Notch1 signaling is mediated by importins alpha 3, 4, and 7

Abstract

The Notch signaling pathway is an important regulation system for the development and self-renewal of different tissues. A specific feature of this signaling cascade is the function of Notch as a surface receptor and regulator of gene expression. Hence, Notch activation and signal transduction requires the proteolytic release of the Notch intracellular domain (NICD), which activates the transcription of cell-specific genes after its transport into the nucleus. To date, little is known about the mechanisms that mediate NICD nuclear import. We here show that transport of NICD into the nucleus is mediated by the canonical importin alpha/beta 1 pathway. GST pull-down experiments revealed that NICD binds via one of its four potential nuclear localization signals to importins alpha 3, alpha 4, and alpha 7, but not to alpha 1 and alpha 5. siRNA-mediated knockdown experiments showed that importins alpha 3, alpha 4 (and to a lesser extent, alpha 7) mediate nuclear import of NICD and thus are directly involved in Notch signaling.