Stabilization of AURKA by the E3 ubiquitin ligase CBLC in lung adenocarcinoma.

CBL family proteins (CBL, CBLB and CBLC in mammals) are E3 ubiquitin ligases of protein tyrosine kinases. CBL mediates the lysosomal degradation of activated EGFR through K63-linked ubiquitination, while CBLC has an oncogenic function by positively regulating EGFR activation through K6 and K11-linked ubiquitination in EGFR mutant lung adenocarcinoma (LAD). Here, we used immunoprecipitation and mass spectrometry to study the CBLC interactome, and found that CBLC is also involved in cell cycle regulation by stabilizing Aurora kinase A (AURKA). CBLC interacted with the kinase domain of AURKA and positively regulated the stability of AURKA by conjugating monoubiquitination and K11/K63-linked polyubiquitination, which are protective from degrading K11/K48 polyubiquitination. CBLC depletion markedly decreased the half-life of AURKA in cycloheximide-treated LAD cells. When LAD cells were synchronized with double thymidine block at the G1/S boundary and then released into mitotic arrest, CBLC depletion delayed the accumulation and activation of AURKA and prevented cancer cells from entering mitosis. CBLC deficiency significantly delayed cell cycle progression, reduced the mitotic population, and increased apoptosis of LAD cells. Targeting CBLC inhibited tumor growth of LAD cells and enhanced their sensitivity to paclitaxel in xenograft models. Immunohistochemical staining of the tissue microarray also revealed a positive correlation between the expression of CBLC and AURKA in normal and LAD tissues, further supporting the positive regulation of AURKA expression by CBLC. In summary, these findings indicate that the oncogenic E3 ligase CBLC plays a role in mitotic entry by stabilizing AURKA via ubiquitination in LAD. This work demonstrates that targeting CBLC combined with paclitaxel might be a potential option for the treatment of LAD patients who have no available targeted therapies.

Alisertib inhibits migration and invasion of EGFR-TKI resistant cells by partially reversing the epithelial-mesenchymal transition.

Epithelial growth factor receptor (EGFR) tyrosine kinase inhibitors (TKIs) have been widely used in the clinical treatment of non-small cell lung cancer (NSCLC) patients with EGFR mutations. Previous studies have shown that Aurora kinase A (AURKA) is overexpressed in a broad spectrum of cancer cells, which can induce epithelial-mesenchymal transition (EMT) and contribute to the occurrence of acquired EGFR-TKI resistance. However, whether the inhibition of AURKA could overcome EGFR-TKI resistance or reverse the EMT in TKI-resistant NSCLC cells remains unclear. In the current study, we established three EGFR-TKI-resistant cell lines and analyzed their expression profiles by RNA sequencing. The results revealed that the EMT pathway is significantly upregulated in the three cell lines with EGFR-TKI resistance. The phosphorylation of AURKA at Thr 288 was also upregulated, suggesting that the activation of AURKA plays an important role in the occurrence of EGFR-TKI resistance. Interestingly, the AURKA inhibitor, alisertib treatment restored the susceptibility of resistant cells to EGFR-TKIs and partially reversed the EMT process, thereby reducing migration and invasion in EGFR-TKI-resistant cells. This study provides evidence that targeting AURKA signaling pathway by alisertib may be a novel approach for overcoming EGFR-TKI resistance and for the treatment of metastatic EGFR-TKIs in NSCLC patients.

Upregulation of E3 Ubiquitin Ligase CBLC Enhances EGFR Dysregulation and Signaling in Lung Adenocarcinoma.

