Identification of Hepatocellular Carcinoma-associated Serum Glycoproteins by Lectin Affinity Purification and 2D Gel Analysis

Identication of early hepatocellular carcinoma (HCC) in patients with chronic liver diseases (CLD) is an important clinical task. Previous studies have shown that patterns of alpha-2,6-sialylation and alpha-1,6-fucosylation change in liver cancer, leading to aberrant glycosylations on some serum proteins. In this study, we purified alpha-2,6-sialylated and alpha1,6-fucosylated serum glycoproteins by using lectin SNAand LCA-affinity chromatography, repectively. The purified serum glycoproteins from 10 CLD patients and 20 HCC patients were then separated by two-dimensional polyacrylamide gel electrophoresis, and the resulted gel images were compared. When analyzing alpha-2,6-sialylated proteins, 85 spots were differentially expressed between HCC and CLD groups, corresponding to 43 glycoproteins (p 0.05). When analyzing alpha-1,6-fucosylated proteins, 27 spots were significant different between the two groups, corresponding to 12 glycoproteins (p 0.05). The protein identities of the differential glycoproteins were uncovered with MALDI-TOF-TOF MS. Haptogloblin was identified to be up-regulated in HCC in both sialylation and fucosylation analyses. By immunoassay, increased serum haptoglobin level was confirmed in independent cases comprising 40 HCC and 30 CLD patients. This is the first study showing the increased serum haptoglobin levels in the HCC patients. Serum haptoglobin, particularly its fucosylated variants, is a potential tumor marker of HCC. (The study was supported by the RGC Earmarked Grant 4466/03M from the University Grants Committee of Hong Kong.)