Induction of Cbl-dependent epidermal growth factor receptor degradation in Ling Zhi-8 suppressed lung cancer.

Activating mutation of epidermal growth factor receptor (EGFR) is correlated with malignant lung tumor. In our study, we demonstrated that recombinant LZ-8 (rLZ-8), a medicinal mushroom Ganoderma lucidum protein, induced cell cycle arrest and apoptosis by downregulating the expression of wild-type and mutated EGFR and inhibiting EGFR downstream effectors, AKT and ERK1/2 in lung cancer cells. We showed that rLZ-8 effectively inhibited lung cancer progression and suppressed EGFR expression of lung tumor lesions in mouse model. Functional studies revealed that rLZ-8 reduced the amount of EGFR in cell membranes by altering EGFR localization to enhance the EGF-induced degradation of EGFR. Mechanistically, we demonstrated that rLZ-8 bound to EGFR to induce EGFR autophosphorylation at tyrosine1045 and trigger ubiquitination by inducing the formation of EGFR/Cbl complexes, resulting in the degradation of EGFR; however, Cbl-shRNA abolished rLZ-8-induced EGFR degradation. We provide the first evidence showing that rLZ-8 inhibits growth and induces apoptosis of lung cancer cells by promoting EGFR degradation. The current findings therefore suggest a novel anti-cancer function of rLZ-8 that targeting EGFR overexpression or mutation as well as EGFR-dependent processes in cancer cells.

Casitas B-lineage lymphoma linker helix mutations found in myeloproliferative neoplasms affect conformation.

BACKGROUND: Casitas B-lineage lymphoma (Cbl or c-Cbl) is a RING ubiquitin ligase that negatively regulates protein tyrosine kinase (PTK) signalling. Phosphorylation of a conserved residue (Tyr371) on the linker helix region (LHR) between the substrate-binding and RING domains is required to ubiquitinate PTKs, thereby flagging them for degradation. This conserved Tyr is a mutational hotspot in myeloproliferative neoplasms. Previous studies have revealed that select point mutations in Tyr371 can potentiate transformation in cells and mice but not all possible mutations do so. To trigger oncogenic potential, Cbl Tyr371 mutants must perturb the LHR-substrate-binding domain interaction and eliminate PTK ubiquitination. Although structures of native and pTyr371-Cbl are available, they do not reveal how Tyr371 mutations affect Cbl's conformation. Here, we investigate how Tyr371 mutations affect Cbl's conformation in solution and how this relates to Cbl's ability to potentiate transformation in cells. RESULTS: To explore how Tyr371 mutations affect Cbl's properties, we used surface plasmon resonance to measure Cbl mutant binding affinities for E2 conjugated with ubiquitin (E2-Ub), small angle X-ray scattering studies to investigate Cbl mutant conformation in solution and focus formation assays to assay Cbl mutant transformation potential in cells. Cbl Tyr371 mutants enhance E2-Ub binding and cause Cbl to adopt extended conformations in solution. LHR flexibility, RING domain accessibility and transformation potential are associated with the extent of LHR-substrate-binding domain perturbation affected by the chemical nature of the mutation. More disruptive mutants like Cbl Y371D or Y371S are more extended and the RING domain is more accessible, whereas Cbl Y371F mimics native Cbl in solution. Correspondingly, the only Tyr371 mutants that potentiate transformation in cells are those that perturb the LHR-substrate-binding domain interaction. CONCLUSIONS: c-Cbl's LHR mutations are only oncogenic when they disrupt the native state and fail to ubiquitinate PTKs. These findings provide new insights into how LHR mutations deregulate c-Cbl.

Deltex1 promotes protein kinase Cθ degradation and sustains Casitas B-lineage lymphoma expression.

