In vivo Charakterisierung von CUX1 bei Tumorgenese und Progression am Pankreaskarzinom
Zusammenfassung der Projektergebnisse
Based on in vitro experiments and in vivo xenograft studies, we previously described the homeodomain transcription factor CUX1 as highly expressed in pancreatic cancer and as important mediator of tumor cell proliferation, invasiveness and resistance to apoptosis. CUX1 is expressed in two major variants, the full-length protein p200 and the N-terminally truncated p110. The latter variant, CUX1p100, results from proteolytical cleavage by nuclear cathepsin L, stably binds to DNA and operates as transcriptional activator or repressor, depending on the cellular context. The contribution of the two different CUX1 variants to the tumor-promoting phenotype remains to be elucidated. Studies in transgenic tumor models of the lung and the mammary gland indicate that CUX1 might cooperate with other oncogenes, thereby fostering tumor development. Therefore, this project aimed to elucidate the impact of the distinct CUX1 isoforms on pancreatic carcinogenesis in the context of mutant Kras, the prototypic oncogene frequently occurring in preinvasive pancreatic precursor lesions and invasive pancreatic cancer. Furthermore, we aimed to characterize relevant downstream signaling cascades conferring the CUX1 phenotype in a Kras-dependent manner. For this purpose, we used two different transgenic mouse models: The R26-Cux1flox (CUX1p110) mouse model conditionally expressing the CUX1p110 variant and the CUX1p200 mouse model expressing the full-length CUX1p200 variant under the control of the tissueunrestricted CMV promoter. We crossbred these mouse lines with the KC (KrasLSL- G12D/+;Ptf1aCre/+) mouse model expressing Kras under the control of the pancreas-specific Ptf1a promoter which is frequently used as genetic model for preinvasive pancreatic precursor lesions (PanIN lesions). Furthermore, we established several in vitro cell models to dissect CUX1-dependent downstream signaling pathways. Expressing both CUX1p200 and CUX1p110 in the context of oncogenic Kras (KCCux1p200 and KCCux1p110 mice) led to increased PanIN formation and development of invasive pancreatic ductal adenocarcinomata (PDAC). In KCCux1p110 mice, tumor development was drastically accelerated compared to KCCUX1p200 mice, with invasive PDAC developing within 4 weeks. This pronounced phenotype seen in KCCux1p110 mice might be related to different promoter activities, but might also indicate that Cux1p110 is the CUX1 variant exhibiting the relevant tumor-promoting effects. In line with this, we and others could detect significant cathepsin L activity in pancreatic cell lines and tissues cleaving CUX1p200 into the active Cux1p110 variant, suggesting that CUX1p110 is also the active variant in KCCUX1p200 mice after proteolytic cleavage. Interestinly, in the Cux1p110 mouse model we also observed a growth retardation phenotype which occurred early after birth and was unrelated to tumor formation, but possibly related to pancreatic exocrine insufficiency due to a subtotal reduction in functional acinar tissue at this early time point. In vitro and in both KCCUX1p200 and KCCux1p110 mice in vivo we could show that CUX1 enhances cell proliferation by activating MEK/ERK signalling independently of mutant Kras. Cux1p110 transcriptionally upregulated ADAM17, a sheddase involved in processing EGFR ligands, leading to CUX1-dependent activation of the EGFR axis. In addition, CUX1 further enhanced MEK/ERK activation through upregulation of the serine/threonine kinase MOS, known to phosophorylate MEK in a Kras-indendent manner. Taken together, in this project we identified CUX1p110 as major driver of mPanIN progression and pancreatic tumor formation in the context of activated Kras. These results provide the first in vivo evidence for the importance of CUX1 in the development of pancreatic cancer in genetic mouse models and highlight the importance of CUX1-dependent signaling pathways as potential therapeutic targets.
Projektbezogene Publikationen (Auswahl)
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miRNA dynamics in tumor-infiltrating myeloid cells modulating tumor progression in pancreatic cancer. Oncoimmunology. 2016;5(6):e1160181
Mühlberg L, Kühnemuth B, Costello E, et al.
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Pharmacological macrophage inhibition decreases metastasis formation in a genetic model of pancreatic cancer. Gut. 2017;66(7):1278–1285
Griesmann H, Drexel C, Milosevic N, et al.
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Stromal biology and therapy in pancreatic cancer: ready for clinical translation? Gut. 2019;68(1):159–171
Neesse A, Bauer CA, Öhlund D, et al.
