α2-Heremans-Schmid glycoprotein (human fetuin) is one of numerous serum proteins produced in the liver. Recently, the biological functions of fetuin, such as calcification and insulin resistance, have been clarified. However, these effects appear to be indirect, occurring through binding to other molecules. When equal amounts of fetuin in sera were treated with chymotrypsin, resistance to the protease treatment was observed in patients with pancreatic cancer, but not in normal volunteers. To investigate the molecular mechanism behind this resistance, gel-filtration chromatography was performed. The results revealed that high molecular types of fetuin showed a resistance to protease treatment. When fetuin was purified from sera of patients with pancreatic cancer and normal volunteers, certain types of proteins, including haptoglobin (which binds to fetuin derived from pancreatic cancer patients), were identified using mass spectrometry. Furthermore, the oligosaccharide structures of fetuin analyzed with lectin microarray differed between pancreatic cancer patients and normal volunteers. This macro/micro heterogeneity of fetuin might contribute to pancreatic cancer resistance to chymotrypsin treatment.

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