Shp2 regulates SRC family kinase activity and Ras/Erk activation by controlling Csk recruitment

SHP2 inhibition displays efficacy as a monotherapy and in combination with JAK2 inhibition in preclinical models of myeloproliferative neoplasms

Myeloproliferative neoplasms (MPNs), including polycythemia vera, essential thrombocytosis, and primary myelofibrosis, are clonal hematopoietic neoplasms driven by mutationally activated signaling by the JAK2 tyrosine kinase. Although JAK2 inhibitors can improve MPN patients' quality of life, they do not induce complete remission as disease-driving cells persistently survive therapy. ERK activation has been highlighted as contributing to JAK2 inhibitor persistent cell survival. As ERK is a component of signaling by activated RAS proteins and by JAK2 activation, we sought to inhibit RAS activation to enhance responses to JAK2 inhibition in preclinical MPN models. We found the SHP2 inhibitor RMC-4550 significantly enhanced growth inhibition of MPN cell lines in combination with the JAK2 inhibitor ruxolitinib, effectively preventing ruxolitinib persistent growth, and the growth and viability of established ruxolitinib persistent cells remained sensitive to SHP2 inhibition. Both SHP2 and JAK2 inhibition diminished cellular RAS-GTP levels, and their concomitant inhibition enhanced ERK inactivation and increased apoptosis. Inhibition of SHP2 inhibited the neoplastic growth of MPN patient hematopoietic progenitor cells and exhibited synergy with ruxolitinib. RMC-4550 antagonized MPN phenotypes and increased survival of an MPN mouse model driven by MPL-W515L. The combination of RMC-4550 and ruxolitinib, which was safe and tolerated in healthy mice, further inhibited disease compared to ruxolitinib monotherapy, including extending survival. Given SHP2 inhibitors are undergoing clinical evaluation in patients with solid tumors, our preclinical findings suggest that SHP2 is a candidate therapeutic target with potential for rapid translation to clinical assessment to improve current targeted therapies for MPN patients.

Pharmacological inhibition of the Src homology phosphatase 2 confers partial protection in a mouse model of alcohol-associated liver disease

Alcohol-associated liver disease (ALD) is a leading factor of liver-related death worldwide. ALD has various manifestations that include steatosis, hepatitis, and cirrhosis and is currently without approved pharmacotherapies. The Src homology phosphatase 2 (Shp2) is a drug target in some cancers due to its positive regulation of Ras-mitogen-activated protein kinase signaling and cell proliferation. Shp2 pharmacological inhibition yields beneficial outcomes in animal disease models, but its impact on ALD remains unexplored. This study aims to investigate the effects of Shp2 inhibition and its validity using a preclinical mouse model of ALD. We report that the administration of SHP099, a potent and selective allosteric inhibitor of Shp2, partially ameliorated ethanol-induced hepatic injury, inflammation, and steatosis in mice. Additionally, Shp2 inhibition was associated with reduced ethanol-evoked activation of extracellular signal-regulated kinase (ERK), oxidative, and endoplasmic reticulum (ER) stress in the liver. Besides the liver, excessive alcohol consumption induces multi-organ injury and dysfunction, including the intestine. Notably, Shp2 inhibition diminished ethanol-induced intestinal inflammation and permeability, abrogated the reduction in tight junction protein expression, and the activation of ERK and stress signaling in the ileum. Collectively, Shp2 pharmacological inhibition mitigates the deleterious effects of ethanol in the liver and intestine in a mouse model of ALD. Given the multifactorial aspects underlying ALD pathogenesis, additional studies are needed to decipher the utility of Shp2 inhibition alone or as a component in a multitherapeutic regimen to combat this deadly malady.

THEMIS promotes T cell development and maintenance by rising the signaling threshold of the inhibitory receptor BTLA

The current paradigm about the function of T cell immune checkpoints is that these receptors switch on inhibitory signals upon cognate ligand interaction. We here revisit this simple switch model and provide evidence that the T cell lineage protein THEMIS enhances the signaling threshold at which the immune checkpoint BTLA (B- and T-lymphocyte attenuator) represses T cell responses. THEMIS is recruited to the cytoplasmic domain of BTLA and blocks its signaling capacity by promoting/stabilizing the oxidation of the catalytic cysteine of the tyrosine phosphatase SHP-1. In contrast, THEMIS has no detectable effect on signaling pathways regulated by PD-1 (Programmed cell death protein 1), which depend mainly on the tyrosine phosphatase SHP-2. BTLA inhibitory signaling is tuned according to the THEMIS expression level, making CD8+ T cells more resistant to BTLA-mediated inhibition than CD4+ T cells. In the absence of THEMIS, the signaling capacity of BTLA is exacerbated, which results in the attenuation of signals driven by the T cell antigen receptor and by receptors for IL-2 and IL-15, consequently hampering thymocyte positive selection and peripheral CD8+ T cell maintenance. By characterizing the pivotal role of THEMIS in restricting the transmission of BTLA signals, our study suggests that immune checkpoint operability is conditioned by intracellular signal attenuators.

Bile acid metabolism and signaling in health and disease: molecular mechanisms and therapeutic targets

Bile acids, once considered mere dietary surfactants, now emerge as critical modulators of macronutrient (lipid, carbohydrate, protein) metabolism and the systemic pro-inflammatory/anti-inflammatory balance. Bile acid metabolism and signaling pathways play a crucial role in protecting against, or if aberrant, inducing cardiometabolic, inflammatory, and neoplastic conditions, strongly influencing health and disease. No curative treatment exists for any bile acid influenced disease, while the most promising and well-developed bile acid therapeutic was recently rejected by the FDA. Here, we provide a bottom-up approach on bile acids, mechanistically explaining their biochemistry, physiology, and pharmacology at canonical and non-canonical receptors. Using this mechanistic model of bile acids, we explain how abnormal bile acid physiology drives disease pathogenesis, emphasizing how ceramide synthesis may serve as a unifying pathogenic feature for cardiometabolic diseases. We provide an in-depth summary on pre-existing bile acid receptor modulators, explain their shortcomings, and propose solutions for how they may be remedied. Lastly, we rationalize novel targets for further translational drug discovery and provide future perspectives. Rather than dismissing bile acid therapeutics due to recent setbacks, we believe that there is immense clinical potential and a high likelihood for the future success of bile acid therapeutics.

The Vitamin K-Dependent Anticoagulant Factor, Protein S, Regulates Vascular Permeability

Protein S (PROS1) is a vitamin K-dependent anticoagulant factor, which also acts as an agonist for the TYRO3, AXL, and MERTK (TAM) tyrosine kinase receptors. PROS1 is produced by the endothelium which also expresses TAM receptors, but little is known about its effects on vascular function and permeability. Transwell permeability assays as well as Western blotting and immunostaining analysis were used to monitor the possible effects of PROS1 on both endothelial cell permeability and on the phosphorylation state of specific signaling proteins. We show that human PROS1, at its circulating concentrations, substantially increases both the basal and VEGFA-induced permeability of endothelial cell (EC) monolayers. PROS1 induces p38 MAPK (Mitogen Activated Protein Kinase), Rho/ROCK (Rho-associated protein kinase) pathway activation, and actin filament remodeling, as well as substantial changes in Vascular Endothelial Cadherin (VEC) distribution and its phosphorylation on Ser665 and Tyr685. It also mediates c-Src and PAK-1 (p21-activated kinase 1) phosphorylation on Tyr416 and Ser144, respectively. Exposure of EC to human PROS1 induces VEC internalization as well as its cleavage into a released fragment of 100 kDa and an intracellular fragment of 35 kDa. Using anti-TAM neutralizing antibodies, we demonstrate that PROS1-induced VEC and c-Src phosphorylation are mediated by both the MERTK and TYRO3 receptors but do not involve the AXL receptor. MERTK and TYRO3 receptors are also responsible for mediating PROS1-induced MLC (Myosin Light Chain) phosphorylation on a site targeted by the Rho/ROCK pathway. Our report provides evidence for the activation of the c-Src/VEC and Rho/ROCK/MLC pathways by PROS1 for the first time and points to a new role for PROS1 as an endogenous vascular permeabilizing factor.

