EML4-ALK is a key oncogenic driver in lung cancer, but variant-specific chemoresistance limits the efficacy of current ALK inhibitors. Because the N-terminus contains an intrinsically disordered region (IDR), how ALK inhibitors affect the structure and dynamics of full-length EML4-ALK remains unclear. Here, using high-speed atomic force microscopy (HS-AFM), we visualize the overall structures of three full-length EML4-ALK variants (v1, v3, and v5) at the single-molecule level. We identified a transient globular subdomain (residues 191-217) within the v3 IDR that contributes to distinct oligomerization patterns. Notably, ALK inhibitors compact the IDR subdomain and reduce oligomerization, whereas this effect is abolished by the resistance mutation ALKG1202R, suggesting that ALK inhibitors not only inhibit kinase activity but also modulate IDR dynamics. Our study reveals a structural basis linking IDR dynamics to variant-specific oligomerization in EML4-ALK, offering further insights into the regulation of oncogenic signaling and the development of targeted therapies.

EML4-ALK is a key oncogenic driver in lung cancer, but variant-specific chemoresistance limits the efficacy of current ALK inhibitors. Because the N-terminus contains an intrinsically disordered region (IDR), how ALK inhibitors affect the structure and dynamics of full-length EML4-ALK remains unclear. Here, using high-speed atomic force microscopy (HS-AFM), we visualize the overall structures of three full-length EML4-ALK variants (v1, v3, and v5) at the single-molecule level. We identified a transient globular subdomain (residues 191–217) within the v3 IDR that contributes to distinct oligomerization patterns. Notably, ALK inhibitors compact the IDR subdomain and reduce oligomerization, whereas this effect is abolished by the resistance mutation ALKG1202R, suggesting that ALK inhibitors not only affect kinase activity but also modulate IDR dynamics. Our findings shed new light on the structural regulation of EML4-ALK and provide a foundation for developing next-generation targeted therapies that account for IDR-driven molecular behavior. Teaser High-speed AFM revealed the full-length EML4-ALK structures and their IDR-mediated plasticity caused by ALK kinase inhibitors ### Competing Interest Statement The authors have declared no competing interest. Collaborative Research Grant of Nano Life Science Institute, Kanazawa University, Kanazawa University Hospital SAKIGAKE project 2022； Extramural Collaborative Research Grant of Cancer Research Institute, Kanazawa University, Boehringer-Ingelheim, and KAKENHI 20K22837 and 22K07208.

The regenerative functions associated with cytokines and growth factors have immense therapeutic potential; however, their poor pharmacokinetics, resulting from structural features, hinder their effectiveness. In this study, we aimed to enhance the pharmacokinetics of growth factors by designing receptor-binding macrocyclic peptides through in vitro mRNA display and grafting them into loops of immunoglobulin's crystallizable region (Fc). As a model, we developed peptide-grafted Fc proteins with hepatocyte growth factor (HGF) functionality that exhibited a prolonged circulation half-life and could be administered subcutaneously. The Fc-based HGF mimetic alleviated liver fibrosis in a mouse model fed a choline-deficient high-fat diet, which induces hepatic features of non-alcoholic steatohepatitis, including fibrosis, showcasing its potential as a therapeutic intervention. This study provides a basis for developing growth factor and cytokine mimetics with improved pharmacokinetics, expanding their therapeutic applications.

Epithelial tissue is at the forefront of innate immunity, playing a crucial role in the recognition and elimination of pathogens. Met is a receptor tyrosine kinase that is necessary for epithelial cell survival, proliferation, and regeneration. Here, we showed that Met is essential for the induction of cytokine production by cytosolic nonself double-stranded RNA through retinoic acid–inducible gene-I-like receptors (RLRs) in epithelial cells. Surprisingly, the tyrosine kinase activity of Met was dispensable for promoting cytokine production. Rather, the intracellular carboxy terminus of Met interacted with mitochondrial antiviral-signaling protein (MAVS) in RLR-mediated signaling to directly promote MAVS signalosome formation. These studies revealed a kinase activity–independent function of Met in the promotion of antiviral innate immune responses, defining dual roles of Met in both regeneration and immune responses in the epithelium.

