Enhanced translation and increased turnover of c-myc proteins occur during differentiation of murine erythroleukemia cells.
To determine whether regulation of c-myc proteins occurs during the differentiation of murine erythroleukemia cells, we examined c-myc protein synthesis and accumulation throughout dimethyl sulfoxide (DMSO)- or hypoxanthine-induced differentiation. c-myc protein expression exhibited an overall biphasic reduction, with an initial concomitant decrease in c-myc RNA, protein synthesis, and protein accumulation early during the commitment phase. However, as the mRNA and protein levels recovered, c-myc protein synthesis levels dissociated from the levels of c-myc mRNA and protein accumulation. This dissociation appears to result from unusual translational and posttranslational regulation during differentiation. Translational enhancement was suggested by the observation that relatively high levels of c-myc proteins were synthesized from relatively moderate levels of c-myc RNA. This translational enhancement was not observed with c-myb. Under certain culture conditions, we also observed a change in the relative synthesis ratio of the two independently initiated c-myc proteins. Posttranslational regulation was evidenced by a dramatic postcommitment decrease in the accumulated c-myc protein levels despite relatively high levels of c-myc protein synthesis. This decrease corresponded with a twofold increase in the turnover of c-myc proteins. The consequence of this regulation was that the most substantial decrease in c-myc protein accumulation occurred during the postcommitment phase of differentiation. This result supports the hypothesis that the reduction in c-myc at relatively late times is most important for completion of murine erythroleukemia cell terminal differentiation.
Spotts
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GD
Department of Cell Biology, Vanderbilt University School of Medicine, Nashville, Tennessee 37232-2175.
Hann
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SR
D000818:Animals; D015153:Blotting, Western; D002454:Cell Differentiation / Q000187:drug effects; D002460:Cell Line; D004121:Dimethyl Sulfoxide / Q000494:pharmacology; D015870:Gene Expression / Q000187:drug effects; D019271:Hypoxanthine; D007042:Hypoxanthines / Q000494:pharmacology; D007700:Kinetics; D004915:Leukemia, Erythroblastic, Acute; D007942:Leukemia, Experimental; D051379:Mice; D014176:Protein Biosynthesis; D011499:Protein Processing, Post-Translational; D011505:Protein-Tyrosine Kinases / Q000235:genetics; D011518:Proto-Oncogene Proteins / Q000235:genetics* / Q000378:metabolism; D016271:Proto-Oncogene Proteins c-myc; D012333:RNA, Messenger / Q000235:genetics; D012334:RNA, Neoplasm / Q000235:genetics / Q000302:isolation & purification; D013997:Time Factors
D007042:Hypoxanthines; D011518:Proto-Oncogene Proteins; D016271:Proto-Oncogene Proteins c-myc; D012333:RNA, Messenger; D012334:RNA, Neoplasm; D019271:Hypoxanthine; D011505:Protein-Tyrosine Kinases; D004121:Dimethyl Sulfoxide