Bone and Extracellular Signal-Related Kinase 5 (ERK5).

Bones are vital for anchoring muscles, tendons, and ligaments, serving as a fundamental element of the human skeletal structure. However, our understanding of bone development mechanisms and the maintenance of bone homeostasis is still limited. Extracellular signal-related kinase 5 (ERK5), a recently identified member of the mitogen-activated protein kinase (MAPK) family, plays a critical role in the pathogenesis and progression of various diseases, especially neoplasms. Recent studies have highlighted ERK5's significant role in both bone development and bone-associated pathologies. This review offers a detailed examination of the latest research on ERK5 in different tissues and diseases, with a particular focus on its implications for bone health. It also examines therapeutic strategies and future research avenues targeting ERK5.

ERK5 Activity Prevention Improves the Antitumor Efficacy of Fluvastatin on Thymic Carcinoma.

BACKGROUND/AIM: Thymic carcinoma is a rare cancer type with limited treatment options. Our previous study demonstrated that statins, which inhibit 3-hydroxy-3-methylglutaryl coenzyme A reductase, can prevent thymic carcinoma. However, the mechanisms through which statins affect intracellular events in cancer cells are not well understood. The aim of the study was to determine how thymic carcinoma modulates the intracellular signals in response to statin administration. MATERIALS AND METHODS: We analyzed statin-induced protein phosphorylation in Ty82 human thymic carcinoma cells, which were cultured with fluvastatin, and protein phosphorylation was examined using western blotting. RESULTS: Treating Ty82 with fluvastatin led to ERK5 phosphorylation via protein prenylation attenuation. The antitumor effects of fluvastatin on thymic carcinoma were enhanced when combined with an ERK5 inhibitor. CONCLUSION: Statin therapy in combination with ERK5 inhibition may be a promising therapeutic approach for treating thymic carcinoma.

GLP-1(7-36) protected against oxidative damage and neuronal apoptosis in the hippocampal CA region after traumatic brain injury by regulating ERK5/CREB.

BACKGROUND: Glucagon-like peptide-1 (GLP-1) (7-36) amide, an endogenous active form of GLP-1, has been shown to modulate oxidative stress and neuronal cell survival in various neurological diseases. OBJECTIVE: This study investigated the potential effects of GLP-1(7-36) on oxidative stress and apoptosis in neuronal cells following traumatic brain injury (TBI) and explored the underlying mechanisms. METHODS: Traumatic brain injury (TBI) models were established in male SD rats for in vivo experiments. The extent of cerebral oedema was assessed using wet-to-dry weight ratios following GLP-1(7-36) intervention. Neurological dysfunction and cognitive impairment were evaluated through behavioural experiments. Histopathological changes in the brain were observed using haematoxylin and eosin staining. Oxidative stress levels in hippocampal tissues were measured. TUNEL staining and Western blotting were employed to examine cell apoptosis. In vitro experiments evaluated the extent of oxidative stress and neural apoptosis following ERK5 phosphorylation activation. Immunofluorescence colocalization of p-ERK5 and NeuN was analysed using immunofluorescence cytochemistry. RESULTS: Rats with TBI exhibited neurological deterioration, increased oxidative stress, and enhanced apoptosis, which were ameliorated by GLP-1(7-36) treatment. Notably, GLP-1(7-36) induced ERK5 phosphorylation in TBI rats. However, upon ERK5 inhibition, oxidative stress and neuronal apoptosis levels were elevated, even in the presence of GLP-1(7-36). CONCLUSION: In summary, this study suggested that GLP-1(7-36) suppressed oxidative damage and neuronal apoptosis after TBI by activating ERK5/CREB.

Identification of mitogen-activated protein kinase 7 inhibitors from natural products: Combined virtual screening and dynamic simulation studies.

