Glypican-3 is a protein that, in humans, is encoded by the GPC3 gene. [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 sulfate proteoglycans 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 glycosyl phosphatidylinositol 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]
Deletion mutations in this gene are associated with Simpson–Golabi–Behmel syndrome. [5]
Glypican 3 immunostaining has utility for differentiating hepatocellular carcinoma (HCC) [19] and dysplastic changes in cirrhotic livers; 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]
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]
In cellular biology, the Wnt signaling pathways are a group of signal transduction pathways which begin with proteins that pass signals into a cell through cell surface receptors. The name Wnt, pronounced "wint", is a portmanteau created from the names Wingless and Int-1. Wnt signaling pathways use either nearby cell-cell communication (paracrine) or same-cell communication (autocrine). They are highly evolutionarily conserved in animals, which means they are similar across animal species from fruit flies to humans.
A single-domain antibody (sdAb), also known as a Nanobody, is an antibody fragment consisting of a single monomeric variable antibody domain. Like a whole antibody, it is able to bind selectively to a specific antigen. With a molecular weight of only 12–15 kDa, single-domain antibodies are much smaller than common antibodies which are composed of two heavy protein chains and two light chains, and even smaller than Fab fragments and single-chain variable fragments.
Simpson–Golabi–Behmel syndrome (SGBS) is a rare inherited congenital disorder that can cause craniofacial, skeletal, vascular, cardiac, and renal abnormalities. There is a high prevalence of cancer associated in those with SGBS which includes wilms tumors, neuroblastoma, tumors of the adrenal gland, liver, lungs and abdominal organs. The syndrome is inherited in an X-linked recessive manner. Females that possess one copy of the mutation are considered to be carriers of the syndrome but may still express varying degrees of the phenotype, suffering mild to severe malady. Males experience a higher likelihood of fetal death.
Perlecan (PLC) also known as basement membrane-specific heparan sulfate proteoglycan core protein (HSPG) or heparan sulfate proteoglycan 2 (HSPG2), is a protein that in humans is encoded by the HSPG2 gene. The HSPG2 gene codes for a 4,391 amino acid protein with a molecular weight of 468,829. It is one of the largest known proteins. The name perlecan comes from its appearance as a "string of pearls" in rotary shadowed images.
Heparan sulfate (HS) is a linear polysaccharide found in all animal tissues. It occurs as a proteoglycan in which two or three HS chains are attached in close proximity to cell surface or extracellular matrix proteins. In this form, HS binds to a variety of protein ligands, including Wnt, and regulates a wide range of biological activities, including developmental processes, angiogenesis, blood coagulation, abolishing detachment activity by GrB, and tumour metastasis. HS has also been shown to serve as cellular receptor for a number of viruses, including the respiratory syncytial virus. One study suggests that cellular heparan sulfate has a role in SARS-CoV-2 Infection, particularly when the virus attaches with ACE2.
Syndecan 1 is a protein which in humans is encoded by the SDC1 gene. The protein is a transmembrane heparan sulfate proteoglycan and is a member of the syndecan proteoglycan family. The syndecan-1 protein functions as an integral membrane protein and participates in cell proliferation, cell migration and cell-matrix interactions via its receptor for extracellular matrix proteins. Syndecan-1 is a sponge for growth factors and chemokines, with binding largely via heparan sulfate chains. The syndecans mediate cell binding, cell signaling, and cytoskeletal organization and syndecan receptors are required for internalization of the HIV-1 tat protein.
Enolase 1 (ENO1), more commonly known as alpha-enolase, is a glycolytic enzyme expressed in most tissues, one of the isozymes of enolase. Each isoenzyme is a homodimer composed of 2 alpha, 2 gamma, or 2 beta subunits, and functions as a glycolytic enzyme. Alpha-enolase, in addition, functions as a structural lens protein (tau-crystallin) in the monomeric form. Alternative splicing of this gene results in a shorter isoform that has been shown to bind to the c-myc promoter and function as a tumor suppressor. Several pseudogenes have been identified, including one on the long arm of chromosome 1. Alpha-enolase has also been identified as an autoantigen in Hashimoto encephalopathy.
