Ligand-induced lysosomal epidermal growth factor receptor (EGFR) degradation is preceded by proteasome-dependent EGFR de-ubiquitination

The involvement of epidermal growth factor receptor/protein kinase B signaling in the tumor intrinsic PD-L1-induced malignant potential of oral squamous cell carcinoma

BACKGROUND

Various antigen-presenting cells and tumor cells-expressing PD-L1 inhibits antitumor immune responses in the tumor microenvironment. Recently, numerous studies have shown that tumor cell intrinsic PD-L1 also plays important roles in tumor growth and progression. On the other hand, oral squamous cell carcinoma (OSCC) cells overexpress epidermal growth factor receptor (EGFR) and EGFR signal pathway exacerbates tumor progression. Therefore, this study assessed whether tumor-intrinsic PD-L1 facilitates malignant potential of OSCC cells through regulation of EGFR signaling.

METHODS

Two OSCC cell lines, SAS and HSC-3, were transfected with PD-L1 and EGFR-specific small interfering RNA (siRNA). Influences of PD-L1 knockdown on malignant potentials of OSCC cells were examined by Cell Counting kit-8 assay, transwell assay, sphere formation assay, flow cytometry, and Western blot. Effects of PD-L1 and EGFR knockdown on each expression were examined by quantitative real-time PCR (qRT-PCR), Western blot, and flow cytometry.

RESULTS

Transfection of an PD-L1-siRNA into OSCC cells decreased the abilities of proliferation, stemness, and mobility of these cells significantly. PD-L1 knockdown also decreased EGFR expression through the promotion of proteasome- and lysosome-mediated degradation and following activation of the EGFR/protekin kinase B (AKT) signal pathway. Meanwhile, EGFR knockdown did not influence PD-L1 expression in SAS and HSC-3 cells, but treatment with a recombinant human EGF induced its expression. Treatment with erlotinib and cetuximab suppressed rhEGF-induced PD-L1 expression and localization in the cellular membrane of both OSCC cells.

CONCLUSION

OSCC cells-expressing PD-L1 induced by EGF stimulation may promote malignancy intrinsically via the activation of the EGFR/AKT signaling cascade.

CASC4/GOLM2 drives high grade serous carcinoma anoikis resistance through the recycling of EGFR

Ovarian cancer is the deadliest gynecological malignancy, and accounts for over 150,000 deaths per year worldwide. The high grade serous ovarian carcinoma (HGSC) subtype accounts for almost 70% of ovarian cancers and is the deadliest. HGSC originates in the fimbria of the fallopian tube and disseminates through the peritoneal cavity. HGSC survival in peritoneal fluid requires cells to resist anoikis (anchorage-independent apoptosis). Most anoikis resistant mechanisms are dependent on microenvironment interactions with cell surface-associated proteins, such as integrins and receptor tyrosine kinases (RTKs). We previously identified the gene CASC4 as a driver of anoikis resistance. CASC4 is predicted to be a Golgi-associated protein that may regulate protein trafficking to the plasma membrane, but CASC4 is largely uncharacterized in literature; thus, we sought to determine how CASC4 confers anoikis resistance to HGSC cells. Mining of publicly available ovarian cancer datasets (TCGA) showed that CASC4 is associated with worse overall survival and increased resistance to platinum-based chemotherapies. For experiments, we cultured three human HGSC cell lines (PEO1, CaOV3, OVCAR3), and a murine HGSC cell line, (ID8) with shRNA-mediated CASC4 knockdowns (CASC4 KD) in suspension, to recapitulate the peritoneal fluid environment in vitro. CASC4 KD significantly inhibited cell proliferation and colony formation ability, and increased apoptosis. A Reverse Phase Protein Assay (RPPA) showed that CASC4 KD resulted in a broad re-programming of membrane-associated proteins. Specifically, CASC4 KD led to decreased protein levels of the RTK Epidermal Growth Factor Receptor (EGFR), an initiator of several oncogenic signaling pathways, leading us to hypothesize that CASC4 drives HGSC survival through mediating recycling and trafficking of EGFR. Indeed, loss of CASC4 led to a decrease in both EGFR membrane localization, reduced turnover of EGFR, and increased EGFR ubiquitination. Moreover, a syngeneic ID8 murine model of ovarian cancer showed that knocking down CASC4 leads to decreased tumor burden and dissemination.

Role of lysosomes in HSV-induced pathogenesis

HSV can evade host defenses and cause lifelong infection and severe illness. Lysosomes are catabolic organelles that play an important role in the regulation of cellular homeostasis. Lysosomal dysfunction and alterations in the process of autophagy have been identified in a variety of diseases, including HSV infection, and targeting lysosomes is a potential anti-HSV therapeutic strategy. This article reviews the role of lysosomes and lysosome-associated proteins in HSV infection, providing attractive targets and novel strategies for the treatment of HSV infection.

Sustaining the Activation of EGFR Signal by Inflammatory Cytokine IL17A Prompts Cell Proliferation and EGFR-TKI Resistance in Lung Cancer

Non-small-cell lung cancer (NSCLC) is a typical inflammation-associated cancer, and lung adenocarcinoma (LUAD) is the most common pathological subtype. Epidermal growth factor (EGF) receptor (EGFR) mutations are the most common driver mutations of LUAD, and they have been identified as important therapeutic targets by EGFR-tyrosine kinase inhibitors (TKIs). The proinflammatory cytokine, interleukin (IL)-17A, and IL-17A-producing cells were reported to be elevated in the tumor microenvironment and peripheral blood of NSCLC patients and to be correlated with tumor progression and poor prognoses. However, the pathophysiological role of IL-17A in NSCLC remains unclear, although some studies suggested its involvement in cancer cell invasion and metastasis. Herein, we observed that expressions of IL-17A and its receptor, IL-17 receptor C (IL-17RC), were elevated in LUAD tissues and were correlated with poor survival in different lung cancer cohorts. In LUAD cells with mutant EGFR, the IL-17A/IL-17RC axis was shown to enhance phosphorylation of EGFR and Met, thereby promoting proliferation and resistance to EGFR-TKIs such as afatinib. In LUAD cells with wild-type (WT) EGFR, we found that the IL-17A/IL-17RC axis enhanced EGF-induced EGFR activation and cell proliferation through causing impairment of EGF-induced EGFR lysosomal degradation. Collectively, our results indicated diverse impacts of the IL-17A/IL-17RC axis on EGFR activation in LUAD cells with WT and mutant EGFR and suggested that developing therapeutic strategies against IL-17A/IL-17RC would be valuable for LUAD treatment.

Mechanistic model of MAPK signaling reveals how allostery and rewiring contribute to drug resistance

BRAF is prototypical of oncogenes that can be targeted therapeutically and the treatment of BRAF^V600E melanomas with RAF and MEK inhibitors results in rapid tumor regression. However, drug-induced rewiring generates a drug adapted state thought to be involved in acquired resistance and disease recurrence. In this article, we study mechanisms of adaptive rewiring in BRAF^V600E melanoma cells using an energy-based implementation of ordinary differential equation (ODE) modeling in combination with proteomic, transcriptomic and imaging data. We develop a method for causal tracing of ODE models and identify two parallel MAPK reaction channels that are differentially sensitive to RAF and MEK inhibitors due to differences in protein oligomerization and drug binding. We describe how these channels, and timescale separation between immediate-early signaling and transcriptional feedback, create a state in which the RAS-regulated MAPK channel can be activated by growth factors under conditions in which the BRAF^V600E -driven channel is fully inhibited. Further development of the approaches in this article is expected to yield a unified model of adaptive drug resistance in melanoma.

Control of protein stability by post-translational modifications

Post-translational modifications (PTMs) can occur on specific amino acids localized within regulatory domains of target proteins, which control a protein's stability. These regions, called degrons, are often controlled by PTMs, which act as signals to expedite protein degradation (PTM-activated degrons) or to forestall degradation and stabilize a protein (PTM-inactivated degrons). We summarize current knowledge of the regulation of protein stability by various PTMs. We aim to display the variety and breadth of known mechanisms of regulation as well as highlight common themes in PTM-regulated degrons to enhance potential for identifying novel drug targets where druggable targets are currently lacking.