The generation of T cell anergy is associated with upregulation of ubiquitin E3 ligases including Casitas B-lineage lymphoma (Cbl-b), Itch, gene related to anergy in lymphocyte, and deltex1 (DTX1). These E3 ligases attenuate T cell activation by targeting to signaling molecules. For example, Cbl-b and Itch promote the degradation of protein kinase Cθ (PKCθ) and phospholipase C-γ1 (PLC-γ1) in anergic Th1 cells. How these anergy-associated E3 ligases coordinate during T cell anergy remains largely unknown. In the current study, we found that PKCθ and PLC-γ1 are also downregulated by DTX1. DTX1 interacted with PKCθ and PLC-γ1 and stimulated the degradation of PKCθ and PLC-γ1. T cell anergy-induced proteolysis of PKCθ was prevented in Dtx1(-/-) T cells, supporting the essential role of DTX1 in PKCθ downregulation. Similar to Cbl-b and Itch, DTX1 promoted monoubiquitination of PKCθ. Proteasome inhibitor did not inhibit DTX1-directed PKCθ degradation, but instead DTX1 directed the relocalization of PKCθ into the lysosomal pathway. In addition, DTX1 interacted with Cbl-b and increased the protein levels of Cbl-b. We further demonstrated the possibility that, through the downregulation of PKCθ, DTX1 prevented PKCθ-induced Cbl-b degradation and increased Cbl-b protein stability. Our results suggest the coordination between E3 ligases during T cell anergy; DTX1 acts with Cbl-b to assure a more extensive silencing of PKCθ, whereas DTX1-mediated PKCθ degradation further stabilizes Cbl-b.

Casitas B lymphoma mutations in childhood acute lymphoblastic leukemia.

Casitas B-lineage lymphoma (CBL) proteins are RING finger ubiquitin E3 ligases that attenuate the signaling of receptor tyrosine kinases and are mutated in a number of myeloid disorders. In this study, mutational screening of the linker-RING domains of CBL and CBLB was performed by denaturing high performance liquid chromatography in a cohort of diagnostic (n = 180) or relapse (n = 46) samples from children with acute lymphoblastic leukemia. Somatic mutations were identified in three children, giving an overall incidence of 1.7% and involved small deletions affecting the intron/exon boundaries of exon 8, leading to skipping of exon 8 and abolishing E3 ligase function. Mutated primary samples were associated with constitutive activation of the RAS pathway and sensitivity to MEK inhibitors was shown. Thus, mutation of CBL is an alternative route to activate the RAS pathway and may identify children who are candidates for MEK inhibitor clinical trials.

The Casitas B lineage lymphoma (Cbl) mutant G306E enhances osteogenic differentiation in human mesenchymal stromal cells in part by decreased Cbl-mediated platelet-derived growth factor receptor alpha and fibroblast growth factor receptor 2 ubiquitination.

Human bone marrow-derived mesenchymal stromal cells (hMSCs) have the capacity to differentiate into several cell types including osteoblasts and are therefore an important cell source for bone tissue regeneration. A crucial issue is to identify mechanisms that trigger hMSC osteoblast differentiation to promote osteogenic potential. Casitas B lineage lymphoma (Cbl) is an E3 ubiquitin ligase that ubiquitinates and targets several molecules for degradation. We hypothesized that attenuation of Cbl-mediated degradation of receptor tyrosine kinases (RTKs) may promote osteogenic differentiation in hMSCs. We show here that specific inhibition of Cbl interaction with RTKs using a Cbl mutant (G306E) promotes expression of osteoblast markers (Runx2, alkaline phosphatase, type 1 collagen, osteocalcin) and increases osteogenic differentiation in clonal bone marrow-derived hMSCs and primary hMSCs. Analysis of molecular mechanisms revealed that the Cbl mutant increased PDGF receptor α and FGF receptor 2 but not EGF receptor expression in hMSCs, resulting in increased ERK1/2 and PI3K signaling. Pharmacological inhibition of FGFR or PDGFR abrogated in vitro osteogenesis induced by the Cbl mutant. The data reveal that specific inhibition of Cbl interaction with RTKs promotes the osteogenic differentiation program in hMSCs in part by decreased Cbl-mediated PDGFRα and FGFR2 ubiquitination, providing a novel mechanistic approach targeting Cbl to promote the osteogenic capacity of hMSCs.

Angiopoietin-1-induced ubiquitylation of Tie2 by c-Cbl is required for internalization and degradation.

