Abstract
Human Interleukin-3 (IL-3) is a lymphokine member of a class of transiently expressed mRNAs harboring Adenosine/Uridine-Rich Elements (ARE) in their 3' untranslated regions (3'-UTRs). The regulatory effects of AREs are often mediated by specific ARE-binding proteins (ARE-BPs). In this report, we show that the human IL-3 3'-UTR plays a post-transcriptional regulation role in two human transformed cell lines. More specifically, we demonstrate that the hIL-3 3'-UTR represses the translation of a luciferase reporter both in HeLa and Jurkat T-cells. These results also revealed that the hIL-3 3'-UTR-mediated translational repression is exerted by an 83 nt region comprised mainly by AREs and some non-ARE sequences. Moreover, electrophoretic mobility shift assays (EMSAs) and UV-crosslinking analysis show that this hIL-3 ARE-rich region recruits five specific protein complexes, including the ARE-BPs HuR and TIA-1. HuR binding to this ARE-rich region appears to be spatially modulated during T-cell activation. Together, these results suggest that HuR recognizes the ARE-rich region and plays a role in the IL-3 3'-UTR-mediated post-transcriptional control in T-cells.
Highlights
Interleukin-3 (IL-3) is a pleiotropic cytokine that promotes the proliferation, survival and differentiation of multiple hematopoietic cell types [1,2,3]
Upon examination of mRNA steady-state levels of the chimeric reporters by quantitative reverse transcriptase polymerase chain reaction (RT-PCR) assays, we did not observe significant differences in mRNA abundance between the luciferase control, the human IL-3 (hIL-3) 3’ untranslated regions (3’-UTRs) and DNA sequence of similar size (DARE) heterologous reporters (Fig. 1C). These results suggest that the hIL-3 3’-UTR acts as a negative regulator of luciferase expression in HeLa cells and this inhibition is influenced by the Adenosine/UridineRich Elements (ARE)-rich region
We demonstrated that the human IL-3 3’-UTR is involved in translational repression in both HeLa and Jurkat Tcells (Fig. 1)
Summary
Interleukin-3 (IL-3) is a pleiotropic cytokine that promotes the proliferation, survival and differentiation of multiple hematopoietic cell types [1,2,3]. Aberrant expression of IL-3 is associated with angiogenesis, chronic inflammation and cancer [4,5,6,7]. IL-3 is overexpressed in the myelomonocytic leukemia cell line WEHI-3B and in multiple myeloma patients [8,9]. IL-3 over-expression in chronic myelogenous leukemia (CML) patients has been associated with imatinib resistance [10]. While the role of IL-3 in cancer is unclear, accumulating evidence suggests that IL-3 is involved in inflammatory and tumor angiogenesis [7,11]. IL-3 expression is restricted to T-lymphocytes and is regulated at the transcriptional level [12,13]. Adenosine/Uridine-Rich Elements (AREs) present in the 3’-UTR of the murine IL-3 (mIL-3) mRNA play a role in the post-transcriptional regulation of IL-3 during T-cell activation [15]
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