Guanine-nucleotide-releasing factor hSos1 binds to Grb2 and links receptor tyrosine kinases to Ras signalling

Chemical Scaffolds for the Clinical Development of Mutant-Selective and Reversible Fourth-Generation EGFR-TKIs in NSCLC

In nonsmall cell lung cancer (NSCLC), as well as in other tumors, the targeted therapy is mainly represented by tyrosine kinase inhibitors (TKIs), small molecules able to target oncogenic driver alterations affecting the gene encoding the epidermal growth factor receptor (EGFR). Up to now, several different TKIs have been developed. However, cancer cells showed an incredible adaptive tumor response to the inhibition of the sequentially mutated EGFR (EGFRM+), triggering the need to explore novel pharmacochemical strategies. This Review summarizes the recent efforts in the development of new reversible next-generation EGFR TKIs to fight the resistance against T790M and C797S mutations. Specifically, after giving an overview of the role of the EGFR's signaling pathways in cancer progression, we are going to discuss the most relevant approved drugs and drug candidates in terms of chemical structure, binding modalities, and their potency and selectivity against the mutated EGFR over the wild-type form. This could provide important guidelines and rationale for the discovery and iterative development of new drugs.

GRB2 stabilizes RAD51 at reversed replication forks suppressing genomic instability and innate immunity against cancer

Growth factor receptor-bound protein 2 (GRB2) is a cytoplasmic adapter for tyrosine kinase signaling and a nuclear adapter for homology-directed-DNA repair. Here we find nuclear GRB2 protects DNA at stalled replication forks from MRE11-mediated degradation in the BRCA2 replication fork protection axis. Mechanistically, GRB2 binds and inhibits RAD51 ATPase activity to stabilize RAD51 on stalled replication forks. In GRB2-depleted cells, PARP inhibitor (PARPi) treatment releases DNA fragments from stalled forks into the cytoplasm that activate the cGAS-STING pathway to trigger pro-inflammatory cytokine production. Moreover in a syngeneic mouse metastatic ovarian cancer model, GRB2 depletion in the context of PARPi treatment reduced tumor burden and enabled high survival consistent with immune suppression of cancer growth. Collective findings unveil GRB2 function and mechanism for fork protection in the BRCA2-RAD51-MRE11 axis and suggest GRB2 as a potential therapeutic target and an enabling predictive biomarker for patient selection for PARPi and immunotherapy combination.

Identification of miR-128 Target mRNAs That Are Expressed in B Cells Using a Modified Dual Luciferase Vector

MicroRNAs (miRNAs) are 21-25 nucleotide long non-coding ribonucleic acids that modulate gene expression by degrading transcripts or inhibiting translation. The miRNA miR-128, originally thought to be brain-specific, was later also found in immune cells. To identify a valuable immune cell model system to modulate endogenous miR-128 amounts and to validate predicted miR-128 target mRNAs in B cells, we first investigated miR-128 expression using Northern blot analysis in several cell lines representing different stages of B cell development. The results showed that only primary brain cells showed significant levels of mature miR-128. To study the function of miR-128 in immune cells, we modified dual luciferase vectors to allow easy transfer of 3' UTR fragments with predicted miR-128 binding sites from widely used single to dual luciferase vectors. Comparison of in silico predicted miR-128-regulated mRNAs in single and dual luciferase constructs yielded similar results, validating the dual luciferase vector for miRNA target analysis. Furthermore, we confirmed miR-128-regulated mRNAs identified in silico and in vivo using the Ago HITS-CLIP technique and known to be expressed in B cells using the dual luciferase assay. In conclusion, this study provides new insights into the expression and function of miR-128 by validating novel target mRNAs expressed in B cells and identifying additional pathways likely controlled by this miRNA in the immune system.

Interactions of the N- and C-Terminal SH3 Domains of Drosophila Drk with the Proline-Rich Peptides from Sos and Dos

Drk, a homologue of human GRB2 in Drosophila, receives signals from outside the cells through the interaction of its SH2 domain with the phospho-tyrosine residues in the intracellular regions of receptor tyrosine kinases (RTKs) such as Sevenless, and transduces the signals downstream through the association of its N- and C-terminal SH3 domains (Drk-NSH3 and Drk-CSH3, respectively) with proline-rich motifs (PRMs) in Son of Sevenless (Sos) or Daughter of Sevenless (Dos). Isolated Drk-NSH3 exhibits a conformational equilibrium between the folded and unfolded states, while Drk-CSH3 adopts only a folded confirmation. Drk interacts with PRMs of the PxxPxR motif in Sos and the PxxxRxxKP motif in Dos. Our previous study has shown that Drk-CSH3 can bind to Sos, but the interaction between Drk-NSH3 and Dos has not been investigated. To assess the affinities of both SH3 domains towards Sos and Dos, we conducted NMR titration experiments using peptides derived from Sos and Dos. Sos-S1 binds to Drk-NSH3 with the highest affinity, strongly suggesting that the Drk-Sos multivalent interaction is initiated by the binding of Sos-S1 and NSH3. Our results also revealed that the two Sos-derived PRMs clearly favour NSH3 for binding, whereas the two Dos-derived PRMs show almost similar affinity for NSH3 and CSH3. We have also performed docking simulations based on the chemical shift perturbations caused by the addition of Sos- and Dos-derived peptides. Finally, we discussed the various modes in the interactions of Drk with Sos/Dos.

Protein quality control machinery supports primary ciliogenesis by eliminating GDP-bound Rab8-family GTPases

The small GTPase Rab8 plays a vital role in the vesicular trafficking of cargo proteins from the trans-Golgi network to target membranes. Upon reaching its target destination, Rab8 is released from the vesicular membrane into the cytoplasm via guanosine triphosphate (GTP) hydrolysis. The fate of GDP-bound Rab8 released from the destination membranes, however, has not been investigated adequately. In this study, we found that GDP-bound Rab8 subfamily proteins are targeted for immediate degradation, and the pre-emptive quality control machinery is responsible for eliminating these proteins in a nucleotide-specific manner. We provide evidence that components of this quality control machinery have a critical role in vesicular trafficking events, including the formation of primary cilia, a process regulated by the Rab8 subfamily. These results suggest that the protein degradation machinery plays a critical role in the integrity of membrane trafficking by limiting the excessive accumulation of GDP-bound Rab8 subfamily proteins.

Development of Son of Sevenless Homologue 1 (SOS1) Modulators To Treat Cancers by Regulating RAS Signaling

Son of sevenless homologue 1 (SOS1) protein is universally expressed in cells and plays an important role in the RAS signaling pathway. Specifically, this protein interacts with RAS in response to upstream stimuli to promote guanine nucleotide exchange in RAS and activates the downstream signaling pathways. Thus, targeting SOS1 is a new approach for treating RAS-driven cancers. In this Perspective, we briefly summarize the structural and functional aspects of SOS1 and focus on recent advances in the discovery of activators, inhibitors, and PROTACs that target SOS1. This review aims to provide a timely and updated overview on the strategies for targeting SOS1 in cancer therapy.

Sex-Based Differences in Human Neutrophil Chemorepulsion

A considerable amount is known about how eukaryotic cells move toward an attractant, and the mechanisms are conserved from Dictyostelium discoideum to human neutrophils. Relatively little is known about chemorepulsion, where cells move away from a repellent signal. We previously identified pathways mediating chemorepulsion in Dictyostelium, and here we show that these pathways, including Ras, Rac, protein kinase C, PTEN, and ERK1 and 2, are required for human neutrophil chemorepulsion, and, as with Dictyostelium chemorepulsion, PI3K and phospholipase C are not necessary, suggesting that eukaryotic chemorepulsion mechanisms are conserved. Surprisingly, there were differences between male and female neutrophils. Inhibition of Rho-associated kinases or Cdc42 caused male neutrophils to be more repelled by a chemorepellent and female neutrophils to be attracted to the chemorepellent. In the presence of a chemorepellent, compared with male neutrophils, female neutrophils showed a reduced percentage of repelled neutrophils, greater persistence of movement, more adhesion, less accumulation of PI(3,4,5)P₃, and less polymerization of actin. Five proteins associated with chemorepulsion pathways are differentially abundant, with three of the five showing sex dimorphism in protein localization in unstimulated male and female neutrophils. Together, this indicates a fundamental difference in a motility mechanism in the innate immune system in men and women.

