c-Src-mediated phosphorylation of the epidermal growth factor receptor on Tyr845 and Tyr1101 is associated with modulation of receptor function

EGFR amplification and EGFRvIII predict and participate in TAT-Cx43266-283 antitumor response in preclinical glioblastoma models

BACKGROUND

Glioblastoma (GBM) commonly displays epidermal growth factor receptor (EGFR) alterations (mainly amplification and EGFRvIII) and TAT-Cx43266-283 is a Src-inhibitory peptide with antitumor properties in preclinical GBM models. Given the link between EGFR and Src, the aim of this study was to explore the role of EGFR in the antitumor effects of TAT-Cx43266-283.

METHODS

The effect of TAT-Cx43266-283, temozolomide (TMZ), and erlotinib (EGFR inhibitor) was studied in patient-derived GBM stem cells (GSCs) and murine neural stem cells (NSCs) with and without EGFR alterations, in vitro and in vivo. EGFR alterations were analyzed by western blot and fluorescence in situ hybridization in these cells, and compared with Src activity and survival in GBM samples from The Cancer Genome Atlas.

RESULTS

The effect of TAT-Cx43266-283 correlated with EGFR alterations in a set of patient-derived GSCs and was stronger than that exerted by TMZ and erlotinib. In fact, TAT-Cx43266-283 only affected NSCs with EGFR alterations, but not healthy NSCs. EGFR alterations correlated with Src activity and poor survival in GBM patients. Finally, tumors generated from NSCs with EGFR alterations showed a decrease in growth, invasiveness, and vascularization after treatment with TAT-Cx43266-283, which enhanced the survival of immunocompetent mice.

CONCLUSIONS

Clinically relevant EGFR alterations are predictors of TAT-Cx43266-283 response and part of its mechanism of action, even in TMZ- and erlotinib-resistant GSCs. TAT-Cx43266-283 targets NSCs with GBM-driver mutations, including EGFR alterations, in an immunocompetent GBM model in vivo, suggesting a promising effect on GBM recurrence. Together, this study represents an important step toward the clinical application of TAT-Cx43266-283.

TGFβ overcomes FGF-induced transinhibition of EGFR in lens cells to enable fibrotic secondary cataract

To cause vision-disrupting fibrotic secondary cataract (PCO), lens epithelial cells that survive cataract surgery must migrate to the posterior of the lens capsule and differentiate into myofibroblasts. During this process, the cells become exposed to the FGF that diffuses out of the vitreous body. In normal development, such relatively high levels of FGF induce lens epithelial cells to differentiate into lens fiber cells. It has been a mystery as to how lens cells could instead undergo a mutually exclusive cell fate, namely epithelial to myofibroblast transition, in the FGF-rich environment of the posterior capsule. We and others have reported that the ability of TGFβ to induce lens cell fibrosis requires the activity of endogenous ErbBs. We show here that lens fiber-promoting levels of FGF induce desensitization of ErbB1 (EGFR) that involves its phosphorylation on threonine 669 mediated by both ERK and p38 activity. Transinhibition of ErbB1 by FGF is overcome by a time-dependent increase in ErbB1 levels induced by TGFβ, the activation of which is increased after cataract surgery. Our studies provide a rationale for why TGFβ upregulates ErbB1 in lens cells and further support the receptor as a therapeutic target for PCO.

Synergy of EGFR and AURKA Inhibitors in KRAS-mutated Non-small Cell Lung Cancers

The most common oncogenic driver mutations for non-small cell lung cancer (NSCLC) activate EGFR or KRAS. Clinical trials exploring treatments for EGFR- or KRAS-mutated (EGFRmut or KRASmut) cancers have focused on small-molecule inhibitors targeting the driver mutations. Typically, these inhibitors perform more effectively based on combination with either chemotherapies, or other targeted therapies. For EGFRmut NSCLC, a combination of inhibitors of EGFR and Aurora-A kinase (AURKA), an oncogene commonly overexpressed in solid tumors, has shown promising activity in clinical trials. Interestingly, a number of recent studies have indicated that EGFR activity supports overall viability of tumors lacking EGFR mutations, and AURKA expression is abundant in KRASmut cell lines. In this study, we have evaluated dual inhibition of EGFR and AURKA in KRASmut NSCLC models. These data demonstrate synergy between the EGFR inhibitor erlotinib and the AURKA inhibitor alisertib in reducing cell viability and clonogenic capacity in vitro, associated with reduced activity of EGFR pathway effectors, accumulation of enhanced aneuploid cell populations, and elevated cell death. Importantly, the erlotinib-alisertib combination also synergistically reduces xenograft growth in vivo. Analysis of signaling pathways demonstrated that the combination of erlotinib and alisertib was more effective than single-agent treatments at reducing activity of EGFR and pathway effectors following either brief or extended administration of the drugs. In sum, this study indicates value of inhibiting EGFR in KRASmut NSCLC, and suggests the specific value of dual inhibition of AURKA and EGFR in these tumors.

SIGNIFICANCE

The introduction of specific KRAS G12C inhibitors to the clinical practice in lung cancer has opened up opportunities that did not exist before. However, G12C alterations are only a subtype of all KRAS mutations observed. Given the high expression of AURKA in KRASmut NSCLC, our study could point to a potential therapeutic option for this subgroup of patients.

YES1 as a potential target to overcome drug resistance in EGFR-deregulated non-small cell lung cancer

Epidermal growth factor receptor (EGFR)-tyrosine kinase inhibitors (TKIs) such as gefitinib and osimertinib have primarily been used as first-line treatments for patients with EGFR-activating mutations in non-small cell lung cancer (NSCLC). Novel biomarkers are required to distinguish patients with lung cancer who are resistant to EGFR-TKIs. The aim of the study is to investigate the expression and functional role of YES1, one of the Src-family kinases, in EGFR-TKI-resistant NSCLC. YES1 expression was elevated in gefitinib-resistant HCC827 (HCC827/GR) cells, harboring EGFR mutations. Moreover, HCC827/GR cells exhibited increased reactive oxygen species (ROS) levels compared to those of the parent cells, resulting in the phosphorylation/activation of YES1 due to oxidation of the cysteine residue. HCC827/GR cells showed elevated expression levels of YES1-associated protein 1 (YAP1), NF-E2-related factor 2 (Nrf2), cancer stemness-related markers, and antioxidant proteins compared to those of the parent cells. Knockdown of YES1 in HCC827/GR cells suppressed YAP1 phosphorylation, leading to the inhibition of Bcl-2, Bcl-xL, and Cyclin D1 expression. Silencing YES1 markedly attenuated the proliferation, migration, and tumorigenicity of HCC827/GR cells. Dasatinib inhibited the proliferation of HCC827/GR cells by targeting YES1-mediated signaling pathways. Furthermore, the combination of gefitinib and dasatinib demonstrated a synergistic effect in suppressing the proliferation of HCC827/GR cells. Notably, YES1- and Nrf2-regulated genes showed a positive regulatory relationship in patients with lung cancer and in TKI-resistant NSCLC cell lines. Taken together, these findings suggest that modulation of YES1 expression and activity may be an attractive therapeutic strategy for the treatment of drug-resistant NSCLC.

Dasatinib suppresses collective cell migration through the coordination of focal adhesion and E-cadherin in colon cancer cells

Collective cell migration is an important process in cancer metastasis. Unlike single-cell migration, collective cell migration requires E-cadherin expression in the cell cohort. However, the mechanisms underlying cellular contact and focal adhesions remain unclear. In this study, Src was hypothesized to coordinate focal adhesion and Rab11-mediated E-cadherin distribution during collective cell migration. This study primarily used confocal microscopy to visualize the 3D structure of cell-cell contacts with associated molecules. These results demonstrate that the clinical Src inhibitor dasatinib was less toxic to HT-29 colon cancer cells; instead, the cells aggregated. 3D immunofluorescence imaging showed that Rab11 was localized with E-cadherin at the adherens junctions of the apical cell-cell contacts. In the transwell assay, Rab11 colocalized with a broad range of E-cadherin proteins in collectively migrated cells, and dasatinib treatment significantly suppressed collective cell migration. Transmission electron microscopy demonstrated that dasatinib treatment increased cell membrane protrusion contacts and generated spaces between cells, which may allow epidermal growth factor receptor activity at the cell-cell contacts. This study suggests that dasatinib treatment does not inhibit cell survival but targets Src at different cellular compartments in the coordination of focal adhesions and cell-cell contacts in collective cell migration through E-cadherin dynamics in colon cancer cells.

