Abstract 2375: Endothelial cells isolated from colorectal carcinoma exhibit tumor microenvironment-dependent plasticity allowing the identification of SPARCL1 as a novel endothelial cell quiescence factor
Authors: Liebl Andrea , Naschberger Elisabeth , Schellerer Vera S. , Schaal Ute , Kölbel Patrick , Grenz Sandra , Britzen-Laurent Nathalie , Rau Tilman T. , Merkel Susanne , Dietel Barbara , Klein-Hitpass Ludger , Hohenberger Werner , Croner Roland S. , Stürzl Michael 
Published: August 2015

Abstract
It is well known that tumor cell heterogeneity and the tumor microenvironment (TME) contribute to tumorigenesis. In contrast, stromal cell heterogeneity and plasticity in response to different TMEs and its impact on tumorigenesis has not been conclusively investigated in human tumors, as yet. Here we analyzed TME-induced heterogeneity of tumor endothelial cells (TECs) in colorectal carcinoma (CRC). To this goal vital and highly pure TEC cultures were isolated from CRC with a Th1-like TME (Th1-TME) and from CRC with a non-Th1-like TME (Ctrl-TME). Tumors with a Th1-TME exhibited a significantly reduced angiogenic activity and were associated with an improved prognosis of CRC patients. Comparative transcriptome analyses of the established TEC cultures identified a cluster of genes which was homogeneously expressed in TECs from Th1-TME but significantly different in TECs from Ctrl-TME. The gene encoding secreted protein, acidic and rich in cysteine-like 1 (SPARCL1) was identified to be most strongly up-regulated in TECs derived from a Th1-TME. We could confirm with in situ hybridization and immunohistochemistry that in normal colon and CRC tissues SPARCL1 expression is associated with endothelial cells (EC). Of note, SPARCL1 was consistently and highly expressed in normal colon, to a lower extent in CRC with a Th1-TME and low or absent in CRC tissues with a Ctrl.-TME. In cell culture SPARCL1 expression was absent in actively proliferating EC, but highly induced in EC reaching a confluent quiescent state. The SPARCL1 induction in confluent cells was reversible after the reduction of cell density. In functional studies SPARCL1 inhibited proliferation, migration and 3D sprouting of cultivated EC indicating potent anti-angiogenic activity. At the morphological level vessels in normal colon and in CRC with a Th1-TME were larger as compared to vessels in tumors with Ctrl-TME. Accordingly, SPARCL1 characterizes quiescent mature vessels that are larger as compared to rapidly sprouting microvessels. Altogether our results show that TECs isolated from CRC with different TMEs exhibit specific and differential long-term gene expression profiles. Characterization of the respective genes identified SPARCL1 as an anti-angiogenic gene associated with EC quiescence. These results demonstrate for the first time that human tumor endothelial cells retain differential TMEs by cellular memory allowing the identification of genes functionally imprinting the TME in these cellular sensors.
Citation Format: Andrea Liebl, Elisabeth Naschberger, Vera S. Schellerer, Ute Schaal, Patrick Kölbel, Sandra Grenz, Nathalie Britzen-Laurent, Tilman T. Rau, Susanne Merkel, Barbara Dietel, Ludger Klein-Hitpass, Werner Hohenberger, Roland S. Croner, Michael Stürzl. Endothelial cells isolated from colorectal carcinoma exhibit tumor microenvironment-dependent plasticity allowing the identification of SPARCL1 as a novel endothelial cell quiescence factor. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 2375. doi:10.1158/1538-7445.AM2015-2375