cbl-b inhibits epidermal growth factor receptor signaling

HUNK as a key regulator of tumor-associated macrophages in triple negative breast cancer

Triple-negative breast cancer (TNBC) lacks the expression of estrogen receptor (ER), progesterone receptor (PR), and human epidermal growth factor receptor 2 (HER2). TNBC tumors are not sensitive to endocrine therapy, and standardized TNBC treatment regimens are lacking. TNBC is a more immunogenic subtype of breast cancer, making it more responsive to immunotherapy intervention. Tumor-associated macrophages (TAMs) constitute one of the most abundant immune cell populations in TNBC tumors and contribute to cancer metastasis. This study examines the role of the protein kinase HUNK in tumor immunity. Gene expression analysis using NanoString's nCounter PanCancer Immune Profiling panel identified that targeting HUNK is associated with changes in the IL-4/IL-4 R cytokine signaling pathway. Experimental analysis shows that HUNK kinase activity regulates IL-4 production in mammary tumor cells, and this regulation is dependent on STAT3. In addition, HUNK-dependent regulation of IL-4 secreted from tumor cells induces polarization of macrophages into an M2-like phenotype associated with TAMs. In return, IL-4 induces cancer metastasis and macrophages to produce epidermal growth factor. These findings delineate a paracrine signaling exchange between tumor cells and TAMs regulated by HUNK and dependent on IL-4/IL-4 R. This highlights the potential of HUNK as a target for reducing TNBC metastasis through modulation of the TAM population.

The ubiquitin ligases Cbl and Cbl-b regulate macrophage growth by controlling CSF-1R import into macropinosomes

The ubiquitination of transmembrane receptors regulates endocytosis, intracellular traffic, and signal transduction. Bone marrow-derived macrophages from myeloid Cbl-/- and Cbl-b-/- double knockout (DKO) mice display sustained proliferation mirroring the myeloproliferative disease that these mice succumb to. Here, we found that the ubiquitin ligases Cbl and Cbl-b have overlapping functions for controlling the endocytosis and intracellular traffic of the CSF-1R. DKO macrophages displayed complete loss of ubiquitination of the CSF-1R whereas partial ubiquitination was observed for either single Cbl-/- or Cbl-b-/- macrophages. Unlike wild type, DKO macrophages were immortal and displayed slower CSF-1R internalization, elevated AKT signaling, and a failure to transport the CSF-1R into the lumen of nascent macropinosomes, leaving its cytoplasmic region available for signaling. CSF-1R degradation depended upon lysosomal vATPase activity in both WT and DKO macrophages, with this degradation confined to macropinosomes in WT but occurring in distributed/tubular lysosomes in DKO cells. RNA-sequencing comparison of Cbl-/-, Cbl-b-/- and DKO macrophages indicated that while the overall macrophage transcriptional program remained intact, DKO macrophages had alterations in gene expression associated with growth factor signaling, cell cycle, inflammation and senescence. Cbl-b-/- had minimal effect on the transcriptional program whereas Cbl-/- led to more alternations but only DKO macrophages demonstrated substantial changes in the transcriptome, suggesting overlapping but unique functions for the two Cbl-family members. Thus, Cbl/Cbl-b-mediated ubiquitination of CSF-1R regulates its endocytic fate, constrains inflammatory gene expression, and regulates signaling for macrophage proliferation.

E3 ubiquitin ligases in lung cancer: Emerging insights and therapeutic opportunities

Aim In this review, we have attempted to provide the readers with an updated account of the role of a family of proteins known as E3 ligases in different aspects of lung cancer progression, along with insights into the deregulation of expression of these proteins during lung cancer. A detailed account of the therapeutic strategies involving E3 ligases that have been developed or currently under development has also been provided in this review. MATERIALS AND METHODS: The review article employs extensive literature search, along with differential gene expression analysis of lung cancer associated E3 ligases using the DESeq2 package in R, and the Gene Expression Profiling Interactive Analysis (GEPIA) database (http://gepia.cancer-pku.cn/). Protein expression analysis of CPTAC lung cancer samples was carried out using the UALCAN webtool (https://ualcan.path.uab.edu/index.html). Assessment of patient overall survival (OS) in response to high and low expression of selected E3 ligases was performed using the online Kaplan-Meier plotter (https://kmplot.com/analysis/index.php?p=background). KEY FINDINGS: SIGNIFICANCE: The review provides an in-depth understanding of the role of E3 ligases in lung cancer progression and an up-to-date account of the different therapeutic strategies targeting oncogenic E3 ligases for improved lung cancer management.

Cbl and Cbl-b independently regulate EGFR through distinct receptor interaction modes

Highly homologous E3 ubiquitin ligases, Cbl and Cbl-b, mediate ubiquitination of EGF receptor (EGFR), leading to its endocytosis and lysosomal degradation. Cbl and Cbl-b, are thought to function in a redundant manner by binding directly to phosphorylated Y1045 (pY1045) of EGFR and indirectly via the Grb2 adaptor. Unexpectedly, we found that inducible expression of Cbl or Cbl-b mutants lacking the E3 ligase activity but fully capable of EGFR binding does not significantly affect EGFR ubiquitination and endocytosis in human oral squamous cell carcinoma (HSC3) cells which endogenously express Cbl-b at a relatively high level. Each endogenous Cbl species remained associated with ligand-activated EGFR in the presence of an overexpressed counterpart species or its mutant, although Cbl-b overexpression partially decreased Cbl association with EGFR. Binding to pY1045 was the preferential mode for Cbl-b:EGFR interaction, whereas Cbl relied mainly on the Grb2-dependent mechanism. Overexpression of the E3-dead mutant of Cbl-b slowed down EGF-induced degradation of active EGFR, while this mutant and a similar mutant of Cbl did not significantly affect MAPK/ERK1/2 activity. EGF-guided chemotaxis migration of HSC3 cells was diminished by overexpression of the E3-dead Cbl-b mutant but was not significantly affected by the E3-dead Cbl mutant. By contrast, the inhibitory effect of the same Cbl mutant on the migration of OSC-19 cells expressing low Cbl-b levels was substantially stronger than that of the Cbl-b mutant. Altogether, our data demonstrate that Cbl and Cbl-b may operate independently through different modes of EGFR binding to jointly control receptor ubiquitination, endocytic trafficking, and signaling.

Targeting the Cbl-b-Notch1 axis as a novel immunotherapeutic strategy to boost CD8+ T-cell responses

A critical feature of cancer is the ability to induce immunosuppression and evade immune responses. Tumor-induced immunosuppression diminishes the effectiveness of endogenous immune responses and decreases the efficacy of cancer immunotherapy. In this study, we describe a new immunosuppressive pathway in which adenosine promotes Casitas B-lineage lymphoma b (Cbl-b)-mediated Notch1 degradation, causing suppression of CD8+ T-cells effector functions. Genetic knockout and pharmacological inhibition of Cbl-b prevents Notch1 degradation in response to adenosine and reactivates its signaling. Reactivation of Notch1 results in enhanced CD8+ T-cell effector functions, anti-cancer response and resistance to immunosuppression. Our work provides evidence that targeting the Cbl-b-Notch1 axis is a novel promising strategy for cancer immunotherapy.

Hypoxia-mediated down-regulation of miRNAs' biogenesis promotes tumor immune escape in bladder cancer

BACKGROUND

The study examines the function of hypoxia-mediated down-regulation of microRNAs (miRNAs) (mir-30c, mir-135a, and mir-27a) in the process of bladder cancer immune escape.

