2 mg of protein) were incubated with anti-APC polyclonal antibody, and the resultant immunocomplexes were separated on SDS/5% PAGE and probed with monoclonal anti-APC antibody (OP44). Lanes: 1, TIG-3; 2, TIG-7; 3, DLD-1; 4, KMS-4; 5, KMS-8; 6, SW480. Exposure for TIG-3, TIG-7 was about two times longer than that for the other cell lines. (B) Association of protein kinase activity with APC. Cell lysates prepared from TIG-3, SW480, and KMS-8 cells were immunoprecipitated with anti-APC polyclonal antibody and incubated for 15 min in the kinase reaction mixture in the presence (+) or absence (−) of 10 ng/ml heparin. The reaction was stopped by adding sample buffer, and radioactive proteins were separated by SDS/5% PAGE and visualized by autoradiography. (C) The protein kinase utilizes GTP as well as ATP. The phosphorylation activity in the immunoprecipitates from SW480 cells was determined in the presence of either [γ-³²P]ATP (left lane) or [γ-³²P]GTP (right lane) in the reaction mixtures. Proteins were separated on SDS/5% PAGE, and phosphorylated proteins were visualized by autoradiography. Truncated APC is indicated by an arrowhead.