Primary cilium projects from cells to provide a communication platform with neighboring cells and the surrounding environment. This is ensured by the selective entry of membrane receptors and signaling molecules, producing fine-tuned and effective responses to the extracellular cues. In this study, we focused on one family of signaling molecules, the fibroblast growth factor receptors (FGFRs), their residence within cilia, and its role in FGFR signaling. We show that FGFR1 and FGFR2, but not FGFR3 and FGFR4, localize to primary cilia of the developing mouse tissues and in vitro cells. For FGFR2, we demonstrate that the ciliary residence is necessary for its signaling and expression of target morphogenic genes. We also show that the pathogenic FGFR2 variants have minimal cilium presence, which can be rescued for the p.P253R variant associated with the Apert syndrome by using the RLY-4008 kinase inhibitor. Finally, we determine the molecular regulators of FGFR2 trafficking to cilia, including IFT144, BBS1, and the conserved T429V430 motif within FGFR2.

• MeSH
• Cilia * metabolism   genetics   MeSH
• Epithelial Cells * metabolism   MeSH
• Humans MeSH
• Mice MeSH
• Receptor, Fibroblast Growth Factor, Type 1 metabolism   genetics   MeSH
• Receptor, Fibroblast Growth Factor, Type 2 * metabolism   genetics   MeSH
• Signal Transduction * MeSH
• Animals MeSH
• Check Tag
• Humans MeSH
• Mice MeSH
• Animals MeSH
• Publication type
• Journal Article MeSH
• Names of Substances
• FGFR2 protein, human MeSH Browser
• Fgfr2 protein, mouse MeSH Browser
• Receptor, Fibroblast Growth Factor, Type 1 MeSH
• Receptor, Fibroblast Growth Factor, Type 2 * MeSH

Cell communication systems based on polypeptide ligands use transmembrane receptors to transmit signals across the plasma membrane. In their biogenesis, receptors depend on the endoplasmic reticulum (ER)-Golgi system for folding, maturation, transport and localization to the cell surface. ER stress, caused by protein overproduction and misfolding, is a well-known pathology in neurodegeneration, cancer and numerous other diseases. How ER stress affects cell communication via transmembrane receptors is largely unknown. In disease models of multiple myeloma, chronic lymphocytic leukemia and osteogenesis imperfecta, we show that ER stress leads to loss of the mature transmembrane receptors FGFR3, ROR1, FGFR1, LRP6, FZD5 and PTH1R at the cell surface, resulting in impaired downstream signaling. This is caused by downregulation of receptor production and increased intracellular retention of immature receptor forms. Reduction of ER stress by treatment of cells with the chemical chaperone tauroursodeoxycholic acid or by expression of the chaperone protein BiP resulted in restoration of receptor maturation and signaling. We show a previously unappreciated pathological effect of ER stress; impaired cellular communication due to altered receptor processing. Our findings have implications for disease mechanisms related to ER stress and are particularly important when receptor-based pharmacological approaches are used for treatment.

• Keywords
• ER, Endoplasmic reticulum, Impaired, Receptor, Signaling, Stress, Transmembrane,
• MeSH
• Endoplasmic Reticulum Chaperone BiP MeSH
• Taurochenodeoxycholic Acid pharmacology   MeSH
• Humans MeSH
• Cell Line, Tumor MeSH
• Receptors, Cell Surface * metabolism   MeSH
• Signal Transduction * drug effects   MeSH
• Endoplasmic Reticulum Stress * drug effects   MeSH
• Animals MeSH
• Check Tag
• Humans MeSH
• Animals MeSH
• Publication type
• Journal Article MeSH
• Names of Substances
• Endoplasmic Reticulum Chaperone BiP MeSH
• Taurochenodeoxycholic Acid MeSH
• Receptors, Cell Surface * MeSH
• ursodoxicoltaurine MeSH Browser

