MAF amplification licenses ERα through epigenetic remodelling to drive breast cancer metastasis.

MAF amplification increases the risk of breast cancer (BCa) metastasis through mechanisms that are still poorly understood yet have important clinical implications. Oestrogen-receptor-positive (ER+) BCa requires oestrogen for both growth and metastasis, albeit by ill-known mechanisms. Here we integrate proteomics, transcriptomics, epigenomics, chromatin accessibility and functional assays from human and syngeneic mouse BCa models to show that MAF directly interacts with oestrogen receptor alpha (ERα), thereby promoting a unique chromatin landscape that favours metastatic spread. We identify metastasis-promoting genes that are de novo licensed following oestrogen exposure in a MAF-dependent manner. The histone demethylase KDM1A is key to the epigenomic remodelling that facilitates the expression of the pro-metastatic MAF/oestrogen-driven gene expression program, and loss of KDM1A activity prevents this metastasis. We have thus determined that the molecular basis underlying MAF/oestrogen-mediated metastasis requires genetic, epigenetic and hormone signals from the systemic environment, which influence the ability of BCa cells to metastasize.

Ecology and evolution of dormant metastasis.

Genetic studies suggest that sequential dissemination from a primary metastasis, usually at the bone, is a major route of metastatic progression in early, radically resected cancer. Disseminated tumor cells (DTCs) can likely infiltrate but not grow, and may remain dormant once disseminated for extended intervals (from months to decades). The stationary nature of DTCs prevents them from being successfully treated as an asymptomatic residual disease in the adjuvant setting; critically, they can eventually relapse, adapt, and develop therapy resistance, causing incurable overt metastasis. Metastatic lesions usually first appear in one tissue, which invigorates metastatic cells for further dissemination to other organs, with a fatal outcome. Clinical and genetic data now indicate that metastatic lesions in one organ can seed secondary metastases in other organs: in other words, metastasis arising from metastasis. Herein we discuss recent insight into metastasis cell dormancy mechanisms, survival, communication with the local microenvironment, and eventual changes that endow DTCs with the capacity to expand and colonize to other metastatic sites.

ERK1/2 Signaling Induces Upregulation of ANGPT2 and CXCR4 to Mediate Liver Metastasis in Colon Cancer.

Carcinoma development in colorectal cancer is driven by genetic alterations in numerous signaling pathways. Alterations in the RAS-ERK1/2 pathway are associated with the shortest overall survival for patients after diagnosis of colorectal cancer metastatic disease, yet how RAS-ERK signaling regulates colorectal cancer metastasis remains unknown. In this study, we used an unbiased screening approach based on selection of highly liver metastatic colorectal cancer cells in vivo to determine genes associated with metastasis. From this, an ERK1/2-controlled metastatic gene set (EMGS) was defined. EMGS was associated with increased recurrence and reduced survival in patients with colorectal cancer tumors. Higher levels of EMGS expression were detected in the colorectal cancer subsets consensus molecular subtype (CMS)1 and CMS4. ANGPT2 and CXCR4, two genes within the EMGS, were subjected to gain-of-function and loss-of-function studies in several colorectal cancer cell lines and then tested in clinical samples. The RAS-ERK1/2 axis controlled expression of the cytokine ANGPT2 and the cytokine receptor CXCR4 in colorectal cancer cells, which facilitated development of liver but not lung metastases, suggesting that ANGPT2 and CXCR4 are important for metastatic outgrowth in the liver. CXCR4 controlled the expression of cytokines IL10 and CXCL1, providing evidence for a causal role of IL10 in supporting liver colonization. In summary, these studies demonstrate that amplification of ERK1/2 signaling in KRAS-mutated colorectal cancer cells affects the cytokine milieu of the tumors, possibly affecting tumor-stroma interactions and favoring liver metastasis formation. SIGNIFICANCE: These findings identify amplified ERK1/2 signaling in KRAS-mutated colorectal cancer cells as a driver of tumor-stroma interactions that favor formation of metastases in the liver.

Complete Regression of Advanced Pancreatic Ductal Adenocarcinomas upon Combined Inhibition of EGFR and C-RAF.

