A conserved AU‐rich element in the 3’ untranslated region ofbcl‐2 mRNA is endowed with a destabilizing function that is involved inbcl‐2 down‐regulation during apoptosis

Abstract

The control of mRNA stability is becoming recognized as a crucial point of gene expression regulation. A common element responsible for mRNA decay modulation is the adenine- and uracil-rich element that is found in the 3' untranslated region of numerous mRNAs subjected to fast expression changes in response to various stimuli. Previously we identified a post-transcriptional regulation level for the antiapoptotic bcl-2 gene, which could be involved in t(14;18) lymphoma-associated bcl-2 overexpression. Here we demonstrate that bcl-2 mRNA is endowed with an adenine- and uracil-rich element (ARE) characterized by high evolutionary conservation not only among all chordates examined, but even between chordates and the nematode Caenorhabditis elegans (ced-9 gene). As for other well-established destabilizing AREs, the insertion of the bcl-2 ARE downstream from stable beta-globin mRNA causes an enhanced decay of the beta-globin transcript, which proves its functional role. This possibility is corroborated by the fact that the pathway leading to the modulating activity of bcl-2 ARE is influenced by PKC, since the addition of DAG and TPA markedly attenuated the bcl-2 ARE destabilizing potential. Conversely, it is noteworthy that when C(2)-ceramide is added to the culture medium as the apoptotic agent, the beta-globin transcript harboring the bcl-2 ARE undergoes a dramatic increase in decay. This observation clearly indicates that the destabilizing function of bcl-2 ARE is enhanced by apoptotic stimuli and suggests that this element could be involved in a post-transcriptional mechanism of bcl-2 down-regulation during apoptosis. The half-life of the mRNA of bcl-2 in Jurkat cells is prolonged by PKC stimulation and shortened by C(2)-ceramide addition, strongly supporting the view that bcl-2 mRNA stability plays a physiological role in modulating bcl-2 expression, particularly in its down-regulation during apoptosis. Thus, this element becomes a new candidate for mediating those bcl-2 gene expression changes-from apoptosis-associated down-regulation to tumor-associated overexpression-observed thus far that profoundly influence single cell fate and tissue homeostasis.

Post‐transcriptional regulation of gene expression by degradation of messenger RNAs

“…Consistent with this possibility are previous observations that some AREs are inactive in selected cell lines and that AREs can be differentially regulated in response to particular extracellular stimuli (submitted for publication; Schuler and Cole, 1988;Lindsten et al, 1989;Nair et al, 1994;Schiavone et al, 2000). Several signaling pathways have been implicated in regulating the decay of specific mRNAs.…”

“…The AREs of mammalian cytokines and oncogenes are more highly conserved than sequences in the open reading frames of the transcripts: for example, whereas only 45% sequence homology was found in the coding region between murine and human interleukin-3, the AU-rich domains in the 3 0 -UTR were highly conserved (93%) (Dorssers et al, 1987). A phylogenetic analysis of bcl-2 AREs shows the remarkably high evolutionary conservation of this element through human, mouse, and chicken bcl-2 genes and even by the bcl-2 orthologue in the nematode Caenorhabditis elegans (Schiavone et al, 2000). More recently, a transcript has been identified in yeast whose stability is regulated by its 3 0 UTR ARE and, in a similar manner, by the AREs of mammalian TNFa and c-fos, which suggests conservation of the ARE-mediated decay process from yeast to humans (Vasudevan and Peltz, 2001).…”

The BCL2 major breakpoint region (mbr) regulates gene expression

“…Given its fundamental importance for cellular fate, BCL2 expression is finely tuned by a variety of environmental and endogenous stimuli and regulated at both transcriptional and posttranscriptional levels (Young and Korsmeyer, 1993;Miyashita et al, 1994;Heckman et al, 2000;Schiavone et al, 2000;Wu et al, 2001;Heckman et al, 2002;Donnini et al, 2004). At the transcriptional level the expression of the BCL2 gene is regulated by both positive and negative elements located within both the promoter and coding regions (Chen and Boxer, 1995;Wilson et al, 1996;Perillo et al, 2000;Lang et al, 2005).…”

Identification of Nucleolin as an AU-rich Element Binding Protein Involved in bcl-2 mRNA Stabilization

“…In addition to its importance in cancer development, high bcl-2 expression in hematological tumors is frequently an obstacle to cancer chemotherapy (3,4). Numerous reports describe the effects of anti-cancer and apoptotic agents on the steady state levels of bcl-2 mRNA and Bcl-2 protein (3,(5)(6)(7). For example, taxol induces apoptosis in ovarian cancer cells through a process that involves bcl-2 mRNA destabilization (5).…”