Proteomic profiling of N-linked glycoproteins identifies ConA-binding procathepsin D as a novel serum biomarker for hepatocellular carcinoma

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Abstract

The aim of this study was to identify novel biomarkers for the diagnosis of, and potential therapeutic targets for, hepatocellular carcinoma (HCC). Multilectin affinity chromatography was used to enrich N-linked glycoproteins from nontumorous liver and HCC tissues followed by 2DE and protein identification by MS. Twenty-eight differentially expressed proteins were identified. Western blotting validated consistently lower concentrations of human liver carboxylesterase 1 and haptoglobin, and higher concentration of procathepsin D (pCD) in HCC tissues. Knockdown of cathepsin D (CD) expression mediated by siRNA significantly inhibited the in vitro invasion of two HCC cell lines, SNU449 and SNU473, which normally secrete high-levels of CD. Prefractionation using individual lectins demonstrated an elevation in ConA-binding glycoforms of proCD and CD in HCC tissues. In the serum of HCC patients, “ConA-binding proCD” (ConA-pCD) is significantly increased in concentration and this increase is comprised of several distinct upregulated acidic isoforms (pI 4.5–5.5). Receiver operating characteristic analysis showed that the sensitivity and specificity of serum ConA-pCD for HCC diagnosis were 85% and 80%, respectively. This is the first report that serum ConA-pCD is increased significantly in HCC and is potentially useful as a serological biomarker for diagnosis of HCC.

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