SMN1, the causative gene for spinal muscular atrophy (SMA), plays a housekeeping role in the biogenesis of small nuclear RNA ribonucleoproteins. SMN is also present in granular foci along axonal projections of motoneurons, which are the predominant cell type affected in the pathology. These so-called RNA granules mediate the transport of specific mRNAs along neurites and regulate mRNA localization, stability, as well as local translation. Recent work has provided evidence suggesting that SMN may participate in the assembly of RNA granules, but beyond that, the precise nature of its role within these structures remains unclear. Here, we demonstrate that SMN associates with polyribosomes and can repress translation in an in vitro translation system. We further identify the arginine methyltransferase CARM1 as an mRNA that is regulated at the translational level by SMN and find that CARM1 is abnormally up-regulated in spinal cord tissue from SMA mice and in severe type I SMA patient cells. We have previously characterized a novel regulatory pathway in motoneurons involving the SMN-interacting RNA-binding protein HuD and CARM1. Thus, our results suggest the existence of a potential negative feedback loop in this pathway. Importantly, an SMA-causing mutation in the Tudor domain of SMN completely abolished translational repression, a strong indication for the functional significance of this novel SMN activity in the pathology.

KH-type splicing regulatory protein (KSRP) is closely related to chick zipcode-binding protein 2 and rat MARTA1, which are involved in neuronal transport and localization of beta-actin and microtubule-associated protein 2 mRNAs, respectively. KSRP is a multifunctional RNA-binding protein that has been implicated in transcriptional regulation, neuro-specific alternative splicing and mRNA decay. More specifically, KSRP is an essential factor for targeting AU-rich element-containing mRNAs to the exosome. We report here that KSRP is arginine methylated and interacts with the Tudor domain of SMN, the causative gene for spinal muscular atrophy (SMA), in a CARM1 methylation-dependent fashion. These two proteins colocalize in granule-like foci in the neurites of differentiating neuronal cells and the CARM1 methyltransferase is required for normal localization of KSRP in neuronal cells. Strikingly, this interaction is abrogated by naturally-occurring Tudor domain mutations found in human patients affected with severe Type I SMA, a strong indication of its functional significance to the etiology of the disease. We also report for the first time that Q136E and I116F Tudor mutations behave similarly to the previously characterized E134K mutation, and cause loss of Tudor interactions with several cellular methylated proteins. Finally, we show that KSRP is misregulated in the absence of SMN, and this correlated with increased mRNA stability of its mRNA target, p21(cip1/waf1), in spinal cord of mild SMA model mice. Our results suggest SMN can act as a molecular chaperone for methylated proteins involved in RNA metabolism and provide new insights into the pathophysiology of SMA.

Several therapeutic approaches are currently being developed for Duchenne muscular dystrophy (DMD) including upregulating the levels of endogenous utrophin A in dystrophic fibers. Here, we examined the role of post-transcriptional mechanisms in controlling utrophin A expression in skeletal muscle. We show that activation of p38 leads to an increase in utrophin A independently of a transcriptional induction. Rather, p38 controls the levels of utrophin A mRNA by extending the half-life of transcripts via AU-rich elements (AREs). This mechanism critically depends on a decrease in the functional availability of KSRP, an RNA-binding protein known to promote decay of ARE-containing transcripts. In vitro and in vivo binding studies revealed that KSRP interacts with specific AREs located within the utrophin A 3' UTR. Electroporation experiments to knockdown KSRP led to an increase in utrophin A in wild-type and mdx mouse muscles. In pre-clinical studies, treatment of mdx mice with heparin, an activator of p38, causes a pronounced increase in utrophin A in diaphragm muscle fibers. Together, these studies identify a pathway that culminates in the post-transcriptional regulation of utrophin A through increases in mRNA stability. Furthermore, our results constitute proof-of-principle showing that pharmacological activation of p38 may prove beneficial as a novel therapeutic approach for DMD.

Prostate cancer is the leading cancer type diagnosed in American men and is the second leading cancer diagnosed in men worldwide. Although studies have been conducted to investigate the association between prostate cancer and exposure to pesticides and/or farming, the results have been inconsistent. We performed a meta-analysis to summarize the association of farming and prostate cancer. The PubMed database was searched to identify all published case–control studies that evaluated farming as an occupational exposure by questionnaire or interview and prostate cancer. Ten published and two unpublished studies were included in this analysis, yielding 3,978 cases and 7,393 controls. Prostate cancer cases were almost four times more likely to be farmers compared with controls with benign prostate hyperplasia (BPH; meta odds ratio [OR], crude = 3.83, 95% confidence interval [CI] = 1.96–7.48, Q-test p value = .352; two studies); similar results were obtained when non-BPH controls were considered, but with moderate heterogeneity between studies (meta OR crude = 1.38, 95% CI = 1.16–1.64, Q-test p value = .216, I2 = 31% [95% CI = 0–73]; five studies). Reported pesticide exposure was inversely associated with prostate cancer (meta OR crude = 0.68, 95% CI = 0.49–0.96, Q-test p value = .331; four studies), whereas no association with exposure to fertilizers was observed. Our findings confirm that farming is a risk factor for prostate cancer, but this increased risk may not be due to exposure to pesticides.

Several reports have previously highlighted the potential role of miR-206 in the post-transcriptional downregulation of utrophin A in cultured cells. Along those lines, we recently identified K-homology splicing regulator protein (KSRP) as an important negative regulator in the post-transcriptional control of utrophin A in skeletal muscle. We sought to determine whether these two pathways act together to downregulate utrophin A expression in skeletal muscle. Surprisingly, we discovered that miR-206 overexpression in cultured cells and dystrophic muscle fibers causes upregulation of endogenous utrophin A levels. We further show that this upregulation of utrophin A results from the binding of miR-206 to conserved sites located in the 3′-UTR (untranslated region) of KSRP, thus causing the subsequent inhibition of KSRP expression. This miR-206-mediated decrease in KSRP levels leads, in turn, to an increase in the expression of utrophin A due to a reduction in the activity of this destabilizing RNA-binding protein. Our work shows that miR-206 can oscillate between direct repression of utrophin A expression via its 3′-UTR and activation of its expression through decreased availability of KSRP and interactions with AU-rich elements located within the 3′-UTR of utrophin A. Our study thus reveals that two apparent negative post-transcriptional pathways can act distinctively as molecular switches causing repression or activation of utrophin A expression.