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, , a member of the serum amyloid A (SAA) apolipoprotein family, is a key mediator of the protumorigenic activity of PDGFRα CAFs. Whereas -competent CAFs stimulate the growth of tumor cells in an orthotopic model,-null CAFs inhibit tumor growth. Saa3 also plays a role in the cross talk between CAFs and tumor cells. Ablation of in pancreatic tumor cells makes them insensitive to the inhibitory effect of-null CAFs. As a consequence, germline ablation of 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,, the ortholog of murine Saa3, is overexpressed in human CAFs. Moreover, high levels of 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.

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 types1. 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 activity2,3, 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.

Highlights d Combined Egfr/Raf1 ablation results in complete regression of a subset of PDACs d Mouse mutant Kras/Trp53-induced PDACs display distinct transcriptional profiles d PDAC transcriptional profiles determine their response to Egfr/Raf1 ablation d EGFR/c-RAF inhibition also prevents proliferation of PDXderived tumor cells

Author contributions J.U., MT.B., A. LL. and A.B. designed and performed experiments and analysed data. M.Cl., M.Ca., E.F., C.F-P and M.G contributed to experiments. A.B-LL. analysed the public transcriptomic datasets of human samples and stats. E.B. and A.R.N. participated in data analyses. R.R.G conceived the project, designed and analysed data and supervised the overall project.

Genetic studies in mice have provided evidence that H-Ras and K-Ras proteins are bioequivalent. However, human tumors display marked differences in the association of RAS oncogenes with tumor type. Thus, to further assess the bioequivalence of oncogenic H-Ras and K-Ras, we replaced the coding region of the murine K-Ras locus with H-Ras oncogene sequences. Germline expression of H-Ras or K-Ras from the K-Ras locus resulted in embryonic lethality. However, expression of these genes in adult mice led to different tumor phenotypes. Whereas H-Ras elicited papillomas and hematopoietic tumors, K-Ras induced lung tumors and gastric lesions. Pulmonary expression of H-Ras created a senescence-like state caused by excessive MAPK signaling. Likewise, H-Ras but not K-Ras induced senescence in mouse embryonic fibroblasts. Label-free quantitative analysis revealed that minor differences in H-Ras expression levels led to drastically different biological outputs, suggesting that subtle differences in MAPK signaling confer nonequivalent functions that influence tumor spectra induced by RAS oncoproteins. Cancer Res; 77(3); 707-18. ©2016 AACR.

Programmed death ligand-1 (PD-L1) is well known for its role as an immune checkpoint regulator, but little is known about its function in other cellular processes. A study now shows that in tumour cells PD-L1 mediates pyroptosis, an inflammatory form of cell death, by activating the expression of Gasdermine c, ultimately leading to tumour necrosis.

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