An Extracellular Domain of the Insulin Receptor β-Subunit with Regulatory Function on Protein-Tyrosine Kinase

Abstract Anti-insulin receptor monoclonal antibody MA-10 inhibits insulin receptor autophosphorylation of purified rat liver insulin receptors without affecting insulin binding (Cordera, R., Andraghetti, G., Gherzi, R., Adezati, L., Montemurro, A., Lauro, R., Goldfine, I. D., and De Pirro, R. (1987) Endocrinology 121, 2007-2010). The effect of MA-10 on insulin receptor autophosphorylation and on two insulin actions (thymidine incorporation into DNA and receptor down-regulation) was investigated in rat hepatoma Fao cells. MA-10 inhibits insulin-stimulated receptor autophosphorylation, thymidine incorporation into DNA, and insulin-induced receptor down-regulation without affecting insulin receptor binding. We show that MA-10 binds to a site of rat insulin receptors different from the insulin binding site in intact Fao cells. Insulin does not inhibit MA-10 binding, and MA-10 does not inhibit insulin binding to rat Fao cells. Moreover, MA-10 binding to down-regulated cells is reduced to the same extent as insulin binding. In rat insulin receptors the MA-10 binding site has been tentatively localized in the extracellular part of the insulin receptor beta-subunit based on the following evidence: (i) MA-10 binds to insulin receptor in intact rat cells; (ii) MA-10 immunoprecipitates isolated insulin receptor beta-subunits labeled with both [35S]methionine and 32P; (iii) MA-10 reacts with rat insulin receptor beta-subunits by the method of immunoblotting, similar to an antipeptide antibody directed against the carboxyl terminus of the insulin receptor beta-subunit. Moreover, MA-10 inhibits autophosphorylation and protein-tyrosine kinase activity of reduced and purified insulin receptor beta-subunits. The finding that MA-10 inhibits insulin-stimulated receptor autophosphorylation and reduces insulin-stimulated thymidine incorporation into DNA and receptor down-regulation suggests that the extracellular part of the insulin receptor beta-subunit plays a role in the regulation of insulin receptor protein-tyrosine kinase activity

KH domains with impaired nucleic acid binding as a tool for functional analysis

In eukaryotes, RNA-binding proteins that contain multiple K homology (KH) domains play a key role in coordinating the different steps of RNA synthesis, metabolism and localization. Understanding how the different KH modules participate in the recognition of the RNA targets is necessary to dissect the way these proteins operate. We have designed a KH mutant with impaired RNA-binding capability for general use in exploring the role of individual KH domains in the combinatorial functional recognition of RNA targets. A double mutation in the hallmark GxxG loop (GxxG-to-GDDG) impairs nucleic acid binding without compromising the stability of the domain. We analysed the impact of the GDDG mutations in individual KH domains on the functional properties of KSRP as a prototype of multiple KH domain-containing proteins. We show how the GDDG mutant can be used to directly link biophysical information on the sequence specificity of the different KH domains of KSRP and their role in mRNA recognition and decay. This work defines a general molecular biology tool for the investigation of the function of individual KH domains in nucleic acid binding proteins

KSRP-PMR1-exosome association determines parathyroid hormone mRNA levels and stability in transfected cells

<p>Abstract</p> <p>Background</p> <p>Parathyroid hormone (PTH) gene expression is regulated post-transcriptionally through the binding of the <it>trans-</it>acting proteins AU rich binding factor 1 (AUF1), Upstream of N-<it>ras </it>(Unr) and KH-type splicing regulatory protein (KSRP) to an AU rich element (ARE) in PTH mRNA 3'-UTR. AUF1 and Unr stabilize PTH mRNA while KSRP, recruiting the exoribonucleolytic complex exosome, promotes PTH mRNA decay.</p> <p>Results</p> <p>PTH mRNA is cleaved by the endoribonuclease polysomal ribonuclease 1 (PMR1) in an ARE-dependent manner. Moreover, PMR1 co-immunoprecipitates with PTH mRNA, the exosome and KSRP. Knock-down of either exosome components or KSRP by siRNAs prevents PMR1-mediated cleavage of PTH mRNA.</p> <p>Conclusion</p> <p>PTH mRNA is a target for the endonuclease PMR1. The PMR1 mediated decrease in PTH mRNA levels involves the PTH mRNA 3'-UTR ARE, KSRP and the exosome. This represents an unanticipated mechanism by which the decay of an ARE-containing mRNA is facilitated by KSRP and is dependent on both the exosome and an endoribonuclease.</p

A cytoplasmic variant of the KH-type splicing regulatory protein serves as a decay-promoting factor for phosphoglycerate kinase 2 mRNA in murine male germ cells

