The Role of Histone Protein Modifications and Mutations in Histone Modifiers in Pediatric B-Cell Progenitor Acute Lymphoblastic Leukemia.

While cancer has been long recognized as a disease of the genome, the importance of epigenetic mechanisms in neoplasia was acknowledged more recently. The most active epigenetic marks are DNA methylation and histone protein modifications and they are involved in basic biological phenomena in every cell. Their role in tumorigenesis is stressed by recent unbiased large-scale studies providing evidence that several epigenetic modifiers are recurrently mutated or frequently dysregulated in multiple cancers. The interest in epigenetic marks is especially due to the fact that they are potentially reversible and thus druggable. In B-cell progenitor acute lymphoblastic leukemia (BCP-ALL) there is a relative paucity of reports on the role of histone protein modifications (acetylation, methylation, phosphorylation) as compared to acute myeloid leukemia, T-cell ALL, or other hematologic cancers, and in this setting chromatin modifications are relatively less well studied and reviewed than DNA methylation. In this paper, we discuss the biomarker associations and evidence for a driver role of dysregulated global and loci-specific histone marks, as well as mutations in epigenetic modifiers in BCP-ALL. Examples of chromatin modifiers recurrently mutated/disrupted in BCP-ALL and associated with disease outcomes include MLL1, CREBBP, NSD2, and SETD2. Altered histone marks and histone modifiers and readers may play a particular role in disease chemoresistance and relapse. We also suggest that epigenetic regulation of B-cell differentiation may have parallel roles in leukemogenesis.

WWOX tumour suppressor gene polymorphisms and ovarian cancer pathology and prognosis.

WWOX is a bona fide tumour suppressor, with hypomorphic and knockout mouse models exhibiting increased tumour susceptibility. In ovarian cancer cells WWOX transfection abolishes tumourigenicity, suppresses tumour cell adhesion to extracellular matrix and induces apoptosis in non-adherent cells. One-third of ovarian tumours show loss of WWOX expression, and this loss significantly associates with clear cell and mucinous histology, advanced stage, low progesterone receptor expression and poor survival, suggesting that WWOX status affects ovarian cancer progression and prognosis. Genetic variation in other tumour suppressors (e.g. p53 and XPD) is reported to modify cancer progression/outcome, and single nucleotide polymorphisms (SNPs) within the WWOX gene are reported to associate with prostate cancer risk. We previously identified polymorphic variants within WWOX, some of which have potential to affect its expression. We therefore examined a cancer modifier role for these WWOX variants. Eight SNPs, based upon location, frequency and potential to affect WWOX expression, were genotyped in 554 ovarian cancer patients (CGP samples), and associations with pathological and survival data were examined. The CGP samples demonstrated significant associations after Bonferroni correction between Isnp1 and both tumour grade (p(corr)=0.033) and histology (p(corr)=0.046), Isnp8 and tumour grade (p(corr)=0.032) and T1497G and progression-free survival (p(corr)=0.037). None of these positive associations were confirmed in an independent ovarian cancer population (Scotroc1 samples, n=863). While these results may suggest that the associations are false positives, differences between the two populations cannot be excluded, and thus highlight the challenges in validation studies.

WWOX gene expression abolishes ovarian cancer tumorigenicity in vivo and decreases attachment to fibronectin via integrin alpha3.

The WW domain-containing oxidoreductase (WWOX) gene is located at FRA16D, a common fragile site involved in human cancer. Targeted deletion of Wwox in mice causes increased spontaneous tumor incidence, confirming that WWOX is a bona fide tumor suppressor gene. We show that stable transfection of WWOX into human PEO1 ovarian cancer cells, containing homozygous WWOX deletion, abolishes in vivo tumorigenicity, but this does not correlate with alteration of in vitro growth. Rather, WWOX restoration in PEO1, or WWOX overexpression in SKOV3 ovarian cancer cells, results in reduced attachment and migration on fibronectin, an extracellular matrix component linked to peritoneal metastasis. Conversely, siRNA-mediated knockdown of endogenous WWOX in A2780 ovarian cancer cells increases adhesion to fibronectin. In addition, whereas there is no WWOX-dependent difference in cell death in adherent cells, WWOX-transfected cells in suspension culture display a proapoptotic phenotype. We further show that WWOX expression reduces membranous integrin alpha(3) protein but not integrin alpha(3) mRNA levels, and that adhesion of PEO1 cells to fibronectin is predominantly mediated through integrin alpha(3). We therefore propose that WWOX acts as an ovarian tumor suppressor by modulating the interaction between tumor cells and the extracellular matrix and by inducing apoptosis in detached cells. Consistent with this, the suppression of PEO1 tumorigenicity by WWOX can be partially overcome by implanting these tumor cells in Matrigel. These data suggest a possible role for the loss of WWOX in the peritoneal dissemination of human ovarian cancer cells.

