Human biliverdin reductase‐based peptides activate and inhibit glucose uptake through direct interaction with the kinase domain of insulin receptor

Abstract

Insulin binding changes conformation of the insulin receptor kinase (IRK) domain and initiates glucose uptake through the insulin, IGF-1, phosphatidyl inositol 3-kinase (PI3K), and MAPK pathways; human biliverdin reductase (hBVR) is an IRK substrate and pathway effector. This is the first report on hBVR peptide-mediated IRK activation and conformational change. (290)KYCCSRK, which increased IRK V(max) without changing K(m), stimulated glucose uptake and potentiated insulin and IGF-1 stimulation in 4 cell lines. KYCCSRK in native hBVR was necessary for the hBVR and IRK cross-activation. Peptide treatment also activated PI3K downstream effectors, Akt and ERK, phosphorylation, and Elk transcriptional activity. In cells transfected with CMV-regulated EGFP-VP-peptide plasmid, C(292)→A mutant did not stimulate glucose uptake; K(296)→A decreased uptake and kinase activity. KEDQYMKMTV, corresponding to hBVR's SH2-binding domain, was a potent inhibitor of glucose uptake and IRK. The mechanism of action of peptides was examined using cells expressing IRK (aa 988-1263) activated by coexpressed KYCCSRK. Three active cys-mutants of IRK, with fluorophore coupled to cysteines, C(1056), C(1138), or C(1234), were examined for changes in fluorescence emission spectra in the presence of peptides. KYCCSRK and KEDQYMKMTV bound to different sites in IRK. The findings identify novel agents for activating or inhibiting insulin signaling and offer a new approach for treatment of type 2 diabetes and hypoglycemia.

Translational Significance of Heme Oxygenase in Obesity and Metabolic Syndrome

“…A potential inducer of bilirubin and HO-1 is the peptide derived from the human biliverdin reductase protein 221 . This peptide, as well as the L-4F (ApoA-1 mimetic) peptide, could have a powerful effect on the induction of HO-1, with a reduction of fatty liver insulin resistance and adiposity.…”

Biliverdin reductase isozymes in metabolism

“…However, later investigations showed that siRNA suppression of BVRA increased pAkt in HK-2 proximal tubule epithelial human cells (41), human macrophages (40) and rat heart H9c2 cells (39), suggesting that BVRA may positively affect glucose uptake. The duality of BVRA on insulin signaling was further highlighted in a recent study using different peptide sequences of BVRA (8). The terminal 290 KYCCSRK peptide was found to increase glucose uptake and potentiate insulin, while a peptide ( 194 KEDQYMKMTV) corresponding to BVRA's SH2-binding domain was a potent inhibitor of glucose uptake and insulin signaling (8).…”

“…The insulin signaling cascade diverges into two major arms, the PI3-kinase/Akt, and the IRK/IRS/PI3-kinase/MAPK pathway. BVRA but not BVRB is known to interact with components in both pathways, and thus may have a role in the regulation of metabolic processes (Figure 3) (8, 18). …”

“…BVRB does contain a similar insulin receptor-interaction domain as BVRA, but whether BVRB can influence insulin signaling is not currently known. Most of what is known about the kinase activity function of BVRA and its involvement in insulin signaling has been pioneered by the Maines laboratory (8, 20), but the interaction between BVRA and PI3K has also been reported by other independent laboratories (39, 40). The effect of BVRA on insulin signaling remains controversial.…”

“…HO catabolizes heme to produce carbon monoxide (CO), iron, and the tetrapyrrolic bile pigment biliverdin, which is further reduced to the antioxidant bilirubin, by the enzyme biliverdin reductase (BVR). Recent studies have demonstrated that BVR, through production of bilirubin as well as direct signaling, may interact with the insulin receptor and thus affect insulin signaling (8), whereas serum total bilirubin levels have been negatively associated with hypertriglyceridemia and abdominal obesity (9). However, the pathways by which BVR and its end product bilirubin signal in tissues like adipose and liver to help prevent insulin resistance and obesity are not well understood.…”