Genetically encodable biosensors for Ras activity

Genetically encoded Ras biosensors have been instrumental in illuminating the spatiotemporal dynamics of Ras activity since the beginning of the imaging revolution of the early 21st century. In general, these sensors employ Ras sensing units coupled with fluorescent proteins. These biosensors have not only helped elucidate Ras signalling dynamics at the plasma membrane but also revealed novel roles for Ras signalling within subcellular compartments such as the Golgi apparatus. In this review, we discuss the different classes of biosensors used to measure Ras activity and discuss their importance in uncovering new roles for Ras activity in cellular signalling and behavior.

Counteracting immunotyrosine-based signaling motifs augment zebrafish leukocyte immune-type receptor-mediated phagocytic activity

Leukocyte immune-type receptors (LITRs) represent a polymorphic and polygenic family of immunoregulatory proteins originally discovered in channel catfish (Ictalurus punctatus; IpLITRs). Belonging to the immunoglobulin superfamily (IgSF), IpLITRs are generally classified as stimulatory or inhibitory types based on their utilization of various intracellular tyrosine-based signaling motifs. While research has shown that IpLITRs can activate as well as abrogate different immune cell effector responses including phagocytosis, recent identification of LITRs within the zebrafish genome (Danio rerio; DrLITRs) revealed the existence of fish LITR-types uniquely containing counteracting stimulatory and inhibitory cytoplasmic tail (CYT) region motifs (i.e., an immunoreceptor tyrosine-based activation motif; ITAM, and immunoreceptor tyrosine-based inhibitory motif; ITIM) within the same receptor. This arrangement is unusual as these motifs typically exist on separate stimulatory (i.e., ITAM-containing) or inhibitory (i.e., ITIM-containing) immunoregulatory receptors that then co-engage to fine-tune cellular signaling and effector responses. Using a flow cytometric-based phagocytosis assay, we show here that engagement of DrLITR 1.2-expressing cells with antibody coated 4.5 μm beads causes a robust ITAM-dependent phagocytic response and reveal that its tandem ITIM motif surprisingly enhances the DrLITR 1.2-induced phagocytic activity while simultaneously decreasing the receptors ability to bind the beads. Confocal microscopy studies also revealed that the ITIM-associated inhibitory signaling molecule SHP-2 is localized to the phagocytic synapse during the phagocytic response. Overall, these results provide the first functional characterization of teleost immune receptors containing a tandem ITAM and ITIM and allow for the proposal of an intracytoplasmic tail signaling model for ITIM-mediated enhancement of ITAM-dependent cellular activation.

Tyrosine phosphatase PTPN11/SHP2 in solid tumors - bull's eye for targeted therapy?

Encoded by PTPN11, the Src-homology 2 domain-containing phosphatase 2 (SHP2) integrates signals from various membrane-bound receptors such as receptor tyrosine kinases (RTKs), cytokine and integrin receptors and thereby promotes cell survival and proliferation. Activating mutations in the PTPN11 gene may trigger signaling pathways leading to the development of hematological malignancies, but are rarely found in solid tumors. Yet, aberrant SHP2 expression or activation has implications in the development, progression and metastasis of many solid tumor entities. SHP2 is involved in multiple signaling cascades, including the RAS-RAF-MEK-ERK-, PI3K-AKT-, JAK-STAT- and PD-L1/PD-1- pathways. Although not mutated, activation or functional requirement of SHP2 appears to play a relevant and context-dependent dichotomous role. This mostly tumor-promoting and infrequently tumor-suppressive role exists in many cancers such as gastrointestinal tumors, pancreatic, liver and lung cancer, gynecological entities, head and neck cancers, prostate cancer, glioblastoma and melanoma. Recent studies have identified SHP2 as a potential biomarker for the prognosis of some solid tumors. Based on promising preclinical work and the advent of orally available allosteric SHP2-inhibitors early clinical trials are currently investigating SHP2-directed approaches in various solid tumors, either as a single agent or in combination regimes. We here provide a brief overview of the molecular functions of SHP2 and collate current knowledge with regard to the significance of SHP2 expression and function in different solid tumor entities, including cells in their microenvironment, immune escape and therapy resistance. In the context of the present landscape of clinical trials with allosteric SHP2-inhibitors we discuss the multitude of opportunities but also limitations of a strategy targeting this non-receptor protein tyrosine phosphatase for treatment of solid tumors.

Hepatic protein tyrosine phosphatase Shp2 disruption mitigates the adverse effects of ethanol in the liver by modulating oxidative stress and ERK signaling

AIMS

Chronic excessive alcohol intake is a significant cause of alcohol-associated liver disease (ALD), a leading contributor to liver-related morbidity and mortality. The Src homology phosphatase 2 (Shp2; encoded by Ptpn11) is a widely expressed protein tyrosine phosphatase that modulates hepatic functions, but its role in ALD is mostly uncharted.

MAIN METHODS

Herein, we explore the effects of liver-specific Shp2 genetic disruption using the established chronic-plus-binge mouse model of ALD.

KEY FINDINGS

We report that the hepatic Shp2 disruption had beneficial effects and partially ameliorated ethanol-induced injury, inflammation, and steatosis in the liver. Consistently, Shp2 deficiency was associated with decreased ethanol-evoked activation of extracellular signal-regulated kinase (ERK) and oxidative stress in the liver. Moreover, primary hepatocytes with Shp2 deficiency exhibited similar outcomes to those observed upon Shp2 disruption in vivo, including diminished ethanol-induced ERK activation, inflammation, and oxidative stress. Furthermore, pharmacological inhibition of ERK in primary hepatocytes mimicked the effects of Shp2 deficiency and attenuated oxidative stress caused by ethanol.

SIGNIFICANCE

Collectively, these findings highlight Shp2 as a modulator of hepatic oxidative stress upon ethanol challenge and suggest the evaluation of this phosphatase as a potential therapeutic target for ALD.

Metabolic control of puberty: 60 years in the footsteps of Kennedy and Mitra's seminal work

An individual's nutritional status has a powerful effect on sexual maturation. Puberty onset is delayed in response to chronic energy insufficiency and is advanced under energy abundance. The consequences of altered pubertal timing for human health are profound. Late puberty increases the chances of cardiometabolic, musculoskeletal and neurocognitive disorders, whereas early puberty is associated with increased risks of adult obesity, type 2 diabetes mellitus, cardiovascular diseases and various cancers, such as breast, endometrial and prostate cancer. Kennedy and Mitra's trailblazing studies, published in 1963 and using experimental models, were the first to demonstrate that nutrition is a key factor in puberty onset. Building on this work, the field has advanced substantially in the past decade, which is largely due to the impressive development of molecular tools for experimentation and population genetics. In this Review, we discuss the latest advances in basic and translational sciences underlying the nutritional and metabolic control of pubertal development, with a focus on perspectives and future directions.

Targeting Src homology phosphatase 2 ameliorates mouse diabetic nephropathy by attenuating ERK/NF-κB pathway-mediated renal inflammation

Renal inflammation is a pivotal mechanism underlying the pathophysiology of diabetic nephropathy (DN). The Src homology phosphatase 2 (SHP2) has been demonstrated to be linked to diabetes-induced inflammation, yet its roles and explicit molecular mechanisms in DN remain unexplored. Here, we report that SHP2 activity is upregulated in both DN patients and db/db mice. In addition, pharmacological inhibition of SHP2 with its specific inhibitor PHPS1 alleviates DN in db/db mice and attenuates renal inflammation. In vitro, PHPS1 administration prevents inflammatory responses in HK-2 cells stimulated by high glucose (HG). Mechanistically, PHPS1 represses HG-induced activation of the proinflammatory ERK/NF-κB signaling pathway, and these inhibitory effects are blocked in the presence of an ERK specific inhibitor, hence demonstrating that PHPS1 suppresses ERK/NF-κB pathway-mediated inflammation. Moreover, PHPS1 retards ERK/NF-κB pathway activation in db/db mice, and histologically, SHP2 activity is positively correlated with ERK/NF-κB activation in DN patients. Taken together, these findings identify SHP2 as a potential therapeutic target and show that its pharmacological inhibition might be a promising strategy to mitigate DN. Video Abstract.