Transactivation of receptor tyrosine kinases by purinergic P2Y and adenosine receptors

Transactivation of receptor tyrosine kinases (RTK) is a crosstalk mechanism exhibited by G-protein-coupled receptors (GPCR) to activate signaling pathways classically associated with growth factors. The discovery of RTK transactivation was a breakthrough in signal transduction that contributed to developing current concepts in intracellular signaling. RTK transactivation links GPCR signaling to important cellular processes, such as cell proliferation and differentiation, and explains the functional diversity of these receptors. Purinergic (P2Y and adenosine) receptors belong to class A of GPCR; in the present work, we systematically review the experimental evidence showing that purinergic receptors have the ability to transactivate RTK in multiple tissues and physiopathological conditions resulting in the modulation of cellular physiology. Of particular relevance, the crosstalk between purinergic receptors and epidermal growth factor receptor is a redundant pathway that participates in multiple pathophysiological processes. Specific and detailed knowledge of purinergic receptor-regulated pathways advances our understanding of the complexity of GPCR signal transduction and opens the way for pharmacologic intervention in the pathological context.

The role of EGFR in vascular AT1R signaling: From cellular mechanisms to systemic relevance

The epidermal growth factor receptor (EGFR) belongs to the ErbB-family of receptor tyrosine kinases that are of importance in oncology. During the last years, substantial evidence accumulated for a crucial role of EGFR concerning the action of the angiotensin II type 1 receptor (AT1R) in blood vessels, resulting form AT1R-induced EGFR transactivation. This transactivation occurs through the release of membrane-anchored EGFR-ligands, cytosolic tyrosine kinases, heterocomplex formation or enhanced ligand expression. AT1R-EGFR crosstalk amplifies the signaling response and enhances the biological effects of angiotensin II. Downstream signaling cascades include ERK1/2 and p38 MAPK, PLCγ and STAT. AT1R-induced EGFR activation contributes to vascular remodeling and hypertrophy via e.g. smooth muscle cell proliferation, migration and extracellular matrix production. EGFR transactivation results in increased vessel wall thickness and reduced vascular compliance. AT1R and EGFR signaling pathways are also implicated the induction of vascular inflammation. Again, EGFR transactivation exacerbates the effects, leading to endothelial dysfunction that contributes to vascular inflammation, dysfunction and remodeling. Dysregulation of the AT1R-EGFR axis has been implicated in the pathogenesis of various cardiovascular diseases and inhibition or prevention of EGFR signaling can attenuate part of the detrimental impact of enhanced renin-angiotensin-system (RAAS) activity, highlighting the importance of EGFR for the adverse consequences of AT1R activation. In summary, EGFR plays a critical role in vascular AT1R action, enhancing signaling, promoting remodeling, contributing to inflammation, and participating in the pathogenesis of cardiovascular diseases. Understanding the interplay between AT1R and EGFR will foster the development of effective therapeutic strategies of RAAS-induced disorders.

Loss of EGF receptor polarity enables homeostatic imbalance in epithelial-cell models

The polarized distribution of membrane proteins into apical and basolateral domains provides the basis for specialized functions of epithelial tissues. The EGF receptor (EGFR) plays important roles in embryonic development, adult-epithelial tissue homeostasis, and growth and survival of many carcinomas. Typically targeted to basolateral domains, there is also considerable evidence of EGFR sorting plasticity but very limited knowledge regarding domain-specific EGFR substrates. Here we have investigated effects of selective EGFR mistargeting because of inactive-basolateral sorting signals on epithelial-cell homeostatic responses to growth-induced stress in MDCK cell models. Aberrant EGFR localization was associated with multilayer formation, anchorage-independent growth, and upregulated expression of the intermediate filament-protein vimentin characteristically seen in cells undergoing epithelial-to-mesenchymal transition. EGFRs were selectively retained following their internalization from apical membranes, and a signaling pathway involving the signaling adaptor Gab1 protein and extracellular signal-regulated kinase ERK5 had an essential role integrating multiple responses to growth-induced stress. Our studies highlight the potential importance of cellular machinery specifying EGFR polarity in epithelial pathologies associated with homeostatic imbalance.

Targeting Epidermal Growth Factor Receptor for Cancer Treatment: Abolishing Both Kinase-Dependent and Kinase-Independent Functions of the Receptor

Epidermal growth factor receptor (EGFR), a receptor tyrosine kinase, is activated by ligand binding, overexpression, or mutation. It is well known for its tyrosine kinase-dependent oncogenic activities in a variety of human cancers. A large number of EGFR inhibitors have been developed for cancer treatment, including monoclonal antibodies, tyrosine kinase inhibitors, and a vaccine. The EGFR inhibitors are aimed at inhibiting the activation or the activity of EGFR tyrosine kinase. However, these agents have shown efficacy in only a few types of cancers. Drug resistance, both intrinsic and acquired, is common even in cancers where the inhibitors have shown efficacy. The drug resistance mechanism is complex and not fully known. The key vulnerability of cancer cells that are resistant to EGFR inhibitors has not been identified. Nevertheless, it has been increasingly recognized in recent years that EGFR also possesses kinase-independent oncogenic functions and that these noncanonical functions may play a crucial role in cancer resistance to EGFR inhibitors. In this review, both kinase-dependent and -independent activities of EGFR are discussed. Also discussed are the mechanisms of actions and therapeutic activities of clinically used EGFR inhibitors and sustained EGFR overexpression and EGFR interaction with other receptor tyrosine kinases to counter the EGFR inhibitors. Moreover, this review discusses emerging experimental therapeutics that have shown potential for overcoming the limitation of the current EGFR inhibitors in preclinical studies. The findings underscore the importance and feasibility of targeting both kinase-dependent and -independent functions of EGFR to enhance therapeutic efficacy and minimize drug resistance. SIGNIFICANCE STATEMENT: EGFR is a major oncogenic driver and therapeutic target, but cancer resistance to current EGFR inhibitors remains a significant unmet clinical problem. This article reviews the cancer biology of EGFR as well as the mechanisms of actions and the therapeutic efficacies of current and emerging EGFR inhibitors. The findings could potentially lead to development of more effective treatments for EGFR-positive cancers.

Bispecific antibody CD73xEGFR more selectively inhibits the CD73/adenosine immune checkpoint on cancer cells and concurrently counteracts pro-oncogenic activities of CD73 and EGFR

BACKGROUND

CD73 is an ecto-enzyme that is involved in the conversion of pro-inflammatory extracellular ATP (eATP) excreted by cancer cells under stress to anti-inflammatory adenosine (ADO). A broad variety of solid cancer types was shown to exploit CD73 overexpression as a suppressive immune checkpoint. Consequently, CD73-antagonistic antibodies, most notably oleclumab, are currently evaluated in several multicenter trials for clinical applicability. However, the efficacy of conventional monospecific CD73-inhibiting antibodies may be limited due to on-target/off-tumor binding to CD73 on normal cells. Therefore, a novel approach that more selectively directs CD73 immune checkpoint inhibition towards cancer cells is warranted.

METHODS

To address this issue, we constructed a novel tetravalent bispecific antibody (bsAb), designated bsAb CD73xEGFR. Subsequently, the anticancer activities of bsAb CD73xEGFR were evaluated using in vitro and in vivo tumor models.

RESULTS

In vitro treatment of various carcinoma cell types with bsAb CD73xEGFR potently inhibited the enzyme activity of CD73 (~71%) in an EGFR-directed manner. In this process, bsAb CD73xEGFR induced rapid internalization of antigen/antibody complexes, which resulted in a prolonged concurrent displacement of both CD73 and EGFR from the cancer cell surface. In addition, bsAb CD73xEGFR sensitized cancer to the cytotoxic activity of various chemotherapeutic agents and potently inhibited the proliferative/migratory capacity (~40%) of cancer cells. Unexpectedly, we uncovered that treatment of carcinoma cells with oleclumab appeared to enhance several pro-oncogenic features, including upregulation and phosphorylation of EGFR, tumor cell proliferation (~20%), and resistance towards cytotoxic agents and ionizing radiation (~39%). Importantly, in a tumor model using immunocompetent BALB/c mice inoculated with syngeneic CD73pos/EGFRpos CT26 cancer cells, treatment with bsAb CD73xEGFR outperformed oleclumab (65% vs 31% tumor volume reduction). Compared with oleclumab, treatment with bsAb CD73xEGFR enhanced the intratumoral presence of CD8pos T cells and M1 macrophages.

CONCLUSIONS

BsAb CD73xEGFR outperforms oleclumab as it inhibits the CD73/ADO immune checkpoint in an EGFR-directed manner and concurrently counteracts several oncogenic activities of EGFR and CD73. Therefore, bsAb CD73xEGFR may be of significant clinical potential for various forms of difficult-to-treat solid cancer types.

