PRMT7 Interacts with ASS1 and Citrullinemia Mutations Disrupt the Interaction

The uncharacterized protein ZNF200 interacts with PRMT3 and aids its stability and nuclear translocation

Protein arginine methyltransferase 3 (PRMT3), a type I arginine methyltransferase is localized predominantly in the cytoplasm and regulates different cellular functions. Nevertheless, PRMT3 also exhibits regulatory functions in the nucleus by interacting with the liver X receptor alpha (LXRα) and catalyzes asymmetric dimethylation modifications at arginine 3 of histone 4 (H4R3me2a). However, very little is known about the regulation of the versatile global regulator PRMT3 and how PRMT3 is translocated to the nucleus. In this study, we identified ZNF200, a hitherto uncharacterized protein, as a potential binding partner of PRMT3 through yeast two-hybrid screening. We confirmed the interaction of PRMT3 with ZNF200 using immunoprecipitation and in vitro pull-down experiments. GST pull-down experiments and molecular docking studies revealed that the N-terminal zinc finger domain of PRMT3 binds to the C-terminal zinc finger regions of ZNF200. Furthermore, the evolutionary conservation of the Znf domain of PRMT3 correlates with the emergence of ZNF200 in mammals. We found that ZNF200 stabilizes PRMT3 by inhibiting its proteasomal degradation. ZNF200, a nuclear-predominant protein, promotes the nuclear translocation of PRMT3, leading to the global increase of H4R3me2a modifications. These findings imply that ZNF200 is a critical regulator of the steady-state levels and nuclear and epigenetic functions of PRMT3.

Identification of Novel Mutations in Chinese Infants With Citrullinemia

Citrullinemia is a rare autosomal recessive disorder characterized by elevated concentrations of citrulline in the blood resulting from malfunction of the urea cycle. It is categorized into two types, types I and II, which are caused by argininosuccinate synthase 1 (ASS1), and citrin (SLC25A13) gene mutations, respectively. In this study, we performed genetic analysis on nine Chinese infants with citrullinemia using next-generation sequencing, which identified a novel mutation (p.Leu313Met) and a rare mutation (p.Thr323Ile, rs1250895424) of ASS1. We also found a novel splicing mutation of SLC25A13: c.1311 + 4_+7del. Functional analysis of the ASS1 missense mutations showed that both significantly impaired the enzyme activity of ASS1, with the p. Thr323Ile mutation clearly affecting the interaction between ASS1 and protein arginine methyltransferase 7 (PRMT7). These findings expand the mutational spectrum of ASS1 and SLC25A13, and further our understanding of the molecular genetic mechanism of citrullinemia in the Chinese population.

Interaction of tau with HNRNPA2B1 and N6-methyladenosine RNA mediates the progression of tauopathy

The microtubule-associated protein tau oligomerizes, but the actions of oligomeric tau (oTau) are unknown. We have used Cry2-based optogenetics to induce tau oligomers (oTau-c). Optical induction of oTau-c elicits tau phosphorylation, aggregation, and a translational stress response that includes stress granules and reduced protein synthesis. Proteomic analysis identifies HNRNPA2B1 as a principle target of oTau-c. The association of HNRNPA2B1 with endogenous oTau was verified in neurons, animal models, and human Alzheimer brain tissues. Mechanistic studies demonstrate that HNRNPA2B1 functions as a linker, connecting oTau with N6-methyladenosine (m6A) modified RNA transcripts. Knockdown of HNRNPA2B1 prevents oTau or oTau-c from associating with m6A or from reducing protein synthesis and reduces oTau-induced neurodegeneration. Levels of m6A and the m6A-oTau-HNRNPA2B1 complex are increased up to 5-fold in the brains of Alzheimer subjects and P301S tau mice. These results reveal a complex containing oTau, HNRNPA2B1, and m6A that contributes to the integrated stress response of oTau.

The ribosomal protein eL21 interacts with the protein lysine methyltransferase SMYD2 and regulates its steady state levels

The protein lysine methyltransferase, SMYD2 is involved in diverse cellular events by regulating protein functions through lysine methylation. Though several substrate proteins of SMYD2 are well-studied, only a limited number of its interaction partners have been identified and characterized. Here, we performed a yeast two-hybrid screening of SMYD2 and found that the ribosomal protein, eL21 could interact with SMYD2. SMYD2-eL21 interaction in the human cells was confirmed by immunoprecipitation methods. In vitro pull-down assays revealed that SMYD2 interacts with eL21 directly through its SET and MYND domain. Computational mapping, followed by experimental studies identified that Lys81 and Lys83 residues of eL21 are important for the SMYD2-eL21 interaction. Evolutionary analysis showed that these residues might have co-evolved with the emergence of SMYD2. We found that eL21 regulates the steady state levels of SMYD2 by promoting its transcription and inhibiting its proteasomal degradation. Importantly, SMYD2-eL21 interaction plays an important role in regulating cell proliferation and its dysregulation might lead to tumorigenesis. Our findings highlight a novel extra-ribosomal function of eL21 on regulating SMYD2 levels and imply that ribosomal proteins might regulate wide range of cellular functions through protein-protein interactions in addition to their core function in translation.