Overcoming Immune Checkpoint Therapy Resistance with SHP2 Inhibition in Cancer and Immune Cells: A Review of the Literature and Novel Combinatorial Approaches

SHP2 (Src Homology 2 Domain-Containing Phosphatase 2) is a protein tyrosine phosphatase widely expressed in various cell types. SHP2 plays a crucial role in different cellular processes, such as cell proliferation, differentiation, and survival. Aberrant activation of SHP2 has been implicated in multiple human cancers and is considered a promising therapeutic target for treating these malignancies. The PTPN11 gene and functions encode SHP2 as a critical signal transduction regulator that interacts with key signaling molecules in both the RAS/ERK and PD-1/PD-L1 pathways; SHP2 is also implicated in T-cell signaling. SHP2 may be inhibited by molecules that cause allosteric (bind to sites other than the active site and attenuate activation) or orthosteric (bind to the active site and stop activation) inhibition or via potent SHP2 degraders. These inhibitors have anti-proliferative effects in cancer cells and suppress tumor growth in preclinical models. In addition, several SHP2 inhibitors are currently in clinical trials for cancer treatment. This review aims to provide an overview of the current research on SHP2 inhibitors, including their mechanism of action, structure-activity relationships, and clinical development, focusing on immune modulation effects and novel therapeutic strategies in the immune-oncology field.

Targeting SHP2 with an Active Site Inhibitor Blocks Signaling and Breast Cancer Cell Phenotypes

The Src homology phosphotyrosyl phosphatase 2 (SHP2) is an oncogenic protein for which targeted therapies are being sought. In line with this idea, we have previously reported the development of a specific active site inhibitor named CNBDA that showed effectivity in suppressing the transformation phenotypes of breast cancer cells. To improve efficacy, we introduced limited modifications to the parent compound and tested potency in vitro and under cell culture conditions. Of these modifications, removal of one of the butyric acid groups led to the production of a compound named CNBCA, which showed a 5.7-fold better potency against the SHP2 enzyme activity in vitro. In addition, CNBCA showed better selectivity to SHP2 than the control PTPs (SHP1 and PTP1B) as determined by the phosphatase assay. Furthermore, CNBCA binds and inhibits enzyme activity of full-length SHP2 in cellular contexts, downregulates SHP2 mediated signaling, and suppresses breast cancer cell phenotypes, including cell proliferation, colony formation, and mammosphere growth. These findings show that targeting SHP2 with CNBCA is effective against the cancerous properties of breast cancer cells.

THEMIS increases TCR signaling in CD4+CD8+ thymocytes by inhibiting the activity of the tyrosine phosphatase SHP1

The T cell lineage-restricted protein THEMIS plays a critical role in T cell development at the positive selection stage. In the SHP1 activation model, THEMIS is proposed to enhance the activity of the tyrosine phosphatase SHP1 (encoded by Ptpn6), thereby dampening T cell antigen receptor (TCR) signaling and preventing the inappropriate negative selection of CD4+CD8+ thymocytes by positively selecting ligands. In contrast, in the SHP1 inhibition model, THEMIS is proposed to suppress SHP1 activity, rendering CD4+CD8+ thymocytes more sensitive to TCR signaling initiated by low-affinity ligands to promote positive selection. We sought to resolve the controversy regarding the molecular function of THEMIS. We found that the defect in positive selection in Themis-/- thymocytes was ameliorated by pharmacologic inhibition of SHP1 or by deletion of Ptpn6 and was exacerbated by SHP1 overexpression. Moreover, overexpression of SHP1 phenocopied the Themis-/- developmental defect, whereas deletion of Ptpn6, Ptpn11 (encoding SHP2), or both did not result in a phenotype resembling that of Themis deficiency. Last, we found that thymocyte negative selection was not enhanced but was instead impaired in the absence of THEMIS. Together, these results provide evidence favoring the SHP1 inhibition model, supporting a mechanism whereby THEMIS functions to enhance the sensitivity of CD4+CD8+ thymocytes to TCR signaling, enabling positive selection by low-affinity, self-ligand-TCR interactions.

Setting sail: Maneuvering SHP2 activity and its effects in cancer

Since the discovery of tyrosine phosphorylation being a critical modulator of cancer signaling, proteins regulating phosphotyrosine levels in cells have fast become targets of therapeutic intervention. The nonreceptor protein tyrosine phosphatase (PTP) coded by the PTPN11 gene "SHP2" integrates phosphotyrosine signaling from growth factor receptors into the RAS/RAF/ERK pathway and is centrally positioned in processes regulating cell development and oncogenic transformation. Dysregulation of SHP2 expression or activity is linked to tumorigenesis and developmental defects. Even as a compelling anti-cancer target, SHP2 was considered "undruggable" for a long time owing to its conserved catalytic PTP domain that evaded drug development. Recently, SHP2 has risen from the "undruggable curse" with the discovery of small molecules that manipulate its intrinsic allostery for effective inhibition. SHP2's unique domain arrangement and conformation(s) allow for a truly novel paradigm of inhibitor development relying on skillful targeting of noncatalytic sites on proteins. In this review we summarize the biological functions, signaling properties, structural attributes, allostery and inhibitors of SHP2.

From Stem to Sternum: The Role of Shp2 in the Skeleton

Src homology-2 domain-containing phosphatase 2 (SHP2) is a ubiquitously expressed phosphatase that is vital for skeletal development and maintenance of chondrocytes, osteoblasts, and osteoclasts. Study of SHP2 function in small animal models has led to insights in phenotypes observed in SHP2-mutant human disease, such as Noonan syndrome. In recent years, allosteric SHP2 inhibitors have been developed to specifically target the protein in neoplastic processes. These inhibitors are highly specific and have great potential for disease modulation in cancer and other pathologies, including bone disorders. In this review, we discuss the importance of SHP2 and related signaling pathways (e.g., Ras/MEK/ERK, JAK/STAT, PI3K/Akt) in skeletal development. We review rodent models of pathologic processes caused by germline mutations that activate SHP2 enzymatic activity, with a focus on the skeletal phenotype seen in these patients. Finally, we discuss SHP2 inhibitors in development and their potential for disease modulation in these genetic diseases, particularly as it relates to the skeleton.

Roles of protein tyrosine phosphatases in hepatocellular carcinoma progression (Review)

Hepatocellular carcinoma (HCC) represents almost 80% of all liver cancers, is the sixth most common cancer and is the second‑highest cause of cancer‑related deaths worldwide. Protein tyrosine phosphatases (PTPs), which are encoded by the largest family of phosphatase genes, play critical roles in cellular responses and are implicated in various signaling pathways. Moreover, PTPs are dysregulated and involved in various cellular processes in numerous cancers, including HCC. Kinases and phosphatases are coordinators that modulate cell activities and regulate signaling responses. There are multiple interacting signaling networks, and coordination of these signaling networks in response to a stimulus determines the physiological outcome. Numerous issues, such as drug resistance and inflammatory reactions in the tumor microenvironment, are implicated in cancer progression, and the role of PTPs in these processes has not been well elucidated. Therefore, the present review focused on discussing the relationship of PTPs with inflammatory cytokines and chemotherapy/targeted drug resistance, providing detailed information on how PTPs can modulate inflammatory reactions and drug resistance to influence progression in HCC.

