Abrogation of Hyperosmotic Impairment of Insulin Signaling by a Novel Class of 1,2-Dithiole-3-thiones through the Inhibition of S6K1 Activation

Abstract

A previous study from this laboratory showed that oltipraz and synthetic dithiolethiones prevent tumor necrosis factor-␣-induced hepatic insulin resistance via AMP-activated protein kinase-dependent p70S6 kinase (S6K) 1 inhibitory pathway. This study investigated whether oltipraz and a novel class of 1,2-dithiole-3-thiones were capable of preventing insulin resistance induced by hyperosmotic stress, thereby enhancing insulin-dependent signals, and, if so, whether the restoration of insulin signal was mediated with the inhibition of S6K1 activity stimulated by hyperosmotic stress. In HepG2 cells, oltipraz treatment inhibited insulin receptor substrate (IRS) 1 serine phosphorylation, a marker of insulin resistance, induced by sorbitol-, mannitol-, or sodium chloride-induced hyperosmotic stress. Consequently, this allowed cells to restore insulin signals, which was evidenced by decrease in the ratio of serine to tyrosine phosphorylations of IRS1 and increase in the phosphorylations of Akt and glycogen synthase kinase (GSK) 3␤. Hyperosmotic stress markedly activated S6K1; S6K1 activation was completely abolished by oltipraz pretreatment. An experiment using dominant-negative S6K1 supports the essential role of S6K1 in the hyperosmolarity-stimulated phosphorylation of IRS1. Transfection of constitutive active mutant S6K1 eliminated the protective effect of oltipraz on GSK3␤ phosphorylation, indicating that oltipraz restores insulin signaling by inhibiting S6K1 activation. A variety of synthetic 1,2-dithiole-3-thione derivatives also inhibited S6K1 activity and insulin resistance induced by hyperosmotic stress in HepG2 cells. The results of this study demonstrate that a novel class of 1,2-dithiole-3-thiones improve insulin sensitivity under the condition of hyperosmotic stress, which results from the inhibition of S6K1 activation.Insulin is an important regulatory hormone that mediates energy uptake by inhibiting glucose production in liver and by increasing glucose uptake into muscle and fat (Saltiel and Kahn, 2001). Insulin resistance is defined as a profound dysregulation of insulin signaling system and thus represents a state of impaired ability of peripheral tissues to respond to the physiological levels of insulin. Insulin resistance may lead to the development of a variety of metabolic diseases, such as type 2 diabetes, cardiovascular disorders, and liver diseases. In the clinical conditions of diabetes or dehydration, hyperosmotic stress accounts, at least in part, for insulin resistance (Bratusch-Marrain and DeFronzo, 1983;Ennis et al., 1994; Gual et al., 2003a,b). Because inhibition of insulin resistance restores the ability of insulin to suppress hepatic glucose production and to promote glucose uptake in peripheral tissues, pharmaceutical interventions to prevent insulin resistance are of great therapeutic interest.Binding of insulin to the insulin receptor (IR) initiates signaling cascades by activating its receptor tyrosine kinase. Most signals of IR are transmitted through complexes assembled a...

Inhibition of Arachidonic Acid and Iron-Induced Mitochondrial Dysfunction and Apoptosis by Oltipraz and Novel 1,2-Dithiole-3-thione Congeners

“…Insulin receptor substrate 1-mediated signaling is protected by 1,2-dithiole-3-thiones via S6K1 inhibition downstream of AMPK (Bae et al, 2007(Bae et al, , 2008. However, we found that rapamycin, an inhibitor of mTOR-S6K1 activity that induces the dissociation of mTOR-raptor complex by binding FKBP12, has no effect in apoptosis induced by AA ϩ iron (data not shown).…”

“…Oltipraz induces phase II enzymes in vitro and in vivo and increases glucose use against TNF␣ or sorbitol (Wang et al, 1999;Kang et al, 2003;Bae et al, 2007Bae et al, , 2008. In this study, the capacity of oltipraz to restore MMP in cells exposed to AA ϩ iron was examined.…”

“…1,2-Dithiole-3-thione compounds were synthesized at CJ Central Laboratories (Ichon City, Korea) as described previously (Bae et al, 2007(Bae et al, , 2008. MitoSOX was obtained from Molecular Probes (Carlsbad, CA).…”

Model-Based Hypothesis Testing in Biomedicine : How Systems Biology Can Drive the Growth of Scientific Knowledge

“…In Paper II, we looked at an experimental technique known as Dominant Negative (DN) inhibition, which can result in only partial inhibition, and at how one has traditionally interpreted the results of such partial inhibitions [137,138]. Imagine three proteins: A, B, and C. We know protein A activates protein B, but are unsure if A activates protein C, or if it is another unknown protein that is responsible.…”

S6K1 controls pancreatic β cell size independently of intrauterine growth restriction

“…The number of diabetics worldwide is presently 347 million (2), with WHO projecting that diabetes will be become the 7th leading cause of death by 2030 (3), underscoring the need for novel therapies (4). Ribosomal protein (RP) S6 kinase 1 (S6K1), a downstream effector of the mTOR Complex 1 (mTORC1) signaling pathway (5), has emerged as a potential drug target in the treatment of T2DM (6)(7)(8). In earlier studies, we demonstrated that mice deficient for S6K1 are resistant to high-fat diet-induced (HFD-induced) obesity due to increased lipolysis (9) and a lesion in adipogenesis, which we subsequently traced to an impairment in the ability of stem cells to commit to the adipocytic lineage (10).…”