Journal
JOURNAL OF BIOLOGICAL CHEMISTRY
Volume 279, Issue 28, Pages 29066-29074Publisher
AMER SOC BIOCHEMISTRY MOLECULAR BIOLOGY INC
DOI: 10.1074/jbc.M402727200
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Funding
- NIAID NIH HHS [AI 50237, T32 AI0747-7/10] Funding Source: Medline
- NIGMS NIH HHS [GM 59803] Funding Source: Medline
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The cellular response to stress involves a rapid inhibition of cap-dependent translation via multiple mechanisms, yet some translation persists. This residual translation may include proteins critical to the cellular stress response. BCL-2 is a key inhibitor of intrinsic apoptotic signaling. Its primary transcript contains a 1.45-kb 5'-untranslated region (UTR) including 10 upstream AUGs that may restrict translation initiation via cap-dependent ribosome scanning. Thus, we hypothesized that this 5'-UTR may contain an internal ribosome entry site (IRES) that facilitates BCL-2 translation, particularly during cell stress. Here we show that the BCL-2 5'-UTR demonstrated IRES activity both when translated in vitro and also when m(7)G-capped and polyadenylated mRNA was transiently transfected into 293T cells. The activity of this IRES in unstressed cells was similar to6% the strength of the hepatitis C virus IRES but was induced 3-6-fold in a dose-dependent manner following short term treatment with either etoposide or sodium arsenite. Thus, the IRES-mediated translation of BCL-2 may enable the cell to replenish levels of this critical protein during cell stress, when cap-dependent translation is repressed, thereby maintaining the balance between pro-and anti-apoptotic BCL-2 family members in the cell and preventing unwarranted induction of apoptosis.
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