An IKKα-E2F1-BMI1 cascade activated by infiltrating B cells controls prostate regeneration and tumor recurrence.

Androgen-deprived prostate cancer (PCa) is infiltrated by B lymphocytes that produce cytokines that activate IκB kinase α (IKKα) to accelerate the emergence of castration-resistant tumors. We now demonstrate that infiltrating B lymphocytes and IKKα are also required for androgen-dependent expansion of epithelial progenitors responsible for prostate regeneration. In these cells and in PCa cells, IKKα phosphorylates transcription factor E2F1 on a site that promotes its nuclear translocation, association with the coactivator CBP, and recruitment to critical genomic targets that include Bmi1, a key regulator of normal and cancerous prostate stem cell renewal. The IKKα-BMI1 pathway is also activated in human PCa.

Tumor promotion via injury- and death-induced inflammation.

Inhibition of programmed cell death is considered to be a major aspect of tumorigenesis. Indeed, several key oncogenic transcription factors, such as NF-κB and STAT3, exert their tumor-promoting activity at least in part through upregulation of survival genes. However, many cancers develop in response to chronic tissue injury, in which the resulting cell death increases the tumorigenic potential of the neighboring cells. In this review, we discuss a resolution to this paradox based on cell death-mediated induction of tumor promoting inflammatory cytokines, which enhance cell survival and trigger compensatory proliferation in response to tissue injury.

AID-induced genotoxic stress promotes B cell differentiation in the germinal center via ATM and LKB1 signaling.

During an immune response, B cells undergo rapid proliferation and activation-induced cytidine deaminase (AID)-dependent remodeling of immunoglobulin (IG) genes within germinal centers (GCs) to generate memory B and plasma cells. Unfortunately, the genotoxic stress associated with the GC reaction also promotes most B cell malignancies. Here, we report that exogenous and intrinsic AID-induced DNA strand breaks activate ATM, which signals through an LKB1 intermediate to inactivate CRTC2, a transcriptional coactivator of CREB. Using genome-wide location analysis, we determined that CRTC2 inactivation unexpectedly represses a genetic program that controls GC B cell proliferation, self-renewal, and differentiation while opposing lymphomagenesis. Inhibition of this pathway results in increased GC B cell proliferation, reduced antibody secretion, and impaired terminal differentiation. Multiple distinct pathway disruptions were also identified in human GC B cell lymphoma patient samples. Combined, our data show that CRTC2 inactivation, via physiologic DNA damage response signaling, promotes B cell differentiation in response to genotoxic stress.

Copy number variant analysis of human embryonic stem cells.

Differences between individual DNA sequences provide the basis for human genetic variability. Forms of genetic variation include single-nucleotide polymorphisms, insertions/duplications, deletions, and inversions/translocations. The genome of human embryonic stem cells (hESCs) has been characterized mainly by karyotyping and comparative genomic hybridization (CGH), techniques whose relatively low resolution at 2-10 megabases (Mb) cannot accurately determine most copy number variability, which is estimated to involve 10%-20% of the genome. In this brief technical study, we examined HSF1 and HSF6 hESCs using array-comparative genomic hybridization (aCGH) to determine copy number variants (CNVs) as a higher-resolution method for characterizing hESCs. Our approach used five samples for each hESC line and showed four consistent CNVs for HSF1 and five consistent CNVs for HSF6. These consistent CNVs included amplifications and deletions that ranged in size from 20 kilobases to 1.48 megabases, involved seven different chromosomes, were both shared and unique between hESCs, and were maintained during neuronal stem/progenitor cell differentiation or drug selection. Thirty HSF1 and 40 HSF6 less consistently scored but still highly significant candidate CNVs were also identified. Overall, aCGH provides a promising approach for uniquely identifying hESCs and their derivatives and highlights a potential genomic source for distinct differentiation and functional potentials that lower-resolution karyotype and CGH techniques could miss. Disclosure of potential conflicts of interest is found at the end of this article.

TORC2 regulates germinal center repression of the TCL1 oncoprotein to promote B cell development and inhibit transformation.

