Interaction of human biliverdin reductase with Akt/protein kinase B and phosphatidylinositol‐dependent kinase 1 regulates glycogen synthase kinase 3 activity: a novel mechanism of Akt activation

ABSTRACT Biliverdin reductase A (BVR) and Akt isozymes have overlapping pleiotropic functions in the insulin/PI3K/MAPK pathway. Human BVR (hBVR) also reduces the hemeoxygenase activity product biliverdin to bilirubin and is directly activated by insulin receptor kinase (IRK). Akt isoenzymes (Akt1‐3) are downstream of IRK and are activated by phosphatidylinositol‐dependent kinase 1 (PDK1) phosphorylating T308 before S473 autophosphorylation. Akt (RxRxxSF) and PDK1 (RFxFPxFS) binding motifs are present in hBVR. Phosphorylation of glycogen synthase kinase 3 (GSK3) isoforms α/β by Akts inhibits their activity; nonphosphorylated GSK3β inhibits activation of various genes. We examined the role of hBVR in PDK1/Akt1/GSK3 signaling and Akt1 in hBVR phosphorylation. hBVR activates phosphorylation of Aktl at S473 independent of hBVR's kinase competency. hBVR and Aktl coimmunoprecipitated, and in‐cell Förster resonance energy transfer (FRET) and glutathione S‐transferase pulldown analyses identified Aktl pleckstrin homology domain as the interactive domain. hBVR activates phosphorylation of Akt1 at S473 independent of hBVR'skinase competency. Site‐directed mutagenesis, mass spectrometry, and kinetic analyses identified S230 in hBVR 225RNRYLSF sequence as the Aktl target. Underlined amino acids are the essential residues of the signaling motifs. In cells, hBVR‐activated Aktl increased both GSK3α/β and forkhead box of the O class transcription class 3 (FoxO3) phosphorylation and inhibited total GSK3 activity; depletion of hBVR released inhibition and stimulated glucose uptake. Immunoprecipitation analysis showed that PDK1 and hBVR interact through hBVR's PDK1 binding 161RFGFPAFS motif and formation of the PDK1/hBVR/Akt1 complex. sihBVR blocked complex formation. Findings identify hBVR as a previously unknown coactivator of Aktl and as a key mediator of Akt1/GSK3 pathway, as well as define a key role for hBVR in Aktl activation by PDKl.—Miralem, T., Lerner‐Marmarosh, N., Gibbs, P. E. M., Jenkins, J. L., Heimiller, C., Maines, M. D. Interactionof human biliverdin reductase with Akt/protein kinase B and phosphatidylinositol‐dependent kinase l regulates glycogen synthase kinase 3 activity: a novel mechanism of Akt activation. FASEB J. 30, 2926‐2944 (20l6). www.fasebj.org