C-terminal deletion of NOTCH1 intracellular domain (N1ICD) increases its stability but does not amplify and recapitulate N1ICD-dependent signalling

Since the generation of a mouse strain conditionally expressing the active intracellular domain of Notch1 (N1 ICD ), many laboratories have exploited this model (Rosa N1-ICD ) to assess the impact of constitutive Notch1 signalling activation in normal and pathological processes. It should be underscored that Cre-recombination leads to the expression of a C-terminally truncated form of N1 ICD (N1 ICDdC ) in the Rosa N1-ICD mutant mice. Given that no studies were undertaken to delineate whether deletion of this region leaves intact N1 ICD function, stable cell lines with single targeted integration of inducible N1 ICD and N1 ICDdC were generated. We found that C-terminal deletion of N1 ICD stabilized the protein but did not promote the activity of Notch responsive promoters. Furthermore, despite higher expression levels, N1 ICDdC failed to phenocopy N1 ICD in the promotion of anchorage-independent growth. Our results thus suggest that the C-terminal region of N1 ICD plays a role in shaping the Notch response. Therefore, it should be taken into consideration that N1 ICD is truncated when interpreting phenotypes of Rosa N1-ICD mutant mice.