Targeting RAS oncogenesis with SOS1 inhibitors

RAS proteins play major roles in many human cancers, but programs to develop direct RAS inhibitors so far have only been successful for the oncogenic KRAS mutant G12C. As an alternative approach, inhibitors for the RAS guanine nucleotide exchange factor SOS1 have been investigated by several academic groups and companies, and major progress has been achieved in recent years in the optimization of small molecule activators and inhibitors of SOS1. Here, we review the discovery and development of small molecule modulators of SOS1 and their molecular binding modes and modes of action. As targeting the RAS pathway is expected to result in the development of resistance mechanisms, SOS1 inhibitors will most likely be best applied in vertical combination approaches where two nodes of the RAS signaling pathway are hit simultaneously. We summarize the current understanding of which combination partners may be most beneficial for patients with RAS driven tumors.

RAS pathway regulation in melanoma

Activating mutations in RAS genes are the most common genetic driver of human cancers. Yet, drugging this small GTPase has proven extremely challenging and therapeutic strategies targeting these recurrent alterations have long had limited success. To circumvent this difficulty, research has focused on the molecular dissection of the RAS pathway to gain a more-precise mechanistic understanding of its regulation, with the hope to identify new pharmacological approaches. Here, we review the current knowledge on the (dys)regulation of the RAS pathway, using melanoma as a paradigm. We first present a map of the main proteins involved in the RAS pathway, highlighting recent insights into their molecular roles and diverse mechanisms of regulation. We then overview genetic data pertaining to RAS pathway alterations in melanoma, along with insight into other cancers, that inform the biological function of members of the pathway. Finally, we describe the clinical implications of RAS pathway dysregulation in melanoma, discuss past and current approaches aimed at drugging the RAS pathway, and outline future opportunities for therapeutic development.

Summary: This Review describes the molecular regulation of the RAS pathway, presents the clinical consequences of its pathological activation in human cancer, and highlights recent advances towards its therapeutic inhibition, using melanoma as an example.

Eph/Ephrin-Based Protein Complexes: The Importance of cis Interactions in Guiding Cellular Processes

Although intracellular signal transduction is generally represented as a linear process that transmits stimuli from the exterior of a cell to the interior via a transmembrane receptor, interactions with additional membrane-associated proteins are often critical to its success. These molecules play a pivotal role in mediating signaling via the formation of complexes in cis (within the same membrane) with primary effectors, particularly in the context of tumorigenesis. Such secondary effectors may act to promote successful signaling by mediating receptor-ligand binding, recruitment of molecular partners for the formation of multiprotein complexes, or differential signaling outcomes. One signaling family whose contact-mediated activity is frequently modulated by lateral interactions at the cell surface is Eph/ephrin (EphA and EphB receptor tyrosine kinases and their ligands ephrin-As and ephrin-Bs). Through heterotypic interactions in cis, these molecules can promote a diverse range of cellular activities, including some that are mutually exclusive (cell proliferation and cell differentiation, or adhesion and migration). Due to their broad expression in most tissues and their promiscuous binding within and across classes, the cellular response to Eph:ephrin interaction is highly variable between cell types and is dependent on the cellular context in which binding occurs. In this review, we will discuss interactions between molecules in cis at the cell membrane, with emphasis on their role in modulating Eph/ephrin signaling.

Cell Signaling and Translational Developmental Therapeutics

The relationships between drug pharmacodynamics and subsequent changes in cellular signaling processes are complex. Many in vitro cell signaling studies often use drug concentrations above physiologically safe drug levels achievable in a patient's plasma. Drug companies develop agents to inhibit or modify the activities of specific target enzymes, often without a full consideration that their compounds have additional unknown targets. These two negative sequelae, when published together, become impediments against successful developmental therapeutics and translation because this data distorts our understanding of signaling mechanisms and reduces the probability of successfully translating drug-based concepts from the bench to the bedside. This article will discuss cellular signaling in isolation and as it relates to extant single and combined therapeutic drug interventions. This will lead to a hypothetical series standardized sequential approaches describing a rigorous concept to drug development and clinical translation.

Allosteric regulation of GRB2 modulates RAS activation

RAS activation is a multiple-step process in which linkage of the extracellular stimuli to the RAS activator SOS1 is the main step in RAS activation. GRB2 adaptor protein is the main modulator in SOS1 recruitment to the plasma membrane and its activation. This interaction is well studied but the exact mechanism of GRB2-SOS1 complex formation and SOS1 activation has yet remained obscure. Here, a new allosteric mechanism for the GRB2 regulation is described as a prerequisite for the modulation of SOS1 activation. This regulatory mechanism comprises a series of intramolecular interactions which are potentiated by GRB2 interaction with upstream ligands.Abbreviations: GRB2, growth factor receptor-bound protein 2; SOS1, son of sevenless 1; RAS, Rat Sarcoma; GEF, guanine nucleotide exchange factor; GAP, GTPase-activating protein; HER2, human epidermal growth factor receptor; SH3, SRC Homology 3; SH2, SRC Homology 2; PRD, proline-rich domain; PRM, proline-rich motif; PRP, proline-rich peptide; RTK, receptor tyrosine kinases.

Relating cellular signaling timescales to single-molecule kinetics: A first-passage time analysis of Ras activation by SOS

Son of Sevenless (SOS) is a Ras guanine nucleotide exchange factor (GEF) that plays a central role in numerous cellular signaling pathways. Like many other signaling molecules, SOS is autoinhibited in the cytosol and activates only after recruitment to the membrane. The mean activation time of individual SOS molecules has recently been measured to be ∼60 s, which is unexpectedly long and seemingly contradictory with cellular signaling timescales, which have been measured to be as fast as several seconds. Here, we rectify this discrepancy using a first-passage time analysis to reconstruct the effective signaling timescale of multiple SOS molecules from their single-molecule activation kinetics. Along with corresponding experimental measurements, this analysis reveals how the functional response time, comprised of many slowly activating molecules, can become substantially faster than the average molecular kinetics. This consequence stems from the enzymatic processivity of SOS in a highly out-of-equilibrium reaction cycle during receptor triggering. Ultimately, rare, early activation events dominate the macroscopic reaction dynamics.

A Rational Design of α-Helix-Shaped Peptides Employing the Hydrogen-Bond Surrogate Approach: A Modulation Strategy for Ras-RasGRF1 Interaction in Neuropsychiatric Disorders

In the last two decades, abnormal Ras (rat sarcoma protein)-ERK (extracellular signal-regulated kinase) signalling in the brain has been involved in a variety of neuropsychiatric disorders, including drug addiction, certain forms of intellectual disability, and autism spectrum disorder. Modulation of membrane-receptor-mediated Ras activation has been proposed as a potential target mechanism to attenuate ERK signalling in the brain. Previously, we showed that a cell penetrating peptide, RB3, was able to inhibit downstream signalling by preventing RasGRF1 (Ras guanine nucleotide-releasing factor 1), a neuronal specific GDP/GTP exchange factor, to bind Ras proteins, both in brain slices and in vivo, with an IC₅₀ value in the micromolar range. The aim of this work was to mutate and improve this peptide through computer-aided techniques to increase its inhibitory activity against RasGRF1. The designed peptides were built based on the RB3 peptide structure corresponding to the α-helix of RasGRF1 responsible for Ras binding. For this purpose, the hydrogen-bond surrogate (HBS) approach was exploited to maintain the helical conformation of the designed peptides. Finally, residue scanning, MD simulations, and MM-GBSA calculations were used to identify 18 most promising α-helix-shaped peptides that will be assayed to check their potential activity against Ras-RasGRF1 and prevent downstream molecular events implicated in brain disorders.

Kinase-Catalyzed Biotinylation to Map Cell Signaling Pathways: Application to Epidermal Growth Factor Signaling

Cell signaling involves a network of protein-protein interactions and post-translational modifications that govern cellular responses to environmental cues. To understand and ultimately modulate these signaling pathways to confront disease, the complex web of proteins that becomes phosphorylated after extracellular stimulation has been studied using mass spectrometry-based proteomics methods. To complement prior work and fully characterize all phosphorylated proteins after the stimulation of cell signaling, we developed K-BMAPS (kinase-catalyzed biotinylation to map signaling), which utilizes ATP-biotin as a kinase cosubstrate to biotin label substrates. As a first application of the K-BMAPS method, the well-characterized epidermal growth factor receptor (EGFR) kinase signaling pathway was monitored by treating epidermal growth factor (EGF)-stimulated HeLa lysates with ATP-biotin, followed by streptavidin enrichment and quantitative mass spectrometry analysis. On the basis of the dynamic phosphoproteins identified, a pathway map was developed considering functional categories and known interactors of EGFR. Remarkably, 94% of the K-BMAPS hit proteins were included in the EGFR pathway map. With many proteins involved in transcription, translation, cell adhesion, and GTPase signaling, K-BMAPS identified phosphoproteins were associated with late and continuous signaling events. In summary, the K-BMAPS method is a powerful tool to map the dynamic phosphorylation governing cell signaling pathways.

