Many solid cancers including pancreatic ductal adenocarcinoma (PDAC) are characterized by an extensive stromal reaction that is accompanied by infiltrating tumor-associated macrophages (TAMs). The role of TAMs in malignant tumors is only partially understood. Previously, we identified the transcription factor CUX1 as an important mediator of tumor progression in PDAC. Interestingly, we found that CUX1 is highly expressed not only in tumor cells but also in TAMs. On the basis of these data, we aimed to elucidate the effects of CUX1 in TAMs in vitro and in vivo. We analyzed the effects of CUX1 on cytokine expression using overexpression and knockdown strategies. The cytokine regulation by CUX1 was further assessed by reporter assays, DNA pulldown experiments and chromatin-immunoprecipitation. CUX1 expression in TAMs was analyzed in human pancreatic cancer tissues and in a genetic mouse model. Immunohistochemical analysis revealed strong expression levels of CUX1 in a distinct subset of TAMs in human PDAC tissues. Furthermore, its expression increased during tumor progression in a genetic mouse model of PDAC. Profiling experiments showed that CUX1 downregulates several NF-κB-regulated chemokines such as CXCL10, which have been associated with M1 polarization and inhibition of angiogenesis and tumor progression. We could demonstrate that CUX1 interacts with NF-κB p65, leading to reduced binding of NF-κB p65 to the chemokine promoters. In addition, CUX1 reduces acetylation of NF-κB p65 at K310 by recruiting HDAC1. Functionally, CUX1 expression in TAMs antagonizes T-cell attraction and enhances angiogenesis in vitro. We identified CUX1 as an important modulator of the TAMs phenotype and function by modulating NF-κB-dependent cytokines.

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Pancreatic neuroendocrine neoplasms (PNENs) constitute a rare tumour entity, and prognosis and treatment options depend on tumour-mediating hallmarks such as angiogenesis, proliferation rate and resistance to apoptosis. The molecular pathways that determine the malignant phenotype are still insufficiently understood and this has limited the use of effective combination therapies in the past. In this study, we aimed to characterise the effect of the oncogenic transcription factor Cut homeobox 1 (CUX1) on proliferation, resistance to apoptosis and angiogenesis in murine and human PNENs. The expression and function of CUX1 were analysed using knockdown and overexpression strategies in Ins-1 and Bon-1 cells, xenograft models and a genetically engineered mouse model of insulinoma (RIP1Tag2). Regulation of angiogenesis was assessed using RNA profiling and functional tube-formation assays in HMEC-1 cells. Finally, CUX1 expression was assessed in a tissue microarray of 59 human insulinomas and correlated with clinicopathological data. CUX1 expression was upregulated during tumour progression in a time-and stage-dependent manner in the RIP1Tag2 model, and associated with pro-invasive and metastatic features of human insulinomas. Endogenous and recombinant CUX1 expression increased tumour cell proliferation, tumour growth, resistance to apoptosis, and angiogenesis in vitro and in vivo. Mechanistically, the pro-angiogenic effect of CUX1 was mediated via upregulation of effectors such as HIF1a and MMP9. CUX1 mediates an invasive pro-angiogenic phenotype and is associated with malignant behaviour in human insulinomas. Key Words" CUX1 " pancreatic neuroendocrine neoplasms " angiogenesis " RIP1Tag2" insulinomas

Pancreatic cancer is characterized by a high degree of resistance to chemotherapy. Epidermal growth factor receptor (EGFR) inhibition using the small-molecule inhibitor erlotinib was shown to provide a small survival benefit in a subgroup of patients. To identify kinases whose inhibition acts synergistically with erlotinib, we employed a kinome-wide small-interfering RNA (siRNA)-based loss-of-function screen in the presence of erlotinib. Of 779 tested kinases, we identified several targets whose inhibition acted synergistically lethal with EGFR inhibition by erlotinib, among them the S6 kinase ribosomal protein S6 kinase 2 (RPS6KA2)/ribosomal S6 kinase 3. Activated RPS6KA2 was expressed in approximately 40% of 123 human pancreatic cancer tissues. RPS6KA2 was shown to act downstream of EGFR/RAS/mitogen-activated protein kinase kinase (MEK)/extracellular-signal regulated kinase (ERK) signaling and was activated by EGF independently of the presence of KRAS mutations. Knockdown of RPS6KA2 by siRNA led to increased apoptosis only in the presence of erlotinib, whereas RPS6KA2 activation or overexpression rescued from erlotinib- and gemcitabine-induced apoptosis. This effect was at least in part mediated by downstream activation of ribosomal protein S6. Genetic as well as pharmacological inhibition of RPS6KA2 by the inhibitor BI-D1870 acted synergistically with erlotinib. By applying this synergistic lethality screen using a kinome-wide RNA interference-library approach, we identified RPS6KA2 as potential drug target whose inhibition synergistically enhanced the effect of erlotinib on tumor cell survival. This kinase therefore represents a promising drug candidate suitable for the development of novel inhibitors for pancreatic cancer therapy.