Five-year survival for pancreatic ductal adenocarcinoma (PDAC) patients remains below 7% due to the lack of effective treatments. Here, we report that combined ablation of EGFR and c-RAF expression results in complete regression of a significant percentage of PDAC tumors driven by Kras/Trp53 mutations in genetically engineered mice. Moreover, systemic elimination of these targets induces toxicities that are well tolerated. Response to this targeted therapy correlates with transcriptional profiles that resemble those observed in human PDACs. Finally, inhibition of EGFR and c-RAF expression effectively blocked tumor progression in nine independent patient-derived xenografts carrying KRAS and TP53 mutations. These results open the door to the development of targeted therapies for PDAC patients.

Saa3 is a key mediator of the protumorigenic properties of cancer-associated fibroblasts in pancreatic tumors.

Pancreatic ductal adenocarcinoma (PDAC) is characterized by the presence of abundant desmoplastic stroma primarily composed of cancer-associated fibroblasts (CAFs). It is generally accepted that CAFs stimulate tumor progression and might be implicated in drug resistance and immunosuppression. Here, we have compared the transcriptional profile of PDGFRα+ CAFs isolated from genetically engineered mouse PDAC tumors with that of normal pancreatic fibroblasts to identify genes potentially implicated in their protumorigenic properties. We report that the most differentially expressed gene, Saa3, a member of the serum amyloid A (SAA) apolipoprotein family, is a key mediator of the protumorigenic activity of PDGFRα+ CAFs. Whereas Saa3-competent CAFs stimulate the growth of tumor cells in an orthotopic model, Saa3-null CAFs inhibit tumor growth. Saa3 also plays a role in the cross talk between CAFs and tumor cells. Ablation of Saa3 in pancreatic tumor cells makes them insensitive to the inhibitory effect of Saa3-null CAFs. As a consequence, germline ablation of Saa3 does not prevent PDAC development in mice. The protumorigenic activity of Saa3 in CAFs is mediated by Mpp6, a member of the palmitoylated membrane protein subfamily of the peripheral membrane-associated guanylate kinases (MAGUK). Finally, we interrogated whether these observations could be translated to a human scenario. Indeed, SAA1, the ortholog of murine Saa3, is overexpressed in human CAFs. Moreover, high levels of SAA1 in the stromal component correlate with worse survival. These findings support the concept that selective inhibition of SAA1 in CAFs may provide potential therapeutic benefit to PDAC patients.

A Braf kinase-inactive mutant induces lung adenocarcinoma.

The initiating oncogenic event in almost half of human lung adenocarcinomas is still unknown, a fact that complicates the development of selective targeted therapies. Yet these tumours harbour a number of alterations without obvious oncogenic function including BRAF-inactivating mutations. Inactivating BRAF mutants in lung predominate over the activating V600E mutant that is frequently observed in other tumour types. Here we demonstrate that the expression of an endogenous Braf(D631A) kinase-inactive isoform in mice (corresponding to the human BRAF(D594A) mutation) triggers lung adenocarcinoma in vivo, indicating that BRAF-inactivating mutations are initiating events in lung oncogenesis. Moreover, inactivating BRAF mutations have also been identified in a subset of KRAS-driven human lung tumours. Co-expression of Kras(G12V) and Braf(D631A) in mouse lung cells markedly enhances tumour initiation, a phenomenon mediated by Craf kinase activity, and effectively accelerates tumour progression when activated in advanced lung adenocarcinomas. We also report a key role for the wild-type Braf kinase in sustaining Kras(G12V)/Braf(D631A)-driven tumours. Ablation of the wild-type Braf allele prevents the development of lung adenocarcinoma by inducing a further increase in MAPK signalling that results in oncogenic toxicity; this effect can be abolished by pharmacological inhibition of Mek to restore tumour growth. However, the loss of wild-type Braf also induces transdifferentiation of club cells, which leads to the rapid development of lethal intrabronchiolar lesions. These observations indicate that the signal intensity of the MAPK pathway is a critical determinant not only in tumour development, but also in dictating the nature of the cancer-initiating cell and ultimately the resulting tumour phenotype.