Menin is a tumor suppressor protein whose loss or inactivation causes multiple endocrine neoplasia type 1 (MEN1), a hereditary autosomal dominant tumor syndrome characterized by tumorigenesis in multiple endocrine organs1. Menin interacts with a multitude of proteins and involves in a variety of cellular processes2–6. Menin binds the Jun family transcription factor JunD and inhibits its transcriptional activity7,8. Several MEN1 missense mutations disrupted the menin-JunD interaction suggestive of a correlation between menin’s tumor suppressor function and its interaction with JunD and suppression of JunD activated transcription8,9. Menin also interacts with mixed lineage leukemia protein 1 MLL1, a histone H3 lysine 4 (H3K4) methyltransferase, and functions as an oncogenic cofactor to upregulate gene (including HOX genes) transcription and promote MLL1 fusion protein (MFP)-induced leukemogenesis10–12. A recent report on menin tethering MLL1 to chromatin binding factor LEDGF indicates menin as a molecular adaptor to coordinate the functions of multiple proteins13. Despite the importance of menin, it still remains poorly understood how menin could interact with many distinct partners and control multiple functions. Here we present the crystal structures of menin, free and in complexes with MLL1 or JunD, or an MLL1-LEDGF heterodimer. These structures show that menin contains a deep pocket that binds short peptides of MLL1 or JunD in the same manner, but oppositely regulates transcription. The menin-JunD interaction blocks JNK kinase-meidated JunD phosphorylation, a crucial event for JunD activation.Moreover, menin functions as a scaffold molecule to promote gene transcription by binding MLL1 through the peptide-pocket yet interacting with LEDGF at a distinct surface.

SummarySLX4 interacts with several endonucleases to resolve structural barriers in DNA metabolism. SLX4 also interacts with telomeric protein TRF2 in human cells. The molecular mechanism of these interactions at telomeres remains unknown. Here, we report the crystal structure of the TRF2-binding motif of SLX4 (SLX4TBM) in complex with the TRFH domain of TRF2 (TRF2TRFH) and map the interactions of SLX4 with endonucleases SLX1, XPF, and MUS81. TRF2 recognizes a unique HxLxP motif on SLX4 via the peptide-binding site in its TRFH domain. Telomeric localization of SLX4 and associated nucleases depend on the SLX4-endonuclease and SLX4-TRF2 interactions and the protein levels of SLX4 and TRF2. SLX4 assembles an endonuclease toolkit that negatively regulates telomere length via SLX1-catalyzed nucleolytic resolution of telomere DNA structures. We propose that the SLX4-TRF2 complex serves as a double-layer scaffold bridging multiple endonucleases with telomeres for recombination-based telomere maintenance.