| Summary: | 碩士 === 國立陽明大學 === 生化暨分子生物研究所 === 102 === Breast cancer is one of the neoplastic lethal diseases for women worldwide. Early detection of breast cancer is always associated with better prognosis and lower mortality. Currently, while mammography and ultrasonography are used to detect early breast cancers, there are no convenient laboratory tests for screening these diseases. We have recently observed the existence of specific proteolytic processing activities in the plasma of breast cancer patients, which might produce the molecular signatures for these neoplastic diseases. For example, proteolytic removal of a specific Arg residue is a structural feature found in 20~25% of breast cancer patients, including those with early-stage neoplasms. Here, using polyclonal antibodies against the C-terminal sequence of α1 fragment of complement C3 protein, we identified a 40-kD C3 species specifically present in the plasma from breast cancer patients. Two-dimensional differential gel electrophoreses not only verified this unique expression, along with other disease-specific proteomic changes, but also suggested that this species is a C3dg variant bases on its overall acidic properties. Liquid chromatography-tandem mass spectrometric analyses revealed that this C3dg variant likely has a novel N-terminal end, specifically Thr-946, which is also different from those ends recently found in ovarian cancer patients. These results together indicate that α1-C3dg junction is highly susceptible to proteolytic processing under different disease conditions and multiple mechanisms, defined by their preferred cleavage sites, are responsible for the processing of this polypeptide segment. Meanwhile, western blot analyses using our antibodies further showed that this 40-kD C3dg variant was indeed present in a high percentage of breast cancer patients, including those with early-stage diseases. Given these preliminary findings, we will further explore the potential of this proteolytic product as a biomarker as well as characterize more proteomic changes associated with early breast cancers.
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