Mitogen-activated protein kinase 7 (MAPK7) is a serine/threonine protein kinase that belongs to the MAPK family and plays a vital role in various cellular processes such as cell proliferation, differentiation, gene transcription, apoptosis, metabolism, and cell survival. The elevated expression of MAPK7 has been associated with the onset and progression of multiple aggressive tumors in humans, underscoring the potential of targeting MAPK7 pathways in therapeutic research. This pursuit holds promise for the advancement of anticancer drug development by developing potential MAPK7 inhibitors. To look for potential MAPK7 inhibitors, we exploited structure-based virtual screening of natural products from the ZINC database. First, the Lipinski rule of five criteria was used to filter a large library of ~90,000 natural compounds, followed by ADMET and pan-assay interference compounds (PAINS) filters. Then, top hits were chosen based on their strong binding affinity as determined by molecular docking. Further, interaction analysis was performed to find effective and specific compounds that can precisely bind to the binding pocket of MAPK7. Consequently, two compounds, ZINC12296700 and ZINC02123081, exhibited significant binding affinity and demonstrated excellent drug-like properties. All-atom molecular dynamics simulations for 200 ns confirmed the stability of MAPK7-ZINC12296700 and MAPK7-ZINC02123081 docked complexes. According to the molecular mechanics Poisson-Boltzmann surface area investigation, the binding affinities of both complexes were considerable. Overall, the result suggests that ZINC12296700 and ZINC02123081 might be used as promising leads to develop novel MAPK7 inhibitors. Since these compounds would interfere with the kinase activity of MAPK7, therefore, may be implemented to control cell growth and proliferation in cancer after required validations.

Design, synthesis and SAR of novel 7-azaindole derivatives as potential Erk5 kinase inhibitor with anticancer activity.

The extracellular signal-regulated kinase 5 (Erk5) signaling plays a crucial role in cancer, and regulating its activity may have potential in cancer chemotherapy. In this study, a series of novel 7-azaindole derivatives (4a-5o) were designed and synthesized. Their antitumor activities on human lung cancer A549 cells was evaluated by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay, 4',6-diamidino-2-phenylindole (DAPI) staining and colony formation assay. Among them, compounds 4a, 4 h, 5d and 5j exhibited good anti-proliferative activity with the IC50 values of 6.23 µg/mL, 8.52 µg/mL, 7.33 µg/mL and 4.56 µg/mL, respectively, equivalent to Erk5 positive control XMD8-92 (IC50 = 5.36 µg/mL). The results of structure-activity relationships (SAR) showed that double bond on the piperidine ring and N atoms at the N7 position of 7-azaindole was essential for their antiproliferative activity. Furthermore, compounds 4a and 5j exhibited good inhibition on Erk5 kinase through Western blot analysis and possible action site of compounds with Erk5 kinase was elucidated by molecular docking.

Cross-species analysis of transcriptome emphasizes a critical role of TNF-α in mediating MAP2K7/AKT2 signaling in zearalenone-induced apoptosis.

Zearalenone (ZEN) is a widespread and transgenerational toxicant that can cause serious reproductive health risks, which poses a potential threat to global agricultural production and human health; its estrogenic activity can lead to reproductive toxicity through the induction of granulosa cell apoptosis. Herein, comparative transcriptome analysis, single-cell transcriptome analysis, and weighted gene co-expression network analysis (WGCNA) combined with gene knockout in vivo and RNA interference in vitro were used to comprehensively describe the damage caused by ZEN exposure on ovarian granulosa cells. Comparative transcriptome analysis and WGCNA suggested that the tumor necrosis factor (TNF)-α-mediated mitogen-activated protein kinase 7 (MAP2K7)/ AKT serine/threonine kinase 2 (AKT2) axis was disordered after ZEN exposure in porcine granulosa cells (pGCs) and mouse granulosa cells (mGCs). In vivo gene knockout and in vitro RNA interference verified that TNF-α-mediated MAP2K7/AKT2 was the guiding signal in ZEN-induced apoptosis in pGCs and mGCs. Moreover, single-cell transcriptome analysis showed that ZEN exposure could induce changes in the TNF signaling pathway in offspring. Overall, we concluded that the TNF-α-mediated MAP2K7/AKT2 axis was the main signaling pathway of ZEN-induced apoptosis in pGCs and mGCs. This work provides new insights into the mechanism of ZEN toxicity and provides new potential therapeutic targets for the loss of livestock and human reproductive health caused by ZEN.