The regenerative functions associated with cytokines and growth factors encompass an enormous therapeutic potential, but are hindered due to their poor pharmacokinetics resulting from their structural features. Here, we designed growth factor mimetics with improved pharmacokinetics by combining receptor-binding macrocyclic peptides discovered from in vitro mRNA display and their grafting into loops of the crystallizable region (Fc) of immunoglobulin. As a model, we developed peptide-grafted Fc proteins with hepatocyte growth factor (HGF) functionality, a long circulation half-life, and availability by subcutaneous administration. The Fc-based HGF mimetic ameliorated liver fibrosis and inflammation in a mouse model of nonalcoholic steatohepatitis, indicating its potential therapeutic application. This study provides a foundation for developing growth factor and cytokine mimetics with the improved pharmacokinetics that could expand their therapeutic applications.

Upon the initiation of collective cell migration, the cells at the free edge are specified as leader cells; however, the mechanism underlying the leader cell specification remains elusive. Here, we show that lamellipodial extension after the release from mechanical confinement causes sustained extracellular signal-regulated kinase (ERK) activation and underlies the leader cell specification. Live-imaging of Madin-Darby canine kidney (MDCK) cells and mouse epidermis through the use of Förster resonance energy transfer (FRET)-based biosensors showed that leader cells exhibit sustained ERK activation in a hepatocyte growth factor (HGF)-dependent manner. Meanwhile, follower cells exhibit oscillatory ERK activation waves in an epidermal growth factor (EGF) signaling-dependent manner. Lamellipodial extension at the free edge increases the cellular sensitivity to HGF. The HGF-dependent ERK activation, in turn, promotes lamellipodial extension, thereby forming a positive feedback loop between cell extension and ERK activation and specifying the cells at the free edge as the leader cells. Our findings show that the integration of physical and biochemical cues underlies the leader cell specification during collective cell migration.

Short half-lives in circulation and poor transport across the blood–brain barrier limit the utility of cytokines and growth factors acting as receptor agonists. Here we show that surrogate receptor agonists with longer half-lives in circulation and enhanced transport rates across the blood–brain barrier can be generated by genetically inserting macrocyclic peptide pharmacophores into the structural loops of the fragment crystallizable (Fc) region of a human immunoglobulin. We used such ‘lasso-grafting’ approach, which preserves the expression levels of the Fc region and its affinity for the neonatal Fc receptor, to generate Fc-based protein scaffolds with macrocyclic peptides binding to the receptor tyrosine protein kinase Met. The Met agonists dimerized Met, inducing biological responses that were similar to those induced by its natural ligand. Moreover, lasso-grafting of the Fc region of the mouse anti-transferrin-receptor antibody with Met-binding macrocyclic peptides enhanced the accumulation of the resulting Met agonists in brain parenchyma in mice. Lasso-grafting may allow for designer protein therapeutics with enhanced stability and pharmacokinetics.

Retinoic acid-inducible gene (RIG)-I is an essential innate immune sensor that recognises pathogen RNAs and induces interferon (IFN) production. However, little is known about how host proteins regulate RIG-I activation. Here, we show that leukocyte cell-derived chemotaxin 2 (LECT2), a hepatokine and ligand of the MET receptor tyrosine kinase is an antiviral regulator that promotes the RIG-I-mediated innate immune response. Upon binding to MET, LECT2 induces the recruitment of the phosphatase PTP4A1 to MET and facilitates the dissociation and dephosphorylation of phosphorylated SHP2 from MET, thereby protecting RIG-I from SHP2/c-Cbl-mediated degradation. In vivo, LECT2 overexpression enhances RIG-I-dependent IFN production and inhibits lymphocytic choriomeningitis virus (LCMV) replication in the liver, whereas these changes are reversed in LECT2 knockout mice. Forced suppression of MET abolishes IFN production and antiviral activity in vitro and in vivo. Interestingly, hepatocyte growth factor (HGF), an original MET ligand, inhibits LECT2-mediated anti-viral signalling; conversely, LECT2-MET signalling competes with HGF-MET signalling. Our findings reveal previously unrecognized crosstalk between MET-mediated proliferation and innate immunity and suggest that targeting LECT2 may have therapeutic value in infectious diseases and cancer.

