Downregulation of Fas ligand by shedding

Abstract

Apoptosis-inducing Fas ligand (FasL) is a type II membrane protein, predominantly expressed in the activated T cells. FasL is cleaved by a putative metalloproteinase to produce a soluble form. Here, we blocked the shedding of human FasL by deleting its cleavage site. Although human Jurkat cells and mouse primary hepatocytes that express a low level of Fas were resistant to the soluble form of FasL, they were efficiently killed by membrane-bound FasL. Furthermore, soluble FasL inhibited cytotoxicity of the membrane-bound FasL. These results indicate that the membrane-bound form of FasL is the functional form and suggest that shedding of FasL is to prevent the killing of the healthy bystander cells by cytotoxic T cells.

ADAM10 regulates FasL cell surface expression and modulates FasL-induced cytotoxicity and activation-induced cell death

“…In agreement with this, the FasL mutant D4, which carries a deletion between aa 111 and 133, was shown to be uncleavable in murine cells. 8 We also found diminished release of sFasL in murine embryonic fibroblasts (MEFs) and in 293T cells expressing this mutant indicating that in both cell types the protein is cleaved in a similar region (Supplementary Figure 1).…”

“…A putative protease ectodomain cleavage site of hFasL has initially been mapped to Lys129-Gln130 in murine cells 8 and to Ser126 and Leu127 in human 293 T cells. 11 These cleavage sites are located outside the region that is required for trimerization and self-assembly allowing the sFasL to form trimers.…”

“…Over the past years, it became evident that FasL might also be released by protease cleavage to act as a soluble cytokine. 8 34 Several MMPs including MMP-3 (stromelysin-1) 35 and MMP-7 (matrilysin) 9,16 have been associated with FasL cleavage in different cellular systems. On the other hand, several other members of the TNF-family and TNF receptor family are proteolytically processed by ADAMs, suggesting that these proteases might also be involved in the FasL cleavage.…”

“…4,5 In several cell types, a soluble form of FasL (sFasL) can be generated through metalloprotease (MPs)-mediated cleavage of the transmembrane molecule shortly after cell surface expression. [6][7][8][9] It has been observed that soluble FasL (sFasL) can have proapoptotic as well as antiapoptotic functions depending on the local microenvironment. 10,11 For both membrane-bound and sFasL, a spontaneous trimer formation has been suggested, which seems indispensable for triggering the death signal via Fas oligomers.…”

Combination of Human Fas (CD95/Apo-1) Ligand with Adriamycin Significantly Enhances the Efficacy of Antitumor Response

“…By engaging its receptor (Fas), membrane-bound FasL induces apoptosis in the target cells. In this manner, FasL plays a central role in both cellmediated immunity and immune downregulation (13,14).…”