METHODS

Quantitative Real-time PCR (qRT-PCR) was carried out to determine gene expression levels of Drosha and Dicer under hypoxia treatment, while western blotting and flow cytometry were used to determine protein expression. Seven reported miRNAs were identified via qRT-PCR assay. Flow cytometry detection of CD3/CD4/CD8-positive expression and statistics. Enzyme-linked immunosorbent assay (ELISA) detected cellular immune factors content. Cell apoptosis was checked via flow cytometry assay. Luciferase report assay and western blot assays were both used to verify the relationship between miRNAs and Casitas B-lineage lymphoma proto-oncogene b (Cbl-b). The animal model was established and Hematoxylin-eosin (HE) staining, TdT-mediated dUTP Nick-End Labeling (TUNEL) staining, and immunohistochemistry (IHC) assays were separately used to verify the conclusions.

RESULTS

The CD3 + /CD4 + expression was increased in the hypoxia group, while CD3 + /CD8 + expression, the cellular immune factors content Interleukin-2 (IL-2) and Tumor Necrosis Factor-α (TNFα) along with the cell apoptosis were suppressed. The protein expression of Cbl-b was found to be up-regulated in the hypoxia group. After constructing the overexpression/ knockdown of Cbl-b in peripheral blood mononuclear cell (PBMC), Cbl-b has been found to promote tumor immune escape in bladder cancer. Furthermore, Cbl-b had been identified as the co-targets of mir-30c, mir-135a, and mir-27a and down-regulation of miRNA biogenesis promotes Cbl-b expression and deactivating T cells in vitro/in vivo.

CONCLUSION

Hypoxia-mediated down-regulation of miRNAs' biogenesis promotes tumor immune escape in bladder cancer, which could bring much more advance to the medical research on tumors.

Implications of protein ubiquitination modulated by lncRNAs in gastrointestinal cancers

Long non-coding RNAs (lncRNAs) are a class of RNA transcripts longer than 200 nucleotides and mostly cannot be translated into proteins. Next-generation transcriptome sequencing of various cell types has enabled the annotation of tens of thousands of lncRNAs in human genome. Varying levels of evidence supports the implications of lncRNAs in the onset and progression of cancers. Ubiquitin is an evolutionarily conserved protein and could post-translationally mark a number of proteins. The most important proteolytic role of ubiquitination is degradation of substrate proteins by the 26S proteasome. Compiling evidences demonstrated that lncRNAs are involved in the accurate execution of protein stability programs via the ubiquitin-proteasome system. In the current review, we systematically summarize the detailed mechanisms how lncRNAs modulate ubiquitination of target proteins, regulate cancerous signaling pathways and control tumorigenesis of gastrointestinal cancers. Although there are still considerable studies on unraveling the complicated interactions between lncRNAs and proteins, we believe that lncRNAs are promising but challenging molecules which may strongly facilitate precision cancer therapeutics in the future.

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.

Umbilical mesenchymal stem cell-derived exosomes facilitate spinal cord functional recovery through the miR-199a-3p/145-5p-mediated NGF/TrkA signaling pathway in rats

Background

Although exosomes, as byproducts of human umbilical cord mesenchymal stem cells (hUC-MSCs), have been demonstrated to be an effective therapy for traumatic spinal cord injury (SCI), their mechanism of action remains unclear.

Methods

We designed and performed this study to determine whether exosomes attenuate the lesion size of SCI by ameliorating neuronal injury induced by a secondary inflammatory storm and promoting neurite outgrowth. We determined the absolute levels of all exosomal miRNAs and investigated the potential mechanisms of action of miR-199a-3p/145-5p in inducing neurite outgrowth in vivo and in vitro.

Results

miR-199a-3p/145-5p, which are relatively highly expressed miRNAs in exosomes, promoted PC12 cell differentiation suppressed by lipopolysaccharide (LPS) in vitro through modulation of the NGF/TrkA pathway. We also demonstrated that Cblb was a direct target of miR-199a-3p and that Cbl was a direct target of miR-145-5p. Cblb and Cbl gene knockdown resulted in significantly decreased TrkA ubiquitination levels, subsequently activating the NGF/TrkA downstream pathways Akt and Erk. Conversely, overexpression of Cblb and Cbl was associated with significantly increased TrkA ubiquitination level, subsequently inactivating the NGF/TrkA downstream pathways Akt and Erk. Western blot and coimmunoprecipitation assays confirmed the direct interaction between TrkA and Cblb and TrkA and Cbl. In an in vivo experiment, exosomal miR-199a-3p/145-5p was found to upregulate TrkA expression at the lesion site and also promote locomotor function in SCI rats.

Conclusions

In summary, our study showed that exosomes transferring miR-199a-3p/145-5p into neurons in SCI rats affected TrkA ubiquitination and promoted the NGF/TrkA signaling pathway, indicating that hUC-MSC-derived exosomes may be a promising treatment strategy for SCI.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13287-021-02148-5.

β-Elemene inhibits the metastasis of multidrug-resistant gastric cancer cells through miR-1323/Cbl-b/EGFR pathway

BACKGROUND

β-Elemene is a natural agent extracted from the traditional Chinese herbal medicine Curcuma wenyujin that is a promising novel plant-derived drug with broad-spectrum anticancer activity. Our previous study identified an enhanced capacity for metastasis in multidrug resistant (MDR) gastric cancer and breast cancer cells. However, the anti-metastatic effects of β-Elemene on MDR cancer cells remain unknown.

PURPOSE

In this study, we posit the hypothesis that β-elemene possesses antimetastatic effects on MDR cancer cells.

METHODS

Cell viability assay was used to assess the resistance of SGC7901/ADR cells and the cytotoxic effects of β-Elemene. Wound healing, transwell assay and lung metastatic mice model were used to the anti-metastasis effects of β-Elemene. MicroRNA microarray analysis was used to explore potential regulated miRNAs. Luciferase reporter assay was used to identify the direct target. Human MMP antibody array, western blot, immunoprecipitation, qRT-PCR analyses and immunohistochemistry were conducted to investigate the underlying anti-metastasis mechanism of β-Elemene.

RESULTS

In this study, we found that β-Elemene significantly inhibited the metastatic capacity of MDR gastric cells in vivo and in vitro. Mechanistically, we found that β-Elemene regulated MMP-2/9 expression and reversed epithelial-mesenchymal transition. Further studies showed that β-Elemene upregulated Cbl-b expression, resulting in inhibition of the EGFR-ERK/AKT pathways, which regulate MMP-2/9. Additionally, we confirmed that β-Elemene upregulated Cbl-b by inhibiting miR-1323 expression. Finally, we found that numbers of metastatic tumor nodules were significantly decreased in the lungs of nude mice after β-Elemene treatment.

CONCLUSION

Our results suggested that β-Elemene inhibits the metastasis of MDR gastric cancer cells by modulating the miR-1323/Cbl-b/EGFR signaling axis.

HUNK phosphorylates EGFR to regulate breast cancer metastasis

Epidermal growth factor receptor (EGFR) is commonly over-expressed in metastatic breast cancer yet metastatic breast cancer is generally resistant to anti-EGFR therapies, and the mechanism for resistance to EGFR inhibitors in this setting is not fully understood. Hormonally up-regulated neu-associated kinase (HUNK) kinase is up-regulated in aggressive breast cancers and is thought to play a role in breast cancer metastasis. However, no studies have been conducted to examine a relationship between EGFR and HUNK in breast cancer metastasis. We performed a kinase substrate screen and identified that EGFR is phosphorylated by HUNK. Our studies show that HUNK phosphorylates EGFR at T654, enhancing receptor stability and downstream signaling. We found that increased phosphorylation of T654 EGFR correlates with increased epithelial to mesenchymal, migration and invasion, and metastasis. In addition, we found that HUNK expression correlates with overall survival and distant metastasis free survival. This study shows that HUNK directly phosphorylates EGFR at T654 to promote metastasis and is the first study to show that the phosphorylation of this site in EGFR regulates metastasis.

