Both GLS silencing and GLS2 overexpression synergize with oxidative stress against proliferation of glioma cells

Abstract

Mitochondrial glutaminase (GA) plays an essential role in cancer cell metabolism, contributing to biosynthesis, bioenergetics and redox balance. Humans contain several GA isozymes encoded by the GLS and GLS2 genes, but the specific roles of each in cancer metabolism are still unclear. In this study, glioma SFxL and LN229 cells with silenced isoenzyme glutaminase KGA (encoded by GLS) showed lower survival ratios and a reduced GSH-dependent antioxidant capacity. These GLS-silenced cells also demonstrated induction of apoptosis indicated by enhanced annexin V binding capacity and caspase 3 activity. GLS silencing was associated with decreased mitochondrial membrane potential (ΔΨm) (JC-1 dye test), indicating that apoptosis was mediated by mitochondrial dysfunction. Similar observations were made in T98 glioma cells overexpressing glutaminase isoenzyme GAB, encoded by GLS2, though some characteristics (GSH/GSSG ratio) were different in the differently treated cell lines. Thus, control of GA isoenzyme expression may prove to be a key tool to alter both metabolic and oxidative stress in cancer therapy. Interestingly, reactive oxygen species (ROS) generation by treatment with oxidizing agents: arsenic trioxide or hydrogen peroxide, synergizes with either KGA silencing or GAB overexpression to suppress malignant properties of glioma cells, including the reduction of cellular motility. Of note, negative modulation of GLS isoforms or GAB overexpression evoked lower c-myc and bcl-2 expression, as well as higher pro-apoptotic bid expression. Combination of modulation of GA expression and treatment with oxidizing agents may become a therapeutic strategy for intractable cancers and provides a multi-angle evaluation system for anti-glioma pre-clinical investigations.

A Tale of Two Glutaminases: Homologous Enzymes with Distinct Roles in Tumorigenesis

“…LGA overexpression was reported to synergize with oxidative stress in killing glioma cells in another study [97]. Consistent with the conflicting reports of the role of LGA in cancer, its expression can be upregulated both by the tumor suppressor p53 [62,118,119] and by the protooncoproteins c-Myc (reported in activated CD4 + T cells) and n-Myc [120,121].…”

“…Although controlled levels of ROS can stimulate cell proliferation, excessive levels lead to cell stress and death [95]. Genetic silencing of GLS can lead to decreased glutathione levels [96,97], as can treatment of cells with a smallmolecule inhibitor of GLS [13]. A novel role of GLS in cancer is in the formation of microvesicles or oncosomes, nontraditional secretory vesicles which mediate signaling between cancer cells and their environment [98].…”

Glutaminases in brain: Multiple isoforms for many purposes

“…They exhibited lower survival ratios, a reduced antioxidant capacity dependent of GSH and induction of apoptosis. Similar observations were made when GLS2 was overexpressed in T98G glioma cells (Martín-Rufián et al, 2014). Although recent efforts on glioblatoma treatment have focused in therapies that target apoptotic pathways and miRNAs (Liu et al, 2013), combination of negative and positive modulation of GLS and GLS2, respectively, may improve therapeutic efficacy.…”

“…Human malignant gliomas express high levels of Gls transcript, while Gls2 transcripts are hardly detectable (Cheng et al, 2011;Szeliga et al, 2009). In a recent study, we sought to compare and contrast the effects of GLS silencing and GLS2 overexpression on malignant properties of glutamine-addicted glioblastoma cells, alone and when combined to oxidative stress (Martín-Rufián et al, 2014). Glioblastoma cells use Gln as the preferred anaplerotic precursor (Cheng et al, 2011;Wise et al, 2008).…”

Targeting metabolism in breast cancer: How far we can go?

“…Cell studies showed that a high glutamine supply protected MCF7 cells from tamoxifen-induced apoptosis [30] . Amino acid transporter-2, glutaminase 1 (GLS) and glutamate dehydrogenase are three key enzymes involved in glutamine metabolism [31] . Immunohistochemical staining of breast cancer tissues indicated that HER-2 positive and TNBC exhibited the most frequent expression of glutamine metabolism related proteins than other types [32] .…”