NNAT is a novel mediator of oxidative stress that suppresses ER + breast cancer

Abstract Background Neuronatin (NNAT) was recently identified as a novel mediator of estrogen receptor-positive (ER+) breast cancer cell proliferation and migration, which correlated with decreased tumorigenic potential and prolonged patient survival. However, despite these observations, the molecular and pathophysiological role(s) of NNAT in ER + breast cancer remains unclear. Based on high protein homology with phospholamban, we hypothesized that NNAT mediates the homeostasis of intracellular calcium [Ca2+]i levels and endoplasmic reticulum (EndoR) function, which is frequently disrupted in ER + breast cancer and other malignancies. Methods To evaluate the role of NNAT on [Ca2+]i homeostasis, we used a combination of bioinformatics, gene expression and promoter activity assays, CRISPR gene manipulation, pharmacological tools and confocal imaging to characterize the association between ROS, NNAT and calcium signaling. Results Our data indicate that NNAT localizes predominantly to EndoR and lysosome, and genetic manipulation of NNAT levels demonstrated that NNAT modulates [Ca2+]i influx and maintains Ca2+ homeostasis. Pharmacological inhibition of calcium channels revealed that NNAT regulates [Ca2+]i levels in breast cancer cells through the interaction with ORAI but not the TRPC signaling cascade. Furthermore, NNAT is transcriptionally regulated by NRF1, PPARα, and PPARγ and is strongly upregulated by oxidative stress via the ROS and PPAR signaling cascades. Conclusion Collectively, these data suggest that NNAT expression is mediated by oxidative stress and acts as a regulator of Ca2+ homeostasis to impact ER + breast cancer proliferation, thus providing a molecular link between the longstanding observation that is accumulating ROS and altered Ca2+ signaling are key oncogenic drivers of cancer

Identification of a Rat Mammary Tumor Risk Locus That Is Syntenic with the Commonly Amplified 8q12.1 and 8q22.1 Regions in Human Breast Cancer Patients

Breast cancer risk is 31% heritable, yet the majority of the underlying risk factors remain poorly defined. Here, we used F2-linkage analysis in a rat mammary tumor model to identify a novel 11.2 Mb modifier locus of tumor incidence and burden on rat chromosome 5 (chr5: 15.4 – 26.6 Mb). Genomic and RNA sequencing analysis identified four differentially expressed candidates: TMEM68, IMPAD1, SDCBP, and RBM12B. Analysis of the human syntenic candidate region revealed that SDCBP is in close proximity to a previously reported genetic risk locus for human breast cancer. Moreover, analysis of the candidate genes in The Cancer Genome Atlas (TCGA) revealed that they fall within the commonly amplified 8q12.1 and 8q22.1 regions in human breast cancer patients and are correlated with worse overall survival. Collectively, this study presents novel evidence suggesting that TMEM68, IMPAD1, SDCBP, and RBM12B are potential modifiers of human breast cancer risk and outcome