Stimulation of c-Jun/AP-1-Activity by the Cell Cycle Inhibitor p57Kip2

GPR120/FFAR4: A Potential New Therapeutic Target for Inflammatory Bowel Disease

Inflammatory bowel disease, whose major forms are Crohn's disease and ulcerative colitis, is characterized by chronic inflammation of the gut due to the loss of tolerance toward antigens normally contained in the gut lumen. G protein-coupled receptor (GPR) 120 has gained considerable attention as a potential therapeutic target for metabolic disorders due to its implication in the production of the incretin hormone glucagon-like peptide 1 and the secretion of cholecystokinin. Recent studies have also highlighted the role of GPR120 in regulating immune system activity and inflammation. GPR120, expressed by intestinal epithelial cells, proinflammatory macrophages, enteroendocrine L cells, and CD4+ T cells, suppresses proinflammatory and enhances anti-inflammatory cytokine production, suggesting that GPR120 might have a pivotal role in intestinal inflammation and represent a possible therapeutic target in inflammatory bowel disease. This narrative review aims at summarizing the role of GPR120 in the maintenance of intestinal homeostasis through the analysis of the most recent studies.

The significance of CDT1 expression in non-cancerous and cancerous liver in cases with hepatocellular carcinoma

We previously reported that chromatin licensing and DNA replication factor 1 (CDT1) expression was associated with the extent of proliferation of atypical hepatocytes and the time to postoperative recurrence in cases of hepatocellular carcinoma (HCC). This study aimed to clarify the clinical significance or pathogenesis of CDT1 expression in both non-cancerous and cancerous liver in HCC cases, including previously published data. We investigated the association between the expression of CDT1 in non-cancerous or cancerous liver tissues and histologic findings or biochemical examination results in 62 cases. We also examined the dual localization between CDT1 and FbxW7, P57kip2, P53 and c-Myc by confocal laser scanning microscopy. CDT1 mRNA expression was significantly higher in cancerous liver than in non-cancerous liver (p<0.0001). Elevated CDT1 mRNA expression indicates a significantly degree of inflammatory cell infiltration within lobules, along with elevated serum transaminase levels, and hepatic spare decline. CDT1 mRNA was highly expressed in a group of poorly differentiated cancer cells. CDT1 co-localized with P57kip2, Fbwx7, P53 and c-Myc in the nucleus or cytoplasm of hepatocytes and cancer cells. We found that CDT1 mRNA expression could represent the degree of hepatic spare ability and the high carcinogenic state.

p57Kip2 acts as a transcriptional corepressor to regulate intestinal stem cell fate and proliferation

p57Kip2 is a cyclin/CDK inhibitor and a negative regulator of cell proliferation. Here, we report that p57 regulates intestinal stem cell (ISC) fate and proliferation in a CDK-independent manner during intestinal development. In the absence of p57, intestinal crypts exhibit an increased proliferation and an amplification of transit-amplifying cells and of Hopx+ ISCs, which are no longer quiescent, while Lgr5+ ISCs are unaffected. RNA sequencing (RNA-seq) analyses of Hopx+ ISCs show major gene expression changes in the absence of p57. We found that p57 binds to and inhibits the activity of Ascl2, a transcription factor critical for ISC specification and maintenance, by participating in the recruitment of a corepressor complex to Ascl2 target gene promoters. Thus, our data suggest that, during intestinal development, p57 plays a key role in maintaining Hopx+ ISC quiescence and repressing the ISC phenotype outside of the crypt bottom by inhibiting the transcription factor Ascl2 in a CDK-independent manner.

Silica nanoparticle exposure inhibits surfactant protein A and B in A549 cells through ROS-mediated JNK/c-Jun signaling pathway

Exposure to silica nanoparticles (SiNPs) is related to the dysregulation of pulmonary surfactant that maintains lung stability and function. Nevertheless, there are limited studies concerning the interaction and influence between SiNPs and pulmonary surfactant, and the damage and mechanism are still unclear. Herein, we used A549 cells to develop an in vitro model, with which we investigated the effect of SiNPs exposure on the expression of pulmonary surfactant and the potential regulatory mechanism. The results showed that SiNPs were of cytotoxicity in regarding of reduced cell viability and promoted the production of excessive reactive oxygen species (ROS). Additionally, the JNK/c-Jun signaling pathway was activated, and the expression of surfactant protein A (SP-A) and surfactant protein B (SP-B) was decreased. After the cells being treated with N-acetyl-L-cysteine (NAC), we found that the ROS content was effectively downregulated, and the expression of proteins related to JNK and c-Jun signaling pathways was suppressed. In contrast, the expression of SP-A and SP-B was enhanced. Furthermore, we treated the cells with JNK inhibitor and c-Jun-siRNA and found that the expression of protein related to JNK and c-Jun signaling pathways, as well as SP-A and SP-B, changed in line with that of NAC treatment. These findings suggest that SiNPs exposure can upregulate ROS and activate the JNK/c-Jun signaling pathway in A549 cells, thereby inhibiting the expression of SP-A and SP-B proteins.