Defining the "Metastasome": Perspectives from the genome and molecular landscape in colorectal cancer for metastasis evolution and clinical consequences

Metastasis still poses the highest challenge for personalized therapy in cancer, partly due to a still incomplete understanding of its molecular evolution. We recently presented the most comprehensive whole-genome study of colorectal metastasis vs. matched primary tumors and suggested novel components of disease progression and metastasis evolution, some of them potentially relevant for targeted therapy. In this review, we try to put these findings into perspective with latest discoveries of colleagues and recent literature, and propose a systematic international team effort to collectively define the "metastasome", a term we introduce to summarize all genomic, epigenomic, transcriptomic, further -omic, molecular and functional characteristics rendering metastases different from primary tumors. Based on recent discoveries, we propose a revised metastasis model for colorectal cancer which is based on a common ancestor clone, early dissemination but flexible early or late stage clonal separation paralleling stromal interactions. Furthermore, we discuss hypotheses on site-specific metastasis, colorectal cancer progression, metastasis-targeted diagnosis and therapy, and metastasis prevention based on latest metastasome data.

Loss of function Cbl-c mutations in solid tumors

Receptor Tyrosine Kinase (RTK) signaling is essential for normal biological processes and disruption of this regulation can lead to tumor initiation and progression. Cbl proteins (Cbl, Cbl-b and Cbl-c) are a family of RING finger (RF) ubiquitin ligases that negatively regulate a variety of RTKs, including EGFR, MET, and RET. Recent studies have identified Cbl mutations associated with human myeloid neoplasias in approximately 5% of the cases. Cbl-c is the most recently identified human Cbl protein and is expressed exclusively in epithelial cells. We identified a novel cDNA that was isolated from a mouse mammary cancer from the C3(1) Large T Antigen transgenic model. This mutant cDNA encodes a protein that has a deletion in the RF domain of Cbl-c, thereby resembling known Cbl family mutations associated with myeoloid neoplasias. Genomic analysis of both parental and transgenic lines shows no evidence of germline mutation indicating that this mutation is likely a somatic mutation. The mutant protein enhances transformation of NIH 3T3 cells when expressed in combination with SV40 Large T antigen. Together these data are consistent with a second hit mutation. In overexpression studies, this mutant Cbl-c protein fails to mediate ubiquitination of activated EGFR and acts in a dominant negative fashion to prevent ubiquitination and downregulation of the activated EGFR by wild type Cbl proteins. Mechanistically, the mutant Cbl-c binds to the EGFR and prevents recruitment of the wild type Cbl protein. Furthermore, data mining reveals Cbl-c mutations associated with solid tumors in humans. Subsequent cell-based analysis demonstrates a similar loss of E3 function and dominant negative effects for one of these human mutations. These data suggest that like Cbl mutations in myeloid neoplasms, loss of Cbl-c function may contribute to the pathogenesis of solid tumors in murine models and in humans.

Molecular pattern of lncRNAs in hepatocellular carcinoma

Hepatocellular carcinoma (HCC) is one of the most notable lethal malignancies worldwide. However, the molecular mechanisms involved in the initiation and progression of this disease remain poorly understood. Over the past decade, many studies have demonstrated the important regulatory roles of long non-coding RNAs (lncRNAs) in HCC. Here, we comprehensively review recent discoveries regarding HCC-associated lncRNA functions, which we have classified and described according to their mechanism models.

Whole genome sequencing puts forward hypotheses on metastasis evolution and therapy in colorectal cancer

Incomplete understanding of the metastatic process hinders personalized therapy. Here we report the most comprehensive whole-genome study of colorectal metastases vs. matched primary tumors. 65% of somatic mutations originate from a common progenitor, with 15% being tumor- and 19% metastasis-specific, implicating a higher mutation rate in metastases. Tumor- and metastasis-specific mutations harbor elevated levels of BRCAness. We confirm multistage progression with new components ARHGEF7/ARHGEF33. Recurrently mutated non-coding elements include ncRNAs RP11-594N15.3, AC010091, SNHG14, 3’ UTRs of FOXP2, DACH2, TRPM3, XKR4, ANO5, CBL, CBLB, the latter four potentially dual protagonists in metastasis and efferocytosis-/PD-L1 mediated immunosuppression. Actionable metastasis-specific lesions include FAT1, FGF1, BRCA2, KDR, and AKT2-, AKT3-, and PDGFRA-3’ UTRs. Metastasis specific mutations are enriched in PI3K-Akt signaling, cell adhesion, ECM and hepatic stellate activation genes, suggesting genetic programs for site-specific colonization. Our results put forward hypotheses on tumor and metastasis evolution, and evidence for metastasis-specific events relevant for personalized therapy.

The evolution and genetic nature of metastatic lesions is not completely characterized. Here the authors perform a comprehensive whole-genome study of colorectal metastases in comparison to matched primary tumors and define a multistage progression model and metastasis-specific changes that, in part, are therapeutically actionable.

Regulation of immune responses by E3 ubiquitin ligase Cbl-b

Casitas B lymphoma-b (Cbl-b), a RING finger E3 ubiquitin ligase, has been identified as a critical regulator of adaptive immune responses. Cbl-b is essential for establishing the threshold for T cell activation and regulating peripheral T cell tolerance through various mechanisms. Intriguingly, recent studies indicate that Cbl-b also modulates innate immune responses, and plays a key role in host defense to pathogens and anti-tumor immunity. These studies suggest that targeting Cbl-b may represent a potential therapeutic strategy for the management of human immune-related disorders such as autoimmune diseases, infections, tumors, and allergic airway inflammation. In this review, we summarize the latest developments regarding the roles of Cbl-b in innate and adaptive immunity, and immune-mediated diseases.

MicroRNA-891b is an independent prognostic factor of pancreatic cancer by targeting Cbl-b to suppress the growth of pancreatic cancer cells

Growing evidence has revealed that microRNAs could regulate the proliferation of pancreatic ductal adenocarcinoma (PDAC) cells and predict the prognosis of PDAC. Here the comparative microRNA expression profiles of the good and poor prognosis groups were performed by microRNA microarray. MicroRNA-891b (miR-891b) was screened and validated to be a prognostic predictor of PDAC in the initial group and further evaluated to be an independent predictor for the overall survival of resectable PDACs in an independent cohort. By a series of cellular and animal experiments, as well as clinical specimen analyses, miR-891b was confirmed to target the Cbl-b gene, promot the expression of tumor suppressor p21 protein and inhibit the proliferation of PDAC cells. The results provide a theoretical basis for the study of miR-891b as an independent prognostic predictor of PDAC and the role of miR-891b/Cbl-b pathway in this prediction, as well as the identification of new targets for PDAC.

Cbl-b predicts postoperative survival in patients with resectable pancreatic ductal adenocarcinoma

Casitas B-lineage lymphoma b (Cbl-b) is a ubiquitin-protein ligase and a signal transducing adaptor protein involved in immune regulation, and it may be involved in the development and progression of cancer. We investigated the association between Cbl-b expression and prognosis in patients with resectable pancreatic ductal adenocarcinoma (PDAC). The clinicopathological characteristics and survival data of 134 patients with surgery for PDAC between January 2009 and February 2012 were retrospectively evaluated, and Cbl-b expression was assayed by immunohistochemical staining. The association of Cbl-b expression with clinicopathological features and postoperative prognosis was analyzed. Cbl-b expression was strongly associated with the pathological primary tumor (pT) category (P = 0.005) and pathological TNM (pTNM) stage (P = 0.035), but not with other clinicopathological characteristics (all P > 0.05). In addition to current markers including pathological regional lymph nodes (pN) category, CA19-9, and histological differentiation, univariate and multivariate analysis found that Cbl-b was independently associated with overall survival (OS) of patients with resectable PDAC. Cbl-b was predictive of OS in a subgroup of patients with serum CA19-9 ≥ 37 U/mL. Cbl-b expression combined with pN, histological differentiation, and CA19-9 level could be used as a novel clinical model predictive of OS for patients with resectable PDAC. In conclusion, Cbl-b in resectable PDAC was an independent predictor of adverse prognosis. Cbl-b expression together with pN, histological differentiation, and CA19-9 level might lead to improved risk stratification and prognosis for patients with resectable PDAC.

