Soluble CD109 binds TGF-β and antagonizes TGF-β signalling and responses

Abstract

Transforming growth factor-β (TGF-β) is a multifunctional cytokine implicated in many diseases, including tissue fibrosis and cancer. TGF-β mediates diverse biological responses by signalling through type I and II TGF-β receptors (TβRI and TβRII). We have previously identified CD109, a glycosylphosphatidylinositol (GPI)-anchored protein, as a novel TGF-β co-receptor that negatively regulates TGF-β signalling and responses and demonstrated that membrane-anchored CD109 promotes TGF-β receptor degradation via a SMAD7/Smurf2-mediated mechanism. To determine whether CD109 released from the cell surface (soluble CD109 or sCD109) also acts as a TGF-β antagonist, we determined the efficacy of recombinant sCD109 to interact with TGF-β and inhibit TGF-β signalling and responses. Our results demonstrate that sCD109 binds TGF-β with high affinity as determined by surface plasmon resonance (SPR) and cell-based radioligand binding and affinity labelling competition assays. SPR detected slow dissociation kinetics between sCD109 and TGF-β at low concentrations, indicating a stable and effective interaction. In addition, sCD109 antagonizes TGF-β-induced Smad2/3 phosphorylation, transcription and cell migration. Together, our results suggest that sCD109 can bind TGF-β, inhibit TGF-β binding to its receptors and decrease TGF-β signalling and TGF-β-induced cellular responses.

Molecular Therapy for Degenerative Disc Disease: Clues from Secretome Analysis of the Notochordal Cell-Rich Nucleus Pulposus

“…Soluble CD109 can bind to all 3 isoforms of TGFβ-1/2/3, thus interfering with the activation of TGFβ dependent signaling34. In fact, membrane bound CD109 acts as a co-receptor for TGFβ1 and results in internalization and degradation of TGFβ receptors via binding to Smad73536.…”

Development of novel monoclonal antibodies against CD109 overexpressed in human pancreatic cancer

“…More recently, CD109 was reported to act as a novel pro-metastatic factor in a lung adenocarcinoma mouse model, and high levels of CD109 resulted in the activation of Jak-Stat3 signalling pathways in cancer cells suggesting that the direct targeting of CD109 could be of therapeutic benefit in the neoadjuvant or adjuvant setting [ 41 ]. While the soluble recombinant form of CD109 was reported to be capable of binding to TGF-β and antagonising TGF-β signalling and cellular responses in experimental system [ 42 , 43 ], it remains unclear whether patients with pancreatic cancer or any other cancer type shed CD109 antigen into their sera and any other body fluids and if so, whether CD109 may confer diagnostic, prognostic and predictive values, and therefore warrants further investigation. Finally, while TMAs are commonly employed in medical research, the heterogeneous nature of both tumour and stroma in patients with pancreatic cancer support the need for further investigations on the relative expression and prognostic significance of CD109 in a larger group of patients using the whole tumour sections or several TMA cores from the same tumours [ 44 , 45 ]…”

CD109: a multifunctional GPI‐anchored protein with key roles in tumor progression and physiological homeostasis

“…Although CD109 function has been extensively studied, its detailed biological role remains unclear. The primary function of CD109 reportedly involves downregulating transforming growth factor (TGF)‐β signaling through its binding to TGF‐β receptor I [activin receptor‐like kinase (ALK)5], TGF‐β, ALK1, and 78‐kDa glucose‐regulated protein (GRP78) in vitro. Both GPI‐anchored CD109 and soluble CD109 bind to TGF‐β receptors and attenuate TGF‐β‐induced SMAD2/3 phosphorylation (Fig.…”

“…Both GPI‐anchored CD109 and soluble CD109 bind to TGF‐β receptors and attenuate TGF‐β‐induced SMAD2/3 phosphorylation (Fig. a) . Particularly in SCCs, CD109 promotes tumor initiation by suppressing the TGF‐β/SMAD/ nuclear factor erythroid 2–related factor‐2 pathway; however, CD109 deficiency has no significant effect on TGF‐β signaling in mouse keratinocytes in vitro and in vivo, suggesting that the function of CD109 in TGF‐β signaling is dependent upon cell type, although the reason for this is not yet fully understood.…”