Tie2 [where 'Tie' is an acronym from tyrosine kinase with Ig and EGF (epidermal growth factor) homology domains] is a receptor tyrosine kinase expressed predominantly on the surface of endothelial cells. Activated by its ligands, the angiopoietins, Tie2 initiates signalling pathways that modulate vascular stability and angiogenesis. Deletion of either the Tie2 or Ang1 (angiopoietin-1) gene in mice results in lethal vascular defects, signifying their importance in vascular development. The mechanism employed by the Tie2 signalling machinery to attenuate or cause receptor trafficking is not well defined. Stimulation of Tie2-expressing cells with Ang1 results in its ubiquitylation, suggesting that this may provide the necessary signal for receptor turnover. Using a candidate molecule approach, we demonstrate that Tie2 co-immunoprecipitates with c-Cbl in an Ang1-dependent manner and its ubiquitylation can be inhibited by the dominant-interfering molecule v-Cbl (a viral form of c-Cbl that contains only the tyrosine kinase-binding domain region). Inhibition of the Tie2-Cbl interaction by overexpression of v-Cbl blocks ligand-induced Tie2 internalization and degradation. In summary, our results illustrate that c-Cbl interacts with the Tie2 signalling complex in a stimulation-dependent manner, and that this interaction is required for Tie2 ubiquitylation, internalization and degradation.

Tumor Fibroblast-Derived FGF2 Regulates Expression of SPRY1 in Esophageal Tumor-Infiltrating T Cells and Plays a Role in T-cell Exhaustion.

T-cell exhaustion was initially identified in chronic infection in mice and was subsequently described in humans with cancer. Although the distinct signature of exhausted T (TEX) cells in cancer has been well investigated, the molecular mechanism of T-cell exhaustion in cancer is not fully understood. Using single-cell RNA sequencing, we report here that TEX cells in esophageal cancer are more heterogeneous than previously clarified. Sprouty RTK signaling antagonist 1 (SPRY1) was notably enriched in two subsets of exhausted CD8+ T cells. When overexpressed, SPRY1 impaired T-cell activation by interacting with CBL, a negative regulator of ZAP-70 tyrosine phosphorylation. Data from the Tumor Immune Estimation Resource revealed a strong correlation between FGF2 and SPRY1 expression in esophageal cancer. High expression of FGF2 was evident in fibroblasts from esophageal cancer tissue and correlated with poor overall survival. In vitro administration of FGF2 significantly upregulated expression of SPRY1 in CD8+ T cells and attenuated T-cell receptor-triggered CD8+ T-cell activation. A mouse tumor model confirmed that overexpression of FGF2 in fibroblasts significantly upregulated SPRY1 expression in TEX cells, impaired T-cell cytotoxic activity, and promoted tumor growth. Thus, these findings identify FGF2 as an important regulator of SPRY1 expression involved in establishing the dysfunctional state of CD8+ T cells in esophageal cancer. SIGNIFICANCE: These findings reveal FGF2 as an important regulator of SPRY1 expression involved in establishing the dysfunctional state of CD8+ T cells and suggest that inhibition of FGF2 has potential clinical value in ESCC. GRAPHICAL ABSTRACT: http://cancerres.aacrjournals.org/content/canres/80/24/5583/F1.large.jpg.

After 95 years, it's time to eRASe JMML.

Juvenile myelomonocytic leukaemia (JMML) is a rare clonal disorder of early childhood. Constitutive activation of the RAS pathway is the initial event in JMML. Around 90% of patients diagnosed with JMML carry a mutation in the PTPN11, NRAS, KRAS, NF1 or CBL genes. It has been demonstrated that after this first genetic event, an additional somatic mutation or epigenetic modification is involved in disease progression. The available genetic and clinical data have enabled researchers to establish relationships between JMML and several clinical conditions, including Noonan syndrome, Ras-associated lymphoproliferative disease, and Moyamoya disease. Despite scientific progress and the development of more effective treatments, JMML is still a deadly disease: the 5-year survival rate is ~50%. Here, we report on recent research having led to a better understanding of the genetic and molecular mechanisms involved in JMML.

