SRSF3 and HNRNPH1 Regulate Radiation-Induced Alternative Splicing of Protein Arginine Methyltransferase 5 in Hepatocellular Carcinoma

Tumor-promoting effect and tumor immunity of SRSFs

Serine/arginine-rich splicing factors (SRSFs) are a family of 12 RNA-binding proteins crucial for the precursor messenger RNA (pre-mRNA) splicing. SRSFs are involved in RNA metabolism events such as transcription, translation, and nonsense decay during the shuttle between the nucleus and cytoplasm, which are important components of genome diversity and cell viability. SRs recognize splicing elements on pre-mRNA and recruit the spliceosome to regulate splicing. In tumors, aberrant expression of SRSFs leads to aberrant splicing of RNA, affecting the proliferation, migration, and anti-apoptotic ability of tumor cells, highlighting the therapeutic potential of targeted SRSFs for the treatment of diseases. The body's immune system is closely related to the occurrence and development of tumor, and SRSFs can affect the function of immune cells in the tumor microenvironment by regulating the alternative splicing of tumor immune-related genes. We review the important role of SRSFs-induced aberrant gene expression in a variety of tumors and the immune system, and prospect the application of SRSFs in tumor. We hope that this review will inform future treatment of the disease.

MACC1 enhances an oncogenic RNA splicing of IRAK1 through interacting with HNRNPH1 in lung adenocarcinoma

Dysregulation of alternative pre-mRNA splicing plays a critical role in the progression of cancers, yet the underlying molecular mechanisms remain largely unknown. It is reported that metastasis-associated in colon cancer 1 (MACC1) is a novel prognostic and predictive marker in many types of cancers, including lung adenocarcinoma. Here, we reveal that the oncogene MACC1 specifically drives the progression of lung adenocarcinoma through its control over cancer-related splicing events. MACC1 depletion inhibits lung adenocarcinoma progression through triggering IRAK1 from its long isoform, IRAK1-L, to the shorter isoform, IRAK1-S. Mechanistically, MACC1 interacts with splicing factor HNRNPH1 to prevent the production of the short isoform of IRAK1 mRNA. Specifically, the interaction between MACC1 and HNRNPH1 relies on the involvement of MACC1's SH3 domain and HNRNPH1's GYR domain. Further, HNRNPH1 can interact with the pre-mRNA segment (comprising exon 11) of IRAK1, thereby bridging MACC1's regulation of IRAK1 splicing. Our research not only sheds light on the abnormal splicing regulation in cancer but also uncovers a hitherto unknown function of MACC1 in tumor progression, thereby presenting a novel potential therapeutic target for clinical treatment.

HNRNPH1 stabilizes FLOT2 mRNA in a non-canonical m6A-dependent manner to promote malignant progression in nasopharyngeal carcinoma

PURPOSE

The mechanism underlying the upregulation of FLOT2 in tumors, especially its regulatory mechanism at the RNA level, remains unclear. The purpose of this study is to investigate the regulatory mechanism of FLOT2 upregulation in tumors, particularly at the RNA level, and its role in nasopharyngeal carcinoma (NPC) progression.

METHODS

We identified the role of HNRNPH1 in maintaining FLOT2 mRNA stability and its dependency on the m6A modification. We explored the interaction between HNRNPH1 and METTL14, a key enzyme in m6A modification, and its impact on FLOT2 mRNA stability. We also assessed the expression levels of HNRNPH1 and METTL14 in NPC and their correlation with patient malignancy and prognosis. Experimental approaches included in vitro and in vivo assays to study the effects of HNRNPH1 knockdown on NPC cell proliferation and invasion.

RESULTS

HNRNPH1 is highly expressed in NPC and stabilizes FLOT2 mRNA through an m6A-dependent mechanism. HNRNPH1 interacts with METTL14 to prevent its degradation by STUB1 E3 ligases, leading to increased m6A modification of FLOT2 by METTL14. Additionally, IGF2BP3 was shown to recognize the m6A modification on FLOT2 mRNA, further stabilizing it. High expression of HNRNPH1 and METTL14 were observed in NPC and were positively associated with increased malignancy and poorer patient outcomes. HNRNPH1 knockdown significantly reduced the proliferation and invasive capabilities of NPC cells. Restoration of METTL14 in HNRNPH1-depleted cells could rescue FLOT2 expression and the malignant phenotype, but this effect was negated by the knockdown of FLOT2.

