Aberrant methylation and silencing of the SPINT2 gene in high-grade gliomas

Hepatocyte growth factor activator inhibitor type 2 (HAI‐2), encoded by the SPINT2 gene, is a membrane‐anchored protein that inhibits proteases involved in the activation of hepatocyte growth factor (HGF), a ligand of MET receptor. Epigenetic silencing of the SPINT2 gene has been reported in a human glioblastoma cell line (U87) and glioblastoma‐derived cancer stem cells. However, the incidence of SPINT2 methylation in tumor tissues obtained from glioma patients is unknown. In this study, we analyzed the methylation status of the SPINT2 gene of eight human glioblastoma cell lines and surgically resected glioma tissues of different grades (II, III, and IV) by bisulfite sequence analysis and methylation‐specific PCR. Most glioblastoma lines (7/8) showed methylation of the SPINT2 gene with a significantly reduced level of SPINT2mRNA compared to cultured astrocytes and normal brain tissues. However, all glioblastoma lines expressed mRNA for HGF activator (HGFAC), a target protease of HAI‐2/SPINT2. Forced expression of SPINT2 reduced MET phosphorylation of U87 glioblastoma cells both in vitro and in intracranial xenografts in nude mice. Methylation‐specific PCR analysis of the resected glioma tissues indicated notable methylation of the SPINT2 gene in 33.3% (2/6), 71.4% (10/14), and 74.3% (26/35) of grade II, III, and IV gliomas, respectively. Analysis of RNA sequencing data in a public database indicated an increased HGFAC/SPINT2 expression ratio in high‐grade compared to low‐grade gliomas (P = .01). In summary, aberrant methylation of the SPINT2 gene is frequently observed in high‐grade gliomas and might confer MET signaling in the glioma cells.

Hepatocyte growth factor activator inhibitors (HAI-1 and HAI-2): Emerging key players in epithelial integrity and cancer

The growth, survival, and metabolic activities of multicellular organisms at the cellular level are regulated by intracellular signaling, systemic homeostasis and the pericellular microenvironment. Pericellular proteolysis has a crucial role in processing bioactive molecules in the microenvironment and thereby has profound effects on cellular functions. Hepatocyte growth factor activator inhibitor type 1 (HAI-1) and HAI-2 are type I transmembrane serine protease inhibitors expressed by most epithelial cells. They regulate the pericellular activities of circulating hepatocyte growth factor activator and cellular type II transmembrane serine proteases (TTSPs), proteases required for the activation of hepatocyte growth factor (HGF)/scatter factor (SF). Activated HGF/SF transduces pleiotropic signals through its receptor tyrosine kinase, MET (coded by the proto-oncogene MET), which are necessary for cellular migration, survival, growth and triggering stem cells for accelerated healing. HAI-1 and HAI-2 are also required for normal epithelial functions through regulation of TTSP-mediated activation of other proteases and protease-activated receptor 2, and also through suppressing excess degradation of epithelial junctional proteins. This review summarizes current knowledge regarding the mechanism of pericellular HGF/SF activation and highlights emerging roles of HAIs in epithelial development and integrity, as well as tumorigenesis and progression of transformed epithelial cells.