NF1 deficiency correlates with estrogen receptor signaling and diminished survival in breast cancer

The key negative regulatory gene of the RAS pathway, NF1, is mutated or deleted in numerous cancer types and is associated with increased cancer risk and drug resistance. Even though women with neurofibromatosis (germline NF1 mutations) have a substantially increased breast cancer risk at a young age and NF1 is commonly mutated in sporadic breast cancers, we have a limited understanding of the role of NF1 in breast cancer. We utilized CRISPR–Cas9 gene editing to create Nf1 rat models to evaluate the effect of Nf1 deficiency on tumorigenesis. The resulting Nf1 indels induced highly penetrant, aggressive mammary adenocarcinomas that express estrogen receptor (ER) and progesterone receptor (PR). We identified distinct Nf1 mRNA and protein isoforms that were altered during tumorigenesis. To evaluate NF1 in human breast cancer, we analyzed genomic changes in a data set of 2000 clinically annotated breast cancers. We found NF1 shallow deletions in 25% of sporadic breast cancers, which correlated with poor clinical outcome. To identify biological networks impacted by NF1 deficiency, we constructed gene co-expression networks using weighted gene correlation network analysis (WGCNA) and identified a network connected to ESR1 (estrogen receptor). Moreover, NF1-deficient cancers correlated with established RAS activation signatures. Estrogen-dependence was verified by estrogen-ablation in Nf1 rats where rapid tumor regression was observed. Additionally, Nf1 deficiency correlated with increased estrogen receptor phosphorylation in mammary adenocarcinomas. These results demonstrate a significant role for NF1 in both NF1-related breast cancer and sporadic breast cancer, and highlight a potential functional link between neurofibromin and the estrogen receptor.
Genetics: Mutant tumor suppressor linked to estrogen receptor signaling Mutations in a tumor suppressor gene called NF1 may be an important prognostic indicator for women with breast cancer and a therapeutic target for tumors resistant to hormone therapy. A team led by Carrie Graveel and Matthew Steensma from the Van Andel Research Institute in Grand Rapids, Michigan, USA, studied a large dataset of well-characterized breast cancer cases. They showed that 25% harbored mutations in NF1, a genetic alteration that correlated with diminished survival. Gene network analyses revealed links between NF1 deficiency, RAS oncogene activity, and signaling through the estrogen receptor, including with genes known to mediate resistance to hormone therapy. The researchers also describe a newly created rat model of NF1-mutant breast cancer that they say could help further interrogate the importance of these genetic connections.