Endoglin expression by untransformed and tumor cells of different histogenesis
Transmembrane protein endoglin (CD105) is a component of a receptor complex for TGF-b family growth factors. It is expressed mainly by the endothelial cells, mesenchymal stromal cells and early hematopoietic precursors. CD105 density increases on the membranes of proliferating endothelium. Soluble endoglin (sEng) is formed by a cleavage of extracellular fragment of the protein. Its level in blood is considered as an indicator of angiogenesis during development of some tumors. The contribution of tumor cells in sEng pool remains un- nown. The expression of CD105, production of sEng, as well as the level of two splicing variants of endoglin gene and MMP-14 gene activity were investigated using the collection of 43 cultures of untransformed and tumor cells of different histogenesis. More than half of tumor cell lines and untransformed stromal cells contained cell populations bearing membrane endoglin. Cytoplasmic endoglin with unknown function was found in the cells of three tumor lines. In all cell cultures mRNA expression of L-endoglin prevailed over the expression of S-endoglin. Formation of sEng has been investigated in stromal and tumor cells for the first time. It was estimated that endothelial cells represent the main source of sEng, whereas the majority of CD105+ tumor cells and untransformed stromal cells showed low sEng production. Among tumor cell lines, the highest concentration of sEng was found in MeWo melanoma cells, which at the same time had the highest activity of MMP-14 gene.