Newt A1 cell-derived extracellular vesicles promote mammalian nerve growth.

Newts have the extraordinary ability to fully regenerate lost or damaged cardiac, neural and retinal tissues, and even amputated limbs. In contrast, mammals lack these broad regenerative capabilities. While the molecular basis of newts' regenerative ability is the subject of active study, the underlying paracrine signaling factors involved remain largely uncharacterized. Extracellular vesicles (EVs) play an important role in cell-to-cell communication via EV cargo-mediated regulation of gene expression patterns within the recipient cells. Here, we report that newt myogenic precursor (A1) cells secrete EVs (A1EVs) that contain messenger RNAs associated with early embryonic development, neuronal differentiation, and cell survival. Exposure of rat primary superior cervical ganglion (SCG) neurons to A1EVs increased neurite outgrowth, facilitated by increases in mitochondrial respiration. Canonical pathway analysis pinpointed activation of NGF/ERK5 signaling in SCG neurons exposed to A1EV, which was validated experimentally. Thus, newt EVs drive neurite growth and complexity in mammalian primary neurons.

Aerobic Exercise Alters the Melanoma Microenvironment and Modulates ERK5 S496 Phosphorylation.

Exercise changes the tumor microenvironment by remodeling blood vessels and increasing infiltration by cytotoxic immune cells. The mechanisms driving these changes remain unclear. Herein, we demonstrate that exercise normalizes tumor vasculature and upregulates endothelial expression of VCAM1 in YUMMER 1.7 and B16F10 murine models of melanoma but differentially regulates tumor growth, hypoxia, and the immune response. We found that exercise suppressed tumor growth and increased CD8+ T-cell infiltration in YUMMER but not in B16F10 tumors. Single-cell RNA sequencing and flow cytometry revealed exercise modulated the number and phenotype of tumor-infiltrating CD8+ T cells and myeloid cells. Specifically, exercise caused a phenotypic shift in the tumor-associated macrophage population and increased the expression of MHC class II transcripts. We further demonstrated that ERK5 S496A knock-in mice, which are phosphorylation deficient at the S496 residue, "mimicked" the exercise effect when unexercised, yet when exercised, these mice displayed a reversal in the effect of exercise on tumor growth and macrophage polarization compared with wild-type mice. Taken together, our results reveal tumor-specific differences in the immune response to exercise and show that ERK5 signaling via the S496 residue plays a crucial role in exercise-induced tumor microenvironment changes. See related Spotlight by Betof Warner, p. 1158.

An ERK5-NRF2 Axis Mediates Senescence-Associated Stemness and Atherosclerosis.

BACKGROUND: ERK5 (extracellular signal-regulated kinase 5) is a dual kinase transcription factor containing an N-terminal kinase domain and a C-terminal transcriptional activation domain. Many ERK5 kinase inhibitors have been developed and tested to treat cancer and inflammatory diseases. However, recent data have raised questions about the role of the catalytic activity of ERK5 in proliferation and inflammation. We aimed to investigate how ERK5 reprograms myeloid cells to the proinflammatory senescent phenotype, subsequently leading to atherosclerosis. METHODS: A ERK5 S496A (dephosphorylation mimic) knock in (KI) mouse model was generated using CRISPR/Cas9 (clustered regularly interspaced short palindromic repeats/clustered regularly interspaced short palindromic repeat-associated 9), and atherosclerosis was characterized by hypercholesterolemia induction. The plaque phenotyping in homozygous ERK5 S496A KI and wild type (WT) mice was studied using imaging mass cytometry. Bone marrow-derived macrophages were isolated from hypercholesterolemic mice and characterized using RNA sequencing and functional in vitro approaches, including senescence, mitochondria reactive oxygen species, and inflammation assays, as well as by metabolic extracellular flux analysis. RESULTS: We show that atherosclerosis was inhibited in ERK5 S496A KI mice. Furthermore, ERK5 S496 phosphorylation mediates both senescence-associated secretory phenotype and senescence-associated stemness by upregulating AHR (aryl hydrocarbon receptor) in plaque and bone marrow-derived macrophages isolated from hypercholesterolemic mice. We also discovered that ERK5 S496 phosphorylation could induce NRF2 (NFE2-related factor 2) SUMOylation at a novel K518 site to inhibit NRF2 transcriptional activity without altering ERK5 catalytic activity and mediates oxidized LDL (low-density lipoprotein)-induced senescence-associated secretory phenotype. Specific ERK5 kinase inhibitors (AX15836 and XMD8-92) also inhibited ERK5 S496 phosphorylation, suggesting the involvement of ERK5 S496 phosphorylation in the anti-inflammatory effects of these ERK5 kinase inhibitors. CONCLUSIONS: We discovered a novel mechanism by which the macrophage ERK5-NRF2 axis develops a unique senescence-associated secretory phenotype/stemness phenotype by upregulating AHR to engender atherogenesis. The finding of senescence-associated stemness phenotype provides a molecular explanation to resolve the paradox of senescence in proliferative plaque by permitting myeloid cells to escape the senescence-induced cell cycle arrest during atherosclerosis formation.

