Low expression of cytosolic NOTCH1 predicts poor prognosis of breast cancer patients.

The incidence of breast cancer is increasing, and is one of the leading causes of cancer death worldwide. Dysregulation of NOTCH1 signaling is reported in breast cancer. In present study, bioinformatics was utilized to study the expression of NOTCH1 gene in breast cancer from public databases, including the Kaplan-Meier Plotter, PrognoScan, Human Protein Atlas, and cBioPortal. The relationship between NOTCH1 mRNA expression and survival of patients was inconsistent in public databases. In addition, we performed immunohistochemistry (IHC) staining of 135 specimens from our hospital. Lower cytoplasmic staining of NOTCH1 protein was correlated with cancer recurrence, bone metastasis, and a worse disease-free survival of patients, especially those with estrogen receptor-positive and human epidermal growth factor receptor 2-positive (HER2+) cancers. In TCGA breast cancer dataset, lower expression of NOTCH1 in breast cancer specimens was correlated with higher level of CCND1 (protein: cyclin D1). Decreased expression of NOTCH1 was correlated with lower level of CCNA1 (protein: cyclin A1), CCND2 (protein: cyclin D2), CCNE1 (protein: cyclin E1), CDK6 (protein: CDK6), and CDKN2C (protein: p18). In conclusion, NOTCH1 mRNA expression is not consistently correlated with clinical outcomes of breast cancer patients. Low cytoplasmic expression of NOTCH1 in IHC study is correlated with poor prognosis of breast cancer patients. Cytoplasmic localization of NOTCH1 protein failed to initial oncogenic signaling in present study. Expression of NOTCH1 mRNA was discordant with cell cycle-related genes. Regulation of NOTCH1 in breast cancer involves gene expression, protein localization and downstream signaling.