Loss of DRO1/CCDC80 in the tumor microenvironment promotes carcinogenesis

Tumors are composed of the tumor cells and the surrounding microenvironment. Both are closely interwoven and interact by a complex and multifaceted cross-talk which plays an integral part in tumor initiation, growth, and progression. Dro1/Ccdc80 has been shown to be a potent suppressor of colorectal cancer and ubiquitous inactivation of Dro1/Ccdc80 strongly promoted colorectal carcinogenesis in Apc^Min/+ mice and in a chemically-induced colorectal cancer model.

The aim of the present study was to investigate whether Dro1/Ccdc80’s tumor suppressive function is tumor-cell-autonomous. Expression of Dro1/Ccdc80 in cancer cells had no effect on both colon tumor development in Apc^Min/+ mice and formation of xenograft tumors. In contrast, DRO1/CCDC80 loss in the microenvironment strongly increased tumor growth in xenograft models, inhibited cancer cell apoptosis, and promoted intestinal epithelial cell migration. Moreover, stromal Dro1/Ccdc80 inactivation facilitated formation of intestinal epithelial organoids. Expression analyses showed Dro1/Ccdc80 to be significantly down-regulated in murine gastric cancer associated fibroblasts, in Apc^Min/+ colon tumor primary stromal cells and in microdissected stroma from human colorectal cancer compared to normal, non-tumor stroma. Our results demonstrate epithelial derived DRO1/CCDC80 to be dispensable for intestinal tissue homeostasis and identify Dro1/Ccdc80 as tumor suppressor in the tumor microenvironment.

Goblet Cell Ratio in Combination with Differentiation and Stem Cell Markers in Barrett Esophagus Allow Distinction of Patients with and without Esophageal Adenocarcinoma

The increasing incidence of esophageal adenocarcinoma (EAC) is mirrored by the increasing prevalence of Barrett esophagus, a precursor lesion resulting in a large number of individuals "at risk" for this lethal malignancy. Among patients with Barrett esophagus, only about 0.3% annually will develop EAC. Because large numbers of patients are followed in endoscopic surveillance, there is a need for risk prediction among a growing population of patients with Barrett esophagus. We identified four potential biomarkers from an inflammation (IL1β)-dependent mouse model of Barrett esophagus and tested them in 189 patients with Barrett esophagus with and without high-grade dysplasia (HGD)/early cancer (T1). The primary goal was to distinguish patients with Barrett esophagus with no evidence of dysplasia from those with dysplasia. Increasing stem cell marker LGR5 and niche cell marker DCLK1 and decreasing differentiation marker (secretory mucus cells, TFF2⁺ cells) correlated with elevated tumor score in the mouse. Having outlined the origin of those markers in the Barrett esophagus mouse model, we showed the applicability for human Barrett esophagus. We compared 94 patients with nondysplastic Barrett esophagus tissue with 95 patients with Barrett esophagus and HGD or early cancer. Low levels of TFF2 (AUC 87.2%) provided the best discrimination between nondysplastic Barrett esophagus and Barrett esophagus with cancer, followed by high levels of DCLK1 (AUC 83.4%), low goblet cell ratio (AUC 79.4%), and high LGR5 (AUC 71.4%). The goblet cell ratio, rather than the presence of goblet cells per se, was found to be an important discriminator. These findings may be useful in developing future risk prediction models for patients with Barrett esophagus and ultimately to improve EAC surveillance. Cancer Prev Res; 10(1); 55-66. ©2016 AACR.

Abstract 928: Myofibroblasts induce poorly differentiated tumor-like spheroids in small intestinal organoids by Wnt-independent mechanism

Recently, three dimensional (3D) organoid cultures were established from different organs; however those organoid cultures are exclusively composed of epithelial cells, thus missing the stromal niche. The later one is believed to play a crucial role during all stages of tumor development and resistance to therapy. One of the most abundant and the most important stromal cell in the tumor microenvironment is a myofibroblast. The contribution of myofibroblasts to tumor progression is well established, however little is known about their role during epithelial cell homeostasis and tumor initiation.

The niche was reconstructed by combining small intestinal (SI) crypts together with different types of mesenchymal cells in 3D culture systems. As mesenchymal cells the following cells were used: murine small intestinal fibroblasts, murine gastric carcinoma associated fibroblasts (CAFs), human fetal esophageal fibroblasts and human cardia myofibroblasts. While SI organoid culture is almost exclusively composed of budding structures, in the co-culture with intestinal myofibroblasts ∼50% of crypts were growing as non-budding spheroids. Those spheroids were positive for Ki-67, and independent of external R-Spondin, EGF and Noggin. Surprisingly, no differences between CAFs and other mesenchymal cells could be observed. Gene expression analysis revealed that myofibroblasts significantly upregulated Sox-9 (∼3 fold) and CD44 (∼4-fold) mRNA levels, and promoted proliferation rather than differentiation in the SI organoids. Clonogenicity assay showed that in the co-culture crypt cells exhibited about 3 times greater self-renewal capacity. Interestingly, by morphology and decreased number of PAS positive cells, the spheroids resembled intestinal organoids from Apc +/1638N mouse tumors. However, in the spheroids induced by co-culture the expression of Axin-2 was not increased, and Wnt inhibitor studies (IWP-2, C59) provided additional evidence that spheroid induction can be mediated by other mechanism than canonical Wnt. Indirect co-culture and conditioned media experiments revealed that spheroid formation was mediated by soluble factors. Mass spectrometric analysis of the secretome from the co-culture suggested the involvement of extracellular matrix-receptor pathway and focal adhesion pathway.

Taken together, our studies demonstrate that the microenvironment shapes intestinal crypts in a similar way as cell-autonomous genetic alterations. The data point out to the contribution of myofibroblasts to tumor initiation phenotype in the intestinal crypts by a mechanism independent of canonical Wnt. The precise signaling pathway remains to be elucidated in the future. Increased knowledge on the cellular communication between stroma and epithelium can contribute to the development of anti-cancer therapeutics that target not only cancer cells, but also the stromal niche.

Citation Format: Agnieszka Pastula, Klaus-Peter Janssen, Stefanie Hauck, Roland M. Schmid, Michael Quante. Myofibroblasts induce poorly differentiated tumor-like spheroids in small intestinal organoids by Wnt-independent mechanism. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 928.

The human core exosome interacts with differentially localized processive RNases: hDIS3 and hDIS3L

The eukaryotic RNA exosome is a ribonucleolytic complex involved in RNA processing and turnover. It consists of a nine-subunit catalytically inert core that serves a structural function and participates in substrate recognition. Best defined in Saccharomyces cerevisiae, enzymatic activity comes from the associated subunits Dis3p (Rrp44p) and Rrp6p. The former is a nuclear and cytoplasmic RNase II/R-like enzyme, which possesses both processive exo- and endonuclease activities, whereas the latter is a distributive RNase D-like nuclear exonuclease. Although the exosome core is highly conserved, identity and arrangements of its catalytic subunits in different vertebrates remain elusive. Here, we demonstrate the association of two different Dis3p homologs--hDIS3 and hDIS3L--with the human exosome core. Interestingly, these factors display markedly different intracellular localizations: hDIS3 is mainly nuclear, whereas hDIS3L is strictly cytoplasmic. This compartmental distribution reflects the substrate preferences of the complex in vivo. Both hDIS3 and hDIS3L are active exonucleases; however, only hDIS3 has retained endonucleolytic activity. Our data suggest that three different ribonucleases can serve as catalytic subunits for the exosome in human cells.