Depletion of eIF2·GTP·Met-tRNAi translation initiation complex up-regulates BRCA1 expression in vitro and in vivo

Role of symmetry in 3,3-diphenyl-1,3-dihydroindol-2-one derivatives as inhibitors of translation initiation

The ternary complex (eIF2·GTP·Met-tRNAiMet) and the eIF4F complex assembly are two major regulatory steps in the eukaryotic translation initiation. Inhibition of the ternary complex assembly is therefore a promising target for the development of novel anti-cancer therapeutics. Building on the finding that clotrimazole (CLT), a molecular probe that depletes intracellular Ca2+ stores and subsequently induce eIF2α phosphorylation, inhibit translation initiation, and reduce preferentially the expression of oncoproteins over "housekeeping" ones,1-3 we undertook structure activity relationship (SAR) studies that identified 3,3-diarylindoline-2-one #1181 as an interesting scaffold. Compound #1181 also induce phosphorylation of eIF2α thereby reducing the availability of the ternary complex, which leads to inhibition of translation initiation.4 Our subsequent efforts focused on understanding SAR iterative lead optimization to enhance potency and improve bioavailability. Herein, we report a complementing study focusing on heavily substituted symmetric and asymmetric 3,3-(o,m-disubstituted)diarylindoline-2-ones. These compounds were evaluated by the dual luciferase reporter ternary complex assay that recapitualates phosphorylation of eIF2α in a quantitative manner. We also evaluated all compounds by sulforhodamine B assay, which measures the overall effect of compounds on cell proliferations and/or viability.

The role of upstream open reading frames in translation regulation in the apicomplexan parasites Plasmodium falciparum and Toxoplasma gondii

During their complex life cycles, the Apicomplexan parasites Plasmodium falciparum and Toxoplasma gondii employ several layers of regulation of their gene expression. One such layer is mediated at the level of translation through upstream open reading frames (uORFs). As uORFs are found in the upstream regions of a majority of transcripts in both the parasites, it is essential that their roles in translational regulation be appreciated to a greater extent. This review provides a comprehensive summary of studies that show uORF-mediated gene regulation in these parasites and highlights examples of clinically and physiologically relevant genes, including var2csa in P. falciparum, and ApiAT1 in T. gondii, that exhibit uORF-mediated regulation. In addition to these examples, several studies that use bioinformatics, transcriptomics, proteomics and ribosome profiling also indicate the possibility of widespread translational regulation by uORFs. Further analysis of these genome-wide datasets, taking into account uORFs associated with each gene, will reveal novel genes involved in key biological pathways such as cell-cycle progression, stress-response and pathogenicity. The cumulative evidence from studies presented in this review suggests that uORFs will play crucial roles in regulating gene expression during clinical disease caused by these important human pathogens.

New activators of eIF2α Kinase Heme-Regulated Inhibitor (HRI) with improved biophysical properties

Heme-regulated inhibitor (HRI), a eukaryotic translation initiation factor 2 alpha (eIF2α) kinase, is critically important for coupling protein synthesis to heme availability in reticulocytes and adaptation to various environmental stressors in all cells. HRI modifies the severity of several hemoglobin misfolding disorders including β-thalassemia. Small molecule activators of HRI are essential for studying normal- and patho-biology of this kinase as well as for the treatment of various human disorders for which activation of HRI or phosphorylation of eIF2α may be beneficial. We previously reported development of 1-((1,4-trans)-4-aryloxycyclohexyl)-3-arylureas (cHAUs) as specific HRI activators and demonstrated their potential as molecular probes for studying HRI biology and as lead compounds for treatment of various human disorders. To develop more druglike cHAUs for in vivo studies and drug development and to expand the chemical space, we undertook bioassay guided structure-activity relationship studies replacing cyclohexyl ring with various 4-6-membered rings and explored further substitutions on the N-phenyl ring. We tested all analogs in the surrogate eIF2α phosphorylation and cell proliferation assays, and a subset of analogs in secondary mechanistic assays that included endogenous eIF2α phosphorylation and expression of C/EBP homologous protein (CHOP), a downstream effector. Finally, we determined specificity of these compounds for HRI by testing their anti-proliferative activity in cells transfected with siRNA targeting HRI or mock. These compounds have significantly improved cLogPs with no loss of potencies, making them excellent candidates for lead optimization for development of investigational new drugs that potently and specifically activate HRI.

