Altered L-Arginine Metabolic Pathways in Gastric Cancer: Potential Therapeutic Targets and Biomarkers

There is a pressing need for molecular targets and biomarkers in gastric cancer (GC). We aimed at identifying aberrations in L-arginine metabolism with therapeutic and diagnostic potential. Systemic metabolites were quantified using mass spectrometry in 293 individuals and enzymes’ gene expression was quantified in 29 paired tumor-normal samples using qPCR and referred to cancer pathology and molecular landscape. Patients with cancer or benign disorders had reduced systemic arginine, citrulline, and ornithine and elevated symmetric dimethylarginine and dimethylamine. Citrulline and ornithine depletion was accentuated in metastasizing cancers. Metabolite diagnostic panel had 91% accuracy in detecting cancer and 70% accuracy in differentiating cancer from benign disorders. Gastric tumors had upregulated NOS2 and downregulated ASL, PRMT2, ORNT1, and DDAH1 expression. NOS2 upregulation was less and ASL downregulation was more pronounced in metastatic cancers. Tumor ASL and PRMT2 expression was inversely related to local advancement. Enzyme up- or downregulation was greater or significant solely in cardia subtype. Metabolic reprogramming in GC includes aberrant L-arginine metabolism, reflecting GC subtype and pathology, and is manifested by altered interplay of its intermediates and enzymes. Exploiting L-arginine metabolic pathways for diagnostic and therapeutic purposes is warranted. Functional studies on ASL, PRMT2, and ORNT1 in GC are needed.

Clinicopathological and Prognostic Significance of PRMT5 in Cancers: A System Review and Meta-Analysis

PURPOSE

Since protein arginine methyltransferase 5 (PRMT5) is abnormally expressed in various tumors, in this study we aim to assess the association between PRMT5 and clinicopathological and prognostic features.

METHODS

Electronic databases including PubMed, Web of Science, Scopus, ScienceDirect, and the Cochrane Library were searched until July 25, 2021. The critical appraisal of the eligible studies was performed using the Newcastle-Ottawa Quality Assessment Scale. Pooled hazard ratios (HR) and pooled odds ratios (OR) were calculated to assess the effect. Engauge Digitizer version 12.1, STATA version 15.1, and R version 4.0.5 were used to obtain and analysis the data.

RESULTS

A total of 32 original studies covering 15,583 patients were included. In our data, it indicated that high level of PRMT5 was significantly correlated with advanced tumor stage (OR = 2.12, 95% CI: 1.22-3.70, P =.008; I2 = 80.7%) and positively correlated with poor overall survival (HR = 1.59, 95% CI: 1.46-1.73, P < .001; I2 = 50%) and progression-free survival (HR = 1.53, 95% CI: 1.24-1.88, P < .001; I2 = 0%). In addition, sub-group analysis showed that high level of PRMT5 was associated with poor overall survival for such 5 kinds of cancers as hepatocellular carcinoma, pancreatic cancer, breast cancer, gastric cancer, and lung cancer.

CONCLUSION

For the first time we found PRMT5 was pan-cancerous as a prognostic biomarker and high level of PRMT5 was associated with poor prognosis for certain cancers.

PRMT7 promotes the growth of renal cell carcinoma through modulating the β-catenin/C-MYC axis

Arginine methylation is mainly catalyzed by protein arginine methyltransferases (PRMTs) and is one of the most common posttranslational modifications closely related to the development of cancer. PRMT7 is overexpressed in various tumors and promotes the malignant progression of tumors, but the expression and role of PRMT7 in renal cell carcinoma (RCC) remains unclear. Here, we report for the first time that the expression of PRMT7 is increased in clear cell renal cell carcinoma (ccRCC) tissues and that it may act as an independent predictor for the poor prognosis of ccRCC patients. We found that PRMT7 promotes RCC cell proliferation both in vitro and in vivo. Moreover, the methyltransferase inhibitor adenosine dialdehyde (Adox) blocks the action of PRMT7 in ccRCC cells. Furthermore, PRMT7 regulates the expression of C-MYC, which plays an important role in promoting ccRCC cell proliferation, and it accelerates the tumor development of RCC in a C-MYC-dependent manner. Mechanistically, PRMT7 upregulates the expression of C-MYC via methylating β-catenin and inhibiting the ubiquitin-mediated degradation of β-catenin. In conclusion, our study demonstrates that overexpressed PRMT7 in ccRCC cells acts as an oncogene to promote the growth of renal cell carcinoma through regulating the β-catenin/C-MYC axis, thereby providing new strategies and targets for the treatment of ccRCC patients.

