Expression of CEA and Tag by gastric carcinoma cell lines derived from CEA424/Tag- or CEA424/Tag × CEA-transgenic mice. (A) Structure of the CEA and CEA424/Tag transgenes. The exons 1–10 of the human CEA gene contained within the insert of cosmid clone cosCEA1 are shown as color coded boxes (light blue, leader; red, IgV-like domain; blue IgC-like domain; gray, transmembrane domain; white, 5' and 3'-untranslated region exons. Flanking vector sequences are indicated as black boxes. The location of the CEA minimal promoter present in the SV40 Tag gene transgene is indicated by dotted lines, the names of the transgenic lines are shown in the left margin. (B) Flow cytometry was performed by labeling of the indicated cells either with the CEA-specific mAb 26/3/13 (filled curves) or an isotype-matched antibody (open curves) followed by PE-labeled goat anti-mouse IgG antibodies. (C, D) For Western analysis, 10 μg of total protein from extracts of 424GC or mGC8 cells established from CEA424/Tag-transgenic mice and mGC2CEA and mGC4CEA cells from CEA424/Tag × CEA-transgenic mice were size separated by SDS polyacrylamide gel electrophoresis, transferred to a membrane and reacted with the CEA-specific mAb 26/3/13 (C) or hamster polyclonal anti-Tag antibodies (D). Extracts from Cos7L-CEA and Meth-A cells stably transfected with expression vectors encoding CEA or a Tag lacking a region with the nuclear localization signal (cTag) served as a positive control. The sizes of protein markers are indicated in the left margins.