A Novel Bispecific Antibody for EpCAM-Directed Inhibition of the CD73/Adenosine Immune Checkpoint in Ovarian Cancer

PD-1/PD-L1-inhibiting antibodies have shown disappointing efficacy in patients with refractory ovarian cancer (OC). Apparently, OC cells exploit nonoverlapping immunosuppressive mechanisms to evade the immune system. In this respect, the CD73-adenosine inhibitory immune checkpoint is of particular interest, as it rapidly converts pro-inflammatory ATP released from cancer cells to immunosuppressive adenosine (ADO). Moreover, cancer-cell-produced ADO is known to form a highly immunosuppressive extra-tumoral 'halo' that chronically inhibits the anticancer activity of various immune effector cells. Thus far, conventional CD73-blocking antibodies such as oleclumab show limited clinical efficacy, probably due to the fact that it indiscriminately binds to and blocks CD73 on a massive surplus of normal cells. To address this issue, we constructed a novel bispecific antibody (bsAb) CD73xEpCAM that inhibits CD73 expressed on the OC cell surface in an EpCAM-directed manner. Importantly, bsAb CD73xEpCAM showed potent capacity to inhibit the CD73 enzyme activity in an EpCAM-directed manner and restore the cytotoxic activity of ADO-suppressed anticancer T cells. Additionally, treatment with bsAb CD73xEpCAM potently inhibited the proliferative capacity of OC cells and enhanced their sensitivity to cisplatin, doxorubicin, 5FU, and ionizing radiation. BsAb CD73xEpCAM may be useful in the development of tumor-directed immunotherapeutic approaches to overcome the CD73-mediated immunosuppression in patients with refractory OC.

NSCLC presents metabolic heterogeneity, and there is still some leeway for EGF stimuli in EGFR-mutated NSCLC

BACKGROUND

Metabolic remodeling is crucial in carcinogenesis and cancer progression. Oncogenic mutations may promote metabolic reprogramming in cancer cells to support their energy and biomass requirements. EGFR mutations are commonly found in non-small cell lung cancer (NSCLC) and may induce NSCLC metabolic rewiring. Whether EGFR-driven metabolic reprogramming triggers cell vulnerabilities with therapeutic potential remains unknown.

METHODS

The role of EGFR signaling activation by EGF was investigated using NSCLC cell lines with different EGFR and KRAS status: A549 (EGFR WT and KRAS c.34G > A), H292 (EGFR WT and KRAS WT) and PC-9 (EGFR exon 19 E746-A750 deletion and KRAS WT). The effect of EGF on NSCLC cell death and cell cycle was evaluated using flow cytometry, and cell migration was assessed through wound healing. EGFR, HER2, MCT1, and MCT4 expression was analyzed through immunofluorescence or western blotting. We explored the impact of glucose and lactate bioavailability on NSCLC cells' metabolic profile using nuclear magnetic resonance (NMR) spectroscopy. Moreover, the expression of several relevant metabolic genes in NSCLC cells or patient samples was determined by RT-qPCR.

RESULTS

We showed that cell lines presented different metabolic profiles, and PC-9 cells were the most responsive to EGF stimulus, as they showed higher rates of cell proliferation and migration, together with altered metabolic behavior. By inhibiting EGFR with gefitinib, a decrease in glucose consumption was observed, which may be related to the fact that despite PC-9 harbor EGFR mutation, they still express the EGFR WT allele. The analysis of NSCLC patients' RNA showed a correlation between MCT1/MCT4 and GLUT1 expression in most cases, indicating that the metabolic information can serve as a reference in patients' follow-up.

CONCLUSION

Together, this study shows that NSCLC cell lines have heterogeneous metabolic profiles, which may be underlaid by different genetic profiles, revealing an opportunity to identify and stratify patients who can benefit from metabolism-targeted therapies.

Functional roles of SRC signaling in pancreatic cancer: Recent insights provide novel therapeutic opportunities

Pancreatic ductal adenocarcinoma (PDAC) is an aggressive malignant disease with a 5-year survival rate of <10%. Aberrant activation or elevated expression of the tyrosine kinase c-SRC (SRC) is frequently observed in PDAC and is associated with a poor prognosis. Preclinical studies have revealed a multifaceted role for SRC activation in PDAC, including promoting chronic inflammation, tumor cell proliferation and survival, cancer cell stemness, desmoplasia, hypoxia, angiogenesis, invasion, metastasis, and drug resistance. Strategies to inhibit SRC signaling include suppressing its catalytic activity, inhibiting protein stability, or by interfering with signaling components of the SRC signaling pathway including suppressing protein interactions of SRC. In this review, we discuss the molecular and immunological mechanisms by which aberrant SRC activity promotes PDAC tumorigenesis. We also provide a comprehensive update of SRC inhibitors in the clinic, and discuss the clinical challenges associated with targeting SRC in pancreatic cancer.

Multiple post-translational modifications ensure EGFR functionality: Potential therapeutic targets to overcome its drug-resistance mutations

Epidermal growth factor receptor (EGFR) mutation is the most common driver mutation in non-small cell lung cancer (NSCLC). The first-line therapy for advanced NSCLC patients with EGFR-sensitive mutation is the EGFR tyrosine kinase inhibitor (EGFR-TKI). However, most NSCLC patients with EGFR mutation will develop resistant mutations in EGFR-TKI therapy. With further studies, resistance mechanisms represented by EGFR-T790M mutations have revealed the impact of EGFR mutations in situ on EGFR-TKIs sensitivity. The third-generation EGFR-TKIs inhibit both EGFR-sensitive mutations and T790M mutations. The emergence of novel mutations such as EGFR-C797S and EGFR-L718Q may decrease efficacy. Searching for new targets to overcome EGFR-TKI resistance becomes a key challenge. Therefore, an in-depth understanding of the regulatory mechanisms of EGFR is essential to find novel targets to overcome drug-resistant mutations in EGFR-TKIs. EGFR, as a receptor-type tyrosine kinase, undergoes homo/heterodimerization and autophosphorylation upon binding to ligands, which activates multiple downstream signaling pathways. Interestingly, there is growing evidence that the kinase activity of EGFR is affected not only by phosphorylation but also by various post-translational modifications (PTMs, such as S-palmitoylation, S-nitrosylation, Methylation, etc.). In this review, we systematically review the effects of different protein PTMs on EGFR kinase activity and its functionality and suggest that influencing EGFR kinase activity by modulating multiple EGFR sites are potential targets to overcome EGFR-TKIs resistance mutations.

Regulation of ErbB Receptors by the Ca2+ Sensor Protein Calmodulin in Cancer

Overexpression and mutations of the epidermal growth factor receptor (EGFR/ErbB1/HER1) and other tyrosine kinase receptors of the ErbB family (ErbB2/HER2, ErbB3/HER3 and ErbB4/HER4) play an essential role in enhancing the proliferation, the migratory capacity and invasiveness of many tumor cells, leading to cancer progression and increased malignancy. To understand these cellular processes in detail is essential to understand at a molecular level the signaling pathways and regulatory mechanisms controlling these receptors. In this regard, calmodulin (CaM) is a Ca2+-sensor protein that directly interacts with and regulates ErbB receptors, as well as some CaM-dependent kinases that also regulate these receptors, particularly EGFR and ErbB2, adding an additional layer of CaM-dependent regulation to this system. In this short review, an update of recent advances in this area is presented, covering the direct action of Ca2+/CaM on the four ErbB family members mostly in tumor cells and the indirect action of Ca2+/CaM on the receptors via CaM-regulated kinases. It is expected that further understanding of the CaM-dependent mechanisms regulating the ErbB receptors in future studies could identify new therapeutic targets in these systems that could help to control or delay cancer progression.

How cells sense and integrate information from different sources

Cell signaling is a fundamental cellular process that enables cells to sense and respond to information in their surroundings. At the molecular level, signaling is primarily carried out by transmembrane protein receptors that can initiate complex downstream signal transduction cascades to alter cellular behavior. In the human body, different cells can be exposed to a wide variety of environmental conditions, and cells express diverse classes of receptors capable of sensing and integrating different signals. Furthermore, different receptors and signaling pathways can crosstalk with each other to calibrate the cellular response. Crosstalk occurs through multiple mechanisms at different levels of signaling pathways. In this review, we discuss how cells sense and integrate different chemical, mechanical, and spatial signals as well as the mechanisms of crosstalk between pathways. To illustrate these concepts, we use a few well-studied signaling pathways, including receptor tyrosine kinases and integrin receptors. Finally, we discuss the implications of dysregulated cellular sensing on driving diseases such as cancer. This article is categorized under: Cancer > Molecular and Cellular Physiology Metabolic Diseases > Molecular and Cellular Physiology.

