Regulation of TNF‐α‐activated PKC‐ζ signaling by the human biliverdin reductase: identification of activating and inhibitory domains of the reductase

Human biliverdin reductase (hBVR) is a dual function enzyme: a catalyst for bilirubin formation and a S/T/Y kinase that shares activators with protein kinase C (PKC) ‐ζ, including cytokines, insulin, and reactive oxygen species (ROS). Presently, we show that hBVR increases PKC‐ζ autophosphorylation, stimulation by TNF‐α, as well as cytokine stimulation of NF‐κB DNA binding and promoter activity. S 149 in hBVR S/T kinase domain and S 230 in YLS 230 F in hBVR's docking site for the SH2 domain of signaling proteins are phosphorylation targets of PKC‐ζ. Two hBVR‐based peptides, KRNRYLS 230 F (#1) and KKRILHC 281 (#2), but not their S→AorC→A derivatives, respectively, blocked PKC‐ζ stimulation by TNF‐α and its membrane translocation. The C‐terminal‐based peptide KY‐CCSRK 296 (#3), enhanced PKC‐ζ stimulation by TNF‐α; for this, Lys 296 was essential. In metabolically 32 P‐labeled HEK293 cells transfected with hBVR or PKC‐ζ, TNF‐α increased hBVR phosphorylation. TNF‐α did not stimulate PKC‐ζ in cells infected with small interfering RNA for hBVR or transfected with hBVR with a point mutation in the nucleotide‐binding loop (G 17 ), S 149 ,orS 230 ; this was similar to the response of “kinase‐dead” PKC‐ζ K281R . We suggest peptide #1 blocks PKC‐ζ‐docking site interaction, peptide #2 disrupts function of the PKC‐ζ C1 domain, and peptide #3 alters ATP presentation to the kinase. The findings are of potential significance for development of modulators of PKC‐ζ activity and cellular response to cyto‐kines.— Lerner‐Marmarosh, N., Miralem, T., Gibbs, P. E. M., Maines, M. D. Regulation of TNF‐α‐activated PKC‐ζ signaling by the human biliverdin reductase: identification of activating and inhibitory domains of the reductase. FASEB J . 21, 3949–3962 (2007)