GABA receptor π forms channels that stimulate ERK through a G-protein-dependent pathway.

The rare γ-aminobutyric acid type-A receptor (GABAR) subunit π (GABRP) is highly expressed in certain cancers, where it stimulates growth through extracellular-regulated kinase (ERK) signaling by an uncharacterized pathway. To elucidate GABRP's signaling mechanism, we determined cryoelectron microscopy (cryo-EM) structures of GABRP embedded in native nanodiscs, both in the presence and absence of GABA. Structurally, GABRP homopentamers closely resemble heteropentameric GABAR anion channels, transitioning from a closed "resting" state to an open "active" state upon GABA binding.

7SK methylation by METTL3 promotes transcriptional activity.

A fundamental feature of cell signaling is the conversion of extracellular signals into adaptive transcriptional responses. The role of RNA modifications in this process is poorly understood. The small nuclear RNA 7SK prevents transcriptional elongation by sequestering the cyclin dependent kinase 9/cyclin T1 (CDK9/CCNT1) positive transcription elongation factor (P-TEFb) complex.

Massively parallel base editing to map variant effects in human hematopoiesis.

Systematic evaluation of the impact of genetic variants is critical for the study and treatment of human physiology and disease. While specific mutations can be introduced by genome engineering, we still lack scalable approaches that are applicable to the important setting of primary cells, such as blood and immune cells. Here, we describe the development of massively parallel base-editing screens in human hematopoietic stem and progenitor cells.

Structural basis for ligand reception by anaplastic lymphoma kinase.

The proto-oncogene ALK encodes anaplastic lymphoma kinase, a receptor tyrosine kinase that is expressed primarily in the developing nervous system. After development, ALK activity is associated with learning and memory and controls energy expenditure, and inhibition of ALK can prevent diet-induced obesity. Aberrant ALK signalling causes numerous cancers.

Inherited myeloproliferative neoplasm risk affects haematopoietic stem cells.

Myeloproliferative neoplasms (MPNs) are blood cancers that are characterized by the excessive production of mature myeloid cells and arise from the acquisition of somatic driver mutations in haematopoietic stem cells (HSCs). Epidemiological studies indicate a substantial heritable component of MPNs that is among the highest known for cancers. However, only a limited number of genetic risk loci have been identified, and the underlying biological mechanisms that lead to the acquisition of MPNs remain unclear.

Kinetics of receptor tyrosine kinase activation define ERK signaling dynamics.

In responses to activation of receptor tyrosine kinases (RTKs), crucial cell fate decisions depend on the duration and dynamics of ERK signaling. In PC12 cells, epidermal growth factor (EGF) induces transient ERK activation that leads to cell proliferation, whereas nerve growth factor (NGF) promotes sustained ERK activation and cell differentiation. These differences have typically been assumed to reflect distinct feedback mechanisms in the Raf-MEK-ERK signaling network, with the receptors themselves acting as simple upstream inputs.

Infantile Myelofibrosis and Myeloproliferation with CDC42 Dysfunction.

Studies of genetic blood disorders have advanced our understanding of the intrinsic regulation of hematopoiesis. However, such genetic studies have only yielded limited insights into how interactions between hematopoietic cells and their microenvironment are regulated. Here, we describe two affected siblings with infantile myelofibrosis and myeloproliferation that share a common de novo mutation in the Rho GTPase CDC42 (Chr1:22417990:C>T, p.

A ligand divided: antagonist, agonist and analog control.

Inhibiting receptor tyrosine kinases has been a cornerstone of cancer therapeutics for decades. Treatment strategies largely involve small-molecule kinase inhibitors and monoclonal antibodies. For receptors activated by constitutively dimeric ligands, another potential mechanism of inhibition exists: developing monomeric ligands that prevent receptor dimerization.

Functional Selectivity in Cytokine Signaling Revealed Through a Pathogenic EPO Mutation.

Cytokines are classically thought to stimulate downstream signaling pathways through monotonic activation of receptors. We describe a severe anemia resulting from a homozygous mutation (R150Q) in the cytokine erythropoietin (EPO). Surprisingly, the EPO R150Q mutant shows only a mild reduction in affinity for its receptor but has altered binding kinetics.