Emerging degrader technologies engaging lysosomal pathways

Targeted protein degradation (TPD) provides unprecedented opportunities for drug discovery. While the proteolysis-targeting chimera (PROTAC) technology has already entered clinical trials and changed the landscape of small-molecule drugs, new degrader technologies harnessing alternative degradation machineries, especially lysosomal pathways, have emerged and broadened the spectrum of degradable targets. We have recently proposed the concept of autophagy-tethering compounds (ATTECs) that hijack the autophagy protein microtubule-associated protein 1A/1B light chain 3 (LC3) for targeted degradation. Other groups also reported degrader technologies engaging lysosomal pathways through different mechanisms including AUTACs, AUTOTACs, LYTACs and MoDE-As. In this review, we analyse and discuss ATTECs along with other lysosomal-relevant degrader technologies. Finally, we will briefly summarize the current status of these degrader technologies and envision possible future studies.

Denis N, Gingras AC, Lukacs GL, Pause A. Endofin is required for HD-PTP and ESCRT-0 interdependent endosomal sorting of ubiquitinated transmembrane cargoes

Internalized and ubiquitinated signaling receptors are silenced by their intraluminal budding into multivesicular bodies aided by the endosomal sorting complexes required for transport (ESCRT) machinery. HD-PTP, an ESCRT protein, forms complexes with ESCRT-0, -I and -III proteins, and binds to Endofin, a FYVE-domain protein confined to endosomes with poorly understood roles. Using proximity biotinylation, we showed that Endofin forms a complex with ESCRT constituents and Endofin depletion increased integrin α5-and EGF-receptor plasma membrane density and stability by hampering their lysosomal delivery. This coincided with sustained receptor signaling and increased cell migration. Complementation of Endofin- or HD-PTP-depleted cells with wild-type Endofin or HD-PTP, but not with mutants harboring impaired Endofin/HD-PTP association or cytosolic Endofin, restored EGFR lysosomal delivery. Endofin also promoted Hrs indirect interaction with HD-PTP. Jointly, our results indicate that Endofin is required for HD-PTP and ESCRT-0 interdependent sorting of ubiquitinated transmembrane cargoes to ensure efficient receptor desensitization and lysosomal delivery.

ZNRF1 Mediates Epidermal Growth Factor Receptor Ubiquitination to Control Receptor Lysosomal Trafficking and Degradation

Activation of the epidermal growth factor receptor (EGFR) is crucial for development, tissue homeostasis, and immunity. Dysregulation of EGFR signaling is associated with numerous diseases. EGFR ubiquitination and endosomal trafficking are key events that regulate the termination of EGFR signaling, but their underlying mechanisms remain obscure. Here, we reveal that ZNRF1, an E3 ubiquitin ligase, controls ligand-induced EGFR signaling via mediating receptor ubiquitination. Deletion of ZNRF1 inhibits endosome-to-lysosome sorting of EGFR, resulting in delayed receptor degradation and prolonged downstream signaling. We further demonstrate that ZNRF1 and Casitas B-lineage lymphoma (CBL), another E3 ubiquitin ligase responsible for EGFR ubiquitination, mediate ubiquitination at distinct lysine residues on EGFR. Furthermore, loss of ZNRF1 results in increased susceptibility to herpes simplex virus 1 (HSV-1) infection due to enhanced EGFR-dependent viral entry. Our findings identify ZNRF1 as a novel regulator of EGFR signaling, which together with CBL controls ligand-induced EGFR ubiquitination and lysosomal trafficking.

Epidermal Growth Factor Receptor and its Trafficking Regulation by Acetylation: Implication in Resistance and Exploring the Newer Therapeutic Avenues in Cancer

BACKGROUND

The EGFR is overexpressed in numerous cancers. So, it becomes one of the most favorable drug targets. Single-acting EGFR inhibitors on prolong use induce resistance and side effects. Inhibition of EGFR and/or its interacting proteins by dual/combined/multitargeted therapies can deliver more efficacious drugs with less or no resistance.

OBJECTIVE

The review delves deeper to cover the aspects of EGFR mediated endocytosis, leading to its trafficking, internalization, and crosstalk(s) with HDACs.

METHODS AND RESULTS

This review is put forth to congregate relevant literature evidenced on EGFR, its impact on cancer prognosis, inhibitors, and its trafficking regulation by acetylation along with the current strategies involved in targeting these proteins (EGFR and HDACs) successfully by involving dual/hybrid/combination chemotherapy.

CONCLUSION

The current information on cross-talk of EGFR and HDACs would likely assist researchers in designing and developing dual or multitargeted inhibitors through combining the required pharmacophores.

Challenges and effective routes for formulating and delivery of epidermal growth factors in skin care

Epidermal growth factors are important morphogenetic proteins that instruct cell behaviour. They have many inferred applications within regenerative medicine and have shown promising results in skincare treatments. Many growth factors are known to have skin anti-ageing benefits along with further potential in resolving scarring, acne and other skin disorders. Incorporation of these biologics into skincare formulations has been greatly hindered by low transdermal delivery efficacy, intricate material interactions and protein instability - especially within common cosmetic emulsions. This review explores the cosmeceutical capability of growth factors in skin care, current understandings of constituent interactions and advantageous delivery approaches for more effective topical delivery. The first section highlights the influences growth factor product formulation has on stability and synergy. Current understandings of growth factor formulating techniques in cosmetic products is limited, and the performance of other protein structures is an adequate point of reference. The second section examines emerging drug delivery systems to overcome the challenges of topical growth factor treatment. It is important to consider the coaction and durability of all components in a formulation simultaneously: active ingredients, product format and delivery vehicle, in order to engineer an optimal cosmeceutical product.

Phosphorylation of PKCδ by FER tips the balance from EGFR degradation to recycling

Receptor degradation terminates signaling by activated receptor tyrosine kinases. Degradation of EGFR occurs in lysosomes and requires the switching of RAB5 for RAB7 on late endosomes to enable their fusion with the lysosome, but what controls this critical switching is poorly understood. We show that the tyrosine kinase FER alters PKCδ function by phosphorylating it on Y374, and that phospho-Y374-PKCδ prevents RAB5 release from nascent late endosomes, thereby inhibiting EGFR degradation and promoting the recycling of endosomal EGFR to the cell surface. The rapid association of phospho-Y374-PKCδ with EGFR-containing endosomes is diminished by PTPN14, which dephosphorylates phospho-Y374-PKCδ. In triple-negative breast cancer cells, the FER-dependent phosphorylation of PKCδ enhances EGFR signaling and promotes anchorage-independent cell growth. Importantly, increased Y374-PKCδ phosphorylation correlating with arrested late endosome maturation was identified in ∼25% of triple-negative breast cancer patients, suggesting that dysregulation of this pathway may contribute to their pathology.

Discovery of a novel EGFR ligand DPBA that degrades EGFR and suppresses EGFR-positive NSCLC growth

Epidermal growth factor receptor (EGFR) activation plays a pivotal role in EGFR-driven non-small cell lung cancer (NSCLC) and is considered as a key target of molecular targeted therapy. EGFR tyrosine kinase inhibitors (TKIs) have been canonically used in NSCLC treatment. However, prevalent innate and acquired resistances and EGFR kinase-independent pro-survival properties limit the clinical efficacy of EGFR TKIs. Therefore, the discovery of novel EGFR degraders is a promising approach towards improving therapeutic efficacy and overcoming drug resistance. Here, we identified a 23-hydroxybetulinic acid derivative, namely DPBA, as a novel EGFR small-molecule ligand. It exerted potent in vitro and in vivo anticancer activity in both EGFR wild type and mutant NSCLC by degrading EGFR. Mechanistic studies disclosed that DPBA binds to the EGFR extracellular domain at sites differing from those of EGF and EGFR. DPBA did not induce EGFR dimerization, phosphorylation, and ubiquitination, but it significantly promoted EGFR degradation and repressed downstream survival pathways. Further analyses showed that DPBA induced clathrin-independent EGFR endocytosis mediated by flotillin-dependent lipid rafts and unaffected by EGFR TKIs. Activation of the early and late endosome markers rab5 and rab7 but not the recycling endosome marker rab11 was involved in DPBA-induced EGFR lysosomal degradation. The present study offers a new EGFR ligand for EGFR pharmacological degradation and proposes it as a potential treatment for EGFR-positive NSCLC, particularly NSCLC with innate or acquired EGFR TKI resistance. DPBA can also serve as a chemical probe in the studies on EGFR trafficking and degradation.

