(Ⅰ) Investigation on the isoforms of γ-glutamyltransferase as diagnostic markers of hepatocellular carcinomaⅡ) Effects of γ-glutamyltransferase inhibition on the susceptibility of cancer cells to oxidative stress and chemotherapy
Date Issued
2009
Date
2009
Author(s)
Li, Yi-Ju
Abstract
γ-glutamyltransferase (GGT), a membrane-bound heterodimeric glycoprotein, is abundant in many tissues, including kidney, intestine and liver. GGT plays a key role in glutathione (GSH) homeostasis by breaking down extracellular GSH, which contributes to providing cysteine for intracellular GSH synthesis. Under pathological conditions, when liver cells are damaged, GGT is released to serum. In clinical examination, serum GGT activity is used to detect alcoholism and obstructive jaundice.n the first part of this study, hepatoma cell lines and clinical HCC serum were used to study the differences on GGT between hepatoma and normal, including HCC-specific mRNA variants and protein isoforms, which might be developed as potent diagnostic markers. The results indicated that HepG2 cells express HCC-specific mRNA variant, V3, which might be a valuable cell model for studying the GGT mRNA expression state in HCC. Besides, we use native PAGE and then GGT activity staining to identify the HCC-specific protein isoforms. Different GGT isoforms were found between normal and liver diseases, while β-GGT might be HCC-specific. Owing to the different definitions of HCC-specific isoforms in previous studies, we also demonstrated that sialyation status and interaction with other components in serum contributed to different GGT electrophoresis mobility. However, the sialic acid content on GGT showed no correlation to its activity. On the other hand, in lectin extraction experiment using fucose-specific AAL (Aleuria aurantia), we found that fucosylation on GGT might be minor but needs further study.he second part of this study, we used an effective GGT inhibitor, GGsTop, to investigate the effect of GGT inhibition on chemotherapy efficacy. Previous researches indicated that GSH can maintain intracellular redox potential and participate in the detoxification of xenobiotic compounds. As the result of the important role of GGT in maintaining GSH homeostasis, cancer cells were found to exhibit higher GGT level to assist rapid growth and to resist oxidative stress. We found that the inhibition of GGT activity resulted in the decrease of intracellular GSH content and the failure to defend the oxidative damage induced by benzoquinone (BQ). Moreover, we also demonstrated that GGT mRNA level was elevated after Cisplatin treatment which caused resistance to Cisplatin (IC50 >50 μM ). When GGT was inhibited, Huh7 cells were more sensitive to the cytotoxic action of Cisplatin. Taken together, we concluded that GGT inhibitor might be promising as adjuvant for cancer therapy.
Subjects
γ-glutamyltransferase
hepatocellular carcinoma
isoforms
oxidative stress
diagnostic marker
chemotherapy
SDGs
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