CONCLUSION

Our study elucidates a novel mechanism where HNRNPH1 and METTL14 work together to maintain the stability of FLOT2 mRNA, thereby promoting NPC progression. Targeting this pathway presents a promising therapeutic strategy for the treatment of NPC.

PPM1G and its diagnostic, prognostic and therapeutic potential in HCC (Review)

Global statistics indicate that hepatocellular carcinoma (HCC) is the sixth most common cancer and the third leading cause of cancer‑related death. Protein phosphatase Mg2+/Mn2+ dependent 1G (PPM1G, also termed PP2Cγ) is one of the 17 members of the PPM family. The enzymatic activity of PPM1G is highly reliant on Mg2+ or Mn2+ and serves as a dephosphorylation regulator for numerous key proteins. PPM1G, functioning as a phosphatase, is involved in a number of significant biological processes such as the regulation of eukaryotic gene expression, DNA damage response, cell cycle and apoptosis, cell migration ability, cell survival and embryonic nervous system development. Additionally, PPM1G serves a role in regulating various signaling pathways. In recent years, further research has increasingly highlighted PPM1G as an oncogene in HCC. A high expression level of PPM1G is closely associated with the occurrence, progression and poor prognosis of HCC, offering notable diagnostic and therapeutic value for this patient population. In the present review, the regulatory role of PPM1G in diverse biological processes and signaling pathway activation in eukaryotes is evaluated. Furthermore, its potential application as a biomarker in the diagnosis and prognosis evaluation of HCC is assessed, and future prospects for HCC treatment strategies centered on PPM1G are discussed.

METTL3-Mediated LINC00475 Alternative Splicing Promotes Glioma Progression by Inducing Mitochondrial Fission

Mitochondrial fission promotes glioma progression. The function and regulation mechanisms of lncRNAs in glioma mitochondrial fission are unclear. The expression of LINC00475 and its correlation with clinical parameters in glioma were analyzed using bioinformatics. Then, in vitro and in vivo assays were performed to explore the function of spliced variant LINC00475 (LINC00475-S) in gliomas. To explore the mechanisms, RNA-seq, MeRIP, RIP, pulldown-IP, dCas9-ALKBH5 editing system, LC/MS, and Western blotting were utilized. LINC00475 was confirmed to be overexpressed and with higher frequencies of AS events in gliomas compared to normal brain tissue and was associated with worse prognosis. In vitro and animal tumor formation experiments demonstrated that the effect of LINC00475-S on proliferation, metastasis, autophagy, and mitochondrial fission of glioma cells was significantly stronger than that of LINC00475. Mechanistically, METTL3 induced the generation of LINC00475-S by splicing LINC00475 through m6A modification and subsequently promotes mitochondrial fission in glioma cells by inhibiting the expression of MIF. Pull-down combined LC/MS and RIP assays identified that the m6A recognition protein HNRNPH1 bound to LINC00475 within GYR and GY domains and promoted LINC00475 splicing. METTL3 facilitated HNRNPH1 binding to LINC00475 in an m6A-dependent manner, thereby inducing generation of LINC00475-S. METTL3 facilitated HNRNPH1-mediated AS of LINC00475, which promoted glioma progression by inducing mitochondrial fission. Targeting AS of LINC00475 and m6A editing could serve as a therapeutic strategy against gliomas.

