Evaluating soluble Axl as a biomarker for glioblastoma: A pilot study.

With current imaging, discriminating tumor progression from treatment effect following immunotherapy or oncolytic virotherapy of glioblastoma (GBM) is challenging. A blood based diagnostic biomarker would therefore be helpful. Axl is a receptor tyrosine kinase that is highly expressed by many cancers including GBM. Axl expression is regulated through enzymatic cleavage of its extracellular domain. The resulting fragment can be detected in serum as soluble Axl (sAxl). sAxl levels can distinguish patients with melanoma, hepatocellular carcinoma, and pancreatic ductal adenocarcinoma from healthy controls. This is a pilot study to determine if sAxl is a candidate biomarker for GBM. The sAxl levels in the serum of 40 healthy volunteers and 20 GBM patients were determined using an enzyme-linked immunosorbent assay (ELISA). Pre- and post- operative sAxl levels were obtained. Volumetric MRI evaluation provided GBM tumor volume metrics. There was no significant difference in the sAxl levels of the volunteers (30.16±1.88 ng/ml) and GBM patients (30.74±1.96 ng/ml) p = 0.27. The postoperative sAxl levels were significantly higher than preoperative levels (32.32±2.26 ng/ml vs 30.74±1.96 ng/ml, p = 0.03). We found no correlation between tumor volume and sAxl levels. Axl expression was low or absent in 6 of 11 (55%) patient derived GBM cell lines. Given the wide range of Axl expression by GBM tumors, sAxl may not be a reliable indicator of GBM. However, given the small sample size in this study, a larger study may be considered.

Structure and Dynamics of Drk-SH2 Domain and Its Site-Specific Interaction with Sev Receptor Tyrosine Kinase.

The Drosophila downstream receptor kinase (Drk), a homologue of human GRB2, participates in the signal transduction from the extracellular to the intracellular environment. Drk receives signals through the interaction of its Src homology 2 (SH2) domain with the phosphorylated tyrosine residue in the receptor tyrosine kinases (RTKs). Here, we present the solution NMR structure of the SH2 domain of Drk (Drk-SH2), which was determined in the presence of a phosphotyrosine (pY)-containing peptide derived from a receptor tyrosine kinase, Sevenless (Sev). The solution structure of Drk-SH2 possess a common SH2 domain architecture, consisting of three ß strands imposed between two α helices. Additionally, we interpret the site-specific interactions of the Drk-SH2 domain with the pY-containing peptide through NMR titration experiments. The dynamics of Drk-SH2 were also analysed through NMR-relaxation experiments as well as the molecular dynamic simulation. The docking simulations of the pY-containing peptide onto the protein surface of Drk-SH2 provided the orientation of the peptide, which showed a good agreement with the analysis of the SH2 domain of GRB2.

The Alk receptor tyrosine kinase regulates Sparkly, a novel activity regulating neuropeptide precursor in the Drosophila central nervous system.

Numerous roles for the Alk receptor tyrosine kinase have been described in Drosophila, including functions in the central nervous system (CNS), however the molecular details are poorly understood. To gain mechanistic insight, we employed Targeted DamID (TaDa) transcriptional profiling to identify targets of Alk signaling in the larval CNS. TaDa was employed in larval CNS tissues, while genetically manipulating Alk signaling output. The resulting TaDa data were analyzed together with larval CNS scRNA-seq datasets performed under similar conditions, identifying a role for Alk in the transcriptional regulation of neuroendocrine gene expression. Further integration with bulk and scRNA-seq datasets from larval brains in which Alk signaling was manipulated identified a previously uncharacterized Drosophila neuropeptide precursor encoded by CG4577 as an Alk signaling transcriptional target. CG4577, which we named Sparkly (Spar), is expressed in a subset of Alk-positive neuroendocrine cells in the developing larval CNS, including circadian clock neurons. In agreement with our TaDa analysis, overexpression of the Drosophila Alk ligand Jeb resulted in increased levels of Spar protein in the larval CNS. We show that Spar protein is expressed in circadian (clock) neurons, and flies lacking Spar exhibit defects in sleep and circadian activity control. In summary, we report a novel activity regulating neuropeptide precursor gene that is regulated by Alk signaling in the Drosophila CNS.

