Differential effect of hemin-controlled eIF-2 alpha kinases from mouse erythroleukemia cells on protein synthesis.
Cultured mouse erythroleukemia (MEL) cells can be induced to erythroid differentiation by a variety of chemical agents. This differentiation process is marked by the onset of globin mRNA and hemoglobin synthesis. In rabbit reticulocytes, globin synthesis is regulated by a hemin-controlled translational inhibitor (HCI) which acts via phosphorylation of the alpha subunit of eukaryotic initiation factor 2 (eIF-2). From both uninduced and induced MEL cells, hemin-controlled eIF-2 alpha kinases have been partially purified. They resemble HCI with respect to their chromatographic behaviour and their sensitivity towards physiological concentrations of hemin (5-10 microM). Further purification on phosphocellulose, however, reveals that the eIF-2 alpha kinase from uninduced MEL cells is chromatographically distinct from HCI, whilst the eIF-2 alpha kinase activity from induced MEL cells represents a mixture of the former and the HCI-type eIF-2 alpha kinase. The latter inhibits protein synthesis in a fractionated system from rabbit reticulocytes which is free of, but sensitive to, HCI, whereas the eIF-2 alpha kinase from uninduced MEL cells does not show any inhibitory activity. This observation is supported by the finding that induced MEL cells respond in vivo to iron depletion with a shut-off of protein synthesis (as do rabbit reticulocytes), whilst uninduced MEL cells do not.
Sarre
T F
TF
Institut für Biologie III, Universität Freiburg im Breisgau, Federal Republic of Germany.
Hermann
M
M
Bader
M
M
D000818:Animals; D002460:Cell Line; D005914:Globins / Q000096:biosynthesis; D006418:Heme / Q000031:analogs & derivatives*; D006427:Hemin / Q000494:pharmacology*; D006454:Hemoglobins / Q000096:biosynthesis; D004915:Leukemia, Erythroblastic, Acute / Q000201:enzymology* / Q000235:genetics / Q000378:metabolism; D051379:Mice; D010766:Phosphorylation; D014176:Protein Biosynthesis / Q000187:drug effects; D011494:Protein Kinases / Q000302:isolation & purification / Q000378:metabolism*; D012333:RNA, Messenger / Q000096:biosynthesis; D011817:Rabbits; D012156:Reticulocytes / Q000378:metabolism; D019892:eIF-2 Kinase
D006454:Hemoglobins; D012333:RNA, Messenger; D006418:Heme; D006427:Hemin; D005914:Globins; D011494:Protein Kinases; D019892:eIF-2 Kinase