CBLC (CBL proto-oncogene c) belongs to the CBL protein family, which has E3 ubiquitin ligase activity toward activated receptor tyrosine kinases. CBLC is frequently upregulated in non-small cell lung cancer (NSCLC), yet very little is known about the functions of CBLC in tumorigenesis. Here we show that CBLC is an epigenetically demethylated target and its expression can be upregulated in NSCLC after treatment with the DNA methylation inhibitor 5'-azacytidine. Depletion of CBLC significantly inhibited cell viability and clonogenicity in vitro and reduced tumor growth in a xenograft model. CBLC silencing further sensitized EGFR-mutated NSCLC cells to treatment with tyrosine kinase inhibitors. Conversely, ectopic expression of CBLC enhanced the activation of EGFR and downstream ERK1/2 signaling after ligand stimulation by competing with CBL for EGFR binding. Analysis of ubiquitin linkages on activated EGFR (aEGFR) revealed that CBLC ubiquitinated and positively regulated aEGFR stability through the conjugation of polyubiquitin by K6 and K11 linkages. This CBLC-mediated polyubiquitination promoted either preferential recycling of aEGFR back to the plasma membrane or trafficking to the cell nucleus. IHC analyses revealed a positive correlation between phospho-EGFR and CBLC in lung adenocarcinoma. In summary, we demonstrate a novel mechanism by which aEGFR escapes lysosomal degradation in a CBLC/ubiquitin-dependent manner to sustain its activation. Our work identifies CBLC as a potential diagnostic biomarker and also points to its utilization as a novel therapeutic target for NSCLC therapy.Significance: This work demonstrates the role of CBLC expression as a diagnostic biomarker and potential therapeutic target in lung adenocarcinoma. Cancer Res; 78(17); 4984-96. ©2018 AACR.

YAP1 is essential for tumor growth and is a potential therapeutic target for EGFR-dependent lung adenocarcinomas.

Epidermal growth factor receptor (EGFR) mutations are found in lung adenocarcinomas leading to tumor cells proliferation and survival. EGFR tyrosine kinase inhibitors (TKIs) that block EGFR activity are effective therapeutics for EGFR-mutant lung adenocarcinoma patients, but TKI-resistance inevitably occurs. The YES-associated protein (YAP1) transcription coactivator has been implicated as an oncogene and is amplified in human cancers and provides tumor cells strong proliferation and survival cues. This study investigated the roles of YAP1 in lung adenocarcinoma by exploring its regulation and functions mediated by EGFR signaling. In this study, we detected a correlation between YAP1 level and EGFR mutation status in lung adenocarcinoma tissues. Using lung adenocarcinoma cell lines, enhanced YAP1 expression and activity mediated by EGFR signaling was detected through enhanced protein stability. A SRC family protein, YES, was involved in EGFR-regulated YAP1 expression and this pathway was crucial for proliferation in EGFR-dependent cells. Small molecules that reduced YAP1 levels by mechanisms bypassing EGFR signaling were effective in reducing viability in EGFR-dependent cells including those with EGFR T790M, the major cause of TKI-resistance. These observations unveiled the significance of YAP1 in EGFR mutant lung adenocarcinomas and identified YAP1 as a promising therapeutic target for EGFR-dependent lung adenocarcinoma patients, including those with EGFR T790M-caused TKI resistance.

Brain metastases in patients with non-small cell lung cancer: the role of mutated-EGFRs with an exon 19 deletion or L858R point mutation in cancer cell dissemination.

