Mapping of the Simpson-Golabi-Behmel overgrowth syndrome gene (GPC3) to chromosome X in human and rat by fluorescence in situ hybridization

Therapeutic potential of targeting glypican-3 in hepatocellular carcinoma

Glypican-3 (GPC3) is a developmentally-regulated oncofetal protein that has been established as a clinically-relevant biomarker for early hepatocellular carcinoma (HCC). It is one of the first transcripts to appear during malignant hepatocyte transformation, and is expressed at the protein level in approximately half of high-grade dysplastic macronodules in cirrhotic liver. Several studies show it is expressed in most (75 to 100%) of HCCs confirmed by histopathology. The protein is anchored to the hepatocyte membrane by a glycosyl-phosphatidylinositol (GPI) anchor and shows consistent membrane immunostaining pattern, making it a viable target for immunotherapeutic approaches. Targeting GPC3 for therapeutic intervention is a promising approach for the clinical management of HCC and selected other tumors that express the marker.

Points of therapeutic intervention along the Wnt signaling pathway in hepatocellular carcinoma

Hepatocellular carcinoma (HCC) is the third leading cause of cancer mortality worldwide. However, there is little known about targeted therapeutics for the treatment of this devastating tumor. Among the growth factor signaling cascades deregulated in HCC, evidences suggest that the WNT/Frizzled-mediated signaling pathway plays a key role in the hepatic carcinogenesis. Aberrant activation of the signaling in HCC is mostly due to deregulated expression of the Wnt/β-catenin signaling components. This leads to the activation of the β-catenin/TCF dependent target genes, which controls cell proliferation, cell cycle, apoptosis or motility. It has been shown that disruption of the Wnt/β-catenin signaling cascade displayed anti-cancer properties in HCC. Currently, no therapeutic molecules targeting the WNT pathway are available or under clinical evaluation for the treatment of HCC. This review will discuss the identified potential molecular targets related to the canonical WNT signaling pathway and their potential therapeutic usefulness.

The oncofetal protein glypican-3 is a novel marker of hepatic progenitor/oval cells

Glypican-3 (Gpc3), a cell surface-linked heparan sulfate proteoglycan is highly expressed during embryogenesis and is involved in organogenesis. Its exact biological function remains unknown. We have studied the expression of Gpc3 in fetal and adult liver, in liver injury models of activation of liver progenitor cells: D-galactosamine and 2-acetylaminofluorene (2-AAF) administration followed by partial hepatectomy (PH) (2-AAF/PH); and in the Solt-Farber carcinogenic model: by initiation with a single dose of diethylnitrosamine and promotion with 2-AAF followed by PH treatment. Gpc3 expression was studied using complementary DNA microarrays, reverse transcriptase-polymerase chain reaction, in situ hybridization (ISH); ISH combined with immunohistochemistry (IHC) and immunofluorescent microscopy. We found that Gpc3 is highly expressed in fetal hepatoblasts from embryonic days 13 through 16 and its expression gradually decreases towards birth. Dual ISH with Gpc3 and alpha-fetoprotein (AFP) probes confirmed that only hepatoblasts and no other fetal liver cells express Gpc3. At 3 weeks after birth the expression of Gpc3 mRNA and protein was hardly detected in the liver. Gpc3 expression was highly induced in oval cell of D-gal and 2-AAF/PH treated animals. Dual ISH/IHC with Gpc3 riboprobe and cytokeratin-19 (CK-19) antibody revealed that Gpc3 is expressed in activated liver progenitor cells. ISH for Gpc3 and AFP performed on serial liver sections also showed coexpression of the two-oncofetal proteins. FACS isolated oval cells with anti-rat Thy1 revealed expression of Gpc3. Gpc3 expression persists in atypical duct-like structures and liver lesions of animals subjected to the Solt-Farber model of initiation and promotion of liver cancer expressing CK-19. In this work we report for the first time that the oncofetal protein Gpc3 is a marker of hepatic progenitor cells and of early liver lesions. Our findings show further that hepatic progenitor/oval cells are the target for malignant transformation in the Solt-Farber model of hepatic carcinogenesis.

Methylation analysis of the glypican 3 gene in embryonal tumours

We have previously shown that the glypican 3 (GPC3) gene was expressed in neuroblastoma (NB) and Wilms' tumour (WT), two embryonal tumours. GPC3 is an X-linked gene that has its peak expression during development and that is downregulated in all investigated tissues after birth. GPC3 expression could be involved in the aetiology of embryonal tumours such as NB and WT. Methylation is known to play a role in gene silencing, notably in chromosome X inactivation. Southern blot- and PCR-based methylation assays were used to assess the methylation status of the GPC3 promoter on genomic DNA from both normal and embryonal tumour cells. In normal cells, the promoter was not methylated in males and partially methylated in females. Our results suggest that DNA methylation of the promoter region is not essential for the transcriptional repression of the GPC3 gene and that the methylation observed in females is probably linked to the inactive X chromosome. In tumour samples, methylation abnormalities have been found exclusively in female NB samples (loss of methylation) and mainly in male WT samples (gain of methylation). Overall, methylation did not significantly correlate with the expression status of GPC3. Although promoter methylation is likely to affect the expression status of the gene, our results suggest that the deregulation of GPC3 transcriptional expression seen in NB and WT involves other regulatory levels.

Mapping of the rat glypican genes

The glypicans compose a family of glycosylphosphatidylinositol (GPI)-anchored heparan sulfate proteoglycans that play a role in the control of cell division and growth regulation. So far, six members (GPC1-6) of this family are known in vertebrates. The rat glypican gene 3 (Gpc3) was previously assigned to chromosome Xq36 (Shen et al., 1997). Using standard and radiation cell hybrids, we localized the five other rat glypican genes.