Curcumin ameliorates PRMT5-MEP50 arginine methyltransferase expression by decreasing the Sp1 and NF-YA transcription factors in the A549 and MCF-7 cells

The protein arginine methyltransferase 5 (PRMT5) and its catalytic partner methylosome protein MEP50 (WDR77) catalyse the mono- and symmetric di-methylation of selective arginines in various histones and non-histone target proteins. It has emerged as a crucial epigenetic regulator in cell proliferation and differentiation; which also reported to be overexpressed in many forms of cancers in humans. In this study, we aimed to assess the modulations in the expression of this enzyme upon exposure to the well-studied natural compound from the spice turmeric, curcumin. We exposed the lung and breast cancer cell lines (A549 and MCF-7) to curcumin (2 and 20 μM) and observed a highly significant inhibitory effect on the expression of both PRMT5 and MEP50. The level of symmetrical dimethylarginine (SDMA) in multiple proteins, and more specifically, the H4R3me2s mark (which predominates in GC-rich motifs in nucleosomal DNA) was also diminished significantly. We also found that curcumin significantly reduced the level and enrichment of the transcription factors Sp1 and NF-YA which shares their binding sites within the GC-rich region of the PRMT5 proximal promoter. Furthermore, the involvement of both PKC-p38-ERK-cFos and AKT-mTOR signalling was observed in reducing the Sp1 and NF-YA expression by curcumin. Therefore, we propose curcumin decreased the expression of PRMT5 in these cells by affecting at least these two transcription factors. Altogether, we report a new molecular target of curcumin and further elucidation of this proposed mechanism through which curcumin affects the PRMT5-MEP50 methyltransferase expression might be explored for its therapeutic application.

Differential expression, distinct localization and opposite effect on Golgi structure and cell differentiation by a novel splice variant of human PRMT5

Alternative splicing contributes greatly to the proteomic diversity of metazoans. Protein arginine methyltransferase 5 (PRMT5) methylates arginines of Golgi components and other factors exerting diverse effects on cell growth/differentiation, but the underlying molecular basis for its subcellular distribution and diverse roles has not been fully understood. Here we show the detailed properties of an evolutionarily emerged splice variant of human PRMT5 (PRMT5S) that is distinct from the original isoform (PRMT5L). The isoforms are differentially expressed among mammalian cells and tissues. The PRMT5S is distributed all over the cell but PRMT5L mainly colocalizes with Giantin, a Golgi marker. PRMT5 knockdown led to an enlarged Giantin pattern, which was prevented by the expression of either isoform. Rescuing PRMT5S also increased the percentage of cells with an interphase Giantin pattern compacted at one end of the nucleus, consistent with its cell cycle-arresting effect, while rescuing PRMT5L increased that of the mitotic Giantin patterns of dynamically fragmented structures. Moreover, the isoforms are differentially expressed during neuronal or dendritic cell differentiation, and their ectopic expression showed an opposite effect on dendritic cell differentiation. Furthermore, besides their differential regulation of gene expression, both isoforms also similarly regulate over a thousand genes particularly those involved in apoptosis and differentiation. Taking these properties together, we propose that their differential expression and subcellular localization contribute to spatial and temporal regulation of arginine methylation and gene expression to exert different effects. The novel PRMT5S likely contributes to the observed diverse effects of PRMT5 in cells.

Proliferative role of TRAF4 in breast cancer by upregulating PRMT5 nuclear expression

In this study, we examined protein arginine methyltransferase 5 (PRMT5) and tumor necrosis factor receptor-associated 4 (TRAF4) expression in breast cancer to find the interaction mechanism between the two. We examined TRAF4 and PRMT5 expression by immunohistochemistry and found that their expression is positively correlated in breast cancer. Besides, PRMT5 expression was significantly associated with histological type and tumor size (p < 0.05). PRMT5 nuclear expression was significantly associated with HER2 expression (p < 0.05). PRMT5 and TRAF4 were both overexpressed in breast cancer tissues and cells, and we found that PRMT5 binds to the zinc finger structures in TRAF4 by coimmunoprecipitation and Western blotting. We also tested the potential regulatory effect between TRAF4 and PRMT5. TRAF4 upregulated PRMT5 expression, which occurred predominantly in the nucleus, on which TRAF4 promotion of cell proliferation in breast cancer is mainly dependent. PRMT5 may play an important role in activation of the NF-κB signaling pathway.