Design and synthesis of improved active-site SHP2 inhibitors with anti-breast cancer cell effects

The Src homology containing phosphotyrosyl phosphatase 2 (SHP2) is a bona fide oncogene particularly in cancers driven by overexpression of receptor tyrosine kinases (RTKs). As such, there is a growing interest to target SHP2 in cancer. Based on these premises, several active site (type I) and allosteric site (type II) inhibitors have been developed, but no SHP2 targeting therapies have reached the clinic yet. In an effort to fill these gaps, we embarked on producing optimized versions of our parent active-site SHP2 inhibitor CNBDA. The objectives were to produce derivatives with increased inhibitory potential and improved selectivity. Accordingly, we designed derivatives around the CNBDA scaffold and predicted their binding property by in silico molecular modeling. Based on comparative differences in free energy of binding to the SHP2 versus the SHP1 active sites, ten were selected, chemically synthesized, and evaluated by NMR and mass spectroscopy for structural integrity. Among the ten derivatives, BPDA2 was found to be the most potent and highly selective compound, inhibiting the SHP2 enzyme activity with an IC₅₀ of 92 nM when DiFMUP was used as a substrate and with an IC₅₀ of 47 nM when pNPP was used as a substrate. Furthermore, enzyme kinetic analyses showed that BPDA2 is a competitive SHP2 inhibitor. Selectivity comparisons in a PTPase assay using DiFMUP as a substrate demonstrated that BPDA2 is more selective to SHP2 than to SHP1 and PTP1B by more than 369-fold and 442-fold, respectively. Evaluation with a cellular thermal shift assay (CETSA) confirmed that BPDA2 binds to wild-type SHP2 in a cellular context, and stabilizes it in solution. Treatment of cells with DBDA2 downregulates mitogenic and cell survival signaling and RTK expression in a concentration dependent manner. Furthermore, treatment of cells with BPDA2 suppresses anchorage independent growth and cancer stem cell properties of breast cancer cells. Overall, data described in this report show that BPDA2 is a more potent derivative of CNBDA with a highly improved selectivity for SHP2.

Progress of small molecules for targeted protein degradation: PROTACs and other technologies

Recent years have witnessed the rapid development of targeted protein degradation (TPD), especially proteolysis targeting chimeras. These degraders have manifested many advantages over small molecule inhibitors. To date, a huge number of degraders have been excavated against over 70 disease-related targets. In particular, degraders against estrogen receptor and androgen receptor have crowded into phase II clinical trial. TPD technologies largely expand the scope of druggable targets, and provide powerful tools for addressing intractable problems that can not be tackled by traditional small molecule inhibitors. In this review, we mainly focus on the structures and biological activities of small molecule degraders as well as the elucidation of mechanisms of emerging TPD technologies. We also propose the challenges that exist in the TPD field at present.

Targeting KRASp.G12C Mutation in Advanced Non-Small Cell Lung Cancer: a New Era Has Begun

OPINION STATEMENT

KRASp.G12C mutation occurs in 12% of newly diagnosed advanced NSCLC and has recently emerged as a positive predictive biomarker for the selection of advanced NSCLC patients who may respond to novel KRASp.G12C inhibitors. The recent discovery of a new binding pocket under the effector region of KRAS G12C oncoprotein has made direct pharmacological inhibition of the KRASp.G12 mutation possible, leading to the clinical development of a new series of direct selective inhibitors, with a potential major impact on patients' survival and quality of life. Promising efficacy and tolerability data emerging from the early phase CodeBreak trial have already supported the regulatory approval of sotorasib as first in class targeted treatment for the second-line treatment of KRASp.G12C-positive NSCLC population, following immunotherapy-based first-line therapies, while the randomized phase III CodeBreak 200 clinical study has recently confirmed a significant superiority of sotorasib over docetaxel in terms of progression-free survival and quality of life. However, KRAS mutant NSCLC is a high heterogeneous disease characterized by a high rate of co-mutations, most frequently involving P53, STK11, and KEAP1 genes, which significantly modulate the composition of the tumor microenvironment and consequently affect clinical responses to both immunotherapy and targeted inhibitors now available in clinical practice. Both pre-clinical and clinical translational series have recently revealed a wide spectrum of resistance mechanisms occurring under selective KRASG12C inhibitors, including both on-target and off-target molecular alterations as well as morphological switching, negatively affecting the antitumor activity of these drugs when used as single agent therapies. The understanding of such biological background along with the emergence of pre-clinical data provided a strong rational to investigate different combination strategies, including the inhibition of SHP2, SOS1, and KRAS G12C downstream effectors, as well as the addition of immunotherapy and/or chemotherapy to targeted therapy. The preliminary results of these trials have recently suggested a promising activity of SHP2 inhibitors in the front-line setting, while toxicity issues limited the concurrent administration of immune-checkpoint inhibitors and sotorasib. The identification of predictive genomic/immunological biomarkers will be crucial to understand how to optimally sequencing/combining different drugs and ultimately personalize treatment strategies under clinical investigation, to definitively increase the survival outcomes of KRASp.G12C mutant advanced NSCLC patients.

Concomitant deletion of Ptpn6 and Ptpn11 in T cells fails to improve anticancer responses

Anticancer T cells acquire a dysfunctional state characterized by poor effector function and expression of inhibitory receptors, such as PD-1. Blockade of PD-1 leads to T cell reinvigoration and is increasingly applied as an effective anticancer treatment. Recent work challenged the commonly held view that the phosphatase PTPN11 (known as SHP-2) is essential for PD-1 signaling in T cells, suggesting functional redundancy with the homologous phosphatase PTPN6 (SHP-1). Therefore, we investigated the effect of concomitant Ptpn6 and Ptpn11 deletion in T cells on their ability to mount antitumour responses. In vivo data show that neither sustained nor acute Ptpn6/11 deletion improves T cell-mediated tumor control. Sustained loss of Ptpn6/11 also impairs the therapeutic effects of anti-PD1 treatment. In vitro results show that Ptpn6/11-deleted CD8+ T cells exhibit impaired expansion due to a survival defect and proteomics analyses reveal substantial alterations, including in apoptosis-related pathways. These data indicate that concomitant ablation of Ptpn6/11 in polyclonal T cells fails to improve their anticancer properties, implying that caution shall be taken when considering their inhibition for immunotherapeutic approaches.

Modeling (not so) rare developmental disorders associated with mutations in the protein-tyrosine phosphatase SHP2

Src homology region 2 (SH2)-containing protein tyrosine phosphatase 2 (SHP2) is a highly conserved protein tyrosine phosphatase (PTP), which is encoded by PTPN11 and is indispensable during embryonic development. Mutations in PTPN11 in human patients cause aberrant signaling of SHP2, resulting in multiple rare hereditary diseases, including Noonan Syndrome (NS), Noonan Syndrome with Multiple Lentigines (NSML), Juvenile Myelomonocytic Leukemia (JMML) and Metachondromatosis (MC). Somatic mutations in PTPN11 have been found to cause cancer. Here, we focus on the role of SHP2 variants in rare diseases and advances in the understanding of its pathogenesis using model systems.

Siglec-6 Signaling Uses Src Kinase Tyrosine Phosphorylation and SHP-2 Recruitment

Preeclampsia is a pregnancy-specific disorder involving placental abnormalities. Elevated placental Sialic acid immunoglobulin-like lectin (Siglec)-6 expression has been correlated with preeclampsia. Siglec-6 is a transmembrane receptor, expressed predominantly by the trophoblast cells in the human placenta. It interacts with sialyl glycans such as sialyl-TN glycans as well as binds leptin. Siglec-6 overexpression has been shown to influence proliferation, apoptosis, and invasion in the trophoblast (BeWo) cell model. However, there is no direct evidence that Siglec-6 plays a role in preeclampsia pathogenesis and its signaling potential is still largely unexplored. Siglec-6 contains an immunoreceptor tyrosine-based inhibitory motif (ITIM) and an ITIM-like motif in its cytoplasmic tail suggesting a signaling function. Site-directed mutagenesis and transfection were employed to create a series of Siglec-6 expressing HTR-8/SVneo trophoblastic cell lines with mutations in specific functional residues to explore the signaling potential of Siglec-6. Co-immunoprecipitation and inhibitory assays were utilized to investigate the association of Src-kinases and SH-2 domain-containing phosphatases with Siglec-6. In this study, we show that Siglec-6 is phosphorylated at ITIM and ITIM-like domains by Src family kinases. Phosphorylation of both ITIM and ITIM-like motifs is essential for the recruitment of phosphatases like Src homology region 2 containing protein tyrosine phosphatase 2 (SHP-2), which has downstream signaling capabilities. These findings suggest Siglec-6 as a signaling molecule in human trophoblasts. Further investigation is warranted to determine which signaling pathways are activated downstream to SHP-2 recruitment and how overexpression of Siglec-6 in preeclamptic placentas impacts pathogenesis.