Non-small cell lung cancer (NSCLC) patients tend to develop brain metastases (BM), but the link between BM occurrence and driver mutations in NSCLC is not very clear. We explored whether activating mutations of epidermal growth factor receptors (EGFRs) in exon 19 deletion or L858R predict BM in NSCLC. A retrospective multivariable logistic regression analysis of 384 patients demonstrated that the presence of mutated-EGFRs was associated with overall BM (OR=2.24, P=0.001) compared to that of wild-type EGFR (WT-EGFR). Moreover, the time-to-event analysis model considering death as a competing risk revealed that, irrespective of survival, mutated-EGFRs predicted subsequent BM (SBM) in stage IIIB-IV patients (37.1% vs. 10.6%, HR=2.98, P=0.002) after adjusting for age (HR=2.00, P=0.012), gender, histological subtype, and smoking history. Notably, the younger mutated-EGFR subgroup was at a higher risk for SBM compared to the older WT-EGFR one (58.1% vs.10.9%, HR=6.57, P<0.001). Additionally, EGFR exon 19 deletion, despite having a slightly longer overall survival (20.6 vs. 14.2 months, P=0.368), was comparable to L858R mutation in predicting SBM (39.5% vs. 34.5%, HR=0.91, P=0.770). In vitro, the overexpression of mutated-EGFRs induced morphological changes towards a mesenchymal-like phenotype and promoted mobility in lung cancer cells. Clinically, mutated-EGFR NSCLC displayed a higher proportion of vimentin-positive expression (75.3% vs. 51.2%; P=0.007) and a shorter median time to SBM (23.5 months vs. not reached, P=0.017) than WT-EGFR NSCLC. These results suggest that NSCLC patients carrying mutated-EGFRs may require a higher frequency of brain imaging assessments than those with WT-EGFR to facilitate earlier SBM detection during follow-up.

Epigenetic Switch between SOX2 and SOX9 Regulates Cancer Cell Plasticity.

Cell differentiation within stem cell lineages can check proliferative potential, but nodal pathways that can limit tumor growth are obscure. Here, we report that lung cancer cell populations generate phenotypic and oncogenic plasticity via a switch between differentiation programs controlled by SOX2 and SOX9, thus altering proliferative and invasive capabilities. In lung cancer cells, SOX2 bound the EPCAM promoter to induce EpCAM-p21Cip1-cyclin A2 signaling, encouraging cell proliferation as well as barrier properties. In contrast, SOX9 bound the SLUG promoter to induce SLUG-mediated cell invasion with a spindle-like phenotype. Pharmacologic inhibition of HDAC elevated a SOX9-positive cell population from SOX2-positive cells, whereas ectopic expression of SOX2 inhibited SOX9 with increased H3K9me2 levels on the SOX9 promoter. In clinical specimens, the expression of SOX2 and SOX9 correlated negatively and positively with lung tumor grade, respectively. Our findings identify SOX2 and SOX9 as nodal epigenetic regulators in determining cancer cell plasticity and metastatic progression. Cancer Res; 76(23); 7036-48. ©2016 AACR.

Hedgehog pathway maintains cell survival under stress conditions, and drives drug resistance in lung adenocarcinoma.

Hedgehog (HH) pathway plays an important role in embryonic development, but is largely inactive in adult except for tissue repair. Aberrant activation of HH pathway has been found in a variety of cancer types. In non-small cell lung cancer, however, the role and importance of HH pathway remain controversial. In the current study, we found that HH pathway was maintained in low activity in lung adenocarcinoma (LAC) cells under normal culture condition, but was highly induced in response to stress conditions. Activation of HH pathway promoted cell survival, growth, and invasion partially through HGF and MET signaling. Hedgehog-Interacting Protein (HHIP), a cell-surface negative regulator of HH pathway, was epigenetically silenced in LAC. Overexpression of HHIP blocked the activation of HH and HGF/MET pathways, and made cells significantly more susceptible to stress conditions. In LAC cells with acquired resistance to Epidermal Growth Factor Receptor Tyrosin Kinase Inhibitor (EGFR-TKI), we found that a part of tumor cells were much more sensitive to HH or HGF/MET inhibitors, suggesting an oncogenic addiction shift from EGFR to HH and HGF/MET pathways. In conclusion, this study showed that HH pathway is a survival signaling that drives LAC cell growth under stress conditions, and HHIP is a key regulator to block the induction of HH pathway. Targeting the HH pathway through inhibitors or HHIP thus holds promise to address EGFR-TKI resistance in LAC in clinic.

EGFR promotes lung tumorigenesis by activating miR-7 through a Ras/ERK/Myc pathway that targets the Ets2 transcriptional repressor ERF.