Small molecule Son of Sevenless 1 (SOS1) inhibitors: a review of the patent literature

Introduction: Up to 30% of all human cancers are driven by the overactivation of RAS signaling. Son of Sevenless 1 (SOS1) is a central node in RAS signaling pathways and modulation of SOS1-mediated RAS activation represents a unique opportunity for treating RAS-addicted cancers. Several recent publications and patent documents have demonstrated the ability of small molecules to affect the activation of RAS by SOS1 and have shown their potential for the treatment of cancers driven by RAS mutants.Areas covered: Documents focusing on both small-molecule inhibitors and activators of the SOS1:RAS interaction and their potential use as cancer therapeutics are covered. A total of 10 documents from 4 applicants are evaluated with discussion focusing on structural modifications of these compounds as well as relevant preclinical data.Expert opinion: The last decade has seen a significant increase in research and disclosures in the development of small-molecule SOS1 inhibitors. Considering the promising data that have been disclosed, interest in this area of research will likely remain strong for the foreseeable future. With the first SOS1 inhibitor currently in phase I clinical trials, the outcome of these trials will likely influence future development of SOS1 inhibitors for treatment of RAS-driven cancers.

The intramolecular allostery of GRB2 governing its interaction with SOS1 is modulated by phosphotyrosine ligands

Growth factor receptor-bound protein 2 (GRB2) is a trivalent adaptor protein and a key element in signal transduction. It interacts via its flanking nSH3 and cSH3 domains with the proline-rich domain (PRD) of the RAS activator SOS1 and via its central SH2 domain with phosphorylated tyrosine residues of receptor tyrosine kinases (RTKs; e.g. HER2). The elucidation of structural organization and mechanistic insights into GRB2 interactions, however, remain challenging due to their inherent flexibility. This study represents an important advance in our mechanistic understanding of how GRB2 links RTKs to SOS1. Accordingly, it can be proposed that (1) HER2 pYP-bound SH2 potentiates GRB2 SH3 domain interactions with SOS1 (an allosteric mechanism); (2) the SH2 domain blocks cSH3, enabling nSH3 to bind SOS1 first before cSH3 follows (an avidity-based mechanism); and (3) the allosteric behavior of cSH3 to other domains appears to be unidirectional, although there is an allosteric effect between the SH2 and SH3 domains.

Regulation of the Small GTPase Ras and Its Relevance to Human Disease

Ras research has experienced a considerable boost in recent years, not least prompted by the Ras initiative launched by the NCI in 2013 ( https://www.cancer.gov/research/key-initiatives/ras ), accompanied and conditioned by a strongly reinvigorated determination within the Ras community to develop therapeutics attacking directly the Ras oncoproteins. As a member of the small G-protein superfamily, function and transforming activity of Ras all revolve about its GDP/GTP loading status. For one thing, the extent of GTP loading will determine the proportion of active Ras in the cell, with implications for intensity and quality of downstream signaling. But also the rate of nucleotide exchange, i.e., the Ras-GDP/GTP cycling rate, can have a major impact on Ras function, as illustrated perhaps most impressively by newly discovered fast-cycling oncogenic mutants of the Ras-related GTPase Rac1. Thus, while the last years have witnessed memorable new findings and technical developments in the Ras field, leading to an improved insight into many aspects of Ras biology, they have not jolted at the basics, but rather deepened our view of the fundamental regulatory principles of Ras activity control. In this brief review, we revisit the role and mechanisms of Ras nucleotide loading and its implications for cancer in the light of recent findings.

Kinase-mediated RAS signaling via membraneless cytoplasmic protein granules

Receptor tyrosine kinase (RTK)-mediated activation of downstream effector pathways such as the RAS GTPase/MAP kinase (MAPK) signaling cascade is thought to occur exclusively from lipid membrane compartments in mammalian cells. Here, we uncover a membraneless, protein granule-based subcellular structure that can organize RTK/RAS/MAPK signaling in cancer. Chimeric (fusion) oncoproteins involving certain RTKs including ALK and RET undergo de novo higher-order assembly into membraneless cytoplasmic protein granules that actively signal. These pathogenic biomolecular condensates locally concentrate the RAS activating complex GRB2/SOS1 and activate RAS in a lipid membrane-independent manner. RTK protein granule formation is critical for oncogenic RAS/MAPK signaling output in these cells. We identify a set of protein granule components and establish structural rules that define the formation of membraneless protein granules by RTK oncoproteins. Our findings reveal membraneless, higher-order cytoplasmic protein assembly as a distinct subcellular platform for organizing oncogenic RTK and RAS signaling.

The RAL signaling network: Cancer and beyond

The RAL proteins RALA and RALB belong to the superfamily of small RAS-like GTPases (guanosine triphosphatases). RAL GTPases function as molecular switches in cells by cycling through GDP- and GTP-bound states, a process which is regulated by several guanine exchange factors (GEFs) and two heterodimeric GTPase activating proteins (GAPs). Since their discovery in the 1980s, RALA and RALB have been established to exert isoform-specific functions in central cellular processes such as exocytosis, endocytosis, actin organization and gene expression. Consequently, it is not surprising that an increasing number of physiological functions are discovered to be controlled by RAL, including neuronal plasticity, immune response, and glucose and lipid homeostasis. The critical importance of RAL GTPases for oncogenic RAS-driven cellular transformation and tumorigenesis still attracts most research interest. Here, RAL proteins are key drivers of cell migration, metastasis, anchorage-independent proliferation, and survival. This chapter provides an overview of normal and pathological functions of RAL GTPases and summarizes the current knowledge on the involvement of RAL in human disease as well as current therapeutic targeting strategies. In particular, molecular mechanisms that specifically control RAL activity and RAL effector usage in different scenarios are outlined, putting a spotlight on the complexity of the RAL GTPase signaling network and the emerging theme of RAS-independent regulation and relevance of RAL.

Elucidation of protein interactions necessary for the maintenance of the BCR-ABL signaling complex

Many patients with chronic myeloid leukemia in deep remission experience return of clinical disease after withdrawal of tyrosine kinase inhibitors (TKIs). This suggests signaling of inactive BCR-ABL, which allows the survival of cancer cells, and relapse. We show that TKI treatment inhibits catalytic activity of BCR-ABL, but does not dissolve BCR-ABL core signaling complex, consisting of CRKL, SHC1, GRB2, SOS1, cCBL, p85a-PI3K, STS1 and SHIP2. Peptide microarray and co-immunoprecipitation results demonstrate that CRKL binds to proline-rich regions located in C-terminal, intrinsically disordered region of BCR-ABL, that SHC1 requires pleckstrin homology, src homology and tyrosine kinase domains of BCR-ABL for binding, and that BCR-ABL sequence motif located in disordered region around phosphorylated tyrosine 177 mediates binding of three core complex members, i.e., GRB2, SOS1, and cCBL. Further, SHIP2 binds to the src homology and tyrosine kinase domains of BCR-ABL and its inositol phosphatase activity contributes to BCR-ABL-mediated phosphorylation of SHC1. Together, this study characterizes protein-protein interactions within the BCR-ABL core complex and determines the contribution of particular BCR-ABL domains to downstream signaling. Understanding the structure and dynamics of BCR-ABL interactome is critical for the development of drugs targeting integrity of the BCR-ABL core complex.

Fibroblast growth factor signalling in osteoarthritis and cartilage repair

Regulated fibroblast growth factor (FGF) signalling is a prerequisite for the correct development and homeostasis of articular cartilage, as evidenced by the fact that aberrant FGF signalling contributes to the maldevelopment of joints and to the onset and progression of osteoarthritis. Of the four FGF receptors (FGFRs 1-4), FGFR1 and FGFR3 are strongly implicated in osteoarthritis, and FGFR1 antagonists, as well as agonists of FGFR3, have shown therapeutic efficacy in mouse models of spontaneous and surgically induced osteoarthritis. FGF18, a high affinity ligand for FGFR3, is the only FGF-based drug currently in clinical trials for osteoarthritis. This Review covers the latest advances in our understanding of the molecular mechanisms that regulate FGF signalling during normal joint development and in the pathogenesis of osteoarthritis. Strategies for FGF signalling-based treatment of osteoarthritis and for cartilage repair in animal models and clinical trials are also introduced. An improved understanding of FGF signalling from a structural biology perspective, and of its roles in skeletal development and diseases, could unlock new avenues for discovery of modulators of FGF signalling that can slow or stop the progression of osteoarthritis.