NK1, a splicing variant of hepatocyte growth factor (HGF), binds to and activates Met receptor by forming an NK1 dimer and 2:2 complex with Met. Although the structural mechanism underlying Met activation by HGF remains incompletely resolved, it has been proposed that the NK1 dimer structure participates in this activation. We investigated the NK1 dimer interface's role in Met activation by HGF. Because N127, V140, and K144 are closely involved in the head-to-tail NK1 dimer formation, mutant NK1 proteins with replacement of these residues by alanine were prepared. In Met tyrosine phosphorylation assays, N127-NK1, V140-NK1, and K144-NK1 showed 8.3%, 23.8%, and 52.2% activity, respectively, compared with wild-type NK1. Although wild-type NK1 promoted cell migration and scattering, N127-NK1, V140-NK1, and K144-NK1 hardly or marginally promoted them, indicating loss of activity of these mutant NK1 proteins to activate Met. In contrast, mutant HGFs (N127-HGF, V140-HGF, and K144-HGF) with the same amino acid replacements as in NK1 induced Met tyrosine phosphorylation and biological responses at levels comparable to those of wild-type HGF. These results indicate that the structural basis responsible for NK1-dependent Met dimer formation and activation differs from, or is at least distinguishable from, the structural basis responsible for HGF-dependent Met activation.

Using a random non-standard peptide integrated discovery system, we obtained cyclic peptides that bind to hepatocyte growth factor (HGF) or mesenchymal-epithelial transition factor. (MET) HGF-inhibitory peptide-8 (HiP-8) selectively bound to two-chain active HGF, but not to single-chain precursor HGF. HGF showed a dynamic change in its molecular shape in atomic force microscopy, but HiP-8 inhibited dynamic change in the molecular shape into a static status. The inhibition of the molecular dynamics of HGF by HiP-8 was associated with the loss of the ability to bind MET. HiP-8 could selectively detect active HGF in cancer tissues, and active HGF probed by HiP-8 showed co-localization with activated MET. Using HiP-8, cancer tissues with active HGF could be detected by positron emission tomography. HiP-8 seems to be applicable for the diagnosis and treatment of cancers. In contrast, based on the receptor dimerization as an essential process for activation, the cross-linking of the cyclic peptides that bind to the extracellular region of MET successfully generated an artificial ligand to MET. The synthetic MET agonists activated MET and exhibited biological activities which were indistinguishable from the effects of HGF. MET agonists composed of cyclic peptides can be manufactured by chemical synthesis but not recombinant protein expression, and thus are expected to be new biologics that are applicable to therapeutics and regenerative medicine.

Aberrant activation of the MET/hepatocyte growth factor (HGF) receptor participates in the malignant behavior of cancer cells, such as invasion-metastasis and resistance to molecular targeted drugs. Many mutations in the MET extracellular region have been reported, but their significance is largely unknown. Here, we report the dysregulation of mutant MET originally found in a lung cancer patient with Val370 to Asp370 (V370D) replacement located in the extracellular SEMA domain. MET-knockout cells were prepared and reconstituted with WT-MET or V370D-MET. HGF stimulation induced MET dimerization and biological responses in cells reconstituted with WT-MET, but HGF did not induce MET dimerization and failed to induce biological responses in V370D-MET cells. The V370D mutation abrogated HGF-dependent drug resistance of lung cancer cells to epidermal growth factor receptor-tyrosine kinase inhibitors (EGFR-TKI). Compared with WT-MET cells, V370D-MET cells showed different activation patterns in receptor tyrosine kinases upon exposure to survival/growth-stressed conditions. Surface plasmon resonance analysis indicated that affinity between the extracellular region of V370D-MET and HGF was reduced compared with that for WT-MET. Further analysis of the association between V370D-MET and the separate domains of HGF indicated that the SP domain of HGF was unchanged, but its association with the NK4 domain of HGF was mostly lost in V370D-MET. These results indicate that the V370D mutation in the MET receptor impairs the functional association with HGF and is therefore a loss-of-function mutation. This mutation may change the dependence of cancer cell growth/survival on signaling molecules, which may promote cancer cell characteristics under certain conditions.

