Leandro Cerchietti

Specific peptide interference reveals BCL6 transcriptional and oncogenic mechanisms in B-cell lymphoma cells.

The BTB/POZ transcriptional repressor and candidate oncogene BCL6 is frequently misregulated in B-cell lymphomas. The interface through which the BCL6 BTB domain mediates recruitment of the SMRT, NCoR and BCoR corepressors was recently identified. To determine the contribution of this interface to BCL6 transcriptional and biological properties, we generated a peptide that specifically binds BCL6 and blocks corepressor recruitment in vivo. This inhibitor disrupts BCL6-mediated repression and establishment of silenced chromatin, reactivates natural BCL6 target genes, and abrogates BCL6 biological function in B cells. In BCL6-positive lymphoma cells, peptide blockade caused apoptosis and cell cycle arrest. BTB domain peptide inhibitors may constitute a novel therapeutic agent for B-cell lymphomas.

Kaiso-deficient mice show resistance to intestinal cancer.

ABSTRACT Kaiso is a BTB domain protein that associates with the signaling molecule p120-catenin and binds to the methylated sequence mCGmCG or the nonmethylated sequence CTGCNA to modulate transcription. In Xenopus laevis, xKaiso deficiency leads to embryonic death accompanied by premature gene activation in blastulae and upregulation of the xWnt11 gene. Kaiso has also been proposed to play an essential role in mammalian synapse-specific transcription. We disrupted the Kaiso gene in mice to assess its role in mammalian development. Kaiso-null mice were viable and fertile, with no detectable abnormalities of development or gene expression. However, when crossed with tumor-susceptible Apc Min/+ mice, Kaiso-null mice showed a delayed onset of intestinal tumorigenesis. Kaiso was found to be upregulated in murine intestinal tumors and is expressed in human colon cancers. Our data suggest that Kaiso plays a role in intestinal cancer and may therefore represent a potential target for therapeutic intervention.

Transcriptional signature with differential expression of BCL6 target genes accurately identifies BCL6-dependent diffuse large B cell lymphomas

Diffuse large B cell lymphomas (DLBCLs) often express BCL6, a transcriptional repressor required for the formation of normal germinal centers. In a subset of DLBCLs, BCL6 is deregulated by chromosomal translocations or aberrant somatic hypermutation; in other tumors, BCL6 expression may simply reflect germinal center lineage. DLBCLs dependent on BCL6-regulated pathways should exhibit differential regulation of BCL6 target genes. Genomic array ChIP-on-chip was used to identify the cohort of direct BCL6 target genes. This set of genes was enriched in modulators of transcription, chromatin structure, protein ubiquitylation, cell cycle, and DNA damage responses. In primary DLBCLs classified on the basis of gene expression profiles, these BCL6 target genes were clearly differentially regulated in “BCR” tumors, a subset of DLBCLs with increased BCL6 expression and more frequent BCL6 translocations. In a panel of DLBCL cell lines analyzed by expression arrays and classified according to their gene expression profiles, only BCR tumors were highly sensitive to the BCL6 peptide inhibitor, BPI. These studies identify a discrete subset of DLBCLs that are reliant on BCL6 signaling and uniquely sensitive to BCL6 inhibitors. More broadly, these data show how genome-wide identification of direct target genes can identify tumors dependent on oncogenic transcription factors and amenable to targeted therapeutics.

Effects of Eicosapentaenoic and Docosahexaenoic n-3 Fatty Acids From Fish Oil and Preferential Cox-2 Inhibition on Systemic Syndromes in Patients With Advanced Lung Cancer

