Invasion and metastasis of carcinomas is promoted by the activation of the embryonic 'epithelial to mesenchymal transition' (EMT) program, which triggers cellular mobility and subsequent dissemination of tumour cells. We recently showed that the EMT-activator ZEB1 (zinc finger E-box binding homeobox 1) is a crucial promoter of metastasis and demonstrated that ZEB1 inhibits expression of the microRNA-200 (miR-200) family, whose members are strong inducers of epithelial differentiation. Here, we report that ZEB1 not only promotes tumour cell dissemination, but is also necessary for the tumour-initiating capacity of pancreatic and colorectal cancer cells. We show that ZEB1 represses expression of stemness-inhibiting miR-203 and that candidate targets of miR-200 family members are also stem cell factors, such as Sox2 and Klf4. Moreover, miR-200c, miR-203 and miR-183 cooperate to suppress expression of stem cell factors in cancer cells and mouse embryonic stem (ES) cells, as demonstrated for the polycomb repressor Bmi1. We propose that ZEB1 links EMT-activation and stemness-maintenance by suppressing stemness-inhibiting microRNAs (miRNAs) and thereby is a promoter of mobile, migrating cancer stem cells. Thus, targeting the ZEB1-miR-200 feedback loop might form the basis of a promising treatment for fatal tumours, such as pancreatic cancer.

Focal-adhesion kinase (FAK) is an important mediator of growth-factor signalling, cell proliferation, cell survival and cell migration. Given that the development of malignancy is often associated with perturbations in these processes, it is not surprising that FAK activity is altered in cancer cells. Mouse models have shown that FAK is involved in tumour formation and progression, and other studies showing that FAK expression is increased in human tumours make FAK a potentially important new therapeutic target.

Metastasis is the major cause of cancer-associated death. Partial activation of the epithelial-to-mesenchymal transition program (partial EMT) was considered a major driver of tumour progression from initiation to metastasis. However, the role of EMT in promoting metastasis has recently been challenged, in particular concerning effects of the Snail and Twist EMT transcription factors (EMT-TFs) in pancreatic cancer. In contrast, we show here that in the same pancreatic cancer model, driven by Pdx1-cre-mediated activation of mutant Kras and p53 (KPC model), the EMT-TF Zeb1 is a key factor for the formation of precursor lesions, invasion and notably metastasis. Depletion of Zeb1 suppresses stemness, colonization capacity and in particular phenotypic/metabolic plasticity of tumour cells, probably causing the observed in vivo effects. Accordingly, we conclude that different EMT-TFs have complementary subfunctions in driving pancreatic tumour metastasis. Therapeutic strategies should consider these potential specificities of EMT-TFs to target these factors simultaneously.

TP53 mutation occurs in 50-75% of human pancreatic ductal adenocarcinomas (PDAC) following an initiating activating mutation in the KRAS gene. These p53 mutations frequently result in expression of a stable protein, p53 R175H , rather than complete loss of protein expression. In this study we elucidate the functions of mutant p53 (Trp53 R172H ), compared to knockout p53 (Trp53 fl ), in a mouse model of PDAC. First we find that although Kras G12D is one of the major oncogenic drivers of PDAC, most Kras G12D-expressing pancreatic cells are selectively lost from the tissue, and those that remain form premalignant lesions. Loss, or mutation, of Trp53 allows retention of the Kras G12D -expressing cells and drives rapid progression of these premalignant lesions to PDAC. This progression is consistent with failed growth arrest and/or senescence of premalignant lesions, since a mutant of p53, p53 R172P, which can still induce p21 and cell cycle arrest, is resistant to PDAC formation. Second, we find that despite similar kinetics of primary tumor formation, mutant p53 R172H , as compared with genetic loss of p53, specifically promotes metastasis. Moreover, only mutant p53 R172H -expressing tumor cells exhibit invasive activity in an in vitro assay. Importantly, in human PDAC, p53 accumulation significantly correlates with lymph node metastasis. In summary, by using 'knock-in' mutations of Trp53 we have identified two critical acquired functions of a stably expressed mutant form of p53 that drive PDAC; first, an escape from Kras G12D -induced senescence/ growth arrest and second, the promotion of metastasis.Kras | metastasis | p53 | pancreatic cancer | senescence P ancreatic ductal adenocarcinoma (PDAC) is the fifth leading cause of cancer deaths in Europe and the United States, with an estimated 5-year overall survival of less than 5% (1, 2). Poor prognosis results from the aggressive nature of the disease, with as many as 90% of patients at the time of diagnosis harboring unresectable cancer that is extremely resistant to chemotherapy. PDAC arises from precursor lesions called pancreatic intraepithelial neoplasms (PanINs), which are characterized by the sequential accumulation of alterations in the KRAS oncogene and loss of the CDKN2A, TP53, and/or SMAD4 tumor suppressors in many cases (3). Although we know the frequencies of such mutations in PDAC, their specific functions during the development of pancreatic cancer remain unclear. Here we have used a genetically engineered mouse model of pancreatic cancer (4) to aid in understanding of the respective roles of gain-of-function Kras and Trp53 mutations.KRAS is mutated in almost all human PDACs (5), and this is one of the earliest genetic events driving development of human PanINs. Studies in murine models have further shown that activating KRAS mutation represents an initiating step in PDAC (6-9). The TP53 tumor suppressor gene is also frequently mutated in human pancreatic cancer (50-75%), predominantly through missense mutations (10). These often result in accumulati...

SUMMARY Tumors and associated stroma manifest mechanical properties that promote cancer. Mechanosensation of tissue stiffness activates the Rho/ROCK pathway to increase actomyosin-mediated cellular tension to re-establish force equilibrium. To determine how actomyosin tension affects tissue homeostasis and tumor development, we expressed conditionally-active ROCK2 in mouse skin. ROCK activation elevated tissue stiffness via increased collagen. β-catenin, a key element of mechanotranscription pathways, was stabilized by ROCK activation leading to nuclear accumulation, transcriptional activation and consequent hyperproliferation and skin thickening. Inhibiting actomyosin contractility by blocking LIMK or myosin ATPase attenuated these responses, as did FAK inhibition. Tumor number, growth and progression were increased by ROCK activation, while ROCK blockade was inhibitory, implicating actomyosin-mediated cellular tension and consequent collagen deposition as significant tumor promoters.