Project description:PBRM1 was found to be mutated in a high percentage of clear cell RCCs. We performed knockdown of PBRM1 via siRNA and compared with scrambled control in three different RCC cell lines. PBRM1 siRNA and mock treated cell lines were normalized together with 'hypoxic' clear cell renal tumors and normal renal tissue samples from GSE17818.
Project description:PBRM1 was found to be mutated in a high percentage of clear cell RCCs. We performed knockdown of PBRM1 via siRNA and compared with scrambled control in three different RCC cell lines.
Project description:PBRM1 is the 2nd-most frequently inactivated gene in clear cell renal cell cancer (RCC) but the oncogenic mechanisms, and hence methods for correction, are unclear. PBRM1 is a subunit of the PBAF coactivator complex that transcription factors use to reposition nucleosomes (‘open chromatin’) for gene activation. We therefore looked for transcription factors that recruit endogenous PBRM1 in kidney lineage/RCC cells, as a waypoint to identifying pathways impacted by PBRM1 loss. Unbiased immunoprecipitation/mass-spectrometry analyses of the endogenous PBRM1 interactome in kidney lineage cells revealed PAX8, a master transcription factor essential for proximal tubule epithelial fates, as the major transcription factor recruiting PBRM1/PBAF. The reverse analyses of the PAX8 interactome confirmed recruitment specifically of PBRM1/PBAF, and not the functionally similar BAF coactivator complex. More conspicuous in the PAX8 hub in RCC cells, however, were several corepressors, e.g. DNMT1, which oppose coactivators to repress instead of activate genes. Accordingly, key PAX8 target genes, e.g., GATA3, LHX1, WT1, and ~1000 other downstream kidney epithelial genes, but not PAX8 or PAX2, demonstrated loss of the histone lysine 27 acetylation (H3K27ac) activation mark, increase in CpG methylation repression marks, and lower expression in RCC vs normal kidney cortex, with the greatest repression in cases with bi-allelic PBRM1 inactivation. PBRM1 re-introduction into RCC cells, or depletion of the corepressor DNMT1 using siRNA or a clinical drug decitabine, rebalanced composition and function of the PAX8 transcription factor hub to coactivators, to thereby activate terminal epithelial-fates in vitro and in vivo. In sum, PBRM1 loss in RCC cells skews coregulator composition of the PAX8 master transcription factor hub toward corepressors and repression instead of activation of the downstream terminal epithelial-program; this oncogenic action could be reversed by pharmacologic corepressor depletion/inhibition.
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:Renal cell carcinoma (RCC) exhibits some unusual features and genes commonly mutated in cancer are rarely mutated in clear-cell RCC (ccRCC), the most common type. The most prevalent genetic alteration in ccRCC is the inactivation of the tumor suppressor gene VHL. Using whole-genome and exome sequencing we discovered BAP1 as a novel tumor suppressor in ccRCC that shows little overlap with mutations in PBRM1, another recent tumor suppressor. Whereas VHL was mutated in 81% of the patients (142/176), PBRM1 was lost in 58% and BAP1 in 15% of the patients analyzed. All these tumor suppressor genes are located in chromosome 3p, which is partially or completely lost in most ccRCC patients. However, BAP1 but not PBRM1 loss was associated with higher Fuhrman grade and, therefore, poorer outcome. Xenograft tumors (tumorgrafts) implanted orthotopically in mice exhibited similar gene expression profiling to corresponding primary tumors. Gene expression profiling of tumors and tumorgrafts displayed different signatures for BAP1- and PBRM1-deficient samples. Thus, after inactivation of VHL, the acquisition of a mutation in BAP1 or PBRM1 defines a different program that might alter the fate of the patient. Our results establish the foundation for an integrated pathological and molecular genetic classification of about 70% of ccRCC patients, paving the way for subtype-specific treatments exploiting genetic vulnerabilities. The RNA of clear-cell renal cell carcinoma (ccRCC) primary tumors, tumors growing in immunodeficient mice (tumorgrafts), and normal kidney cortices were labeled and hybridized to Affymetrix Human Genome U133 Plus 2.0 arrays.