Loss of CARM1 is linked to reduced HuR function in replicative senescence

Abstract

BackgroundThe co-activator-associated arginine methyltransferase 1 (CARM1) catalyzes the methylation of HuR. However, the functional impact of this modification is not fully understood. Here, we investigated the influence of HuR methylation by CARM1 upon the turnover of HuR target mRNAs encoding senescence-regulatory proteins.ResultsChanging the methylation status of HuR in HeLa cells by either silencing CARM1 or mutating the major methylation site (R217K) greatly diminished the effect of HuR in regulating the turnover of mRNAs encoding cyclin A, cyclin B1, c-fos, SIRT1, and p16. Although knockdown of CARM1 or HuR individually influenced the expression of cyclin A, cyclin B1, c-fos, SIRT1, and p16, joint knockdown of both CARM1 and HuR did not show further effect. Methylation by CARM1 enhanced the association of HuR with the 3′UTR of p16 mRNA, but not with the 3′UTR of cyclin A, cyclin B1, c-fos, or SIRT1 mRNAs. In senescent human diploid fibroblasts (HDFs), reduced CARM1 was accompanied by reduced HuR methylation. In addition, knockdown of CARM1 or mutation of the major methylation site of HuR in HDF markedly impaired the ability of HuR to regulate the expression of cyclin A, cyclin B1, c-fos, SIRT1, and p16 as well to maintain a proliferative phenotype.ConclusionCARM1 represses replicative senescence by methylating HuR and thereby enhancing HuR’s ability to regulate the turnover of cyclin A, cyclin B1, c-fos, SIRT1, and p16 mRNAs.

Coactivator-Associated Arginine Methyltransferase-1 Function in Alveolar Epithelial Senescence and Elastase-Induced Emphysema Susceptibility

“…These are two of the widely used senescence markers known to increase with aging in several rodent and human tissues and most importantly in alveolar epithelial cells of COPD patients (41,47,48). Moreover, previous studies showed CARM1-dependent posttranslational methylation of HuR enhancing its association with p16 or p21 mRNA and leading to transcript degradation, whereas absence of CARM1 led to transcript stabilization (22,24,49). The impact of CARM1-mediated regulation on senescence was confirmed by increased numbers of β-galactosidase positive alveolar epithelial cells, which was augmented after CSE stimulation demonstrating that CARM1 deficiency could further enhance the senescence induction following injury stimulus in ATII cells.…”

“…Interestingly, CARM1-dependent methylated HuR is reported to stabilize SIRT1 transcript (22,23). Therefore, we investigated whether reduced CARM1 could regulate alveolar epithelial cell senescence in emphysematous lungs by modulating SIRT1.…”

“…It is likely that the SIRT1 alteration in alveolar epithelial cells is being masked by other lung cell types expressing SIRT1. Several authors reported that besides stabilizing SIRT1, CARM1-dependent methylation can also destabilize transcripts of p16, which is a hallmark marker for senescence (22,30,31).…”

“…Moreover, CARM1 also plays a role in regulating cellular senescence via CARM1-dependent methylation of HuR, which stabilizes SIRT1 transcripts (22,23). HuR, an RNA binding protein is specifically methylated by CARM1mainly at Arg 217 of its hinge region (24).…”

Modulation of the cytoplasmic functions of mammalian post-transcriptional regulatory proteins by methylation and acetylation: a key layer of regulation waiting to be uncovered?

“…However, its role in RNA-binding appears complex as methylated ELAVL1 is proposed to concomitantly increase and decrease the stability of some mRNAs (e.g. cyclin A and cyclindependent kinase inhibitor 2A (CDKN2A) respectively) to inhibit replicative senescence [29]. Surprisingly, a role for arginine methylation in the best studied function of ELAVL1 in promoting mRNA translation and stability (i.e.…”