Young and undamaged recombinant albumin alleviates T2DM by improving hepatic glycolysis through EGFR and protecting islet β cells in mice

BACKGROUND

Albumin is the most abundant protein in serum and serves as a transporter of free fatty acids (FFA) in blood vessels. In type 2 diabetes mellitus (T2DM) patients, the reduced serum albumin level is a risk factor for T2DM development and progression, although this conclusion is controversial. Moreover, there is no study on the effects and mechanisms of albumin administration to relieve T2DM. We examined whether the administration of young and undamaged recombinant albumin can alleviate T2DM in mice.

METHODS

The serum albumin levels and metabolic phenotypes including fasting blood glucose, glucose tolerance tests, and glucose-stimulated insulin secretion were studied in db/db mice or diet-induced obesity mice treated with saline or young, undamaged, and ultrapure rMSA. Apoptosis assays were performed at tissue and cell levels to determine the function of rMSA on islet β cell protection. Metabolic flux and glucose uptake assays were employed to investigate metabolic changes in saline-treated or rMSA-treated mouse hepatocytes and compared their sensitivity to insulin treatments.

RESULTS

In this study, treatment of T2DM mice with young, undamaged, and ultrapure recombinant mouse serum albumin (rMSA) increased their serum albumin levels, which resulted in a reversal of the disease including reduced fasting blood glucose levels, improved glucose tolerance, increased glucose-stimulated insulin secretion, and alleviated islet atrophy. At the cellular level, rMSA improved glucose uptake and glycolysis in hepatocytes. Mechanistically, rMSA reduced the binding between CAV1 and EGFR to increase EGFR activation leading to PI3K-AKT activation. Furthermore, rMSA extracellularly reduced the rate of fatty acid uptake by islet β-cells, which relieved the accumulation of intracellular ceramide, endoplasmic reticulum stress, and apoptosis. This study provided the first clear demonstration that injections of rMSA can alleviate T2DM in mice.

CONCLUSION

Our study demonstrates that increasing serum albumin levels can promote glucose homeostasis and protect islet β cells, which alleviates T2DM.

Antibody-Drug Conjugates for the Treatment of HER2-Positive Breast Cancer

Human epidermal growth factor receptor 2 (HER2) receptor tyrosine kinase is overexpressed in 20-30% of breast cancers and is associated with poor prognosis and worse overall patient survival. Most women with HER2-positive breast cancer receive neoadjuvant chemotherapy plus HER2-targeted therapies. The development of HER2-directed therapeutics is an important advancement in targeting invasive breast cancer. Despite the efficacy of anti-HER2 monoclonal antibodies, they are still being combined with adjuvant chemotherapy to improve overall patient outcomes. Recently, significant progress has been made towards the development of a class of therapeutics known as antibody-drug conjugates (ADCs), which leverage the high specificity of HER2-targeted monoclonal antibodies with the potent cytotoxic effects of various small molecules, such as tubulin inhibitors and topoisomerase inhibitors. To date, two HER2-targeting ADCs have been approved by the FDA for the treatment of HER2-positive breast cancer: Ado-trastuzumab emtansine (T-DM1; Kadcyla^®) and fam-trastuzumab deruxtecan-nxki (T-Dxd; Enhertu^®). Kadcyla and Enhertu are approved for use as a second-line treatment after trastuzumab-taxane-based therapy in patients with HER2-positive breast cancer. The success of ADCs in the treatment of HER2-positive breast cancer provides novel therapeutic advancements in the management of the disease. In this review, we discuss the basic biology of HER2, its downstream signaling pathways, currently available anti-HER2 therapeutic modalities and their mechanisms of action, and the latest clinical and safety characteristics of ADCs used for the treatment of HER2-positive breast cancer.

The AhR-SRC axis as a therapeutic vulnerability in BRAFi-resistant melanoma

The nongenetic mechanisms required to control tumor phenotypic plasticity and shape drug-resistance remain unclear. We show here that the Aryl hydrocarbon Receptor (AhR) transcription factor directly regulates the gene expression program associated with the acquisition of resistance to BRAF inhibitor (BRAFi) in melanoma. In addition, we show in melanoma cells that canonical activation of AhR mediates the activation of the SRC pathway and promotes the acquisition of an invasive and aggressive resistant phenotype to front-line BRAFi treatment in melanoma. This nongenetic reprogramming identifies a clinically compatible approach to reverse BRAFi resistance in melanoma. Using a preclinical BRAFi-resistant PDX melanoma model, we demonstrate that SRC inhibition with dasatinib significantly re-sensitizes melanoma cells to BRAFi. Together we identify the AhR/SRC axis as a new therapeutic vulnerability to trigger resistance and warrant the introduction of SRC inhibitors during the course of the treatment in combination with front-line therapeutics to delay BRAFi resistance.

Quantitative Phosphoproteomics and Acetylomics of Safranal Anticancer Effects in Triple-Negative Breast Cancer Cells

Safranal, as an aroma in saffron, is one of the cytotoxic compounds in saffron that causes cell death in triple-negative breast cancer cells. Our recent research reported the anti-cancer effects of safranal, which further demonstrated its impact on protein translation, mitochondrial dysfunction, and DNA fragmentation. To better understand the underlying mechanisms, we identified acetylated and phosphorylated peptides in safranal-treated cancer cells. We conducted a comprehensive phosphoproteomics and acetylomics analysis of safranal-treated MDA-MB-231 cells by using a combination of TMT labeling and enrichment methods including titanium dioxide and immunoprecipitation. We provide a wide range of phosphoproteome regulation in different signaling pathways that are disrupted by safranal treatment. Safranal influences the phosphorylation level on proteins involved in DNA replication and repair, translation, and EGFR activation/accumulation, which can lead the cells into apoptosis. Safranal causes DNA damage which is followed by the activation of cell cycle checkpoints for DNA repair. Over time, checkpoints and DNA repair are inhibited and cells are under a mitotic catastrophe. Moreover, safranal prevents repair by the hypo-acetylation of H4 and facilitates the transcription of proapoptotic genes by hyper-acetylation of H3, which push the cells to the brink of death.

Modulation of autophagy as a therapeutic strategy for Toxoplasma gondii infection

Toxoplasma gondii infection is a severe health threat that endangers billions of people worldwide. T. gondii utilizes the host cell membrane to form a parasitophorous vacuole (PV), thereby fully isolating itself from the host cell cytoplasm and making intracellular clearance difficult. PV can be targeted and destroyed by autophagy. Autophagic targeting results in T. gondii killing via the fusion of autophagosomes and lysosomes. However, T. gondii has developed many strategies to suppress autophagic targeting. Accordingly, the interplay between host cell autophagy and T. gondii is an emerging area with important practical implications. By promoting the canonical autophagy pathway or attenuating the suppression of autophagic targeting, autophagy can be effectively utilized in the development of novel therapeutic strategies against T gondii. Here, we have illustrated the complex interplay between host cell mediated autophagy and T. gondii. Different strategies to promote autophagy in order to target the parasite have been elucidated. Besides, we have analyzed some potential new drug molecules from the DrugBank database using bioinformatics tools, which can modulate autophagy. Various challenges and opportunities focusing autophagy mediated T. gondii clearance have been discussed, which will provide new insights for the development of novel drugs against the parasite.

Loss of Polycystin-1 causes cAMP-dependent switch from tubule to cyst formation

Autosomal dominant polycystic kidney disease is the most common monogenic disease that causes end-stage renal failure. It primarily results from mutations in the PKD1 gene that encodes for Polycystin-1. How loss of Polycystin-1 translates into bilateral renal cyst development is mostly unknown. cAMP is significantly involved in cyst enlargement but its role in cyst initiation has remained elusive. Deletion of Polycystin-1 in collecting duct cells resulted in a switch from tubule to cyst formation and was accompanied by an increase in cAMP. Pharmacological elevation of cAMP in Polycystin-1-competent cells caused cyst formation, impaired plasticity, nondirectional migration, and mis-orientation, and thus strongly resembled the phenotype of Polycystin-1-deficient cells. Mis-orientation of developing tubule cells in metanephric kidneys upon loss of Polycystin-1 was phenocopied by pharmacological increase of cAMP in wildtype kidneys. In vitro, cAMP impaired tubule formation after capillary-induced injury which was further impaired by loss Polycystin-1.