Molecular characterisation and inductive expression of a fish protein arginine methyltransferase 1 gene in response to virus infection

Protein arginine methyltransferase 1 (PRMT1) is currently thought as an effector to regulate interferon (IFN) signalling. Here Paralichthys olivaceus PRMT1 (PoPRMT1) gene was identified as a virally induced gene from UV-inactivated Scophthalmus maximus Rhabdovirus (SMRV)-infected flounder embryonic cells (FEC). PoPMRT1 encodes a 341-amino-acid protein that shares the conserved domains including post-I, motif I, II and III. Homology comparisons show that the putative PoPMRT1 protein is the closest to zebrafish PMRT1 and belongs to type I PRMT family (including PRMT1, PRMT2, PRMT3, PRMT4, PRMT6, PRMT8). Expression analyses revealed an extensive distribution of PoPMRT1 in all tested tissues of flounder. In vitro induction of PoPRMT1 was determined in UV-inactivated SMRV-infected FEC cells, and under the same conditions, flounder Mx was also transcriptionally up-regulated, indicating that an IFN response might be triggered. Additionally, live SMRV infection of flounders induced an increased expression of PoPRMT1 mRNA and protein significantly in spleen, and to a lesser extent in head kidney and intestine. Immunofluorescence analysis revealed a major cyptoplasmic distribution of PoPRMT1 in normal FEC but an obvious increase occurred in nucleus in response to UV-inactivated SMRV. This is the first report on in vitro and in vivo expression of fish PRMT1 by virus infection, suggesting that PoPRMT1 might be implicated in flounder antiviral immune response.

Effects of ADMA upon gene expression: an insight into the pathophysiological significance of raised plasma ADMA

BACKGROUND

Asymmetric dimethylarginine (ADMA) is a naturally occurring inhibitor of nitric oxide synthesis that accumulates in a wide range of diseases associated with endothelial dysfunction and enhanced atherosclerosis. Clinical studies implicate plasma ADMA as a major novel cardiovascular risk factor, but the mechanisms by which low concentrations of ADMA produce adverse effects on the cardiovascular system are unclear.

METHODS AND FINDINGS

We treated human coronary artery endothelial cells with pathophysiological concentrations of ADMA and assessed the effects on gene expression using U133A GeneChips (Affymetrix). Changes in several genes, including bone morphogenetic protein 2 inducible kinase (BMP2K), SMA-related protein 5 (Smad5), bone morphogenetic protein receptor 1A, and protein arginine methyltransferase 3 (PRMT3; also known as HRMT1L3), were confirmed by Northern blotting, quantitative PCR, and in some instances Western blotting analysis to detect changes in protein expression. To determine whether these changes also occurred in vivo, tissue from gene deletion mice with raised ADMA levels was examined. More than 50 genes were significantly altered in endothelial cells after treatment with pathophysiological concentrations of ADMA (2 microM). We detected specific patterns of changes that identify pathways involved in processes relevant to cardiovascular risk and pulmonary hypertension. Changes in BMP2K and PRMT3 were confirmed at mRNA and protein levels, in vitro and in vivo.

CONCLUSION

Pathophysiological concentrations of ADMA are sufficient to elicit significant changes in coronary artery endothelial cell gene expression. Changes in bone morphogenetic protein signalling, and in enzymes involved in arginine methylation, may be particularly relevant to understanding the pathophysiological significance of raised ADMA levels. This study identifies the mechanisms by which increased ADMA may contribute to common cardiovascular diseases and thereby indicates possible targets for therapies.

PRMT8, a new membrane-bound tissue-specific member of the protein arginine methyltransferase family

Protein arginine methylation is a common post-translational modification that has been implicated in signal transduction, RNA processing, transcriptional regulation, and DNA repair. A search of the human genome for additional members of the protein arginine N-methyltransferase (PRMT) family of enzymes has identified a gene on chromosome 12 that we have termed PRMT8. This novel enzyme is most closely related to PRMT1, although it has a distinctive N-terminal region. The unique N-terminal end harbors a myristoylation motif, and we have shown here that PRMT8 is indeed modified by the attachment of a myristate to the glycine residue after the initiator methionine. The myristoylation of PRMT8 results in its association with the plasma membrane. The second singular property of PRMT8 is its tissue-specific expression pattern; it is largely expressed in the brain. A glutathione S-transferase fusion protein of PRMT8 has type I PRMT activity, catalyzing the formation of omega-NG-monomethylated and asymmetrically omega-NG,NG-dimethylated arginine residues on a recombinant glycine- and arginine-rich substrate. PRMT8 is thus an active arginine methyltransferase that is membrane-associated and tissue-specific, two firsts for this family of enzymes.

Aberrant expression of CARM1, a transcriptional coactivator of androgen receptor, in the development of prostate carcinoma and androgen-independent status

BACKGROUND

Coactivator-associated arginine methyltransferase 1 (CARM1) is a transcriptional coactivator of the androgen receptor (AR). It is involved in the regulation of the biologic functions of the AR. It remains to be determined whether CARM1 is involved in prostatic carcinogenesis.

METHODS

The expression of CARM1 in normal prostate epithelium, high-grade prostatic intraepithelial neoplasia (PIN), and prostate carcinoma tissue was examined in 66 previously untreated patients with prostate carcinomas, as well as 12 patients with hormone-independent prostate carcinoma, using immunohistochemical methods.

