Human Molecular Genetics Advance Access published online on November 9, 2006
Human Molecular Genetics, doi:10.1093/hmg/ddl425
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Published by Oxford University Press 2006
Itch Genetically Interacts with Notch1 in a Mouse Autoimmune Disease Model
1 Mouse Cancer Genetics Program, Center for Cancer Research, National Cancer Institute, Frederick, MD 21702 USA 2 Pathology/Histotechnology Laboratory, SAIC-Frederick, Frederick, MD 21702 USA
* Department of Biological Sciences, CLS 703, University of South Carolina, Columbia, SC 29208, lmatesic{at}biol.sc.edu
Received September 11, 2006; Revised October 16, 2006; Accepted October 26, 2006
Homozygous itchy mice develop a fatal, late-onset autoimmune-like disease due to a loss of function mutation in an ubiquitin protein ligase. Phylogenetic and in vitro analyses suggest that Itch is a negative regulator of Notch signaling. Since Notch proteins have many important functions in the immune system, we determined whether Itch regulates Notch signaling in vivo. This was accomplished by breeding homozygous itch mice to mice carrying an activated Notch1 transgene that was specifically overexpressed in developing thymocytes. Interestingly, all itch mice carrying this transgene were smaller than their littermates and died by 12 weeks of age. These mice had a similar autoimmune disease to that seen in itch animals. However, the lesions were more severe with a much earlier age of onset, supporting the assertion that these mutations genetically interact. In addition, the combination of these mutations produced novel phenotypes including a perturbation in T cell development, with a reduction in the number of double positive and an increase in the number of double negative and single positive T cells. TUNEL staining showed reduced apoptosis in the thymus of itch animals that carry the Notch1 transgene. Antibody staining displayed increased levels of full length Notch1 and phospho-AKT specifically in double positive thymocytes but no change in other signaling pathways including MAPK, p38, and JNK. These results provide the first direct demonstration that increased AKT-mediated Notch1 signaling results in autoimmunity and may provide insight into the treatment of a group of diseases that affect a significant proportion of the population.