The long noncoding RNA lnc-EGFR stimulates T-regulatory cells differentiation thus promoting hepatocellular carcinoma immune evasion

Long noncoding RNAs play a pivotal role in T-helper cell development but little is known about their roles in Treg differentiation and functions during the progression of hepatocellular carcinoma (HCC). Here, we show that lnc-epidermal growth factor receptor (EGFR) upregulation in Tregs correlates positively with the tumour size and expression of EGFR/Foxp3, but negatively with IFN-γ expression in patients and xenografted mouse models. Lnc-EGFR stimulates Treg differentiation, suppresses CTL activity and promotes HCC growth in an EGFR-dependent manner. Mechanistically, lnc-EGFR specifically binds to EGFR and blocks its interaction with and ubiquitination by c-CBL, stabilizing it and augmenting activation of itself and its downstream AP-1/NF-AT1 axis, which in turn elicits EGFR expression. Lnc-EGFR links an immunosuppressive state to cancer by promoting Treg cell differentiation, thus offering a potential therapeutic target for HCC.

The role of long noncoding RNAs in regulating T-cell differentiation within the tumour microenvironment is unclear. Here the authors identify a lncRNA that, through direct interactions with EGFR, promotes T-regulatory cell differentiation within the microenvironment of hepatocellular carcinoma, thus promoting tumour growth via immune suppression.

Involvement of Cbl-b-mediated macrophage inactivation in insulin resistance

Aging and overnutrition cause obesity in rodents and humans. It is well-known that obesity causes various diseases by producing insulin resistance (IR). Macrophages infiltrate the adipose tissue (AT) of obese individuals and cause chronic low-level inflammation associated with IR. Macrophage infiltration is regulated by the chemokines that are released from hypertrophied adipocytes and the immune cells in AT. Saturated fatty acids are recognized by toll-like receptor 4 (TLR4) and induce inflammatory responses in AT macrophages (ATMs). The inflammatory cytokines that are released from activated ATMs promote IR in peripheral organs, such as the liver, skeletal muscle and AT. Therefore, ATM activation is a therapeutic target for IR in obesity. The ubiquitin ligase Casitas b-lineage lymphoma-b (Cbl-b) appears to potently suppress macrophage migration and activation. Cbl-b is highly expressed in leukocytes and negatively regulates signals associated with migration and activation. Cbl-b deficiency enhances ATM accumulation and IR in aging- and diet-induced obese mice. Cbl-b inhibits migration-related signals and SFA-induced TLR4 signaling in ATMs. Thus, targeting Cbl-b may be a potential therapeutic strategy to reduce the IR induced by ATM activation. In this review, we summarize the regulatory functions of Cbl-b in ATMs.

Resveratrol mediates cell cycle arrest and cell death in human esophageal squamous cell carcinoma by directly targeting the EGFR signaling pathway

Resveratrol is a small polyphenol that has been intensively studied in a wide spectrum of therapeutic fields. More recently, resveratrol has been demonstrated to exert its antitumor activity in numerous tumor models. The present study reported that resveratrol exhibited a marked anti-proliferative effect on human esophageal squamous cell carcinoma (ESCC) cells by inducing cell cycle G₀/G₁ phase arrest and cell death, which was associated with a decrease in the expression levels of cyclin D1 and an increase in cleaved PARP/cleaved caspase-3 expression levels. The mechanisms underlying the antitumor potency of resveratrol were principally attributed to the downregulation of epidermal growth factor receptor (EGFR) signaling. The western blotting results showed that exposure of ESCC cells to resveratrol inhibited EGF-induced EGFR activation in addition to decreasing the total protein levels of EGFR and membrane/nuclear localization. In summary, the results suggested that resveratrol, or an associated analog, may have a role in the management of human ESCC.

E3 ubiquitin ligase Cbl-b negatively regulates C-type lectin receptor-mediated antifungal innate immunity

Innate immune responses mediated by C-type lectin receptors Dectin-2 and Dectin-3 against fungal infections are negatively regulated by Cbl-b ubiquitination.

Activation of various C-type lectin receptors (CLRs) initiates potent proinflammatory responses against various microbial infections. However, how activated CLRs are negatively regulated remains unknown. In this study, we report that activation of CLRs Dectin-2 and Dectin-3 by fungi infections triggers them for ubiquitination and degradation in a Syk-dependent manner. Furthermore, we found that E3 ubiquitin ligase Casitas B–lineage lymphoma protein b (Cbl-b) mediates the ubiquitination of these activated CLRs through associating with each other via adapter protein FcR-γ and tyrosine kinase Syk, and then the ubiquitinated CLRs are sorted into lysosomes for degradation by an endosomal sorting complex required for transport (ESCRT) system. Therefore, the deficiency of either Cbl-b or ESCRT subunits significantly decreases the degradation of activated CLRs, thereby resulting in the higher expression of proinflammatory cytokines and inflammation. Consistently, Cbl-b–deficient mice are more resistant to fungi infections compared with wild-type controls. Together, our study indicates that Cbl-b negatively regulates CLR-mediated antifungal innate immunity, which provides molecular insight for designing antifungal therapeutic agents.

Balancing Protein Stability and Activity in Cancer: A New Approach for Identifying Driver Mutations Affecting CBL Ubiquitin Ligase Activation

Oncogenic mutations in the monomeric Casitas B-lineage lymphoma (Cbl) gene have been found in many tumors, but their significance remains largely unknown. Several human c-Cbl (CBL) structures have recently been solved, depicting the protein at different stages of its activation cycle and thus providing mechanistic insight underlying how stability-activity tradeoffs in cancer-related proteins-may influence disease onset and progression. In this study, we computationally modeled the effects of missense cancer mutations on structures representing four stages of the CBL activation cycle to identify driver mutations that affect CBL stability, binding, and activity. We found that recurrent, homozygous, and leukemia-specific mutations had greater destabilizing effects on CBL states than random noncancer mutations. We further tested the ability of these computational models, assessing the changes in CBL stability and its binding to ubiquitin-conjugating enzyme E2, by performing blind CBL-mediated EGFR ubiquitination assays in cells. Experimental CBL ubiquitin ligase activity was in agreement with the predicted changes in CBL stability and, to a lesser extent, with CBL-E2 binding affinity. Two thirds of all experimentally tested mutations affected the ubiquitin ligase activity by either destabilizing CBL or disrupting CBL-E2 binding, whereas about one-third of tested mutations were found to be neutral. Collectively, our findings demonstrate that computational methods incorporating multiple protein conformations and stability and binding affinity evaluations can successfully predict the functional consequences of cancer mutations on protein activity, and provide a proof of concept for mutations in CBL.