Fibroblast growth factors (FGFs) control organ morphogenesis during development as well as tissue homeostasis and repair in the adult organism. Despite their importance, many mechanisms that regulate FGF function are still poorly understood. Interestingly, the thermodynamic stability of 22 mammalian FGFs varies widely, with some FGFs remaining stable at body temperature for more than 24 h, while others lose their activity within minutes. How thermodynamic stability contributes to the function of FGFs during development remains unknown. Here we show that FGF10, an important limb and lung morphogen, exists as an intrinsically unstable protein that is prone to unfolding and is rapidly inactivated at 37 °C. Using rationally driven directed mutagenesis, we have developed several highly stable (STAB) FGF10 variants with a melting temperature of over 19 °C more than that of wildtype FGF10. In cellular assays in vitro, the FGF10-STABs did not differ from wildtype FGF10 in terms of binding to FGF receptors, activation of downstream FGF receptor signaling in cells, and induction of gene expression. In mouse embryonal lung explants, FGF10-STABs, but not wildtype FGF10, suppressed branching, resulting in increased alveolarization and expansion of epithelial tissue. Similarly, FGF10-STAB1, but not FGF10 wildtype, inhibited the growth of mouse embryonic tibias and markedly altered limb morphogenesis when implanted into chicken limb buds, collectively demonstrating that thermal instability should be considered an important regulator of FGF function that prevents ectopic signaling. Furthermore, we show enhanced differentiation of human iPSC-derived lung organoids and improved regeneration in ex vivo lung injury models mediated by FGF10-STABs, suggesting an application in cell therapy.

• Keywords
• Development, FGF10, Fibroblast growth factor, Lung, Morphogen, Stability,
• MeSH
• Fibroblast Growth Factor 10 * metabolism   genetics   chemistry   MeSH
• Humans MeSH
• Mice MeSH
• Lung metabolism   embryology   MeSH
• Receptors, Fibroblast Growth Factor metabolism   MeSH
• Signal Transduction * MeSH
• Protein Stability MeSH
• Animals MeSH
• Check Tag
• Humans MeSH
• Mice MeSH
• Animals MeSH
• Publication type
• Journal Article MeSH
• Names of Substances
• Fgf10 protein, mouse MeSH Browser
• Fibroblast Growth Factor 10 * MeSH
• Receptors, Fibroblast Growth Factor MeSH

Impaired fibroblast growth factor receptor (FGFR) signaling is associated with many human conditions, including growth disorders, degenerative diseases, and cancer. Current FGFR therapeutics are based on chemical inhibitors of FGFR tyrosine kinase activity (TKIs). However, FGFR TKIs are limited in their target specificity as they generally inhibit all FGFRs and other receptor tyrosine kinases. In the search for specific inhibitors of human FGFR1, we identified VZ23, a DNA aptamer that binds to FGFR1b and FGFR1c with a KD of 55 nM and 162 nM, respectively, but not to the other FGFR variants (FGFR2b, FGFR2c, FGFR3b, FGFR3c, FGFR4). In cells, VZ23 inhibited the activation of downstream FGFR1 signaling and FGFR1-mediated regulation of cellular senescence, proliferation, and extracellular matrix homeostasis. Consistent with the specificity toward FGFR1 observed in vitro, VZ23 did not inhibit FGFR2-4 signaling in cells. We show that the VZ23 inhibits FGFR1 signaling in the presence of cognate fibroblast growth factor (FGF) ligands and its inhibitory activity is linked to its capacity to form unusual G-quadruplex structure. Our data suggest that targeting FGFR1 with DNA aptamers could be an effective alternative to TKIs for treating impaired FGFR1 signaling in human craniosynostoses.

• Keywords
• DNA aptamer, FGFR signaling, FGFR1, MT: Oligonucleotides: Therapies and Applications, craniosynostosis, extracellular domain, inhibitor, skeletal dysplasia,
• Publication type
• Journal Article MeSH

Most of our knowledge of protein structure and function originates from experiments performed with purified proteins resuspended in dilute, buffered solutions. However, most proteins function in crowded intracellular environments with complex compositions. Significant efforts have been made to develop tools to study proteins in their native cellular settings. Among these tools, in-cell NMR spectroscopy has been the sole technique for characterizing proteins in the intracellular space of living cells at atomic resolution and physiological temperature. Nevertheless, due to technological constraints, in-cell NMR studies have been limited to asynchronous single-cell suspensions, precluding obtaining information on protein behavior in different cellular states. In this study, we present a methodology that allows for obtaining an atomically resolved NMR readout of protein structure and interactions in living human cells synchronized in specific cell cycle phases and within 3D models of human tissue. The described approach opens avenues for investigating how protein structure or drug recognition responds to cell-cell communication or changes in intracellular space composition during transitions among cell cycle phases.

