Impact of inducible nitric oxide synthase (iNOS) expression on triple negative breast cancer outcome and activation of EGFR and ERK signaling pathways

Abstract

Inflammation is implicated in triple negative breast cancer (TNBC) progression. TNBC carries a worse prognosis than other breast cancer subtypes, and with the clinical and molecular heterogeneity of TNBC, there is a lack of effective therapeutic targets available. Identification of molecular targets for TNBC subtypes is crucial towards personalized patient stratification. Inducible nitric oxide synthase (iNOS) has been shown to induce p53 mutation accumulation, basal-like gene signature enrichment and transactivation of the epidermal growth factor receptor (EGFR) via s-nitrosylation. Herein we report that iNOS is associated with disease recurrence, distant metastasis and decreased breast cancer specific survival in 209 cases of TNBC. Employing TNBC cell lines representing normal basal breast, and basal-like 1 and basal-like 2 tumors, we demonstrate that nitric oxide (NO) induces EGFR-dependent ERK phosphorylation in basal-like TNBC cell lines. Moreover NO mediated cell migration and cell invasion was found to be dependent on EGFR and ERK activation particularly in basal-like 2 TBNC cells. This occurred in conjunction with NF-κB activation and increased secretion of pro-inflammatory cytokines IL-8, IL-1β and TNF-α. This provides substantial evidence for EGFR as a therapeutic target to be taken into consideration in the treatment of a specific subset of basal-like TNBC overexpressing iNOS.

DNA Methylation in Human Breast Cancer Cell Lines Adapted to High Nitric Oxide

“…We found a significantly elevated level of methylation of RASSF1A promoter only in the BT-20-derived cell line out of four HNO-adapted breast cancer cell lines. In penwork from our laboratory, it was observed that iNOS and eNOS expression was significantly up-regulated in BT-20 HNO cells compared to the parental cell line (5), which was in agreement with the literature reporting the link of high NOS expression and NO levels with breast cancer (8,9).…”

“…It plays a critical role in physiological as well as pathological processes such as inflammation and cancer (32,33). It has been shown that NO levels are higher in breast cancer as compared to that in benign breast epithelium (8,9). Our previous studies characterized some molecular and cellular alterations induced by high NO concentration in human breast cancer using a model cell line system which was developed by our laboratory.…”

“…It has multiple effects on tumor biology. Depending on the dose and duration of exposure, NO exhibits its biological effects by either inhibiting or stimulating cell proliferation, migration and apoptosis (8). NO is reported to cause harm in the adipogenic environment of the breast, and thus initiates and promotes tumor development.…”

“…NO is produced by nitric oxide synthase (NOS) which has three isoforms, neuronal, endothelial (eNOS) and inducible (iNOS) (5). Increased expression of NOS has been identified in human tumors including breast cancer (4,5,8,9). iNOS is a proinflammatory enzyme involved in chronic inflammation.…”

“…iNOS is a proinflammatory enzyme involved in chronic inflammation. It has been shown that in patients with triple-negative breast tumors, iNOS expression is associated with worse prognosis and poor survival (5,8,9).…”