Molecular Characterization of the MouseTem1/endosialin Gene Regulated by Cell Density in Vitro and Expressed in Normal Tissues in Vivo

Abstract

Human tumor endothelial marker 1/endosialin (TEM1/ endosialin) was recently identified as a novel tumor endothelial cell surface marker potentially involved in angiogenesis, although no specific function for this novel gene has been assigned so far. It was reported to be expressed in tumor endothelium but not in normal endothelium with the exception of perhaps the corpus luteum. Here we describe the cDNA and genomic sequences for the mouse Tem1/endosialin homolog, the identification and characterization of its promoter region, and an extensive characterization of its expression pattern in murine and human tissues and murine cell lines in vitro. The single copy gene that was mapped to chromosome 19 is intronless and encodes a 92-kDa protein that has 77.5% overall homology to the human protein. The remarkable findings are 1) this gene is ubiquitously expressed in normal human and mouse somatic tissues and during development, and 2) its expression at the mRNA level is density-dependent and up-regulated in serum-starved cells. In vitro, its expression is limited to cells of embryonic, endothelial, and preadipocyte origin, suggesting that the wide distribution of its expression in vivo is due to the presence of vascular endothelial cells in all the tissues. The ubiquitous expression in vivo is in contrast to previously reported expression limited to corpus luteum and highly angiogenic tissues such as tumors and wound tissue.

Endosialin (CD248) is a marker of tumor-associated pericytes in high-grade glioma

“…7 In cultured cells, expression of endosialin has only been reported on fibroblasts and some neuroblastoma cell lines. [6][7][8][9] This pattern is reflected in normal adult tissue, where endosialin expression is predominantly restricted to stromal fibroblasts, and in agreement with the SAGE analysis of St Croix et al 5 little or no endosialin is detected in the mature, normal vasculature. [9][10][11][12][13] In contrast, there is a marked upregulation of endosialin expression in the angiogenic vasculature of a wide variety of different tumor types including those of the brain, colon, breast and in tumor xenografts.…”

“…This banding pattern has been reported previously for both human and mouse endosialin detected with other monoclonal antibodies and polyclonal antibodies. 7,8,12,13 The 80 kDa band most likely represents a population of intracellular immaturely glycosylated endosialin as both these monoclonal antibodies have previously been shown to only recognize the 175 kDa endosialin following immunoprecipitation of cell surface labeled human fibroblasts. 9 Neither monoclonal antibody demonstrated any reactivity with lysates from endosialinnegative MCF7 cells (Figure 1a).…”

Hypoxia upregulates expression of human endosialin gene via hypoxia-inducible factor 2

“…Given that high cell density increases the expression of the mouse endosialin gene (Opavsky et al, 2001), we analysed the effect of cell crowding on expression levels of the human endosialin gene by qRT -PCR. As shown in Figure 6A, increased cell density led to elevated expression of endosialin mRNA.…”

“…However, present research suffers from inadequate knowledge of factors and pathways that control endosialin expression and determine its tissue distribution. There is only a single study showing that mouse endosialin gene transcription is induced by high cell density, but the underlying molecular mechanism has not been elucidated (Opavsky et al, 2001).…”

Characteristics of human Ewing/PNET sarcoma models

“…However, endosialin transcript was found to be ubiquitously expressed in normal adult tissues in addition to somatic tissues during development, both in humans and mice 52. Tissues with high levels of endosialin transcript seemed to express the protein, while tissues with lower levels of the transcript seemed negative for the protein 53.…”