use-two-dimensional-semi-denaturing-detergent-agarose-gel

Use of Two Dimensional Semi-denaturing Detergent Agarose Gel Electrophoresis to Confirm Size Heterogeneity of Amyloid or Amyloid-like Fibers

Amyloid or amyloid-like fibers have been associated with many human diseases, and are now being discovered to be important for many signaling pathways. ...

UT Southwestern Medical Center

Mixed-lineage kinase domain-like protein (MLKL) is essential for TNF-α-induced necroptosis. How MLKL promotes cell death is still under debate. Here we report that MLKL forms SDS-resistant, disulfide bond-dependent polymers during necroptosis in both human and mouse cells. MLKL polymers are independent of receptor-interacting protein kinase 1 and 3 (RIPK1/RIPK3) fibers. Large MLKL polymers are more than 2 million Da and are resistant to proteinase K digestion. MLKL polymers are fibers 5 nm in diameter under electron microscopy. Furthermore, the recombinant N-terminal domain of MLKL forms amyloid-like fibers and binds Congo red dye. MLKL mutants that cannot form polymers also fail to induce necroptosis efficiently. Finally, the compound necrosulfonamide conjugates cysteine 86 of human MLKL and blocks MLKL polymer formation and subsequent cell death. These results demonstrate that disulfide bond-dependent, amyloid-like MLKL polymers are necessary and sufficient to induce necroptosis.

MLKL forms disulfide bond-dependent amyloid-like polymers to induce necroptosis.

Necroptosis is an immunogenic cell death program that is associated with a host of human diseases, including inflammation, infections, and cancer. Receptor-interacting protein kinase 3 (RIPK3) and its substrate mixed lineage kinase domain-like protein (MLKL) are required for necroptosis activation. Specifically, RIPK3-dependent MLKL phosphorylation promotes the assembly of disulfide bond-dependent MLKL polymers that drive the execution of necroptosis. However, how MLKL disulfide bond formation is regulated is not clear. In this study we discovered that the MLKL-modifying compound necrosulfonamide cross-links cysteine 86 of human MLKL to cysteine 32 of the thiol oxidoreductase thioredoxin-1 (Trx1). Recombinant Trx1 preferentially binds to monomeric MLKL and blocks MLKL disulfide bond formation and polymerization  Inhibition of MLKL polymer formation requires the reducing activity of Trx1. Importantly, shRNA-mediated knockdown of Trx1 promotes MLKL polymerization and sensitizes cells to necroptosis. Furthermore, pharmacological inhibition of Trx1 with compound PX-12 induces necroptosis in multiple cancer cell lines. Altogether, these findings demonstrate that Trx1 is a critical regulator of necroptosis that suppresses cell death by maintaining MLKL in a reduced inactive state. Our results further suggest new directions for targeted cancer therapy in which thioredoxin inhibitors like PX-12 could potentially be used to specifically target cancers expressing high levels of MLKL or MLKL short isoforms.

Zhigao Wang

Department of Molecular Biology

UT Southwestern Medical Center

Use of Two Dimensional Semi-denaturing Detergent Agarose Gel Electrophoresis to Confirm Size Heterogeneity of Amyloid or Amyloid-like Fibers

Zhigao Wang

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UT Southwestern Medical Center

Use of Two Dimensional Semi-denaturing Detergent Agarose Gel Electrophoresis to Confirm Size Heterogeneity of Amyloid or Amyloid-like Fibers

Department of Molecular Biology