We studied chemical level and glycosylation status of haptoglobin in sera of patients with prostate cancer, as compared to benign prostate disease and normal subjects, with the following results. (i) Haptoglobin level was enhanced significantly in sera of prostate cancer. (ii) Sialylated bi-antennary glycans were the dominant structures in haptoglobins from all 3 sources, regardless of different site of N-linked glycan. The N-linked glycans at N184 were exclusively bi-antennary, and showed no difference between prostate cancer vs. benign prostate disease. (iii) Tri-antennary. N-linked, fucosylated glycans, carrying at least 1 sialyl-Lewisx/a antenna, were predominantly located on N207 or N211 within the amino acid 203-215 sequence of the β-chain of prostate cancer, and were minimal in benign prostate disease. Fucosylated glycans were not observed in normal subjects. A minor tri-antennary N-linked glycan was observed at N241 of the β-chain in prostate cancer, which was absent in benign prostate disease. (iv) None of these N-linked structures showed the expected presence of disialylated antennae with GalNAcβ4(NeuAcα 3)Galβ3(NeuAcα6)GlcNAcβGal, or its analogue, despite cross-reactivity of prostate cancer haptoglobin with monoclonal antibody RM2. (v) Minor levels of O-glycosylation were identified in prostate cancer haptoglobin for the first time. Monoand disialyl core Type 1 O-linked structures were identified after reductive β-elimination followed by methylation and mass spectrometric analysis. No evidence was found for the presence of specific RM2 or other tumor-associated glycosyl epitopes linked to this O-glycan core. In summary, levels of haptoglobin are enhanced in sera of prostate cancer patients, and the N-glycans attached to a defined peptide region of its β-chain are characterized by enhanced branching as well as antenna fucosylation.
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