Abstract
The cellular inhibitor of apoptosis 1 (cIAP1) is an E3-ubiquitin ligase that regulates cell signaling pathways involved in fundamental cellular processes including cell death, cell proliferation, cell differentiation and inflammation. It recruits ubiquitination substrates thanks to the presence of three baculoviral IAP repeat (BIR) domains at its N-terminal extremity. We previously demonstrated that cIAP1 promoted the ubiquitination of the E2 factor 1 (E2F1) transcription factor. Moreover, we showed that cIAP1 was required for E2F1 stabilization during the S phase of cell cycle and in response to DNA damage. Here, we report that E2F1 binds within the cIAP1 BIR3 domain. The BIR3 contains a surface hydrophobic groove that specifically anchors a conserved IAP binding motif (IBM) found in a number of intracellular proteins including Smac. The Smac N-7 peptide that includes the IBM, as well as a Smac mimetic, competed with E2F1 for interaction with cIAP1 demonstrating the importance of the BIR surface hydrophobic groove. We demonstrated that the first alpha-helix of BIR3 was required for E2F1 binding, as well as for the binding of Smac and Smac mimetics. Overexpression of cIAP1 modified the ubiquitination profile of E2F1, increasing the ratio of E2F1 conjugated with K11- and K63-linked ubiquitin chains, and decreasing the proportion of E2F1 modified by K48-linked ubiquitin chains. ChIP-seq analysis demonstrated that cIAP1 was required for the recruitment of E2F1 onto chromatin. Lastly, we identified an E2F-binding site on the cIAP1-encoding birc2 gene promoter, suggesting a retro-control regulation loop.
Highlights
Inhibitors of Apoptosis (IAPs) are a family of cell signaling regulators involved in a large panel of fundamental cellular processes including cell death, cell proliferation, cell differentiation, innate immunity and inflammatory responses [1]
We demonstrate that E2 factor 1 (E2F1) binds the BIR3 domain of cellular inhibitor of apoptosis 1 (cIAP1) in a peptide-binding groove-dependent manner and that the first alpha helix of BIR3 is required for the interaction
Most IAP partners, including Smac, contact a surface hydrophobic groove located in the BIR2 and/or BIR3 domains [36, 37]
Summary
Inhibitors of Apoptosis (IAPs) are a family of cell signaling regulators involved in a large panel of fundamental cellular processes including cell death, cell proliferation, cell differentiation, innate immunity and inflammatory responses [1] Belonging to this family, cIAP1 is a really interesting new gene (RING)-containing E3-ubiquitine ligase. E3-ligases carry out the final step of the ubiquitination cascade aiming to covalently conjugate single ubiquitin molecules or polyubiquitin chains to a substrate protein This post-translational modification is a very efficient and fast mechanism of controlling the fate of intracellular proteins. Alternative modes of interaction with BIR3 exist, involving unconventional IBMs [15] or attachment to another BIR-binding interface [16]
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