Analysis of the correlation between alterations in N-glycans and invasiveness in liver cancer cell lines

The N-glycoforms of glycoproteins modify protein function and control a number of biological pathways. The aim of the present study was to investigate the correlation between alterations in N-glycans and cancer aggressiveness in terms of cancer cell invasion ability. The expression of urokinase-type plasminogen activator (uPA) and N-acetylglucosaminyltransferase V (GnT-V) in liver cancer cell lines was analyzed by western blotting. Cell invasiveness was analyzed by Matrigel invasion assays. uPA and GnT-V expression in liver cancer cell lines was knocked down by RNA interference. Furthermore, uPA was overexpressed in liver cancer cells using lentiviral vectors, and a mutant strain of HepG2 cells overexpressing uPA deficient in N-glycans was established. A glycoblotting-assisted matrix-assisted laser desorption/ionization-time-of-flight/mass spectrometry-based quantitative analysis of liver cancer cell lines was performed, in which invasiveness was altered by modifying the expression of uPA and GnT-V. N-glycan profiles were found to differ between the highly invasive liver cancer cell line HLE and the less invasive cell line HepG2. The expression of several N-glycans, including a form with m/z=1892, was changed according to invasiveness controlled by knockdown and overexpression of uPA. The invasiveness of HepG2 cells with mutant uPA did not increase regardless of the level of expression of uPA. Following GnT-V knockdown and N-glycan alteration, uPA expression did not change, whereas cell invasiveness decreased. One N-glycan (m/z=1892) was common among N-glycans in the comparative analysis between HLE and HepG2, HLE and uPA knockdown HLE, HepG2 and uPA-overexpressing HepG2, and HLE and GnT-V knockdown HLE cells and among N-glycan profiles in human uPA. Therefore, N-glycosylation is an important factor controlling invasiveness of liver cancer cells, and a specific N-glycan (m/z=1892) associated with the invasion of liver cancer cells via uPA was identified in the present study.