Gas6 and Protein S Ligands Cooperate to Regulate MerTK Rhythmic Activity Required for Circadian Retinal Phagocytosis.

Among the myriad of existing tyrosine kinase receptors, the TAM family-abbreviated from Tyro3, Axl, and Mer tyrosine kinase (MerTK)-has been extensively studied with an outstanding contribution from the team of Prof. Greg Lemke. MerTK activity is implicated in a wide variety of functions involving the elimination of apoptotic cells and has recently been linked to cancers, auto-immune diseases, and atherosclerosis/stroke. In the retina, MerTK is required for the circadian phagocytosis of oxidized photoreceptor outer segments by the retinal-pigment epithelial cells, a function crucial for the long-term maintenance of vision. We previously showed that MerTK ligands carry the opposite role in vitro, with Gas6 inhibiting the internalization of photoreceptor outer segments while Protein S acts conversely. Using site-directed mutagenesis and ligand-stimulated phagocytosis assays on transfected cells, we presently demonstrate, for the first time, that Gas6 and Protein S recognize different amino acids on MerTK Ig-like domains. In addition, MerTK's function in retinal-pigment epithelial cells is rhythmic and might thus rely on the respective stoichiometry of both ligands at different times of the day. Accordingly, we show that ligand bioavailability varies during the circadian cycle using RT-qPCR and immunoblots on retinal and retinal-pigment epithelial samples from control and beta5 integrin knockout mice where retinal phagocytosis is arrhythmic. Taken together, our results suggest that Gas6 and Protein S might both contribute to refine the acute regulation of MerTK in time for the daily phagocytic peak.

The combination therapy using tyrosine kinase receptors inhibitors and repurposed drugs to target patient-derived glioblastoma stem cells.

The lesson from many studies investigating the efficacy of targeted therapy in glioblastoma (GBM) showed that a future perspective should be focused on combining multiple target treatments. Our research aimed to assess the efficacy of drug combinations against glioblastoma stem cells (GSCs). Patient-derived cells U3042, U3009, and U3039 were obtained from the Human Glioblastoma Cell Culture resource. Additionally, the study was conducted on a GBM commercial U251 cell line. Gene expression analysis related to receptor tyrosine kinases (RTKs), stem cell markers and genes associated with significant molecular targets was performed, and selected proteins encoded by these genes were assessed using the immunofluorescence and flow cytometry methods. The cytotoxicity studies were preceded by analyzing the expression of specific proteins that serve as targets for selected drugs. The cytotoxicity study using the MTS assay was conducted to evaluate the effects of selected drugs/candidates in monotherapy and combinations. The most cytotoxic compounds for U3042 cells were Disulfiram combined with Copper gluconate (DSF/Cu), Dacomitinib, and Foretinib with IC50 values of 52.37 nM, 4.38 µM, and 4.54 µM after 24 h incubation, respectively. Interactions were assessed using SynergyFinder Plus software. The analysis enabled the identification of the most effective drug combinations against patient-derived GSCs. Our findings indicate that the most promising drug combinations are Dacomitinib and Foretinib, Dacomitinib and DSF/Cu, and Foretinib and AZD3759. Since most tested combinations have not been previously examined against glioblastoma stem-like cells, these results can shed new light on designing the therapeutic approach to target the GSC population.

Co-targeting JAK1/STAT6/GAS6/TAM signaling improves chemotherapy efficacy in Ewing sarcoma.

Ewing sarcoma is a pediatric bone and soft tissue tumor treated with chemotherapy, radiation, and surgery. Despite intensive multimodality therapy, ~50% patients eventually relapse and die of the disease due to chemoresistance. Here, using phospho-profiling, we find Ewing sarcoma cells treated with chemotherapeutic agents activate TAM (TYRO3, AXL, MERTK) kinases to augment Akt and ERK signaling facilitating chemoresistance. Mechanistically, chemotherapy-induced JAK1-SQ phosphorylation releases JAK1 pseudokinase domain inhibition allowing for JAK1 activation. This alternative JAK1 activation mechanism leads to STAT6 nuclear translocation triggering transcription and secretion of the TAM kinase ligand GAS6 with autocrine/paracrine consequences. Importantly, pharmacological inhibition of either JAK1 by filgotinib or TAM kinases by UNC2025 sensitizes Ewing sarcoma to chemotherapy in vitro and in vivo. Excitingly, the TAM kinase inhibitor MRX-2843 currently in human clinical trials to treat AML and advanced solid tumors, enhances chemotherapy efficacy to further suppress Ewing sarcoma tumor growth in vivo. Our findings reveal an Ewing sarcoma chemoresistance mechanism with an immediate translational value.

