Dankert, Erin N.

Abstract One of the greatest barriers to curative treatment of neuroblastoma is its frequent metastatic outgrowth prior to diagnosis, especially in cases driven by amplification of the MYCN oncogene. However, only a limited number of regulatory proteins that contribute to this complex MYCN-mediated process have been elucidated. Here we show that the growth arrest-specific 7 (GAS7) gene, located at chromosome band 17p13.1, is preferentially deleted in high-risk MYCN-driven neuroblastoma. GAS7 expression was also suppressed in MYCN-amplified neuroblastoma lacking 17p deletion. GAS7 deficiency led to accelerated metastasis in both zebrafish and mammalian models of neuroblastoma with overexpression or amplification of MYCN. Analysis of expression profiles and the ultrastructure of zebrafish neuroblastoma tumors with MYCN overexpression identified that GAS7 deficiency led to (i) downregulation of genes involved in cell–cell interaction, (ii) loss of contact among tumor cells as critical determinants of accelerated metastasis, and (iii) increased levels of MYCN protein. These results provide the first genetic evidence that GAS7 depletion is a critical early step in the cascade of events culminating in neuroblastoma metastasis in the context of MYCN overexpression. Significance: Heterozygous deletion or MYCN-mediated repression of GAS7 in neuroblastoma releases an important brake on tumor cell dispersion and migration to distant sites, providing a novel mechanism underlying tumor metastasis in MYCN-driven neuroblastoma. See related commentary by Menard, p. 2815

Abstract Neuroblastoma is an embryonal tumor arising in the peripheral sympathetic nervous system (PSNS), and often presents with widespread metastasis at diagnosis. We recently demonstrated that overexpression of LMO1 can synergize with MYCN to promote tumor metastasis in our zebrafish model system. Here, we identify a “metastasis suppressor” gene – growth arrest specific 7 (GAS7) – whose loss of function or reduced expression can promote dissemination and migration of neuroblastoma cells with MYCN overexpression, both in vitro and in vivo. GAS7 resides on chromosome 17p13.1, a region that is deleted in high-risk neuroblastomas with higher frequency in MYCN-amplified cases. Expression levels of GAS7 are also significantly downregulated in MYCN-amplified or otherwise MYCN-overexpressing human neuroblastoma cells, as well as MYCN-overexpressing zebrafish PSNS cells, suggesting an inverse relationship between the oncogenic activities of MYCN and GAS7downregulation. To determine whether loss of function or reduced expression of GAS7 could contribute to neuroblastoma pathogenesis in the context of MYCN overexpression, we developed a gas7 knockout zebrafish line using a transcription activator-like effector nucleases (TALEN) method. Loss of function of gas7 promoted hematogenous metastasis of MYCN-overexpressing tumor cells to tissues and organs that paralleled the common sites of metastasis in neuroblastoma patients. Further RNA-sequencing and qRT-PCR analyses showed that representative signature genes encoding proteins involved in tumor cell-cell or cell-extracellular matrix interactions were significantly downregulated in fish tumors with loss of function of gas7, consistent with our electron microscopic finding in the fish model showing a loss of contact among tumor cells in fish lacking functional gas7, suggesting that GAS7 may physically act as a metastasis suppressor. Thus, in high-risk neuroblastoma with MYCNamplification or overexpression, we propose that deletion or reduced expression of GAS7 cooperates with MYCN to promote neuroblastoma cell dissemination. Although the precise mechanism of this interaction remains unclear, we suggest that it relies, in part, on the downregulation of pivotal genes involved in tumor cell-cell or cell-extracellular matrix contacts. Citation Format: Zhiwei Dong, Gonzalo Lepez Garcia, Cheng Zhang, Erin N. Dankert, Jo Lynne Harenza, Xiaonan Hou, Hu Li, John M. Maris, Shizhen (Jane) Zhu. Loss of function of GAS7 promotes neuroblastoma metastasis in the context of MYCN overexpression [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr LB-127.

