Fas ligand or FasL (CD178 or CD95L) is a homotrimeric human type II transmembrane protein. The Fas ligand gene (FASLG) on chromosome 1q24.3 encodes the Fas ligand protein. Cytotoxic T lymphocytes express FasL on their surfaces that belong to the TNF family of proteins. By binding to its receptors, FasL induces apoptosis in cells. A matrix metalloproteinase MMP-7 cleaves membrane-bound FasL and generates a soluble FasL. FasL interacts with its receptors and plays a crucial role in immune system regulation and cancer progression.
The Fas receptor (FasR) is one of the most widely studied receptors of the death receptor family. FasR is present on the surface of the target cell. Post FasL/FasR binding, FasR trimerizes and signals the cell for apoptosis. Studies have discovered around eight splice variants that translate into seven protein isoforms, and they associate many of these isoforms with disease states. Another recently discovered receptor, Decoy receptor 3 (DcR3), is a soluble receptor that binds to the FasL. As the name suggests, DcR3 cannot induce signal transduction. It competitively binds to the membrane-bound FasL and inhibits its binding to FasR, eventually rendering them inactive.
Some of the aliases that you will come across when searching ‘what is FASL’ are ALPS1b, APT1LG1, APTL, CD178, CD H 95-L, TNFSF6, TNLG1A.
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FasL/FasR binding forms a death-inducing signaling complex (DISC). DISC formation is followed by FasR trimerization and death domain protein (DD) accumulation at the receptor complex. This aggregated DD along with the receptor complex is internalized by the cellular endosomal machinery internalizes the whole receptor complex. During this process, the Fas-associated death domain (FADD) adaptor molecule binds to the DD of the Fas receptor complex. Formation of this complex promotes FADD’s death effector domain (DED), binding to the DED of caspase-8. This binding promotes Fas ligand induced proteolytic cleavage of caspase-8 into p10 and p18 subunits and helps caspase-8 activate itself. The cleaved p10 and p18 subunits form an active heterotetrameric enzyme, which, once released into the cytosol, cleaves other effector caspases that lead to membrane blebbing, DNA degradation, and other characteristic features of apoptosis.
Post activation, T cells express FasL on their membrane. The longer the T cells are activated, the more progressively sensitive they become, causing activation-induced cell death. This process is crucial as it keeps autoreactive T-cells in check and prevents excessive T cell-induced immune responses. Fas-induced cell death is a major pathway through which cytotoxic T-cells induce apoptosis in foreign antigen-expressing cells.
How long do you think it takes for a new drug to get approved in the US? About 12-15 years, that’s roughly 1/3rd duration of the entire professional career for any of us. Next, how much investment do you think is required to bring a new drug to market?
We, at NorthEast BioLabs, use MSD, ELISA, and Luminex assays to detect FasL protein in human serum, plasma, and cell culture supernatants. Below, we explain a Sandwich-based ELISA protocol for detecting Fas ligand protein in human samples.
We begin with adding an capture antibody to coat the microplate by incubating them for 2.5 hrs at room temperature (RT) or O/N at 4℃. After this incubation, we block the plates with 1% bovine serum albumin or skimmed milk for 1 hr at RT. Next with 100 μl of serially diluted standards and samples are added to respective wells and incubate them for 2.5 hrs at room temperature (RT). We then wash the plate using a plate washer and introduce a biotinylated antibody in each well and incubate it for 1 hr at RT. Then 100 μl of streptavidin-conjugated HRP is added to each well and incubated for 45 mins at RT. We then incubate the reaction mixture with TMB one-step substrate reagent for 30 min at RT. Lastly, we add 50 μl of stop solution and read the reaction at 450 nm.
The Fas ligand assay is a quantitative, colorimetric-based assay for the detection of FasL. The assay has 2 pg/ml sensitivity and can detect between 2 pg/ml to 1000 pg/ml.
Fas Ligand studies have explored some fascinating facts of its role in oncogenesis. Dysfunction in Fas-mediated apoptosis leads to carcinogenesis and drug resistance in existing anti-tumor therapies. Studies associate germ-line Fas-mutation with a childhood disorder called an autoimmune lymphoproliferative syndrome. Moreover, research has implicated that an increase in Fas-mediated signaling plays a role in the pathophysiology of glioblastoma and myelodysplastic syndromes.
To learn more about FasL and FasL antibody research, explore the resources below.
https://www.frontiersin.org/articles/10.3389/fimmu.2016.00382/full
https://www.genecards.org/cgi-bin/carddisp.pl?gene=FASLG
https://www.pnas.org/content/96/26/14871
https://www.sciencedirect.com/topics/neuroscience/fas-ligand
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC1783263/
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