TRAF6-mediated ubiquitination of MST1/STK4 attenuates the TLR4-NF-κB signaling pathway in macrophages

METTL3 modification of circStk4 affects mouse glomerular messangial cell autophagy, proliferation and apotosis by regulating miR-133a-3p/C1 axis

OBJECTIVE

The study aimed to explore the impact of N6-methyladenosine (m6A) modification in circStk4 on glomerular mesangial cells (GMCs) autophagy, proliferation and apoptosis.

METHODS

The interactions between circStk4 and miR-133a-3p, miR-133a-3p and C1 were demonstrated through luciferase reporter assays. The circStk4 localization was analyzed using fluorescence in situ hybridization and nuclear/cytosol fractionation assays. Colorimetric assays, MeRIP-qPCR, and western blot (WB) were employed to confirm the m6A modification of circStk4 and identify the key methylation enzyme. RT-qPCR was conducted to determine the impact of METTL3 on the circStk4 RNA expression. Additionally, CCK-8, flow cytometry, transmission electron microscopy, immunofluorescence, WB and RT-qPCR were employed to investigate the effects of METTL3 or circStk4 on the proliferation, autophagy and apoptosis of GMCs. Enzyme-linked immunosorbent assay was utilized to assess the inflammatory factors.

RESULTS

m6A modifications were found in circStk4 and METTL3 was a key methylating enzyme. Furthermore, it was observed that circStk4 competitively bound miR-133a-3p and increased C1 levels. Silencing circStk4 resulted in decreased GMCs proliferation, increased autophagy and apoptosis, and reduced inflammation levels. Additionally, METTL3 played a role in inhibiting GMCs proliferation and promoting autophagy and apoptosis by regulating the circStk4 expression. On verifying the interplay between autophagy, proliferation and apoptosis, and found that the inhibition of autophagy led to an increase in cell proliferation and a decrease in apoptosis.

CONCLUSION

m6A modification of circStk4 mediated by METTL3 influenced circStk4 expression and impacted autophagy, proliferation and apoptosis in GMCs via the miR-133a-3p/C1 axis. This discovery introduces a novel therapeutic approach for CGN treatment.

MST1/2: Important regulators of Hippo pathway in immune system associated diseases

The Hippo signaling pathway is first found in Drosophila and is highly conserved in evolution. Previous studies on this pathway in mammals have revealed its key role in cell proliferation and differentiation, organ size control, and carcinogenesis. Apart from these, recent findings indicate that mammalian Ste20-like kinases 1 and 2 (MST1/2) have significant effects on immune regulation. In this review, we summarize the updated understanding of how MST1/2 affect the regulation of the immune system and the specific mechanism. The effect of MST1/2 on immune cells and its role in the tumor immune microenvironment can alter the body's response to tumor cells. The relationship between MST1/2 and the immune system suggests new directions in the manipulation of immune responses for clinical immunotherapy, especially for tumor treatment.

MST1/2 in inflammation and immunity

The mammalian Sterile 20-like kinase 1/2 (MST1/2) belongs to the serine/threonine (GC) protein kinase superfamily. Collective studies confirm the vital role MST1/2 in inflammation and immunity. MST1/2 is closely related to the progress of inflammation. Generally, MST1/2 aggravates the inflammatory injury through MST1-JNK, MST1-mROS, MST1-Foxo3, and NF-κB pathways, as well as several regulatory factors such as tumor necrosis factor-α (TNF-α), mitochondrial extension factor 1 (MIEF1), and lipopolysaccharide (LPS). Moreover, MST1/2 is also involved in the regulation of immunity to balance immune activation and tolerance by regulating MST1/2-Rac, MST1-Akt1/c-myc, MST1-Foxos, MST1-STAT, Btk pathways, and lymphocyte function-related antigen 1 (LFA-1), which subsequently prevents immunodeficiency syndrome and autoimmune diseases. This article reviews the effects of MST1/2 on inflammation and immunity.

The role of ubiquitination in microbial infection induced endothelial dysfunction: potential therapeutic targets for sepsis

INTRODUCTION

The ubiquitin system is an evolutionarily conserved and universal means of protein modification that regulates many essential cellular processes. Endothelial dysfunction plays a critical role in the pathophysiology of sepsis and organ failure. However, the mechanisms underlying the ubiquitination-mediated regulation on endothelial dysfunction are not fully understood.

AREAS COVERED

Here we review the advances in basic and clinical research for relevant papers in PubMed database. We attempt to provide an updated overview of diverse ubiquitination events in endothelial cells, discussing the fundamental role of ubiquitination mediated regulations involving in endothelial dysfunction to provide potential therapeutic targets for sepsis.

EXPERT OPINION

The central event underlying sepsis syndrome is the overwhelming host inflammatory response to the pathogen infection, leading to endothelial dysfunction. As the key components of the ubiquitin system, E3 ligases are at the center stage of the battle between host and microbial pathogens. Such a variety of ubiquitination regulates a multitude of cellular regulatory processes, including signal transduction, autophagy, inflammasome activation, redox reaction and immune response and so forth. In this review, we discuss the many mechanisms of ubiquitination-mediated regulation with a focus on those that modulate endothelial function to provide potential therapeutic targets for the management of sepsis.

