Background: Free ubiquitin (FUb) conjugates various proteins selectively intracellularly and forms multi-Ub chain (MUC) to activate degradation of these proteins by proteasome. Accordingly, ubiquitin (Ub) exists in vivo as FUb prior to ubiquitination and as MUC after functional modification or degradation. As degradation of nuclear proteins such as cyclins and p53 protein are dependent on Ub, Ub mediated proteolitic systems are regarded to play an important role in cartinogenesis. We have previously reported by immunohistochemical analysis that Ub immunoreactivity is higher in various malingnant tumors than normal tissues. The purpose of this study was to examine the levels of FUb and MUC in precancerous and cancerous gastric tissues.
Method: Nine pairs of gastric cancers and adjacent normal tissues were obtained by surgery. Another 9 samples of atrophic gastritis mucosa were obtained at the time of endoscopic examination. As reported by Takada et al. (Eur J Biochem 1995), we used specific immunoassay systems to measure levels of the two forms of Ub in each tissue specimen. Ub-immunoreactive proteins were analyzed by Western blotting. Serum Ub was also measured.
Result: As compared with normal gastric tissue, the concentration of MUC was higher in gastric cancer (p<0.05). The concentration of FUb was much higher in atrophic gastritis mucosa(p<0.05). Various bands of MUC were present in both cancerous and normal tissues. In gastric cancer, some peculiar bands which were absent in the normal tissue were recognized.
Conclusion: The levels of FUb and MUC were upregulated in precancerous and cancerous gastric tissues. Ub seems important in tumorigenesis.