Perspectives on Epidermal Growth Factor Receptor Regulation in Triple-Negative Breast Cancer: Ligand-Mediated Mechanisms of Receptor Regulation and Potential for Clinical Targeting

Currently, there are no effective targeted therapies for triple-negative breast cancer (TNBC) indicating a critical unmet need for breast cancer patients. Tumors that fall into the triple-negative category of breast cancers do not respond to the targeted therapies currently approved for breast cancer treatment, such as endocrine therapy (tamoxifen, aromatase inhibitors) or human epidermal growth factor receptor-2 (HER2) inhibitors (trastuzumab, lapatinib), because these tumors lack the most common breast cancer markers: estrogen receptor, progesterone receptor, and HER2. While many patients with TNBC respond to chemotherapy, subsets of patients fare poorly and relapse very quickly. Studies indicate that epidermal growth factor receptor (EGFR) is frequently overrepresented in TNBC (>50%), suggesting EGFR could be used as a biomarker and target in breast cancer. While it is clear that this growth factor receptor plays an integral role in TNBC, little is known about the mechanisms of sustained EGFR activation and how to target this protein despite availability of EGFR-targeted inhibitors, suggesting that our understanding of EGFR deregulation in TNBC is incomplete.

Temporal proteomics of NGF-TrkA signaling identifies an inhibitory role for the E3 ligase Cbl-b in neuroblastoma cell differentiation

SH-SY5Y neuroblastoma cells respond to nerve growth factor (NGF)-mediated activation of the tropomyosin-related kinase A (TrkA) with neurite outgrowth, thereby providing a model to study neuronal differentiation. We performed a time-resolved analysis of NGF-TrkA signaling in neuroblastoma cells using mass spectrometry-based quantitative proteomics. The combination of interactome, phosphoproteome, and proteome data provided temporal insights into the molecular events downstream of NGF binding to TrkA. We showed that upon NGF stimulation, TrkA recruits the E3 ubiquitin ligase Cbl-b, which then becomes phosphorylated and ubiquitylated and decreases in abundance. We also found that recruitment of Cbl-b promotes TrkA ubiquitylation and degradation. Furthermore, the amount of phosphorylation of the kinase ERK and neurite outgrowth increased upon Cbl-b depletion in several neuroblastoma cell lines. Our findings suggest that Cbl-b limits NGF-TrkA signaling to control the length of neurites.

Lung Tumor Suppressor GPRC5A Binds EGFR and Restrains Its Effector Signaling

GPRC5A is a G-protein-coupled receptor expressed in lung tissue but repressed in most human lung cancers. Studies in Gprc5a(-/-) mice have established its role as a tumor-suppressor function in this setting, but the basis for its role has been obscure. Here, we report that GPRC5A functions as a negative modulator of EGFR signaling. Mouse tracheal epithelial cells (MTEC) from Gprc5a(-/-) mice exhibited a relative increase in EGFR and downstream STAT3 signaling, whereas GPRC5A expression inhibited EGFR and STAT3 signaling. GPRC5A physically interacted with EGFR through its transmembrane domain, which was required for its EGFR inhibitory activity. Gprc5a(-/-) MTEC were much more susceptible to EGFR inhibitors than wild-type MTEC, suggesting their dependence on EGFR signaling for proliferation and survival. Dysregulated EGFR and STAT3 were identified in the normal epithelia of small and terminal bronchioles as well as tumors of Gprc5a(-/-) mouse lungs. Moreover, in these lungs EGFR inhibitor treatment inhibited EGFR and STAT3 activation along with cell proliferation. Finally, overexpression of ectopic GPRC5A in human non-small cell lung carcinoma cells inhibited both EGF-induced and constitutively activated EGFR signaling. Taken together, our results show how GPRC5A deficiency leads to dysregulated EGFR and STAT3 signaling and lung tumorigenesis. Cancer Res; 75(9); 1801-14. ©2015 AACR.

E3 ubiquitin ligase Cbl-b in innate and adaptive immunity

Casitas B-lineage lymphoma proto-oncogene-b (Cbl-b), a RING finger E3 ubiquitin-protein ligase, has been demonstrated to play a crucial role in establishing the threshold for T-cell activation and controlling peripheral T-cell tolerance via multiple mechanisms. Accumulating evidence suggests that Cbl-b also regulates innate immune responses and plays an important role in host defense to pathogens. Understanding the signaling pathways regulated by Cbl-b in innate and adaptive immune cells is therefore essential for efficient manipulation of Cbl-b in emerging immunotherapies for human disorders such as autoimmune diseases, allergic inflammation, infections, and cancer. In this article, we review the latest developments in the molecular structural basis of Cbl-b function, the regulation of Cbl-b expression, the signaling mechanisms of Cbl-b in immune cells, as well as the biological function of Cbl-b in physiological and pathological immune responses in animal models and human diseases.

Enigma prevents Cbl-c-mediated ubiquitination and degradation of RETMEN2A

The Cbl proteins (Cbl, Cbl-b, and Cbl-c) are a highly conserved family of RING finger ubiquitin ligases (E3s) that function as negative regulators of tyrosine kinases in a wide variety of signal transduction pathways. In this study, we identify a new Cbl-c interacting protein, Enigma (PDLIM7). This interaction is specific to Cbl-c as Enigma fails to bind either of its closely related homologues, Cbl and Cbl-b. The binding between Enigma and Cbl-c is mediated through the LIM domains of Enigma as removal of all three LIM domains abrogates this interaction, while only LIM1 is sufficient for binding. Here we show that Cbl-c binds wild-type and MEN2A isoforms of the receptor tyrosine kinase, RET, and that Cbl-c enhances ubiquitination and degradation of activated RET. Enigma blocks Cbl-c-mediated RETMEN2A ubiquitination and degradation. Cbl-c decreased downstream ERK activation by RETMEN2A and co-expression of Enigma blocked the Cbl-c-mediated decrease in ERK activation. Enigma showed no detectable effect on Cbl-c-mediated ubiquitination of activated EGFR suggesting that this effect is specific to RET. Through mapping studies, we show that Cbl-c and Enigma bind RETMEN2A at different residues. However, binding of Enigma to RETMENA prevents Cbl-c recruitment to RETMEN2A. Consistent with these biochemical data, exploratory analyses of breast cancer patients with high expression of RET suggest that high expression of Cbl-c correlates with a good outcome, and high expression of Enigma correlates with a poor outcome. Together, these data demonstrate that Cbl-c can ubiquitinate and downregulate RETMEN2A and implicate Enigma as a positive regulator of RETMEN2A through blocking of Cbl-mediated ubiquitination and degradation.

Myostatin induces insulin resistance via Casitas B-lineage lymphoma b (Cblb)-mediated degradation of insulin receptor substrate 1 (IRS1) protein in response to high calorie diet intake

To date a plethora of evidence has clearly demonstrated that continued high calorie intake leads to insulin resistance and type-2 diabetes with or without obesity. However, the necessary signals that initiate insulin resistance during high calorie intake remain largely unknown. Our results here show that in response to a regimen of high fat or high glucose diets, Mstn levels were induced in muscle and liver of mice. High glucose- or fat-mediated induction of Mstn was controlled at the level of transcription, as highly conserved carbohydrate response and sterol-responsive (E-box) elements were present in the Mstn promoter and were revealed to be critical for ChREBP (carbohydrate-responsive element-binding protein) or SREBP1c (sterol regulatory element-binding protein 1c) regulation of Mstn expression. Further molecular analysis suggested that the increased Mstn levels (due to high glucose or fatty acid loading) resulted in increased expression of Cblb in a Smad3-dependent manner. Casitas B-lineage lymphoma b (Cblb) is an ubiquitin E3 ligase that has been shown to specifically degrade insulin receptor substrate 1 (IRS1) protein. Consistent with this, our results revealed that elevated Mstn levels specifically up-regulated Cblb, resulting in enhanced ubiquitin proteasome-mediated degradation of IRS1. In addition, over expression or knock down of Cblb had a major impact on IRS1 and pAkt levels in the presence or absence of insulin. Collectively, these observations strongly suggest that increased glucose levels and high fat diet, both, result in increased circulatory Mstn levels. The increased Mstn in turn is a potent inducer of insulin resistance by degrading IRS1 protein via the E3 ligase, Cblb, in a Smad3-dependent manner.

