A Structural Basis for the Acute Effects of HIV Protease Inhibitors on GLUT4 Intrinsic Activity

Abstract

Human immunodeficiency virus (HIV) protease inhibitors (PIs) act as reversible noncompetitive inhibitors of GLUT4 with binding affinities in the low micromolar range and are known to contribute to alterations in glucose homeostasis during treatment of HIV infection. As aspartyl protease inhibitors, these compounds all possess a core peptidomimetic structure together with flanking hydrophobic moieties. To determine the molecular basis for GLUT4 inhibition, a family of related oligopeptides containing structural elements found in PIs was screened for their ability to inhibit 2-deoxyglucose transport in primary rat adipocytes. The peptide oxybenzylcarbonyl-His-Phe-Phe-O-ethyl ester (zHFFe) was identified as a potent inhibitor of zero-trans glucose flux with a K i of 26 M. Similar to PIs, transport inhibition by this peptide was acute, noncompetitive, and reversible. Within a Xenopus oocyte expression system, zHFFe acutely and reversibly inhibited GLUT4-mediated glucose uptake, whereas GLUT1 activity was unaffected at concentrations as high as 1 mM. The related photoactivatable peptide zHFF-p-benzoylphenylalanine-[125 I]Tyr-O-ethyl ester selectively labeled GLUT4 in rat adipocytes and indinavir effectively protected against photolabeling. Furthermore, GLUT4 bound to a peptide affinity column containing the zHFF sequence and was eluted by indinavir. These data establish a structural basis for PI effects on GLUT4 activity and support the direct binding of PIs to the transport protein as the mechanism for acute inhibition of insulin-stimulated glucose uptake.

Isoform-selective Inhibition of Facilitative Glucose Transporters

“…We have shown previously that the peptide Z-HFFe, similar to indinavir, acts as a potent noncompetitive inhibitor of zerotrans GLUT4-mediated glucose transport but has little effect on GLUT1 transporter activity (11). Furthermore, a structurally related photoactivatable peptide, Z-HFF-Bpa-125 I-Tyr-Oethyl ester, selectively labeled GLUT4 in rat adipocytes in an indinavir-inhibitable manner (11). To facilitate identification of the peptide binding site in GLUT4, HR-1, a modified form of Z-HFF-Bpa-125 I-Tyr-O-ethyl ester in which the radioactive label is replaced by two Ahx spacer linkages and a FLAG epitope, was created.…”

“…Recognition that all first generation PIs contain a peptidomimetic core structure led to our identification of several hydrophobic oligopeptides exhibiting similar selectivity and potency as GLUT4 antagonists (11). The unique structural features present in GLUT4 that confer susceptibility to binding and inactivation by indinavir, however, remain unknown.…”

How Sweet It Is? Susceptibility to Diabetes Mellitus in HIV-1 Treatment

“…All PIs acutely reduced insulin-stimulated glucose uptake in adipocytes [48]. Cell culture studies found that PIs reduce GLUT4 trans location independently of insulin signaling pathways [49]. Reduced phosphorylation of the key post receptor insulin signaling pathway signaling molecule MAPK has also been demonstrated [50].…”

Highly Active Antiretroviral Therapy (HAART) and Metabolic Complications

“…Activation of the UPR leading to a decrease in insulin signaling may only be part of the story. Others have shown that PIs can actually inhibit the glucose transporter directly (Hertel et al 2004). It has been proposed that this inhibition induces a starvation-like state in the cell with the decrease of intracellular glucose, causing activation of ER stress.…”