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Loss of Polycystin-1 switches renal cells from tubule to cyst formation

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Deletion of Polycystin-1 leads to increase in cAMP

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Elevation of cAMP in wildtype cells phenocopies Polycystin-1-deficient features

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Features are: impaired plasticity, nondirectional migration, and mis-orientation

Asporin Interacts With HER2 to Promote Thyroid Cancer Metastasis via the MAPK/EMT Signaling Pathway

Approximately 85% of histological subtypes of thyroid cancer are papillary thyroid cancer (PTC), and the morbidity and mortality of PTC patients rapidly increased due to lymph node metastases or distant metastasis. Therefore, it needs to distill an enhanced understanding of the pathogenesis of PTC patients with lymph node metastases or distant metastasis. We employed the TMT-based quantitative proteomics approach to identify and analyze differentially expressed proteins in PTC with different degrees of lymph node metastases. Compared with paired normal tissues, asporin is overexpressed in PTC-N0, PTC-N1a, and PTC-N1b tumorous tissues via proteomics, western blotting, and immunohistochemistry assays. Functionally, asporin is mainly expressed in the extracellular matrix, cell membrane, and cytoplasm of PTC tumorous tissues, and promotes thyroid cancer cell proliferation, migration, and invasion. Mechanistically, asporin, interacting with HER2, co-localizes HER2 on the cell membrane and cytoplasm, and the asporin/HER2/SRC/EGFR axis upregulate the expression of EMT-activating transcription factors through the MAPK signaling pathway. Clinically, asporin can be regarded as a serological biomarker to identify PTC patients with or without lymph node metastasis, and high expression of asporin in PTC tumorous tissues is a risk factor for poor prognosis.

Optimization of endothelial growth factor receptor monoclonal antibody-gold nanorods photothermal therapy for laryngeal squamous cell carcinoma

It reported that heat generated by near-infrared laser irradiation of gold nanorods (AuNRs) effectively inhibited tumor cells, and the conjugate of epidermal growth factor receptor monoclonal antibody (EGFRmAb) and gold nanorods could selectively binded to the surface of cancer cell membrane expressing EGFR. However, there are few research reports on EGFRmAb-AuNRs in laryngeal squamous cell carcinoma. Therefore, our study aimed to investigate the photothermal effect of EGFRmAb modified AuNRs in inducing tumor cell death in an animal model of laryngeal squamous cell carcinoma. We showed that the conjugates of EGFRmAb and AuNRs selectively entered laryngeal squamous cell carcinoma cells. We analyzed the parameters of laser irradiation by controlling the near-infrared to optimize the condition and procedure of targeted treatment in nude mice treated with EGFRmAb and AuNRs. In addition, we examined the safety of the combined therapy. Test results showed that EGFRmAb-AuNRs inhibited the growth of Hep-2 and CNE-2 cells but not normal epithelial cells, and the semi-inhibitor concentration of EGFRmAb in Hep-2 and CNE-2 cells was 4 pmol/ml and 2 pmol/ml, respectively. AuNRs injected into the tumor and irradiated by near-infrared laser effectively inhibited tumor growth in nude mice without toxic effect in mice. We further confirmed that the apoptosis and necrosis rates of tumor cells in mice were highest under 3 W/cm² near-infrared laser irradiation and AuNRs minimum concentration of 280 μg/kg. In conclusion, we developed a new method of targeting EGFRmAb combined with AuNRs to achieve photothermal effect in the treatment of laryngeal squamous cell carcinoma.

SRC kinase-mediated signaling pathways and targeted therapies in breast cancer

Breast cancer (BC) has been ranked the most common malignant tumor throughout the world and is also a leading cause of cancer-related deaths among women. SRC family kinases (SFKs) belong to the non-receptor tyrosine kinase (nRTK) family, which has eleven members sharing similar structure and function. Among them, SRC is the first identified proto-oncogene in mammalian cells. Oncogenic overexpression or activation of SRC has been revealed to play essential roles in multiple events of BC progression, including tumor initiation, growth, metastasis, drug resistance and stemness regulations. In this review, we will first give an overview of SRC kinase and SRC-relevant functions in various subtypes of BC and then systematically summarize SRC-mediated signaling transductions, with particular emphasis on SRC-mediated substrate phosphorylation in BC. Furthermore, we will discuss the progress of SRC-based targeted therapies in BC and the potential future direction.

YES1 as a Therapeutic Target for HER2-Positive Breast Cancer after Trastuzumab and Trastuzumab-Emtansine (T-DM1) Resistance Development

Trastuzumab-emtansine (T-DM1) is a therapeutic agent molecularly targeting human epidermal growth factor receptor 2 (HER2)-positive metastatic breast cancer (MBC), and it is especially effective for MBC with resistance to trastuzumab. Although several reports have described T-DM1 resistance, few have examined the mechanism underlying T-DM1 resistance after the development of acquired resistance to trastuzumab. We previously reported that YES1, a member of the Src family, plays an important role in acquired resistance to trastuzumab in HER2-amplified breast cancer cells. We newly established a trastuzumab/T-DM1-dual-resistant cell line and analyzed the resistance mechanisms in this cell line. At first, the T-DM1 effectively inhibited the YES1-amplified trastuzumab-resistant cell line, but resistance to T-DM1 gradually developed. YES1 amplification was further enhanced after acquired resistance to T-DM1 became apparent, and the knockdown of the YES1 or the administration of the Src inhibitor dasatinib restored sensitivity to T-DM1. Our results indicate that YES1 is also strongly associated with T-DM1 resistance after the development of acquired resistance to trastuzumab, and the continuous inhibition of YES1 is important for overcoming resistance to T-DM1.

EGFR transactivates RON to drive oncogenic crosstalk

Crosstalk between different receptor tyrosine kinases (RTKs) is thought to drive oncogenic signaling and allow therapeutic escape. EGFR and RON are two such RTKs from different subfamilies, which engage in crosstalk through unknown mechanisms. We combined high-resolution imaging with biochemical and mutational studies to ask how EGFR and RON communicate. EGF stimulation promotes EGFR-dependent phosphorylation of RON, but ligand stimulation of RON does not trigger EGFR phosphorylation – arguing that crosstalk is unidirectional. Nanoscale imaging reveals association of EGFR and RON in common plasma membrane microdomains. Two-color single particle tracking captured formation of complexes between RON and EGF-bound EGFR. Our results further show that RON is a substrate for EGFR kinase, and that transactivation of RON requires formation of a signaling competent EGFR dimer. These results support a role for direct EGFR/RON interactions in propagating crosstalk, such that EGF-stimulated EGFR phosphorylates RON to activate RON-directed signaling.

Expanding the Disorder-Function Paradigm in the C-Terminal Tails of Erbbs

ErbBs are receptor tyrosine kinases involved not only in development, but also in a wide variety of diseases, particularly cancer. Their extracellular, transmembrane, juxtamembrane, and kinase folded domains were described extensively over the past 20 years, structurally and functionally. However, their whole C-terminal tails (CTs) following the kinase domain were only described at atomic resolution in the last 4 years. They were shown to be intrinsically disordered. The CTs are known to be tyrosine-phosphorylated when the activated homo- or hetero-dimers of ErbBs are formed. Their phosphorylation triggers interaction with phosphotyrosine binding (PTB) or Src Homology 2 (SH2) domains and activates several signaling pathways controling cellular motility, proliferation, adhesion, and apoptosis. Beyond this passive role of phosphorylated domain and site display for partners, recent structural and function studies unveiled active roles in regulation of phosphorylation and interaction: the CT regulates activity of the kinase domain; different phosphorylation states have different compaction levels, potentially modulating the succession of phosphorylation events; and prolines have an important role in structure, dynamics, and possibly regulatory interactions. Here, we review both the canonical role of the disordered CT domains of ErbBs as phosphotyrosine display domains and the recent findings that expand the known range of their regulation functions linked to specific structural and dynamic features.

Phosphorylation of Na+,K+-ATPase at Tyr10 of the α1-Subunit is Suppressed by AMPK and Enhanced by Ouabain in Cultured Kidney Cells

Na⁺,K⁺-ATPase (NKA) is essential for maintenance of cellular and whole-body water and ion homeostasis. In the kidney, a major site of ion transport, NKA consumes ~ 50% of ATP, indicating a tight coordination of NKA and energy metabolism. AMP-activated protein kinase (AMPK), a cellular energy sensor, regulates NKA by modulating serine phosphorylation of the α1-subunit, but whether it modulates other important regulatory phosphosites, such as Tyr10, is unknown. Using human kidney (HK-2) cells, we determined that the phosphorylation of Tyr10 was stimulated by the epidermal growth factor (EGF), which was opposed by inhibitors of Src kinases (PP2), tyrosine kinases (genistein), and EGF receptor (EGFR, gefitinib). AMPK activators AICAR and A-769662 suppressed the EGF-stimulated phosphorylation of EGFR (Tyr1173) and NKAα1 at Tyr10. The phosphorylation of Src (Tyr416) was unaltered by AICAR and increased by A-769662. Conversely, ouabain (100 nM), a pharmacological NKA inhibitor and a putative adrenocortical hormone, enhanced the EGF-stimulated Tyr10 phosphorylation without altering the phosphorylation of EGFR (Tyr1173) or Src (Tyr416). Ouabain (100–1000 nM) increased the ADP:ATP ratio, while it suppressed the lactate production and the oxygen consumption rate in a dose-dependent manner. Treatment with ouabain or gene silencing of NKAα1 or NKAα3 subunit did not activate AMPK. In summary, AMPK activators and ouabain had antagonistic effects on the phosphorylation of NKAα1 at Tyr10 in cultured HK-2 cells, which implicates a role for Tyr10 in coordinated regulation of NKA-mediated ion transport and energy metabolism.