Ascorbic acid improves thrombotic function of platelets during living donor liver transplantation by modulating the function of the E3 ubiquitin ligases c-Cbl and Cbl-b.

OBJECTIVE: To investigate the effect of ascorbic acid (AA) on hemostatic function during living donor liver transplantation (LDLT). METHODS: Blood samples from 21 LDLT recipients were taken within 30 minutes after induction and at 120 minutes after reperfusion. Rotational thromboelastography (TEG) and western blot analysis were used to analyze for fibrinolysis and functional changes in c-Cbl and Cbl-b, respectively. TEG test samples were prepared as one of three groups: C group (0.36 mL of blood), N group (0.324 mL of blood + 0.036 mL of 0.9% normal saline), and A group (0.324 mL of blood + 0.036 mL of 200 µmol/L-AA dissolved in 0.9% normal saline). RESULTS: AA decreased fibrinolysis and increased clot rigidity at baseline and 120 minutes after reperfusion. Cbl-b expression was significantly increased at baseline and 120 minutes after reperfusion in the A group compared with the C and N groups. However, c-Cbl phosphorylation was most significantly decreased in the A group at baseline and 120 minutes after reperfusion. CONCLUSION: AA can significantly decrease fibrinolysis and improve clot rigidity in LT recipients during LDLT, and functional changes in Cbl-b and c-Cbl might represent the underlying mechanism. AA may be considered for use during LDLT to decrease hyperfibrinolysis.

Association with HSP90 inhibits Cbl-mediated down-regulation of mutant epidermal growth factor receptors.

Activating mutations in the epidermal growth factor receptor (EGFR), localized in the activation loop within the kinase domain, have been discovered in non-small cell lung cancers (NSCLC). Most of these mutants are exquisitely sensitive to EGFR tyrosine kinase inhibitors, suggesting that they generate receptor dependence in the cancers that express them. 32D cells stably expressing EGFR-L861Q and EGFR-L858R but not wild-type EGFR exhibited ligand-independent receptor phosphorylation and viability. Ligand-induced receptor down-regulation (LIRD) was impaired in mutant-expressing cells. The EGFR mutants were constitutively associated with the E3 ubiquitin ligase Cbl but did not associate with the adaptor protein CIN85 on the addition of ligand. Inhibition of HSP90 activity with geldanamycin restored Cbl function as indicated by receptor ubiquitination and LIRD. These results suggest that EGFR mutants form defective endocytic complexes. In addition, HSP90 plays a role in maintaining the functional conformation of EGFR mutants and protecting activated receptors from LIRD.

Selective modulation of the CAP/Cbl pathway in the adipose tissue of high fat diet treated rats.

A high-fat diet (HFD) is associated with reduced glucose uptake in muscle, but not in adipose tissue. In the present study, we investigated whether a HFD can modulate glucose uptake in adipose tissue by increasing signal transduction through the CAP/Cbl pathway, independently of the PI3-K/Akt pathway. Our results suggest that, in HFD, the differential regulation of insulin-induced glucose uptake between skeletal muscle and adipose tissue may, in part, be a consequence of the CAP/Cbl/C3G pathway, since the expression of CAP and Cbl, and also the activation of this pathway were increased in adipose tissue but not in muscle.

Casitas B-cell lymphoma mutation in childhood T-cell acute lymphoblastic leukemia.

Somatic CBL mutations have been reported in a variety of myeloid neoplasms but are rare in acute lymphoblastic leukemia (ALL). We analyzed 77 samples from hematologic malignancies, identifying a somatic mutation in CBL (p.C381R) in one patient with T-ALL that was associated with a uniparental disomy at the CBL locus and a germline heterozygous mutation in one patient with JMML. Two NOTCH1 mutations and homozygous deletions in LEF1 and CDKN2A were identified in T-ALL cells. The activation of the RAS pathway was enhanced, and activation of the NOTCH1 pathway was inhibited in NIH 3T3 cells that expressed p.C381R. This study appears to be the first to identify a CBL mutation in T-ALL.

Real-time quantitative polymerase chain reaction analysis of patients with refractory chronic periodontitis.