Long noncoding RNA AC092171.4 promotes hepatocellular carcinoma progression by sponging microRNA-1271 and upregulating GRB2

In this study, we investigated the mechanistic role of the long non-coding RNA (lncRNA) AC092171.4 in hepatocellular carcinoma (HCC). AC092171.4 was significantly upregulated in HCC tumor tissues compared to normal liver tissues. HCC patients with high AC092171.4 expression showed poorer overall survival (OS) and disease-free survival (DFS) than those with low AC092171.4 expression. In vitro cell proliferation, migration and invasiveness were all higher in AC092171.4-overexpressing HCC cells, but lower in AC092171.4-silenced HCC cells, than in controls. Balb/c nude mice injected with AC092171.4-silenced HCC cells had smaller xenograft tumors, which showed less growth and pulmonary metastasis than control tumors. Bioinformatics analyses and dual luciferase reporter assays confirmed that AC092171.4 binds directly to miR-1271, which targets the 3’UTR of GRB2 mRNA. AC092171.4 expression correlates negatively with miR1271 expression and correlates positively with GRB2 mRNA expression in HCC tissues from patients. HCC cells co-transfected with miR-1271 mimics and sh-AC092171.4 show less proliferation, migration, invasiveness, GRB2 protein, and epithelial to mesencyhmal transition (EMT) than sh-AC092171.4-transfected HCC cells. These findings demonstrate that AC092171.4 promotes growth and progression of HCC by sponging miR-1271 and upregulating GRB2. This makes AC092171.4 a potential prognostic indicator and therapeutic target for HCC patients.

Biology, pathology, and therapeutic targeting of RAS

RAS was identified as a human oncogene in the early 1980s and subsequently found to be mutated in nearly 30% of all human cancers. More importantly, RAS plays a central role in driving tumor development and maintenance. Despite decades of effort, there remain no FDA approved drugs that directly inhibit RAS. The prevalence of RAS mutations in cancer and the lack of effective anti-RAS therapies stem from RAS' core role in growth factor signaling, unique structural features, and biochemistry. However, recent advances have brought promising new drugs to clinical trials and shone a ray of hope in the field. Here, we will exposit the details of RAS biology that illustrate its key role in cell signaling and shed light on the difficulties in therapeutically targeting RAS. Furthermore, past and current efforts to develop RAS inhibitors will be discussed in depth.

SOS1 Gain-of-Function Variants in Dilated Cardiomyopathy

BACKGROUND

Dilated cardiomyopathy (DCM) is a genetically heterogeneous cardiac disease characterized by progressive ventricular enlargement and reduced systolic function. Here, we report genetic and functional analyses implicating the rat sarcoma signaling protein, SOS1 (Son of sevenless homolog 1), in DCM pathogenesis.

METHODS

Exome sequencing was performed on 412 probands and family members from our DCM cohort, identifying several SOS1 variants with potential disease involvement. As several lines of evidence have implicated dysregulated rat sarcoma signaling in the pathogenesis of DCM, we assessed functional impact of each variant on the activation of ERK (extracellular signal-regulated kinase), AKT (protein kinase B), and JNK (c-Jun N-terminal kinase) pathways. Relative expression levels were determined by Western blot in HEK293T cells transfected with variant or wild-type human SOS1 expression constructs.

RESULTS

A rare SOS1 variant [c.571G>A, p.(Glu191Lys)] was found to segregate alongside an A-band TTN truncating variant in a pedigree with aggressive, early-onset DCM. Reduced disease severity in the absence of the SOS1 variant suggested its potential involvement as a genetic risk factor for DCM in this family. Exome sequencing identified 5 additional SOS1 variants with potential disease involvement in 4 other families [c.1820T>C, p.(Ile607Thr); c.2156G>C, p.(Gly719Ala); c.2230A>G, p.(Arg744Gly); c.2728G>C, p.(Asp910His); c.3601C>T, p.(Arg1201Trp)]. Impacted amino acids occupied a number of functional domains relevant to SOS1 activity, including the N-terminal histone fold, as well as the C-terminal REM (rat sarcoma exchange motif), CDC25 (cell division cycle 25), and PR (proline-rich) tail domains. Increased phosphorylated ERK expression relative to wild-type levels was seen for all 6 SOS1 variants, paralleling known disease-relevant SOS1 signaling profiles.

CONCLUSIONS

These data support gain-of-function variation in SOS1 as a contributing factor to isolated DCM.

Insulin-PI3K signalling: an evolutionarily insulated metabolic driver of cancer

Cancer is driven by incremental changes that accumulate, eventually leading to oncogenic transformation. Although genetic alterations dominate the way cancer biologists think about oncogenesis, growing evidence suggests that systemic factors (for example, insulin, oestrogen and inflammatory cytokines) and their intracellular pathways activate oncogenic signals and contribute to targetable phenotypes. Systemic factors can have a critical role in both tumour initiation and therapeutic responses as increasingly targeted and personalized therapeutic regimens are used to treat patients with cancer. The endocrine system controls cell growth and metabolism by providing extracellular cues that integrate systemic nutrient status with cellular activities such as proliferation and survival via the production of metabolites and hormones such as insulin. When insulin binds to its receptor, it initiates a sequence of phosphorylation events that lead to activation of the catalytic activity of phosphoinositide 3-kinase (PI3K), a lipid kinase that coordinates the intake and utilization of glucose, and mTOR, a kinase downstream of PI3K that stimulates transcription and translation. When chronically activated, the PI3K pathway can drive malignant transformation. Here, we discuss the insulin-PI3K signalling cascade and emphasize its roles in normal cells (including coordinating cell metabolism and growth), highlighting the features of this network that make it ideal for co-option by cancer cells. Furthermore, we discuss how this signalling network can affect therapeutic responses and how novel metabolic-based strategies might enhance treatment efficacy for cancer.

Defining the TLT-1 interactome from resting and activated human platelets

The triggering receptor expressed on myeloid cells (TREM) protein family forms a class of type I transmembrane proteins expressed in immune cells that play important roles in innate and adaptive immune responses. The TREM family member TREM-like transcript 1 (TLT-1, also TREML1) is expressed in megakaryocytes and packaged into platelet granules. TLT-1 binds fibrinogen and plays a role in bleeding initiated by inflammatory insults. Here, we describe a proteomics screen that maps the TLT-1 interactome in resting and activated human platelets. Several identified TLT-1 interactors are involved in cell adhesion and migration, as well as platelet activation. Select interactors, including β3-integrin, RACK1, GRB2, and Rabs 5A, 7, and 11A, were additionally characterized in co-immunoprecipitation/immunoblotting experiments. Finally, several phosphorylation sites were found on immunoprecipitated TLT-1, including Thr280, a novel, regulated site on a conserved residue near the TLT-1 ITIM regulatory sequence. SIGNIFICANCE: Platelet function relies on the secretion of active molecules from intracellular vesicles, or granules, which contain soluble and membrane-bound proteins that are essential for platelet aggregation, coagulation reactions, and pathogen defense mechanisms. TLT-1 is sequestered in α-granules and transported to the plasma membrane, where it plays a unique role in hemostasis after inflammatory insults. Despite the known importance of TLT-1 in platelet biology, our knowledge of TLT-1 mechanistic signaling is limited. This study defines the TLT-1 interactome in resting and active human platelets, identifying several novel TLT-1 interactors, as well as TLT-1 phosphorylation sites, all with likely signaling implications in platelet aggregation dynamics.