Aberrant expression of the TCL1 oncoprotein promotes malignant transformation of germinal center (GC) B cells. Repression of TCL1 in GC B cells facilitates FAS-mediated apoptosis and prevents lymphoma formation. However, the mechanism for this repression is unknown. Here we show that the CREB coactivator TORC2 directly regulates TCL1 expression independent of CREB Ser-133 phosphorylation and CBP/p300 recruitment. GC signaling through CD40 or the BCR, which activates pCREB-dependent genes, caused TORC2 phosphorylation, cytosolic emigration, and TCL1 repression. Signaling via cAMP-inducible pathways inhibited TCL1 repression and reduced apoptosis, consistent with a prosurvival role for TCL1 before GC selection and supporting an initiating role for aberrant TCL1 expression during GC lymphomagenesis. Our data indicate that a novel CREB/TORC2 regulatory mode controls the normal program of GC gene activation and repression that promotes B cell development and circumvents oncogenic progression. Our results also reconcile a paradox in which signals that activate pCREB/CBP/p300 genes concurrently repress TCL1 to initiate its silencing.

B29 gene silencing in pituitary cells is regulated by its 3' enhancer.

B cell-specific B29 (Igbeta, CD79b) genes in rat, mouse, and human are situated between the 5' growth hormone (GH) locus control region and the 3' GH gene cluster. The entire GH genomic region is DNase 1 hypersensitive in GH-expressing pituitary cells, which predicts an "open" chromatin configuration, and yet B29 is not expressed. The B29 promoter and enhancers exhibit histone deacetylation in pituitary cells, but histone deacetylase inhibition failed to activate B29 expression. The B29 promoter and a 3' enhancer showed local dense DNA methylation in both pituitary and non-lymphoid cells consistent with gene silencing. However, DNA methyltransferase inhibition did not activate B29 expression either. B29 promoter constructs were minimally activated in transfected pituitary cells. Co-transfection of the B cell-specific octamer transcriptional co-activator Bob1 with the B29 promoter construct resulted in high level promoter activity in pituitary cells comparable to B29 promoter activity in transfected B cells. Unexpectedly, inclusion of the B29 3' enhancer in B29 promoter constructs strongly inhibited B29 transcriptional activity even when pituitary cells were co-transfected with Bob1. Both Oct-1 and Pit-1 bind the B29 3' enhancer in in vitro electrophoretic mobility shift assay and in in vivo chromatin immunoprecipitation analyses. These data indicate that the GH locus-embedded, tissue-specific B29 gene is silenced in GH-expressing pituitary cells by epigenetic mechanisms, the lack of a B cell-specific transcription factor, and likely by the B29 3' enhancer acting as a powerful silencer in a context and tissue-specific manner.

Combined analysis of genome scans of dutch and finnish families reveals a susceptibility locus for high-density lipoprotein cholesterol on chromosome 16q.

Several genomewide screens have been performed to identify novel loci predisposing to unfavorable serum lipid levels and coronary heart disease (CHD). We hypothesized that the accumulating data of these screens in different study populations could be combined to verify which of the identified loci truly harbor susceptibility genes. The power of this strategy has recently been demonstrated with other complex diseases, such as inflammatory bowel disease and asthma. We assessed the largely unknown genetic background of CHD by investigating the most common dyslipidemia predisposing to CHD, familial combined hyperlipidemia (FCHL), affecting 1%-2% of Western populations and 10%-20% of families with premature CHD. To be able to perform a combined data analysis, we unified the diagnostic criteria for FCHL and its component traits and combined the data from two genomewide scans performed in two populations, the Finns and the Dutch. As a result of our pooled data analysis, we identified three chromosomal regions, on chromosomes 2p25.1, 9p23, and 16q24.1, exceeding the statistical significance level of a LOD score >2.0. The 2p25.1 region was detected for the FCHL trait, and the 9p23 and 16q24.1 regions were detected for the low high-density lipoprotein cholesterol (HDL-C) trait. In addition, the previously recognized 1q21 region also obtained additional support in the other study sample, when the triglyceride trait was used. Analysis of the 16q24.1 region resulted in a statistically significant LOD score of 3.6 when the data from Finnish families with low HDL-C were included in the analysis. To search for the underlying gene in the 16q24.1 region, we investigated a novel functional and positional candidate gene, helix/forkhead transcription factor (FOXC2), by sequencing and by genotyping of two single-nucleotide polymorphisms in the families.