Tumor Endothelial Marker 1 (TEM1)

TEM1 expression was restricted to neoplastic endothelial tissue and to metastatic lesions.Sequence analysis predicted that the 757-amino acid type I membrane protein contains a signal peptide; 5 globular extracellular domains, including a C-type lectin domain, a Sushi/SCR/CCP domain, and 3 EGF repeats; a mucin-like region; a transmembrane segment; and a short cytoplasmic tail. Carbohydrate analysis indicated that the endosialin protein carries abundantly sialylated, O-linked oligosaccharides and is reduced to 120 kD by sialidase treatment or to 95 kD with additional O-glycanase treatment. The N-terminal 360 residues of endosialin are homologous to thrombomodulin (THBD) and complement component 1q receptor. Northern blot analysis revealed expression of a single 2.6-kb transcript in endosialin-expressing cell lines.