ALK Inhibitor and Chemotherapy Combinations in Models of ALK-Translocated NSCLC.

BACKGROUND/AIM: Randomized trials have shown the benefit of combining tyrosine kinase inhibitors (TKI) and chemotherapy in the treatment of epidermal growth factor receptor-mutant non-small-cell lung cancer (NSCLC). For anaplastic lymphoma kinase-rearranged (ALK+) NSCLC, prospective trial results of the combination are not available and have not even been thoroughly investigated in vitro. In this study, we investigated combinations of TKI and chemotherapy using in vitro models of ALK+ NSCLC. MATERIALS AND METHODS: ALK+ cell line models H3122, H2228, and DFCI032 with differing primary resistance to ALK receptor TKIs were used. We investigated short-(viability assay) and long-term (colony-formation assay) cytotoxicity, apoptosis, and cell signaling in response to the combinations of agents. We selected the most commonly used agents, alectinib, cisplatin, and pemetrexed, to investigate the combination effects. RESULTS: In the combination experiments with short-term exposure, synergism between TKI and pemetrexed was observed, while cisplatin had antagonistic effects. In the long-term experiments, the combination of cisplatin and TKI was synergistic in all lines, while no synergism was observed with pemetrexed. Among the chemotherapy and TKI sequences, cisplatin followed by TKI was more cytotoxic than the opposite in two out of the three models. In the TKI-sensitive H3122 cell line, the combination of chemotherapy and TKI combination increased apoptosis. Interestingly, pemetrexed treatment resulted in the activation of ALK, which was abolished with TKI. CONCLUSION: Combining TKI and chemotherapy in ALK+ models has some synergistic effects that overcome primary TKI resistance. However, the synergy varies depending on the chemotherapeutic agent, cytotoxic assay, and the cell line used. Prospective clinical trials are warranted to fully characterize the potential of combination chemotherapy with TKIs in ALK+ NSCLC.

Identification of the Binding Site between Aptamer sgc8c and PTK7.

Aptamers are single-stranded RNA or DNA molecules that can specifically bind to targets and have found broad applications in cancer early-stage detection, accurate drug delivery, and precise treatment. Although various aptamer screening methods have been developed over the past several decades, the accurate binding site between the target and the aptamer cannot be characterized during a typical aptamer screening process. In this research, we chose a widely used aptamer screened by our group, sgc8c, and its target protein tyrosine kinase 7 (PTK7) as the model aptamer and target and tried to determine the binding site between aptamer sgc8c and PTK7. Through sequential protein truncation, we confirmed that the exact binding site of sgc8c was within the region of Ig 3 to Ig 4 in the extracellular domain of PTK7. Using in vitro expressed Ig (3-4), we successfully acquired the crystal of an sgc8c-Ig (3-4) binding complex. The possible sgc8c-binding amino acid residues on PTK7 and PTK7-binding nucleotide residues on sgc8c were further identified and simulated by mass spectrometry and molecular dynamics simulation and finally verified by aptamer/protein truncation and mutation.

RP11-874 J12.4 promotes erlotinib resistance in non-small cell lung cancer via increasing AXL expression.