Nedd4l downregulation of NRG1 in the mPFC induces depression-like behaviour in CSDS mice

The occurrence of major depressive disorders has been closely related to the vulnerability of stress. The medial prefrontal cortex (mPFC) is involved in regulating pathological reactivity to stress, changes in affective behaviour and cognitive functions by distress. Increasing evidence indicates that neuregulin 1 (NRG1) plays an important role in psychiatric illnesses, including depression, schizophrenia and bipolar disorder. However, whether NRG1 in the mPFC is related to stress vulnerability remains unclear. We here assessed the regulation of NRG1 by the E3 ubiquitin ligase Nedd4l (neural precursor cell expressed developmentally downregulated 4-like) and investigated whether NRG1 changes in the mPFC might lead to vulnerability to depression-like behaviours. We've identified a deficiency of NRG1 in the mPFC as a key factor that contributes to the regulation of stress susceptibility in mice, as further suggested by the finding that overexpression of NRG1 attenuated depression-like behaviours in the animal model of chronic social defeat stress (CSDS). Interestingly, RNA sequencing in the mPFC brain region showed no differences in NRG1 mRNA levels between control animals and stress-susceptible (SS) or resilient mice (RES) following CSDS. However, mRNA and protein levels of Nedd4l were markedly increased in SS mice, but not in RES mice compared to controls. Furthermore, ubiquitination of NRG1 was increased in SS mice. Remarkably, overexpression of Nedd4l in mouse mPFC induced a decrease in NRG1 level and caused vulnerability to stress by subthreshold social defeat stress (SSDS), while downregulation of Nedd4l expression in the mPFC rescued the vulnerability to stress-induced social avoidance and anhedonia. Our data strongly indicate that the Nedd4l-mediated downregulation of NRG1 acts as a critical role in depression-like phenotypes of mice in CSDS.

Deficiency of GABARAP but not its Paralogs Causes Enhanced EGF-induced EGFR Degradation

The γ-aminobutyric acid type A receptor-associated protein (GABARAP) and its close paralogs GABARAPL1 and GABARAPL2 constitute a subfamily of the autophagy-related 8 (Atg8) protein family. Being associated with a variety of dynamic membranous structures of autophagic and non-autophagic origin, Atg8 proteins functionalize membranes by either serving as docking sites for other proteins or by acting as membrane tethers or adhesion factors. In this study, we describe that deficiency for GABARAP alone, but not for its close paralogs, is sufficient for accelerated EGF receptor (EGFR) degradation in response to EGF, which is accompanied by the downregulation of EGFR-mediated MAPK signaling, altered target gene expression, EGF uptake, and EGF vesicle composition over time. We further show that GABARAP and EGFR converge in the same distinct compartments at endogenous GABARAP expression levels in response to EGF stimulation. Furthermore, GABARAP associates with EGFR in living cells and binds to synthetic peptides that are derived from the EGFR cytoplasmic tail in vitro. Thus, our data strongly indicate a unique and novel role for GABARAP during EGFR trafficking.

GPAT4-Generated Saturated LPAs Induce Lipotoxicity through Inhibition of Autophagy by Abnormal Formation of Omegasomes

Excessive levels of saturated fatty acids are toxic to vascular smooth muscle cells (VSMCs). We previously reported that mice lacking VSMC-stearoyl-CoA desaturase (SCD), a major enzyme catalyzing the detoxification of saturated fatty acids, develop severe vascular calcification from the massive accumulation of lipid metabolites containing saturated fatty acids. However, the mechanism by which SCD deficiency causes vascular calcification is not completely understood. Here, we demonstrate that saturated fatty acids significantly inhibit autophagic flux in VSMCs, contributing to vascular calcification and apoptosis. Mechanistically, saturated fatty acids are accumulated as saturated lysophosphatidic acids (LPAs) (i.e. 1-stearoyl-LPA) possibly synthesized through the reaction of GPAT4 at the contact site between omegasomes and the MAM. The accumulation of saturated LPAs at the contact site causes abnormal formation of omegasomes, resulting in accumulation of autophagosomal precursor isolation membranes, leading to inhibition of autophagic flux. Thus, saturated LPAs are major metabolites mediating autophagy inhibition and vascular calcification.

The ubiquitin system: orchestrating cellular signals in non-small-cell lung cancer

The ubiquitin system, known as a common feature in eukaryotes, participates in multiple cellular processes, such as signal transduction, cell-cycle progression, receptor trafficking and endocytosis, and even the immune response. In lung cancer, evidence has revealed that aberrant events in ubiquitin-mediated processes can cause a variety of pathological outcomes including tumorigenesis and metastasis. Likewise, ubiquitination on the core components contributing to the activity of cell signaling controls bio-signal turnover and cell final destination. Given this, inhibitors targeting the ubiquitin system have been developed for lung cancer therapies and have shown great prospects for clinical application. However, the exact biological effects and physiological role of the drugs used in lung cancer therapies are still not clearly elucidated, which might seriously impede the progress of treatment. In this work, we summarize current research advances in cell signal regulation processes mediated through the ubiquitin system during the development of lung cancer, with the hope of improving the therapeutic effects by means of aiming at efficient targets.

Oxygen Tension Regulates Lysosomal Activation and Receptor Tyrosine Kinase Degradation

Oxygen sensing is crucial for adaptation to variable habitats and physiological conditions. Low oxygen tension, or hypoxia, is a common feature of solid tumors, and hypoxic tumors are often more aggressive and resistant to therapy. Here we show that, in cultured mammalian cells, hypoxia suppressed lysosomal acidification/activation and receptor tyrosine kinase (RTK) degradation. Hypoxia down-regulated mTORc1, reducing its ability to activate transcription factor EB (TFEB), a master regulator of V-ATPase, the lysosomal proton pump. Hypoxia prevented epidermal growth factor receptor (EGFR) degradation in tumor tissues, whereas activation of lysosomes enhanced tumor cell response to anti-EGFR treatment. Our results link oxygen tension and lysosomal activity, provide a molecular explanation of the malignant phenotype associated with hypoxic tumors, and suggest activation of lysosomes may provide therapeutic benefit in RTK-targeted cancer therapy.

Myeloid Cell-Derived HB-EGF Drives Tissue Recovery After Pancreatitis

BACKGROUND & AIMS

Pancreatitis is a major cause of morbidity and mortality and is a risk factor for pancreatic tumorigenesis. Upon tissue damage, an inflammatory response, made up largely of macrophages, provides multiple growth factors that promote repair. Here, we examine the molecular pathways initiated by macrophages to promote pancreas recovery from pancreatitis.

METHODS

To induce organ damage, mice were subjected to cerulein-induced experimental pancreatitis and analyzed at various times of recovery. CD11b-DTR mice were used to deplete myeloid cells. Hbegf^f/f;LysM-Cre mice were used to ablate myeloid cell-derived heparin-binding epidermal growth factor (EGF)-like growth factor (HB-EGF). To ablate EGFR specifically during recovery, pancreatitis was induced in Egfr^f/f;Ptf1a^FlpO/+;FSF-Rosa26^CAG-CreERT2 mice followed by tamoxifen treatment.