Ubiquitin ligase Cbl-b and obesity-induced insulin resistance

Obesity causes type 2 diabetes, atherosclerosis and cardiovascular diseases by inducing systemic insulin resistance. It is now recognized that obesity is related to chronic low-grade inflammation in adipose tissue. Specifically, activated immune cells infiltrate adipose tissue and cause inflammation. There is increasing evidence that activated macrophages accumulate in the hypertrophied adipose tissue of rodents and humans and induce systemic insulin resistance by secreting inflammatory cytokines. Accordingly, a better understanding of the molecular mechanisms underlying macrophage activation in adipose tissue will facilitate the development of new therapeutic strategies. Currently, little is known about the regulation of macrophage activation, although E3 ubiquitin ligase Casitas B-lineage lymphoma (Cbl)-b was identified recently as a novel negative regulator of macrophage activation in adipose tissue. Cbl-b, which is a suppressor of T- and B-cell activation, inhibits intracellular signal transduction by targeting some tyrosine kinases. Notably, preventing Cbl-b-mediated macrophage activation improves obesity-induced insulin resistance in mice. c-Cbl is another member of the Cbl family that is associated with insulin resistance in obesity. These reports suggest that Cbl-b and c-Cbl are potential therapeutic targets for treating obesity-induced insulin resistance. In this review, we focus on the importance of Cbl-b in macrophage activation in aging-induced and high-fat diet-induced obesity.

Cbl-b enhances sensitivity to 5-fluorouracil via EGFR- and mitochondria-mediated pathways in gastric cancer cells

5-Fluorouracil (5-FU) is an essential component of anticancer chemotherapy against gastric cancer. However, the response rate of single drug is still limited. The ubiquitin ligase Cbl-b is a negative regulator of growth factor receptor signaling and is involved in the suppression of cancer cell proliferation. However, whether Cbl-b could affect 5-FU sensitivity remains unclear. The present study showed that Cbl-b knockdown caused higher proliferation concomitant with the decrease of apoptosis induced by 5-FU treatment in gastric cancer cell. Further mechanism investigation demonstrated that Cbl-b knockdown caused significant increase of phosphorylation of EGFR, ERK and Akt, decrease of mitochondrial membrane potential, and increase of expression ratio of Bcl-2/Bax. These results suggest that Cbl-b enhances sensitivity to 5-FU via EGFR- and mitochondria-mediated pathways in gastric cancer cells.

Sustained activation of protein kinase C induces delayed phosphorylation and regulates the fate of epidermal growth factor receptor

It is well established that acute activation of members of the protein kinase C (PKC) family induced by activation of cellular receptors can transduce extracellular stimuli to intracellular signaling. However, the functions of sustained activation of PKC are not well studied. We have previously shown that sustained activation of classical PKC isoforms over 15-60 min induced the formation of the pericentrion, a subset of recycling endosomes that are sequestered perinuclearly in a PKC- and phospholipase D (PLD)-dependent manner. In this study, we investigated the role of this process in the phosphorylation of EGFR on threonine 654 (Thr-654) and in the regulation of intracellular trafficking and fate of epidermal growth factor receptor (EGFR). Sustained stimulation of the angiotensin II receptor induced translocation of the EGFR to the pericentrion, which in turn prevents full access of EGF to the EGFR. These effects required PKC and PLD activities, and direct stimulation of PKC with phorbol esters was sufficient to reproduce these effects. Furthermore, activation of PKC induced delayed phosphorylation of EGFR on Thr-654 that coincided with the formation of the pericentrion and which was dependent on PLD and endocytosis of EGFR. Thus, Thr-654 phosphorylation required the formation of the pericentrion. On the other hand, using a T654A mutant of EGFR, we find that the phosphorylation on Thr-654 was not required for translocation of EGFR to the pericentrion but was required for protection of EGFR from degradation in response to EGF. Taken together, these results demonstrate a novel role for the pericentrion in the regulation of EGFR phosphorylation, which in turn is important for the fates of EGFR.

Role of E3 ubiquitin ligases in lung cancer

E3 ubiquitin ligases are a large family of proteins that catalyze the ubiquitination of many protein substrates for targeted degradation by the 26S proteasome. Therefore, E3 ubiquitin ligases play an essential role in a variety of biological processes including cell cycle regulation, proliferation and apoptosis. E3 ubiquitin ligases are often found overexpressed in human cancers, including lung cancer, and their deregulation has been shown to contribute to cancer development. However, the lack of specific inhibitors in clinical trials is a major issue in targeting E3 ubiquitin ligases with currently only one E3 ubiquitin ligase inhibitor being tested in the clinical setting. In this review, we focus on E3 ubiquitin ligases that have been found deregulated in lung cancer. Furthermore, we discuss the processes in which they are involved and evaluate them as potential anti-cancer targets. By better understanding the mechanisms by which E3 ubiquitin ligases regulate biological processes and their exact role in carcinogenesis, we can improve the development of specific E3 ubiquitin ligase inhibitors and pave the way for novel treatment strategies for cancer patients.

Genomic compartmentalization of gene families encoding core components of metazoan signaling systems

To investigate the role of gene localization and genome organization in cell-cell signalling and regulation, we mapped the distribution pattern of gene families that comprise core components of intercellular communication networks. Our study is centered on the distinct evolutionarily conserved metazoan signalling pathways that employ proteins in the receptor tyrosine kinase, WNT, hedgehog, NOTCH, Janus kinase/STAT, transforming growth factor beta, and nuclear hormone receptor protein families. Aberrant activity of these signalling pathways is closely associated with the promotion and maintenance of human cancers. The cataloguing and mapping of genes encoding these signalling proteins and comparisons across species has led us to propose that the genome can be subdivided into six genome-wide primary linkage groups (PLGs). PLGs are composed of assemblages of gene families that are often mutually exclusive, raising the possibility of unique functional identities for each group. Examination of the localization patterns of genes with distinct functions in signal transduction demonstrates dichotomous segregation patterns. For example, gene families of cell-surface receptors localize to genomic compartments that are distinct from the locations of their cognate ligand gene families. Additionally, genes encoding negative-acting components of signalling pathways (inhibitors and antagonists) are topologically separated from their positive regulators and other signal transducer genes. We, therefore, propose the existence of conserved genomic territories that encode key proteins required for the proper activity of metazoan signaling and regulatory systems. Disruption in this pattern of topologic genomic organization may contribute to aberrant regulation in hereditary or acquired diseases such as cancer. We further propose that long-range looping genomic regulatory interactions may provide a mechanism favouring the remarkable retention of these conserved gene clusters during chordate evolution.

Casitas B lineage lymphoma b is a key regulator of peripheral tolerance in systemic lupus erythematosus

OBJECTIVE

To analyze whether the expression and modulation of T cell receptor (TCR) signaling is dependent on Casitas B lineage lymphoma b (Cbl-b) in T cells from patients with systemic lupus erythematosus (SLE) upon stimulation with a tolerogenic substance.

METHODS

Peripheral blood mononuclear cells were obtained from 20 patients with SLE (active disease or in remission) and 20 healthy controls. Levels of Cbl-b expression were measured using reverse transcription-polymerase chain reaction and Western blotting in peripheral CD4+ T cells from SLE patients and healthy controls upon anergy induction. Cell proliferation was measured using the carboxyfluorescein diacetate succinimidyl ester dilution method. Cytokine production was analyzed by luminometry, and surface expression of activation markers was assessed by flow cytometry. Transfection assays were performed to induce overexpression of Cbl-b, and phosphorylation of TCR-associated kinases was evaluated.

