Oxidant stress stimulates phosphorylation of eIF4E without an effect on global protein synthesis in smooth muscle cells. Lack of evidence for a role of H202 in angiotensin II-induced hypertrophy.
Reactive oxygen species (ROS) are implicated in the pathogenesis of several proliferative diseases, including atherosclerosis and cancer. Eukaryotic translation initiation factor 4E (eIF4E) plays an important role in cell proliferation and differentiation. To gain insight into molecular mechanisms by which ROS influence the pathogenesis of these diseases, I have studied the effect of H(2)O(2), a ROS, on eIF4E phosphorylation. H(2)O(2) induced eIF4E phosphorylation in a dose- and time-dependent manner in growth-arrested smooth muscle cells (SMC). H(2)O(2)-induced eIF4E phosphorylation occurred on serine residues. PD098059, a specific inhibitor of mitogen-activated protein kinase (MAPK)/extracellular signal-regulated kinase (ERK) kinase inhibited ERK activities but had no significant effect on eIF4E phosphorylation induced by H(2)O(2). Similarly, SB203580, a specific inhibitor of p38 MAPK, although inhibiting H(2)O(2)-induced p38 MAPK activity, had no effect on H(2)O(2)-induced eIF4E phosphorylation. Calphostin C, a specific inhibitor of protein kinase C, also had no effect on H(2)O(2)-induced eIF4E phosphorylation. In contrast, trifluoperazine, an antagonist of calcium/calmodulin kinases, completely blocked H(2)O(2)-induced eIF4E phosphorylation. In addition, intracellular and extracellular Ca(2+) chelators significantly inhibited H(2)O(2)-induced eIF4E phosphorylation. Despite its ability to induce eIF4E phosphorylation, H(2)O(2) had no significant effect on protein levels and new protein synthesis as compared with control. In contrast, it induced the expression of c-Fos, c-Jun, and HSP70 in a time-dependent manner in SMC. Together, these results suggest that H(2)O(2), a ROS and a cellular oxidant, induces eIF4E phosphorylation in a manner that is dependent on Ca(2+) and Ca(2+)/calmodulin kinases and independent of ERKs, p38 MAPK, and protein kinase C. These results also suggest that enhanced eIF4E phosphorylation by H(2)O(2) appears to be an important event in SMC in response to oxidant stress and that eIF4E phosphorylation may be associated with the translation of a small subset of mRNAs such as c-fos, c-jun, and HSP70 gene mRNAs, whose products may have a critical role in cell survival.
Rao
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Department of Anatomy and Neurosciences, University of Texas Medical Branch, Galveston, Texas 77555, USA. grao@utmb.edu
D000818:Animals; D039561:Eukaryotic Initiation Factor-4E; D018840:HSP70 Heat-Shock Proteins / Q000235:genetics; D008297:Male; D009124:Muscle Proteins / Q000096:biosynthesis*; D018384:Oxidative Stress; D010448:Peptide Initiation Factors / Q000378:metabolism*; D010766:Phosphorylation; D014176:Protein Biosynthesis; D016760:Proto-Oncogene Proteins c-fos / Q000235:genetics; D016755:Proto-Oncogene Proteins c-jun / Q000235:genetics; D012333:RNA, Messenger / Q000235:genetics; D051381:Rats; D017207:Rats, Sprague-Dawley
D039561:Eukaryotic Initiation Factor-4E; D018840:HSP70 Heat-Shock Proteins; D009124:Muscle Proteins; D010448:Peptide Initiation Factors; D016760:Proto-Oncogene Proteins c-fos; D016755:Proto-Oncogene Proteins c-jun; D012333:RNA, Messenger