RESULTS

Macrophages infiltrating the pancreas in experimental pancreatitis make high levels of HB-EGF. Both depletion of myeloid cells and ablation of myeloid cell HB-EGF delayed recovery from experimental pancreatitis, resulting from a decrease in cell proliferation and an increase in apoptosis. Mechanistically, ablation of myeloid cell HB-EGF impaired epithelial cell DNA repair, ultimately leading to cell death. Soluble HB-EGF induced EGFR nuclear translocation and methylation of histone H4, facilitating resolution of DNA damage in pancreatic acinar cells in vitro. Consistent with its role as the primary receptor of HB-EGF, in vivo ablation of EGFR from pancreatic epithelium during recovery from pancreatitis resulted in accumulation of DNA damage.

CONCLUSIONS

By using novel conditional knockout mouse models, we determined that HB-EGF derived exclusively from myeloid cells induces epithelial cell proliferation and EGFR-dependent DNA repair, facilitating pancreas healing after injury.

EGF-mCherry Fusion Protein Expressed in E. coli Shows Product Heterogeneity but a High Biological Activity

The epidermal growth factor receptor (EGFR) is a transmembrane protein involved in cell signaling processes, and dysregulation of its activity often drives tumor growth. EGFR is a clinically validated tumor marker and target for antibodies and tyrosine kinase inhibitors. We demonstrate that a fusion protein of the natural ligand epidermal growth factor (EGF) with the fluorescent reporter mCherry can be expressed in the cytosol of E. coli in high yields and with a high biological activity. Biophysical characterization by mass spectrometry analysis confirmed three disulfide bonds that are crucial for protein structure. Biolayer interferometry data of the protein-protein interaction of EGF-mCherry with the soluble EGFR are comparable to that of unmodified EGF. Cell culture experiments demonstrated that this fusion replicates all important features of the natural ligand. Finally, fluorescent assays based on EGF-mCherry provided a simple and convenient method to compare EGFR levels on cells and to determine competition of EGFR-binding molecules. These assays will help to rank competitive properties of EGFR inhibitors.

V-ATPases and osteoclasts: ambiguous future of V-ATPases inhibitors in osteoporosis

Vacuolar ATPases (V-ATPases) play a critical role in regulating extracellular acidification of osteoclasts and bone resorption. The deficiencies of subunit a3 and d2 of V-ATPases result in increased bone density in humans and mice. One of the traditional drug design strategies in treating osteoporosis is the use of subunit a3 inhibitor. Recent findings connect subunits H and G1 with decreased bone density. Given the controversial effects of ATPase subunits on bone density, there is a critical need to review the subunits of V-ATPase in osteoclasts and their functions in regulating osteoclasts and bone remodeling. In this review, we comprehensively address the following areas: information about all V-ATPase subunits and their isoforms; summary of V-ATPase subunits associated with human genetic diseases; V-ATPase subunits and osteopetrosis/osteoporosis; screening of all V-ATPase subunits variants in GEFOS data and in-house data; spectrum of V-ATPase subunits during osteoclastogenesis; direct and indirect roles of subunits of V-ATPases in osteoclasts; V-ATPase-associated signaling pathways in osteoclasts; interactions among V-ATPase subunits in osteoclasts; osteoclast-specific V-ATPase inhibitors; perspective of future inhibitors or activators targeting V-ATPase subunits in the treatment of osteoporosis.

Real-time imaging of sodium glucose transporter (SGLT1) trafficking and activity in single cells

The processes controlling targeting of glucose transporters to apical and basolateral membranes of polarized cells are complex and not-well understood. We have engineered SGLT1 and GLUT4 constructs linked to fluorescent proteins to highlight the differences in transporter expression and trafficking, in real time, in different cell types. Activity was assessed in parallel using a FRET glucose sensor. In COS cells and HEK cells, SGLT1 was distributed between the plasma membrane and intracellular compartments, but there was little expression in CHO cells. Trafficking was investigated using the lysosome inhibitors NH₄Cl (10 mmol/L) and chloroquine (150 μmol/L) and the proteasome inhibitors MG-262 (1 μmol/L) and lactacystin (5 μmol/L). Lysosome inhibitors caused SGLT1 accumulation into intracellular bodies, whereas proteasome inhibitors induced SGLT1 accumulation in the plasma membrane, even in CHO cells. Our data suggest that a fraction of SGLT1 is rapidly degraded by lysosomes and never reached the plasma membrane; another fraction reaches the membrane and is subsequently degraded by lysosomes following internalization. The latter process is regulated by the ubiquitin/proteasome pathway, acting at a late stage of the lysosomal pathway. Using the cholesterol inhibitor MβCD (3 mmol/L), a dominant negative dynamin (K44A) and caveolin, we showed that SGLT1 internalization is lipid raft-mediated, but caveolin-independent. In contrast, GLUT4 internalization is dynamin-dependent, but cholesterol-independent. The physiological relevance of these data is discussed in terms of differential membrane compartmentalization of the transporters and expression under stress conditions.

Development of a macrophage-targeting and phagocytosis-inducing bio-nanocapsule-based nanocarrier for drug delivery

Macrophage hyperfunction or dysfunction is tightly associated with various diseases, such as osteoporosis, inflammatory disorder, and cancers. However, nearly all conventional drug delivery system (DDS) nanocarriers utilize endocytosis for entering target cells; thus, the development of macrophage-targeting and phagocytosis-inducing DDS nanocarriers for treating these diseases is required. In this study, we developed a hepatitis B virus (HBV) envelope L particle (i.e., bio-nanocapsule (BNC)) outwardly displaying a tandem form of protein G-derived IgG Fc-binding domain and protein L-derived IgG Fab-binding domain (GL-BNC). When conjugated with the macrophage-targeting ligand, mouse IgG2a (mIgG2a), the GL-BNC itself, and the liposome-fused GL-BNC (i.e., GL-virosome) spontaneously initiated aggregation by bridging between the Fc-binding domain and Fab-binding domain with mIgG2a. The aggregates were efficiently taken up by macrophages, whereas this was inhibited by latrunculin B, a phagocytosis-specific inhibitor. The mIgG2a-GL-virosome containing doxorubicin exhibited higher cytotoxicity toward macrophages than conventional liposomes and other BNC-based virosomes. Thus, GL-BNCs and GL-virosomes may constitute promising macrophage-targeting and phagocytosis-inducing DDS nanocarriers.

STATEMENT OF SIGNIFICANCE

We have developed a novel macrophage-targeting and phagocytosis-inducing bio-nanocapsule (BNC)-based nanocarrier named GL-BNC, which comprises a hepatitis B virus envelope L particle outwardly displaying protein G-derived IgG Fc- and protein L-derived IgG Fab-binding domains in tandem. The GL-BNC alone or liposome-fused form (GL-virosomes) could spontaneously aggregate when conjugated with macrophage-targeting IgGs, inducing phagocytosis by the interaction between IgG Fc of aggregates and FcγR on phagocytes. Thereby these aggregates were efficiently taken up by macrophages. GL-virosomes containing doxorubicin exhibited higher cytotoxicity towards macrophages than ZZ-virosomes and liposomes. Our results suggested that GL-BNCs and GL-virosomes would serve as promising drug delivery system nanocarriers for targeting delivery to macrophages.

Dopamine Receptor Subtypes Differentially Regulate Autophagy

Some dopamine receptor subtypes were reported to participate in autophagy regulation, but their exact functions and mechanisms are still unclear. Here we found that dopamine receptors D2 and D3 (D2-like family) are positive regulators of autophagy, while dopamine receptors D1 and D5 (D1-like family) are negative regulators. Furthermore, dopamine and ammonia, the two reported endogenous ligands of dopamine receptors, both can induce dopamine receptor internalization and degradation. In addition, we found that AKT (protein kinase B)-mTOR (mechanistic target of rapamycin) and AMPK (AMP-activated protein kinase) pathways are involved in DRD3 (dopamine receptor D3) regulated autophagy. Moreover, autophagy machinery perturbation inhibited DRD3 degradation and increased DRD3 oligomer. Therefore, our study investigated the functions and mechanisms of dopamine receptors in autophagy regulation, which not only provides insights into better understanding of some dopamine receptor-related neurodegeneration diseases, but also sheds light on their potential treatment in combination with autophagy or mTOR pathway modulations.