RESULTS

CD4+ T cells from SLE patients displayed resistance to anergy (as evidenced by increased cell proliferation, interleukin-2 production, and expression of activation and costimulatory markers), and this was associated with altered Cbl-b expression. Upon ionomycin treatment, primary T cells showed enhanced MAPK activity and decreased Akt phosphorylation, which was representative of the anergic state. In T cells from lupus patients, Cbl-b overexpression led to increased expression of phosphorylated MAPK, thus indicating the reversibility of anergy resistance.

CONCLUSION

These findings suggest that abnormal peripheral tolerance in SLE is caused by a deficiency in Cbl-b, and that this ubiquitin ligase plays a key role in regulating TCR signaling during the induction of peripheral tolerance.

Cbl-c ubiquitin ligase activity is increased via the interaction of its RING finger domain with a LIM domain of the paxillin homolog, Hic 5

Cbl proteins (Cbl, Cbl-b and Cbl-c) are ubiquitin ligases that are critical regulators of tyrosine kinase signaling. In this study we identify a new Cbl-c interacting protein, Hydrogen peroxide Induced Construct 5 (Hic-5). The two proteins interact through a novel interaction mediated by the RING finger of Cbl-c and the LIM2 domain of Hic-5. Further, this interaction is mediated and dependent on specific zinc coordinating complexes within the RING finger and LIM domain. Binding of Hic-5 to Cbl-c leads to an increase in the ubiquitin ligase activity of Cbl-c once Cbl-c has been activated by Src phosphorylation or through an activating phosphomimetic mutation. In addition, co-transfection of Hic-5 with Cbl-c leads to an increase in Cbl-c mediated ubiquitination of the EGFR. These data suggest that Hic-5 enhances Cbl-c ubiquitin ligase activity once Cbl-c has been phosphorylated and activated. Interactions between heterologous RING fingers have been shown to activate E3s. This is the first demonstration of enhancement of ubiquitin ligase activity of a RING finger ubiquitin ligase by the direct interaction of a LIM zinc coordinating domain.

SH3GL2 is frequently deleted in non-small cell lung cancer and downregulates tumor growth by modulating EGFR signaling

The purpose of this study was to identify key genetic pathways involved in non-small cell lung cancer (NSCLC) and understand their role in tumor progression. We performed a genome wide scanning using paired tumors and corresponding 16 mucosal biopsies from four follow-up lung cancer patients on Affymetrix 250K-NSpI array platform. We found that a single gene SH3GL2 located on human chromosome 9p22 was most frequently deleted in all the tumors and corresponding mucosal biopsies. We further validated the alteration pattern of SH3GL2 in a substantial number of primary NSCLC tumors at DNA and protein level. We also overexpressed wild-type SH3GL2 in three NSCLC cell lines to understand its role in NSCLC progression. Validation in 116 primary NSCLC tumors confirmed frequent loss of heterozygosity of SH3GL2 in overall 51 % (49/97) of the informative cases. We found significantly low (p = 0.0015) SH3GL2 protein expression in 71 % (43/60) primary tumors. Forced overexpression of wild-type (wt) SH3GL2 in three NSCLC cell lines resulted in a marked reduction of active epidermal growth factor receptor (EGFR) expression and an increase in EGFR internalization and degradation. Significantly decreased in vitro (p = 0.0015-0.030) and in vivo (p = 0.016) cellular growth, invasion (p = 0.029-0.049), and colony formation (p = 0.023-0.039) were also evident in the wt-SH3GL2-transfected cells accompanied by markedly low expression of activated AKT(Ser(473)), STAT3 (Tyr(705)), and PI3K. Downregulation of SH3GL2 interactor USP9X and activated ß-catenin was also evident in the SH3GL2-transfected cells. Our results indicate that SH3GL2 is frequently deleted in NSCLC and regulates cellular growth and invasion by modulating EGFR function.

Akap200 suppresses the effects of Dv-cbl expression in the Drosophila eye

The Drosophila melanogaster orthologue of the c-Cbl proto-oncogene acts to downregulate signalling from receptor tyrosine kinases by enhancing endocytosis of activated receptors. Expression of an analogue of the C-terminally truncated v-Cbl oncogene, Dv-cbl, in the developing Drosophila eye conversely leads to excess signalling and disruption to the well-ordered adult compound eye. Co-expression of activated Ras with Dv-cbl leads to a severe disruption of eye development. We have used a transposon-based inducible expression system to screen for molecules that can suppress the Dv-cbl phenotype and have identified an allele that upregulates the A-kinase anchoring protein, Akap200. Overexpression of Akap200 not only suppresses the phenotype caused by Dv-cbl expression, but also the severe disruption to eye development caused by the combined expression of Dv-cbl and activated Ras. Akap200 is also endogenously expressed in the developing Drosophila eye at a level that modulates the effects of excessive signalling caused by expression of Dv-cbl.

Targeting erbB receptors

Our work is concerned with the origins and therapy of human cancers. Members of the epidermal growth factor receptor (EGFR) family of tyrosine kinases, also known as erbB or HER receptors, are over expressed and/or activated in many types of human tumors and represent important therapeutic targets in cancer therapy. Studies from our laboratory identified targeted therapy as a way to treat cancer. Rational therapeutics targeting and disabling erbB receptors have been developed to reverse the malignant properties of tumors. Reversal of the malignant phenotype, best seen with disabling the HER2 receptors using monoclonal antibodies is a distinct process from that seen with blocking of ligand binding to cognate receptors as has been done for EGFr receptors. Here we review the mechanisms of action deduced from a number of approaches developed in our laboratory and elsewhere, including monoclonal antibodies, peptide mimetics, recombinant proteins and small molecules. The biochemical and biological principles which have been uncovered during these studies of disabling HER2 homomeric or HER2-EGFr heteromeric receptors will help the development of novel and more efficient therapeutics targeting erbB family receptors.

The B-lymphoid Grb2 interaction code

The growth factor receptor-bound protein 2 (Grb2) is a ubiquitously expressed and evolutionary conserved adapter protein possessing a plethora of described interaction partners for the regulation of signal transduction. In B lymphocytes, the Grb2-mediated scaffolding function controls the assembly and subcellular targeting of activating as well as inhibitory signalosomes in response to ligation of the antigen receptor. Also, integration of simultaneous signals from B-cell coreceptors that amplify or attenuate antigen receptor signal output relies on Grb2. Hence, Grb2 is an essential signal integrator. The key question remains, however, of how pathway specificity can be maintained during signal homeostasis critically required for the balance between immune cell activation and tolerance induction. Here, we summarize the molecular network of Grb2 in B cells and introduce a proteomic approach to elucidate the interactome of Grb2 in vivo.

Role of TI-VAMP and CD82 in EGFR cell-surface dynamics and signaling

The v-SNARE TI-VAMP (VAMP7) mediates exocytosis during neuritogenesis, phagocytosis and lysosomal secretion. It localizes to endosomes and lysosomes but also to the trans-Golgi network. Here we show that depletion of TI-VAMP enhances the endocytosis of activated EGF receptor (EGFR) without affecting constitutive endocytosis of EGFR, or transferrin uptake. This increased EGFR internalization is mainly clathrin dependent. Searching for defects in EGFR regulators, we found that TI-VAMP depletion reduces the cell surface amount of CD82, a tetraspanin known to control EGFR localization in microdomains. We further show that TI-VAMP is required for secretion from the Golgi apparatus to the cell surface, and that TI-VAMP-positive vesicles transport CD82. Quantum dots video-microscopy indicates that depletion of TI-VAMP, or its cargo CD82, restrains EGFR diffusion and the area explored by EGFR at the cell surface. Both depletions also impair MAPK signaling and enhance endocytosis of activated EGFR by increased recruitment of AP-2. These results highlight the role of TI-VAMP in the secretory pathway of a tetraspanin, and support a model in which CD82 allows EGFR entry in microdomains that control its clathrin-dependent endocytosis and signaling.

