Biology subjects

Schlessinger, J.

Publications and source records attributed to Schlessinger, J..

6 recordsLinked to original sources

bioRxiv2025

Cellular responses to FGF1 are modulated by palmitoylation of the docking protein FRS2α

An important mechanism by which receptor tyrosine kinases (RTKs) mediate cellular responses involves the formation of signaling complexes through direct interactions with membrane-associated docking proteins, followed by phosphorylation of multiple tyrosine residues. These docking proteins recruit and activate downstream signaling molecules and enzymes following ligand stimulation. The docking protein FRS2 has been established as a major signaling hub activated by fibroblast growth factors (FGFs), neurotrophic factors, and other extracellular cues. Here, we show that palmitoylation of FRS2 at two sites is essential for stabilizing its myristoylation-dependent association with the plasma membrane. FGF1-induced MAPK activation and other cellular responses are partially restored in cells expressing FRS2 mutants deficient in either one of the two palmitoylation sites. However full restoration of signal strength including MAPK response and other FGF1-induced cellular activities requires palmitoylation at both FRS2 sites. In addition to enhancing signaling robustness, anchoring of FRS2 to the plasma membrane creates a structural platform for assembling multi-protein complexes essential for cytoskeletal reorganization associated with membrane ruffling, macropinocytosis, and other FGF1-induced processes. Finally, we demonstrate that while PC12 cells lacking FRS2 or deficient in FRS2 palmitoylation can proliferate, FGF1-induced neuronal differentiation strictly depends on the palmitoylation of the docking protein.

biochemistry↗

bioRxiv2024

Inducible FAK Deletion but not FAK Inhibition in Endothelial Cells Activates p53 to Suppress Tumor Growth in PYK2-null Mice

Focal adhesion kinase (FAK) functions as a signaling and scaffolding protein within endothelial cells (ECs) impacting blood vessel function and tumor growth. Interpretations of EC FAK-null phenotypes are complicated by related PYK2 (protein tyrosine kinase 2) expression, and to test this, we created PYK2-/- FAKfl/fl mice with tamoxifen-inducible EC-specific Cre recombinase expression. At 11 weeks of age, EC FAK inactivation resulted in increased heart and lung mass and vascular leakage only on a PYK2-/- background. Surprisingly, [~]90% of PYK2-/- EC FAK-/- mice survived to 75 weeks of age. Syngeneic melanoma, breast, or lung carcinoma tumors did not grow in PYK2-/- EC FAK-/- mice, but tumors grew normally in PYK2-/- EC FAKfl/fl mice lacking Cre. This tumor inhibitory phenotype was associated with abortive EC vessel sprouting, enhanced EC p53 tumor suppressor and p21CIP1 (cyclin-dependent inhibitor 1) expression, and alterations in serum cytokine levels. To discern the role of FAK kinase versus scaffolding activity in ECs, we generated kinase defective (FAK K454R, KD) PYK2-/- EC FAKfl/KD and PYK2-/- EC FAKfl/WT (WT, wildtype) mice. Hemizygous EC FAK-/KD expression supported primary tumor growth but not metastasis, implicating EC FAK activity in tumor dissemination. In vitro, hemizygous expression of either WT or KD FAK suppressed EC p21CIP1 levels and cell death observed in primary PYK2-/- EC FAK-/- ECs. Combined FAK and PYK2 knockdown in tumor cells also increased p21CIP1 and PARP1 (poly ADP-ribose polymerase 1) levels in a p53-associated manner impacting anchorage-independent growth. Together, these results underscore the linkage between PYK2 and FAK loss with p53 activation impacting tumor growth. Impact StatementPYK2-null combined with endothelial cell-specific FAK transgenic mouse models show that loss of FAK activity limits tumor spread and that genetic or chemical degradation preventing combined FAK-PYK2 expression may be an approach to induce a p53-associated anti-tumor response.

cell biology↗

bioRxiv2023

Modulation of FGF pathway signaling and vascular differentiation using designed oligomeric assemblies