Curcumin targets the TFEB-lysosome pathway for induction of autophagy

Curcumin is a hydrophobic polyphenol derived from the herb Curcumalonga and its wide spectrum of pharmacological activities has been widely studied. It has been reported that Curcumin can induce autophagy through inhibition of the Akt-mTOR pathway. However, the effect of Curcumin on lysosome remains largely elusive. In this study, we first found that Curcumin treatment enhances autophagic flux in both human colon cancer HCT116 cells and mouse embryonic fibroblasts (MEFs). Moreover, Curcumin treatment promotes lysosomal function, evidenced by the increased lysosomal acidification and enzyme activity. Second, Curcumin is capable of suppressing the mammalian target of rapamycin (mTOR). Interestingly, Curcumin fails to inhibit mTOR and to activate lysosomal function in Tsc2^−/−MEFs with constitutive activation of mTOR, indicating that Curcumin-mediated lysosomal activation is achieved via suppression of mTOR. Third, Curcumin treatment activates transcription factor EB (TFEB), a key nuclear transcription factor in control of autophagy and lysosome biogenesis and function, based on the following observations: (i) Curcumin directly binds to TFEB, (ii) Curcumin promotes TFEB nuclear translocation; and (iii) Curcumin increases transcriptional activity of TFEB. Finally, inhibition of autophagy and lysosome leads to more cell death in Curcumin-treated HCT116 cells, suggesting that autophagy and lysosomal activation serves as a cell survival mechanism to protect against Curcumin-mediated cell death. Taken together, data from our study provide a novel insight into the regulatory mechanisms of Curcumin on autophagy and lysosome, which may facilitate the development of Curcumin as a potential cancer therapeutic agent.

The Function of V-ATPases in Cancer

The vacuolar ATPases (V-ATPases) are a family of proton pumps that couple ATP hydrolysis to proton transport into intracellular compartments and across the plasma membrane. They function in a wide array of normal cellular processes, including membrane traffic, protein processing and degradation, and the coupled transport of small molecules, as well as such physiological processes as urinary acidification and bone resorption. The V-ATPases have also been implicated in a number of disease processes, including viral infection, renal disease, and bone resorption defects. This review is focused on the growing evidence for the important role of V-ATPases in cancer. This includes functions in cellular signaling (particularly Wnt, Notch, and mTOR signaling), cancer cell survival in the highly acidic environment of tumors, aiding the development of drug resistance, as well as crucial roles in tumor cell invasion, migration, and metastasis. Of greatest excitement is evidence that at least some tumors express isoforms of V-ATPase subunits whose disruption is not lethal, leading to the possibility of developing anti-cancer therapeutics that selectively target V-ATPases that function in cancer cells.

Endocytosis and membrane receptor internalization: implication of F-BAR protein Carom

Endocytosis is a cellular process mostly responsible for membrane receptor internalization. Cell membrane receptors bind to their ligands and form a complex which can be internalized. We previously proposed that F-BAR protein initiates membrane curvature and mediates endocytosis via its binding partners. However, F-BAR protein partners involved in membrane receptor endocytosis and the regulatory mechanism remain unknown. In this study, we established database mining strategies to explore mechanisms underlying receptor-related endocytosis. We identified 34 endocytic membrane receptors and 10 regulating proteins in clathrin-dependent endocytosis (CDE), a major process of membrane receptor internalization. We found that F-BAR protein FCHSD2 (Carom) may facilitate endocytosis via 9 endocytic partners. Carom is highly expressed, along with highly expressed endocytic membrane receptors and partners, in endothelial cells and macrophages. We established 3 models of Carom-receptor complexes and their intracellular trafficking based on protein interaction and subcellular localization. We conclude that Carom may mediate receptor endocytosis and transport endocytic receptors to the cytoplasm for receptor signaling and lysosome/proteasome degradation, or to the nucleus for RNA processing, gene transcription and DNA repair.

Recent progress in protein-protein interaction study for EGFR-targeted therapeutics

INTRODUCTION

Epidermal growth factor receptor (EGFR) expression is upregulated in many tumors and its aberrant signaling drives progression of many cancer types. Consequently, EGFR has become a clinically validated target as extracellular tumor marker for antibodies as well as for tyrosine kinase inhibitors. Within the last years, new mechanistic insights were uncovered and, based on clinical experience as well as progress in protein engineering, novel bio-therapeutic approaches were developed and tested.

AREAS COVERED

The potential therapeutic targeting arsenal in the fight against cancer now encompasses bispecific or biparatopic antibodies, DARPins, Adnectins, Affibodies, peptides and combinations of these binding molecules with viral- and nano-particles. We review past and recent binding proteins from the literature and include a brief description of the various targeting approaches. Special attention is given to the binding modes with the EGFR. Expert commentary: Clinical data from the three approved anti EGFR antibodies indicate that there is room for improved therapeutic efficacy. Having choices in size, affinity, avidity and the mode of EGFR binding as well as the possibility to combine various effector functions opens the possibility to rationally design more effective therapeutics.

Sustained Mutant KIT Activation in the Golgi Complex Is Mediated by PKC-θ in Gastrointestinal Stromal Tumors

PURPOSE

Tumorigenesis of gastrointestinal stromal tumors (GIST) is driven by gain-of-function mutations in the KIT gene, which result in overexpression of activated mutant KIT proteins (MT-KIT). However, the mechanism of MT-KIT overexpression is poorly understood.

EXPERIMENTAL DESIGN

By protein expression analysis and immunofluorescent microscopic analysis, we determine the stability and localization of MT-KIT in four GIST cell lines with different mutations and HeLa cells transfected with mutant KIT model vectors. We also used 154 human GIST tissues to analyze the relationship between the expression of PKC-θ and MT-KITs, and correlations between PKC-θ overexpression and clinicopathological parameters.

RESULTS

We report that four different MT-KIT proteins are intrinsically less stable than wild-type KIT due to proteasome-mediated degradation and abnormally localized to the endoplasmic reticulum (ER) or the Golgi complex. By screening a MT-KIT-stabilizing factor, we find that PKC-θ is strongly and exclusively expressed in GISTs and interacts with intracellular MT-KIT to promote its stabilization by increased retention in the Golgi complex. In addition, Western blotting analysis using 50 GIST samples shows strong correlation between PKC-θ and MT-KIT expression (correlation coefficient = 0.682, P < 0.000001). Immunohistochemical analysis using 154 GISTs further demonstrates that PKC-θ overexpression significantly correlates with several clinicopathological parameters such as high tumor grade, frequent recurrence/metastasis, and poor patient survival.

CONCLUSIONS

Our findings suggest that sustained MT-KIT overexpression through PKC-θ-mediated stabilization in the Golgi contributes to GIST progression and provides a rationale for anti-PKC-θ therapy in GISTs. Clin Cancer Res; 23(3); 845-56. ©2016 AACR.

New anti-cancer chemicals Ertredin and its derivatives, regulate oxidative phosphorylation and glycolysis and suppress sphere formation in vitro and tumor growth in EGFRvIII-transformed cells

BACKGROUND

EGFRvIII is a mutant form of the epidermal growth factor receptor gene (EGFR) that lacks exons 2-7. The resulting protein does not bind to ligands and is constitutively activated. The expression of EGFRvIII is likely confined to various types of cancer, particularly glioblastomas. Although an anti-EGFRvIII vaccine is of great interest, low-molecular-weight substances are needed to obtain better therapeutic efficacy. Thus, the purpose of this study is to identify low molecular weight substances that can suppress EGFRvIII-dependent transformation.