CBL is frequently altered in lung cancers: its relationship to mutations in MET and EGFR tyrosine kinases

Background

Non-small cell lung cancer (NSCLC) is a heterogeneous group of disorders with a number of genetic and proteomic alterations. c-CBL is an E3 ubiquitin ligase and adaptor molecule important in normal homeostasis and cancer. We determined the genetic variations of c-CBL, relationship to receptor tyrosine kinases (EGFR and MET), and functionality in NSCLC.

Methods and Findings

Using archival formalin-fixed paraffin embedded (FFPE) extracted genomic DNA, we show that c-CBL mutations occur in somatic fashion for lung cancers. c-CBL mutations were not mutually exclusive of MET or EGFR mutations; however they were independent of p53 and KRAS mutations. In normal/tumor pairwise analysis, there was significant loss of heterozygosity (LOH) for the c-CBL locus (22%, n = 8/37) and none of these samples revealed any mutation in the remaining copy of c-CBL. The c-CBL LOH also positively correlated with EGFR and MET mutations observed in the same samples. Using select c-CBL somatic mutations such as S80N/H94Y, Q249E and W802* (obtained from Caucasian, Taiwanese and African-American samples, respectively) transfected in NSCLC cell lines, there was increased cell viability and cell motility.

Conclusions

Taking the overall mutation rate of c-CBL to be a combination as somatic missense mutation and LOH, it is clear that c-CBL is highly mutated in lung cancers and may play an essential role in lung tumorigenesis and metastasis.

CBL is frequently altered in lung cancers: its relationship to mutations in MET and EGFR tyrosine kinases

The mechanisms of hypertrophic scar formation are not fully understood. We previously screened the differentially expressed genes of human hypertrophic scar tissue and identified P311 gene as upregulated. As the activities of P311 in human fibroblast function are unknown, we examined the distribution of it and the effects of forced expression or silencing of expression of P311. P311 expression was detected in fibroblast-like cells from the hypertrophic scar of burn injury patients but not in peripheral blood mononuclear cells, bone marrow mesenchymal stem cells, epidermal cells or normal skin dermal cells. Transfection of fibroblasts with P311 gene stimulated the expression of alpha-smooth muscle actin (α-SMA), TGF-β1 and α1(I) collagen (COL1A1), and enhanced the contraction of fibroblast populated collagen lattices (FPCL). In contrast, interference of fibroblast P311 gene expression decreased the TGF-β1 mRNA expression and reduced the contraction of fibroblasts in FPCL. These results suggest that P311 may be involved in the pathogenesis of hypertrophic scar via induction of a myofibroblastic phenotype and of functions such as TGF-β1 expression. P311 could be a novel target for the control of hypertrophic scar development.

Roles of E3 ubiquitin ligases in cell adhesion and migration

Recent studies have demonstrated that a number of E3 ubiquitin ligases, including Cbl, Smurf1, Smurf2, HDM2, BCA2, SCF(beta-TRCP) and XRNF185, play important roles in cell adhesion and migration. Cbl negatively regulates cell adhesion via alpha integrin and Rap1 and inhibits actin polymerization by ubiquitinating mDab1 and WAVE2. Smurf1 regulates cell migration through ubiquitination of RhoA, talin head domain and hPEM2, while Smurf2 ubiquitinates Smurf1, TGFbeta type I receptor and RaplB to modulate cell migration and adhesion. HDM2 negatively regulates cell migration by targeting NFAT (a transcription factor) for ubiquitination and degradation, while SCF(beta-TRCP) ubiquitinates Snail (a transcriptional repressor of E-cadherin) to inhibit cell migration. TRIM32 promotes cell migration through ubiquitination of Abl interactor 2 (Abi2), a tumor suppressor. RNF5 and XRNF185 modulate cell migration by ubiquitinating paxillin. Thus, these E3 ubiquitin ligases regulate cell adhesion and (or) migration through ubiquitination of their specific substrates.

G protein-coupled receptor 30 expression is up-regulated by EGF and TGF alpha in estrogen receptor alpha-positive cancer cells

In the present study, we evaluated the regulation of G protein-coupled receptor (GPR)30 expression in estrogen receptor (ER)-positive endometrial, ovarian, and estrogen-sensitive, as well as tamoxifen-resistant breast cancer cells. We demonstrate that epidermal growth factor (EGF) and TGF alpha transactivate the GPR30 promoter and accordingly up-regulate GPR30 mRNA and protein levels only in endometrial and tamoxifen-resistant breast cancer cells. These effects exerted by EGF and TGF alpha were dependent on EGF receptor (EGFR) expression and activation and involved phosphorylation of the Tyr(1045) and Tyr(1173) EGFR sites. Using gene-silencing experiments and specific pharmacological inhibitors, we have ascertained that EGF and TGF alpha induce GPR30 expression through the EGFR/ERK transduction pathway, and the recruitment of c-fos to the activator protein-1 site located within GPR30 promoter sequence. Interestingly, we show that functional cross talk of GPR30 with both activated EGFR and ER alpha relies on a physical interaction among these receptors, further extending the potential of estrogen to trigger a complex stimulatory signaling network in hormone-sensitive tumors. Given that EGFR/HER2 overexpression is associated with tamoxifen resistance, our data may suggest that ligand-activated EGFR could contribute to the failure of tamoxifen therapy also by up-regulating GPR30, which in turn could facilitates the action of estrogen. In addition, important for resistance is the ability of tamoxifen to bind to and activate GPR30, the expression of which is up-regulated by EGFR activation. Our results emphasize the need for new endocrine agents able to block widespread actions of estrogen without exerting any stimulatory activity on transduction pathways shared by the steroid and growth factor-signaling networks.

Transcript level modulates the inherent oncogenicity of RET/PTC oncoproteins

Mutations to the RET proto-oncogene occur in as many as one in three cases of thyroid cancer and have been detected in both the medullary (MTC) and the papillary (PTC) forms of the disease. Of the nearly 400 chromosomal rearrangements resulting in oncogenic fusion proteins that have been identified to date, the rearrangements that give rise to RET fusion oncogenes in PTC remain the paradigm for chimeric oncoprotein involvement in solid tumors. RET-associated PTC tumors are phenotypically indolent and relatively less aggressive than RET-related MTCs. The mechanism(s) contributing to the differences in oncogenicity of RET-related MTC and PTC remains unexplained. Here, through cellular and molecular characterization of the two most common RET/PTC rearrangements (PTC1 and PTC3), we show that RET/PTC oncoproteins are highly oncogenic when overexpressed, with the ability to increase cell proliferation and transformation. Further, RET/PTCs activate similar downstream signaling cascades to wild-type RET, although at different levels, and are relatively more stable as they avoid lysosomal degradation. Absolute quantitation of transcript levels of RET, CCDC6, and NCOA4 (the 5' fusion genes involved in PTC1 and PTC3, respectively) suggest that these rearrangements result in lower RET expression in PTCs relative to MTCs. Together, our findings suggest PTC1 and PTC3 are highly oncogenic proteins when overexpressed, but result in indolent disease compared with RET-related MTCs due to their relatively low expression from the NCOA4 and CCDC6 promoters in vivo.