Project description:To development our gene expression approach, we have employed whole genome microarray expression profiling as a discovery platform to identify genes potentialy regulated by the transcription factor MAX.Human SCLC cell lines waere analyzed for mutations at the MAX locus. Those cell lines that were found mutated in MAX and showed no MAX protein expression were used as a models to restore the expression of MAX transcription factor, and Identify MAX signature on Human SCLC.
Project description:To development our gene expression approach, we have employed whole genome microarray expression profiling as a discovery platform to identify genes potentialy regulated by the transcription factor MAX.Human SCLC cell lines waere analyzed for mutations at the MAX locus. Those cell lines that were found mutated in MAX and showed no MAX protein expression were used as a models to restore the expression of MAX transcription factor, and Identify MAX signature on Human SCLC. Human SCLC cell lines were hybridyzed in the following manner according for different conditions (Mock -Ø, MAX, shBRG1, MAX-shBRG1): 3 different biological samples for Mock, 3 different biological samples for MAX, 3 different samples for shBRG1 and 3 replicates of the same sample for MAX-shBRG1.
Project description:The MYC axis is commonly disrupted in cancer, mostly by activation of the MYC family of oncogenes, but also by genetic inactivation of MAX, the obligate partner of MYC, and of the MAX partner, MGA, both of which are members of the polycomb repressive complex, ncPRC1.6. While the oncogenic properties of the MYC family have been extensively studied, the tumor suppressor functions of MAX and MGA and the role of the MYC genes in MAX-mutant cells remain unclear. To address these knowledge gaps, we used chromatin immunoprecipitation, RNA-sequencing and mass spectrometry-based proteomic analysis in MAX-restituted and MYC oncogenic-transformed cell lines derived from human small cell lung cancer (SCLC), which is a high-grade neuroendocrine type of lung cancer. We found that MAX-mutant SCLC cells express ASCL1 and ASCL1-dependent targets, implying that these cells belong to the ASCL1-dependent group of SCLCs. In the absence of MAX, even after ectopic overexpression of MYC, we found no recruitment of MYC to the DNA. Furthermore, MAX reconstitution triggered pro-differentiation expression profiles that shifted when MAX and oncogenic MYC were co-expressed. Although ncPRC1.6 could be formed, the lack of MAX restricted global MGA occupancy, selectively driving its recruitment towards E2F6 motifs. Conversely, MAX restitution enhanced MGA occupancy and global gene repression of genes involved in different functions, including stem-cell and DNA repair/replication. Our data reveal that MAX-mutant SCLCs have ASCL1 characteristics, and are MYC-independent, and that their oncogenic features include deficient ncPRC1.6-mediated gene repression.
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.
Project description:The MYC-axis is disrupted in cancer, mostly by activation of the MYC-oncogenes but also through inactivation of the MYC-partner, MAX, or of the MAX-partner, MGA, both also members of the polycomb repressive complex, ncPRC1.6. Here, we use genetically modified MAX-deficient small cell lung cancer (SCLC) cells and apply genome wide and proteomics analysis to study the tumor suppressor function of MAX. We find that MAX-mutant SCLCs classify as ASCL1-type and lack MYC-transcriptional activities. MAX-restitution triggers pro-differentiation expression profiles that shift when MAX and oncogenic MYC (HMYC/MAX) are co-expressed. Despite the ncPRC1.6 can be formed, the lack of MAX restricts global MGA-occupancy, selectively driving its recruitment towards E2F6-motifs. Conversely, MAX-restitution enhances MGA-occupancy and global gene repression of genes involved in different functionalities, including stem-cell and DNA repair/replication. Collectively, these findings reveal that MAX-mutant SCLCs have ASCL1-characteristics, are MYC-independent and their oncogenic features include a deficient ncPRC1.6-mediated gene repression.