Autoantibody-Specific Signalling in Pemphigus

Pemphigus is a severe autoimmune disease impairing barrier functions of epidermis and mucosa. Autoantibodies primarily target the desmosomal adhesion molecules desmoglein (Dsg) 1 and Dsg 3 and induce loss of desmosomal adhesion. Strikingly, autoantibody profiles in pemphigus correlate with clinical phenotypes. Mucosal-dominant pemphigus vulgaris (PV) is characterised by autoantibodies (PV-IgG) against Dsg3 whereas epidermal blistering in PV and pemphigus foliaceus (PF) is associated with autoantibodies against Dsg1. Therapy in pemphigus is evolving towards specific suppression of autoantibody formation and autoantibody depletion. Nevertheless, during the acute phase and relapses of the disease additional treatment options to stabilise desmosomes and thereby rescue keratinocyte adhesion would be beneficial. Therefore, the mechanisms by which autoantibodies interfere with adhesion of desmosomes need to be characterised in detail. Besides direct inhibition of Dsg adhesion, autoantibodies engage signalling pathways interfering with different steps of desmosome turn-over. With this respect, recent data indicate that autoantibodies induce separate signalling responses in keratinocytes via specific signalling complexes organised by Dsg1 and Dsg3 which transfer the signal of autoantibody binding into the cell. This hypothesis may also explain the different clinical pemphigus phenotypes.

Angiotensin II-Induced Vasoconstriction via Rho Kinase Activation in Pressure-Overloaded Rat Thoracic Aortas

Angiotensin II (Ang II) induces vasoconstriction through myosin light chain (MLC) kinase activation and MLC phosphatase inactivation via phosphorylation of myosin phosphatase targeting subunit 1 (MYPT1) by Rho kinase. However, the detailed mechanism underlying Rho kinase activation by Ang II is still unknown. We investigated the mechanism of Ang II-induced vasoconstriction mediated by Rho kinase in pressure-overloaded rat thoracic aortas. Pressure-overloaded rats were produced by coarctation of the suprarenal abdominal aorta in four-week-old male Wistar rats. The contractile response to Ang II was significantly enhanced in the pressure-overloaded rats. Ang II-induced vasoconstriction was attenuated by inhibitors of Rho kinase, extracellular signal-regulated kinase 1 and 2 (Erk1/2), and epidermal growth factor receptor (EGFR) in both the sham-operated and pressure-overloaded rats. The Ang II-induced vasoconstriction was attenuated by a Janus kinase 2 (JAK2) inhibitor in only the pressure-overloaded rats. The protein levels of MYPT1 and JAK2 increased only in the pressure-overloaded rat thoracic aortas. These results suggested that Ang II-induced contraction is mediated by Rho kinase activation via EGFR, Erk1/2, and JAK2 in pressure-overloaded rat thoracic aortas. Moreover, Ang II-induced contraction was enhanced in pressure-overloaded rats probably because the protein levels of MYPT1 and JAK2 increased in the thoracic aortas.

Morphine Prevents Ischemia/Reperfusion-Induced Myocardial Mitochondrial Damage by Activating δ-opioid Receptor/EGFR/ROS Pathway

OBJECTIVE

The purpose of this study was to determine whether the epidermal growth factor receptor (EGFR), which is a classical receptor tyrosine kinase, is involved in the protective effect of morphine against ischemia/reperfusion (I/R)-induced myocardial mitochondrial damage.

METHODS

Isolated rats hearts were subjected to global ischemia followed by reperfusion. Cardiac H9c2 cells were exposed to a simulated ischemia solution followed by Tyrode's solution to induce hypoxia/reoxygenation (H/R) injury. Triphenyltetrazolium chloride (TTC) was used to measure infarct size. The mitochondrial morphological and functional changes were determined using transmission election microscopy (TEM), mitochondrial stress assay, and mitochondrial swelling, respectively. Mitochondrial fluorescence indicator JC-1, DCFH-DA, and Mitosox Red were used to determine mitochondrial membrane potential (△Ψm), intracellular reactive oxygen species (ROS) and mitochondrial superoxide. A TUNUL assay kit was used to detect the level of apoptosis. Western blotting analysis was used to measure the expression of proteins.

RESULTS

Treatment of isolated rat hearts with morphine prevented I/R-induced myocardial mitochondrial injury, which was inhibited by the selective EGFR inhibitor AG1478, suggesting that EGFR is involved in the mitochondrial protective effect of morphine under I/R conditions. In support of this hypothesis, the selective EGFR agonist epidermal growth factor (EGF) reduced mitochondrial morphological and functional damage similarly to morphine. Further study demonstrated that morphine may alleviate I/R-induced cardiac damage by inhibiting autophagy but not apoptosis. Morphine increased protein kinase B (Akt), extracellular regulated protein kinases (ERK) and signal transducer and activator of transcription-3 (STAT-3) phosphorylation, which was inhibited by AG1478, and EGF had similar effects, indicating that morphine may activate Akt, ERK, and STAT-3 via EGFR. Morphine and EGF increased intracellular reactive oxygen species (ROS) generation. This effect of morphine was inhibited by AG1478, indicating that morphine promotes intracellular ROS generation by activating EGFR. However, morphine did not increase ROS generation when cells were transfected with siRNA against EGFR. In addition, EGFR activity was markedly increased by morphine, but the effect of morphine was reversed by naltrindole. These results suggest that morphine may activate EGFR via δ-opioid receptor activation.

CONCLUSIONS

Morphine may prevent I/R-induced myocardial mitochondrial damage by activating EGFR through δ-opioid receptors, in turn increasing RISK and SAFE pathway activity via intracellular ROS. Moreover, morphine may reduce myocardial injury by regulating autophagy but not apoptosis.

Interleukin-1β Induces Tissue Factor Expression in A549 Cells via EGFR-Dependent and -Independent Mechanisms

Tissue factor (TF) plays an important role in the progression and angiogenesis of tumor cells. The present study investigated the mechanism of interleukin-1β (IL-1β)-induced TF expression in A549 lung cancer cells. Based on mRNA and protein analyses, including appropriate inhibitor experiments, IL-1β was shown to induce TF expression in a time-dependent manner, mediated by IL-1 receptor-dependent phosphorylation of the mitogen-activated protein kinases (MAPK) p38, p42/44 and c-jun N-terminal kinase (JNK), as well as the Src kinase and the epidermal growth factor receptor (EGFR). Thereby, inhibition of EGFR transactivation by the Src inhibitor PP1 or direct EGFR inhibition by the EGFR tyrosine kinase inhibitor (TKI) erlotinib led to a reduction of IL-1β-induced TF expression and to a suppression of p42/44 MAPK and EGFR activation, while IL-1β-induced p38 MAPK and JNK activation remained unchanged. A knockdown of EGFR by siRNA was associated with decreased IL-1β-mediated p42/44 MAPK activation, which was no longer inhibitable by erlotinib. Concentration-dependent inhibition of IL-1β-induced TF expression was also observed in the presence of gefitinib and afatinib, two other EGFR TKIs. In summary, our results suggest that IL-1β leads to increased TF formation in lung cancer cells via both Src/EGFR/p42/44 MAPK-dependent and EGFR-independent signaling pathways, with the latter mediated via p38 MAPK and JNK.