Alternative splicing and related RNA binding proteins in human health and disease

Alternative splicing (AS) serves as a pivotal mechanism in transcriptional regulation, engendering transcript diversity, and modifications in protein structure and functionality. Across varying tissues, developmental stages, or under specific conditions, AS gives rise to distinct splice isoforms. This implies that these isoforms possess unique temporal and spatial roles, thereby associating AS with standard biological activities and diseases. Among these, AS-related RNA-binding proteins (RBPs) play an instrumental role in regulating alternative splicing events. Under physiological conditions, the diversity of proteins mediated by AS influences the structure, function, interaction, and localization of proteins, thereby participating in the differentiation and development of an array of tissues and organs. Under pathological conditions, alterations in AS are linked with various diseases, particularly cancer. These changes can lead to modifications in gene splicing patterns, culminating in changes or loss of protein functionality. For instance, in cancer, abnormalities in AS and RBPs may result in aberrant expression of cancer-associated genes, thereby promoting the onset and progression of tumors. AS and RBPs are also associated with numerous neurodegenerative diseases and autoimmune diseases. Consequently, the study of AS across different tissues holds significant value. This review provides a detailed account of the recent advancements in the study of alternative splicing and AS-related RNA-binding proteins in tissue development and diseases, which aids in deepening the understanding of gene expression complexity and offers new insights and methodologies for precision medicine.

Alternative splicing: a bridge connecting NAFLD and HCC

Non-alcoholic fatty liver disease (NAFLD) is becoming the most important risk factor for hepatocellular carcinoma (HCC). Understanding the progression of benign diseases to HCC is crucial for early prevention and reversal of malignant transformation. Alternative splicing (AS) of RNA plays a role in the pathogenicity, initiation, and transformation of liver disease. We summarize the changes or mutations in the activity of splicing factors in NAFLD and HCC, as well as the impact of AS mediated by epigenetic modifications such as DNA methylation, RNA methylation, histone modification, and protein phosphorylation on liver cell fate. We also summarize therapeutic methods and drugs that are helpful for treating NAFLD, HCC, and the early stages of NAFLD progression to HCC.

Research Progress on the Structural and Functional Roles of hnRNPs in Muscle Development

Heterogeneous nuclear ribonucleoproteins (hnRNPs) are a superfamily of RNA-binding proteins consisting of more than 20 members. These proteins play a crucial role in various biological processes by regulating RNA splicing, transcription, and translation through their binding to RNA. In the context of muscle development and regeneration, hnRNPs are involved in a wide range of regulatory mechanisms, including alternative splicing, transcription regulation, miRNA regulation, and mRNA stability regulation. Recent studies have also suggested a potential association between hnRNPs and muscle-related diseases. In this report, we provide an overview of our current understanding of how hnRNPs regulate RNA metabolism and emphasize the significance of the key members of the hnRNP family in muscle development. Furthermore, we explore the relationship between the hnRNP family and muscle-related diseases.

Discovery of tetrahydroisoquinolineindole derivatives as first dual PRMT5 inhibitors/hnRNP E1 upregulators: Design, synthesis and biological evaluation

Protein arginine methyltransferase 5 (PRMT5) is an epigenetics related enzyme that has been validated as an important therapeutic target for treating various types of cancer. Upregulation of tumor suppressor hnRNP E1 has also been considered as an effective antitumor therapy. In this study, a series of tetrahydroisoquinolineindole hybrids were designed and prepared, and compounds 3m and 3s4 were found to be selective inhibitors of PRMT5 and upregulators of hnRNP E1. Molecular docking studies indicated that compounds 3m occupied the substrate site of PRMT5 and formed essential interactions with amino acid residues. Furthermore, compounds 3m and 3s4 exerted antiproliferative effects against A549 cells by inducing apoptosis and inhibiting cell migration. Importantly, silencing of hnRNP E1 eliminated the antitumor effect of 3m and 3s4 on the apoptosis and migration in A549 cells, suggesting a regulatory relationship between PRMT5 and hnRNP E1. Additionally, compound 3m exhibited high metabolic stability on human liver microsomes (T_1/2 = 132.4 min). In SD rats, the bioavailability of 3m was 31.4%, and its PK profiles showed satisfactory AUC and C_max values compared to the positive control. These results suggest that compound 3m is the first class of dual PRMT5 inhibitor and hnRNP E1 upregulator that deserves further investigation as a potential anticancer agent.