• MeSH
• Cell Cycle * MeSH
• Protein Conformation MeSH
• Humans MeSH
• Magnetic Resonance Spectroscopy methods   MeSH
• Proteins * chemistry   metabolism   MeSH
• Check Tag
• Humans MeSH
• Publication type
• Journal Article MeSH
• Names of Substances
• Proteins * MeSH

The eIF4F translation initiation complex plays a critical role in melanoma resistance to clinical BRAF and MEK inhibitors. In this study, we uncover a function of eIF4F in the negative regulation of the rat sarcoma (RAS)/rapidly accelerated fibrosarcoma (RAF)/mitogen-activated protein kinase kinase (MEK)/extracellular signal-regulated kinase (ERK) mitogen-activated protein kinase (MAPK) signaling pathway. We demonstrate that eIF4F is essential for controlling ERK signaling intensity in treatment-naïve melanoma cells harboring BRAF or NRAS mutations. Specifically, the dual-specificity phosphatase DUSP6/MKP3, which acts as a negative feedback regulator of ERK activity, requires continuous production in an eIF4F-dependent manner to limit excessive ERK signaling driven by oncogenic RAF/RAS mutations. Treatment with small-molecule eIF4F inhibitors disrupts the negative feedback control of MAPK signaling, leading to ERK hyperactivation and EGR1 overexpression in melanoma cells in vitro and in vivo. Furthermore, our quantitative analyses reveal a high spare signaling capacity in the ERK pathway, suggesting that eIF4F-dependent feedback keeps the majority of ERK molecules inactive under normal conditions. Overall, our findings highlight the crucial role of eIF4F in regulating ERK signaling flux and suggest that pharmacological eIF4F inhibitors can disrupt the negative feedback control of MAPK activity in melanomas with BRAF and NRAS activating mutations.

• Keywords
• DUSP6, ERK, MAP kinase, eIF4F, melanoma,
• MeSH
• Eukaryotic Initiation Factor-4F * metabolism   genetics   MeSH
• Extracellular Signal-Regulated MAP Kinases metabolism   MeSH
• Dual Specificity Phosphatase 6 metabolism   genetics   MeSH
• GTP Phosphohydrolases * metabolism   genetics   MeSH
• Humans MeSH
• MAP Kinase Signaling System * genetics   MeSH
• Melanoma * genetics   metabolism   pathology   MeSH
• Membrane Proteins * metabolism   genetics   MeSH
• Mutation * MeSH
• Mice MeSH
• Cell Line, Tumor MeSH
• Proto-Oncogene Proteins B-raf * genetics   metabolism   MeSH
• Animals MeSH
• Check Tag
• Humans MeSH
• Mice MeSH
• Animals MeSH
• Publication type
• Journal Article MeSH
• Names of Substances
• BRAF protein, human MeSH Browser
• DUSP6 protein, human MeSH Browser
• EIF4E protein, human MeSH Browser
• Eukaryotic Initiation Factor-4F * MeSH
• Extracellular Signal-Regulated MAP Kinases MeSH
• Dual Specificity Phosphatase 6 MeSH
• GTP Phosphohydrolases * MeSH
• Membrane Proteins * MeSH
• NRAS protein, human MeSH Browser
• Proto-Oncogene Proteins B-raf * MeSH

The differential signaling of multiple FGF ligands through a single fibroblast growth factor (FGF) receptor (FGFR) plays an important role in embryonic development. Here, we use quantitative biophysical tools to uncover the mechanism behind differences in FGFR1c signaling in response to FGF4, FGF8, and FGF9, a process which is relevant for limb bud outgrowth. We find that FGF8 preferentially induces FRS2 phosphorylation and extracellular matrix loss, while FGF4 and FGF9 preferentially induce FGFR1c phosphorylation and cell growth arrest. Thus, we demonstrate that FGF8 is a biased FGFR1c ligand, as compared to FGF4 and FGF9. Förster resonance energy transfer experiments reveal a correlation between biased signaling and the conformation of the FGFR1c transmembrane domain dimer. Our findings expand the mechanistic understanding of FGF signaling during development and bring the poorly understood concept of receptor tyrosine kinase ligand bias into the spotlight.

