Heme responsiveness in vitro is a common feature shared by the eukaryotic initiation factor 2á kinase family
An. R. Acad. Farm
; 72(4): 611-627, oct. 2006. ilus, tab
Article
em En
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| ID: ibc-051855
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RESUMEN
Four distinct eukaryotic initiation factor 2á (eIF2á) kinases phosphorylate eIF2á at Ser-51 and regulate protein synthesis in response to cellular stress conditions. This kinase family includes the hemin-regulated inhibitor (HRI); the doublestranded RNA-dependent kinase (PKR); the GCN2 protein kinase; and the endoplasmic reticulum-resident kinase (PERK). HRI mediates protein synthesis inhibition in heme-deficient reticulocyte lysates. Although HRI contains two putative heme regulatory motifs (HRMs) that are not present in other eIF2á kinases, the significance of these motifs in heme regulation is not clear. In fact, it had been characterized two novel eIF2á kinases from Schizosaccharomyces pombe that lacked any of the HRMs, but were sensitive to heme regulation in vitro. To investigate the importance of different regions in the regulation of HRI by heme, specific HRI mutants were generated, and kinase activities and heme responsiveness were analyzed in vitro. Mutational analysis indicated that the heme regulatory motifs were spread around some regions in the HRI catalytic domain, outside of the HRMs. In accordance with these results, both the autokinase and the eIF2á kinase activities of three distinct eIF2á kinases, including the human PKR, the mouse GCN2 and the Drosophila PERK were inhibited in vitro by hemin. Although the known regulatory mechanisms of these eIF2á kinases are very different, the data reported here indicate that all known eIF2á kinases are regulated in vitro by hemin. This finding provides evidence that hemin represents a regulatory mechanism unique to eIF2á kinases and underscores the role of hemin in the translational regulation of eukaryotic cells
ABSTRACT
Las cuatro eIF2á quinasas eucarióticas fosforilan el residuo Ser-51 de la subunidad alfa del factor de iniciación 2 y regulan la síntesis de proteínas en respuesta a situaciones de estrés celular. Esta familia de proteínas quinasas está formada por el inhibidor regulado por hemina (HRI); la quinasa dependiente de RNA de doble cadena (PKR); la proteína quinasa GCN2 y la quinasa residente en el retículo endoplásmico (PERK). El HRI inhibe la síntesis de proteínas en lisados de reticulocitos de conejo deficientes de hemina. Aunque el HRI contiene dos supuestos motivos reguladores de hemina (HRMs), que no están presentes en las otras eIF2á quinasas, no está claro aún el papel de estos motivos en la regulación por hemina. De hecho, se han caracterizado dos nuevas eIF2á quinasas de Schizosaccharomyces pombe que carecen de dichos HRMs, pero son sensibles a la regulación por hemina in vitro. Un análisis mutacional indicó que los motivos reguladores de hemina estaban dispersos a lo largo del dominio catalítico, fuera de los HRMs. De acuerdo con estos resultados, las actividades autoquinasa y eIF2á quinasa de tres eIF2á quinasas distintas, la PKR humana, la GCN2 de ratón y la PERK de Drosophila, se inhibían por hemina in vitro. Aunque los mecanismos de regulación de todas estas eIF2á quinasas son muy diferentes, nuestros resultados indican que todas las eIF2á quinasas se regulan por hemina in vitro. Este descubrimiento soporta la evidencia de que la hemina representa un mecanismo de regulación específico de las eIF2á quinasas, y subraya su papel en la regulación de la traducción de células eucarióticas
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06-national
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ES
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IBECS
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Animals
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Humans
Idioma:
En
Ano de publicação:
2006
Tipo de documento:
Article