Overexpression of eukaryotic protein synthesis initiation factor 4E in HeLa cells results in aberrant growth and morphology.
Eukaryotic protein synthesis initiation factor 4E (eIF-4E) is a 25-kDa polypeptide that binds to the 7-methylguanosine-containing cap of mRNA and participates in the transfer of mRNA to the 40S ribosomal subunit, a step that is rate-limiting for protein synthesis under most cellular conditions. eIF-4E is the least abundant of the initiation factors, is present at approximately 10% of molar concentration of mRNA, and thus may serve as a site of regulation for the recruitment of mRNA into polysomes. Previous studies have indicated that phosphorylation of eIF-4E at Ser-53 is correlated with an increased rate of protein synthesis in a variety of systems in vivo and is required for eIF-4E to become bound to the 48S initiation complex. In this study we show that overexpression of eIF-4E in HeLa cells using an episomally replicating, BK virus-based vector leads to an unusual phenotype: cells grow rapidly, forming densely packed, multilayered foci. They progressively form syncytia, some containing as many as six nuclei, and ultimately lyse 1 month after transfection. Some of these properties are reminiscent of oncogenically transformed cells. Cells transfected with the identical vector expressing a variant of eIF-4E, which contains alanine at position 53 and thus cannot be phosphorylated at the major in vivo site, grow normally. Estimations using the Ala-53 variant or a bacterial chloramphenicol acetyltransferase reporter gene in the same vector indicate that the degree of eIF-4E overexpression is 3- to 9-fold more than the endogenous level. These results suggest that eIF-4E may play a key role in cell cycle progression.
De Benedetti
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Department of Biochemistry, University of Kentucky College of Medicine, Lexington 40536.
Rhoads
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D002455:Cell Division; D015500:Chloramphenicol O-Acetyltransferase / Q000235:genetics / Q000378:metabolism; D039561:Eukaryotic Initiation Factor-4E; D005822:Genetic Vectors; D006367:HeLa Cells / Q000166:cytology / Q000378:metabolism; D006801:Humans; D009363:Neoplasm Proteins / Q000096:biosynthesis; D010448:Peptide Initiation Factors / Q000235:genetics* / Q000378:metabolism; D010957:Plasmids; D012694:Serine; D014162:Transfection
D039561:Eukaryotic Initiation Factor-4E; D009363:Neoplasm Proteins; D010448:Peptide Initiation Factors; D012694:Serine; D015500:Chloramphenicol O-Acetyltransferase