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Mol Cell. 2007 Dec 14;28(5):914-22.

c-IAP1 cooperates with Myc by acting as a ubiquitin ligase for Mad1.

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  • 1Department of Cell Biology, Harvard Medical School, Boston, MA 02115, USA.


c-IAP1, a member of the inhibitor of apoptosis protein (IAP) family and a RING finger ubiquitin ligase (E3), has been proposed to be an important oncogene. In many types of cancers, the levels of c-IAP1 are upregulated, which contributes positively to tumorigenesis. However, the mechanism by which c-IAP1 promotes tumorigenesis has proven elusive. Although proteins in the IAP family may function as caspase inhibitors, c-IAP1 was shown to be a poor inhibitor of caspases. Here we show that c-IAP1 catalyzes ubiquitination of Max-dimerization protein-1 (Mad1), a cellular antagonist of Myc. Ubiquitination of Mad1 by c-IAP1 accelerates its degradation by the 26S proteasome pathway, and this reduction of the Mad1 levels cooperates with Myc to promote cell proliferation. Our results demonstrate that c-IAP1 exerts its oncogenic functions by promoting the degradation of an important negative regulator in the Myc pathway.

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