title: BCL-2 translation is mediated via internal ribosome entry during cell stress.
abstract: 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 approximately 6% 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.
authors.affiliation: Department of Molecular Virology and Microbiology, Baylor College of Medicine, Houston, Texas 77030, USA.
authors.forename: Kyle W
authors.initials: KW
authors.lastname: Sherrill
authors.forename: Marshall P
authors.initials: MP
authors.lastname: Byrd
authors.forename: Marc E
authors.initials: ME
authors.lastname: Van Eden
authors.forename: Richard E
authors.initials: RE
authors.lastname: Lloyd
mesh_terms: D020121:5' Untranslated Regions; D000818:Animals; D001483:Base Sequence; D002460:Cell Line; D004249:DNA Damage; D005047:Etoposide / Q000378:metabolism; D017930:Genes, Reporter; D006801:Humans; D008969:Molecular Sequence Data; D009690:Nucleic Acid Conformation; D019384:Nucleic Acid Synthesis Inhibitors / Q000378:metabolism; D011401:Promoter Regions, Genetic; D014176:Protein Biosynthesis; D019253:Proto-Oncogene Proteins c-bcl-2 / Q000235:genetics / Q000378:metabolism*; D012315:RNA Caps; D034622:RNA Interference; D012270:Ribosomes / Q000378:metabolism*
chemical_list: D020121:5' Untranslated Regions; D019384:Nucleic Acid Synthesis Inhibitors; D019253:Proto-Oncogene Proteins c-bcl-2; D012315:RNA Caps; D005047:Etoposide