Author Affiliations: Department of Immunology, Medical School of Nantong University (Yao M) and Research Center of Clinical Medicine, Affiliated Hospital of Nantong University (Pan LH and Yao DF), Nantong 226001, China

Corresponding Author: Deng-Fu Yao, MD, PhD, Research Center of Clinical Medicine, Affiliated Hospital of Nantong University, 20 West Temple Road, Nantong 226001, China (Tel: +86-513-85052297; Fax: +86- 513-85052254; Email: yaodf@ahnmc.com)

 

© 2015, Hepatobiliary Pancreat Dis Int. All rights reserved.

doi: 10.1016/S1499-3872(15)60350-2

Published online March 13, 2015.

 

 

Contributors: YM, PLH and YDF wrote the manuscript. YDF is the guarantor.

Funding: This study was supported in part by a grant-in-aid from the Qinglan Projects of the Higher Education and the Six Talent Peak, Jiangsu Province, China (YY-028).

Ethical approval: Not needed.

Competing interest: No benefits in any form have been received or will be received from a commercial party related directly or indirectly to the subject of this article.

 

 

Glypican (GPC) is a family of heparan sulfate proteoglycans bounded to the cell surface through a lipid glycosyl-phosphatidylinositol anchor. GPC-3 that its gene located at Xq26.1 area on chromosome, is one of the six mammalian glypicans (GPC-1 to GPC-6), causes the Simpson-Golabi-Behmel overgrowth syndrome, and displays developmental overgrowth in null mice.^[1] GPC-3 promotes cell proliferation by stimulating canonical Wnt signaling, and acts as an inhibitor of Hedgehog signaling pathway. The structural requirements for GPC-3 activity are cell type specific, and its core protein is processed by a furin-like convertase.^[2,3] Several studies^[4-6] have shown that GPC-3 is specifically overexpressed in hepatocellular carcinoma (HCC), which is characterized by a multi-cause, multi-stage and multi-focus process of tumor progression with poor prognosis and difficulty in diagnosis at early stage, and its etiologies are chronic HBV or HCV infection along with alcohol and aflatoxin B1 intake. Increasing evidence indicates that abnormal GPC-3 expression is associated with the occurrence and progression of HCC.

 

Although serum alpha-fetoprotein (AFP) is a useful marker for the diagnosis of HCC and the evaluation of therapy, it is sometimes very difficult to differentiate tumors from benign liver diseases causing AFP elevation. Increasing GPC-3 expression acts as a promising molecular biomarker for the malignant transformation of hepatocytes.^[7] In the mentioned study, the dynamic alterations of oncofetal GPC-3 expression and GPC-3 gene transcription were investigated in a rat model of hepatocarcinogenesis. GPC-3 was expressed in the cytoplasm during morphological stages of granule-like degeneration and atypical hyperplasia (pre-cancerous), and progressively increased in the process of malignant transformation at mRNA and protein level, which cause the increase of GPC-3 in circulation. GPC-3 may be a biomarker in screening patients at risk for HCC.

 

Specific diagnosis of HCC at early stage is of utmost importance. Although many biomarkers have been used in the diagnosis of HCC, a few markers have a higher sensitivity or specificity, such as hepatoma-specific γ-glutamyltransferase (HS-GGT or GGT subtype-II, GGT-II),^[8] hepatoma-specific AFP (HS-AFP or AFP-L3, Lens culinaris agglutinin-reactive AFP)^[9] and oncofetal antigen GPC-3. GPC-3 expression was found abnormal in HCC patients (sensitivity 52.8% and specificity 99.5%) with a frequency of 80.0% in the <3 cm group significantly higher than 41.7% in the ≥3 cm group, and it was very lower from 1.4% to 2.0% in benign liver diseases or non-liver tumors.^[10] Serum HS-GGT concentration was significantly elevated as high as 5.5 IU/L in 156 HCC patients. The results showed that serum AFP level is not a specific marker for the diagnosis of HCC because 14.3% to 35.0% of patients with benign liver diseases also have a high level of serum AFP. However, AFP-L3 has a higher sensitivity of 53.3% and a specificity of 88.9%^[9] for HCC, especially for those with portal vein invasion, lower tumor differentiation and in an advanced stage. AFP-L3 is not affected by tumor size and AFP level. Circulating GPC-3 in HCC is superior to AFP in specificity, positive or negative predictive value, and accuracy. The positive rate of GPC-3 is significantly higher in patients with small HCC (≤3 cm) than that of AFP. Moreover, GPC-3 is positive in 90% of patients with AFP-negative HCC. Simultaneous measurement of circulating GPC-3 and AFP can significantly improve the sensitivity of the current screening protocol for high-risk patients, suggesting that GPC-3 is an important factor in the diagnosis, treatment and prognosis of HCC patients.

 

Metastasis is responsible for up to 90% of HCC deaths. Metastasis has the following process: cancerous cells enter the circulation, and eventually grow into lethal tumor in distal organs.^{[11, 12]} GPC-3 mRNA from peripheral blood mononuclear cells is of value in monitoring HCC with extrahepatic metastasis. Hepatic GPC-3 mRNA increases dynamically during HCC formation. Circulating GPC-3 mRNA can be detected in 70.7% of cases of HCC, with clinicopathological characteristics related to TNM stage, periportal cancerous embolus and extrahepatic metastasis. Circulating GPC-3, GPC-3 mRNA and AFP in combination have complementary values and could increase the diagnostic rate of HCC to 94.3%. There is a higher GPC-3 positive rate in HCC patients at stages I and II, with HBV infection or small size tumor, especially in the periportal cancer embolus or extrahepatic metastasis group,^[13] suggesting that the up-regulation of GPC-3 gene transcription is a more sensitive and specific biomarker for HCC metastasis.

 

Two new findings about circulating GPC-3 biomarker have been reported recently. One^[14] is its prognostic value in HCC patients with HBV-associated cirrhosis after liver transplantation. In this study, the 5-year survival and disease-free survival rates were lower in GPC-3-positive patients than in GPC-3-negative patients (38.2% vs 75.4%; 30.8% vs 69.7%). Multivariate Cox-regression analysis revealed that GPC-3 is an independent risk factor for the 5-year survival (P=0.031) and disease-free survival rates (P=0.047). Together with tumor differentiation, the Milan criteria and pre-operative AFP, it is a potential biomarker for poor prognosis after liver transplantation in HCC patients with HBV-associated cirrhosis. The other^[15] is that GPC-3 is an emerging molecular target for HCC gene therapy, the oncofetal GPC-3 through the up-regulating key molecules (cyclin D1, β-catenin, and GSK3β) in the Wnt/β-catenin signaling pathway stimulates cell proliferation. Intervening its gene transcription by specific short hairpin RNA or miRNA inhibits cell proliferation with apoptosis mechanism in vitro,^[16] suggesting that the GPC-3 gene should be a novel therapeutic target for HCC.

 

Early detection of HCC or monitoring after surgery remains an objective for the improvement of prognosis and the justification of screening programs of patients at risk, such as chronic carriers of HBV and individuals with cirrhotic HCV. GPC-3 as a specific marker for HCC diagnosis and prognosis has been confirmed by basic and clinical studies, but further studies should focus on the combination of miRNA and multi-targeting strategies for HCC therapy.

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