Pathophysiological Impact of the MEK5/ERK5 Pathway in Oxidative Stress.

Oxidative stress regulates many physiological and pathological processes. Indeed, a low increase in the basal level of reactive oxygen species (ROS) is essential for various cellular functions, including signal transduction, gene expression, cell survival or death, as well as antioxidant capacity. However, if the amount of generated ROS overcomes the antioxidant capacity, excessive ROS results in cellular dysfunctions as a consequence of damage to cellular components, including DNA, lipids and proteins, and may eventually lead to cell death or carcinogenesis. Both in vitro and in vivo investigations have shown that activation of the mitogen-activated protein kinase kinase 5/extracellular signal-regulated kinase 5 (MEK5/ERK5) pathway is frequently involved in oxidative stress-elicited effects. In particular, accumulating evidence identified a prominent role of this pathway in the anti-oxidative response. In this respect, activation of krüppel-like factor 2/4 and nuclear factor erythroid 2-related factor 2 emerged among the most frequent events in ERK5-mediated response to oxidative stress. This review summarizes what is known about the role of the MEK5/ERK5 pathway in the response to oxidative stress in pathophysiological contexts within the cardiovascular, respiratory, lymphohematopoietic, urinary and central nervous systems. The possible beneficial or detrimental effects exerted by the MEK5/ERK5 pathway in the above systems are also discussed.

Erk5 functions in modulation of zebrafish intestinal permeability.

The intestine of zebrafish consists of mucosa, muscularis and serosa. Intestinal epithelial cells (IECs) act as a physical and biochemical barrier to protect against invasion by external commensal bacteria. Cell junction is one of the crucial basis of the barrier function. When cell junctions were disrupted, intestinal permeability would be naturally impeded. Extracellular signal-regulated kinase 5 (ERK5), belonging to the Mitogen-activated protein kinase (MAPK) family, is involved in the normal physiological development of the cardiovascular system and nervous system. But the role of erk5 in intestinal morphogenesis and intestinal function is yet to know. Here, we showed that knockout of the erk5 in zebrafish larvae resulted in intestinal wall hypoplasia, including the thinned intestinal wall, reduced intestinal folds, and disrupted cell junctions. In addition, the intestinal permeability assay demonstrated that knockout of erk5 resulted in increased intestinal permeability. All of these showed that erk5 plays an essential role in the maintenance of intestinal barrier function. Thus, our data indicate that erk5 is a critical effector in intestinal morphogenesis and intestinal function, and dysfunction of erk5 would lead to intestinal diseases.

Novel trajectories of the NK1R antagonist aprepitant in rotenone-induced Parkinsonism-like symptoms in rats: Involvement of ERK5/KLF4/p62/Nrf2 signaling axis.