The eIF2-alpha kinase HRI: a potential target beyond the red blood cell

INTRODUCTION

The eIF2α kinase heme-regulated inhibitor (HRI) is one of four well-described kinases that phosphorylate eIF2α in response to various cell stressors, resulting in reduced ternary complex formation and attenuation of mRNA translation. Although HRI is well known for its role as a heme sensor in erythroid progenitors, pharmacologic activation of HRI has been demonstrated to have anti-cancer activity across a wide range of tumor sub-types. Here, the potential of HRI activators as novel cancer therapeutics is explored. Areas covered: We provide an introduction to eIF2 signaling pathways in general, and specifically review data on the eIF2α kinase HRI in erythroid and non-erythroid cells. We review aspects of targeting eIF2 signaling in cancer and highlight promising data using HRI activators against tumor cells. Expert opinion: Pharmacologic activation of HRI inhibits tumor growth as a single agent without appreciable toxicity in vivo. The ability of HRI activators to provide direct and sustained eIF2α phosphorylation without inducing oxidative stress or broad eIF2α kinase activation may be especially advantageous for tolerability. Combination therapy with established therapeutics may further augment anti-cancer activity to overcome disease resistance.

Development of 1-((1,4-trans)-4-Aryloxycyclohexyl)-3-arylurea Activators of Heme-Regulated Inhibitor as Selective Activators of the Eukaryotic Initiation Factor 2 Alpha (eIF2α) Phosphorylation Arm of the Integrated Endoplasmic Reticulum Stress Response

Heme-regulated inhibitor (HRI), an eukaryotic translation initiation factor 2 alpha (eIF2α) kinase, plays critical roles in cell proliferation, differentiation, adaptation to stress, and hemoglobin disorders. HRI phosphorylates eIF2α, which couples cellular signals, including endoplasmic reticulum (ER) stress, to translation. We previously identified 1,3-diarylureas and 1-((1,4-trans)-4-aryloxycyclohexyl)-3-arylureas (cHAUs) as specific activators of HRI that trigger the eIF2α phosphorylation arm of ER stress response as molecular probes for studying HRI biology and its potential as a druggable target. To develop drug-like cHAUs needed for in vivo studies, we undertook bioassay-guided structure-activity relationship studies and tested them in the surrogate eIF2α phosphorylation and cell proliferation assays. We further evaluated some of these cHAUs in endogenous eIF2α phosphorylation and in the expression of the transcription factor C/EBP homologous protein (CHOP) and its mRNA, demonstrating significantly improved solubility and/or potencies. These cHAUs are excellent candidates for lead optimization for development of investigational new drugs that potently and specifically activate HRI.

Identification and proteomic analysis of osteoblast-derived exosomes

Exosomes are nanometer-sized vesicles with the function of intercellular communication, and they are released by various cell types. To reveal the knowledge about the exosomes from osteoblast, and explore the potential functions of osteogenesis, we isolated microvesicles from supernatants of mouse Mc3t3 by ultracentrifugation, characterized exosomes by electron microscopy and immunoblotting and presented the protein profile by proteomic analysis. The result demonstrated that microvesicles were between 30 and 100 nm in diameter, round shape with cup-like concavity and expressed exosomal marker tumor susceptibility gene (TSG) 101 and flotillin (Flot) 1. We identified a total number of 1069 proteins among which 786 proteins overlap with ExoCarta database. Gene Oncology analysis indicated that exosomes mostly derived from plasma membrane and mainly involved in protein localization and intracellular signaling. The Ingenuity Pathway Analysis showed pathways are mostly involved in exosome biogenesis, formation, uptake and osteogenesis. Among the pathways, eukaryotic initiation factor 2 pathways played an important role in osteogenesis. Our study identified osteoblast-derived exosomes, unveiled the content of them, presented potential osteogenesis-related proteins and pathways and provided a rich proteomics data resource that will be valuable for further studies of the functions of individual proteins in bone diseases.