The mTOR target 4E-BP1 contributes to differential protein expression during normoxia and hypoxia through changes in mRNA translation efficiency.
Hypoxia causes a rapid and sustained inhibition in mRNA translation that is characterized by both a transient phosphorylation of eukaryotic initiation factor 2-alpha (eIF2alpha) and by inhibition of the mRNA cap binding protein eIF4E via activation of two distinct inhibitory proteins, the mammalian target of rapamycin (mTOR) target 4E-BP1 and the eIF4E transporter 4E-T. Although the importance of eIF2alpha phosphorylation during hypoxia has been clearly demonstrated, there is little information on the potential relevance of eIF4E regulation. We generated HeLa cells stably expressing a short hairpin interfering RNA (shRNA) against 4E-BP1 and found that despite efficient knockdown, no significant changes occurred in the overall inhibition of mRNA translation during hypoxia. However, using a proteomics approach we identified seven proteins that were exclusively expressed in the 4E-BP1 knockdown cells during both normoxic and hypoxic conditions. Further investigation of the transcriptional and translational regulation of these genes by quantitative RT-PCR indicated that the loss of 4E-BP1 causes a significant increase in the rate of protein synthesis of S100 calcium-binding protein A4 (S100A4) and transgelin 2. These 4E-BP1 regulated proteins have previously been associated with tumor cell motility, invasion and metastasis and may thus contribute to an adverse tumor phenotype.
Magagnin
Michaël G
MG
Department of Radiation Oncology (Maastro Lab), GROW Research Institute, Maastricht University, Maastricht, The Netherlands.
van den Beucken
Twan
T
Sergeant
Kjell
K
Lambin
Philippe
P
Koritzinsky
Marianne
M
Devreese
Bart
B
Wouters
Bradly G
BG
D048868:Adaptor Proteins, Signal Transducing / Q000235:genetics / Q000378:metabolism*; D018797:Cell Cycle Proteins; D049109:Cell Proliferation; D005786:Gene Expression Regulation; D006367:HeLa Cells; D006801:Humans; D000860:Hypoxia; D008840:Microfilament Proteins / Q000235:genetics; D009124:Muscle Proteins / Q000235:genetics; D009369:Neoplasms / Q000378:metabolism; D010750:Phosphoproteins / Q000235:genetics / Q000378:metabolism*; D014176:Protein Biosynthesis; D022661:RNA, Untranslated / Q000235:genetics; D000071999:S100 Calcium-Binding Protein A4; D009418:S100 Proteins / Q000235:genetics
D048868:Adaptor Proteins, Signal Transducing; D018797:Cell Cycle Proteins; C087000:EIF4EBP1 protein, human; D008840:Microfilament Proteins; D009124:Muscle Proteins; D010750:Phosphoproteins; D022661:RNA, Untranslated; D000071999:S100 Calcium-Binding Protein A4; D009418:S100 Proteins; C051615:transgelin; C077591:S100A4 protein, human