ABSTRACT
Control of mitogen-activated protein kinase (MAPK) cascades is central to regulation of many cellular responses. We describe here human tribbles homologues (Htrbs) that control MAPK activity. MAPK kinases interact with Trbs and regulate their steady state levels. Further, Trbs selectively regulate the activation of extracellular signal-regulated kinases, c-Jun NH2-terminal kinases, and p38 MAPK with different relative levels of activity for the three classes of MAPK observed depending on the level of Trb expression. These results suggest that Trbs control both the extent and the specificity of MAPK kinase activation of MAPK.
Subject(s)
Cell Cycle Proteins/physiology , Drosophila Proteins/physiology , Intracellular Signaling Peptides and Proteins/physiology , MAP Kinase Signaling System , Protein Serine-Threonine Kinases/physiology , Animals , Blotting, Western , Calcium-Calmodulin-Dependent Protein Kinases , Cell Cycle Proteins/chemistry , Dose-Response Relationship, Drug , Drosophila Proteins/chemistry , Enzyme Activation , Gene Expression Regulation , Genes, Reporter , HeLa Cells , Humans , Immunoprecipitation , Interleukin-1/metabolism , Interleukin-8/metabolism , Intracellular Signaling Peptides and Proteins/chemistry , Luciferases/metabolism , Mice , Mitogen-Activated Protein Kinases/metabolism , Models, Biological , Molecular Sequence Data , NIH 3T3 Cells , Oligonucleotides, Antisense/chemistry , Plasmids/metabolism , Protein Binding , Protein Serine-Threonine Kinases/chemistry , Repressor Proteins , Transfection , p38 Mitogen-Activated Protein Kinases/metabolismABSTRACT
Bid, a BH3-only Bcl-2 protein, is activated by proteolytic cleavage exposing the BH3 domain, which then induces apoptosis by interacting with pro-apoptotic Bcl-2 family proteins (e.g. Bax and Bak) at the mitochondrial surface. The arrangement of domains within Bid suggested that Bid function might be regulated in part by alternative splicing. We have determined the gene structure of human Bid and identified a number of novel exons. We have also demonstrated endogenous mRNA and protein expression for three novel isoforms of Bid, generated using these exons. Bid(S) contains the N-terminal regulatory domains of Bid without the BH3 domain; Bid(EL) corresponds to full-length Bid with additional N-terminal sequence; and Bid(ES) contains only the Bid sequence downstream of the BH3 domain. Expression of these isoforms is regulated during granulocyte maturation. In functional studies Bid(EL) induces apoptosis, whereas Bid(S) abrogates the pro-apoptotic effects of truncated Bid and inhibits Fas-mediated apoptosis. Bid(ES) induces apoptosis but is also able to partially inhibit the pro-apoptotic effects of truncated Bid. These three novel endogenously expressed isoforms of Bid are distinct in their expression, their cellular localization, and their effects upon cellular apoptosis. Differential expression of these novel Bid isoforms may regulate the function of Bid following cleavage and thus influence the fate of cells exposed to a range of pro-apoptotic stimuli.