The uncharacterized protein FAM47E interacts with PRMT5 and regulates its functions

Protein arginine methyltransferase 5 (PRMT5) symmetrically dimethylates arginine residues in various proteins affecting diverse cellular processes such as transcriptional regulation, splicing, DNA repair, differentiation, and cell cycle. Elevated levels of PRMT5 are observed in several types of cancers and are associated with poor clinical outcomes, making PRMT5 an important diagnostic marker and/or therapeutic target for cancers. Here, using yeast two-hybrid screening, followed by immunoprecipitation and pull-down assays, we identify a previously uncharacterized protein, FAM47E, as an interaction partner of PRMT5. We report that FAM47E regulates steady-state levels of PRMT5 by affecting its stability through inhibition of its proteasomal degradation. Importantly, FAM47E enhances the chromatin association and histone methylation activity of PRMT5. The PRMT5-FAM47E interaction affects the regulation of PRMT5 target genes expression and colony-forming capacity of the cells. Taken together, we identify FAM47E as a protein regulator of PRMT5, which promotes the functions of this versatile enzyme. These findings imply that disruption of PRMT5-FAM47E interaction by small molecules might be an alternative strategy to attenuate the oncogenic function(s) of PRMT5.

PRMT3 interacts with ALDH1A1 and regulates gene-expression by inhibiting retinoic acid signaling

Protein arginine methyltransferase 3 (PRMT3) regulates protein functions by introducing asymmetric dimethylation marks at the arginine residues in proteins. However, very little is known about the interaction partners of PRMT3 and their functional outcomes. Using yeast-two hybrid screening, we identified Retinal dehydrogenase 1 (ALDH1A1) as a potential interaction partner of PRMT3 and confirmed this interaction using different methods. ALDH1A1 regulates variety of cellular processes by catalyzing the conversion of retinaldehyde to retinoic acid. By molecular docking and site-directed mutagenesis, we identified the specific residues in the catalytic domain of PRMT3 that facilitate interaction with the C-terminal region of ALDH1A1. PRMT3 inhibits the enzymatic activity of ALDH1A1 and negatively regulates the expression of retinoic acid responsive genes in a methyltransferase activity independent manner. Our findings show that in addition to regulating protein functions by introducing methylation modifications, PRMT3 could also regulate global gene expression through protein-protein interactions.

Here, the authors demonstrate that protein arginine methyltransferase 3 (PRMT3) interacts with and inhibits the retinal dehydrogenase ALDH1A1, negatively regulating the expression of retinoic acid responsive genes. This study shows that PRMT3 affects diverse biological processes not only by globally regulating protein function through methylation but also by regulating gene expression.

Hypoxia-induced TGF-β-RBFOX2-ESRP1 axis regulates human MENA alternative splicing and promotes EMT in breast cancer

Hypoxic microenvironment heralds epithelial-mesenchymal transition (EMT), invasion and metastasis in solid tumors. Deregulation of alternative splicing (AS) of several cancer-associated genes has been instrumental in hypoxia-induced EMT. Our study in breast cancer unveils a previously unreported mechanism underlying hypoxia-mediated AS of hMENA, a crucial cytoskeleton remodeler during EMT. We report that the hypoxia-driven depletion of splicing regulator ESRP1 leads to skipping of hMENA exon 11a producing a pro-metastatic isoform, hMENAΔ11a. The transcriptional repression of ESRP1 is mediated by SLUG, which gets stimulated via hypoxia-driven TGF-β signaling. Interestingly, RBFOX2, an otherwise RNA-binding protein, is also found to transcriptionally repress ESRP1 while interacting with SLUG. Similar to SLUG, RBFOX2 gets upregulated under hypoxia via TGF-β signaling. Notably, we found that the exosomal delivery of TGF-β contributes to the elevation of TGF-β signaling under hypoxia. Moreover, our results show that in addition to hMENA, hypoxia-induced TGF-β signaling contributes to global changes in AS of genes associated with EMT. Overall, our findings reveal a new paradigm of hypoxia-driven AS regulation of hMENA and insinuate important implications in therapeutics targeting EMT.

The phenotype of adult versus pediatric patients with inborn errors of metabolism

Until recently, inborn errors of metabolism (IEM) were considered a pediatric specialty, as emphasized by the term "inborn," and the concept of adult onset IEM has only very recently reached the adult medical community. Still, an increasing number of adult onset IEM have now been recognized, as new metabolomics and molecular diagnostic techniques have become available. Here, we discuss possible mechanisms underlying phenotypic variability in adult versus children with IEM. Specifically, phenotypic severity and age of onset are expected to be modulated by differences in residual protein activity possibly driven by various genetic factors. Phenotypic variability may also occur in the context of similar protein expression, which suggests the intervention of environmental, ontogenic, and aging factors.