MicroRNAs (miRNA) mediate distinct gene regulatory pathways triggered by epidermal growth factor receptor (EGFR) activation, which occurs commonly in lung cancers with poor prognosis. In this study, we report the discovery and mechanistic characterization of the miRNA miR-7 as an oncogenic "oncomiR" and its role as a key mediator of EGFR signaling in lung cancer cells. EGFR activation or ectopic expression of Ras as well as c-Myc stimulated miR-7 expression in an extracellular signal-regulated kinase (ERK)-dependent manner, suggesting that EGFR induces miR-7 expression through a Ras/ERK/Myc pathway. In support of this likelihood, c-Myc bound to the miR-7 promoter and enhanced its activity. Ectopic miR-7 promoted cell growth and tumor formation in lung cancer cells, significantly increasing the mortality of nude mice hosts, which were orthotopically implanted with lung cancers. Quantitative proteomic analysis revealed that miR-7 decreased levels of the Ets2 transcriptional repression factor ERF, the coding sequence of which was found to contain a miR-7 complementary sequence. Indeed, ectopic miR-7 inhibited production of ERF messages with a wild-type but not a silently mutated coding sequence, and ectopic miR-7 rescued growth arrest produced by wild-type but not mutated ERF. Together, these results identified that ERF is a direct target of miR-7 in lung cancer. Our findings suggest that miR-7 may act as an important modulator of EGFR-mediated oncogenesis, with potential applications as a novel prognostic biomarker and therapeutic target in lung cancer.

Expression of axl in lung adenocarcinoma and correlation with tumor progression.

We used the Transwell system to select highly invasive cell lines from minimally invasive parent cells, and we compared gene expression in paired cell lines with high and low invasive potentials. Axl was relatively overexpressed in the highly invasive cell lines when compared with their minimally invasive counterparts. However, there is only limited information about the role of Axl in cancer invasion. The biologic function of Axl in tumor invasion was investigated by overexpression of full-length Axl in minimally invasive cells and by siRNA knockdown of Axl expression in highly invasive cells. Overexpression of Axl in minimally invasive cells increased their invasiveness. siRNA reduced cell invasiveness as Axl was downregulated in highly invasive cells. We further investigated the protein expression of Axl by immunohistochemistry and its correlation with clinicopathologic features. Data from a study of 58 patient specimens showed that Axl immunoreactivity was statistically significant with respect to lymph node status (P < .0001) and the patient's clinical stage (P < .0001). Our results demonstrate that Axl protein kinase seems to play an important role in the invasion and progression of lung cancer.

Inhibition of invasion and angiogenesis by zinc-chelating agent disulfiram.

Cell invasion and angiogenesis are crucial processes in cancer metastasis that require extracellular matrix (ECM) degradation. Proteolytic degradation of the ECM components is a central event of invasion and angiogenesis processes. During these processes, matrix metalloproteinases (MMPs) seem to be primarily responsible for much of the ECM degradation. Disulfiram is frequently used in the treatment of alcoholism and has been reported to possess antiretroviral activity and can eject intrinsic zinc out of human immunodeficiency virus (HIV) nucleocapsid protein. In this report, we show that disulfiram inhibited invasion and angiogenesis in both tumor and endothelial cells at nontoxic concentrations. The 3H-labeled type IV collagen degradation assay suggested that disulfiram has type IV collagenase inhibitory activity, and this inhibition was responsible for blocking invasion and angiogenesis through cell-mediated and non-cell-mediated pathways. However, the mechanisms underlying cell-mediated signal pathways are not fully characterized. Our data demonstrate that the non-cell-mediated pathway is dominant. Thus, disulfiram could directly interact with MMP-2 and MMP-9 and inhibit their proteolytic activity through a zincchelating mechanism. Addition of zinc could reverse the inhibition of invasiveness and collagenase inhibition through disulfiram treatment. This finding implies that MMP-2 and MMP-9 may be the inhibitory targets for a potential disulfiram treatment. These observations raise the possibility clinical therapeutic applications for disulfiram used as a potential inhibitor of metastatic cell invasion and angiogenesis.