Enhanced expression of stomach cancer antigen derived from malignantly transformed bloom syndrome cells previously labeled with bromodeoxyuridine.

Bromodeoxyuridine (BrdU) greatly enhanced expression of stomach (ST) cancer antigen (CA) that originated from a malignantly transformed Bloom syndrome (BS) cell line (BS-SHI-4M), although the expression was suppressed with a decrease in sister chromatid exchange (SCE) in the presence of deoxythymidine (dT) or deoxycytidine (dC) and enhanced with an increase in SCE with deoxyguanosine (dG) or deoxyadenosine (dA). Although the exact mechanisms for enhancing CA by BrdU treatment are unknown, these findings appeared to be of special interest because of the parallelism of CA expression and SCE alterations. The finding that BrdU enhancement of the ST CA was effective not only in the immunofluorescence (IF) protocol but also in the band appearance of Western blotting would be worthwhile as a sensitive serodiagnosis of cancer. The 118-kd band obtained from proteins of ST CA cells previously labeled with BrdU was clearly more darkly stained than that from nonlabeled cells and enabled eight weak-positive ST CA to show strong-positive levels retaining complete negativity to nonmalignant sera. Some ST cancer sera (advanced cancer), which originally gave a negative reaction in the nonlabeled condition, still inhibited negative reaction even in BrdU-labeled ST CA cells, however. The inability to detect cancer antibody in our assay might be due to immunocomplexes. Acid dissociation and ultrafiltration of sera from six of seven advanced ST cancers (originally IF negative) have allowed detection of antibody responses to ST CA by Western blot assay with enhanced reactivity as compared with the negativity under native serum conditions. This technique provides a reasonable avenue for study of the mechanisms of CA expression and serodiagnosis.