Lamin B1 co-precipitates with endogenous APC using APC-M2 pAb. (A) APC-M2 pAb specifically detects full-length (~310 kDa) APC in HCT116βw cell lysates and truncated (~150 kDa) APC in SW480 cell lysates by immunoblot. APC-M2 pAb does not detect APC in HCA46 cell lysates, null for APC. Equivalent total protein (30 μg) was resolved in each lane. Blot shows entire spectrum of proteins from > 300 kDa to ~15 kDa. α-tubulin is shown as a loading control. (B) APC-M2 pAb immunoprecipitates APC from HCT116βw (left panel) and SW480 (right panel) cell lysates. β-catenin co-precipitates with full-length APC (left panel, middle blot). Neither APC nor β-catenin co-precipitated with preimmunue sera (Preim). P, precipitated proteins from 270 μg protein lysates; S, 10% of non-precipitated supernatant proteins (27 μg). Input, 5% of total input proteins (25 μg). (C) Endogenous lamin B1 co-precipitated with APC using APC-M2 pAb, but not preimmune sera. Precipitated proteins from 376 μg protein lysates were loaded. Input, 6% of total input proteins (37.5 μg). The lower band in the APC IP lane represents degradation products.