CEACAM5 and CEACAM6 are major target genes for Smad3-mediated TGF-beta signaling.

The carcinoembryonic antigen (CEAs) family consists of a large group of evolutionarily and structurally divergent glycoproteins. The transforming growth factor-beta (TGF-beta) signaling pathway has been implicated in the stimulation of CEA secretion in TGF-beta-sensitive colon cells, thereby possibly modulating cell adhesion and differentiation. However, the specific CEAs targeted by TGF-beta signaling or underlying mechanism of the expression of CEAs has not yet been clarified. In this study, we investigated the specific CEAs targeted by the TGF-beta signaling pathway. In nine human gastric cancer cell lines examined, TGF-beta-responsive cell lines showed positive expression of CEAs. Expression patterns of CEA proteins correlated well with the level of CEA (CEACAM5) and CEACAM6 transcripts in these cell lines, but CEACAM1 expression was not observed in all of these cells. To investigate the role of TGF-beta signaling in CEA expression, we selected two TGF-beta unresponsive gastric cancer cell lines; SNU638 cells that contain a mutation in the TGF-beta type II receptor and SNU484 cells that express low to undetectable level of the TGF-beta pathway intermediate protein, Smad3. Restoration of TGF-beta signaling in these cells induced expression of the CEAs and increased activity of both CEA (CEACAM5) and CEACAM6 promoters. CEA expression was observed in the epithelium of the stomach of wild-type mice, but was markedly decreased in Smad3 null mice. These findings suggest that CEA (CEACAM5) and CEACAM6 are major target genes for Smad3-mediated TGF-beta signaling.

K-ras oncogene mutation in cancer and precancerous lesions of the gallbladder.

BACKGROUND AND OBJECTIVES: To determine whether K-ras mutation plays any role in the development and progression of gallbladder cancer, or has any clinical or pathological significance in gallbladder cancer patients, we investigated the presence and incidence of this mutation in the normal mucosa, and precancerous and cancerous lesions of the gallbladder. METHODS: DNA was obtained from normal mucosa, dysplastic mucosa, primary cancer tissues, and metastatic lymph nodes that were identified and microdissected from the paraffin blocks of 20 gallbladder cancer cases. K-ras codon 12 mutations were investigated using a modified two-step polymerase chain reaction and the restriction fragment length polymorphism method, and by direct sequencing with an automated sequencer. RESULTS: K-ras mutations were detected in the tissues of 10 out of the 20 patients. A mutation was present in the dysplastic epithelium associated with the primary carcinoma in 3 out of 12 specimens, in metastatic carcinoma in 1 out of 5 patients, and in primary carcinoma in 8 out of 20 patients. Mutation was found only once in the dysplastic, noncancerous epithelium, and only once in a metastatic tumor although not detectable in the primary cancer. Direct sequencing showed that the mutations were G to C substitutions (GGT-->CGT) at the first site of codon 12, except in two cases (GGT-->TGT). There were no correlations between K-ras mutations and clinicopathological factors. CONCLUSIONS: K-ras mutations were detected in half of the gallbladder cancer cases. We suggest that K-ras mutation may play a role in the development of premalignant lesions or early carcinogenesis in some gallbladder cancers. We were unable to find any evidence that K-ras mutation plays any role in tumor progression or metastasis, or that it has any clinicopathological significance.