Regulation of the interplay between autophagy and oxidative stress is vital in maintaining neuronal homeostasis during neurotoxicity. The interesting involvement of NK1 receptor (NK1R) in neurodegeneration has highlighted the value of investigating the neuroprotective effect of aprepitant (Aprep), an NK1R antagonist in Parkinson's disease (PD). This study was conducted to disclose Aprep's ability to modulate extracellular signal-regulated kinase 5/Krüppel-like factor 4 (ERK5/KLF4) cue as molecular signaling implicated in regulating autophagy and redox signaling in response to rotenone neurotoxicity. Rotenone (1.5 mg/kg) was administered on alternate days, and rats were given Aprep simultaneously with or without PD98059, an ERK inhibitor, for 21 days. Aprep ameliorated motor deficits as verified by restored histological features, and intact neurons count in SN and striata along with tyrosine hydroxylase immunoreactivity in SN. The molecular signaling of Aprep was illustrated by the expression of KLF4 following the phosphorylation of its upstream target, ERK5. Nuclear factor erythroid 2-related factor 2 (Nrf2) was up-regulated, shifting the oxidant/antioxidant balance towards the antioxidant side, as evidenced by elevated GSH and suppressed MDA levels. In parallel, Aprep noticeably reduced phosphorylated α-synuclein aggregates due to autophagy induction as emphasized by marked LC3II/LC3I elevation and p62 level reduction. These effects were diminished upon PD98059 pre-administration. In conclusion, Aprep showed neuroprotective effects against rotenone-induced PD, which may be partially attributed to the activation of the ERK5/KLF4 signaling pathway. It modulated p62-mediated autophagy and Nrf2 axis which act cooperatively to counter rotenone-associated neurotoxicity pointing to Aprep's prospect as a curious candidate in PD research.

Modulation of ERK5 Activity as a Therapeutic Anti-Cancer Strategy.

The extracellular signal-regulated kinase 5 (ERK5) signaling pathway is one of four conventional mitogen-activated protein (MAP) kinase pathways. Genetic perturbation of ERK5 has suggested that modulation of ERK5 activity may have therapeutic potential in cancer chemotherapy. This Miniperspective examines the evidence for ERK5 as a drug target in cancer, the structure of ERK5, and the evolution of structurally distinct chemotypes of ERK5 kinase domain inhibitors. The emerging complexities of ERK5 pharmacology are discussed, including the confounding phenomenon of paradoxical ERK5 activation by small-molecule ERK5 inhibitors. The impact of the recent development and biological evaluation of potent and selective bifunctional degraders of ERK5 and future opportunities in ERK modulation are also explored.

VEGF Stimulates Activation of ERK5 in the Absence of C-Terminal Phosphorylation Preventing Nuclear Localization and Facilitating AKT Activation in Endothelial Cells.

Extracellular-signal-regulated kinase 5 (ERK5) is critical for normal cardiovascular development. Previous studies have defined a canonical pathway for ERK5 activation, showing that ligand stimulation leads to MEK5 activation resulting in dual phosphorylation of ERK5 on Thr218/Tyr220 residues within the activation loop. ERK5 then undergoes a conformational change, facilitating phosphorylation on residues in the C-terminal domain and translocation to the nucleus where it regulates MEF2 transcriptional activity. Our previous research into the importance of ERK5 in endothelial cells highlighted its role in VEGF-mediated tubular morphogenesis and cell survival, suggesting that ERK5 played a unique role in endothelial cells. Our current data show that in contrast to EGF-stimulated HeLa cells, VEGF-mediated ERK5 activation in human dermal microvascular endothelial cells (HDMECs) does not result in C-terminal phosphorylation of ERK5 and translocation to the nucleus, but instead to a more plasma membrane/cytoplasmic localisation. Furthermore, the use of small-molecule inhibitors to MEK5 and ERK5 shows that instead of regulating MEF2 activity, VEGF-mediated ERK5 is important for regulating AKT activity. Our data define a novel pathway for ERK5 activation in endothelial cells leading to cell survival.

The Investigation of MAPK7 Gene Variations in Colorectal Cancer Risk.

