Modulation of insulin signal transduction by eutopic overexpression of the receptor-type protein-tyrosine phosphatase LAR.

Abstract

Protein-tyrosine phosphatases (PTPases) regulate insulin signaling by catalyzing the tyrosine dephosphorylation of the insulin receptor and its substrate proteins. Previous studies have implicated a PTPase localized to a cell membrane fraction in the regulation of the insulin receptor in situ. LAR (leukoyte antigen related) is a transmembrane PTPase in insulin-sensitive tissues with in vitro catalytic specificity for the insulin receptor kinase domain. When transfected into Chinese hamster ovary cells overexpressing the human insulin receptor (CHO-hlR), the LAR protein was processed as expected into an 85-kDa subunit containing the transmembrane and cytoplasmic domains. LAR was increased an average of 6-fold in clonal lines of stably transfected cells, and cell fractionation confirmed its localization in the cell membrane. After stimulation with 100 nM insulin, tyrosine phosphorylation of the insulin receptor was decreased by 31% at 1 min (P < 0.01) and by 42% at 10 min (P < 0.01), and that of IRS-1 was decreased by 34% (P < 0.01) at 1 min and by 56% (P < 0.01) at 10 min in the LAR-overexpressing cells compared with empty vector transfectants. LAR overexpression also blocked insulin-stimulated receptor kinase activation as well as thymidine incorporation into DNA. Quantitatively similar results were obtained in populations of CHO-hlR cells transfected transiently by electroporation. In contrast, overexpression of recombinant LAR cytoplasmic domain, detected as a 72-kDa protein in the cell cytosol, did not significantly affect the insulin-stimulated tyrosine phosphorylation of the insulin receptor or IRS-1 (99% and 93% of control at 10 min, respectively). These studies provide the first evidence that increased expression of LAR has negative regulatory effects at a proximal site in the insulin-signaling pathway. Since this effect occurs only when LAR is eutopically expressed at the cell membrane, these data further suggest that LAR requires a transmembrane localization to directly interact with the insulin receptor in situ.

Coordinated action of protein tyrosine phosphatases in insulin signal transduction

“…Consistent with these results, overexpression or antisense suppression studies of LAR showed that this rPTP could negatively regulate IR, IRS‐1 and Shc phosphorylation, as well as the PI3‐kinase and MAPK pathways [35–37]. In CHO‐hIR cells expression of LAR reduced insulin stimulated tyrosine phosphorylation of IR and IRS‐1, as well as DNA synthesis [38]. Importantly, proper membrane localization of LAR seems to be required, as expression of the cytoplasmic domain of LAR alone does not recapitulate these effects.…”

Involvement of protein tyrosine phosphatases and inflammation in hypothalamic insulin resistance associated with ageing: Effect of caloric restriction

“…On the other hand, aged ptp1b null mice present a leaner phenotype than wild type mice and are protected against ageassociated insulin resistance (Gonzalez-Rodriguez et al, 2012), and neuronal-specific PTP1B Knockout mice have reduced weight and adiposity as well as increased physical activity and energy expenditure (Bence et al, 2006). Tyrosine-phosphorylated insulin receptor can also be dephosphorylated by LAR (Hashimoto et al, 1992) which has been shown to be a negative modulator of insulin action implicated in insulin resistance states (Kulas et al, 1995;Zabolotny et al, 2001;Zhang et al, 1996). Nevertheless, other authors observed that the decrease of LAR protein tyrosine phosphatase induces insulin resistance and defects in glucose homeostasis (Mander et al, 2005;Ren et al, 1998).…”

Small molecule inhibitors of dual specificity protein phosphatases

“…For example, tyrosine phosphorylation is a key reaction in the initiation and propagation of insulin action (Myers and White, 1996;White and Kahn, 1994). Thus, PTP1B (Ahmad et al, 1995;Kenner et al, 1996;Kole et al, 1996), LAR (Kulas et al, 1995;Zhang et al, 1996) and PTBa (Lammers et al, 1997;Moller et al, 1995) have been implicated as negative regulators of insulin receptor signaling. Consequently, protein phosphatase inhibitors may have use in the treatment of diabetes and obesity.…”