• Keywords
• FGFR, biased signaling, molecular biophysics, none, signal transduction, structural biology,
• MeSH
• Fibroblast Growth Factors * MeSH
• Phosphorylation MeSH
• Humans MeSH
• Ligands MeSH
• Receptor, Fibroblast Growth Factor, Type 1 genetics   MeSH
• Signal Transduction * MeSH
• Pregnancy MeSH
• Bias MeSH
• Check Tag
• Humans MeSH
• Pregnancy MeSH
• Female MeSH
• Publication type
• Journal Article MeSH
• Names of Substances
• FGFR1 protein, human MeSH Browser
• Fibroblast Growth Factors * MeSH
• Ligands MeSH
• Receptor, Fibroblast Growth Factor, Type 1 MeSH

Luciferase reporter assays represent a simple and sensitive experimental system in cell and molecular biology to study multiple biological processes. However, the application of these assays is often limited by the costs of conventional luminometer instruments and the versatility of their use in different experimental conditions. Therefore, we aimed to develop a small, affordable luminometer allowing continuous measurement of luciferase activity, designed for inclusion into various kinds of tissue culture incubators. Here, we introduce LuminoCell-an open-source platform for the construction of an affordable, sensitive, and portable luminometer capable of real-time monitoring in-cell luciferase activity. The LuminoCell costs $40, requires less than 1 h to assemble, and it is capable of performing real-time sensitive detection of both magnitude and duration of the activity of major signalling pathways in cell cultures, including receptor tyrosine kinases (EGF and FGF), WNT/β-catenin, and NF-κB. In addition, we show that the LuminoCell is suitable to be used in cytotoxicity assays as well as for monitoring periodic circadian gene expression.

• MeSH
• Luciferases genetics   metabolism   MeSH
• NF-kappa B * metabolism   MeSH
• Signal Transduction * MeSH
• Publication type
• Journal Article MeSH
• Research Support, Non-U.S. Gov't MeSH
• Names of Substances
• Luciferases MeSH
• NF-kappa B * MeSH

BRAF inhibitors can delay the progression of metastatic melanoma, but resistance usually emerges, leading to relapse. Drugs simultaneously targeting two or more pathways essential for cancer growth could slow or prevent the development of resistant clones. Here, we identified pyridinyl imidazole compounds SB202190, SB203580, and SB590885 as dual inhibitors of critical proliferative pathways in human melanoma cells bearing the V600E activating mutation of BRAF kinase. We found that the drugs simultaneously disrupt the BRAF V600E-driven extracellular signal-regulated kinase (ERK) mitogen-activated protein kinase (MAPK) activity and the mechanistic target of rapamycin complex 1 (mTORC1) signaling in melanoma cells. Pyridinyl imidazole compounds directly inhibit BRAF V600E kinase. Moreover, they interfere with the endolysosomal compartment, promoting the accumulation of large acidic vacuole-like vesicles and dynamic changes in mTOR signaling. A transient increase in mTORC1 activity is followed by the enrichment of the Ragulator complex protein p18/LAMTOR1 at contact sites of large vesicles and delocalization of mTOR from the lysosomes. The induced disruption of the endolysosomal pathway not only disrupts mTORC1 signaling, but also renders melanoma cells sensitive to endoplasmic reticulum (ER) stress. Our findings identify new activities of pharmacologically relevant small molecule compounds and provide a biological rationale for the development of anti-melanoma therapeutics based on the pyridinyl imidazole core.

• Keywords
• BRAF V600E, BRAF inhibitor, ER stress, endosome, lysosome, mTORC1, melanoma, pyridinyl imidazole, small molecule drug,
• Publication type
• Journal Article MeSH

Many tyrosine kinase inhibitors (TKIs) have failed to reach human use due to insufficient activity in clinical trials. However, the failed TKIs may still benefit patients if their other kinase targets are identified by providing treatment focused on syndromes driven by these kinases. Here, we searched for novel targets of AZD1480, an inhibitor of JAK2 kinase that recently failed phase two cancer clinical trials due to a lack of activity. Twenty seven human receptor tyrosine kinases (RTKs) and 153 of their disease-associated mutants were in-cell profiled for activity in the presence of AZD1480 using a newly developed RTK plasmid library. We demonstrate that AZD1480 inhibits ALK, LTK, FGFR1-3, RET and TRKA-C kinases and uncover a physical basis of this specificity. The RTK activity profiling described here facilitates inhibitor repurposing by enabling rapid and efficient identification of novel TKI targets in cells.

• Keywords
• AZD1480, drug repurposing, in-cell profiling, inhibitor, receptor tyrosine kinase,
• Publication type
• Journal Article MeSH