title: Rab39a binds caspase-1 and is required for caspase-1-dependent interleukin-1beta secretion.
abstract: Interleukin-1beta (IL-1beta) is an important pro-inflammatory cytokine that is secreted by unconventional means in a caspase-1-dependent manner. Using a one-step immunoprecipitation approach to isolate endogenous caspase-1 from the monocytic THP1 cell line, we identified previously undescribed binding partners using mass spectrometry. One of the proteins identified was Rab39a, a member of the Rab GTPase family, a group of proteins that have important roles in protein trafficking and secretion. We confirmed by co-immunoprecipitation that Rab39a binds caspase-1. Knock down of Rab39a with small interfering RNA resulted in diminished levels of secreted IL-1beta but had no effect on induction of pro-IL-1beta mRNA by lipopolysaccharide. Rab39a contains a highly conserved caspase-1 cleavage site and was cleaved in the presence of recombinant caspase-1 or lipopolysaccharide. Finally, overexpression of Rab39a results in an increase in IL-1beta secretion, and furthermore, overexpression of a Rab39a construct lacking the caspase-1 cleavage site leads to an additional increase in IL-1beta secretion. Altogether, our findings show that Rab39a interacts with caspase-1 and suggest that Rab39a functions as a trafficking adaptor linking caspase-1 to IL-1beta secretion.
authors.affiliation: School of Biochemistry and Immunology, Trinity College, Dublin 2, Ireland.
authors.forename: Christine E
authors.initials: CE
authors.lastname: Becker
authors.forename: Emma M
authors.initials: EM
authors.lastname: Creagh
authors.forename: Luke A J
authors.initials: LA
authors.lastname: O'Neill
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D001483:Base Sequence; D020170:Caspase 1 / Q000235:genetics / Q000378:metabolism*; D002478:Cells, Cultured; D006801:Humans; D053583:Interleukin-1beta / Q000235:genetics / Q000378:metabolism*; D008969:Molecular Sequence Data; D016297:Mutagenesis, Site-Directed; D011485:Protein Binding; D020033:Protein Isoforms / Q000235:genetics / Q000378:metabolism*; D034741:RNA, Small Interfering / Q000235:genetics / Q000378:metabolism; D014409:Tumor Necrosis Factor-alpha / Q000378:metabolism; D020691:rab GTP-Binding Proteins / Q000235:genetics / Q000378:metabolism*
chemical_list: D053583:Interleukin-1beta; D020033:Protein Isoforms; D034741:RNA, Small Interfering; D014409:Tumor Necrosis Factor-alpha; D020170:Caspase 1; C474116:RAB39A protein, human; D020691:rab GTP-Binding Proteins