Translational regulation of ribonucleotide reductase by eukaryotic initiation factor 4E links protein synthesis to the control of DNA replication.
Ribonucleotide reductase synthesizes dNDPs, a specific and limiting step in DNA synthesis, and can participate in neoplastic transformation when overexpressed. The small subunit (ribonucleotide reductase 2 (RNR2)) was cloned as a major product in a subtraction library from eukaryotic initiation factor 4E (eIF4E)-transformed cells (Chinese hamster ovary-4E (CHO-4E)). CHO-4E cells have 20-40-fold elevated RNR2 protein, reflecting an increased distribution of RNR2 mRNA to the heavy polysomes. CHO-4E cells display an altered cell cycle with shortened S phase, similar to cells selected for RNR2 overexpression with hydroxyurea. The function of ribonucleotide reductase as a checkpoint component of S progression was studied in yeast in which elevated eIF4E rescued S-arrested rnr2-68(ts) cells, by increasing recruitment of its mRNA to polysomes. Crosses between rnr2-68(ts) and mutant eIF4E (cdc33-1(ts)) engendered conditional synthetic lethality, with extreme sensitivity to hydroxyurea and the microtubule depolymerizing agent, benomyl. The double mutant (cdc33-1 rnr2-68) also identified a unique terminal phenotype, arrested with small bud and a randomly distributed single nucleus, which is distinct from those of both parental single mutants. This phenotype defines eIF4E and RNR2 as determinants in an important cell cycle checkpoint, in early/mid-S phase. These results also provide a link between protein and DNA synthesis and provide an explanation for cell cycle alterations induced by elevated eIF4E.
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Department of Biochemistry, Louisiana State University Medical Center, Shreveport, Louisiana 71130-3932, USA.
Li
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Y
Anthony
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C
De Benedetti
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A
D000818:Animals; D001542:Benomyl / Q000494:pharmacology; D016466:CHO Cells; D002453:Cell Cycle / Q000502:physiology; D003001:Cloning, Molecular; D006224:Cricetinae; D004261:DNA Replication; D039561:Eukaryotic Initiation Factor-4E; D005346:Fibroblast Growth Factors / Q000235:genetics; D005786:Gene Expression Regulation / Q000187:drug effects; D006918:Hydroxyurea / Q000494:pharmacology; D008870:Microtubules / Q000187:drug effects / Q000648:ultrastructure; D009955:Ornithine Decarboxylase / Q000235:genetics; D010448:Peptide Initiation Factors / Q000235:genetics / Q000378:metabolism*; D011132:Polyribosomes / Q000378:metabolism; D014176:Protein Biosynthesis; D012333:RNA, Messenger / Q000235:genetics; D011994:Recombinant Proteins / Q000378:metabolism; D012264:Ribonucleotide Reductases / Q000096:biosynthesis / Q000235:genetics*; D016196:S Phase; D012441:Saccharomyces cerevisiae / Q000235:genetics; D014158:Transcription, Genetic; D014162:Transfection
D039561:Eukaryotic Initiation Factor-4E; D010448:Peptide Initiation Factors; D012333:RNA, Messenger; D011994:Recombinant Proteins; D005346:Fibroblast Growth Factors; D012264:Ribonucleotide Reductases; D009955:Ornithine Decarboxylase; D001542:Benomyl; D006918:Hydroxyurea