EGFR tyrosine kinase inhibitor (TKI) resistance is a major challenge for EGFR-mutant non-small cell lung cancer (NSCLC) treatment. Our previous work revealed that overexpression of AXL promoted EGFR-TKI resistance through epithelial-mesenchymal transition (EMT) in a subset of NSCLC patients. Compared with erlotinib resistant and sensitive cells, RP11-874 J12.4 was upregulated in erlotinib-resistant NSCLC cells (HCC827-ER3). Interestingly, the expression of RP11-874 J12.4 positively correlated with AXL. Besides, RP11-874 J12.4 promotes NSCLC cell proliferation and metastasis in vitro. Mechanistically, RP11-874 J12.4 promoted AXL expression through sponge with miR-34a-5p, which was reported to inhibit the translation of AXL mRNA. Meanwhile, the expression of RP11-874 J12.4 in lung cancer tumors were higher than the adjacent tissue, and those patients with high expression of RP11-874 J12.4 showed a poor prognosis in clinical. High expression of RP11-874 J12.4 might be a biomarker for NSCLC patients with erlotinib resistance. These findings reveal a novel insight into the mechanism of erlotinib resistance in NSCLC, and it might be a promising target for the diagnosis and treatment of NSCLC.

Decoding how receptor tyrosine kinases (RTKs) mediate nuclear calcium signaling.

Calcium (Ca2+) is a highly versatile intracellular messenger that regulates several cellular processes. Although it is unclear how a single-second messenger coordinates various effects within a cell, there is growing evidence that spatial patterns of Ca2+ signals play an essential role in determining their specificity. Ca2+ signaling patterns can differ in various cell regions, and Ca2+ signals in the nuclear and cytoplasmic compartments have been observed to occur independently. The initiation and function of Ca2+ signaling within the nucleus are not yet fully understood. Receptor tyrosine kinases (RTKs) induce Ca2+ signaling resulting from phosphatidylinositol 4,5-bisphosphate (PIP2) hydrolysis and inositol 1,4,5-trisphosphate (InsP3) formation within the nucleus. This signaling mechanism may be responsible for the effects of specific growth factors on cell proliferation and gene transcription. This review highlights the recent advances in RTK trafficking to the nucleus and explains how these receptors initiate nuclear calcium signaling.

Building, Breaking, and Repairing Neuromuscular Synapses.

A coordinated and complex interplay of signals between motor neurons, skeletal muscle cells, and Schwann cells controls the formation and maintenance of neuromuscular synapses. Deficits in the signaling pathway for building synapses, caused by mutations in critical genes or autoantibodies against key proteins, are responsible for several neuromuscular diseases, which cause muscle weakness and fatigue. Here, we describe the role that four key genes, Agrin, Lrp4, MuSK, and Dok7, play in this signaling pathway, how an understanding of their mechanisms of action has led to an understanding of several neuromuscular diseases, and how this knowledge has contributed to emerging therapies for treating neuromuscular diseases.

Polyfluoroalkyl Tag Decoration Enables Significantly Enhanced Tumor Penetration Ability of a PTK7 Targeting Aptamer.

Aptamers are widely used molecular recognition tools in targeted therapy, but their ability to effectively penetrate deep into solid tumors remains a significant challenge, leading to suboptimal treatment efficacy. Here, we developed a polyfluoroalkyl (PFA) decoration strategy to enhance aptamer recognition, cell internalization, and solid tumor penetration. Our results indicate that PFA with around 11 fluorine atoms significantly improves aptamer internalization both in vitro and in vivo settings. However, we also observed that the use of PFA tags containing 19 and 23 fluorine atoms on aptamers resulted in nonspecific cell anchoring in control cell lines, affecting the specificity of aptamers. Overall, we found that using a chemical modification strategy could enhance the deep tumor penetration ability of aptamers and validate their effectiveness in vivo. This approach has significant practical applications in targeted drug delivery for cancer treatment.

Recent insights into the therapeutic strategies targeting the pseudokinase PTK7 in cancer.

The generation of drugs counteracting deregulated protein kinases has been a major focus in cancer therapy development. Breakthroughs in this effort have produced many therapeutic agents to the benefit of patients, mostly through the development of chemical or antibody-based drugs targeting active kinases. These strategies are challenged when considering catalytically inactive protein kinases (or pseudokinases), which represent 10% of the human kinome with many of relevance in cancer. Among the so-called pseudotyrosine kinases, the PTK7 receptor tyrosine kinase (RTK) stands as a bona fide target overexpressed in several solid tumors and hematological malignancies and linked to metastasis, poor prognosis, and resistance to treatment. Despite the lack of catalytic activity, PTK7 has signaling capacities through heterodimerization with active RTKs and offers pharmacological targeting opportunities through its inactive kinase domain. Moreover, PTK7-targeting strategies based on antibody-drug conjugates, aptamers, and CAR-T cell-based therapies have demonstrated encouraging results in preclinical and clinical settings. We review the most recent data assigning to PTK7 a prominent role in cancer progression as well as current preclinical and clinical targeting strategies against RTK family pseudokinases including PTK7.

