Accumulating evidence indicates that ROS generated by members of the NOX family contribute importantly to immunological defense and the regulation of cell differentiation, proliferation, apoptosis, and intercellular signaling pathways. Excessive ROS generation causes oxidative stress, which accelerates the pathogenesis of inflammation, fibrosis, and tumor survival. Thus, NOX can be key factor in cancer initiation and progression, while also serving for diagnosis and prognostic estimation. Previous evidence indicates that loss of NOX1 activity is associated with poor patient survival or drug-resistance in human tumors, and may thus hold some promise as a therapeutic target [24]. NOX1-mediated ROS production regulating exocytosis is a vital factor for development in human cancers, which has an association with unfavorable metastasis risk and poor OS. Thus, NOX1 activity is a biomarker of prognosis for progression in a variety of human cancers[25].
More importantly, recent studies have shown that ROS produced by NOX1 plays a key role in cancer transformation and invasive progression [25, 26], with notable overexpression in cancers of the breast, colon, stomach and prostate, among others [25, 27, 28]. Indeed, NOX1 has been proposed to function as an oncogene and a therapeutic target [29, 30]. In addition, NOX1 may have constitutively high expression in human colon epithelial cells compared with other normal cell types [31].
Given this background, we investigated the association between NOX1 expression and clinicopathological features of GIST. After showing that NOX1 is mainly localized in the cytoplasm, we revealed a low intensity of NOX1 in GIST cells from 78 of our 146 cases, As shown in Table 2, our statistical analyses show that low NOX1 staining and mitotic index were associated with poor survival in GIST patients, suggesting that inadequate NOS generation may favor tumor progression. Indeed, the Kaplan-Meier survival curves showed that longer OS was strongly associated with a low NOX1 expression and a favorable prognosis for GIST patients. Meanwhile, the positive expression rate of NOX1 increased along with the mitotic index (per 50 HPFs).
We also examined the expression of NOX1 mRNA in tissue samples from GIST patients reported in the Oncomine online databases. This revealed that NOX1 protein and mRNA expression levels were both significantly higher in GIST samples compared with normal tissue tissues (Figure. 4), thus concurring with the present findings with IHC.
The main novelty of the present study is our finding that low NOX1 expression is confirmed to be useful prognostic marker for the progression of GIST. This result was obtained in material from patients of all disease stages, none of whom had received preoperative radiotherapy or chemotherapy. GIST patients with high expression of NOX1 did not manifest a significant difference in survival or disease progression. It remains an open matter who NOX1 mediates effects on cancer cell proliferation, migration, and invasion, but we propose that ROS production in macrophages may be decisive in this regard. Pharmacological inhibition of NOX1 or ROS-related redox signaling pathways might be used as tools for preclinical studies of the underlying mechanisms [32]. Another matter for future consideration is the possibility that genetic variants in the NOX-1 or other NOX isoforms may contribute to individual differences in cancer progression.
Taken together, we present an association between low NOX1 expression with high mitotic index in GIST samples with unfavorable prognosis. Therefore, low NOX1 expression emerges as a potentially useful predictive marker for prognosis of GIST. Targeted inhibition of NOX1 could be an attractive strategy for the treatment and management of GIST recurrence and progression.