Src: coordinating metabolism in cancer

Metabolism must be tightly regulated to fulfil the dynamic requirements of cancer cells during proliferation, migration, stemness and differentiation. Src is a node of several signals involved in many of these biological processes, and it is also an important regulator of cell metabolism. Glucose uptake, glycolysis, the pentose-phosphate pathway and oxidative phosphorylation are among the metabolic pathways that can be regulated by Src. Therefore, this oncoprotein is in an excellent position to coordinate and finely tune cell metabolism to fuel the different cancer cell activities. Here, we provide an up-to-date summary of recent progress made in determining the role of Src in glucose metabolism as well as the link of this role with cancer cell metabolic plasticity and tumour progression. We also discuss the opportunities and challenges facing this field.

A germline SNP in BRMS1 predisposes patients with lung adenocarcinoma to metastasis and can be ameliorated by targeting c-fos

About 50% of patients with early-stage, surgically resected lung cancer will develop distant metastasis. There remains an unmet need to identify patients likely to develop recurrence and to design innovative therapies to decrease this risk. Two primary isoforms of BRMS1, v1 and v2, are present in humans. Using next-generation sequencing of BRMS1 on matched human noncancerous lung tissue and non-small cell lung cancer (NSCLC) specimens, we identified single-nucleotide polymorphism (SNP) rs1052566 that results in an A273V mutation of BRMS1v2. This SNP is homozygous (BRMS1v2^A273V/A273V) in 8% of the population and correlates with aggressive biology in lung adenocarcinoma (LUAD). Mechanistically, we show that BRMS1v2 A273V abolishes the metastasis suppressor function of BRMS1v2 and promotes robust cell invasion and metastases by activation of c-fos-mediated gene-specific transcriptional regulation. BRMS1v2 A273V increases cell invasion in vitro and increases metastases in both tail-vein injection xenografts and LUAD patient-derived organoid (PDO) intracardiac injection metastasis in vivo models. Moreover, we show that BRMS1v2 A273V fails to interact with nuclear Src, thereby activating intratumoral c-fos in vitro. Higher c-fos results in up-regulation of CEACAM6, which drives metastases in vitro and in vivo. Using both xenograft and PDO metastasis models, we repurposed T5224 for treatment, a c-fos pharmacologic inhibitor investigated in clinical trials for arthritis, and observed suppression of metastases in BRMS1v2^A273V/A273V LUAD in mice. Collectively, we elucidate the mechanism of BRMS1v2^A273V/A273V-induced metastases and offer a putative therapeutic strategy for patients with LUAD who have this germline alteration.

Deficiency of the Src homology phosphatase 2 in podocytes is associated with renoprotective effects in mice under hyperglycemia

Diabetic nephropathy (DN) is a significant complication of diabetes and the leading cause of end-stage renal disease. Hyperglycemia-induced dysfunction of the glomerular podocytes is a major contributor to the deterioration of renal function in DN. Previously, we demonstrated that podocyte-specific disruption of the Src homology phosphatase 2 (Shp2) ameliorated lipopolysaccharide-induced renal injury. This study aims to evaluate the contribution of Shp2 to podocyte function under hyperglycemia and explore the molecular underpinnings. We report elevated Shp2 in the E11 podocyte cell line under high glucose and the kidney under streptozotocin- and high-fat diet-induced hyperglycemia. Consistently, Shp2 disruption in podocytes was associated with partial renoprotective effects under hyperglycemia, as evidenced by the preserved renal function. At the molecular level, Shp2 deficiency was associated with altered renal insulin signaling and diminished hyperglycemia-induced renal endoplasmic reticulum stress, inflammation, and fibrosis. Additionally, Shp2 knockdown in E11 podocytes mimicked the in vivo deficiency of this phosphatase and ameliorated the deleterious impact of high glucose, whereas Shp2 reconstitution reversed these effects. Moreover, Shp2 deficiency attenuated high glucose-induced E11 podocyte migration. Further, we identified the protein tyrosine kinase FYN as a putative mediator of Shp2 signaling in podocytes under high glucose. Collectively, these findings suggest that Shp2 inactivation may afford protection to podocytes under hyperglycemia and highlight this phosphatase as a potential target to ameliorate glomerular dysfunction in DN.

A comprehensive review of SHP2 and its role in cancer

Src homology 2-containing protein tyrosine phosphatase 2 (SHP2) is a non-receptor protein tyrosine phosphatase ubiquitously expressed mainly in the cytoplasm of several tissues. SHP2 modulates diverse cell signaling events that control metabolism, cell growth, differentiation, cell migration, transcription and oncogenic transformation. It interacts with diverse molecules in the cell, and regulates key signaling events including RAS/ERK, PI3K/AKT, JAK/STAT and PD-1 pathways downstream of several receptor tyrosine kinases (RTKs) upon stimulation by growth factors and cytokines. SHP2 acts as both a phosphatase and a scaffold, and plays prominently oncogenic functions but can be tumor suppressor in a context-dependent manner. It typically acts as a positive regulator of RTKs signaling with some inhibitory functions reported as well. SHP2 expression and activity is regulated by such factors as allosteric autoinhibition, microRNAs, ubiquitination and SUMOylation. Dysregulation of SHP2 expression or activity causes many developmental diseases, and hematological and solid tumors. Moreover, upregulated SHP2 expression or activity also decreases sensitivity of cancer cells to anticancer drugs. SHP2 is now considered as a compelling anticancer drug target and several classes of SHP2 inhibitors with different mode of action are developed with some already in clinical trial phases. Moreover, novel SHP2 substrates and functions are rapidly growing both in cell and cancer. In view of this, we comprehensively and thoroughly reviewed literatures about SHP2 regulatory mechanisms, substrates and binding partners, biological functions, roles in human cancers, and different classes of small molecule inhibitors target this oncoprotein in cancer.

High-risk neuroblastoma with NF1 loss of function is targetable using SHP2 inhibition

Reoccurring/high-risk neuroblastoma (NB) tumors have the enrichment of non-RAS/RAF mutations along the mitogen-activated protein kinase (MAPK) signaling pathway, suggesting that activation of MEK/ERK is critical for their survival. However, based on preclinical data, MEK inhibitors are unlikely to be active in NB and have demonstrated dose-limiting toxicities that limit their use. Here, we explore an alternative way to target the MAPK pathway in high-risk NB. We find that NB models are among the most sensitive among over 900 tumor-derived cell lines to the allosteric SHP2 inhibitor SHP099. Sensitivity to SHP099 in NB is greater in models with loss or low expression of the RAS GTPase activation protein (GAP) neurofibromin 1 (NF1). Furthermore, NF1 is lower in advanced and relapsed NB and NF1 loss is enriched in high-risk NB tumors regardless of MYCN status. SHP2 inhibition consistently blocks tumor growth in high-risk NB mouse models, revealing a new drug target in relapsed NB.

Endothelial SIRPα signaling controls VE-cadherin endocytosis for thymic homing of progenitor cells

Thymic homing of hematopoietic progenitor cells (HPCs) is tightly regulated for proper T cell development. Previously we have identified a subset of specialized thymic portal endothelial cells (TPECs), which is important for thymic HPC homing. However, the underlying molecular mechanism still remains unknown. Here, we found that signal regulatory protein alpha (SIRPα) is preferentially expressed on TPECs. Disruption of CD47-SIRPα signaling in mice resulted in reduced number of thymic early T cell progenitors (ETPs), impaired thymic HPC homing, and altered early development of thymocytes. Mechanistically, Sirpa-deficient ECs and Cd47-deficient bone marrow progenitor cells or T lymphocytes demonstrated impaired transendothelial migration (TEM). Specifically, SIRPα intracellular ITIM motif-initiated downstream signaling in ECs was found to be required for TEM in an SHP2- and Src-dependent manner. Furthermore, CD47 signaling from migrating cells and SIRPα intracellular signaling were found to be required for VE-cadherin endocytosis in ECs. Thus, our study reveals a novel role of endothelial SIRPα signaling for thymic HPC homing for T cell development.