TRIM21 is a druggable target for the treatment of metastatic colorectal cancer through ubiquitination and activation of MST2

Metastatic colorectal cancer (mCRC) is characterized by poorer prognosis of patients and limited therapeutic approach, partly due to the lack of effective target. Using mouse models and tumor organoids, this study reported a tripartite motif 21 (TRIM21) protein, exerting potential inhibitory effects on the invasion and metastasis of CRC. Mechanistically, TRIM21 directly interacted with and ubiquitinated MST2 at lysine 473 (K473) via K63-linkage. This ubiquitination enabled the formation of MST2 homodimer and enhanced its kinase activity, ultimately resulting in the functional inactivation of yes-associated protein (YAP) and inhibition of an epithelial-mesenchymal transition (EMT) feature. We identified that vilazodone, an antidepressant, directly bound to TRIM21 to exert effective anti-metastatic action both in vitro and in vivo. Collectively, these findings revealed a previously unrecognized interplay between TRIM21 and the Hippo-YAP signaling. These results suggested that vilazodone could be repositioned as an anti-tumor drug to inhibit CRC metastasis by targeting TRIM21.

The hippo kinases MST1/2 in cardiovascular and metabolic diseases: A promising therapeutic target option for pharmacotherapy

Cardiovascular diseases (CVDs) and metabolic disorders are major components of noncommunicable diseases, causing an enormous health and economic burden worldwide. There are common risk factors and developmental mechanisms among them, indicating the far-reaching significance in exploring the corresponding therapeutic targets. MST1/2 kinases are well-established proapoptotic effectors that also bidirectionally regulate autophagic activity. Recent studies have demonstrated that MST1/2 influence the outcome of cardiovascular and metabolic diseases by regulating immune inflammation. In addition, drug development against them is in full swing. In this review, we mainly describe the roles and mechanisms of MST1/2 in apoptosis and autophagy in cardiovascular and metabolic events as well as emphasis on the existing evidence for their involvement in immune inflammation. Moreover, we summarize the latest progress of pharmacotherapy targeting MST1/2 and propose a new mode of drug combination therapy, which may be beneficial to seek more effective strategies to prevent and treat CVDs and metabolic disorders.

MST1: A future novel target for cardiac diseases

Major heart diseases pose a serious threat to human health. Finding early diagnostic markers and key therapeutic targets is an urgent scientific problem in this field. Mammalian sterile 20-like kinase 1 (MST1) is a protein kinase, and the occurrence of many heart diseases is related to the continuous activation of the MST1 gene. With the deepening of the research, the potential role of MST1 in promoting the development of heart disease has become more apparent. Therefore, to better understand the role of MST1 in the pathogenesis of heart disease, this work systematically summarizes the role of MST1 in the pathogenesis of heart disease, gives a comprehensive overview of its possible strategies in the diagnosis and treatment of heart disease, and analyzes its potential significance as a marker for the diagnosis and treatment of heart disease.

Alkaloid leonurine exerts anti-inflammatory effects via modulating MST1 expression in trophoblast cells

BACKGROUND

Pre-eclampsia (PE) is mainly attributed to the inflammation of trophoblast cells in pregnant women, which results in damage to the maternal organs and growth retardation of the fetus. Alkaloid leonurine (LNR) is a plant compound and has anti-inflammatory effects. Here we aimed to investigate the effects of LNR on human and mouse trophoblast cells and the underlying mechanisms.

METHODS

The levels of the inflammatory factors in trophoblast cells under lipopolysaccharides (LPS) stimulation were analyzed with ELISA. Western blot was employed to examine the protein expression. Trophoblast cells in Mammalian ste20-like kinase 1 (MST1-/- ) or wild type (WT) mice were isolated to examine the expression of signal molecules in the nuclear factor-κB (NF-κB) pathway. Concentration-dependent activity of NF-κB was examined. The regulation of LNR and MST1 in MST1-/- trophoblast cells was studied as well.

RESULTS

Our data showed that LNR exhibited anti-inflammatory effects and suppressed the NF-κB signaling by inhibiting LPS-induced inflammation in trophoblast cells. LNR upregulated the expression of MST1, and the anti-inflammatory role of LNR was greatly relieved in MST1-knockout trophoblast cells, although it displayed weak roles in NF-κB signaling.

CONCLUSION

LNR exhibits anti-inflammatory effects on human and mouse trophoblast cells by upregulating MST1 in the NF-κB signal pathway.

MST4 attenuates NLRP3 inflammasome-mediated neuroinflammation and affects the prognosis after intracerebral hemorrhage in mice

BACKGROUND

The kinase MST4 limits inflammatory responses through direct phosphorylation of the adaptor TRAF6. TRAF6 interacts with NLRP3 to promote the activation of NLRP3 inflammasome. However, the role of MST4 in neuroinflammation after intracerebral hemorrhage (ICH) and how it interacts with NLRP3 inflammasome remain unclear.

METHODS

Mice were administered MST4 AAV four weeks before collagenase-induced ICH. ICH mice received either hesperadin (MST4 selective inhibitor), or MCC950 (NLRP3 inflammasome selective inhibitor). Neurological deficits and brain water content were assessed. Western blot and immunofluorescence were performed to evaluate the proteins content and localization in MST4/NLRP3 signaling pathway.

RESULTS

The expression of endogenous MST4 and NLRP3 was increased after ICH compared to sham group. MST4 and NLRP3 were respectively colocalized in microglia. Upregulation of MST4 gene inhibited the activation of NLRP3 inflammasome, the release of IL-1β and TNF-α, and significantly improved brain edema and neurological deficits. Hesperadin pretreatment inhibited the expression of MST4 and increased the expression of NLRP3 inflammasome-mediated proteins, which aggravated neurological deficits and cerebral edema. MCC950 markedly alleviated neurological deficits and brain edema but had no effect on the expression of MST4 protein.

CONCLUSIONS

MST4 alleviates inflammatory progression and brain injury in ICH mice possibly by inhibiting NLRP3 inflammasome activation.