Nanoparticle Delivered Human Biliverdin Reductase-Based Peptide Increases Glucose Uptake by Activating IRK/Akt/GSK3 Axis: The Peptide Is Effective in the Cell and Wild-Type and Diabetic Ob/Ob Mice

Figure 4

P2 activation of IRK. (a) P2 stimulate IRK autophosphorylation in vitro. IRK was incubated in vitro with 20 μM of peptide P2 (KYCCSRK), peptide-A (KKRILHC), or peptide-B (KRNRYLSF) and [³²P]-ATP. The [³²P] incorporation was quantified as described in Section 2,  . (b) P2 stimulate IRK kinase activity in vitro, identification of IRK inhibitory peptide. A similar assay was performed as in (a), except that the IRK peptide substrate was included . (c) P2 is both a substrate and activator of IRK kinase activity in vitro. Assays using sequence variant (P2Y-F; KFCCSRK) of P2 were performed as in (b) . (d) P2 stimulates IRK kinase activity in the cell; peptide-A is an inhibitor. HEK cells were serum-starved overnight and treated with the indicated myristoylated peptides (40 μM) for 15 min. IRK was immunoprecipitated from cell lysates and assayed using the IRS peptide as substrate . (e) Activation of liver IRK by nanoparticle P2. C57Bl/6J mice were deprived of food overnight, anesthetized with ketamine, and injected with P2- or control nanoparticles. The mice were sacrificed 30 min later, and the liver was harvested. 100–200 mg liver was homogenized; IRK was assayed in immunoprecipitates as in (d). The data shown are the mean ± sem for four mice under each treatment.

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