Project description:We performed a loss-of-function, RNA interference screen to define new therapeutic targets in multiple myeloma, a genetically diverse plasma cell malignancy. Unexpectedly, we discovered that all myeloma lines require caspase-10 for survival, irrespective of their genetic abnormalities. The transcription factor IRF4 induces both caspase-10 and its associated protein cFLIPL in myeloma, generating a protease that does not induce apoptosis but rather blocks an autophagy-dependent cell death pathway. Caspase-10 inhibits autophagy by cleaving the BCL2-interacting protein BCLAF1, itself a strong inducer of autophagy that acts by displacing beclin-1 from BCL2. While myeloma cells require a basal level of autophagy for survival, caspase-10 tempers this response to avoid cell death. Drugs that disrupt this vital balance may have therapeutic potential in myeloma. To generate a gene expression signature of caspase 10 signaling in multiple myeloma, cell lines (SKMM1 n=16, KMS12 n=8 and H929 n=12) were transduced with retroviral vectors expressing either shCasp10-2 or shCasp10-3. Similarly, lymphoma cell lines (OCI-Ly7 n=2 and OCI-Ly19 n=2) were transduced and used as a control. Following puromycin selection, shRNA expression was induced for 24 to 120 hours and gene expression was measured, comparing uninduced (Cy3) to induced (Cy5) cells, using lymphochip microarrays. Biological repeats were performed of H929 and SKMM1 samples.
Project description:We performed a loss-of-function, RNA interference screen to define new therapeutic targets in multiple myeloma, a genetically diverse plasma cell malignancy. Unexpectedly, we discovered that all myeloma lines require caspase-10 for survival, irrespective of their genetic abnormalities. The transcription factor IRF4 induces both caspase-10 and its associated protein cFLIPL in myeloma, generating a protease that does not induce apoptosis but rather blocks an autophagy-dependent cell death pathway. Caspase-10 inhibits autophagy by cleaving the BCL2-interacting protein BCLAF1, itself a strong inducer of autophagy that acts by displacing beclin-1 from BCL2. While myeloma cells require a basal level of autophagy for survival, caspase-10 tempers this response to avoid cell death. Drugs that disrupt this vital balance may have therapeutic potential in myeloma.
Project description:Formation of the Death-Inducing Signalling Complex (DISC) initiates the extrinsic apoptotic signalling cascade. Caspase-8 and its regulator cFLIP control death signalling by binding to the receptor via DISC-bound FADD. By elucidating the function of Caspase-10, a close homologue of caspase-8, we unexpectedly found that caspase-10 negatively regulates caspase-8-mediated cell death signalling in the DISC. We demonstrate that caspase-10 inhibits the activation of caspase-8 independent of cFLIP. Furthermore, we show that caspase-8 does not compete with other tandem DED proteins such as cFLIP or caspase-10 in binding via FADD to the receptor as current models suggest. By utilizing caspase-8 knockout cells, we demonstrate that caspase-8 has to be placed upstream of both cFLIP and caspase-10 in the DISC. We further show that DISC formation and/or stability depends on caspase-8 but is independent from its enzymatic activity. Surprisingly, we identified caspase-10 to rewire DISC-signalling to NF-kB activation and cell survival. Our data are consistent with a model in which caspase-10 and cFLIP co-ordinately regulate caspase-8-mediated cell death signalling.
Project description:Kynureninase is a member of a large family of catalytically diverse but structurally homologous pyridoxal 5'-phosphate (PLP) dependent enzymes known as the aspartate aminotransferase superfamily or alpha-family. The Homo sapiens and other eukaryotic constitutive kynureninases preferentially catalyze the hydrolytic cleavage of 3-hydroxy-l-kynurenine to produce 3-hydroxyanthranilate and l-alanine, while l-kynurenine is the substrate of many prokaryotic inducible kynureninases. The human enzyme was cloned with an N-terminal hexahistidine tag, expressed, and purified from a bacterial expression system using Ni metal ion affinity chromatography. Kinetic characterization of the recombinant enzyme reveals classic Michaelis-Menten behavior, with a Km of 28.3 +/- 1.9 microM and a specific activity of 1.75 micromol min-1 mg-1 for 3-hydroxy-dl-kynurenine. Crystals of recombinant kynureninase that diffracted to 2.0 A were obtained, and the atomic structure of the PLP-bound holoenzyme was determined by molecular replacement using the Pseudomonas fluorescens kynureninase structure (PDB entry 1qz9) as the phasing model. A structural superposition with the P. fluorescens kynureninase revealed that these two structures resemble the "open" and "closed" conformations of aspartate aminotransferase. The comparison illustrates the dynamic nature of these proteins' small domains and reveals a role for Arg-434 similar to its role in other AAT alpha-family members. Docking of 3-hydroxy-l-kynurenine into the human kynureninase active site suggests that Asn-333 and His-102 are involved in substrate binding and molecular discrimination between inducible and constitutive kynureninase substrates.