YAP/TAZ Inhibition Induces Metabolic and Signaling Rewiring Resulting in Targetable Vulnerabilities in NF2-Deficient Tumor Cells

Merlin/NF2 is a bona fide tumor suppressor whose mutations underlie inherited tumor syndrome neurofibromatosis type 2 (NF2), as well as various sporadic cancers including kidney cancer. Multiple Merlin/NF2 effector pathways including the Hippo-YAP/TAZ pathway have been identified. However, the molecular mechanisms underpinning the growth and survival of NF2-mutant tumors remain poorly understood. Using an inducible orthotopic kidney tumor model, we demonstrate that YAP/TAZ silencing is sufficient to induce regression of pre-established NF2-deficient tumors. Mechanistically, YAP/TAZ depletion diminishes glycolysis-dependent growth and increases mitochondrial respiration and reactive oxygen species (ROS) buildup, resulting in oxidative-stress-induced cell death when challenged by nutrient stress. Furthermore, we identify lysosome-mediated cAMP-PKA/EPAC-dependent activation of RAF-MEK-ERK signaling as a resistance mechanism to YAP/TAZ inhibition. Finally, unbiased analysis of TCGA primary kidney tumor transcriptomes confirms a positive correlation of a YAP/TAZ signature with glycolysis and inverse correlations with oxidative phosphorylation and lysosomal gene expression, supporting the clinical relevance of our findings.

Proliferative signaling by ERBB proteins and RAF/MEK/ERK effectors in polycystic kidney disease

A primary pathological feature of polycystic kidney disease (PKD) is the hyperproliferation of epithelial cells in renal tubules, resulting in formation of fluid-filled cysts. The proliferative aspects of the two major forms of PKD-autosomal dominant PKD (ADPKD), which arises from mutations in the polycystins PKD1 and PKD2, and autosomal recessive PKD (ARPKD), which arises from mutations in PKHD1-has encouraged investigation into protein components of the core cell proliferative machinery as potential drivers of PKD pathogenesis. In this review, we examine the role of signaling by ERBB proteins and their effectors, with a primary focus on ADPKD. The ERBB family of receptor tyrosine kinases (EGFR/ERBB1, HER2/ERBB2, ERBB3, and ERBB4) are activated by extracellular ligands, inducing multiple pro-growth signaling cascades; among these, activation of signaling through the RAS GTPase, and the RAF, MEK1/2, and ERK1/2 kinases enhance cell proliferation and restrict apoptosis during renal tubuloepithelial cyst formation. Characteristics of PKD include overexpression and mislocalization of the ERBB receptors and ligands, leading to enhanced activation and increased activity of downstream signaling proteins. The altered regulation of ERBBs and their effectors in PKD is influenced by enhanced activity of SRC kinase, which is promoted by the loss of cytoplasmic Ca²⁺ and an increase in cAMP-dependent PKA kinase activity that stimulates CFTR, driving the secretory phenotype of ADPKD. We discuss the interplay between ERBB/SRC signaling, and polycystins and their depending signaling, with emphasis on thes changes that affect cell proliferation in cyst expansion, as well as the inflammation-associated fibrogenesis, which characterizes progressive disease. We summarize the current progress of preclinical and clinical trials directed at inhibiting this signaling axis, and discuss potential future strategies that may be productive for controlling PKD.

RAS in pancreatic cancer

The pancreas is a gland composed mainly by endocrine and exocrine cells, giving rise to three main tumour types. Pancreatic neuroendocrine tumour or PNET arise from the endocrine portion of the pancreas. On the contrary, pancreatic exocrine neoplasms include pancreatic ductal adenocarcinoma (PDAC) and acinar cell carcinoma. PDAC is the most common type of pancreatic cancer and one of the leading causes of cancer-related death. It has been shown that less than 3% of PDAC patients have an overall survival of up to 5 years in the U.K. This mainly arises since the majority of patients diagnosed with PDAC present with advanced unresectable disease, which is highly resistant to all forms of chemotherapy and radiotherapy. Activating mutations of an isoform of the RAS protein, KRAS, are found in almost all PDAC cases and occur during early stages of malignant transformation. KRAS mutations play a critical role as they are involved in both initiating and maintaining PDAC development. The interaction of RAS with GDP/GTP along with its recruitment to the membrane affects transduction of its activating signals to downstream effectors. In this review, we aim to summarise different mutations of RAS and their prevalence in pancreatic cancer along with other RAS-induced tumours. In addition, we briefly discuss the genetically engineered mouse models that have been developed to study KRAS-mutated adenocarcinomas in the pancreas. These provide an opportunity to also address the importance of targeting RAS for better treatment response in PDAC patients along with the challenges incurred herein.

Bisphenol A induces human uterine leiomyoma cell proliferation through membrane-associated ERα36 via nongenomic signaling pathways

The role of ERα36 in regulating BPA's effects and its potential as a risk factor for human uterine fibroids were evaluated. BPA at low concentrations (10^-6 μM - 10 μM) increased proliferation by facilitating progression of hormonally regulated, immortalized human uterine leiomyoma (ht-UtLM; fibroid) cells from G₀-G₁ into S phase of the cell cycle; whereas, higher concentrations (100 μM-200 μM) decreased growth. BPA upregulated ERα36 gene and protein expression, and induced increased SOS1 and Grb2 protein expression, both of which are mediators of the MAPK_p44/42/ERK1/2 pathway. EGFR (pEGFR), Ras, and MAPK_p44/42 were phosphorylated with concurrent Src activation in ht-UtLM cells within 10 min of BPA exposure. BPA enhanced colocalization of phosphorylated Src (pSrc) to ERα36 and coimmunoprecipitation of pSrc with pEGFR. Silencing ERα36 with siERα36 abolished the above effects. BPA induced proliferation in ht-UtLM cells through membrane-associated ERα36 with activation of Src, EGFR, Ras, and MAPK nongenomic signaling pathways.

The Interdependent Activation of Son-of-Sevenless and Ras

The guanine-nucleotide exchange factor (GEF) Son-of-Sevenless (SOS) plays a critical role in metazoan signaling by converting Ras•GDP (guanosine diphosphate) to Ras•GTP (guanosine triphosphate) in response to tyrosine kinase activation. Structural studies have shown that SOS differs from other Ras-specific GEFs in that SOS is itself activated by Ras•GTP binding to an allosteric site, distal to the site of nucleotide exchange. The activation of SOS involves membrane recruitment and conformational changes, triggered by lipid binding, that open the allosteric binding site for Ras•GTP. This is in contrast to other Ras-specific GEFs, which are activated by second messengers that more directly affect the active site. Allosteric Ras•GTP binding stabilizes SOS at the membrane, where it can turn over other Ras molecules processively, leading to an ultrasensitive response that is distinct from that of other Ras-specific GEFs.

The CSN3 subunit of the COP9 signalosome interacts with the HD region of Sos1 regulating stability of this GEF protein

Sos1 is an universal, widely expressed Ras guanine nucleotide-exchange factor (RasGEF) in eukaryotic cells. Its N-terminal HD motif is known to be involved in allosteric regulation of Sos1 GEF activity through intramolecular interaction with the neighboring PH domain. Here, we searched for other cellular proteins also able to interact productively with the Sos1 HD domain. Using a yeast two-hybrid system, we identified the interaction between the Sos1 HD region and CSN3, the third component of the COP9 signalosome, a conserved, multi-subunit protein complex that functions in the ubiquitin–proteasome pathway to control degradation of many cellular proteins. The interaction of CSN3 with the HD of Sos1 was confirmed in vitro by GST pull-down assays using truncated mutants and reproduced in vivo by co-immunoprecipitation with the endogenous, full-length cellular Sos1 protein. In vitro kinase assays showed that PKD, a COP9 signalosome-associated-kinase, is able to phosphorylate Sos1. The intracellular levels of Sos1 protein were clearly diminished following CSN3 or PKD knockdown. A sizable fraction of the endogenous Sos1 protein was found ubiquitinated in different mammalian cell types. A significant reduction of RasGTP formation upon growth factor stimulation was also observed in CSN3-silenced as compared with control cells. Our data suggest that the interaction of Sos1 with the COP9 signalosome and PKD plays a significant role in maintenance of cellular Sos1 protein stability and homeostasis under physiological conditions and raises the possibility of considering the CSN/PKD complex as a potential target for design of novel therapeutic drugs.

