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In several cancers, the acidic microenvironment of cancer cells has been implicated in enhanced malignancy and metastasis. In the present study, it was observed that gastric cancer cell lines, SNU601 and AGS, exposed to an acidic medium had increased invasiveness, as assessed using Matrigel‑coated Transwell analysis. The factors regulating such acidity‑mediated enhancement of invasiveness were investigated and it was revealed that a low‑pH environment markedly increased kallikrein‑related peptidase 7 (KLK7) and kallikrein‑related peptidase 8 (KLK8) expression. Gene silencing assays confirmed that these peptidases were involved in acidity‑promoted invasion. Acidic conditions also increased the expression of cyclooxygenases (COX), key regulatory enzymes in the catalytic pathway of prostaglandin production. Notably, these enzymes appeared to be involved in the acidity‑mediated expression of KLK7 and KLK8, as revealed using COX inhibitors. Therefore, it was indicated that tumor invasion enhancement by extracellular acidity is regulated at least in part through the induction of the COX/KLK7 and KLK8 axis in gastric cancer cells.

We analyzed six cystectomized specimens diagnosed as transitional cell carcinoma by immunohistochemical evaluation to determine the presence of c-erbB2, transforming growth factor-alpha (TGF-alpha), c-myc, c-fos, and c-fms. Representative sections of flat lesions with atypia (e.g., reactive atypia, dysplasia, and carcinoma in situ) and invasive neoplasms (transitional cell carcinoma, TCC) were selected for each cystectomy specimen according to the new WHO/ISUP classification. The average percentage of cells found positive for c-erbB2 were 16.3%, 45.5%, 46.1% and 67.7% in the reactive atypia, dysplasia, carcinoma in situ, and invasive TCC, respectively. The average percentage of cells found positive for TGF-alpha were 9.7%, 13.3%, 13.5%, 30.3%, respectively. The cells were negative for the oncoproteins c-myc and c-fos. The average percentage of cells found positive for the oncoprotein c-fms was 10.6%, 15.5%, 16.7%, and 45.5% respectively. The results of this study indicated that various oncoproteins are expressed differently. c-erbB2, TGF-alpha and c-fms expression was gradually increased during tumorous progression of the urothelium from reactive atypia to invasive carcinoma. The presence of c-erbB2, TGF-alpha and c-fms is an important marker for detection of an early precursor lesions of invasive carcinoma. However, c-myc and c-fos were not expressed in the urothelial reactive atypia and dysplasia and did not correlate with tumor progression.