SUMMARY Sonic hedgehog (Shh), a soluble ligand overexpres sed by neoplastic cells in pancreatic ductal adenocarcinoma (PDAC), drives formation of a fibroblast-rich desmoplastic stroma. To better understand its role in malignant progression, we deleted Shh in a well-defined mouse model of PDAC. As predicted, Shh-deficient tumors had reduced stromal content. Surprisingly, such tumors were more aggressive and exhibited undifferentiated histology, increased vascularity, and heightened proliferation – features that were fully recapitulated in control mice treated with a Smoothened inhibitor. Furthermore, administration of VEGFR blocking antibody selectively improved survival of Shh-deficient tumors, indicating that Hedgehog-driven stroma suppresses tumor growth in part by restraining tumor angiogenesis. Together, these data demonstrate that some components of the tumor stroma can act to restrain tumor growth.

Bone marrow endothelial cells (ECs) are essential for reconstitution of hematopoiesis, but their role in self-renewal of long term-hematopoietic stem cells (LT-HSCs) is unknown. We have developed angiogenic models to demonstrate that EC-derived angiocrine growth factors support in vitro self-renewal and in vivo repopulation of authentic LT-HSCs. In serum/cytokine-free co-cultures, ECs through direct cellular contact, stimulated incremental expansion of repopulating CD34−Flt3−cKit+Lineage−Sca1+ LT-HSCs, which retained their self-renewal ability, as determined by single cell and serial transplantation assays. Angiocrine expression of Notch-ligands by ECs promoted proliferation and prevented exhaustion of LT-HSCs derived from wild-type, but not Notch1/Notch2 deficient mice. In transgenic notch-reporter (TNR.Gfp) mice, regenerating TNR.Gfp+ LT-HSCs were detected in cellular contact with sinusoidal ECs and interfering with angiocrine, but not perfusion function, of SECs impaired repopulation of TNR.Gfp+ LT-HSCs. ECs establish an instructive vascular niche for clinical scale expansion of LT-HSCs and a cellular platform to identify stem cell-active trophogens.

Summary Esophageal adenocarcinoma (EAC) arises from Barrett esophagus (BE), intestinal-like columnar metaplasia linked to reflux esophagitis. In a transgenic mouse model of BE, esophageal overexpression of interleukin-1β phenocopies human pathology with evolution of esophagitis, Barrett’s-like metaplasia and EAC. Histopathology and gene signatures resembled closely human BE, with upregulation of TFF2, Bmp4, Cdx2, Notch1 and IL-6. The development of BE and EAC was accelerated by exposure to bile acids and/or nitrosamines, and inhibited by IL-6 deficiency. Lgr5+ gastric cardia stem cells present in BE were able to lineage trace the early BE lesion. Our data suggest that BE and EAC arise from gastric progenitors due to a tumor-promoting IL-1β-IL-6 signaling cascade and Dll1-dependent Notch signaling.

Notch signaling promotes commitment of keratinocytes to differentiation and suppresses tumorigenesis. p63, a p53 family member, has been implicated in establishment of the keratinocyte cell fate and/or maintenance of epithelial self-renewal. Here we show that p63 expression is suppressed by Notch1 activation in both mouse and human keratinocytes through a mechanism independent of cell cycle withdrawal and requiring down-modulation of selected interferon-responsive genes, including IRF7 and/or IRF3. In turn, elevated p63 expression counteracts the ability of Notch1 to restrict growth and promote differentiation. p63 functions as a selective modulator of Notch1-dependent transcription and function, with the Hes-1 gene as one of its direct negative targets. Thus, a complex cross-talk between Notch and p63 is involved in the balance between keratinocyte self-renewal and differentiation. Normal tissue homeostasis is determined by a complex interplay between developmental signals and other cell regulatory pathways. Notch cell surface receptors and their ligands belonging to the Delta and Serrate/Jagged families play a crucial role in cell fate determination and differentiation, functioning in a cell-and context-specific manner (Artavanis-Tsakonas et al. 1999). In mammalian cells, Notch activation is generally thought to maintain stem cell potential and inhibit differentiation, thereby promoting carcinogenesis (Artavanis-Tsakonas et al. 1999). However, in specific cell types such as keratinocytes, increased Notch activity causes exit from the cell cycle and commitment to differentiation (Lowell et al. 2000;Rangarajan et al. 2001;Nickoloff et al. 2002), whereas down-modulation or loss of Notch1 function promotes carcinogenesis (Talora et al. 2002;Nicolas et al. 2003).In the human epidermis, localized expression of the Notch-ligand Delta in putative "stem cells" has been proposed to induce commitment of neighboring Notch1-expressing keratinocytes to a "transit-amplifying" phenotype, through a negative feedback mechanism of lateral inhibition (Lowell et al. 2000). On the other hand, in both mouse and human epidermis, Jagged 1/2, Notch1, and Notch2 are coexpressed in differentiating keratinocytes of the supra-basal layers, consistent with a positive feedback loop between these molecules that serves to reinforce and synchronize Notch activation with differentiation (Luo et al. 1997;Rangarajan et al. 2001;Nickoloff et al. 2002).The best characterized "canonical" pathway of Notch activation involves proteolytic cleavage and translocation of the cytoplasmic domain of the receptor to the nucleus, where it associates with the DNA-binding protein RBP-J (CBF-1, CSL), converting it from a repressor

The formation of new blood vessels, or angiogenesis, is a complex process that plays important roles in growth and development, tissue and organ regeneration, as well as numerous pathological conditions. Angiogenesis undergoes multiple discrete steps that can be individually evaluated and quantified by a large number of bioassays. These independent assessments hold advantages but also have limitations. This article describes in vivo, ex vivo, and in vitro bioassays that are available for the evaluation of angiogenesis and highlights critical aspects that are relevant for their execution and proper interpretation. As such, this collaborative work is the first edition of consensus guidelines on angiogenesis bioassays to serve for current and future reference.