The 11-Kilodalton Nonstructural Protein of Human Parvovirus B19 Facilitates Viral DNA Replication by Interacting with Grb2 through Its Proline-Rich Motifs

Lytic infection of human parvovirus B19 (B19V) takes place exclusively in human erythroid progenitor cells of bone marrow and fetal liver, which disrupts erythropoiesis. During infection, B19V expresses three nonstructural proteins (NS1, 11-kDa, and 7.5-kDa) and two structural proteins (VP1 and VP2). While NS1 is essential for B19V DNA replication, 11-kDa enhances viral DNA replication significantly. In this study, we confirmed the enhancement role of 11-kDa in viral DNA replication and elucidated the underlying mechanism. We found that 11-kDa specially interacts with cellular growth factor receptor-bound protein 2 (Grb2) during virus infection and in vitro We determined a high affinity interaction between 11-kDa and Grb2 that has an equilibrium dissociation constant (KD ) value of 18.13 nM. In vitro, one proline-rich motif was sufficient for 11-kDa to sustain a strong interaction with Grb2. In consistence, in vivo during infection, one proline-rich motif was enough for 11-kDa to significantly reduce phosphorylation of extracellular signal-regulated kinase (ERK). Mutations of all three proline-rich motifs of 11-kDa abolished its capability to reduce ERK activity and, accordingly, decreased viral DNA replication. Transduction of a lentiviral vector encoding a short hairpin RNA (shRNA) targeting Grb2 decreased the expression of Grb2 as well as the level of ERK phosphorylation, which resulted in an increase of B19V replication. These results, in concert, indicate that the B19V 11-kDa protein interacts with cellular Grb2 to downregulate ERK activity, which upregulates viral DNA replication.IMPORTANCE Human parvovirus B19 (B19V) infection causes hematological disorders and is the leading cause of nonimmunological fetal hydrops during pregnancy. During infection, B19V expresses two structural proteins, VP1 and VP2, and three nonstructural proteins, NS1, 11-kDa, and 7.5-kDa. While NS1 is essential, 11-kDa plays an enhancing role in viral DNA replication. Here, we elucidated a mechanism underlying 11-kDa protein-regulated B19V DNA replication. 11-kDa is tightly associated with cellular growth factor receptor-bound protein 2 (Grb2) during infection. In vitro, 11-kDa interacts with Grb2 with high affinity through three proline-rich motifs, of which at least one is indispensable for the regulation of viral DNA replication. 11-kDa and Grb2 interaction disrupts extracellular signal-regulated kinase (ERK) signaling, which mediates upregulation of B19V replication. Thus, our study reveals a novel mechanism of how a parvoviral small nonstructural protein regulates viral DNA replication by interacting with a host protein that is predominately expressed in the cytoplasm.

Different Isoforms of the Neuronal Guidance Molecule Slit2 Directly Cause Chemoattraction or Chemorepulsion of Human Neutrophils

The movement of neutrophils between blood and tissues appears to be regulated by chemoattractants and chemorepellents. Compared with neutrophil chemoattractants, relatively little is known about neutrophil chemorepellents. Slit proteins are endogenously cleaved into a variety of N- and C-terminal fragments, and these fragments are neuronal chemorepellents and inhibit chemoattraction of many cell types, including neutrophils. In this report, we show that the ∼140-kDa N-terminal Slit2 fragment (Slit2-N) is a chemoattractant and the ∼110-kDa N-terminal Slit2 fragment (Slit2-S) is a chemorepellent for human neutrophils. The effects of both Slit2 fragments were blocked by Abs to the Slit2 receptor Roundabout homolog 1 or the Slit2 coreceptor Syndecan-4. Slit2-N did not appear to activate Ras but increased phosphatidylinositol 3,4,5-triphosphate levels. Slit2-N-induced chemoattraction was unaffected by Ras inhibitors, reversed by PI3K inhibitors, and blocked by Cdc42 and Rac inhibitors. In contrast, Slit2-S activated Ras but did not increase phosphatidylinositol 3,4,5-triphosphate levels. Slit2-S-induced chemorepulsion was blocked by Ras and Rac inhibitors, not affected by PI3K inhibitors, and reversed by Cdc42 inhibitors. Slit2-N, but not Slit2-S, increased neutrophil adhesion, myosin L chain 2 phosphorylation, and polarized actin formation and single pseudopods at the leading edge of cells. Slit2-S induced multiple pseudopods. These data suggest that Slit2 isoforms use similar receptors but different intracellular signaling pathways and have different effects on the cytoskeleton and pseudopods to induce neutrophil chemoattraction or chemorepulsion.

Runs of homozygosity associate with decreased risks of lung cancer in never-smoking East Asian females

Although genome-wide association studies (GWASs) have identified some risk single-nucleotide polymorphisms in East Asian never-smoking females, the unexplained missing heritability is still required to be investigated. Runs of homozygosity (ROHs) are thought to be a type of genetic variation acting on human complex traits and diseases. We detected ROHs in 8,881 East Asian never-smoking women. The summed ROHs were used to fit a logistic regression model which noteworthily revealed a significant association between ROHs and the decreased risk of lung cancer (P < 0.05). We identified 4 common ROHs regions located at 2p22.1, which were significantly associated with decreased risk of lung cancer (P = 2.00 × 10^-4 - 1.35 × 10^-4). Functional annotation was conducted to investigate the regulatory function of ROHs. The common ROHs were overlapped with potential regulatory elements, such as active epigenome elements and chromatin states in lung-derived cell lines. SOS1 and ARHGEF33 were significantly up-regulated as the putative target genes of the identified ROHs in lung cancer samples according to the analysis of differently expressed genes. Our results suggest that ROHs could act as recessive contributing factors and regulatory elements to influence the risk of lung cancer in never-smoking East Asian females.

The "Yin and Yang" of Natural Compounds in Anticancer Therapy of Triple-Negative Breast Cancers

Among the different types of breast cancers, triple-negative breast cancers (TNBCs) are highly aggressive, do not respond to conventional hormonal/human epidermal growth factor receptor 2 (HER2)-targeted interventions due to the lack of the respective receptor targets, have chances of early recurrence, metastasize, tend to be more invasive in nature, and develop drug resistance. The global burden of TNBCs is increasing regardless of the number of cytotoxic drugs being introduced into the market each year as they have only moderate efficacy and/or unforeseen side effects. Therefore, the demand for more efficient therapeutic interventions, with reduced side effects, for the treatment of TNBCs is rising. While some plant metabolites/derivatives actually induce the risk of cancers, many plant-derived active principles have gained attention as efficient anticancer agents against TNBCs, with fewer adverse side effects. Here we discuss the possible oncogenic molecular pathways in TNBCs and how the purified plant-derived natural compounds specifically target and modulate the genes and/or proteins involved in these aberrant pathways to exhibit their anticancer potential. We have linked the anticancer potential of plant-derived natural compounds (luteolin, chalcones, piperine, deguelin, quercetin, rutin, fisetin, curcumin, resveratrol, and others) to their ability to target multiple dysregulated signaling pathways (such as the Wnt/β-catenin, Notch, NF-κB, PI3K/Akt/mammalian target of rapamycin (mTOR), mitogen-activated protein kinase (MAPK) and Hedgehog) leading to suppression of cell growth, proliferation, migration, inflammation, angiogenesis, epithelial-mesenchymal transition (EMT) and metastasis, and activation of apoptosis in TNBCs. Plant-derived compounds in combination with classical chemotherapeutic agents were more efficient in the treatment of TNBCs, possibly with lesser side effects.

Small-Molecule Modulation of Lipid-Dependent Cellular Processes against Cancer: Fats on the Gunpoint

Lipid cell membrane composed of various distinct lipids and proteins act as a platform to assemble various signaling complexes regulating innumerous cellular processes which are strongly downregulated or altered in cancer cells emphasizing the still-underestimated critical function of lipid biomolecules in cancer initiation and progression. In this review, we outline the current understanding of how membrane lipids act as signaling hot spots by generating distinct membrane microdomains called rafts to initiate various cellular processes and their modulation in cancer phenotypes. We elucidate tangible drug targets and pathways all amenable to small-molecule perturbation. Ranging from targeting membrane rafts organization/reorganization to rewiring lipid metabolism and lipid sorting in cancer, the work summarized here represents critical intervention points being attempted for lipid-based anticancer therapy and future directions.