METHODS

We constructed a new throughput screening system and searched for substances that decreased cell survival of NIH3T3/EGFRvIII spheres under 3-dimensional (3D)-culture conditions, but retained normal NIH3T3 cell growth under 2D-culture conditions. In vivo activity was examined using a mouse transplantation model, and derivatives were chemically synthesized. Functional characterization of the candidate molecules was investigated using an EGFR kinase assay, immunoprecipitation, western blotting, microarray analysis, quantitative polymerase chain reaction analysis, and measurement of lactate and ATP synthesis.

RESULTS

In the course of screening 30,000 substances, a reagent, "Ertredin" was found to inhibit anchorage-independent 3D growth of sphere-forming cells transfected with EGFRvIII cDNA. Ertredin also inhibited sphere formation in cells expressing wild-type EGFR in the presence of EGF. However, it did not affect anchorage-dependent 2D growth of parental NIH3T3 cells. The 3D-growth-inhibitory activity of some derivatives, including those with new structures, was similar to Ertredin. Furthermore, we demonstrated that Ertredin suppressed tumor growth in an allograft transplantation mouse model injected with EGFRvIII- or wild-type EGFR-expressing cells; a clear toxicity to host animals was not observed. Functional characterization of Ertredin in cells expressing EGFRvIII indicated that it stimulated EGFRvIII ubiquitination, suppressed both oxidative phosphorylation and glycolysis under 3D conditions, and promoted cell apoptosis.

CONCLUSION

We developed a high throughput screening method based on anchorage-independent sphere formation induced by EGFRvIII-dependent transformation. In the course of screening, we identified Ertredin, which inhibited anchorage-independent 3D growth and tumor formation in nude mice. Functional analysis suggests that Ertredin suppresses both mitochondrial oxidative phosphorylation and cytosolic glycolysis in addition to promoting EGFRvIII degradation, and stimulates apoptosis in sphere-forming, EGFRvIII-overexpressing cells.

Cathepsin S attenuates endosomal EGFR signalling: A mechanical rationale for the combination of cathepsin S and EGFR tyrosine kinase inhibitors

EGF-mediated EGFR endocytosis plays a crucial role in the attenuation of EGFR activation by sorting from early endosomes to late endosomes and transporting them into lysosomes for the final proteolytic degradation. We previously observed that cathepsin S (CTSS) inhibition induces tumour cell autophagy through the EGFR-mediated signalling pathway. In this study, we further clarified the relationship between CTSS activities and EGFR signalling regulation. Our results revealed that CTSS can regulate EGFR signalling by facilitating EGF-mediated EGFR degradation. CTSS inhibition delayed the EGFR degradation process and caused EGFR accumulation in the late endosomes at the perinuclear region, which provides spatial compartments for prolonged EGFR and sustained downstream signal transducer and activator of transcription 3 and AKT signalling. Notably, cellular apoptosis was markedly enhanced by combining treatment with the EGFR inhibitor Iressa and CTSS inhibitor 6r. The data not only reveal a biological role of CTSS in EGFR signalling regulation but also evidence a rationale for its clinical evaluation in the combination of CTSS and EGFR tyrosine kinase inhibitors.

Differential effects of BDNF and neurotrophin 4 (NT4) on endocytic sorting of TrkB receptors

Neurotrophins are a family of growth factors playing key roles in the survival, development, and function of neurons. The neurotrophins brain-derived neurotrophic factor (BDNF) and NT4 both bind to and activate TrkB receptors, however, they mediate distinct neuronal functions. The molecular mechanism of how TrkB activation by BDNF and NT4 leads to diverse outcomes is unknown. Here, we report that BDNF and NT4 lead to differential endocytic sorting of TrkB receptors resulting in diverse biological functions in cultured cortical neurons. Fluorescent microscopy and surface biotinylation experiments showed that both neurotrophins stimulate internalization of TrkB with similar kinetics. Exposure to BDNF for 2-3 h reduced the surface pool of TrkB receptors to half, whereas a longer treatment (4-5 h) with NT4 was necessary to achieve a similar level of down-regulation. Although BDNF and NT4 induced TrkB phosphorylation with similar intensities, BDNF induced more rapid ubiquitination and degradation of TrkB than NT4. Interestingly, TrkB receptor ubiquitination by these ligands have substantially different pH sensitivities, resulting in varying degrees of receptor ubiquitination at lower pH levels. Consequently, NT4 was capable of maintaining longer sustained downstream signaling activation that correlated with reduced TrkB ubiquitination at endosomal pH. Thus, by leading to altered endocytic trafficking itineraries for TrkB receptors, BDNF and NT4 elicit differential TrkB signaling in terms of duration, intensity, and specificity, which may contribute to their functional differences in vivo. The neurotrophins, brain-derived neurotrophic factor (BDNF) and neurotrophin-4 (NT4), both bind to and activate TrkB receptors, however, they mediate distinct neuronal functions. Here, we propose that BDNF and NT4 lead to differential endocytic sorting of TrkB receptors resulting in diverse biological functions. BDNF induces more rapid ubiquitination and degradation of TrkB than NT4. Consequently, NT4 is capable of maintaining more sustained signaling downstream of TrkB receptors.

Parallel Regulation of von Hippel-Lindau Disease by pVHL-Mediated Degradation of B-Myb and Hypoxia-Inducible Factor α

pVHL, the protein product of the von Hippel-Lindau (VHL) tumor suppressor gene, is a ubiquitin ligase that targets hypoxia-inducible factor α (HIF-α) for proteasomal degradation. Although HIF-α activation is necessary for VHL disease pathogenesis, constitutive activation of HIF-α alone did not induce renal clear cell carcinomas and pheochromocytomas in mice, suggesting the involvement of an HIF-α-independent pathway in VHL pathogenesis. Here, we show that the transcription factor B-Myb is a pVHL substrate that is degraded via the ubiquitin-proteasome pathway and that vascular endothelial growth factor (VEGF)- and/or platelet-derived growth factor (PDGF)-dependent tyrosine 15 phosphorylation of B-Myb prevents its degradation. Mice injected with B-Myb knockdown 786-O cells developed dramatically larger tumors than those bearing control cell tumors. Microarray screening of B-Myb-regulated genes showed that the expression of HIF-α-dependent genes was not affected by B-Myb knockdown, indicating that B-Myb prevents HIF-α-dependent tumorigenesis through an HIF-α-independent pathway. These data indicate that the regulation of B-Myb by pVHL plays a critical role in VHL disease.

Celecoxib increases EGF signaling in colon tumor associated fibroblasts, modulating EGFR expression and degradation

We previously demonstrated that non-toxic doses of Celecoxib induced the immediate phosphorylation of Erk1-2 in colon tumor associated fibroblasts (TAFs), increasing their responsiveness to epidermal growth factor (EGF). We have now identified two concomitant mechanisms explaining the EGF-Celecoxib cooperation. We found that a 24-48h Celecoxib priming increased EGF receptor (EGFR) mRNA and protein levels in colon TAFs, promoting EGF binding and internalization. Celecoxib-primed TAFs showed a reduced EGFR degradation after EGF challenge. This delay corresponded to a deferred dissociation of EEA1 from EGFR positive endosomes and the accumulation of Rab7, pro Cathepsin-D and SQSTM1/p62, suggesting a shared bottleneck in the pathways of late-endosomes/autophagosomes maturation. Celecoxib modulated the levels of target proteins similarly to the inhibitors of endosome/lysosome acidification Bafilomycin-A1 and NH₄Cl. Cytoplasmic vesicles fractionation showed a reduced maturation of Cathepsin-D in late endosomes and an increased content of EGFR and Rab7 in lysosomes of Celecoxib-treated TAFs.

Our data indicate a double mechanism mediating the increased response to EGF of colon TAFs treated with Celecoxib. While EGFR overexpression could be targeted using anti EGFR drugs, the effects on endosome trafficking and protein turnover represents a more elusive target and should be taken into account for any long-term therapy with Celecoxib.