BACKGROUND/AIM: Mitogen-activated protein kinases (MAPKs) are important regulatory molecules, which have essential roles in physiology and pathology. In the present study, we examined the possible correlation between the MAPK7 gene and colorectal cancer risk in the Turkish population. MATERIALS AND METHODS: A total of 100 human DNA samples (50 colorectal cancer patients and 50 healthy individuals) were sequenced using next-generation sequencing to define the potential genetic variations in the MAPK7 gene. RESULTS: Five genetic variations (MAPK7; rs2233072, rs2233076, rs181138364, rs34984998, rs148989290) were detected in our study group. The G (variant) allele of the MAPK7; rs2233072 (T>G) gene polymorphism was found in 76% of colorectal cancer cases, and 66% of controls. The prevalence of rs2233076, rs181138364, rs34984998, and rs148989290 gene variations was quite rare in the subjects and no significant association in terms of genotype and allele frequencies was observed between the cases and controls. CONCLUSION: No statistically significant correlation between the MAP7 kinase gene variations and colorectal cancer risk was observed. This is the first investigation in the Turkish population that may initiate additional studies in larger populations to analyze the effect of MAPK7 gene on the colorectal cancer risk.

Extracellular signal-Regulated Kinase 5 (ERK5) is required for the Yes-associated protein (YAP) co-transcriptional activity.

YES-associated protein (YAP) is a transcriptional cofactor with a key role in the regulation of several physio-pathological cellular processes, by integrating multiple cell autonomous and microenvironmental cues. YAP is the main downstream effector of the Hippo pathway, a tumor-suppressive signaling able to transduce several extracellular signals. The Hippo pathway acts restraining YAP activity, since its activation induces YAP phosphorylation and cytoplasmic sequestration. However, recent observations indicate that YAP activity can be also modulated by Hippo independent/integrating pathways, still largely unexplored. In this study, we demonstrated the role of the extracellular signal-regulated kinase 5 (ERK5)/mitogen-activated protein kinase in the regulation of YAP activity. By means of ERK5 inhibition/silencing and overexpression experiments, and by using as model liver stem cells, hepatocytes, and hepatocellular carcinoma (HCC) cell lines, we provided evidence that ERK5 is required for YAP-dependent gene expression. Mechanistically, ERK5 controls the recruitment of YAP on promoters of target genes and its physical interaction with the transcriptional partner TEAD; moreover, it mediates the YAP activation occurring in cell adhesion, migration, and TGFß-induced EMT of liver cells. Furthermore, we demonstrated that ERK5 signaling modulates YAP activity in a LATS1/2-independent manner. Therefore, our observations identify ERK5 as a novel upstream Hippo-independent regulator of YAP activity, thus unveiling a new target for therapeutic approaches aimed at interfering with its function.

The Integration of Proteome-Wide PTM Data with Protein Structural and Sequence Features Identifies Phosphorylations that Mediate 14-3-3 Interactions.

14-3-3s are abundant proteins that regulate essentially all aspects of cell biology, including cell cycle, motility, metabolism, and cell death. 14-3-3s work by docking to phosphorylated Ser/Thr residues on a large network of client proteins and modulating client protein function in a variety of ways. In recent years, aided by improvements in proteomics, the discovery of 14-3-3 client proteins has far outpaced our ability to understand the biological impact of individual 14-3-3 interactions. The rate-limiting step in this process is often the identification of the individual phospho-serines/threonines that mediate 14-3-3 binding, which are difficult to distinguish from other phospho-sites by sequence alone. Furthermore, trial-and-error molecular approaches to identify these phosphorylations are costly and can take months or years to identify even a single 14-3-3 docking site phosphorylation. To help overcome this challenge, we used machine learning to analyze predictive features of 14-3-3 binding sites. We found that accounting for intrinsic protein disorder and the unbiased mass spectrometry identification rate of a given phosphorylation significantly improves the identification of 14-3-3 docking site phosphorylations across the proteome. We incorporated these features, coupled with consensus sequence prediction, into a publicly available web app, called "14-3-3 site-finder". We demonstrate the strength of this approach through its ability to identify 14-3-3 binding sites that do not conform to the loose consensus sequence of 14-3-3 docking phosphorylations, which we validate with 14-3-3 client proteins, including TNK1, CHEK1, MAPK7, and others. In addition, by using this approach, we identify a phosphorylation on A-kinase anchor protein-13 (AKAP13) at Ser2467 that dominantly controls its interaction with 14-3-3.