Targeting SHP2 phosphatase in breast cancer overcomes RTK-mediated resistance to PI3K inhibitors

Background

PI3K signaling is frequently activated in breast cancer and is targeted by PI3K inhibitors. However, resistance of tumor cells to PI3K inhibition, often mediated by activated receptor tyrosine kinases, is commonly observed and reduces the potency of PI3K inhibitors. Therefore, new treatment strategies to overcome resistance to PI3K inhibitors are urgently needed to boost their efficacy. The phosphatase SHP2, which plays a crucial role in mediating signal transduction between receptor tyrosine kinases and both the PI3K and MAPK pathways, is a potential target for combination treatment.

Methods

We tested combinations of PI3K and SHP2 inhibitors in several experimental breast cancer models that are resistant to PI3K inhibition. Using cell culturing, biochemical and genetic approaches, we evaluated tumor cell proliferation and signaling output in cells treated with PI3K and SHP2 inhibitors.

Results

Combination treatment with PI3K and SHP2 inhibitors counteracted both acquired and intrinsic breast cancer cell resistance to PI3K inhibition that is mediated by activated receptor tyrosine kinases. Dual PI3K and SHP2 inhibition blocked proliferation and led to sustained inactivation of PI3K and MAPK signaling, where resistant cells rapidly re-activated these pathways upon PI3K inhibitor monotreatment. In addition, we demonstrate that overexpression of SHP2 induced resistance to PI3K inhibition, and that SHP2 was frequently activated during the development of PI3K inhibitor resistance after prolonged treatment of sensitive cells.

Conclusions

Our results highlight the importance of SHP2 as a player in resistance to PI3K inhibitors. Combination treatment with PI3K and SHP2 inhibitors could pave the way for significant improvements in therapies for breast cancer.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13058-022-01521-3.

T-cell Lymphoblastic Lymphoma in a Patient With Chromosome 8q21.11 Microdeletion

The chromosome 8q21.11 deletion syndrome is an extremely rare genetic condition characterized by facial dysmorphic features, Peters anomaly and impaired intellectual development. We report a case of a 2-year-old female with chromosome 8q21.11-q21.2 microdeletion complicated by T-cell lymphoblastic lymphoma. Whole genome single-nucleotide polymorphism microarray detected an interstitial deletion of 8q21.11 to q.21.2, including 16 genes. Autopsy findings revealed a T-cell lymphoblastic lymphoma presenting as an anterior mediastinal mass, encroaching upon the aortic arch, left subclavian artery, left carotid bifurcation and trachea. The genes that may contribute to a neoplastic process are identified (PKIA, IL7, TPD52, PAG1, and FABP5) and discussed in this article.

Immune Checkpoint Receptors Signaling in T Cells

The characterization of the receptors negatively modulating lymphocyte function is rapidly advancing, driven by success in tumor immunotherapy. As a result, the number of immune checkpoint receptors characterized from a functional perspective and targeted by innovative drugs continues to expand. This review focuses on the less explored area of the signaling mechanisms of these receptors, of those expressed in T cells. Studies conducted mainly on PD-1, CTLA-4, and BTLA have evidenced that the extracellular parts of some of the receptors act as decoy receptors for activating ligands, but in all instances, the tyrosine phosphorylation of their cytoplasmatic tail drives a crucial inhibitory signal. This negative signal is mediated by a few key signal transducers, such as tyrosine phosphatase, inositol phosphatase, and diacylglycerol kinase, which allows them to counteract TCR-mediated activation. The characterization of these signaling pathways is of great interest in the development of therapies for counteracting tumor-infiltrating lymphocyte exhaustion/anergy independently from the receptors involved.

Recent advances in the discovery of protein tyrosine phosphatase SHP2 inhibitors

Src homology 2 domain-containing protein tyrosine phosphatase (SHP2) is a non-receptor protein tyrosine phosphatase encoded by the Ptpn11 gene, which regulates cell growth, differentiation and apoptosis via modulating various signaling pathways, such as the RAS/ERK signaling pathway, and participates in the PD-1/PD-L1 pathway governing immune surveillance. It has been recognized as a breakthrough antitumor therapeutic target. Besides, numerous studies have shown that SHP2 plays an important role in the regulation of inflammatory diseases. However, inhibitors targeting the active site of SHP2 lack drug-likeness due to their low selectivity and poor bioavailability, thus none has advanced to clinical development. Recently, allosteric inhibitors that stabilize the inactive conformation of SHP2 have achieved breakthrough progress, providing the clinical proof for the druggability of SHP2 as an antitumor drug target. This paper reviews the recently reported design and discovery of SHP2 small molecule inhibitors, focused on the structure-activity relationship (SAR) analysis of several representative SHP2 inhibitors, outlining the evolution and therapeutic potential of the small molecule inhibitors targeting SHP2.

GSK3 inhibition circumvents and overcomes acquired lorlatinib resistance in ALK-rearranged non-small-cell lung cancer

Anaplastic lymphoma kinase (ALK) fusion is found in ~3%–5% of patients with non-small-cell lung cancers (NSCLCs). Although the third-generation ALK tyrosine kinase inhibitor (TKI) lorlatinib shows high clinical efficacy in ALK-positive NSCLC, most of the patients eventually relapse with acquired resistance. Recently, drug-tolerant persister (DTP) cells have been considered an important seed of acquired resistance cells. In this study, we established lorlatinib intermediate resistant cells from a patient-derived cell model. Glycogen synthase kinase 3 (GSK3) inhibitions significantly suppressed lorlatinib intermediate resistant cell growth. GSK3 inhibition also sensitized acquired resistance cells derived from alectinib-treated patients with or without secondary mutations to lorlatinib. Therefore, GSK3 plays a crucial role in developing acquired resistance against lorlatinib in ALK-positive NSCLC mediated by lorlatinib intermediate resistant cells and could be a potential molecular target to prevent acquired lorlatinib resistance and overcome ALK-TKI resistance.

A JAM-A-tetraspanin-αvβ5 integrin complex regulates contact inhibition of locomotion

Contact inhibition of locomotion (CIL) is a process that regulates cell motility upon collision with other cells. Improper regulation of CIL has been implicated in cancer cell dissemination. Here, we identify the cell adhesion molecule JAM-A as a central regulator of CIL in tumor cells. JAM-A is part of a multimolecular signaling complex in which tetraspanins CD9 and CD81 link JAM-A to αvβ5 integrin. JAM-A binds Csk and inhibits the activity of αvβ5 integrin-associated Src. Loss of JAM-A results in increased activities of downstream effectors of Src, including Erk1/2, Abi1, and paxillin, as well as increased activity of Rac1 at cell-cell contact sites. As a consequence, JAM-A-depleted cells show increased motility, have a higher cell-matrix turnover, and fail to halt migration when colliding with other cells. We also find that proper regulation of CIL depends on αvβ5 integrin engagement. Our findings identify a molecular mechanism that regulates CIL in tumor cells and have implications on tumor cell dissemination.

Targeting KRAS Mutant in Non-Small Cell Lung Cancer: Novel Insights Into Therapeutic Strategies

Although KRAS-activating mutations represent the most common oncogenic driver in non-small cell lung cancer (NSCLC), various attempts to inhibit KRAS failed in the past decade. KRAS mutations are associated with a poor prognosis and a poor response to standard therapeutic regimen. The recent development of new therapeutic agents (i.e., adagrasib, sotorasib) that target specifically KRAS G12C in its GDP-bound state has evidenced an unprecedented success in the treatment of this subgroup of patients. Despite providing pre-clinical and clinical efficacy, several mechanisms of acquired resistance to KRAS G12C inhibitors have been reported. In this setting, combined therapeutic strategies including inhibition of either SHP2, SOS1 or downstream effectors of KRAS G12C seem particularly interesting to overcome acquired resistance. In this review, we will discuss the novel therapeutic strategies targeting KRAS G12C and promising approaches of combined therapy to overcome acquired resistance to KRAS G12C inhibitors.

