Glypican-3 is a protein that, in humans, is encoded by the GPC3gene.[5][6][7][8] The GPC3 gene is located on human X chromosome (Xq26) where the most common gene (Isoform 2, GenBank Accession No.: NP_004475) encodes a 70-kDa core protein with 580 amino acids.[9] Three variants have been detected that encode alternatively spliced forms termed Isoforms 1 (NP_001158089), Isoform 3 (NP_001158090) and Isoform 4 (NP_001158091).[9]
The protein core of GPC3 consists of two subunits, where the N-terminal subunit has a size of ~40 kDa and the C-terminal subunit is ~30 kDa.[9] Six glypicans (GPC1-6) have been identified in mammals. Cell surface heparan sulfateproteoglycans are composed of a membrane-associated protein core substituted with a variable number of heparan sulfate chains. Members of the glypican-related integral membrane proteoglycan family (GRIPS) contain a core protein anchored to the cytoplasmic membrane via a glycosylphosphatidylinositol linkage. These proteins may play a role in the control of cell division and growth regulation.[7] GPC3 has been found to regulate Wnt/β-catenin and Yap signaling pathways.[9][10][11][12][13][14][15][16] GPC3 interacts with both Wnt and frizzled (FZD) to form a complex and triggers downstream signaling.[11][17] The core protein of GPC3 may serve as a co-receptor or a receiver for Wnt. A cysteine-rich domain at the N-lobe of GPC3 has been identified as a hydrophobic groove that interacts with Wnt3a.[17] Blocking the Wnt binding domain on GPC3 using the HN3 single domain antibody can inhibit Wnt activation.[17] Wnt also recognizes a heparan sulfate structure on GPC3, which contains IdoA2S and GlcNS6S, and that the 3-O-sulfation in GlcNS6S3S significantly enhances the binding of Wnt to heparan sulfate.[10] GPC3 also modulates Yap signaling.[12] It interacts with FAT1, a potential upstream cell surface receptor of YAP1 in human cells.[15] GPC3 is also found to bind Alpha-fetoprotein in liver cancer.[18]
Glypican 3 immunostaining has utility for differentiating hepatocellular carcinoma (HCC)[19] and dysplastic changes in cirrhoticlivers; HCC stains with glypican 3, while liver with dysplastic changes and/or cirrhotic changes does not.[20] Using the YP7 murine monoclonal antibody, GPC3 protein expression is found in HCC, not in normal liver and cholangiocarcinoma.[21] The YP7 murine antibody has been humanized and named as 'hYP7'.[22] GPC3 is also expressed to a lesser degree in melanoma, ovarian clear-cell carcinomas, yolk sac tumors, neuroblastoma, hepatoblastoma, Wilms' tumor cells, and other tumors.[9] However, the significance of GPC3 as a diagnostic tool for human tumors other than HCC is unclear.[9]
Therapeutic potential
To validate GPC3 as a therapeutic target in liver cancer, the anti-GPC3 therapeutic antibodies GC33,[23] YP7,[21] HN3[12] and HS20[13][24] have been made and widely tested. The laboratory of Dr. Mitchell Ho at the National Cancer Institute, NIH (Bethesda, Maryland, US) has generated YP7 murine monoclonal antibody that recognizes the C-lobe of GPC3 by hybridoma technology.[21] The antibody has been humanized (named hYP7) via antibody engineering for clinical applications.[22] The Ho lab has also identified the human single-domain antibody ('human nanobody') HN3[12] targeting the N-lobe of GPC3 [17] and the human monoclonal antibody HS20[13][24] targeting the heparan sulfate chains on GPC3 by phage display technology. Both HN3 and HS20 antibodies inhibit Wnt signaling in liver cancer cells . The immunotoxins based on HN3,[14][25][26] the antibody-drug conjugates based on hYP7[27] and the T-cell engaging bispecific antibodies derived from YP7[28][29] and GC33,[30] have been developed for treating liver cancer. The chimeric antigen receptor (CAR) T cell immunotherapies based on GC33,[31] hYP7[32][33] and HN3[34] are being reported at various stages for treating liver cancer. In mice with xenograft or orthoptic liver tumors, CAR (hYP7) T cells can eliminate GPC3-positive cancer cells, by inducing perforin- and granzyme-mediated cell death and reducing Wnt signaling in tumor cells.[33] CAR (hYP7) T cells are being evaluated at a clinical trial at the NIH.[35]
^"Human PubMed Reference:". National Center for Biotechnology Information, U.S. National Library of Medicine.
^"Mouse PubMed Reference:". National Center for Biotechnology Information, U.S. National Library of Medicine.
^ abPilia G, Hughes-Benzie RM, MacKenzie A, Baybayan P, Chen EY, Huber R, et al. (March 1996). "Mutations in GPC3, a glypican gene, cause the Simpson-Golabi-Behmel overgrowth syndrome". Nature Genetics. 12 (3): 241–247. doi:10.1038/ng0396-241. PMID8589713. S2CID38846721.
^Veugelers M, Vermeesch J, Watanabe K, Yamaguchi Y, Marynen P, David G (October 1998). "GPC4, the gene for human K-glypican, flanks GPC3 on xq26: deletion of the GPC3-GPC4 gene cluster in one family with Simpson-Golabi-Behmel syndrome". Genomics. 53 (1): 1–11. doi:10.1006/geno.1998.5465. PMID9787072.
^Jakubovic BD, Jothy S (April 2007). "Glypican-3: from the mutations of Simpson-Golabi-Behmel genetic syndrome to a tumor marker for hepatocellular carcinoma". Experimental and Molecular Pathology. 82 (2): 184–189. doi:10.1016/j.yexmp.2006.10.010. PMID17258707.
^Filmus J, Capurro M (2004). "Glypican-3 and alphafetoprotein as diagnostic tests for hepatocellular carcinoma". Molecular Diagnosis. 8 (4): 207–212. doi:10.1007/bf03260065. PMID15887976. S2CID6312940.
^Anatelli F, Chuang ST, Yang XJ, Wang HL (August 2008). "Value of glypican 3 immunostaining in the diagnosis of hepatocellular carcinoma on needle biopsy". American Journal of Clinical Pathology. 130 (2): 219–223. doi:10.1309/WMB5PX57Y4P8QCTY. PMID18628090. S2CID45888415.
^Ishiguro T, Sugimoto M, Kinoshita Y, Miyazaki Y, Nakano K, Tsunoda H, et al. (December 2008). "Anti-glypican 3 antibody as a potential antitumor agent for human liver cancer". Cancer Research. 68 (23): 9832–9838. doi:10.1158/0008-5472.CAN-08-1973. PMID19047163.
^Li D, Li N, Zhang Y, Fu H, Torres MB, Wang Q, Greten TF, Ho M (2018-07-01). "Abstract 2549: Development of CAR T-cell therapy targeting glypican-3 in liver cancer". Immunology. 78 (13_Supplement). American Association for Cancer Research: 2549. doi:10.1158/1538-7445.AM2018-2549. S2CID81043794.
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Shen T, Sonoda G, Hamid J, Li M, Filmus J, Buick RN, Testa JR (January 1997). "Mapping of the Simpson-Golabi-Behmel overgrowth syndrome gene (GPC3) to chromosome X in human and rat by fluorescence in situ hybridization". Mammalian Genome. 8 (1): 72. doi:10.1007/s003359900357. PMID9021160. S2CID9804496.
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