Processing of CD109 by furin and its role in the regulation of TGF-β signaling

Abstract

CD109 is a glycosylphosphatidylinositol (GPI)-anchored glycoprotein, whose expression is upregulated in squamous cell carcinomas of the lung, esophagus, uterus and oral cavity. CD109 negatively regulates transforming growth factor (TGF)-b signaling in keratinocytes by directly modulating receptor activity. In this study, we further characterized CD109 regulation of TGF-b signaling and cell proliferation. We found that CD109 is produced as a 205 kDa glycoprotein, which is then processed in the Golgi apparatus into 180 kDa and 25 kDa proteins by furin (furinase). 180 kDa CD109 associated with GPI-anchored 25 kDa CD109 on the cell surface and was also secreted into the culture medium. To investigate whether furinase cleavage of CD109 is necessary for its biological activity, we mutated arginine 1273 in the CD109 furinase cleavage motif (amino acid 1270-RRRR-1273) to serine (R1273S). Interestingly, CD109 R1273S neither significantly impaired TGF-b signaling nor affected TGF-b-mediated suppression of cell growth, although it was expressed on the cell surface as a 205 kDa protein. Consistent with this finding, the 180 kDa and 25 kDa CD109 complex, but not CD109 R1273S, associated with the type I TGF-b receptor. These findings indicate that processing of CD109 into 180 kDa and 25 kDa proteins by furin, followed by complex formation with the type I TGF-b receptor is required for the regulation of TGF-b signaling in cancer cells and keratinocytes.

CD109 attenuates TGF-β1 signaling and enhances EGF signaling in SK-MG-1 human glioblastoma cells

“…Expression of the soluble form of CD109 attenuated TGF-b1 signaling in HEK293 cells, and addition of recombinant soluble CD109 to culture media attenuated TGF-b1 signaling and enhanced phosphorylation of STAT3 [16,18], indicating that the secreted form of CD109 is important for signal transduction in the TGF-b1 and STAT pathways. Compatible with these previous reports, we demonstrated a negative effect of the secreted N-terminal CD109 fragment in TGF-b1 signaling; however, it did not modulate EGF signaling.…”

“…Variable forms of cellular CD109 protein are summarized in Fig. 1B [16]. Two CD109 fragments of 180 and 190 kDa were detected in whole cell lysates using the anti-CD109 (C-9) antibody, whereas two CD109 fragments of 190 and 25 kDa were detected using the anti-CD109 (11H3) antibody ( Fig.…”

“…CD109 promotes TGF-b receptor internalization and degradation by regulation of SMAD7 and SMURF2 activity in ubiquitin-mediated proteolysis [14,15]. It was also reported that proteolytic processing of CD109 by furin or mesotrypsin is required for its function in cultured cells [16,17]. After cleavage by furin, a proportion of N-terminal 180-kDa fragment of CD109 is secreted from cells with the rest remaining on the cell surface.…”

“…The C-terminal 25-kDa fragment is anchored to GPI on the cell surface. The secreted fragment of CD109 is important for the regulation of TGF-b1 signaling [16]. CD109 is also associated with several nontumorigenic disorders in human and mouse.…”

Dynamic Sialylation in Transforming Growth Factor-β (TGF-β)-induced Epithelial to Mesenchymal Transition

“…5F). CD109 antigen is reported to regulate TGF-␤ signaling (41,42) and associate with cancer metastasis (43). Integrin signaling plays important roles in cell adhesion and migration both in normal and tumor cells (33).…”