Posttranscriptional Regulation of the Inflammatory Marker C-Reactive Protein by the RNA-Binding Protein HuR and MicroRNA 637

Abstract

C-reactive protein (CRP), an acute-phase plasma protein, is a major component of inflammatory reactions functioning as a mediator of innate immunity. It has been widely used as a validated clinical biomarker of the inflammatory state in trauma, infection, and age-associated chronic diseases, including cancer and cardiovascular disease (CVD). Despite this, the molecular mechanisms that regulate CRP expression are not well understood. Given that the CRP 3= untranslated region (UTR) is long and AU rich, we hypothesized that CRP may be regulated posttranscriptionally by RNA-binding proteins (RBPs) and by microRNAs. Here, we found that the RBP HuR bound directly to the CRP 3= UTR and affected CRP mRNA levels. Through this interaction, HuR selectively increased CRP mRNA stability and promoted CRP translation. Interestingly, treatment with the age-associated inflammatory cytokine interleukin-6 (IL-6) increased binding of HuR to CRP mRNA, and conversely, HuR was required for IL-6-mediated upregulation of CRP expression. In addition, we identified microRNA 637 (miR-637) as a microRNA that potently inhibited CRP expression in competition with HuR. Taken together, we have uncovered an important posttranscriptional mechanism that modulates the expression of the inflammatory marker CRP, which may be utilized in the development of treatments for inflammatory processes that cause CVD and age-related diseases.I nflammatory processes and their inherent regulatory controls are critical for the immune response to injury and pathogens throughout the life span. However, inflammation has now been identified as an important underlying factor in many chronic diseases, including cardiovascular disease (CVD), diabetes mellitus, cancer, and metabolic disorders. Age itself is a critical factor in the development of the inflammatory state and risk for these conditions. This age-associated inflammatory state, known as inflammaging, is defined as a state of low-grade, sterile inflammation that occurs with age and is characterized by elevations of serum concentrations of proinflammatory cytokines, including interleukin-6 (IL-6) and tumor necrosis factor alpha (TNF-␣), as well as the acute-phase reactant C-reactive protein (CRP) (1). Given the incidence, morbidity, and mortality of inflammation-based chronic disease, proinflammatory molecules, including CRP, are avidly studied.CRP, a pentraxin protein, is an established marker of acutephase reactions (2). It is an important inflammatory biomarker that is influenced by the action of numerous activated cytokines, such as IL-6, IL-1␤, and TNF-␣ (3, 4). It is well established that circulating levels of CRP and IL-6 are correlated in humans (5, 6). CRP has been widely used as a validated clinical biomarker of the inflammatory state and an independent predictor of cardiovascular disease. There is some evidence that CRP is not only a biomarker of cardiovascular and metabolic disease but also a specific risk factor for disease, with some data supporting the idea that CRP is an active participant in ath...

Loss of RNA-binding protein HuR facilitates cellular senescence through posttranscriptional regulation of TIN2 mRNA

“…Cells were transfected with empty vector or Flag-HuR and incubated with 100 μg/ml cycloheximide for 10 min and lysed with polysome extraction buffer containing 20 mM Tris–HCl, pH 7.5, 100 mM KCl, 5 mM MgCl 2 and 0.5% NP-40 as previously described ( 48 ). Cytoplasmic lysates were fractionated by ultracentrifugation through 10–50% linear sucrose gradients and divided into 24 fractions.…”

The Interplay between the RNA Decay and Translation Machinery in Eukaryotes

“…As miRNAmediated regulation is explained in detail in Fabian (2017), we will touch on a few notable RBPs that co-regulate decay and translation via interactions with the 3 0 UTR. As mentioned previously, HuR is a widely studied RBP that promotes both mRNA stabilization as well as translation by preventing the interaction of repressive factors with the mRNA via competition for common binding regions (Lal et al 2004;Kim et al 2015;Liu et al 2015;Blackinton and Keene 2016;Bose et al 2016;Zhang et al 2017). However, several studies have also implicated HuR in destabilization of transcripts through recruitment of other RBPs (Chang et al 2010) and the miRISC complex (Kim et al 2009).…”

Regulation of HuR structure and function by dihydrotanshinone-I

“…HuR regulates cellular responses to differentiation, senescence, inflammatory factors, and immune stimuli by tightly controlling the post-transcriptional fate of specific mRNAs ( 9 – 12 ). Notably, HuR binds to and regulates the half-life of mRNAs and/or the translation of mRNAs encoding key inflammatory cytokines and interleukins, such as tumor necrosis factor-α (TNFα) ( 13 ) and interleukin IL-1β, IL-3 ( 14 ), IL-6 ( 15 ), IL-8, IL-10, IL-4, CXCL1 ( 16 – 18 ), in turn governing the development and maturation of B and T lymphocytes ( 19 , 20 ). HuR is highly expressed in many cancer types, and is believed to promote tumorigenesis by interacting with mRNAs encoding proteins implicated in cell proliferation and survival, angiogenesis, invasion, pharmacoresistance and metastasis ( 21 – 27 ).…”