Glypicans constitute one of the two major families of heparan sulfate proteoglycans, with the other major family being syndecans. Six glypicans have been identified in mammals, and are referred to as GPC1 through GPC6. In Drosophila two glypicans have been identified, and these are referred to as dally and dally-like. One glypican has been identified in C. elegans. Glypicans seem to play a vital role in developmental morphogenesis, and have been suggested as regulators for the Wnt and Hedgehog cell signaling pathways. They have additionally been suggested as regulators for fibroblast growth factor and bone morphogenic protein signaling.
Liver cancer, also known as hepatic cancer, primary hepatic cancer, or primary hepatic malignancy, is cancer that starts in the liver. Liver cancer can be primary in which the cancer starts in the liver, or it can be liver metastasis, or secondary, in which the cancer spreads from elsewhere in the body to the liver. Liver metastasis is the more common of the two liver cancers. Instances of liver cancer are increasing globally.
Leucine-rich repeat-containing G-protein coupled receptor 5 (LGR5) also known as G-protein coupled receptor 49 (GPR49) or G-protein coupled receptor 67 (GPR67) is a protein that in humans is encoded by the LGR5 gene. It is a member of GPCR class A receptor proteins. R-spondin proteins are the biological ligands of LGR5. LGR5 is expressed across a diverse range of tissue such as in the muscle, placenta, spinal cord and brain and particularly as a biomarker of adult stem cells in certain tissues.
Secreted frizzled-related protein 1, also known as SFRP1, is a protein which in humans is encoded by the SFRP1 gene.
Glypican-1 (GPC1) is a protein that in humans is encoded by the GPC1 gene. GPC1 is encoded by human GPC1 gene located at 2q37.3. GPC1 contains 558 amino acids with three predicted heparan sulfate chains.
Fibroblast growth factor 19 is a protein that in humans is encoded by the FGF19 gene. It functions as a hormone, regulating bile acid synthesis, with effects on glucose and lipid metabolism. Reduced synthesis, and blood levels, may be a factor in chronic bile acid diarrhea and in certain metabolic disorders.
Zinc transporter SLC39A7 (ZIP7), also known as solute carrier family 39 member 7, is a transmembrane protein that in humans is encoded by the SLC39A7 gene. It belongs to the ZIP family, which consists of 14 proteins that transport zinc into the cytoplasm. Its primary role is to control the transport of zinc from the ER and Golgi apparatus to the cytoplasm. It also plays a role in glucose metabolism. Its structure consists of helices that bind to zinc in a binuclear metal center. Its fruit fly orthologue is Catsup.
Glypican-4 is a protein that in humans is encoded by the GPC4 gene.
Sulfatase 1, also known as SULF1, is an enzyme which in humans is encoded by the SULF1 gene.
Glypican 2 (GPC2), also known cerebroglycan, is a protein which in humans is encoded by the GPC2 gene. The GPC2 gene is at locus 7q22.1 and encodes for a 579 amino acid protein. The C-terminus of GPC2 has the GPI attachment site, at G554, and the N-terminus encodes a signal peptide, from M1 to S24. Multiple GPC2 mRNA transcripts have been identified. GPC2-201 is the isoform overexpressed in pediatric cancers. Tumor-associated exon 3 of GPC2 shows the lowest expression in normal tissues compared with other exons.
A431 cells are a model human cell line used in biomedical research.
The Hippo signaling pathway, also known as the Salvador-Warts-Hippo (SWH) pathway, is a signaling pathway that controls organ size in animals through the regulation of cell proliferation and apoptosis. The pathway takes its name from one of its key signaling components—the protein kinase Hippo (Hpo). Mutations in this gene lead to tissue overgrowth, or a "hippopotamus"-like phenotype.
George K. Michalopoulos is a Greek-American pathologist and academic. He served as Maud L. Menten Professor of Experimental Pathology and Chair of the Department of Pathology at the University of Pittsburgh and UPMC from 1991 to 2023.
