Cell cycle genes and ovarian cancer susceptibility: a tagSNP analysis

Background:

Dysregulation of the cell cycle is a hallmark of many cancers including ovarian cancer, a leading cause of gynaecologic cancer mortality worldwide.

Methods:

We examined single nucleotide polymorphisms (SNPs) (n=288) from 39 cell cycle regulation genes, including cyclins, cyclin-dependent kinases (CDKs) and CDK inhibitors, in a two-stage study. White, non-Hispanic cases (n=829) and ovarian cancer-free controls (n=941) were genotyped using an Illumina assay.

Results:

Eleven variants in nine genes (ABL1, CCNB2, CDKN1A, CCND3, E2F2, CDK2, E2F3, CDC2, and CDK7) were associated with risk of ovarian cancer in at least one genetic model. Seven SNPs were then assessed in four additional studies with 1689 cases and 3398 controls. Association between risk of ovarian cancer and ABL1 rs2855192 found in the original population [odds ratio, OR_{BB vs AA} 2.81 (1.29–6.09), P=0.01] was also observed in a replication population, and the association remained suggestive in the combined analysis [OR_{BB vs AA} 1.59 (1.08–2.34), P=0.02]. No other SNP associations remained suggestive in the replication populations.

Conclusion:

ABL1 has been implicated in multiple processes including cell division, cell adhesion and cellular stress response. These results suggest that characterization of the function of genetic variation in this gene in other ovarian cancer populations is warranted.

Progesterone receptor variation and risk of ovarian cancer is limited to the invasive endometrioid subtype: results from the Ovarian Cancer Association Consortium pooled analysis

There is evidence that progesterone plays a role in the aetiology of invasive epithelial ovarian cancer. Therefore, genes involved in pathways that regulate progesterone may be candidates for susceptibility to this disease. Previous studies have suggested that genetic variants in the progesterone receptor gene (PGR) may be associated with ovarian cancer risk, although results have been inconsistent. We have established an international consortium to pool resources and data from many ovarian cancer case–control studies in an effort to identify variants that influence risk. In this study, three PGR single nucleotide polymorphisms (SNPs), for which previous data have suggested they affect ovarian cancer risk, were examined. These were +331 C/T (rs10895068), PROGINS (rs1042838), and a 3′ variant (rs608995). A total of 4788 ovarian cancer cases and 7614 controls from 12 case–control studies were included in this analysis. Unconditional logistic regression was used to model the association between each SNP and ovarian cancer risk and two-sided P-values are reported. Overall, risk of ovarian cancer was not associated with any of the three variants studied. However, in histopathological subtype analyses, we found a statistically significant association between risk of endometrioid ovarian cancer and the PROGINS allele (n=651, OR=1.17, 95% CI=1.01–1.36, P=0.036). We also observed borderline evidence of an association between risk of endometrioid ovarian cancer and the +331C/T variant (n=725 cases; OR=0.80, 95% CI 0.62–1.04, P=0.100). These data suggest that while these three variants in the PGR are not associated with ovarian cancer overall, the PROGINS variant may play a modest role in risk of endometrioid ovarian cancer.

Relation of contraceptive and reproductive history to ovarian cancer risk in carriers and noncarriers of BRCA1 gene mutations

In the general population, ovarian cancer risk is inversely associated with oral contraceptive use, tubal ligation, and childbearing. Among carriers of BRCA1 gene mutations, the data are conflicting. The authors identified women diagnosed with incident invasive epithelial ovarian cancer in the San Francisco Bay Area of California from March 1997 through July 2001. They compared the contraceptive and reproductive histories of 36 carrier cases and 381 noncarrier cases with those of 568 controls identified by random digit dialing who were frequency matched to cases on age and race/ethnicity. In both carriers and noncarriers, reduced risk was associated with ever use of oral contraceptives (odds ratio = 0.54 (95% confidence interval (CI): 0.26, 1.13) for carriers and 0.55 (95% CI: 0.41, 0.73) for noncarriers), duration of oral contraceptive use (risk reduction per year = 13% (p = 0.01) for carriers and 6% (p < 0.001) for noncarriers), history of tubal ligation (odds ratio = 0.68 (95% CI: 0.25, 1.90) for carriers and 0.65 (95% CI: 0.45, 0.95) for noncarriers), and increasing parity (risk reduction per childbirth = 16% (p = 0.26) for carriers and 24% (p < 0.001) for noncarriers). These data suggest that BRCA1 mutation carriers and noncarriers have similar risk reductions associated with oral contraceptive use, tubal ligation, and parity.

In vitro synthesis of carbohydrate-binding proteins by human leucocytes

A carbohydrate-binding protein (CBP) synthesized in vitro by normal human peripheral leucocytes was isolated by affinity chromatography on asialofetuin-Sepharose. The CBP was eluted with lactose and it had a native molecular mass of 15,500 daltons. Analysis by SDS-PAGE revealed a single polypeptide of 18,000 daltons. CBP synthesis was time dependent and cell concentration dependent. The CBP appeared to be both cell bound and secreted with the apparent amount secreted inversely proportional to cell concentration. CBP did not appear to be synthesized by T and B leukemic cell lines examined. Promyelocytic HL-60 cells, however, synthesized at least two lactose-eluted CBP's corresponding to native molecular masses of 28,000 and 19,500 daltons. SDS-PAGE analysis of radiolabelled HL-60 CBP's showed the presence of two polypeptides of MM 17,700 and 16,000 daltons suggesting that one of the CBP's was a dimer.

Effect of bleomycin on deoxynucleotide-polymerizing enzymes from human cells

DNA polymerases alpha and beta from Molt-4 cells are inhibited by bleomycin, whereas DNA polymerase gamma assayed with poly-(A)-(dT)12-18 as the template primer or terminal deoxynucleotidyl transferase assayed with activated DNA, poly(dA), (dG)12-18 or (dA)12-18 as the initiator are not inhibited by this antibiotic. Inhibition by bleomycin increased the Km for template DNA but not that for dTTP. Increasing amounts of bleomycin did not affect the Vmax for DNA polymerase alpha or beta when the amount of template DNA was varied but it reduced the Vmax for these enzymes when dTTP was varied. Moreover, the addition of extra template reversed the bleomycin inhibition but the addition of extra enzyme did not. Although dithiothreitol was required for bleomycin inhibition of DNA polymerase activity, bleomycin preincubated with dithiothreitol (or beta-mercaptoethanol) at pH 6.5 to 9.0 lost its inhibitory activity. This was not the case when DNA was also included in the preincubation mixture. The results obtained in this study indicate that bleomycin inhibits DNA polymerases alpha and beta by a thiol reagent-dependent interaction with the template. Thus, the antitumor activity of bleomycin may be greatly influenced by the concentration of sulfhydryl compounds and their proximity to DNA in the target cells.