Carbonic anhydrase IV inhibits colon cancer development by inhibiting the Wnt signalling pathway through targeting the WTAP-WT1-TBL1 axis.

OBJECTIVE: We found that carbonic anhydrase IV (CA4), a member of the carbonic anhydrases, is silenced in colorectal cancer (CRC). We analysed its epigenetic inactivation, biological effects and prognostic significance in CRC. DESIGN: The biological functions of CA4 were determined by in vitro and in vivo tumorigenicity assays. The CA4 co-operator was identified by immunoprecipitation and mass spectrometry. CA4 downstream effectors and signalling pathways were elucidated by promoter luciferase assay, electrophoretic mobility shift assay and chromatin immunoprecipitation. The clinical impact of CA4 was assessed in 115 patients with CRC. RESULTS: CA4 was silenced in all nine CRC cell lines and 92.6% of CRC tumours. The promoter hypermethylation contributed to the inactivation of CA4, and it was detected in 75.7% of the patients with CRC. After a median follow-up of 49.3 months, multivariate analysis showed that the patients with CA4 hypermethylation had a recurrence of Stage II/III CRC. The re-expression of CA4 inhibited cell proliferation, induced apoptosis and cell cycle arrest in the G1 phase. CA4 inhibited the activity of the Wnt signalling pathway and mediated the degradation of ß-catenin. CA4 interacted with Wilms' tumour 1-associating protein (WTAP) and induced WTAP protein degradation through polyubiquitination. Moreover, CA4 promoted the transcriptional activity of Wilms' tumour 1 (WT1), an antagonist of the Wnt pathway, which resulted in the induction of transducin ß-like protein 1 (TBL1) and the degradation of ß-catenin. CONCLUSIONS: CA4 is a novel tumour suppressor in CRC through the inhibition of the Wnt signalling pathway by targeting the WTAP-WT1-TBL1 axis. CA4 methylation may serve as an independent biomarker for the recurrence of CRC.

Different cell kinetic changes in rat stomach cancer after treatment with celecoxib or indomethacin: implications on chemoprevention.

AIM: Mechanisms underlying the chemopreventive effects of cyclooxygenase (COX) inhibitors remain elusive. We have previously shown that celecoxib but not indomethacin could prevent carcinogen-induced gastric cancer development in Wistar rats. This chemopreventive effect appeared to be independent of COX-2 and prostaglandin (PG) E2 suppression since the lowest PGE2 was obtained in indomethacin group. This study compared the cell kinetic changes in stomachs of rats after treatment with celecoxib (5, 10, 20 mg/(kg.d)) or indomethacin (3 mg/(kg.d)) to gain more insights into the chemopreventive mechanism. METHODS: The apoptosis and proliferation indexes in gastric tumor, adjacent non-cancer tissues and normal gastric tissues were determined. Apoptosis was quantified by apoptotic nuclei counting and TUNEL, whereas proliferation was determined by Ki67 immunostaining. RESULTS: Treatment with either celecoxib or indomethacin inhibited gastric tumor proliferation by more than 65% (P<0.02). However, celecoxib caused a dose-dependent increase in apoptosis (P<0.05) which was not seen in indomethacin-treated tumors (P = 0.54). The highest apoptosis to proliferation ratio was seen in tumors treated with celecoxib at 10 mg/(kg.d). Treatment with this dose of celecoxib was associated with the lowest incidence of gastric cancer development. CONCLUSION: Our findings suggest that the difference in chemopreventive effects of indomethacin and celecoxib in this animal model of gastric carcinogenesis is largely due to the differential cell kinetic changes, which does not correlate with the degree of COX-2 and PG suppression.

Expression of HBx and COX-2 in chronic hepatitis B, cirrhosis and hepatocellular carcinoma: implication of HBx in upregulation of COX-2.

Hepatitis B virus is a major etiological factor of hepatocellular carcinoma, but the underlying mechanisms remain unclear. We have previously demonstrated that upregulation of cyclooxygenase (COX)-2 in chronic hepatitis B persisted despite successful antiviral therapy. In this study, we investigated the relationship between the transactivator HBx and COX-2 in hepatitis B virus-associated chronic liver diseases. Expressions of HBx and COX-2 in tissue specimens were determined by single and double immunohistochemistry. The effects of HBx on COX-2 and prostaglandin E2 production were studied by transfection. HBx was expressed in 11/11 (100%) of chronic hepatitis B, 23/23 (100%) of cirrhosis, and 18/23 (78%) of hepatocellular carcinoma, whereas no immunoreactivity was found in four nonalcoholic steato-hepatitis controls. COX-2 expression was also detected in all specimens of liver lesions except in only 29% of poorly differentiated hepatocellular carcinoma. Significant correlation between HBx and COX-2 immunoreactivity scores was found in different types of chronic liver diseases (chronic hepatitis B, rs = 0.68; cirrhosis, rs = 0.57; hepatocellular carcinoma, rs = 0.45). Double immunohistochemistry showed colocalization of HBx and COX-2 in hepatic parenchymal cells. Similar to COX-2, there was no significant change in HBx expression in patients with chronic hepatitis B after interferon and lamivudine therapy when hepatitis B virus DNA became undetectable and inflammation subsided. Transfection of Hep3B hepatocellular carcinoma cells with HBx increased COX-2 expression and prostaglandin E2 production. HBx was localized mainly in the cytoplasm and less in nucleus, as found in the liver lesions. In conclusion, our results strongly suggested that there was a close relationship between HBx and COX-2. COX-2 might represent an important cellular effector of HBx that contributes to hepatitis B virus-associated hepatocarcinogenesis.