We are what we eat: macrophages and efferocytosis.

Liebold et al. recently revealed how the identity of dying cells drives distinct changes to the macrophages which engulf and clear them, a process known as efferocytosis. During infection with the helminth Schistosoma mansoni, liver macrophages recapitulate these phenotypes, mediated by Axl/MerTK receptors and regulating egg burdens.

Differential regulation of lung homeostasis and silicosis by the TAM receptors MerTk and Axl.

Introduction: TAM receptor-mediated efferocytosis plays an important function in immune regulation and may contribute to antigen tolerance in the lungs, a site with continuous cellular turnover and generation of apoptotic cells. Some studies have identified failures in efferocytosis as a common driver of inflammation and tissue destruction in lung diseases. Our study is the first to characterize the in vivo function of the TAM receptors, Axl and MerTk, in the innate immune cell compartment, cytokine and chemokine production, as well as the alveolar macrophage (AM) phenotype in different settings in the airways and lung parenchyma. Methods: We employed MerTk and Axl defective mice to induce acute silicosis by a single exposure to crystalline silica particles (20 mg/50 µL). Although both mRNA levels of Axl and MerTk receptors were constitutively expressed by lung cells and isolated AMs, we found that MerTk was critical for maintaining lung homeostasis, whereas Axl played a role in the regulation of silica-induced inflammation. Our findings imply that MerTk and Axl differently modulated inflammatory tone via AM and neutrophil recruitment, phenotype and function by flow cytometry, and TGF-ß and CXCL1 protein levels, respectively. Finally, Axl expression was upregulated in both MerTk-/- and WT AMs, confirming its importance during inflammation. Conclusion: This study provides strong evidence that MerTk and Axl are specialized to orchestrate apoptotic cell clearance across different circumstances and may have important implications for the understanding of pulmonary inflammatory disorders as well as for the development of new approaches to therapy.

Phosphatidylserine and Tyro3-Axl-Mertk Receptor Tyrosine Kinase level detection in plasma and on plasma-derived extracellular vesicle surface in chronic lymphocytic leukemia.

Chronic lymphocytic leukemia (CLL) is a chronic lymphoproliferative disorder characterized by monoclonal B cell proliferation. Studies carried out in recent years suggest that extracellular vesicles (EVs) may be a potential biomarker in cancer. Tyro3-Axl-Mertk (TAM) Receptor Tyrosine Kinases (RTKs) and Phosphatidylserine (PS) have crucial roles in macrophage-mediated immune response under normal conditions. In the tumor microenvironment, these molecules contribute to immunosuppressive signals and prevent the formation of local and systemic antitumor immune responses. Based on this, we aimed to evaluate the amount of PS and TAM RTK in plasma and on the surface of EVs in CLL patients and healthy volunteers in this study. In this study, 25 CLL (11 F/14 M) patients in the Rai (O-I) stage, newly diagnosed or followed up without treatment, and 15 healthy volunteers (11 F/4 M) as a control group were included. For all samples, PS and TAM RTK levels were examined first in the plasma and then in the EVs obtained from the plasma. We detected a significant decrease in plasma PS, and TAM RTK levels in CLL patients compared to the control. Besides, we determined a significant increase in TAM RTK levels on the EV surface in CLL, except for PS. In conclusion, these receptor levels measured by ELISA in plasma may not be effective for the preliminary detection of CLL. However, especially TAM RTKs on the surface of EVs may be good biomarkers and potential targets for CLL therapies.

Establishment and characterization of TK-ALCL1: a novel NPM-ALK-positive anaplastic large-cell lymphoma cell line.