Abstract Lung cancer is the deadliest and most frequently diagnosed type of tumor worldwide, with 1.6 million deaths reported annually. Non-small cell lung cancer (NSCLC) represents 85% of all lung cancer cases and carries a poor 5-year survival rate below 15%. Prognoses remain dismal due to the large number of patients diagnosed with advanced stage disease and the development of resistance to current therapies. A better understanding of acquired drug resistance will help to circumvent the progression of lung cancer and make significant strides in improving NSCLC patient treatment. Our recent work demonstrates that dopamine and cAMP-regulated phosphoprotein, Mr 32000 (DARPP-32) and its amino-terminally truncated splice variant (t-DARPP) promote lung tumor growth in orthotopic mouse models. IHC staining of 62 human lung adenocarcinoma tissues showed that t-DARPP expression is elevated with increasing tumor (T) staging score, which represents the size of the primary tumor and whether it has grown into nearby areas, as a metric of tumor progression and growth. Correspondingly, a computational biology analysis of 513 lung adenocarcinoma patients revealed upregulation of t-DARPP isoform expression correlates with advanced T stage and is associated with poor overall survival. We identified a novel physical interaction between DARPP-32 and inhibitory kappa B kinase-α (IKKα) that promotes NSCLC cell migration through activation of non-canonical NF-κB2 signaling. It has been shown that DARPP-32 overexpression inhibits gefitinib-induced apoptosis in gastric cancer and t-DARPP contributes to the trastuzumab resistance phenotype in breast cancer. Our recent findings suggest DARPP-32 and t-DARPP overexpression in NSCLC promotes resistance to specific molecular targeted inhibitors by enabling tumor cells to evade apoptosis via Akt- and Erk-dependent cell survival mechanisms. Current ongoing studies are focused on manipulating expression of DARPP-32 isoforms in lung tumor cells to prevent resistance to targeted therapies in NSCLC patients. Citation Format: SK Kayum Alam, Matteo Astone, Ping Liu, Li Wang, Abbygail M. Coyle, Erin N. Dankert, Dane K. Hoffman, Stephanie R. Hall, Wei Zhang, Rui Kuang, Anja C. Roden, Aaron S. Mansfield, Luke H. Hoeppner. Molecular mechanisms of non-small cell lung cancer growth and drug resistance [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 873.

Abstract Lung cancer is the leading cause of cancer-related death worldwide. In this study, we demonstrate that elevated expression of dopamine and cyclic adenosine monophosphate-regulated phosphoprotein, Mr 32000 (DARPP-32) and its truncated splice variant t-DARPP promotes lung tumor growth, while abrogation of DARPP-32 expression in human non-small cell lung cancer (NSCLC) cells reduces tumor growth in orthotopic mouse models. We observe a novel physical interaction between DARPP-32 and inhibitory kappa B kinase-α (IKKα) that promotes NSCLC cell migration through non-canonical nuclear factor kappa-light-chain-enhancer of activated B cells 2 (NF-κB2) signaling. Bioinformatics analysis of 513 lung adenocarcinoma patients reveals elevated t-DARPP isoform expression is associated with poor overall survival. Histopathological investigation of 62 human lung adenocarcinoma tissues also showed that t-DARPP expression is elevated with increasing tumor (T) stage. Our data suggest that DARPP-32 is a negative prognostic marker associated with increasing stages of NSCLC and may represent a novel therapeutic target. Citation Format: Sk. Kayum Alam, Matteo Astone, Ping Liu, Stephanie R. Hall, Abbygail M. Coyle, Erin N. Dankert, Dane K. Hoffman, Wei Zhang, Rui Kuang, Anja C. Roden, Aaron S. Mansfield, Luke H. Hoeppner. DARPP-32 and t-DARPP promote non-small cell lung cancer growth through regulation of IKKα-dependent cell migration and Akt/Erk-mediated cell survival [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 5161.