Usefulness of the real-time reverse transcription-polymerase chain reaction assay targeted to alpha1,4-N-acetylglucosaminyltransferase for the detection of gastric cancer.

alpha1,4-N-acetylglucosaminyltransferase (alpha4GnT) is a glycosyltransferase that forms a unique glycan, GlcNAcalpha1-->4Galbeta-->R, specifically present in gastric gland mucous cell-type mucin. Recently, we molecularly cloned human alpha4GnT and showed that alpha4GnT is expressed in the mucous cells that secrete this particular mucin. In the present study, we first demonstrated that alpha4GnT was frequently expressed in gastric cancer cells but not in peripheral blood cells using immunohistochemistry. To detect gastric cancer cells circulating in the peripheral blood of gastric cancer patients, we quantitatively analyzed the expression level of alpha4GnT mRNA in the mononuclear cell fraction of peripheral blood using real-time reverse transcription polymerase chain reaction. The transcripts of alpha4GnT were detected in the mononuclear cell fraction isolated from 62.2% of 37 gastric cancer patients but not from any of 23 healthy individuals. Significant correlation was found in the expression levels of alpha4GnT mRNA in peripheral blood and alpha4GnT protein in gastric cancer cells. Surprisingly, alpha4GnT mRNA was detectable in 80% of five patients with an early stage of gastric cancer when the cancer cells were limited to the gastric mucosa, and the expression levels of alpha4GnT mRNA were increased in association with tumor progression. In three patients with gastric cancer, during postsurgical follow-up, the expression levels of alpha4GnT mRNA were decreased after surgical removal of gastric cancer. However, significant amounts of the alpha4GnT transcripts were again detected in two patients, who eventually developed to the recurrence of gastric cancer. Although alpha4GnT was detected in 33.3% of nine patients with Helicobacter pylori-infected chronic active gastritis as well as all of four patients with peptic ulcer, the mean expression level of alpha4GnT mRNA in these benign disorders was lower than that in gastric cancer. These results altogether indicate that the quantitative analysis of alpha4GnT mRNA expressed in the peripheral blood is useful for the detection and, possibly, monitoring of gastric cancer.

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