Altered splicing of ATG16-L1 mediates acquired resistance to tyrosine kinase inhibitors of EGFR by blocking autophagy in non-small cell lung cancer.

Despite the initial efficacy of using tyrosine kinase inhibitors of epidermal growth factor receptors (EGFR-TKIs) for treating patients with non-small cell lung cancer (NSCLC), resistance inevitably develops. Recent studies highlight a link between alternative splicing and cancer drug response. Therefore, we aimed to identify deregulated splicing events that play a role in resistance to EGFR-TKI. By using RNA sequencing, reverse-transcription PCR (RT-PCR), and RNA interference, we showed that overexpression of a splice variant of the autophagic gene ATG16-L1 that retains exon 8 and encodes the ß-isoform of autophagy-related protein 16-1 (ATG16-L1 ß) concurs acquired resistance to EGFR-TKI in NSCLC cells. Using matched biopsies, we found increased levels of ATG16-L1 ß at the time of progression in 3 of 11 NSCLC patients treated with EGFR-TKI. Mechanistically, gefitinib-induced autophagy was impaired in resistant cells that accumulated ATG16-L1 ß. Neutralization of ATG16-L1 ß restored autophagy in response to gefitinib, induced apoptosis, and inhibited the growth of in ovo tumor xenografts. Conversely, overexpression of ATG16-L1 ß in parental sensitive cells prevented gefitinib-induced autophagy and increased cell survival. These results support a role of defective autophagy in acquired resistance to EGFR-TKIs and identify splicing regulation of ATG16-L1 as a therapeutic vulnerability that could be explored for improving EGFR-targeted cancer therapy.

ARF promotes the degradation of the Epidermal Growth Factor Receptor by the lysosome.

Epidermal Growth Factor Receptor (EGFR) signaling regulates multiple cellular processes including proliferation, survival and apoptosis, and is attenuated by lysosomal receptor degradation. EGFR is a potent oncogene and activating mutations of EGFR are critical determinants of oncogenic transformation as well as therapeutic targets in non-small cell lung cancer. We previously demonstrated that wild type and mutant EGFRs repress the expression of the ARF tumor suppressor to promote the survival of lung tumor cells. In this study, using transient transfection systems in CHO EGFR-null cells as well as in various lung tumor cell lines carrying wild type or activated mutant EGFR, we show that ARF downregulates the expression of EGFR protein by reducing its half life. In wild type EGFR cells, ARF promotes canonical lysosomal degradation of the receptor through enhanced phosphorylation of EGFR-Y1045 and Cbl-Y731. In contrast, in mutant EGFR cells, ARF induces EGFR degradation by activating a non-canonical AKT-dependent lysosomal pathway. Taken together, these results uncover a feedback loop by which ARF may control EGFR turnover to restrain oncogenic signaling. They also highlight distinct degradation promoting pathways between wild type and mutant EGFRs in response to ARF.

Nuclear translocation of IGF1R by intracellular amphiregulin contributes to the resistance of lung tumour cells to EGFR-TKI.

Many Receptor Tyrosine Kinases translocate from the cell surface to the nucleus in normal and pathological conditions, including cancer. Here we report the nuclear expression of insulin-like growth factor-1 receptor (IGF1R) in primary human lung tumours. Using lung cancer cell lines and lung tumour xenografts, we demonstrate that the epidermal growth factor receptor-tyrosine kinase inhibitor (EGFR-TKI) gefitinib induces the nuclear accumulation of IGF1R in mucinous lung adenocarcinoma by a mechanism involving the intracellular re-localization of the growth factor amphiregulin. Amphiregulin allows the binding of IGF1R to importin-ß1 and promotes its nuclear transport. The nuclear accumulation of IGF1R by amphiregulin induces cell cycle arrest through p21WAF1/CIP1 upregulation, and prevents the induction of apoptosis in response to gefitinib. These results identify amphiregulin as the first nuclear localization signal-containing protein that interacts with IGF1R and allows its nuclear translocation. Furthermore they indicate that nuclear expression of IGF1R contributes to EGFR-TKI resistance in lung cancer.

Development of autologous cytotoxic CD4+ T clones in a human model of B-cell non-Hodgkin follicular lymphoma.

Immunotherapy for cancer aims to generate cytotoxic cells that are capable of eradicating tumour cells. It has been well demonstrated that helper, non-cytotoxic CD4(+) T cells are important for the induction and maintenance of anti-tumour immunity exerted by cytotoxic CD8(+) T cells. In contrast, the existence of direct anti-tumour, effector cytotoxic CD4(+) T cells remains elusive, mainly due to the paucity of reliable experimental data, especially in human B-cell non-Hodgkin lymphomas. This study developed an appropriate, autologous follicular B-cell non-Hodgkin follicular lymphoma model, including the in vitro establishment of a malignant, human leucocyte antigen class I (HLA-I) deficient B-cell line, and the generation of three autologous anti-tumour cytotoxic CD4(+) T-cell clones originating from the peripheral blood of the same patient. These three clones were considered as tumour specific, because they were capable of killing the malignant, HLA-I-deficient B-cell line through a classical HLA-II restricted perforin-mediated pathway, but did not lyse the Epstein-Barr virus-infected autologous normal B lymphocytes. All three CD4(+)clones were T-cell receptor Vbeta17-Dbeta1-Jbeta1.2 and exhibited an identical complementarity-determining region 3, suggesting the immunodominance of a single peptide antigen presented by tumour cells. Such lymphoma models would provide a useful tool for in vivo expansion and the adoptive transfer of selected CD4(+) cytotoxic cells in immunotherapeutic strategies.

Quantitating effector and regulatory T lymphocytes in immune responses by limiting dilution analysis modeling.

Although there is currently no doubt that regulatory lymphocytes represent a master player in the immune system, a major unresolved problem is the accurate quantitation of these cells among unfractionated cell populations. This difficulty mainly arises because there are no specific immunophenotypic markers that can reliably discriminate between effector and regulatory lymphocytes. To face this problem, we have developed computational models of limiting dilution analyses addressing the question of the accurate estimation of the frequencies of effector and regulatory cells functionally engaged in an immune response. A set of generic equations were provided to form a framework for modeling limiting dilution data, enabling discrimination between qualitatively different models of suppression. These models include either one or two subpopulations of regulatory cells, featured by either low or potent regulatory activity. The potential of this modeling approach was illustrated by the accurate determination of the frequencies of effector and regulatory T lymphocytes in one real limiting dilution experiment of CD4+ CD25+ T lymphocytes performed in the context of an allogeneic response in the human system. The crucial advantage of the limiting dilution method over the "static, phenotype-based" method is the dynamic evaluation of effector and regulatory T cell biology through their actual functional activity.