The adaptor protein Grb2 regulates cell surface Fas ligand in Schwann cells.

Fas Ligand (FasL, CD178) is a cytokine that may be secreted or expressed as a transmembrane ligand at the cell surface, and induces apoptosis by binding to the "death receptor" Fas (CD95). Here, we show that Grb2, an SH3 domain-containing adaptor protein, binds to the proline-rich domain of FasL and regulates its cell surface expression. We found that knocking down Grb2 expression decreased the amount of FasL at the cell surface and increased the abundance of intracellular vesicles containing FasL. Furthermore, we showed that Grb2 acts as an adaptor for FasL to interact with adaptin beta, a molecule known to regulate trafficking. Our data reveal that Grb2 facilitates the association of FasL with adaptin beta, and promotes sorting of FasL to the cell surface. As FasL is a potent regulator of cell death, dynamic regulation of its cell surface localization is critical for controlling local tissue remodeling and inflammation.

A proteomic screen reveals novel Fas ligand interacting proteins within nervous system Schwann cells.

Fas ligand (FasL) binds Fas (CD95) to induce apoptosis or activate other signaling pathways. In addition, FasL transduces bidirectional or 'reverse signals'. The intracellular domain of FasL contains consensus sequences for phosphorylation and an extended proline rich region, which regulate its surface expression through undetermined mechanism(s). Here, we used a proteomics approach to identify novel FasL interacting proteins in Schwann cells to investigate signaling through and trafficking of this protein in the nervous system. We identified two novel FasL interacting proteins, sorting nexin 18 and adaptin beta, as well as two proteins previously identified as FasL interacting proteins in T cells, PACSIN2 and PACSIN3. These proteins are all associated with endocytosis and trafficking, highlighting the tight regulation of cell surface expression of FasL in the nervous system.