Proof of the tumor suppressor function of DRO1 via endothelial cells

• Applicant: Dr. Jessica Christian
• Subject Area: Hematology, Oncology ; Veterinary Medical Science
• Term: since 2016
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 290140694

We identified Dro1 as tumor suppressor of the colon. Ubiquitous inactivation of Dro1 in ApcMin/+ mice resulted in a dramatic increase in colonic tumor burden and in the formation of colorectal carcinoma. Further analyses revealed that loss of DRO1 specifically in the intestinal epithelium has no effect on colon carcinogenesis in the ApcMin/+ mouse. In contrast, DRO1 loss in the microenvironment strongly increased tumor growth rate and tumor volume in syngenic xenograft models using MC38 colon carcinoma and B16 melanoma cells. Consistently, reduction of DRO1 specifically in mesenchymal cells promoted colon carcinogenesis in ApcMin/+ mice. Moreover, Dro1 inactivation in primary stromal cells (fibroblasts + endothelial cells) promoted intestinal epithelial cell migration, inhibited cancer cell apoptosis, and facilitated formation of intestinal epithelial organoids. Further studies clearly demonstrated that Dro1`s tumor suppressive function is not mediated by fibroblasts. In contrast, loss of DRO1 in primary embryonic endothelial cells promoted endothelial cell migration and endothelial tube formation. We detected high DRO1/Dro1 expression in HUVEC and primary mouse endothelial cells. Furthermore, upon Dro1 inactivation we found changes in the secretome, including a proangiogenic milieu, of primary stromal and primary endothelial cells as well as in ApcMin/+ colon tumors. Our data support the hypothesis that DRO1 regulates functional und molecular characteristics of endothelial cells and that the tumor suppressor effect of Dro1 is mediated by endothelial cells. Purpose of this renewal proposal is to investigate DRO1`s role in endothelial cells and the causal proof of the tumor suppressor function of DRO1 via endothelial cells. Therefore, the effect of DRO1 loss on functional and molecular properties of primary endothelial cells and on an in vivo angiogenesis assay shall be studied in detail on the ApcMin/+ background. Moreover, DRO1 shall be inactivated in human endothelial cells. To investigate whether DRO1`s tumor suppressive function is mediated by endothelial cells, Dro1 shall be inactivated specifically in endothelial cells in ApcMin/+ mice and in syngenic xenograft experiments. Additionally, the effect of Dro1 inactivation in endothelial cells on functional and molecular properties of cancer cells and the impact of DRO1 expression on microvessels in human colorectal carcinoma shall be studied. Collectively, these experiments which are based on a wealth of previous work shall clarify the tumor suppressor function of DRO1 and hereby contribute to a better understanding of colorectal carcinogenesis. The DRO1 colon carcinoma model has the potential to become a valuable instrument for the further study of the widespread disease colorectal cancer and may become a preclinical model for the development of new preventive and therapeutic approaches.

• DFG Programme: Research Grants