From cyclins to CDKIs: Cell cycle regulation of skeletal muscle stem cell quiescence and activation

After extensive proliferation during development, the adult skeletal muscle cells remain outside the cell cycle, either as post-mitotic myofibers or as quiescent muscle stem cells (MuSCs). Despite its terminally differentiated state, adult skeletal muscle has a remarkable regeneration potential, driven by MuSCs. Upon injury, MuSC quiescence is reversed to support tissue growth and repair and it is re-established after the completion of muscle regeneration. The distinct cell cycle states and transitions observed in the different myogenic populations are orchestrated by elements of the cell cycle machinery. This consists of i) complexes of cyclins and Cyclin-Dependent Kinases (CDKs) that ensure cell cycle progression and ii) their negative regulators, the Cyclin-Dependent Kinase Inhibitors (CDKIs). In this review we discuss the roles of these factors in developmental and adult myogenesis, with a focus on CDKIs that have emerging roles in stem cell functions.

The cyclin-dependent kinase inhibitor p27Kip1 interacts with the aryl hydrocarbon receptor and negatively regulates its transcriptional activity

p27^Kip1 functions to coordinate cell cycle progression through the inhibition of cyclin-dependent kinase (CDK) complexes. p27^Kip1 also exerts distinct activities beyond CDK-inhibition, including functioning as a transcriptional regulator. The aryl hydrocarbon receptor (AhR) is a ligand-activated transcription factor with diverse biological roles. The regulatory inputs that control AhR-mediated transcriptional responses are an active area of investigation. AhR was previously established as a direct regulator of p27^Kip1 transcription. Here, we report the physical interaction of AhR and p27^Kip1 and show that p27^Kip1 expression negatively regulates AhR-mediated transcription. p27^Kip1 knockout cells display increased AhR nuclear localisation and significantly higher expression of AhR target genes. This work thus identifies new regulatory cross-talk between p27^Kip1 and AhR.

Based on Network Pharmacology Tools to Investigate the Mechanism of Tripterygium wilfordii Against IgA Nephropathy

Background: Immunoglobulin A nephropathy (IgAN) is the most common primary glomerular disease and poses a global major public health burden. The preparation of Tripterygium wilfordii Hook F (TwHF) is widely applied for treating patients with Immunoglobulin A nephropathy in China, while the molecular mechanisms remain unclear. This study aimed to verify the therapeutic mechanism of TwHF on IgAN by undertaking a holistic network pharmacology strategy in combination with in vitro and in vivo experiments.

Methods: TwHF active ingredients and their targets were obtained via the Traditional Chinese Medicine Systems Pharmacology Database. The collection of IgAN-related target genes was collected from GeneCards and OMIM. TwHF-IgAN common targets were integrated and visualized by Cytoscape. Gene ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) analyses were performed to determine the predominant molecular mechanisms and pathways of TwHF on the treatment of IgAN. The protein-protein interaction network was constructed by the STRING online search tool, and hub genes were identified using R software. The expression of hub gene and related signaling were evaluated in TwHF-treated mice through immunohistochemistry and western blot and further validated in human mesangial cells (HMCs). In addition, Cell counting kit 8 (CCK8) and flow cytometry were used to detect the effects of TwHF on cell proliferation and cell cycle of mesangial cells.

Results: A total of 51 active ingredients were screened from TwHF and 61 overlapping targets related to IgAN were considered potential therapeutic targets, GO functions and KEGG analyses demonstrated that these genes were primarily associated with DNA-binding transcription factor binding, lipid and atherosclerosis pathway. Genes with higher degrees including AKT1, CXCL8, MMP9, PTGS2, CASP3, JUN are hub genes of TwHF against IgAN. Verification of hub gene JUN both in vitro and in vivo showed that TwHF significantly attenuated JUN phosphorylation in the kidneys of IgAN mice and aIgA1-activated HMCs, meanwhile suppressing HMCs proliferation and arresting G1-S cell cycle progression.

Conclusion: Our research strengthened the mechanisms of TwHF in treating IgAN, inhibition of JUN activation may play a pivotal role in TwHF in alleviating IgAN renal injury.