Transcriptional activation of Nlp by estrogen-ERa in breast cancer

Estrogen Receptor-a （ERa） is the key transcription factor that regulates cell proliferation and homeosta- sis. In this pathway, estrogen plays an important role in genomic instability and cell cycle regulation pro- cesses and the mechanisms of its action are multifaceted. In this study, we showed that estrogen regulates genomic instability through promoting the expression of Nip, a BRCAl-associated centrosomal protein which is involved in microtubule nucleation, spindle formation, chromosomal missegregation and abnormal cytokinesis. We demonstrated that the expression of Nip is strongly associated with ERa and FOXAI level in clinical breast cancer samples with poor clinical outcomes to breast cancer patients. Addition of estrogen in the ER-positive breast cancer cells resulted in elevation of NLP mRNA. Significantly, we identified that estrogen-ERa is capable of regulating Nlp expression through specifically binding ERa to the proximal region and the Estrogen Responsive Elements （ERE） enhancer in the distal region of NLP gene. Reporter assays demonstrated that estrogen directly activated Nlp promoter. ChIP assay results showed that E2-ERa directly bound to the EREs of Nip. Therefore, overexpression of Nip in breast cancer exhibits a hormone-dependent pattern, and estrogen participates in the regulation of genome instability and cell cycle in breast cancer cells partially through transcriptional activation of NLP gene. Overexpression of Nlp enhances the malignant progression of ERa-positive breast cancer cells in vitro, whereas knockdown of Nip suppresses this biological effects in ERa-positive breast cancer ceils. ERa/NIp axis may serve as a promising target against breast cancer.