Acute pharmacological degradation of ERK5 does not inhibit cellular immune response or proliferation.

Recent interest in the role that extracellular signal-regulated kinase 5 (ERK5) plays in various diseases, particularly cancer and inflammation, has grown. Phenotypes observed from genetic knockdown or deletion of ERK5 suggested that targeting ERK5 could have therapeutic potential in various disease settings, motivating the development ATP-competitive ERK5 inhibitors. However, these inhibitors were unable to recapitulate the effects of genetic loss of ERK5, suggesting that ERK5 may have key kinase-independent roles. To investigate potential non-catalytic functions of ERK5, we report the development of INY-06-061, a potent and selective heterobifunctional degrader of ERK5. In contrast to results reported through genetic knockdown of ERK5, INY-06-061-induced ERK5 degradation did not induce anti-proliferative effects in multiple cancer cell lines or suppress inflammatory responses in primary endothelial cells. Thus, we developed and characterized a chemical tool useful for validating phenotypes reported to be associated with genetic ERK5 ablation and for guiding future ERK5-directed drug discovery efforts.

OXTRHigh stroma fibroblasts control the invasion pattern of oral squamous cell carcinoma via ERK5 signaling.

The Pattern Of Invasion (POI) of tumor cells into adjacent normal tissues clinically predicts postoperative tumor metastasis/recurrence of early oral squamous cell carcinoma (OSCC), but the mechanisms underlying the development of these subtypes remain unclear. Focusing on the highest score of POIs (Worst POI, WPOI) present within each tumor, we observe a disease progression-driven shift of WPOI towards the high-risk type 4/5, associated with a mesenchymal phenotype in advanced OSCC. WPOI 4-5-derived cancer-associated fibroblasts (CAFsWPOI4-5), characterized by high oxytocin receptor expression (OXTRHigh), contribute to local-regional metastasis. OXTRHigh CAFs induce a desmoplastic stroma and CCL26 is required for the invasive phenotype of CCR3+ tumors. Mechanistically, OXTR activates nuclear ERK5 transcription signaling via Gαq and CDC37 to maintain high levels of OXTR and CCL26. ERK5 ablation reprograms the pro-invasive phenotype of OXTRHigh CAFs. Therefore, targeting ERK5 signaling in OXTRHigh CAFs is a potential therapeutic strategy for OSCC patients with WPOI 4-5.

Ulinastatin promotes macrophage efferocytosis and ameliorates lung inflammation via the ERK5/Mer signaling pathway.

Acute lung injury (ALI) is a pneumonic response characterized by neutrophil infiltration. Macrophage efferocytosis is the process whereby macrophages remove apoptotic cells, and is required for ALI inflammation to subside. The glycoprotein ulinastatin (UTI) has an anti-inflammatory effect during the acute stages of ALI, but its effect on efferocytosis and the subinflammatory stage of ALI is unclear. Extracellular signal-regulated kinase 5 (ERK5) is a key protein in efferocytosis, and we thus hypothesized that it may be activated by UTI to regulate efferocytosis and the resolution of pneumonia. To test this hypothesis, here we monitored phagocytosis of macrophages through in vivo and in vitro experiments. Pulmonary edema, neutrophil infiltration, protein exudation, and inflammatory factor regression were observed on days 1, 3, 5, and 7 in vivo. RAW264.7 cells were pretreated with different concentrations of UTI and ERK5 inhibitors, and the expression of tyrosine-protein kinase Mer (Mer) protein on macrophage membrane was detected. UTI increased the phagocytosis of apoptotic neutrophils by macrophages in vitro and in vivo, and promoted the resolution of pneumonia. The protein expression of ERK5 and Mer increased with UTI concentration, while the expression of Mer was down-regulated by ERK5 inhibitors. Therefore, our results suggest that UTI enhances efferocytosis and reduces lung inflammation and injury through the ERK5/Mer signaling pathway, which may be one of the targets of UTI in the treatment of lung injury.