Phosphorylation of REPS1 at Ser709 by RSK attenuates the recycling of transferrin receptor

RalBP1 associated EPS domain containing 1 (REPS1) is conserved from Drosophila to humans and implicated in the endocytic system. However, an exact role of REPS1 remains largely unknown. Here, we demonstrated that mitogen activated protein kinase kinase (MEK)-p90 ribosomal S6 Kinase (RSK) signaling pathway directly phosphorylated REPS1 at Ser709 upon stimulation by epidermal growth factor (EGF) and amino acid. While REPS2 is known to be involved in the endocytosis of EGF receptor (EGFR), REPS1 knockout (KO) cells did not show any defect in the endocytosis of EGFR. However, in the REPS1 KO cells and the KO cells reconstituted with a non-phosphorylatable REPS1 (REPS1 S709A), the recycling of transferrin receptor (TfR) was attenuated compared to the cells reconstituted with wild type REPS1. Collectively, we suggested that the phosphorylation of REPS1 at S709 by RSK may have a role of the trafficking of TfR.

Plant Occurring Flavonoids as Modulators of the Aryl Hydrocarbon Receptor

The aryl hydrocarbon receptor (AhR) is a transcription factor deeply implicated in health and diseases. Historically identified as a sensor of xenobiotics and mainly toxic substances, AhR has recently become an emerging pharmacological target in cancer, immunology, inflammatory conditions, and aging. Multiple AhR ligands are recognized, with plant occurring flavonoids being the largest group of natural ligands of AhR in the human diet. The biological implications of the modulatory effects of flavonoids on AhR could be highlighted from a toxicological and environmental concern and for the possible pharmacological applicability. Overall, the possible AhR-mediated harmful and/or beneficial effects of flavonoids need to be further investigated, since in many cases they are contradictory. Similar to other AhR modulators, flavonoids commonly exhibit tissue, organ, and species-specific activities on AhR. Such cellular-context dependency could be probably beneficial in their pharmacotherapeutic use. Flavones, flavonols, flavanones, and isoflavones are the main subclasses of flavonoids reported as AhR modulators. Some of the structural features of these groups of flavonoids that could be influencing their AhR effects are herein summarized. However, limited generalizations, as well as few outright structure-activity relationships can be suggested on the AhR agonism and/or antagonism caused by flavonoids.

Standard of Care and Promising New Agents for the Treatment of Mesenchymal Triple-Negative Breast Cancer

The pathologic definition of triple negative breast cancer (TNBC) relies on the absence of expression of estrogen, progesterone and HER2 receptors. However, this BC subgroup is distinguished by a wide biological, molecular and clinical heterogeneity. Among the intrinsic TNBC subtypes, the mesenchymal type is defined by the expression of genes involved in the epithelial to mesenchymal transition, stromal interaction and cell motility. Moreover, it shows a high expression of genes involved in proliferation and an immune-suppressive microenvironment. Several molecular alterations along different pathways activated during carcinogenesis and tumor progression have been outlined and could be involved in immune evasion mechanisms. Furthermore, reverting epithelial to mesenchymal transition process could lead to the overcoming of immune-resistance. This paper reviews the current knowledge regarding the mesenchymal TNBC subtype and its response to conventional therapeutic strategies, as well as to some promising molecular target agents and immunotherapy. The final goal is a tailored combination of cytotoxic drugs, target agents and immunotherapy in order to restore immunocompetence in mesenchymal breast cancer patients.

Bombesin, endothelin, neurotensin and pituitary adenylate cyclase activating polypeptide cause tyrosine phosphorylation of receptor tyrosine kinases

Numerous peptides including bombesin (BB), endothelin (ET), neurotensin (NTS) and pituitary adenylate cyclase-activating polypeptide (PACAP) are growth factors for lung cancer cells. The peptides bind to G protein-coupled receptors (GPCRs) resulting in elevated cAMP and/or phosphatidylinositol (PI) turnover. In contrast, growth factors such as epidermal growth factor (EGF) or neuregulin (NRG)-1 bind to receptor tyrosine kinases (RTKs) such as the EGFR or HER3, increasing tyrosine kinase activity, resulting in the phosphorylation of protein substrates such as PI3K or phospholipase (PL)C. Peptide GPCRs can transactivate numerous RTKs, especially members of the EGFR/HER family resulting in increased phosphorylation of ERK, leading to cellular proliferation or increased phosphorylation of AKT, leading to cellular survival. GRCR antagonists and tyrosine kinase inhibitors are useful agents to prevent RTK transactivation and inhibit proliferation of cancer cells.

Overcoming Obstacles to Targeting Muscarinic Receptor Signaling in Colorectal Cancer

Despite great advances in our understanding of the pathobiology of colorectal cancer and the genetic and environmental factors that mitigate its onset and progression, a paucity of effective treatments persists. The five-year survival for advanced, stage IV disease remains substantially less than 20%. This review examines a relatively untapped reservoir of potential therapies to target muscarinic receptor expression, activation, and signaling in colorectal cancer. Most colorectal cancers overexpress M₃ muscarinic receptors (M₃R), and both in vitro and in vivo studies have shown that activating these receptors stimulates cellular programs that result in colon cancer growth, survival, and spread. In vivo studies using mouse models of intestinal neoplasia have shown that using either genetic or pharmacological approaches to block M₃R expression and activation, respectively, attenuates the development and progression of colon cancer. Moreover, both in vitro and in vivo studies have shown that blocking the activity of matrix metalloproteinases (MMPs) that are induced selectively by M₃R activation, i.e., MMP1 and MMP7, also impedes colon cancer growth and progression. Nonetheless, the widespread expression of muscarinic receptors and MMPs and their importance for many cellular functions raises important concerns about off-target effects and the safety of employing similar strategies in humans. As we highlight in this review, highly selective approaches can overcome these obstacles and permit clinicians to exploit the reliance of colon cancer cells on muscarinic receptors and their downstream signal transduction pathways for therapeutic purposes.

Updated Insights on EGFR Signaling Pathways in Glioma

Nowadays, due to recent advances in molecular biology, the pathogenesis of glioblastoma is better understood. For the newly diagnosed, the current standard of care is represented by resection followed by radiotherapy and temozolomide administration, but because median overall survival remains poor, new diagnosis and treatment strategies are needed. Due to the quick progression, even with aggressive multimodal treatment, glioblastoma remains almost incurable. It is known that epidermal growth factor receptor (EGFR) amplification is a characteristic of the classical subtype of glioma. However, targeted therapies against this type of receptor have not yet shown a clear clinical benefit. Many factors contribute to resistance, such as ineffective blood-brain barrier penetration, heterogeneity, mutations, as well as compensatory signaling pathways. A better understanding of the EGFR signaling network, and its interrelations with other pathways, are essential to clarify the mechanisms of resistance and create better therapeutic agents.

c-Src and EGFR Inhibition in Molecular Cancer Therapy: What Else Can We Improve?

The proto-oncogene c-Src is a non-receptor tyrosine kinase playing a key role in many cellular pathways, including cell survival, migration and proliferation. c-Src de-regulation has been observed in several cancer types, making it an appealing target for drug discovery efforts. Recent evidence emphasizes its crucial role not only in promoting oncogenic traits, but also in the acquisition and maintenance of cancer resistance to various chemotherapeutic or molecular target drugs. c-Src modulates epidermal growth factor receptor (EGFR) activation and amplifies its downstream oncogenic signals. In this review, we report several studies supporting c-Src kinase role in the intricate mechanisms of resistance to EGFR tyrosine kinase inhibitors (TKIs). We further highlighted pre- and clinical progresses of combined treatment strategies made in recent years. Several pre-clinical data have encouraged the use of c-Src inhibitors in combination with EGFR inhibitors. However, clinical trials provided controversial outcomes in some cancer types. Despite c-Src inhibitors showed good tolerability in cancer patients, no incontrovertible and consistent clinical responses were recorded, supporting the idea that a better selection of patients is needed to improve clinical outcome. Currently, the identification of biological markers predictive of therapy response and the accurate molecular screening of cancer patients aimed to gain most clinical benefits become decisive and mandatory.

Desmoglein-2 modulates tumor progression and osimertinib drug resistance through the EGFR/Src/PAK1 pathway in lung adenocarcinoma

Desmoglein-2 (DSG2), a member of the cadherin superfamily, has been implicated in cell-cell adhesion and tumorigenesis. Here, we demonstrate that high DSG2 expression in both lung adenocarcinoma (LUAD) cell lines and tissues is associated with poor prognosis in LUAD patients. Notably, DSG2 overexpression promoted cell proliferation and migration, and increased resistance to the EGFR tyrosine kinase inhibitor osimertinib, whereas DSG2 silencing could reverse these results. Moreover, direct interaction between DSG2 and EGFR in the cell membrane stimulated EGFR signaling to promote tumorigenesis, and loss of DSG2 resulted in EGFR translocation into the cytoplasm. In addition, DSG2 was required for EGFR binding to Src; consequently, DSG2 silencing inhibited tumor cell malignancy via suppression of the EGFR-Src-Rac1-PAK1 signaling pathway. Consistent with these findings, a nude mouse xenograft model using H1975 cells demonstrated that DSG2 promoted LUAD cell growth in vivo and increased osimertinib resistance. Collectively, these observations are the first to elucidate a unique role for DSG2 in the development and progression of lung adenocarcinoma via EGFR signaling.

