Alternative polyadenylation variants of the RNA binding protein, HuR: abundance, role of AU-rich elements and auto-Regulation

Abstract

The RNA-binding protein, HuR, is involved in the stabilization of AU-rich element-containing mRNAs with products that are involved in cell-cycle progression, cell differentiation and inflammation. We show that there are multiple polyadenylation variants of HuR mRNA that differ in their abundance, using both bioinformatics and experimental approaches. A polyadenylation variant with distal poly(A) signal is a rare transcript that harbors functional AU-rich elements (ARE) in the 3′UTR. A minimal 60-nt region, but not a mutant form, fused to reporter-3′UTR constructs was able to downregulate the reporter activity. The most predominant and alternatively polyadenylated mature transcript does not contain the ARE. HuR itself binds HuR mRNA, and upregulated the activity of reporter from constructs fused with ARE-isoform and the HuR ARE. Wild-type tristetraprolin (TTP), but not the zinc finger mutant TTP, competes for HuR binding and upregulation of HuR mRNA. The study shows that the HuR gene codes for several polyadenylation variants differentially regulated by AU-rich elements, and demonstrates an auto-regulatory role of HuR.

Regulation of CUG-binding Protein 1 (CUGBP1) Binding to Target Transcripts upon T Cell Activation

“…Thus, CUGBP1 may be similar to other RNA-binding proteins in exhibiting autoregulatory behavior and functions as a "regulator of regulators" (33,34). Here we also confirmed the previous reports that CUGBP1 seems to be targeting transcripts that are involved in cellular proliferation and cell death (13,35).…”

IL-1β potently stabilizes IL-6 mRNA in human astrocytes

“…the use of an upstream polyadenylation signal, resulting in a shorter mRNA, could possibly contribute to changes in mRNA stability. This mechanism has been convincingly described for COX-2 [83] and HuR [84]. The human IL-6 gene contains an alternative polyadenylation signal less than 100 bp upstream from the canonical polyadenylation site [85], and alternative polyadenylation would lead to the exclusion of several AU-rich regions in the alternative mRNA species.…”

The role of the 3' untranslated region in post-transcriptional regulation of protein expression in mammalian cells.

“…47,48 Furthermore, competition between TTP and HuR in binding to HuR mRNA may influence HuR overexpression and in turn an increased cytoplasmic localization within several cancers. 49 AU-binding factor 1 (AUF1; formerly known as hnRNP D) is a family of four isoforms produced by alternative splicing of a single pre-mRNA (p37, p40, p42 and p45). 50 These proteins are mostly involved in mRNA degradation, however several cases were described that stabilize ARE-mRNA and enhance translation.…”