Abstract Under the common denomination of Systemic Immune-Metabolic Syndrome (SIMS), we grouped many symptoms that share a similar pathophysiologic background. SIMS is the result of the dysfunctional interaction of tumor cells, stroma cells, and the immune system, leading to the release of cytokines and other systemic mediators such as eicosanoids. SIMS includes systemic syndromes such as paraneoplastic hemopathies, hypercalcemia, coagulopathies, fatigue, weakness, cachexia, chronic nausea, anorexia, and early satiety among others. Eicosapentaenoic and docosahexaenoic n-3 fatty acids from fish oil can help in the management of persistent chronic inflammatory states, but treatments compliance is generally poor. Preferentially, Cox-2 inhibition can create a favorable pattern of cytokines by decreasing the production of certain eicosanoids, although their role in SIMS is unknown. The aim of this study was to test the hypothesis that by modulating systemic inflammation through an eicosanoid-targeted approach, some of the symptoms of the SIMS could be controlled. We exclusively evaluated 12 patients for compliance. Patients were assigned 1 of the 4 treatment groups (15-, 12-, 9-, or 6-g dose, fractionated every 8 h). For patients assigned to 15 and 12 doses, the overall compliance was very poor and unsatisfactory for patients receiving the 9-g dose. The maximum tolerable dose was calculated to be around 2 capsules tid (6 g of fish oil per day). A second cohort of 22 patients with advanced lung cancer and SIMS were randomly assigned to receive either fish oil, 2 g tid, plus placebo capsules bid (n = 12) or fish oil, 2 g tid, plus celecoxib 200 mg bid (n = 10). All patients in both groups received oral food supplementation. After 6 wk of treatment, patients receiving fish oil + placebo or fish oil + celecoxib showed significantly more appetite, less fatigue, and lower C-reactive protein (C-RP) values than their respective baselines values (P < 0.02 for all the comparisons). Additionally, patients in the fish oil + celecoxib group also improved their body weight and muscle strength compared to baseline values (P < 0.02 for all the comparisons). Comparing both groups, patients receiving fish oil + celecoxib showed significantly lower C-RP levels (P = 0.005, t-test), higher muscle strength (P = 0.002, t-test) and body weight (P = 0.05, t-test) than patients receiving fish oil + placebo. The addition of celecoxib improved the control of the acute phase protein response, total body weight, and muscle strength. Additionally, the consistent nutritional support used in our patients could have helped to maximize the pharmacological effects of fish oil and/or celecoxib. This study shows that by modulating the eicosanoid metabolism using a combination of n-3 fatty acids and cyclooxygenase-2 inhibitor, some of the signs and symptoms associated with a SIMS could be ameliorated.

Structure of a BCOR Corepressor Peptide in Complex with the BCL6 BTB Domain Dimer

The transcriptional corepressors BCOR, SMRT, and NCoR are known to bind competitively to the BCL6 BTB domain despite the fact that BCOR has no detectable sequence similarity to the other two corepressors. We have identified a 17 residue motif from BCOR that binds directly to the BCL6 BTB domain and determined the crystal structure of the complex to a resolution of 2.6 A. Remarkably, the BCOR BCL6 binding domain (BCOR(BBD)) peptide binds in the same BCL6 binding site as the SMRT(BBD) peptide despite the lack of any significant sequence similarity between the two peptides. Mutations of critical BCOR(BBD) residues cause the disruption of the BCL6 corepression activities of BCOR, and a BCOR(BBD) peptide blocks BCL6-mediated transcriptional repression and kills lymphoma cells.

Sequential Transcription Factor Targeting for Diffuse Large B-Cell Lymphomas

Transcription factors play a central role in malignant transformation by activating or repressing waves of downstream target genes. Therapeutic targeting of transcription factors can reprogram cancer cells to lose their advantages in growth and survival. The BCL6 transcriptional repressor plays a central role in the pathogenesis of diffuse large B-cell lymphomas (DLBCL) and controls downstream checkpoints, including the p53 tumor suppressor gene. We report that a specific inhibitor of BCL6 called BPI can trigger a p53 response in DLBCL cells. This was partially due to induction of p53 activity and partially due to relief of direct repression by BCL6 of p53 target genes. BPI could thus induce a p53-like response even in the presence of mutant p53. Moreover, sequential BCL6 peptide inhibitors followed by p53 peptide or small-molecule activators provided a more powerful antilymphoma effect than either treatment alone by maximally restoring p53 target gene expression. Therefore, tandem targeting of the overlapping BCL6 and p53 transcriptional programs can correct aberrant survival pathways in DLBCL and might provide an effective therapeutic approach to lymphoma therapy.