Formation of Ternary Complex of Human Biliverdin Reductase-Protein Kinase Cδ-ERK2 Protein Is Essential for ERK2-mediated Activation of Elk1 Protein, Nuclear Factor-κB, and Inducible Nitric-oxidase Synthase (iNOS)

Growth factors, insulin, oxidative stress, and cytokines activate ERK1/2 by PKC delta and MEK1/2. Human biliverdin reductase (hBVR), a Ser/Thr/Tyr kinase and intracellular scaffold/bridge/anchor, is a nuclear transporter of MEK1/2-stimulated ERK1/2 (Lerner-Marmarosh, N., Miralem, T., Gibbs, P. E., and Maines, M. D. (2008) Proc. Natl. Acad. Sci. U. S. A. 105, 6870-6875). hBVR, PKC delta, and MEK1/2 overlap in their tissue expression profile and type of activators. Presently, we report on formation of an hBVR-PKC delta-ERK2 ternary complex that is essential for ERK2 signal transduction and activation of genes linked to cell proliferation and cancer. MEK1/2 and the protein phosphatase PP2A were also present in the complex. When cells were stimulated with insulin-like growth factor-1 (IGF-1), an increased interaction between hBVR and PKC delta was detected by FRET-fluorescence lifetime imaging microscopy. hBVR and ERK2 were phosphorylated by PKC delta; however, the PKC was not a substrate for either ERK2 or hBVR. IGF-1 and phorbol ester increased hBVR/PKC delta binding; hBVR was required for the activation of PKC delta and its interaction with ERK2. The C-terminal phenylalanine residues of PKC delta (Phe(660), Phe(663), and Phe(665)) were necessary for binding to ERK2 but not for hBVR binding. Formation of the hBVR-PKC delta-ERK2 complex required the hBVR docking site for ERK, FXFP (DEF, C-box) and D(delta)-box (ILXXLXL) motifs. The hBVR-based peptide KKRILHCLGLA inhibited PKC activation and PKC delta/ERK2 interaction. Phorbol ester-and TNF-alpha-dependent activation of the ERK-regulated transcription factors Elk1 and NF-kappa B and expression of the iNOS gene were suppressed by hBVR siRNA; those activities were rescued by hBVR. The findings reveal the direct input of hBVR in PKC delta/ERK signaling and identify hBVR-based peptide regulators of ERK-mediated gene activation.