PPM1D is a potential therapeutic target in ovarian clear cell carcinomas.

PURPOSE: To identify therapeutic targets in ovarian clear cell carcinomas, a chemoresistant and aggressive type of ovarian cancer. EXPERIMENTAL DESIGN: Twelve ovarian clear cell carcinoma cell lines were subjected to tiling path microarray comparative genomic hybridization and genome-wide expression profiling analysis. Regions of high-level amplification were defined and genes whose expression levels were determined by copy number and correlated with gene amplification were identified. The effects of inhibition of PPM1D were assessed using short hairpin RNA constructs and a small-molecule inhibitor (CCT007093). The prevalence of PPM1D amplification and mRNA expression was determined using chromogenic in situ hybridization and quantitative real-time reverse transcription-PCR in a cohort of pure ovarian clear cell carcinomas and on an independent series of unselected epithelial ovarian cancers. RESULTS: Array-based comparative genomic hybridization analysis revealed regions of high-level amplification on 1q32, 1q42, 2q11, 3q24-q26, 5p15, 7p21-p22, 11q13.2-q13.4, 11q22, 17q21-q22, 17q23.2, 19q12-q13, and 20q13.2. Thirty-four genes mapping to these regions displayed expression levels that correlated with copy number gains/amplification. PPM1D had significantly higher levels of mRNA expression in ovarian clear cell carcinoma cell lines harboring gains/amplifications of 17q23.2. PPM1D inhibition revealed that PPM1D expression and phosphatase activity are selectively required for the survival of ovarian clear cell carcinoma cell lines with 17q23.2 amplification. PPM1D amplification was significantly associated with ovarian clear cell carcinoma histology (P = 0.0003) and found in 10% of primary ovarian clear cell carcinomas. PPM1D expression levels were significantly correlated with PPM1D gene amplification in primary ovarian clear cell carcinomas. CONCLUSION: Our data provide strong circumstantial evidence that PPM1D is a potential therapeutic target for a subgroup of ovarian clear cell carcinomas.

Pharmaco(epi)genomics in ovarian cancer.

Ovarian cancer shows considerable variability in its chemoresponse, however, the prospect of individualized medicine holds high hopes for improving patient survival. The influence of interindividual genomic polymorphisms on drug response (pharmacogenomics) is well established, and a variety of candidate loci in ovarian tumors have been identified, including ERCC1, ABCB1 and p53 variants. Recently pharmacoepigenomic modulators of key genes and pathways, such as promoter methylation (MLH1 and BRCA1 genes) and microRNA regulation (PTEN/AKT and NF-kappaB pathways) have been implicated in ovarian cancer chemoresponse. Epigenomic studies have until now mainly focused on tumor-specific changes, although germ-line epigenetic change may also be of importance. However, assessing the relevance of these potential pharmaco(epi)genomic biomarkers in clinical trials requires well powered studies in homogeneous populations, with independent validation sets, to distinguish real associations from false-positives. In addition, the selection of one gene or locus as having sufficient phenotypic effect to impact on clinical outcome may be an oversimplification. Integrated approaches that identify stable pharmacogenomic and epigenomic patterns and their relationship with expression patterns and gene function will be increasingly necessary.

Homozygous deletions may be markers of nearby heterozygous mutations: The complex deletion at FRA16D in the HCT116 colon cancer cell line removes exons of WWOX.

Homozygous deletions in cancer cells have been thought to harbor tumor suppressor genes. We show that the 25 and 50 kb homozygous deletions in WWOX in the colon cancer cell line HCT116 result from a complex set of heterozygous deletions, some of which overlap to give homozygous loss. One of the heterozygous deletions has removed exons 6-8 of one allele of WWOX, and there is also a third copy of the distal region of WWOX in an unbalanced translocation. The exon 6-8 deletion results in allele-specific expression of a deleted transcript, which seems likely to be the main biological consequence of the deletions, since similar transcripts are found in other tumors. We show that such a complex set of deletions could form in a single exchange event between two homologous chromosomes, so that the selective advantage of such rearrangements need not be within the homozygous deletion. We conclude that homozygous deletions can be markers of complex rearrangements that have targets outside the homozygous deletion itself and that the target of deletions in the FRA16D region is indeed WWOX, the common outcome being the removal of particular WWOX exons. This article contains supplementary material available at http://www.interscience.wiley.com/jpages/1045-2257/suppmat.