Negative times negative equals positive, THEMIS sets the rule on thymic selection and peripheral T cell responses

The activity of T cells is finely controlled by a set of negative regulators of T-cell antigen receptor (TCR)-mediated signaling. However, how those negative regulators are themselves controlled to prevent ineffective TCR-mediated responses remain poorly understood. Thymocyte-expressed molecule involved in selection (THEMIS) has been characterized over a decade ago as an important player of T cell development. Although the molecular function of THEMIS has long remained puzzling and subject to controversies, latest investigations suggest that THEMIS stimulates TCR-mediated signaling by repressing the tyrosine phosphatases SHP-1 and SHP-2 which exert regulatory function on T cell activation. Recent evidences also point to a role for THEMIS in peripheral T cells beyond its role on thymic selection. Here, we present an overview of the past research on THEMIS in the context of T cell development and peripheral T cell function and discuss the possible implication of THEMIS-based mechanisms on TCR-dependent and independent signaling outcomes.

Inhibition of SHP2 as an approach to block RAS-driven cancers

The non-receptor protein tyrosine phosphatase SHP2 (encoded by PTPN11) is a critical component of RAS/MAPK signaling by acting upstream of RAS to promote oncogenic signaling and tumor growth. Over three decades, SHP2 was considered "undruggable" because enzymatic active-site inhibitors generally showed off-target inhibition of other proteins and low membrane permeability. More recently, allosteric SHP2 inhibitors with striking inhibitory potency have been developed. These small molecules effectively block the signal transduction between receptor tyrosine kinases (RTKs) and RAS/MAPK signaling and show efficacy in preclinical cancer models. Moreover, clinical evaluation of these allosteric SHP2 inhibitors is ongoing. RAS proteins which harbor transforming properties by gain-of-function mutations are present in various cancer types. While inhibitors of KRASG12C show early clinical promise, resistance remains a challenge and other forms of oncogenic RAS remain to be selectively inhibited. Here, we summarize the role of SHP2 in RAS-driven cancers and the therapeutic potential of allosteric SHP2 inhibitors as a strategy to block RAS-driven cancers.

Protein tyrosine phosphatases in skeletal development and diseases

Skeletal development and homeostasis in mammals are modulated by finely coordinated processes of migration, proliferation, differentiation, and death of skeletogenic cells originating from the mesoderm and neural crest. Numerous molecular mechanisms are involved in these regulatory processes, one of which is protein posttranslational modifications, particularly protein tyrosine phosphorylation (PYP). PYP occurs mainly through the action of protein tyrosine kinases (PTKs), modifying protein enzymatic activity, changing its cellular localization, and aiding in the assembly or disassembly of protein signaling complexes. Under physiological conditions, PYP is balanced by the coordinated action of PTKs and protein tyrosine phosphatases (PTPs). Dysregulation of PYP can cause genetic, metabolic, developmental, and oncogenic skeletal diseases. Although PYP is a reversible biochemical process, in contrast to PTKs, little is known about how this equilibrium is modulated by PTPs in the skeletal system. Whole-genome sequencing has revealed a large and diverse superfamily of PTP genes (over 100 members) in humans, which can be further divided into cysteine (Cys)-, aspartic acid (Asp)-, and histidine (His)-based PTPs. Here, we review current knowledge about the functions and regulatory mechanisms of 28 PTPs involved in skeletal development and diseases; 27 of them belong to class I and II Cys-based PTPs, and the other is an Asp-based PTP. Recent progress in analyzing animal models that harbor various mutations in these PTPs and future research directions are also discussed. Our literature review indicates that PTPs are as crucial as PTKs in supporting skeletal development and homeostasis.

Strategies to overcome drug resistance using SHP2 inhibitors

Encoded by PTPN11, the SHP2 (Src homology-2 domain-containing protein tyrosine phosphatase-2) is widely recognized as a carcinogenic phosphatase. As a promising anti-cancer drug target, SHP2 regulates many signaling pathways such as RAS-RAF-ERK, PI3K-AKT and JAK-STAT. Meanwhile, SHP2 plays a significant role in regulating immune cell function in the tumor microenvironment. Heretofore, five SHP2 allosteric inhibitors have been recruited in clinical studies for the treatment of cancer. Most recently, studies have proved the therapeutic potential of SHP2 inhibitor in overcoming drug resistance of kinase inhibitors and programmed cell death-1 (PD-1) blockade. Herein, we review the structure, function and small molecular inhibitors of SHP2, and highlight recent progress in overcoming drug resistance using SHP2 inhibitor. We hope this review would facilitate the future clinical development of SHP2 inhibitors.

Protein Tyrosine Phosphatases: Mechanisms in Cancer

Protein tyrosine kinases, especially receptor tyrosine kinases, have dominated the cancer therapeutics sphere as proteins that can be inhibited to selectively target cancer. However, protein tyrosine phosphatases (PTPs) are also an emerging target. Though historically known as negative regulators of the oncogenic tyrosine kinases, PTPs are now known to be both tumor-suppressive and oncogenic. This review will highlight key protein tyrosine phosphatases that have been thoroughly investigated in various cancers. Furthermore, the different mechanisms underlying pro-cancerous and anti-cancerous PTPs will also be explored.

Mycobacterium tuberculosis effector PPE36 attenuates host cytokine storm damage via inhibiting macrophage M1 polarization

Tuberculosis caused by Mycobacterium tuberculosis remains a serious global public health threat. Macrophage polarization is crucial for the innate immunity against M. tuberculosis. However, how M. tuberculosis interferes with macrophage polarization is elusive. We demonstrated here that M. tuberculosis PPE36 (Rv2108) blocked macrophage M1 polarization, preventing the cytokine storm, and alleviating inflammatory damage to mouse immune organs. PPE36 inhibited the polarization of THP-1 cell differentiation to M1 macrophages, reduced mitochondrial dehydrogenase activity, inhibited the expression of CD16, and repressed the expression of pro-inflammatory cytokines IL-6 and TNF-α, as well as chemokines CXCL9, CXCL10, CCL3, and CCL5. Intriguingly, in the mouse infection model, PPE36 significantly alleviated the inflammatory damage of immune organs caused by a cytokine storm. Furthermore, we found that PPE36 inhibited the polarization of macrophages into mature M1 macrophages by suppressing the ERK signaling. The study provided novel insights into the function and mechanism of action of M. tuberculosis effector PPE36 both at the cellular and animal level.

Protein tyrosine phosphatase 1B targets focal adhesion kinase and paxillin in cell-matrix adhesions

Protein tyrosine phosphatase 1B (PTP1B, also known as PTPN1) is an established regulator of cell-matrix adhesion and motility. However, the nature of substrate targets at adhesion sites remains to be validated. Here, we used bimolecular fluorescence complementation assays, in combination with a substrate trapping mutant of PTP1B, to directly examine whether relevant phosphotyrosines on paxillin and focal adhesion kinase (FAK, also known as PTK2) are substrates of the phosphatase in the context of cell-matrix adhesion sites. We found that the formation of catalytic complexes at cell-matrix adhesions requires intact tyrosine residues Y31 and Y118 on paxillin, and the localization of FAK at adhesion sites. Additionally, we found that PTP1B specifically targets Y925 on the focal adhesion targeting (FAT) domain of FAK at adhesion sites. Electrostatic analysis indicated that dephosphorylation of this residue promotes the closed conformation of the FAT 4-helix bundle and its interaction with paxillin at adhesion sites.