Regulation of Monocarboxylic Acid Transporter 1 Trafficking by the Canonical Wnt/β-Catenin Pathway in Rat Brain Endothelial Cells Requires Cross-talk with Notch Signaling

The transport of monocarboxylate fuels such as lactate, pyruvate, and ketone bodies across brain endothelial cells is mediated by monocarboxylic acid transporter 1 (MCT1). Although the canonical Wnt/β-catenin pathway is required for rodent blood-brain barrier development and for the expression of associated nutrient transporters, the role of this pathway in the regulation of brain endothelial MCT1 is unknown. Here we report expression of nine members of the frizzled receptor family by the RBE4 rat brain endothelial cell line. Furthermore, activation of the canonical Wnt/β-catenin pathway in RBE4 cells via nuclear β-catenin signaling with LiCl does not alter brain endothelialMct1mRNA but increases the amount of MCT1 transporter protein. Plasma membrane biotinylation studies and confocal microscopic examination of mCherry-tagged MCT1 indicate that increased transporter results from reduced MCT1 trafficking from the plasma membrane via the endosomal/lysosomal pathway and is facilitated by decreased MCT1 ubiquitination following LiCl treatment. Inhibition of the Notch pathway by the γ-secretase inhibitorN-[N-(3,5-difluorophenacetyl)-l-alanyl]-S-phenylglycinet-butyl ester negated the up-regulation of MCT1 by LiCl, demonstrating a cross-talk between the canonical Wnt/β-catenin and Notch pathways. Our results are important because they show, for the first time, the regulation of MCT1 in cerebrovascular endothelial cells by the multifunctional canonical Wnt/β-catenin and Notch signaling pathways.

Engineering growth factors for regenerative medicine applications

Growth factors are important morphogenetic proteins that instruct cell behavior and guide tissue repair and renewal. Although their therapeutic potential holds great promise in regenerative medicine applications, translation of growth factors into clinical treatments has been hindered by limitations including poor protein stability, low recombinant expression yield, and suboptimal efficacy. This review highlights current tools, technologies, and approaches to design integrated and effective growth factor-based therapies for regenerative medicine applications. The first section describes rational and combinatorial protein engineering approaches that have been utilized to improve growth factor stability, expression yield, biodistribution, and serum half-life, or alter their cell trafficking behavior or receptor binding affinity. The second section highlights elegant biomaterial-based systems, inspired by the natural extracellular matrix milieu, that have been developed for effective spatial and temporal delivery of growth factors to cell surface receptors. Although appearing distinct, these two approaches are highly complementary and involve principles of molecular design and engineering to be considered in parallel when developing optimal materials for clinical applications.

STATEMENT OF SIGNIFICANCE

Growth factors are promising therapeutic proteins that have the ability to modulate morphogenetic behaviors, including cell survival, proliferation, migration and differentiation. However, the translation of growth factors into clinical therapies has been hindered by properties such as poor protein stability, low recombinant expression yield, and non-physiological delivery, which lead to suboptimal efficacy and adverse side effects. To address these needs, researchers are employing clever molecular and material engineering and design strategies to both improve the intrinsic properties of growth factors and effectively control their delivery into tissue. This review highlights examples of interdisciplinary tools and technologies used to augment the therapeutic potential of growth factors for clinical applications in regenerative medicine.

Caveolin-1 regulates osteoclast differentiation by suppressing cFms degradation

Caveolae are flask-shaped cell-surface membranes, which consist of cholesterol, sphingolipids and caveolin proteins. In a microarray analysis, we found that caveolin-1 (Cav-1) was upregulated by receptor activator of NFκB ligand (RANKL), the osteoclast differentiation factor. Silencing of Cav-1 inhibited osteoclastogenesis and also decreased the activation of mitogen-activated protein kinase and the induction of NFATc1 by RANKL. Cav-1 knockdown suppressed the expression of cFms and RANK, two major receptors for osteoclastogenesis. Interestingly, cFms expression was decreased only at the protein level, not at the messenger RNA (mRNA) level, whereas RANK expression was decreased at both the mRNA and protein levels. Furthermore, Cav-1 deficiency increased the lysosomal degradation of cFms. Taken together, these results demonstrate that Cav-1-dependent cFms stabilization contributes to efficient osteoclastogenesis.

Luteolin is effective in the non-small cell lung cancer model with L858R/T790M EGF receptor mutation and erlotinib resistance

BACKGROUND AND PURPOSE

Non-small cell lung cancer (NSCLC) is one of the most commonly diagnosed malignancies in the world. Small-molecule inhibitors of the EGF receptor's tyrosine kinase domain (TKIs), including gefitinib and erlotinib, have been widely used for treating NSCLC. Unfortunately, nearly all patients after initially experiencing a marked improvement while on these drugs, eventually progress to acquire resistance to TKIs. Because there is no effective therapeutic strategy to treat TKI-resistant NSCLC, we evaluated the effects of luteolin, a naturally occurring flavanoid, on T790M mutant NSCLC cells.

EXPERIMENTAL APPROACH

The effect of luteolin on the viability of NSCLC and normal cell lines was investigated using the Cell Counting Kit-8 (CCK-8) assay. Luteolin-induced apoptosis was assessed by bivariate FITC-annexin V/PI assay, and Western blots were used to measured apoptotic proteins. Co-immunoprecipitation was used to determine the effect of luteolin on the interaction between Hsp90 and mutant EGF receptors. The effect of luteolin on the Akt/mTOR pathway was studied using Western blotting analysis. Its anti-tumour efficacy in vivo was examined in a mouse xenograft model.

KEY RESULTS

Luteolin exerted significant anti-tumourigenic effects on the EGF receptor L858R/T790M mutation and erlotinib-resistant NSCLC both at the cellular and animal levels. Mechanistically, luteolin induced degradation of the EGF receptor by inhibiting the association of Hsp90 with the mutant EGF receptor, and, therefore, prevented PI3K/Akt/mTOR signalling, which resulted in NSCLC cell apoptosis.

CONCLUSION AND IMPLICATIONS

Luteolin may be a potential candidate for NSCLC therapy, especially for treatment of patients with acquired erlotinib-resistant NSCLC.

The TWEAK Receptor Fn14 Is an Src-Inducible Protein and a Positive Regulator of Src-Driven Cell Invasion

The TNF receptor superfamily member Fn14 (TNFRSF12A) is the sole signaling receptor for the proinflammatory cytokine TWEAK (TNFSF12).

TWEAK

Fn14 engagement stimulates multiple signal transduction pathways, including the NF-κB pathway, and this triggers important cellular processes (e.g., growth, differentiation, migration, and invasion). The TWEAK-Fn14 axis is thought to be a major physiologic mediator of tissue repair after acute injury. Various studies have revealed that Fn14 is highly expressed in many solid tumor types, and that Fn14 signaling may play a role in tumor growth and metastasis. Previously, it was shown that Fn14 levels are frequently elevated in non-small cell lung cancer (NSCLC) tumors and cell lines that exhibit constitutive EGFR phosphorylation (activation). Furthermore, elevated Fn14 levels increased NSCLC cell invasion in vitro and lung metastatic tumor colonization in vivo. The present study reveals that EGFR-mutant NSCLC cells that express high levels of Fn14 exhibit constitutive activation of the cytoplasmic tyrosine kinase Src, and that treatment with the Src family kinase (SFK) inhibitor dasatinib decreases Fn14 gene expression at both the mRNA and protein levels. Importantly, siRNA-mediated depletion of the SFK member Src in NSCLC cells also decreases Fn14 expression. Finally, expression of the constitutively active v-Src oncoprotein in NIH 3T3 cells induces Fn14 gene expression, and NIH 3T3/v-Src cells require Fn14 expression for full invasive capacity.

IMPLICATIONS

These results indicate that oncogenic Src may contribute to Fn14 overexpression in solid tumors, and that Src-mediated cell invasion could potentially be inhibited with Fn14-targeted therapeutics.