A threshold model for receptor tyrosine kinase signaling specificity and cell fate determination

Upon ligand engagement, the single-pass transmembrane receptor tyrosine kinases (RTKs) dimerize to transmit qualitatively and quantitatively different intracellular signals that alter the transcriptional landscape and thereby determine the cellular response. The molecular mechanisms underlying these fundamental events are not well understood. Considering recent insights into the structural biology of fibroblast growth factor signaling, we propose a threshold model for RTK signaling specificity in which quantitative differences in the strength/longevity of ligand-induced receptor dimers on the cell surface lead to quantitative differences in the phosphorylation of activation loop (A-loop) tyrosines as well as qualitative differences in the phosphorylation of tyrosines mediating substrate recruitment. In this model, quantitative differences on A-loop tyrosine phosphorylation result in gradations in kinase activation, leading to the generation of intracellular signals of varying amplitude/duration. In contrast, qualitative differences in the pattern of tyrosine phosphorylation on the receptor result in the recruitment/activation of distinct substrates/intracellular pathways. Commensurate with both the dynamics of the intracellular signal and the types of intracellular pathways activated, unique transcriptional signatures are established. Our model provides a framework for engineering clinically useful ligands that can tune receptor dimerization stability so as to bias the cellular transcriptome to achieve a desired cellular output.

Liposomal Grb2 antisense oligodeoxynucleotide (BP1001) in patients with refractory or relapsed haematological malignancies: a single-centre, open-label, dose-escalation, phase 1/1b trial

BACKGROUND

Activating mutations of tyrosine kinases are common in leukaemias. Oncogenic tyrosine kinases use the growth factor receptor-bound protein 2 (Grb2) for signal transduction, leading to activation of mitogen-activated protein kinase (MAPK) 1 and MAPK3 (ERK2 and ERK1). We hypothesised that inhibition of Grb2 would suppress ERK1 and ERK2 activation and inhibit leukaemia progression. To inhibit Grb2, a liposome-incorporated antisense oligodeoxynucleotide that blocks Grb2 protein expression, BP1001, was developed. We report the first phase 1 findings of BP1001.

METHODS

In this single-centre, open-label, dose-escalation phase 1/1b trial, we enrolled participants (aged ≥18 years) with refractory or relapsed acute myeloid leukaemia, Philadelphia-chromosome-positive chronic myeloid leukaemia (in chronic, accelerated, or blast phase), acute lymphoblastic leukaemia, or myelodysplastic syndrome, at MD Anderson Cancer Center (Houston, TX, USA). We used a 3 + 3 dose escalation strategy, with at least three patients enrolled at each dose level. We administered BP1001 intravenously, twice weekly, for 28 days, with a starting dose of 5 mg/m². If two or more patients developed toxic effects of grade 3 or higher, that dose level was deemed toxic. The dose was escalated if it did not produce dose-limiting toxic effects, and patients would be sequentially enrolled into cohort 2 (10 mg/m²), cohort 3 (20 mg/m²), cohort 4 (40 mg/m²), cohort 5 (60 mg/m²), or cohort 6 (90 mg/m²). After completion of monotherapy, we assessed the safety and toxicity of BP1001 (60 or 90 mg/m²) in combination with 20 mg low-dose cytarabine (twice-daily subcutaneous injections) in a phase 1b study in patients with refractory or relapsed acute myeloid leukaemia (ie, those who were refractory to at least one previous therapy regimen and no more than one previous salvage regimen). The objectives of this study were to establish the toxicity and tolerance of escalating doses of BP1001 monotherapy in patients with refractory or relapsed leukaemia, to assess the maximum tolerated dose of BP1001, and to determine the optimal biologically active dose of BP1001, defined as a 50% reduction in Grb2 expression in circulating leukaemia cells. We also aimed to assess the in-vivo pharmacokinetics of BP1001 and tumour response. The study is completed and is registered with ClinicalTrials.gov, number NCT01159028.

FINDINGS

Between July 23, 2010, and Feb 23, 2016, we enrolled and treated 39 patients, of whom 27 were assessable for dose-limiting toxicity. The first patient treated had mucositis and hand-foot syndrome, which were assessed as possibly related to BP1001 and counted as a dose-limiting toxicity. We noted no other dose-limiting toxicities, and a maximum tolerated dose was not identified. The highest tested dose of BP1001 was 90 mg/m². The most common grade 3-4 adverse events were cardiopulmonary disorders (25 [64%] of 39 patients), and fever (including neutropenic fever) and infections (17 [44%] patients). Grade 5 adverse events were cardiopulmonary disorders (two [5%] of 39 patients), fever (including neutropenic fever) and infections (two [5%] of 39 patients), and multi-organ failure (one [3%] of 39 patients). Nine (33%) of 27 patients who had peripheral blood blasts at the start of therapy had a reduction of 50% or more in peripheral blood blasts while receiving BP1001 montherapy. Three (10%) of 29 patients who had bone marrow blasts at the start of therapy had a reduction in bone marrow blasts of 50% or more while receiving BP1001 monotherapy. Per investigator's assessment, seven (22%) of 32 patients benefited from BP1001 monotherapy and had extended cycles of treatment. Of seven patients receiving BP1001 plus low-dose cytarabine combination therapy, two had complete remission, one had complete remission with incomplete haematological recovery, and two had stable disease with no dose-limiting toxicity; one patient died and one withdrew, both because of disease progression. There were eight deaths; none were treatment related.

INTERPRETATION

BP1001 is well tolerated, with early evidence of anti-leukaemic activity in combination with low-dose cytarabine. To further explore this anti-leukaemic activity, the efficacy of BP1001 plus low-dose cytarabine combination is being investigated in an ongoing phase 2 study in patients with previously untreated acute myeloid leukaemia who are ineligible for intensive induction therapy.

FUNDING

Bio-Path Holdings Inc.

MAPK and PI3K signaling: At the crossroads of neural crest development

Receptor tyrosine kinase-mediated growth factor signaling is essential for proper formation and development of the neural crest. The many ligands and receptors implicated in these processes signal through relatively few downstream pathways, frequently converging on the MAPK and PI3K pathways. Despite decades of study, there is still considerable uncertainty about where and when these signaling pathways are required and how they elicit particular responses. This review summarizes our current understanding of growth factor-induced MAPK and PI3K signaling in the neural crest.

miR-564 inhibits hepatocellular carcinoma cell proliferation and invasion by targeting the GRB2-ERK1/2-AKT axis

Recent studies have shown that miR-564 is closely related to the development of various tumors, including breast cancer, lung cancer and glioma. However, few studies have examined miR-564 in hepatocellular carcinoma (HCC). Here, we demonstrated that miR-564 expression in HCC tissues was lower than that in adjacent noncancerous tissues and that miR-564 expression was associated with tumor size, tumor number and vein invasion. Bioinformatics analyses showed that low levels of miR-564 were correlated with poor prognosis. Furthermore, upregulation of miR-564 impaired SMCC7721 and MHCC97H cell proliferation, migration and invasion in vitro and reduced tumorigenesis in vivo. Next, we found that GRB2 was a direct target gene of miR-564 in the HCC cell lines. GRB2 was highly expressed in HCC tissues and negatively correlated with miR-564 expression levels. When GRB2 was downregulated by GRB2-siRNA, HCC cell proliferation, invasion and metastasis were impaired, and restoring GRB2 expression partially reversed the inhibitory effects of miR-564. Western blot analysis showed that miR-564 overexpression reduced GRB2 expression in HCC cell lines and inhibited ERK1/2 and AKT phosphorylation. miR-564 overexpression also upregulated the epithelial-like cell marker E-cadherin and downregulated the interstitial cell-like markers N-cadherin and vimentin. These results suggest that miR-564 inhibits the malignant phenotype of HCC cells by targeting the GRB2-ERK1/2-AKT axis. Consequently, miR-564 may be used as a prognostic marker and therapeutic target for HCC.

Epidermal growth factor receptors containing a single tyrosine in their C-terminal tail bind different effector molecules and are signaling-competent

The EGF receptor is a classic receptor tyrosine kinase. It contains nine tyrosines in its C-terminal tail, many of which are phosphorylated and bind proteins containing SH2 or phosphotyrosine-binding (PTB) domains. To determine how many and which tyrosines are required to enable EGF receptor-mediated signaling, we generated a series of EGF receptors that contained only one tyrosine in their C-terminal tail. Assays of the signaling capabilities of these single-Tyr EGF receptors indicated that they can activate a range of downstream signaling pathways, including MAP kinase and Akt. The ability of the single-Tyr receptors to signal correlated with their ability to bind Gab1 (Grb2-associated binding protein 1). However, Tyr-992 appeared to be almost uniquely required to observe activation of phospholipase Cγ. These results demonstrate that multiply phosphorylated receptors are not required to support most EGF-stimulated signaling but identify Tyr-992 and its binding partners as a unique node within the network. We also studied the binding of the isolated SH2 domain of Grb2 (growth factor receptor-bound protein 2) and the isolated PTB domain of Shc (SHC adaptor protein) to the EGF receptor. Although these adapter proteins bound readily to wild-type EGF receptor, they bound poorly to the single-Tyr EGF receptors, even those that bound full-length Grb2 and Shc well. This suggests that in addition to pTyr-directed associations, secondary interactions between the tail and regions of the adapter proteins outside of the SH2/PTB domains are important for stabilizing the binding of Grb2 and Shc to the single-Tyr EGF receptors.