Protein tyrosine phosphatase Shp2 positively regulates cold stress-induced tyrosine phosphorylation of SIRPα in neurons

The membrane protein SIRPα is a cold stress-responsive signaling molecule in neurons. Cold stress directly induces tyrosine phosphorylation of SIRPα in its cytoplasmic region, and phosphorylated SIRPα is involved in regulating experience-dependent behavioral changes in mice. Here, we examined the mechanism of cold stress-induced SIRPα phosphorylation in vitro and in vivo. The levels of activated Src family protein tyrosine kinases (SFKs), which phosphorylate SIRPα, were not increased by lowering the temperature in cultured neurons. Although the SFK inhibitor dasatinib markedly reduced SIRPα phosphorylation, low temperature induced an increase in SIRPα phosphorylation even in the presence of dasatinib, suggesting that SFK activation is not required for low temperature-induced SIRPα phosphorylation. However, in the presence of pervanadate, a potent inhibitor of protein tyrosine phosphatases (PTPases), SIRPα phosphorylation was significantly reduced by lowering the temperature, suggesting that either the inactivation of PTPase(s) that dephosphorylate SIRPα or increased protection of phosphorylated SIRPα from the PTPase activity is important for low temperature-induced SIRPα phosphorylation. Inactivation of PTPase Shp2 by the allosteric Shp2 inhibitor SHP099, but not by the competitive inhibitor NSC-87877, reduced SIRPα phosphorylation in cultured neurons. Shp2 knockout also reduced SIRPα phosphorylation in the mouse brain. Our data suggest that Shp2, but not SFKs, positively regulates cold stress-induced SIRPα phosphorylation in a PTPase activity-independent manner.

Double-edged roles of protein tyrosine phosphatase SHP2 in cancer and its inhibitors in clinical trials

Phosphorylation is a reversible post-translational modification regulated by phosphorylase and dephosphorylase to mediate important cellular events. Src homology-2-containing protein tyrosine phosphatase 2 (SHP2) encoded by PTPN11 is the first identified oncogenic protein in protein tyrosine phosphatases family. Serving as a convergent node, SHP2 is involved in multiple cascade signaling pathways including Ras-Raf-MEK-ERK, PI3K-AKT, JAK-STAT and PD-1/PD-L1 pathways. Especially, the double-edged roles of SHP2 based on the substrate specificity in various biological contexts dramatically increase the effect complexity in different SHP2-associated diseases. Evidences suggest that by collaborating with other mutations in associated pathways, dysregulation of SHP2 contributes to the pathogenesis of different cancers, making SHP2 a promising therapeutic target for cancer treatment. SHP2 can either act as oncogenic factor or tumor suppressor in different diseases, and both the conserved catalytic dephosphorylation mechanism and the unique allosteric regulation mechanism of SHP2 provide opportunities for the development of SHP2 inhibitors and activators. To date, several small-molecule SHP2 inhibitors have advanced into clinical trials for mono- or combined therapy of cancers. Moreover, SHP2 activators and proteolysis-targeting chimera (PROTAC)-based degraders also display therapeutic promise. In this review, we comprehensively summarize the overall structures, regulation mechanisms, double-edged roles of SHP2 in both physiological and carcinogenic pathways, and SHP2 inhibitors in clinical trials. SHP2 activators and degraders are also briefly discussed. This review aims to provide in-depth understanding of the biological roles of SHP2 and highlight therapeutic potential of targeting SHP2.

SHP2 Targets ITK Downstream of PD-1 to Inhibit T Cell Function

PD-1 is a critical therapeutic target in cancer immunotherapy and antibodies blocking PD-1 are approved for multiple types of malignancies. The phosphatase SHP2 is the main effector mediating PD-1 downstream signaling and accordingly attempts have been made to target this enzyme as an alternative approach to treat immunogenic tumors. Unfortunately, small molecule inhibitors of SHP2 do not work as expected, suggesting that the role of SHP2 in T cells is more complex than initially hypothesized. To better understand the perplexing role of SHP2 in T cells, we performed interactome mapping of SAP, an adapter protein that is associated with SHP2 downstream signaling. Using genetic and pharmacological approaches, we discovered that SHP2 dephosphorylates ITK specifically downstream of PD-1 and that this event was associated with PD-1 inhibitory cellular functions. This study suggests that ITK is a unique target in this pathway, and since ITK is a SHP2-dependent specific mediator of PD-1 signaling, the combination of ITK inhibitors with PD-1 blockade may improve upon PD-1 monotherapy in the treatment of cancer.

ALK-positive non-small cell lung cancer; potential combination drug treatments

Advances in chromosomally rearranged ALK positive non-small cell lung cancer have been dramatic in only the last few years. Survival times have improved dramatically due to the introduction of ever more efficacious ALK inhibitors. These improvements have been due largely to improvements in blood-brain barrier penetration and the breadth of ligand binding pocket mutations against which the drugs are effective. However, the advances maybe slow as compared to the frequency of cancers with compound resistance mutations are appearing, suggesting the need to develop multiple ALK inhibitors to target different compound mutations.Another research area that promises to provide further gains is the use of drug combinations, with an ALK inhibitor combined with a drug targeting a "second driver" to overcome resistance. In this review, the range of secondary targets for ALK+ lung cancer and the potential for their clinical success are reviewed.

α2β1 integrins spatially restrict Cdc42 activity to stabilise adherens junctions

Background

Keratinocytes form the main protective barrier in the skin to separate the underlying tissue from the external environment. In order to maintain this barrier, keratinocytes form robust junctions between neighbouring cells as well as with the underlying extracellular matrix. Cell–cell adhesions are mediated primarily through cadherin receptors, whereas the integrin family of transmembrane receptors is predominantly associated with assembly of matrix adhesions. Integrins have been shown to also localise to cell–cell adhesions, but their role at these sites remains unclear.

Results

Here we show that α2β1 integrins are enriched at mature keratinocyte cell–cell adhesions, where they play a crucial role in organising cytoskeletal networks to stabilize adherens junctions. Loss of α2β1 integrin has significant functional phenotypes associated with cell–cell adhesion destabilisation, including increased proliferation, reduced migration and impaired barrier function. Mechanistically, we show that α2β1 integrins suppress activity of Src and Shp2 at cell–cell adhesions leading to enhanced Cdc42–GDI interactions and stabilisation of junctions between neighbouring epithelial cells.

Conclusion

Our data reveals a new role for α2β1 integrins in controlling integrity of epithelial cell–cell adhesions.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12915-021-01054-9.

Accessory proteins of the RAS-MAPK pathway: moving from the side line to the front line

Health and disease are directly related to the RTK-RAS-MAPK signalling cascade. After more than three decades of intensive research, understanding its spatiotemporal features is afflicted with major conceptual shortcomings. Here we consider how the compilation of a vast array of accessory proteins may resolve some parts of the puzzles in this field, as they safeguard the strength, efficiency and specificity of signal transduction. Targeting such modulators, rather than the constituent components of the RTK-RAS-MAPK signalling cascade may attenuate rather than inhibit disease-relevant signalling pathways.

Identification of a novel conserved signaling motif in CD200 receptor required for its inhibitory function

The inhibitory signaling of CD200 receptor 1 (CD200R) has been attributed to its NPxY signaling motif. However, NPxY-motifs are present in multiple protein families and are mostly known to mediate protein trafficking between subcellular locations rather than signaling. Therefore, we investigated whether additional motifs specify the inhibitory function of CD200R. We performed phylogenetic analysis of the intracellular domain of CD200R in mammals, birds, bony fish, amphibians and reptiles. Indeed, the tyrosine of the NPxY-motif is fully conserved across species, in line with its central role in CD200R signaling. In contrast, P295 of the NPxY-motif is not conserved. Instead, a conserved stretch of negatively charged amino acids, EEDE279, and two conserved residues P285 and K292 in the flanking region prior to the NPxY-motif are required for CD200R mediated inhibition of p-Erk, p-Akt308, p-Akt473, p-rpS6 and LPS-induced IL-8 secretion. Altogether, we show that instead of the more common NPxY-motif, CD200R signaling can be assigned to a unique signaling motif in mammals defined by: EEDExxPYxxYxxKxNxxY.