Hepatocyte growth factor (HGF) is secreted as an inactive single-chain HGF (scHGF); however, only proteolytically processed two-chain HGF (tcHGF) can activate the MET receptor. We investigated the localization of tcHGF and activated/phosphorylated MET (pMET) using a tcHGF-specific antibody. In day 16.5 mouse embryos, total HGF (scHGF + tcHGF) was mainly localized in smooth muscle cells close to, but separate from, MET-positive epithelial cells in endodermal organs, including the stomach. In the adult stomach, total HGF was localized in smooth muscle cells, and tcHGF was mainly localized in the glandular base region. Immunostaining for pMET and Lgr5-driven green fluorescent protein (GFP) indicated that pMET localization overlapped with Lgr5+ gastric stem cells. HGF promoted organoid formation similar to EGF, indicating the potential for HGF to promote the survival and growth of gastric stem cells. pMET and tcHGF localizations changed during regeneration following gastric injury. These results indicate that MET is constantly activated in gastric stem cells and that the localization of pMET differs from the primary localization of precursor HGF but has a close relationship to tcHGF. Our results suggest the importance of the microenvironmental generation of tcHGF in the regulation of development, regeneration, and stem cell behavior.

The indolylmaleimide (IM) derivative IM-17 shows inhibitory activity against oxidative-stress-induced necrotic cell death and cardioprotective activity in rat ischemia-reperfusion injury models. In order to develop a more potent derivative, we conducted a detailed structure-activity relationship study of IM derivatives and identified IM-93 as the most potent derivative with good water solubility. IM-93 inhibited ferroptosis and NETosis, but not necroptosis or pyroptosis. In contrast, ferrostatin-1 (Fer-1), a ferroptosis inhibitor, did not inhibit NETosis, although the accompanying lipid peroxidation was partially inhibited by Fer-1, as well as by IM-93. Thus, IM derivatives have a unique activity profile and appear to be promising candidates for in vivo application.

Mortality from infections has been reported to be higher in hemodialysis (HD) patients. Although dysfunction of neutrophils against bacterial infection was reported in HD patients, the precise mechanism remains to be clarified. We therefore examined the impacts of neutrophil inflammatory signaling on bactericidal activity in HD patients. Comprehensive analyses of intracellular signalings were performed in whole blood of HD patients and control using a microarray system. To confirm the contribution of the signaling to bactericidal activity in neutrophils, we examined the phosphorylation, bacterial killing function, reactive oxygen species (ROS) production, and myeloperoxidase (MPO) release in neutrophils against Staphylococcus aureus. RNA microarray analysis showed the suppression of p38 mitogen activated protein kinase (MAPK) signaling in HD patients. Neutrophils in HD patients showed the impairment of bactericidal activity against S. aureus compared to healthy subjects. Phosphorylation rate of p38MAPK of neutrophils in response to S. aureus was lower in HD patients than healthy subjects. The levels of ROS produced by neutrophils after co-culture with S. aureus were lower in HD patients, on the other hand, there was no difference of MPO release between HD patients and healthy subjects. A selective pharmacological inhibitor of p38MAPK suppressed bacterial killing function as well as ROS production in neutrophils of healthy subjects. Impairment of p38MAPK signaling pathway might contribute to the suppression of neutrophil bactericidal activity in HD patients through less production of ROS.