Inhibition of cytohesins by SecinH3 leads to hepatic insulin resistance

Abstract

G proteins are an important class of regulatory switches in all living systems. They are activated by guanine nucleotide exchange factors (GEFs), which facilitate the exchange of GDP for GTP. This activity makes GEFs attractive targets for modulating disease-relevant G-protein-controlled signalling networks. GEF inhibitors are therefore of interest as tools for elucidating the function of these proteins and for therapeutic intervention; however, only one small molecule GEF inhibitor, brefeldin A (BFA), is currently available. Here we used an aptamer displacement screen to identify SecinH3, a small molecule antagonist of cytohesins. The cytohesins are a class of BFA-resistant small GEFs for ADP-ribosylation factors (ARFs), which regulate cytoskeletal organization, integrin activation or integrin signalling. The application of SecinH3 in human liver cells showed that insulin-receptor-complex-associated cytohesins are required for insulin signalling. SecinH3-treated mice show increased expression of gluconeogenic genes, reduced expression of glycolytic, fatty acid and ketone body metabolism genes in the liver, reduced liver glycogen stores, and a compensatory increase in plasma insulin. Thus, cytohesin inhibition results in hepatic insulin resistance. Because insulin resistance is among the earliest pathological changes in type 2 diabetes, our results show the potential of chemical biology for dissecting the molecular pathogenesis of this disease.

The Drosophila Arf1 homologue Arf79F is essential for lamellipodium formation

“…BFA eliminated lamellipodia and Sra1 at the cell cortex in ,84% of cells. Differences in effectiveness between inhibitors is probably due to their mechanism where SecinH3 targets the cytohesin-family of Arf GTPase activators, Steppke in Drosophila (Donaldson and Jackson, 2011;Fuss et al, 2006;Hafner et al, 2006), while BFA forms a ternary complex with Arf1-GDP and Arf GEFs that would sequester class 1 Arf GTPase(s) (Mossessova et al, 2003). To dissect whether the reduction in Sra1 localisation ensues directly from inhibiting Arf or indirectly as a consequence of inhibiting lamellipodia, we uncoupled the two with the actin polymerisation inhibitors latrunculin B (LatB) and cytochalasin (Fig.…”

Luteinizing hormone/chorionic gonadotrophin receptor overexpressed in granulosa cells from polycystic ovary syndrome ovaries is functionally active

“…We and others have shown the involvement of cytohesin2, through ARF6 activation, in agonist-induced internalisation of LHCGR (Hunzicker-Dunn et al, 2002, Kanamarlapudi et al, 2012b. We investigated here whether the chemical inhibitor of cytohesin family of ARF GEFs, secinH3 (Hafner et al, 2006), inhibits LHCGR internalisation and thereby increases cAMP production in GCs (Figure 4B). SecinH3, but not BFA (which inhibits the activation of ARFs1-5 but not ARF6), caused significant increase in HCG-induced cAMP levels in both groups, suggesting that there are no alterations in LHCGR internalisation in PCOS GCs.…”

“…The activation of ARFs1-5, but not ARF6, is inhibited by the fungal toxin brefeldinA (BFA). However, ARF6 activation by the cytohesin family of ARF GEFs is inhibited by a chemical inhibitor secinH3 (Hafner et al, 2006).…”

Arf6 regulates tumour angiogenesis and growth through HGF-induced endothelial β1 integrin recycling

“…14a), the latter of which is widely used as a model cell for physiological studies of endothelial cells. To examine whether the cytohesins function upstream of Arf6 in the HGF/cMet-dependent b1 integrin recycling signalling pathway, SecinH3, a cytohesin family-specific inhibitor 38 , was used. SecinH3 significantly inhibited HGF-dependent Arf6 activation and the increase of surface b1 integrin level in control iECs ( Fig.…”