BACKGROUND: Periodontitis is a complex multifactorial disease and is typically polygenic in origin. Genes play a fundamental part in each biologic process forming complex networks of interactions. However, only some genes have a high number of interactions with other genes in the network and may, therefore, be considered to play an important role. In a preliminary bioinformatic analysis, five genes that showed a higher number of interactions were identified and termed leader genes. In the present study, we use real-time quantitative polymerase chain reaction (PCR) technology to evaluate the expression levels of leader genes in the leukocytes of 10 patients with refractory chronic periodontitis and compare the expression levels with those of the same genes in 24 healthy patients. METHODS: Blood was collected from 24 healthy human subjects and 10 patients with refractory chronic periodontitis and placed into heparinized blood collection tubes by personnel trained in phlebotomy using a sterile technique. Blood leukocyte cells were immediately lysed by using a kit for total RNA purification from human whole blood. Complementary DNA (cDNA) synthesis was obtained from total RNA and then real-time quantitative PCR was performed. PCR efficiencies were calculated with a relative standard curve derived from a five cDNA dilution series in triplicate that gave regression coefficients >0.98 and efficiencies >96%. The standard curves were obtained using glyceraldehyde-3-phosphate dehydrogenase (GAPDH) and growth factor receptor binding protein 2 (GRB2), casitas B-lineage lymphoma (CBL), nuclear factor-KB1 (NFKB1), and REL-A (gene for transcription factor p65) gene primers and amplified with 1.6, 8, 40, 200, and 1,000 ng/µL total cDNA. Curves obtained for each sample showed a linear relationship between RNA concentrations and the cycle threshold value of real-time quantitative PCR for all genes. Data were expressed as mean ± SE (SEM). The groups were compared to the analysis of variance. A probability value <0.01 was considered statistically significant. RESULTS: The present study agrees with the preliminary bioinformatics analysis. In our experiments, the association of pathology with the genes was statistically significant for GRB2 and CBL (P <0.01), and it was not statistically significant for REL-A and NFKB1. CONCLUSION: This article lends support to our preliminary hypothesis that assigned an important role in refractory aggressive periodontitis to leader genes.

Methylation of TET2, CBL and CEBPA in Ph-negative myeloproliferative neoplasms.

A loss-of-function mutation of TET2, CBL and CEBPA has been implicated in the pathogenesis or leukaemic transformation of myeloproliferative neoplasm. As tumour suppressor genes may potentially be inactivated by promoter hypermethylation, the authors studied the methylation status of these genes in three cell lines and diagnostic marrow samples from 45 patients with myeloproliferative neoplasm (MPN) (essential thrombocythaemia, N=34; polycythaemia vera, N=7 and primary myelofibrosis, N=4) by methylation-specific PCR. TET2 was heterozygously methylated in MEG-01 and K562 but completely unmethylated in HEL. On the other hand, both CBL and CEBPA were completely unmethylated in all three cell lines. In the primary marrow samples, methylation of TET2 occurred in two (5.9%) patients with essential thrombocythaemia (4.4% of all patients), both without JAK2 V617 mutation, but not in polycythaemia vera or primary myelofibrosis. There was no association between TET2 methylation with the type of MPN (p=0.713). Hypermethylation of CBL or CEBPA was not detected in any patients. In summary, methylation of TET2, CBL and CEBPA is infrequent in MPN at diagnosis. The role of methylation of these genes at the time of leukaemic transformation warrants further study.

Cbl-phosphatidylinositol 3 kinase interaction differentially regulates macrophage colony-stimulating factor-mediated osteoclast survival and cytoskeletal reorganization.