Growth factors and cytokines signal by binding to the extracellular domains of their receptors and drive association and transphosphorylation of the receptor intracellular tyrosine kinase domains, initiating downstream signaling cascades. To enable systematic exploration of how receptor valency and geometry affects signaling outcomes, we designed cyclic homo-oligomers with up to 8 subunits using repeat protein building blocks that can be modularly extended. By incorporating a de novo designed fibroblast growth-factor receptor (FGFR) binding module into these scaffolds, we generated a series of synthetic signaling ligands that exhibit potent valency- and geometry-dependent Ca2+ release and MAPK pathway activation. The high specificity of the designed agonists reveal distinct roles for two FGFR splice variants in driving endothelial and mesenchymal cell fates during early vascular development. The ability to incorporate receptor binding domains and repeat extensions in a modular fashion makes our designed scaffolds broadly useful for probing and manipulating cellular signaling pathways. HighlightsO_LIDe novo designed cyclic oligomers with tunable geometric properties C_LIO_LICyclic, homo-oligomeric FGFR binding modules induce geometry- and valency-dependent activity of isoform-specific FGF signaling C_LIO_LIModulation of FGFR isoform activity controls bifurcation of endothelial and mesenchymal fate during vascular development C_LIO_LIC-isoform activation favors arterial endothelial cell formation while B-isoform induces pericyte differentiation C_LI Graphical Abstract O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=135 SRC="FIGDIR/small/532666v1_ufig1.gif" ALT="Figure 1"> View larger version (35K): org.highwire.dtl.DTLVardef@151f6eforg.highwire.dtl.DTLVardef@2ae877org.highwire.dtl.DTLVardef@103e0d1org.highwire.dtl.DTLVardef@19cd695_HPS_FORMAT_FIGEXP M_FIG C_FIG

bioengineering↗

bioRxiv2022

Cryo-EM analyses of wild-type and oncogenic KIT mutants reveal structural oncogenic plasticity and a novel Achilles heel for therapeutic intervention

The receptor tyrosine kinase KIT and its ligand SCF are required for the development of hematopoietic stem cells, germ cells, and other cells. A variety of human cancers, such as acute myeloid leukemia and mast cell leukemia, are driven by somatic gain-of-function KIT mutations. Here, we report cryo-EM structural analyses of full-length wild-type and two oncogenic KIT mutants, which show that the symmetric arrangement of ligand-occupied KIT dimers is converted into asymmetric D5 homotypic contacts juxtaposing the plasma membrane. Mutational analysis of KIT reveals in D5 region an "Achilles heel" for therapeutic intervention. A ligand-sensitized oncogenic KIT mutant exhibits a more comprehensive and stable D5 asymmetric conformation. A constitutively active ligand-independent oncogenic KIT mutant adopts a V-shaped conformation solely held by D5-mediated contacts. SCF binding to this mutant fully restores the conformation of wild-type KIT dimers, revealing an unexpected structural plasticity of oncogenic mutants that may offer new therapeutic modality.

biochemistry↗

bioRxiv2022

Regulation of EGF-stimulated activation of the PI-3K/AKT pathway by exocyst-mediated exocytosis

The phosphoinositide-3 kinase (PI-3K)/AKT cell survival pathway is an important pathway activated by EGFR signaling. Here we show, that in addition to previously described critical components of this pathway, i.e., the docking protein Gab1, the PI-3K/AKT pathway in epithelial cells is regulated by the exocyst complex, which is a vesicle tether that is essential for exocytosis. Using live-cell imaging, we demonstrate that PI(3,4,5)P3 levels fluctuate at the membrane on a minutes time scale and that these fluctuations are associated with local PI(3,4,5)P3 increases at sites where recycling vesicles undergo exocytic fusion. Supporting a role for exocytosis in PI(3,4,5)P3 generation, acute promotion of exocytosis by optogenetically driving exocyst-mediated vesicle tethering upregulates PI(3,4,5)P3 production and AKT activation. Conversely, acute inhibition of exocytosis using Endosidin2, a small-molecule inhibitor of the exocyst subunit Exo70, impairs PI(3,4,5)P3 production and AKT activation induced by EGF stimulation of epithelial cells. Moreover, prolonged inhibition of EGF signaling by EGFR tyrosine kinase inhibitors results in spontaneous reactivation of AKT without a concomitant relief of EGFR inhibition. However, this reactivation can be negated by acutely inhibiting the exocyst. These experiments demonstrate that exocyst-mediated exocytosis - by regulating PI(3,4,5)P3 levels at the plasma membrane - subserves activation of the PI-3K/AKT pathway by EGFR in epithelial cells.

cell biology↗

bioRxiv2021

Robust de novo design of protein binding proteins from target structural information alone

The design of proteins that bind to a specific site on the surface of a target protein using no information other than the three-dimensional structure of the target remains an outstanding challenge. We describe a general solution to this problem which starts with a broad exploration of the very large space of possible binding modes and interactions, and then intensifies the search in the most promising regions. We demonstrate its very broad applicability by de novo design of binding proteins to 12 diverse protein targets with very different shapes and surface properties. Biophysical characterization shows that the binders, which are all smaller than 65 amino acids, are hyperstable and bind their targets with nanomolar to picomolar affinities. We succeeded in solving crystal structures of four of the binder-target complexes, and all four are very close to the corresponding computational design models. Experimental data on nearly half a million computational designs and hundreds of thousands of point mutants provide detailed feedback on the strengths and limitations of the method and of our current understanding of protein-protein interactions, and should guide improvement of both. Our approach now enables targeted design of binders to sites of interest on a wide variety of proteins for therapeutic and diagnostic applications.

synthetic biology↗