Structural Basis of Neurohormone Perception by the Receptor Tyrosine Kinase Torso.

In insects, brain-derived Prothoracicotropic hormone (PTTH) activates the receptor tyrosine kinase (RTK) Torso to initiate metamorphosis through the release of ecdysone. We have determined the crystal structure of silkworm PTTH in complex with the ligand-binding region of Torso. Here we show that ligand-induced Torso dimerization results from the sequential and negatively cooperative formation of asymmetric heterotetramers.

Sequential conformational rearrangements in flavivirus membrane fusion.

The West Nile Virus (WNV) envelope protein, E, promotes membrane fusion during viral cell entry by undergoing a low-pH triggered conformational reorganization. We have examined the mechanism of WNV fusion and sought evidence for potential intermediates during the conformational transition by following hemifusion of WNV virus-like particles (VLPs) in a single particle format. We have introduced specific mutations into E, to relate their influence on fusion kinetics to structural features of the protein.

Structure of a dengue virus envelope protein late-stage fusion intermediate.

The final stages of dengue virus fusion are thought to occur when the membrane-proximal stem drives the transmembrane anchor of the viral envelope protein (E) toward the fusion loop, buried in the target cell membrane. Crystal structures of E have lacked this essential stem region. We expressed and crystallized soluble mutant forms of the dengue virus envelope protein (sE) that include portions of the juxtamembrane stem.

Structural basis for negative cooperativity in growth factor binding to an EGF receptor.

Transmembrane signaling by the epidermal growth factor receptor (EGFR) involves ligand-induced dimerization and allosteric regulation of the intracellular tyrosine kinase domain. Crystallographic studies have shown how ligand binding induces dimerization of the EGFR extracellular region but cannot explain the "high-affinity" and "low-affinity" classes of cell-surface EGF-binding sites inferred from curved Scatchard plots. From a series of crystal structures of the Drosophila EGFR extracellular region, we show here how Scatchard plot curvature arises from negatively cooperative ligand binding.

ErbB2 resembles an autoinhibited invertebrate epidermal growth factor receptor.

The orphan receptor tyrosine kinase ErbB2 (also known as HER2 or Neu) transforms cells when overexpressed, and it is an important therapeutic target in human cancer. Structural studies have suggested that the oncogenic (and ligand-independent) signalling properties of ErbB2 result from the absence of a key intramolecular 'tether' in the extracellular region that autoinhibits other human ErbB receptors, including the epidermal growth factor (EGF) receptor. Although ErbB2 is unique among the four human ErbB receptors, here we show that it is the closest structural relative of the single EGF receptor family member in Drosophila melanogaster (dEGFR).

Structural basis for EGFR ligand sequestration by Argos.

Members of the epidermal growth factor receptor (EGFR) or ErbB/HER family and their activating ligands are essential regulators of diverse developmental processes. Inappropriate activation of these receptors is a key feature of many human cancers, and its reversal is an important clinical goal. A natural secreted antagonist of EGFR signalling, called Argos, was identified in Drosophila.

Computational analysis of EGFR inhibition by Argos.

Argos, a secreted inhibitor of the Drosophila epidermal growth factor receptor, and the only known secreted receptor tyrosine kinase inhibitor, acts by sequestering the EGFR ligand Spitz. We use computational modeling to show that this biochemically-determined mechanism of Argos action can explain available genetic data for EGFR/Spitz/Argos interactions in vivo. We find that efficient Spitz sequestration by Argos is key for explaining the existing data and for providing a robust feedback loop that modulates the Spitz gradient in embryonic ventral ectoderm patterning.

Argos inhibits epidermal growth factor receptor signalling by ligand sequestration.

The epidermal growth factor receptor (EGFR) has critical functions in development and in many human cancers. During development, the spatial extent of EGFR signalling is regulated by feedback loops comprising both well-understood activators and less well-characterized inhibitors. In Drosophila melanogaster the secreted protein Argos functions as the only known extracellular inhibitor of EGFR, with clearly identified roles in multiple stages of development.