TK-ALCL1, a novel anaplastic lymphoma kinase (ALK)-positive anaplastic large-cell lymphoma (ALK+ ALCL) cell line, was established from the primary tumor site of a 59-year-old Japanese male patient. The immune profile of TK-ALCL1 corresponds to that seen typically in primary ALCL cells, i.e., positive for ALK, CD30, EMA, and CD4, but negative for CD2, CD3, CD5, CD8a, and EBV-related antigens. The rearrangement of the T cell receptor-gamma locus shows that TK-ALCL1 is clonally derived from T-lineage lymphoid cells. FISH and RT-PCR analysis revealed that TK-ALCL1 has the nucleophosmin (NPM)-ALK fusion transcript, which is typical for ALK+ ALCL cell lines. When TK-ALCL1 was subcutaneously inoculated into 6-week-old BALB/c Rag2-/-/Jak3-/- (BRJ) mice, it formed tumor masses within 4-6 weeks. Morphological, immunohistochemical, and molecular genetic investigations confirmed that the xenograft and the original ALCL tumor were identical. The ALK inhibitors Alectinib and Lorlatinib suppressed proliferation in a dose-dependent manner. Thus, TK-ALCL1 provides a useful in vitro and in vivo model for investigation of the biology of ALK+ ALCL and of novel therapeutic approaches targeting ALK.

Expression levels of tam receptors and ligands in the testes of rats exposed to short and middle-term 2100 MHz radiofrequency radiation.

With advances in technology, the emission of radiofrequency radiation (RFR) into the environment, particularly from mobile devices, has become a growing concern. Tyro 3, Axl, and Mer (TAM) receptors and their ligands are essential for spermatogenesis and testosterone production. RFR has been shown to induce testicular cell apoptosis by causing inflammation and disrupting homeostasis. This study aimed to investigate the role of TAM receptors and ligands in the maintenance of homeostasis and elimination of apoptotic cells in the testes (weeks), short-term sham exposure (sham/1 week), and middle-term sham exposure (sham/10 weeks). Testicular morphology was assessed using hematoxylin-eosin staining, while immunohistochemical staining was performed to assess expression levels of TAM receptors and ligands in the testes of all groups. The results showed that testicular morphology was normal in the control, sham/1 week, and sham/10 weeks groups. However, abnormal processes of spermatogenesis and seminiferous tubule morphology were observed in RFR exposure groups. Cleaved Caspase 3 immunoreactivity showed statistically significant difference in 1 and 10 weeks exposure groups compared to control group. Moreover, there was no significant difference in the immunoreactivity of Tyro 3, Axl, Mer, Gas 6, and Pros 1 between groups. Moreover, Tyro 3 expression in Sertoli cells was statistically significantly increased in RFR exposure groups compared to the control. Taken together, the results suggest that RFR exposure negatively affects TAM signalling, preventing the clearance of apoptotic cells, and this process may lead to infection and inflammation. As a result, rat testicular morphology and function may be impaired.

m6A reader YTHDF1 promotes cardiac fibrosis by enhancing AXL translation.

Cardiac fibrosis caused by ventricular remodeling and dysfunction such as post-myocardial infarction (MI) can lead to heart failure. RNA N6-methyladenosine (m6A) methylation has been shown to play a pivotal role in the occurrence and development of many illnesses. In investigating the biological function of the m6A reader YTHDF1 in cardiac fibrosis, adeno-associated virus 9 was used to knock down or overexpress the YTHDF1 gene in mouse hearts, and MI surgery in vivo and transforming growth factor-ß (TGF-ß)-activated cardiac fibroblasts in vitro were performed to establish fibrosis models. Our results demonstrated that silencing YTHDF1 in mouse hearts can significantly restore impaired cardiac function and attenuate myocardial fibrosis, whereas YTHDF1 overexpression could further enhance cardiac dysfunction and aggravate the occurrence of ventricular pathological remodeling and fibrotic development. Mechanistically, zinc finger BED-type containing 6 mediated the transcriptional function of the YTHDF1 gene promoter. YTHDF1 augmented AXL translation and activated the TGF-ß-Smad2/3 signaling pathway, thereby aggravating the occurrence and development of cardiac dysfunction and myocardial fibrosis. Consistently, our data indicated that YTHDF1 was involved in activation, proliferation, and migration to participate in cardiac fibrosis in vitro. Our results revealed that YTHDF1 could serve as a potential therapeutic target for myocardial fibrosis.