RESULTS

Cell staining was observed in the cytoplasm and the nucleus. In 66 patients without previous hormonal treatment, the percentage of cells that stained positively for CARM1 in benign prostate tissue specimens (mean values: cytoplasm, 23%; nucleus, 16%) was statistically significantly less than the percentage of positively stained cells in PIN (mean values: cytoplasm, 56%; nucleus, 30%; P < 0.001) and in prostatic adenocarcinoma specimens (mean values: cytoplasm, 79%; nucleus, 53%; P < 0.001). The difference between adenocarcinoma and PIN also was statistically significant (P < 0.001). The staining intensity for CARM1 was significantly lower in benign prostate tissue specimens compared with PIN and prostatic adenocarcinoma specimens (P < 0.001). In the 12 patients with androgen-independent prostatic adenocarcinoma, the expression of CARM1 was significantly increased when compared with patients without previous hormonal treatment. Expression of CARM1 was not correlated with age, Gleason score sum, pathologic stage, lymph node metastasis, extraprostatic extension, surgical margin status, vascular invasion, or perineural invasion.

CONCLUSIONS

The authors found that overexpression of CARM1 was involved in the development of prostate carcinoma as well as androgen-independent prostate carcinoma. Since CARM1 is functionally different from most other transcriptional coactivators of the AR, it may serve as a new target for the treatment of hormone-independent prostate carcinoma.

[Effect of eukaryotic expression plasmid DNA methyltransferase gene on methylation status and transcription level of DNA mismatch repair genes in human colon cancer cell line]

OBJECTIVE

To analyze the effect of eukaryotic plasmids containing sense or antisense DNA methyltransferase (Dnmt1) genes on the methylation status and transcription level of DNA mismatch repair (MMR) genes and microsatellite instability (MSI) in human colon cancer cell line.

METHODS

Human colorectal cells of the SW1116 line were cultured. Recombinant plasmids containing sense Dnmt1 (HMT) or antisense Dnmt1 (THM) gene, pCMV-HMT and pCMV-THM, were constructed. Then pCMV-HMT, pCMV-THM, and pcMV blank plasmid were transfected into SW1116 cells respectively by using lipofectAMINE. The expression of Dnmt1 protein was examined by Western blotting. The transcription levels of hMLH1 and hMSH2 genes were detected by using real-time (RT-PCR). The status of methylation in promoters of hMLH1 and hMSH2 genes were examined with methylation specific PCR (MSP). The MSI of DNA in SW1116 cells was evaluated by silver-stained polyacrylamide gel electrophoresis.

RESULTS

Both the expressions of the hMLH1 and hMSH2 gene mRNAs were remarkably decreased in the SW1116-HMT cells in comparison with those in the untransfected cells. The expression of hMSH2 gene mRNA in the SW1116-THM cells was remarkably increased in comparison with that in the untransfected cells. No significant difference in the expressions of the hMLH1 and hMSH2 gene mRNAs was found between the SW1116 cells transfected with blank pCMV and the untransfected SW1116 cells. MSP showed that the methylation level in the regions of hMLH1 and hMSH2 promoters was remarkably increased in the SW1116 cells transfected with sense Dnmtl plasmid. However, in the SW1116 cells the hMSH2 promoter region was changed from partially-methylated into de-methylated, and the hMLH1 promoter region remained non-methylated. MST test showed that extra bands indicating MSI were seen only in the D2S123 groups.

CONCLUSION

Dnmt1 regulates the expression and methylation status of MMR genes and affects MSI in human colon cancer cell line SW1116.

Regulation of myelin basic protein (arginine) methyltransferase by thyroid hormone in myelinogenic cultures of cells dissociated from embryonic mouse brain

The ontogenetic expression of myelin basic protein (arginine) methyltransferase in myelinogenic cultures of cells dissociated from embryonic mouse brain is highly dependent on the presence of thyroid hormone. Restoration of myelin basic protein methyltransferase to normal activities occurred 16 h after the addition of 100 nM L-3,5,3'-triiodothyronine to hypothyroid medium. These data demonstrate that thyroid hormone can regulate a posttranslational event. On the other hand, histone (arginine) methyltransferase has a different temporal activity pattern, which is not coordinated with myelination, and is not influenced by the lack of thyroid hormone. These data, which suggest the existence of two methyltransferases, were substantiated by demonstrating that the total amount of methylation of added myelin basic protein and histone is the same whether they are incubated together or separately. The requirement of thyroid hormone for the expression of the myelin basic protein methyltransferase and not for histone methyltransferase suggests that thyroid hormone preferentially regulates myelin-associated events in these cultures.