The Cbl protein is a key player in macrophage colony-stimulating factor (M-CSF)-induced signaling. To examine the role of Cbl in M-CSF-mediated cellular events, we used Cbl(YF/YF) knockin mice in which the regulatory tyrosine 737, which when phosphorylated binds to the p85 subunit of phosphatidylinositol 3 kinase (PI3K), is substituted to phenylalanine. In ex vivo cultures, M-CSF and receptor activator of nuclear factor-kappaB ligand-mediated differentiation of bone marrow precursors from Cbl(YF/YF) mice generated increased number of osteoclasts; however, osteoclast numbers in Cbl(YF/YF) cultures were unchanged with increasing doses of M-CSF. We found that Cbl(YF/YF) osteoclasts have enhanced intrinsic ability to survive, and this response was further augmented upon exposure to M-CSF. Treatment of osteoclasts with M-CSF-induced actin reorganization and lamellipodia formation in wild-type osteoclasts; however, in Cbl(YF/YF) osteoclasts lamellipodia formation was compromised. Collectively, these results indicate that abrogation of the Cbl-PI3K interaction, although not affecting M-CSF-induced proliferation and differentiation of precursors, is required for regulation of survival and actin cytoskeletal reorganization of mature osteoclasts.

Regulation of LFA-1-dependent inflammatory cell recruitment by Cbl-b and 14-3-3 proteins.

Inside-out signaling regulation of the beta2-integrin leukocyte function-associated antigen-1 (LFA-1) by different cytoplasmic proteins, including 14-3-3 proteins, is essential for adhesion and migration of immune cells. Here, we identify a new pathway for the regulation of LFA-1 activity by Cbl-b, an adapter molecule and ubiquitin ligase that modulates several signaling pathways. Cbl-b-/- mice displayed increased macrophage recruitment in thioglycollate-induced peritonitis, which was attributed to Cbl-b deficiency in macrophages, as assessed by bone marrow chimera experiments. In vitro, Cbl-b-/- bone marrow-derived mononuclear phagocytes (BMDMs) displayed increased adhesion to endothelial cells. Activation of LFA-1 in Cbl-b-deficient cells was responsible for their increased endothelial adhesion in vitro and peritoneal recruitment in vivo, as the phenotype of Cbl-b deficiency was reversed in Cbl-b-/-LFA-1-/- mice. Consistently, LFA-1-mediated adhesion of BMDM to ICAM-1 but not VLA-4-mediated adhesion to VCAM-1 was enhanced by Cbl-b deficiency. Cbl-b deficiency resulted in increased phosphorylation of T758 in the beta2-chain of LFA-1 and thereby in enhanced association of 14-3-3beta protein with the beta2-chain, leading to activation of LFA-1. Consistently, disruption of the 14-3-3/beta2-integrin interaction abrogated the enhanced ICAM-1 adhesion of Cbl-b-/- BMDMs. In conclusion, Cbl-b deficiency activates LFA-1 and LFA-1-mediated inflammatory cell recruitment by stimulating the interaction between the LFA-1 beta-chain and 14-3-3 proteins.

[Construction of cblN/Zap and its down-regulating effect on TCRzeta protein in Jurkat cells].

AIM: To construct the chimeric cblN/Zap molecule, and to observe its effect on TCRzeta protein in pcDNA3.1(+)-cblN/Zab transfected Jurkat cells. METHODS: Total RNA of Jurkat cells were isolated and reversely transcribed into cDNA, which were used as templates to amplify Zap SH2 by PCR. cblN gene tagged with 24 bp flag was amplified by PCR using pEFHAcbl plasmid encoding human cbl as templates. BamH I and EcoR V restriction enzyme digestion sites were introduced into flank SH2 in pcDNA3.1(+) cblN by overlapping extension PCR. Then pcDNA3.1(+)-cblN/Zap was obtained by replacing SH2 of cblN with ZapSH2. After confirmation by enzyme digestion and sequencing, the recombined vector was stably transfected into Jurkat cells with lipofectin. The expression of flag-cblN/Zap was detected by RT-PCR and Western blot, and its effect on TCRzeta protein was analyzed by Western blot. RESULTS: Restriction enzyme digestion analysis of the pcDNA3.1(+)-cblN/Zap recombinant vector showed that the expected fragments were produced and confirmed by sequencing. pcDNA3.1(+)-cblN/Zap was stably transfected into Jurkat cells and the expression of flag-cblN/Zap in the stable clones was confirmed by both RT-PCR and Western blot. The expressed cblN/Zap down-regulated TCRzeta protein in Jurkat cells. CONCLUSION: Chimeric cblN/Zap is able to down-regulate TCRzeta in Jurkat cells.