High ErbB3 activating activity in human blood is not due to circulating neuregulin-1 beta

Neuregulin-1β (NRG-1) is a membrane-bound or secreted growth and differentiation factor that mediates its action by binding to ErbB receptors. Circulating levels of NRG-1 are characterized by large inter-individual variability with the range of absolute values covering two orders of magnitude, from hundreds to tens of thousands of picograms per milliliter of blood. NRG-1 signaling via ErbB receptors contributes to the cell survival and downregulation of the inflammatory response. A higher level of circulating NRG-1 may indicate increased shedding of membrane-bound NRG-1, which in turn can contribute to better protection against cardiovascular stress or injury. However, it is unknown whether circulating NRG-1 can induce activation of ErbB receptors. In the current study, we performed an analysis of circulating NRG-1 functional activity using a cell-based ELISA measuring phosphorylation of ErbB3 induced by blood plasma obtained from healthy donors. We found high levels of ErbB3 activating activity in human plasma. No correlations were found between the levels of circulating NRG-1 and plasma ErbB3 activating activity. To determine the direct effect of circulating NRG-1, we incubated plasma with neutralizing antibody, which prevented the stimulatory effect of recombinant NRG-1 on activation of ErbB3. No effect of the neutralizing antibody was found on plasma-induced phosphorylation of ErbB3. We also found that a significant portion of circulating NRG-1 is comprised of full-length NRG-1 associated with large extracellular vesicles. Our results demonstrate that circulating NRG-1 does not contribute to plasma-induced ErbB3 activating activity and emphasizes the importance of functional testing of NRG-1 proteins in biological samples.

Kinase inhibition profiles as a tool to identify kinases for specific phosphorylation sites

There are thousands of known cellular phosphorylation sites, but the paucity of ways to identify kinases for particular phosphorylation events remains a major roadblock for understanding kinase signaling. To address this, we here develop a generally applicable method that exploits the large number of kinase inhibitors that have been profiled on near-kinome-wide panels of protein kinases. The inhibition profile for each kinase provides a fingerprint that allows identification of unknown kinases acting on target phosphosites in cell extracts. We validate the method on diverse known kinase-phosphosite pairs, including histone kinases, EGFR autophosphorylation, and Integrin β1 phosphorylation by Src-family kinases. We also use our approach to identify the previously unknown kinases responsible for phosphorylation of INCENP at a site within a commonly phosphorylated motif in mitosis (a non-canonical target of Cyclin B-Cdk1), and of BCL9L at S915 (PKA). We show that the method has clear advantages over in silico and genetic screening.

Activation of Protein Kinase Cδ Contributes to the Induction of Src/EGF Receptor/ERK Signaling in Ammonia-treated Astrocytes

Previously, we showed that Src-mediated EGF receptor transactivation/ERK activation mediates ammonia-induced astrocyte swelling, which represents a major component of brain edema in hyperammonemic disorders. Here, we tested the role of PKC in the induction of this signaling pathway and its involvement in ammonia-mediated cell swelling. We found that incubating astrocytes with bisindolylmaleimide (BIM, an inhibitor of classical and novel PKC isoforms) or rottlerin, a PKCδ-specific inhibitor, attenuated the ammonia-induced phosphorylation of EGFR, while GF109203X had no effect on this pathway. We further found that BIM or rottlerin pretreatment inhibited the ammonia-induced phosphorylation of Src and that ammonia significantly increased the level of PKCδ pulled down by a Src antibody. AG1478, a specific EGFR kinase activity inhibitor, effectively inhibited phosphorylation at Tyr1068 but had no discernable effect on phosphorylation at Tyr845. Moreover, BIM or rottlerin abrogated ammonia-induced ERK phosphorylation. BIM-, rottlerin-, or GF109203X-treated astrocytes showed a significant reduction in cell swelling compared to that observed after treatment with ammonia alone. Finally, it was found that AG1478 attenuated ammonia-induced PKCα translocation to the particulate fraction. Taken together, our results indicate that PKCδ mediates ammonia-induced astrocyte swelling by activating Src and downstream EGF receptor/ERK signaling, which may contribute to the pathogenesis of neuropsychiatric disorders associated with hyperammonemia.

Synergistic Anti-Tumour Effect of Syk Inhibitor and Olaparib in Squamous Cell Carcinoma: Roles of Syk in EGFR Signalling and PARP1 Activation

Syk is a non-receptor tyrosine kinase involved in the signalling of immunoreceptors and growth factor receptors. Previously, we reported that Syk mediates epidermal growth factor receptor (EGFR) signalling and plays a negative role in the terminal differentiation of keratinocytes. To understand whether Syk is a potential therapeutic target of cancer cells, we further elucidated the role of Syk in disease progression of squamous cell carcinoma (SCC), which is highly associated with EGFR overactivation, and determined the combined effects of Syk and PARP1 inhibitors on SCC viability. We found that pharmacological inhibition of Syk could attenuate the EGF-induced phosphorylation of EGFR, JNK, p38 MAPK, STAT1, and STAT3 in A431, CAL27 and SAS cells. In addition, EGF could induce a Syk-dependent IL-8 gene and protein expression in SCC. Confocal microscopic data demonstrated the ability of the Syk inhibitor to change the subcellular distribution patterns of EGFR after EGF treatment in A431 and SAS cells. Moreover, according to Kaplan-Meier survival curve analysis, higher Syk expression is correlated with poorer patient survival rate and prognosis. Notably, both Syk and EGFR inhibitors could induce PARP activation, and synergistic cytotoxic actions were observed in SCC cells upon the combined treatment of the PARP1 inhibitor olaparib with Syk or the EGFR inhibitor. Collectively, we reported Syk as an important signalling molecule downstream of EGFR that plays crucial roles in SCC development. Combining Syk and PARP inhibition may represent an alternative therapeutic strategy for treating SCC.

Augmented Pulmonary Vasoconstrictor Reactivity after Chronic Hypoxia Requires Src Kinase and Epidermal Growth Factor Receptor Signaling

Chronic hypoxia augments pressure- and agonist-induced pulmonary vasoconstriction through myofilament calcium sensitization. NADPH oxidases contribute to the development of pulmonary hypertension, and both epidermal growth factor receptor and Src kinases can regulate NADPH oxidase. We tested the hypothesis that Src-epidermal growth factor receptor (EGFR) signaling mediates enhanced vasoconstrictor sensitivity after chronic hypoxia through NADPH oxidase-derived superoxide generation. Protocols employed pharmacological inhibitors in isolated, pressurized rat pulmonary arteries to examine the contribution of a variety of signaling moieties to enhanced vascular tone after chronic hypoxia. Superoxide generation in pulmonary arterial smooth muscle cells was assessed using the fluorescent indicator dihydroethidium. Indices of pulmonary hypertension were measured in rats treated with the EGFR inhibitor gefitinib. Inhibition of NADPH oxidase, Rac1 (Ras-related C3 botulinum toxin substrate 1), and EGFR abolished pressure-induced pulmonary arterial tone and endothelin-1 (ET-1)-dependent calcium sensitization and vasoconstriction after chronic hypoxia. Consistently, chronic hypoxia augmented ET-1-induced superoxide production through EGFR signaling, and rats treated chronically with gefitinib displayed reduced right ventricular pressure and diminished arterial remodeling. Src kinases were also activated by ET-1 after chronic hypoxia and contributed to enhanced basal arterial tone and vasoconstriction in response to ET-1. A role for matrix metalloproteinase 2 to mediate Src-dependent EGFR activation is further supported by our findings. Our studies support a novel role for an Src kinase-EGFR-NADPH oxidase signaling axis to mediate enhanced pulmonary vascular smooth muscle Ca2+ sensitization, vasoconstriction, and pulmonary hypertension after chronic hypoxia.

Regulation of PTP1B activation through disruption of redox-complex formation

We have identified a molecular interaction between the reversibly oxidized form of protein tyrosine phosphatase 1B (PTP1B) and 14-3-3ζ that regulates PTP1B activity. Destabilizing the transient interaction between 14-3-3ζ and PTP1B prevented PTP1B inactivation by reactive oxygen species and decreased epidermal growth factor receptor phosphorylation. Our data suggest that destabilizing the interaction between 14-3-3ζ and the reversibly oxidized and inactive form of PTP1B may establish a path to PTP1B activation in cells.

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.