Phosphoglycerate kinase 2 (PGK2) is a germ cell-specific protein whose mRNA is translationally regulated in the mammalian testis. Using RNA affinity chromatography with the 3′-untranslated region (UTR) of Pgk2 mRNA and adult testis extracts, several associated proteins including a novel isoform of the AU-rich element RNA-binding protein and KH-type splicing regulatory protein (KSRP) were identified. KSRP, a protein of ∼75 kDa, is widely expressed in somatic and germ cells where it is primarily nuclear. In addition to the ∼75-kDa KSRP, a ∼52-kD KSRP, t-KSRP, is present in the cytoplasm of a subpopulation of germ cells. t-KSRP binds directly to a 93-nt sequence (designated the F1 region) of the 3′-UTR of the Pgk2 mRNA and destabilizes Pgk2 mRNA constructs in testis extracts and in transfected cells. We conclude that this testicular variant of the multifunctional nucleic acid–binding protein, KSRP, serves as a decay-promoting factor for Pgk2 mRNA in male germ cells

H19 long noncoding RNA controls the mRNA decay promoting function of KSRP

Long noncoding RNAs (lncRNAs) interact with protein factors to regulate different layers of gene expression transcriptionally or posttranscriptionally. Here we report on the functional consequences of the unanticipated interaction of the RNA binding protein K homology-type splicing regulatory protein (KSRP) with the H19 lncRNA (H19). KSRP directly binds to H19 in the cytoplasm of undifferentiated multipotent mesenchymal C2C12 cells, and this interaction favors KSRP-mediated destabilization of labile transcripts such as myogenin. AKT activation induces KSRP dismissal from H19 and, as a consequence, myogenin mRNA is stabilized while KSRP is repurposed to promote maturation of myogenic microRNAs, thus favoring myogenic differentiation. Our data indicate that H19 operates as a molecular scaffold that facilitates effective association of KSRP with myogenin and other labile transcripts, and we propose that H19 works with KSRP to optimize an AKT-regulated posttranscriptional switch that controls myogenic differentiation

KSRP and MicroRNA 145 are negative regulators of lipolysis in white adipose tissue

White adipose tissue (WAT) releases fatty acids from stored triacylglycerol for an energy source. Here, we report that targeted deletion of KH-type splicing regulatory protein (KSRP), an RNA-binding protein that regulates gene expression at multiple levels, enhances lipolysis in epididymal WAT (eWAT) because of the upregulation of genes promoting lipolytic activity. Expression of microRNA 145 (miR-145) is decreased because of impaired primary miR-145 processing in Ksrp-/- eWAT. We show that miR-145 directly targets and represses Foxo1 and Cgi58, activators of lipolytic activity, and forced expression of miR-145 attenuates lipolysis. This study reveals a novel in vivo function of KSRP in controlling adipose lipolysis through posttranscriptional regulation of miR-145 expression

Economic crisis and the construction of a neo-liberal regulatory regime in Korea

A consistent theme of the literature on the ontology of the 1997 South Korean crisis is the key role played by regulatory failures and the growing weakness of the state. This paper seeks to briefly highlight both the insights and the limitations of this approach to understanding the crisis. Having done so, we shall set out the argument that the crisis created an opportunity for reformist Korean élites to advance their longstanding, but previously frustrated, project to create a comprehensive unambiguously neo-liberal regulatory regime. This paper will also seek to highlight the implications of our reading of the development of the Korean political economy for broader debates on economic liberalisation, crisis and the future of the developmental state

PI3K/AKT signaling determines a dynamic switch between distinct KSRP functions favoring skeletal myogenesis

Skeletal myogenesis is orchestrated by distinct regulatory signaling pathways, including PI3K/AKT, that ultimately control muscle gene expression. Recently discovered myogenic micro-RNAs (miRNAs) are deeply implicated in muscle biology. Processing of miRNAs from their primary transcripts is emerging as a major step in the control of miRNA levels and might be well suited to be regulated by extracellular signals. Here we report that the RNA binding protein KSRP is required for the correct processing of primary myogenic miRNAs upon PI3K/AKT activation in myoblasts C2C12 and in the course of injury-induced muscle regeneration, as revealed by Ksrp knock-out mice analysis. PI3K/AKT activation regulates in opposite ways two distinct KSRP functions inhibiting its ability to promote decay of myogenin mRNA and activating its ability to favor maturation of myogenic miRNAs. This dynamic regulatory switch eventually contributes to the activation of the myogenic program

Multi-market firms and export quota: effects of withdrawal of the multi fiber arrangement

The international trade in goods and services is dominated by multi-market firms. A firm’s decision to sell in the domestic market vis-à-vis the foreign market depends on a number of factors including transport costs, price uncertainties and the barriers to trade. We study the effect of a reduction in non-tariff barriers or quotas on the optimal decision of firms to allocate output between the domestic market and the foreign market. We offer a theoretical analysis on how the firms reallocate sales between multiple markets when the exogenous barriers are lifted. We find that the theoretical conjecture might get valid support from the evolving pattern of exports by a large number of textile and apparel manufacturing firms originating in India. Principally, we obtain a condition under which the choice of the firm to operate in multiple markets depends on the relative strengths of how profit at the margin reacts to price uncertainty in one of the markets as compared to the effect of the sales in one market on the price of another. It seems that the withdrawal of the quota since 2005 has led to a greater focus on the domestic market for Indian firms and within the country there has also been an increased concentration of firms. We used the Hirschman-Herfindahl Index to measure if the Indian firms have become more concentrated in terms of sales during the previous two decades. The concentration of firms has unambiguously increased in the last two years