Elevated expression of endoglin, a component of the TGF-beta-receptor complex, correlates with proliferation of tumor endothelial cells

Endoglin/CD105 is a membrane protein involved in the TGF-P receptor signall ing pathway, Endoglin expression has been reported to be selective for a fe w cell types, in particular endothelial cells, although a number of conflic ting reports have been published. In this study, we performed a detailed an alysis of endoglin expression in human lung tumors and different tumor and endothelial cell lines, employing reverse-transcriptase-polymerase-chain re action as well as immunoblotting and immunohistochemistry using verified an tibodies to endoglin. Our data show a clearly preferential expression of bo th endoglin mRNA and protein in endothelial cells. In tumors, endoglin expr ession was strongly elevated in the angiogenic endothelium at the tumor edg es. In agreement with this observation, we find a clear correlation between endoglin expression and markers of proliferation, such as cyclin A and Ki- 67, suggesting that endoglin expression is linked to cell-cycle regulation. These findings not only resolve some of the discrepancies in the literatur e, but also provide the basis for further applications making use of its se lective localization and expression in the tumor vasculature. (C) 1999 Wile y-Liss, Inc.