title: A link between the cytoplasmic engulfment protein Elmo1 and the Mediator complex subunit Med31.
abstract: The cytoplasmic Elmo1:Dock180 complex acts as a guanine nucleotide exchange factor (GEF) for the small GTPase Rac and functions downstream of the phagocytic receptor BAI1 during apoptotic cell clearance, and in the entry of Salmonella and Shigella into cells. We discovered an unexpected binding between Elmo1 and the Mediator complex subunit Med31. The Mediator complex is a regulatory hub for nearly all gene transcription via RNA polymerase II, bridging the general transcription machinery with gene-specific regulatory proteins. Med31 is the smallest and the most evolutionarily conserved Mediator subunit, and knockout of Med31 results in embryonic lethality in mice; however, Med31 function in specific biological contexts is poorly understood. We observed that in primary macrophages, during Salmonella infection, Elmo1 and Med31 specifically affected expression of the cytokine genes Il10 and Il33 among the >25 genes monitored. Although endogenous Med31 is predominantly nuclear localized, Elmo1 increased the cytoplasmic localization of Med31. We identify ubiquitination as a novel posttranslational modification of Med31, with the cytoplasmic monoubiquitinated form of Med31 being enhanced by Elmo1. These data identify Elmo1 as a novel regulator of Med31, revealing a previously unrecognized link between cytoplasmic signaling proteins and the Mediator complex.
authors.affiliation: Department of Cell Biology, University of Virginia, Charlottesville, VA 22908, USA.
authors.forename: Joshua P
authors.initials: JP
authors.lastname: Mauldin
authors.forename: Mingjian
authors.initials: M
authors.lastname: Lu
authors.forename: Soumita
authors.initials: S
authors.lastname: Das
authors.forename: Daeho
authors.initials: D
authors.lastname: Park
authors.forename: Peter B
authors.initials: PB
authors.lastname: Ernst
authors.forename: Kodi S
authors.initials: KS
authors.lastname: Ravichandran
mesh_terms: D048868:Adaptor Proteins, Signal Transducing / Q000378:metabolism*; D000595:Amino Acid Sequence; D000818:Animals; D015870:Gene Expression; D057809:HEK293 Cells; D006801:Humans; D016753:Interleukin-10 / Q000378:metabolism; D000067596:Interleukin-33; D007378:Interleukins / Q000378:metabolism; D008264:Macrophages / Q000378:metabolism* / Q000382:microbiology; D056892:Mediator Complex / Q000378:metabolism*; D051379:Mice; D008810:Mice, Inbred C57BL; D008969:Molecular Sequence Data; D041681:NIH 3T3 Cells; D012481:Salmonella Infections, Animal / Q000378:metabolism*; D054875:Ubiquitination
chemical_list: D048868:Adaptor Proteins, Signal Transducing; C510359:ELMO1 protein, mouse; C556062:IL10 protein, mouse; C506535:Il33 protein, mouse; D000067596:Interleukin-33; D007378:Interleukins; C549839:MED31 protein, mouse; D056892:Mediator Complex; D016753:Interleukin-10