title: Human biliverdin reductase is an ERK activator; hBVR is an ERK nuclear transporter and is required for MAPK signaling.
abstract: Activation of the MEK/ERK/Elk-signaling cascade is a mechanism for relaying mitogenic and stress stimuli for gene activation. MEK1 is the proximate kinase for activation of ERK1/2, and nuclear targeting of ERK1/2 is obligatory for Elk1 transcriptional activity. Human biliverdin reductase (hBVR) is a recently described Ser/Thr/Tyr kinase in the MAPK insulin/insulin-like growth factor 1 (IGF1)-signaling cascade. Using 293A cells and in vitro experiments, we detail the formation of a ternary complex of MEK/ERK/hBVR, activation of MEK1 and ERK1/2 kinase activities by hBVR, and phosphorylation of hBVR by ERK1/2. hBVR is nearly as effective as IGF1 in activating ERK; intact hBVR ATP-binding domain is necessary for Elk1 activation, whereas protein-protein interaction is the basis for hBVR activation of MEK1 and ERK. The two MAPK docking consensus sequences present in hBVR, F(162)GFP and K(275)KRILHCLGL (C- and D-box, respectively), are ERK interactive sites; interaction at each site is critical for ERK/Elk1 activation. Transfection with mutant hBVR-P(165) or peptides corresponding to the C- or D-box blocked activation of ERK by IGF1. Transfection with D-box mutant hBVR prevented the activation of ERK by wild-type protein and dramatically decreased Elk1 transcriptional activity. hBVR is a nuclear transporter of ERK; experiments with hBVR nuclear export signal (NES) and nuclear localization signal (NLS) mutants demonstrated its critical role in the nuclear localization of IGF-stimulated ERK for Elk1 activation. These findings, together with observations that si-hBVR blocked activation of ERK and Elk1 by IGF1 and prevented formation of ternary complex between MEK/ERK/hBVR, define the critical role of hBVR in ERK signaling and nuclear functions of the kinase.
authors.affiliation: University of Rochester School of Medicine, Department of Biochemistry and Biophysics, Rochester, NY 14642, USA.
authors.forename: Nicole
authors.initials: N
authors.lastname: Lerner-Marmarosh
authors.forename: Tihomir
authors.initials: T
authors.lastname: Miralem
authors.forename: Peter E M
authors.initials: PE
authors.lastname: Gibbs
authors.forename: Mahin D
authors.initials: MD
authors.lastname: Maines
mesh_terms: D020816:Amino Acid Motifs; D002460:Cell Line; D002467:Cell Nucleus / Q000187:drug effects / Q000201:enzymology*; D004789:Enzyme Activation / Q000187:drug effects; D020536:Enzyme Activators / Q000378:metabolism*; D005786:Gene Expression Regulation / Q000187:drug effects; D006801:Humans; D007334:Insulin-Like Growth Factor I / Q000494:pharmacology; D020935:MAP Kinase Signaling System / Q000187:drug effects; D019950:Mitogen-Activated Protein Kinase 1 / Q000378:metabolism*; D048052:Mitogen-Activated Protein Kinase 3 / Q000378:metabolism*; D020929:Mitogen-Activated Protein Kinase Kinases / Q000378:metabolism; D008954:Models, Biological; D049790:Nuclear Export Signals; D019913:Nuclear Localization Signals; D044925:Oxidoreductases Acting on CH-CH Group Donors / Q000737:chemistry / Q000378:metabolism*; D010766:Phosphorylation / Q000187:drug effects; D011485:Protein Binding / Q000187:drug effects; D021381:Protein Transport / Q000187:drug effects; D014158:Transcription, Genetic / Q000187:drug effects; D015533:Transcriptional Activation; D050807:ets-Domain Protein Elk-1 / Q000378:metabolism
chemical_list: D020536:Enzyme Activators; D049790:Nuclear Export Signals; D019913:Nuclear Localization Signals; D050807:ets-Domain Protein Elk-1; D007334:Insulin-Like Growth Factor I; D044925:Oxidoreductases Acting on CH-CH Group Donors; C019789:biliverdin reductase; D019950:Mitogen-Activated Protein Kinase 1; D048052:Mitogen-Activated Protein Kinase 3; D020929:Mitogen-Activated Protein Kinase Kinases