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 ϳ6% 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.

Regulation of humanPTCH1bexpression by different 5' untranslated regioncis-regulatory elements

“…Such genes, having at least 3 CGG repeats within their IRES motifs, include previously mentioned FMR1 gene, jun proto-oncogene (JUN), ornithine decarboxylase 1 (ODC1), B-cell CLL/lymphoma 2 (BCL2), and BCL2-associated athanogene (BAG1). [64][65][66][67][68] Since it was discovered that hypoxic conditions activate the Hh-Gli pathway, and it is already known that several genes are being translated under the hypoxia by IRES-dependent mechanism, we wanted to explore if the putative PTCH1b 5'UTR IRES can be activated by oxygen deprivation condition. 42,69 The increased activity of putative IRES element within the 5'UTR of PTCH1b has been observed in transfected MCF7 cells after exposure to strong hypoxic conditions, while in HEK 293T hypoxia did not increase, in fact decreased, the activity of PTCH1b IRES element.…”

Cell stress modulates the function of splicing regulatory protein RBM4 in translation control

“…For Bcl-2 mRNAs, two sets of the primers were used; one was specific to its IRES region. Indeed, IRES-containing transcripts of Bcl-2 were the major products yielded from promoter P1 in nonneuronal cells, including HEK 293 cells (23). Arsenite treatment induced association of RBM4 and eIF4A with the IRES of Bcl-2 (Fig.…”

“…5D), as reported in ref. 23. Therefore, RBM4 probably modulates IRES-mediated gene expression at the translation level in response to cellular stress.…”

Cytoplasmic Relocalization of Heterogeneous Nuclear Ribonucleoprotein A1 Controls Translation Initiation of Specific mRNAs

“…scripts (Sherrill et al, 2004) (Supplemental Figure S2). In this experiment intact bicistronic mRNAs containing both the RLuc and FLuc open reading frames are targeted by the RLuc siRNA, and therefore the levels of both RLuc and FLuc should be reduced comparably.…”

“…Small interfering RNA (siRNA) oligonucleotides against hnRNP A1 (A1-1: 5Ј-AAGGGAGGAAAUUUUGGAGGC-3Ј [Patry et al, 2003]; A1-2: 5Ј-GCU-CUUCAUUGGAGGGUUG-3Ј [Bonnal et al, 2005]), PTB (PTB-P1: 5Ј-AACU-UCCAUCAUUCCAGAGAA-3Ј [Wollerton et al, 2004); PTB-Bis: 5Ј-AAGCCU-CUUUAUUCUUUUCGG-3Ј), unr (5Ј-AAUGGUACUUCAGCAGCACUG-3Ј), a control siRNA (control: 5Ј-GGUCCGGCUCCCCCAAAUG-3Ј), and an siRNA targeting the RLuc open reading frame (ORF) (5Ј-GGGAUGAAUGGCCU-GAUAUUGA-3Ј [Sherrill et al, 2004]) were synthesized by Eurogentec (Seraing, Belgium). Transfections were performed on 30 -50% confluent cells with a siRNA concentration of 200 nM.…”