The Breast Cancer Protooncogenes HER2, BRCA1 and BRCA2 and Their Regulation by the iNOS/NOS2 Axis

Abstract

The expression of inducible nitric oxide synthase (iNOS; NOS2) and derived NO in various cancers was reported to exert pro- and anti-tumorigenic effects depending on the levels of expression and the tumor types. In humans, the breast cancer level of iNOS was reported to be overexpressed, to exhibit pro-tumorigenic activities, and to be of prognostic significance. Likewise, the expression of the oncogenes HER2, BRCA1, and BRCA2 has been associated with malignancy. The interrelationship between the expression of these protooncogenes and oncogenes and the expression of iNOS is not clear. We have hypothesized that there exist cross-talk signaling pathways between the breast cancer protooncogenes, the iNOS axis, and iNOS-mediated NO mutations of these protooncogenes into oncogenes. We review the molecular regulation of the expression of the protooncogenes in breast cancer and their interrelationships with iNOS expression and activities. In addition, we discuss the roles of iNOS, HER2, BRCA1/2, and NO metabolism in the pathophysiology of cancer stem cells. Bioinformatic analyses have been performed and have found suggested molecular alterations responsible for breast cancer aggressiveness. These include the association of BRCA1/2 mutations and HER2 amplifications with the dysregulation of the NOS pathway. We propose that future studies should be undertaken to investigate the regulatory mechanisms underlying the expression of iNOS and various breast cancer oncogenes, with the aim of identifying new therapeutic targets for the treatment of breast cancers that are refractory to current treatments.

Keywords: BRCA1; BRCA2; HER2; TNBC; breast cancer; iNOS/NOS2; nitric oxide.

Figure 1

NOS enzymatic reaction. The chemical reaction catabolized by all the three human NOS enzymes involves the formation of L-citrulline and NO from L-arginine and in presence of O₂ and NADPH. The three known human NOS genes are: NOS1 or neuronal NOS (nNOS), NOS2 or inducible NOS (iNOS), and NOS3 or endothelial NOS (eNOS).

Figure 2

Role of NO in breast cancer (BC) and other relevant cancers. (A) Pathways regulated by NO in BC and relative intracellular NO-mediated effects. (B) Direct (plain lines) and indirect (dotted lines) pathways correlating NO with HER2 (top), (C) BRCA1 (middle), and (D) BRCA2 (bottom). OC, ovarian cancer; PC, pancreatic cancer; EMT, epithelial–mesenchymal transition.

Figure 3

mRNA differential expression of iNOS and iNOS-inducing genes in CD133+/CD44+ CSCs isolated by the PDAC cell lines MiaPaca2 and PANC1. For gene microarray analysis, Agilent Array platform was employed. Quantile normalization and subsequent raw data processing were performed using the GeneSpring GX v11.5.1 software package (Agilent Technologies). Differentially expressed mRNAs between compared samples (CD44+/CD133+ vs. CD44-/CD133-) of each cell line were identified through fold change (FC) filtering (FC ≥ 2 was set as a cut-off value). Columns represent mean fold change of gene expression ± SDEV.

Figure 4

Differential expression of BRCA1, BRCA2, and HER2 mRNA transcripts in CD133+/CD44+ CSCs isolated by the PDAC cell lines MiaPaca2 and PANC1. For gene microarray analysis, Agilent Array platform was employed. Quantile normalization and subsequent raw data processing were performed using the GeneSpring GX v11.5.1 software package (Agilent Technologies). Differentially expressed mRNAs between compared samples (CD44+/CD133+ vs. CD44-/CD133-) of each cell line were identified through fold change (FC) filtering (FC ≥ 2 was set as a cut-off value). Columns represent mean fold change of gene expression ± SDEV.

Figure 5

Correlation analyses between the expression levels of ErbB2 and NOS genes in TCGA breast cancer patients with HER2 amplification. Each black dot represents a cancer patient.

Figure 6

Correlation analyses between the expression levels of BRCA2 and NOS genes in TCGA breast cancer patients with mutations affecting BRCA2. Each black square represents a cancer patient.

Figure 7

Correlation analyses between the expression levels of BRCA1 and NOS genes in TCGA breast cancer patients with mutations affecting BRCA1. Each black triangle represents a cancer patient.