Either depletion of NQO1 or overexpression of PTEN reduced cell proliferation, and the peak effect was observed when PTEN was overexpressed and NQO1 was depleted at the same time in LN229/EGFR cells (Figure 5(h)). 3.6. NQO1 displays a paradoxical role in mediating GBM growth in response to tumor suppressor PTEN. 1. Introduction Glioblastoma multiforme (GBM) is the most malignant human brain tumor. It is highly aggressive, infiltrative, and destructive. In clinical trials of radiation therapy and temozolomide chemotherapy following surgical resection, the average survival period for the patient is around 60C70 weeks [1]. Specific therapeutic targeting of GBM subclasses remains a goal in neurooncology. The key features of primary GBM include amplification of epidermal growth factor receptor (EGFR) activity, deletion or mutation of homozygous cyclin-dependent kinase (CDK) inhibitor p16INK4A (CDKN2A), alterations in phosphatase and tensin homolog (PTEN) on chromosome 10, and deletion of INK4a [2]. As a receptor tyrosine kinase (RTK), EGFR mediates cell growth and proliferation via downstream effectors such as Ras and PI-3-Kinase (PI3K) and is regulated by tumor suppressor genes NF1 and PTEN. PTEN, a protein implicated in various cellular processes including metabolism, apoptosis, cell proliferation, and survival, suppresses the PI3K/Akt pathway via dephosphorylating PIP3 (phosphatidyl-3,4,5-triphosphate) into PIP2 (phosphatidyl-4,5-diphosphate). One of the most selective genetic alterations in GBM is the amplification of EGFR, which occurs in approximately 40% of GBMs. Either wild-type or mutated forms of EGFR can be amplified. The most common mutated form lacks exons 2C7, resulting in constitutively active tyrosine kinase activity (EGFRvIII) [3]. In clinical trials, patients carrying EGFR-driven tumors with PTEN mutation do not respond to anti-EGFR treatment, but the molecular mechanisms for this resistance remain unknown [4]. Amplification of EGFR activity or its constitutive activation due to truncation, PTEN mutation, and loss of chromosome 10 is found in primary GBM tumors, while TP53 mutations are common in secondary GBM [5, 6]. These mutations affect the redox balance in the cancer cells. For instance, EGFR activation by EGF induces endogenous production of intracellular reactive oxygen species (ROS) and H2O2 in cancer cell lines [7, 8]. Upon ligand binding, EGFR forms homo- and heterodimers that activate several intracellular signal pathways, such as PI3K/Akt and Ras/mitogen-activated protein kinase (MAPK), Tecadenoson resulting in DNA synthesis augmentation [7]. High doses of H2O2 (200?pM) escalate EGFR Tyr autophosphorylation, leading to generation of ROS [7]. In acting as a tumor suppressor, PTEN Rabbit Polyclonal to MAP9 negatively regulates the PI3K/Akt pathway via hydrolyzing the key second messenger PI-(3,4,5)P3 [9, 10]. PTEN is also regulated by redox status, specifically by H2O2, which can trigger a disulfide bond formation between Cys71 and Cys124 in the phosphatase domain [11], altering its interaction with signaling and regulatory proteins [11, 12]. Presumably, overexpression of EGFR may increase H2O2 Tecadenoson levels, disturbing a number of signaling pathways and stimulating cell survival and proliferation. NAD (P)H: quinone oxidoreductase (NQO1, also called as DT-diaphorase) is a cytosolic flavoenzyme Tecadenoson that is crucial in protecting against endogenous and exogenous quinones via catalyzing two- or four-electron reductions of the substrates [13]. NQO1 possesses multiple enzymatic and nonenzymatic functions. For instance, NQO1 has superoxide scavenging activity, stabilizing p53 and other 20S proteasome-degradable tumor suppressor proteins [14]. NQO1 occurs in all tissues with the highest expression levels in epithelial, vascular endothelial, adipocytes, and cancer cells, especially liver tumors [15]. NQO1 gene expression is mainly regulated by the ARE (antioxidant response element) under both normal and oxidative stress conditions [16]. The NQO1 gene contains ARE in its promoter region and is regulated by the nuclear factor (erythroid-derived)-like 2 (Nrf2) [17]. Xenobiotics, antioxidants, oxidants, UV light, and ionizing radiations mediate NQO1 expression via Keap1/Nrf2/ARE pathway [18]. Interestingly, two polymorphic forms of NQO1 that reduce cellular NQO1 activity are associated with increased risk of cancers [19C21]. Although a lowered or absent NQO1 activity is correlated with increased susceptibility for human cancer development [19, 22], several studies reveal that NQO1 is upregulated in a number of cancers [23C25]. Consequently, identification of high affinity and selective inhibitors of NQO1 might be an attractive strategy for treating cancers. In the current study, we provide innovative evidence demonstrating that NQO1 acts as a downstream target of PTEN in glioblastoma cells, promoting GBM cell proliferation and suppressing ROS. In alignment with its paradoxical roles as both anticancer enzyme and oncogene, NQO1 augments GBM cell growth in response to PTEN expression, which is in sharp contrast to another downstream target of PTEN, PINK1, which also possesses antioxidant activity. This.