Modelling GTPase dynamics to understand RhoA-driven cancer cell invasion

Metastasis, initially driven by cells migrating and invading through the local environment, leads to most cancer-associated deaths. Cells can use a variety of modes to move in vitro, all of which depend on Rho GTPases at some level. While traditionally it was thought that Rac1 activity drives protrusive lamellipodia at the leading edge of a polarised cell while RhoA drives rear retraction, more recent work in 3D microenvironments has revealed a much more complicated picture of GTPase dynamics. In particular, RhoA activity can dominate the leading edge polymerisation of actin to form filopodial actin-spike protrusions that drive more invasive cell migration. We recently described a potential mechanism to abrogate this pro-invasive localised leading edge Rac1 to RhoA switch via manipulation of a negative feedback loop that was revealed by adopting a logical modelling approach. Both challenging dogma and taking a formal, mathematical approach to understanding signalling involved in motility may be vital to harnessing harmful cell migration and preventing metastasis in future research.

Epidermal Growth Factor Receptor Cell Proliferation Signaling Pathways

The epidermal growth factor receptor (EGFR) is a receptor tyrosine kinase that is commonly upregulated in cancers such as in non-small-cell lung cancer, metastatic colorectal cancer, glioblastoma, head and neck cancer, pancreatic cancer, and breast cancer. Various mechanisms mediate the upregulation of EGFR activity, including common mutations and truncations to its extracellular domain, such as in the EGFRvIII truncations, as well as to its kinase domain, such as the L858R and T790M mutations, or the exon 19 truncation. These EGFR aberrations over-activate downstream pro-oncogenic signaling pathways, including the RAS-RAF-MEK-ERK MAPK and AKT-PI3K-mTOR pathways. These pathways then activate many biological outputs that are beneficial to cancer cell proliferation, including their chronic initiation and progression through the cell cycle. Here, we review the molecular mechanisms that regulate EGFR signal transduction, including the EGFR structure and its mutations, ligand binding and EGFR dimerization, as well as the signaling pathways that lead to G1 cell cycle progression. We focus on the induction of CYCLIN D expression, CDK4/6 activation, and the repression of cyclin-dependent kinase inhibitor proteins (CDKi) by EGFR signaling pathways. We also discuss the successes and challenges of EGFR-targeted therapies, and the potential for their use in combination with CDK4/6 inhibitors.

Epidermal Growth Factor Receptor Cell Proliferation Signaling Pathways

The epidermal growth factor receptor (EGFR) is a receptor tyrosine kinase that is commonly upregulated in cancers such as in non-small-cell lung cancer, metastatic colorectal cancer, glioblastoma, head and neck cancer, pancreatic cancer, and breast cancer. Various mechanisms mediate the upregulation of EGFR activity, including common mutations and truncations to its extracellular domain, such as in the EGFRvIII truncations, as well as to its kinase domain, such as the L858R and T790M mutations, or the exon 19 truncation. These EGFR aberrations over-activate downstream pro-oncogenic signaling pathways, including the RAS-RAF-MEK-ERK MAPK and AKT-PI3K-mTOR pathways. These pathways then activate many biological outputs that are beneficial to cancer cell proliferation, including their chronic initiation and progression through the cell cycle. Here, we review the molecular mechanisms that regulate EGFR signal transduction, including the EGFR structure and its mutations, ligand binding and EGFR dimerization, as well as the signaling pathways that lead to G1 cell cycle progression. We focus on the induction of CYCLIN D expression, CDK4/6 activation, and the repression of cyclin-dependent kinase inhibitor proteins (CDKi) by EGFR signaling pathways. We also discuss the successes and challenges of EGFR-targeted therapies, and the potential for their use in combination with CDK4/6 inhibitors.

Mechanism of SOS PR-domain autoinhibition revealed by single-molecule assays on native protein from lysate

The guanine nucleotide exchange factor (GEF) Son of Sevenless (SOS) plays a critical role in signal transduction by activating Ras. Here we introduce a single-molecule assay in which individual SOS molecules are captured from raw cell lysate using Ras-functionalized supported membrane microarrays. This enables characterization of the full-length SOS protein, which has not previously been studied in reconstitution due to difficulties in purification. Our measurements on the full-length protein reveal a distinct role of the C-terminal proline-rich (PR) domain to obstruct the engagement of allosteric Ras independently of the well-known N-terminal domain autoinhibition. This inhibitory role of the PR domain limits Grb2-independent recruitment of SOS to the membrane through binding of Ras·GTP in the SOS allosteric binding site. More generally, this assay strategy enables characterization of the functional behaviour of GEFs with single-molecule precision but without the need for purification.

Genetically Encoded 2-Aryl-5-carboxytetrazoles for Site-Selective Protein Photo-Cross-Linking

The genetically encoded photo-cross-linkers promise to offer a temporally controlled tool to map transient and dynamic protein–protein interaction complexes in living cells. Here we report the synthesis of a panel of 2-aryl-5-carboxytetrazole-lysine analogs (ACTKs) and their site-specific incorporation into proteins via amber codon suppression in Escherichia coli and mammalian cells. Among five ACTKs investigated, N-methylpyrroletetrazole-lysine (mPyTK) was found to give robust and site-selective photo-cross-linking reactivity in E. coli when placed at an appropriate site at the protein interaction interface. A comparison study indicated that mPyTK exhibits higher photo-cross-linking efficiency than a diazirine-based photo-cross-linker, AbK, when placed at the same location of the interaction interface in vitro. When mPyTK was introduced into the adapter protein Grb2, it enabled the photocapture of EGFR in a stimulus-dependent manner. The design of mPyTK along with the identification of its cognate aminoacyl-tRNA synthetase makes it possible to map transient protein–protein interactions and their interfaces in living cells.

Targeted Covalent Inhibition of Grb2-Sos1 Interaction through Proximity-Induced Conjugation in Breast Cancer Cells

Targeted covalent inhibitors of protein-protein interactions differ from reversible inhibitors in that the former bind and covalently bond the target protein at a specific site of the target. The site specificity is the result of the proximity of two reactive groups at the bound state, for example, one mild electrophile in the inhibitor and a natural cysteine in the target close to the ligand binding site. Only a few pharmaceutically relevant proteins have this structural feature. Grb2, a key adaptor protein in maintaining the ERK activity via binding Sos1 to activated RTKs, is one: the N-terminal SH3 domain of Grb2 (Grb2^N-SH3) carries a unique solvent-accessible cysteine Cys³² close to its Sos1-binding site. Here we report the design of a peptide-based antagonist (a reactive peptide) that specifically binds to Grb2^N-SH3 and subsequently undergoes a nucleophilic reaction with Cys³² to form a covalent bond thioether, to block Grb2-Sos1 interaction. Through rounds of optimization, we eventually obtained a dimeric reaction reactive peptide that can form a covalent adduct with endogenous Grb2 protein inside the cytosol of SK-BR-3 human breast cancer cells with pronounced inhibitory effect on cell mobility and viability. This work showcases a rational design of Grb2-targeted site-specific covalent inhibitor and its pronounced anticancer effect by targeting Grb2-Sos1 interaction.

How Genetics Has Helped Piece Together the MAPK Signaling Pathway

Cells respond to changes in their environment, to developmental cues, and to pathogen aggression through the action of a complex network of proteins. These networks can be decomposed into a multitude of signaling pathways that relay signals from the microenvironment to the cellular components involved in eliciting a specific response. Perturbations in these signaling processes are at the root of multiple pathologies, the most notable of these being cancer. The study of receptor tyrosine kinase (RTK) signaling led to the first description of a mechanism whereby an extracellular signal is transmitted to the nucleus to induce a transcriptional response. Genetic studies conducted in drosophila and nematodes have provided key elements to this puzzle. Here, we briefly discuss the somewhat lesser known contribution of these multicellular organisms to our understanding of what has come to be known as the prototype of signaling pathways. We also discuss the ostensibly much larger network of regulators that has emerged from recent functional genomic investigations of RTK/RAS/ERK signaling.