Ubiquitin-specific protease USP2-45 acts as a molecular switch to promote α2δ-1-induced downregulation of Cav1.2 channels

Availability of voltage-gated calcium channels (Ca_v) at the plasma membrane is paramount to maintaining the calcium homeostasis of the cell. It is proposed that the ubiquitylation/de-ubiquitylation balance regulates the density of ion channels at the cell surface. Voltage-gated calcium channels Ca_v1.2 have been found to be ubiquitylated under basal conditions both in vitro and in vivo. In a previous study, we have shown that Ca_v1.2 channels are ubiquitylated by neuronal precursor cell-expressed developmentally downregulated 4 (Nedd4-1) ubiquitin ligases, but the identity of the counterpart de-ubiquitylating enzyme remained to be elucidated. Regarding sodium and potassium channels, it has been reported that the action of the related isoform Nedd4-2 is counteracted by the ubiquitin-specific protease (USP) 2-45. In this study, we show that USP 2-45 also de-ubiquitylates Ca_v channels. We co-expressed USPs and Ca_v1.2 channels together with the accessory subunits β₂ and α₂δ-1, in tsA-201 and HEK-293 mammalian cell lines. Using whole-cell current recordings and surface biotinylation assays, we show that USP2-45 specifically decreases both the amplitude of Ca_v currents and the amount of Ca_v1.2 subunits inserted at the plasma membrane. Importantly, co-expression of the α₂δ-1 accessory subunit is necessary to support the effect of USP2-45. We further show that USP2-45 promotes the de-ubiquitylation of both Ca_v1.2 and α₂δ-1 subunits. Remarkably, α₂δ-1, but not Ca_v1.2 nor β₂, co-precipitated with USP2-45. These results suggest that USP2-45 binding to α₂δ-1 promotes the de-ubiquitylation of both Ca_v1.2 and α₂δ-1 subunits, in order to regulate the expression of Ca_v1.2 channels at the plasma membrane.

Ubiquitination of pattern recognition receptors in plant innate immunity

Lacking an adaptive immune system, plants largely rely on plasma membrane-resident pattern recognition receptors (PRRs) to sense pathogen invasion. The activation of PRRs leads to the profound immune responses that coordinately contribute to the restriction of pathogen multiplication. Protein post-translational modifications dynamically shape the intensity and duration of the signalling pathways. In this review, we discuss the specific regulation of PRR activation and signalling by protein ubiquitination, endocytosis and degradation, with a particular focus on the bacterial flagellin receptor FLS2 (flagellin sensing 2) in Arabidopsis.

Enteropathogenic Escherichia coli dynamically regulates EGFR signaling in intestinal epithelial cells

The diarrheagenic pathogen enteropathogenic Escherichia coli (EPEC) dynamically modulates the survival of infected host intestinal epithelial cells. In the initial stages of infection, several prosurvival signaling events are activated in host cells. These include the phosphorylation of epidermal growth factor receptor (EGFR) and the consequent activation of the phosphatidylinositol-3 kinase/Akt pathway. While studying this pathway in infected epithelial cells, we observed EGFR depletion at later stages of infection, followed subsequently by a decrease in phospho-EGFR. EGFR loss was not dependent on receptor phosphorylation, or on canonical proteasome- and lysosome-dependent processes. Although a type III secretion mutant (ΔescN) stimulated EGFR phosphorylation, it failed to induce receptor degradation. To identify the specific EPEC effector molecule(s) that influenced EGFR stability, epithelial cells infected with isogenic mutant EPEC strains were examined. An EPEC ΔespF strain failed to induce EGFR degradation, whereas EPEC ΔespZ accentuated receptor loss in infected cells. Given the known and contrasting effects of EspF and EspZ on caspase activation, and the known role of proteases in cleaving EGFR, we explored the effect of caspase inhibitors on infection-dependent EGFR loss. The pan-caspase inhibitor Q-VD-OPh blocked EPEC-induced EGFR cleavage in a dose-dependent manner. Taken together, our data suggest that EPEC EspF stimulates caspase-dependent EGFR cleavage and loss, whereas EspZ inhibits this process. Whereas EGFR phosphorylation contributes to the survival of host cells early in infection, EspF-driven caspase activation and consequent EGFR loss likely induce a precipitous increase in host cell death later in the infectious process.

Extracellular signal-regulated kinases 1/2 and Akt contribute to triclosan-stimulated proliferation of JB6 Cl 41-5a cells

Triclosan is a broad spectrum anti-bacterial agent widely used in many personal care products, household items, medical devices, and clinical settings. Human exposure to triclosan is mainly through oral and dermal routes. In previous studies, we found that sub-chronic dermal exposure of B6C3F1 mice to triclosan induced epidermal hyperplasia and focal necrosis; however, the mechanisms for these responses remain elusive. In this study, using mouse epidermis-derived JB6 Cl 41-5a cells, we found that triclosan stimulated cell growth in a concentration- and time-dependent manner. Enhanced cell proliferation was demonstrated by a substantial increase in the percentage of BrdU-positive cells, an elevation in the protein levels of cyclin D1 and cyclin A, and a reduction in the protein level of p27(Kip1). Western blotting analysis revealed that triclosan induced the activation of extracellular signal-regulated kinases 1/2 (ERK1/2), c-Jun N-terminal kinases (JNK), p38, and Akt. Pre-treatment of the cells with PD184352, an inhibitor of the upstream kinase MEK1/2, or with wortmannin, an inhibitor of phosphoinositide 3-kinase, blocked triclosan-mediated phosphorylation of ERK1/2 and Akt, respectively, and substantially suppressed triclosan-stimulated cell proliferation, whereas the JNK inhibitor SP600125 or the p38 inhibitor SB203580 had little to no effect on triclosan-stimulated cell proliferation. The phosphorylation activation of ERK1/2 and Akt was further confirmed on the skin of mice dermally administered triclosan. These data suggest that the activation of ERK1/2 and Akt is involved in triclosan-stimulated proliferation of JB6 Cl 41-5a cells.

Ubiquitin ligase Cbl-b acts as a negative regulator in discoidin domain receptor 2 signaling via modulation of its stability

Discoidin domain receptor 2 (DDR2), a collagen receptor tyrosine kinase, initiates signal transduction upon collagen binding, but little is known as to how DDR2 signaling is negatively regulated. Herein we demonstrate that Cbl family member Cbl-b predominantly promotes the ubiquitination of DDR2 upon collagen II stimulation. Cbl-b-mediated ubiquitination accelerates the degradation of activated DDR2. Finally, the production of MMP-13, a downstream target of DDR2, is enhanced in Cbl-b-knocked down MC3T3-E1 cells and Cbl-b-deficient mouse primary synovial fibroblasts. Thus, Cbl-b, by promoting the ubiquitination and degradation of DDR2, functions as a negative regulator in the DDR2 signaling pathway.

Electroporation and microinjection successfully deliver single-stranded and duplex DNA into live cells as detected by FRET measurements

Förster resonance energy transfer (FRET) technology relies on the close proximity of two compatible fluorophores for energy transfer. Tagged (Cy3 and Cy5) complementary DNA strands forming a stable duplex and a doubly-tagged single strand were shown to demonstrate FRET outside of a cellular environment. FRET was also observed after transfecting these DNA strands into fixed and live cells using methods such as microinjection and electroporation, but not when using lipid based transfection reagents, unless in the presence of the endosomal acidification inhibitor bafilomycin. Avoiding the endocytosis pathway is essential for efficient delivery of intact DNA probes into cells.

Cell and molecular biology of epidermal growth factor receptor

The epidermal growth factor receptor (EGFR) has been one of the most intensely studied cell surface receptors due to its well-established roles in developmental biology, tissue homeostasis, and cancer biology. The EGFR has been critical for creating paradigms for numerous aspects of cell biology, such as ligand binding, signal transduction, and membrane trafficking. Despite this history of discovery, there is a continual stream of evidence that only the surface has been scratched. New ways of receptor regulation continue to be identified, each of which is a potential molecular target for manipulating EGFR signaling and the resultant changes in cell and tissue biology. This chapter is an update on EGFR-mediated signaling, and describes some recent developments in the regulation of receptor biology.