RNA-binding protein HuR autoregulates its expression by promoting alternative polyadenylation site usage

Abstract

RNA-binding protein HuR modulates the stability and translational efficiency of messenger RNAs (mRNAs) encoding essential components of the cellular proliferation, growth and survival pathways. Consistent with these functions, HuR levels are often elevated in cancer cells and reduced in senescent and quiescent cells. However, the molecular mechanisms that control HuR expression are poorly understood. Here we show that HuR protein autoregulates its abundance through a negative feedback loop that involves interaction of the nuclear HuR protein with a GU-rich element (GRE) overlapping with the HuR major polyadenylation signal (PAS2). An increase in the cellular HuR protein levels stimulates the expression of long HuR mRNA species containing an AU-rich element (ARE) that destabilizes the mRNAs and thus reduces the protein production output. The PAS2 read-through occurs due to a reduced recruitment of the CstF-64 subunit of the pre-mRNA cleavage stimulation factor in the presence of the GRE-bound HuR. We propose that this mechanism maintains HuR homeostasis in proliferating cells. Since only the nuclear HuR is expected to contribute to the auto-regulation, our model may explain the longstanding observation that the increase in the total HuR expression in cancer cells often correlates with the accumulation of its substantial fraction in the cytoplasm.

A recently evolved class of alternative 3′-terminal exons involved in cell cycle regulation by topoisomerase inhibitors

“…5a-c). Consistently, genome-wide mapping of HuR-binding sites revealed its binding to many pre-mRNAs, and HuR can regulate both splicing and polyA site use [37][38][39][40][41][42] . The configuration of HuR-binding sites in CENPN exon 12, with two centrally located strong binding sites and additional (potentially weaker) binding sites along the exon (Supplementary Fig.…”

“…Alternatively, HuR could locally regulate the 3 0 -splice site or the polyA site of exon 12, because one CLIP-seq study found HuR-binding sites in their vicinity ( Supplementary Fig. 6), and HuR can bind or affect the recruitment of splicing and polyadenylation factors to exons and polyA sites, respectively 39,41,42 . HuR dissociation from CENPN pre-mRNA in response to DOXO and CPT is consistent with ARTICLE previous evidence that HuR binding to RNA is affected by DNA damage [45][46][47] .…”

“…The second factor, HuR/ELAVL1, is an RNA-binding protein that has long been involved in the regulation of cytoplasmic mRNA stability and translation in response to DNA damage (reviewed by Gorospe 36 ) and more recently in pre-mRNA splicing and polyA site use in the nucleus [37][38][39][40][41][42] . As expected from the anti-correlation data, the depletion of HuR using a specific siRNA in MCF-7 cells (Fig.…”

Neuroprotection requires the functions of the RNA-binding protein HuR

“…Next, DEGs were compared with interacting mRNAs to reveal 61 Elavl targets misexpressed in HuR lo cells (Supplementary Figure 10c and Supplementary Tables 1 and 2). The Elavl1/HuR mRNA was among those identified validating our approach as it is regulated both by its protein and nElavls 12,35 and has been knocked down in HT-22 cells. To restrict our analyses to putative HuR targets, we examined whether the human homologs of these 61 mRNAs were identified to physically interact with HuR in PAR-CLiP 36,37 assays deposited in the DoRiNA 38 database; based on phenotypic relevance, we selected six such mRNAs.…”

Alternative polyadenylation: New insights from global analyses

“…For example, it was shown that the mammalian PTB and Drosophila sex lethal proteins can modulate PAS recognition by competing with CstF64 for binding to the DSEs (Castelo-Branco et al 2004;Gawande et al 2006). Similarly, recent studies demonstrated that the RNA-binding protein HuR regulates the APA of its own transcripts by competing with CstF64 for binding to one of the alternative PASs, thereby suppressing its usage (Dai et al 2012;Mansfield and Keene 2012). Global analyses revealed that when Nova2, a brain-specific RNA-binding protein, binds to RNAs within the PAS regions, it tends to inhibit the usage of that PAS, possibly by a steric hindrance mechanism (Licatalosi et al 2008).…”