Autoregulatory circuit of human rpL3 expression requires hnRNP H1, NPM and KHSRP

Abstract

Alternative pre-mRNA splicing (AS) is a major mechanism that allows proteomic variability in eukaryotic cells. However, many AS events result in mRNAs containing a premature termination codon, which are degraded by nonsense-mediated mRNA decay (NMD) pathway. We have previously demonstrated that human rpL3 autoregulates its expression through the association of AS with NMD. In fact, overexpression of rpL3 promotes downregulation of canonical splicing and upregulation of alternative splicing that produces an NMD-targeted mRNA isoform. The result of these events is a decreased production of rpL3. We have also identified heterogeneous nuclear ribonucleoprotein (hnRNP) H1 as a splicing factor involved in the regulation of rpL3 alternative splicing and identified its regulatory cis-elements within intron 3 transcript. Here, we report that NPM and KHSRP are two newly identified proteins involved in the regulation of rpL3 gene expression via AS-NMD. We demonstrate that hnRNP H1, KHSRP and NPM can be found associated, and present also in ribonucleoproteins (RNPs) including rpL3 and intron 3 RNA in vivo, and describe protein–protein and RNA–protein interactions. Moreover, our data provide an insight on the crucial role of hnRNP H1 in the regulation of the alternative splicing of the rpL3 gene.

Human rpL3 induces G₁/S arrest or apoptosis by modulating p21waf1/cip1 levels in a p53-independent manner

“…22 Furthermore, our previous results demonstrated that NPM is able to interact directly with rpL3, and that this interaction is functional to the regulation of the rpL3 protein levels inside the cells. 24 Data reported in this paper clearly demonstrate that NPM represents a positive regulator of rpL3-mediated transactivation of p21 gene, although it is not a crucial player in this event (Fig. 3).…”

“…To this purpose, a ChIp experiment in condition of mythramycin A (MTM) decay (AS-NMD). 24,25 In this paper, we demonstrate that rpL3 is a positive regulator of p21 expression. We show that rpL3 is able to modulate the protein amounts of p21 through a novel pathway independent from p53 involving Sp1 and NPM.…”

“…We have previously reported a direct protein-protein interaction between rpL3 and NPM and demonstrated that this interaction is functional to the regulation of the rpL3 gene alternative splicing. 24 Here, we explored the possibility that the rpL3-NPM complex was involved in the transactivation of the p21 gene transcription.…”

Regulatory role of rpL3 in cell response to nucleolar stress induced by Act D in tumor cells lacking functional p53

“…25,36 We have previously reported that rpL3-mediated p21 upregulation requires the specific interaction between rpL3 and Sp1. 36 It has been shown that ERK1/2 is involved in p21 dependent G1 cell cycle arrest 37 and that ERK1/2 can phosphorylate Sp1 on Threonines 453 and 739 in vitro and in vivo. 21 These Sp1 phosphorylations were also detected when perifosine induced p21 CIP1 transcription via MEK/ERK.…”

Nutritional control of mRNA isoform expression during developmental arrest and recovery in C. elegans

“…of C. elegans rpl-3 and rpl-32, respectively, which catalyze their own splicing in a post-transcriptional feedback circuit (Vilardell and Warner 1997;Russo et al 2011). Regulation by nonsense-mediated decay is also common (Cuccurese et al 2005).…”