CD109 is a glycosylphosphatidylinositol-anchored cell surface protein that is frequently detected in squamous cell carcinomas. CD109 is a negative regulator of TGF-beta 1 signaling in human keratinocytes, and the N-terminal fragment of CD109 secreted from cells after cleavage by the furin protease is important for modulating TGF-beta 1 signaling. Previously, we found that CD109 is expressed in human glioblastoma cells; however, the role of CD109 in glioblastoma cells is not established. Here, we describe the effects of CD109 in human glioblastoma cell lines. Three glioblastoma cell lines, SR-MG-1, U251MG and MG178, were tested and CD109 overexpression attenuated TGF-beta 1 signaling and enhanced EGF signaling in SR-MG-1, but not in U251MG or MG178. The N-terminal CD109 fragment in SR-MG-1 was hyperglycosylated compared with that in MG178 or U251MG. The conditioned medium of CD109-overexpressing SR-MG-1, containing the secreted N-terminal CD109, had a negative effect on TGF-beta 1 signaling in wild-type SR-MG-1 and MG178, whereas it did not show any effect on EGF signaling. In addition, cell surface CD109 interacts with EGF receptor in SK-MG-1 overexpressing CD109, and exhibited enhanced cell migration and invasion. These findings suggest that CD109 attenuates TGF-beta 1 signaling and enhances EGF signaling in SR-MG-1 cells and that the membrane-anchored CD109 may play major roles in the EGF signaling pathway. (C) 2015 The Authors. Published by Elsevier Inc.