High Mutability of the Tumor Suppressor Genes RASSF1 and RBSP3 (CTDSPL) in Cancer

BACKGROUND:Many different genetic alterations are observed in cancer cells. Individual cancer genes display point mutations such as base changes, insertions and deletions that initiate and promote cancer growth and spread. Somatic hypermutation is a powerful mechanism for generation of different mutations. It was shown previously that somatic hypermutability of proto-oncogenes can induce development of lymphomas. METHODOLOGY/PRINCIPAL FINDINGS:We found an exceptionally high incidence of single-base mutations in the tumor suppressor genes RASSF1 and RBSP3 (CTDSPL) both located in 3p21.3 regions, LUCA and AP20 respectively. These regions contain clusters of tumor suppressor genes involved in multiple cancer types such as lung, kidney, breast, cervical, head and neck, nasopharyngeal, prostate and other carcinomas. Altogether in 144 sequenced RASSF1A clones (exons 1-2), 129 mutations were detected (mutation frequency, MF = 0.23 per 100 bp) and in 98 clones of exons 3-5 we found 146 mutations (MF = 0.29). In 85 sequenced RBSP3 clones, 89 mutations were found (MF = 0.10). The mutations were not cytidine-specific, as would be expected from alterations generated by AID/APOBEC family enzymes, and appeared de novo during cell proliferation. They diminished the ability of corresponding transgenes to suppress cell and tumor growth implying a loss of function. These high levels of somatic mutations were found both in cancer biopsies and cancer cell lines. CONCLUSIONS/SIGNIFICANCE:This is the first report of high frequencies of somatic mutations in RASSF1 and RBSP3 in different cancers suggesting it may underlay the mutator phenotype of cancer. Somatic hypermutations in tumor suppressor genes involved in major human malignancies offer a novel insight in cancer development, progression and spread

NAP Family CG5017 Chaperone Pleiotropically Regulates Human AHR Target Genes Expression in Drosophila Testis

To study the regulatory mechanism of the Aryl hydrocarbon receptor (AHR), target genes of transcription are necessary for understanding the normal developmental and pathological processes. Here, we examined the effects of human AHR ligands on male fecundity. To induce ectopic human AhR gene expression, we used Drosophila melanogaster transformed with human AhR under the control of a yeast UAS promoter element capable of activation in the two-component UAS-GAL4 system. We found that exogenous AHR ligands decrease the number of Drosophila gonadal Tj-positive cells. We also found both an increase and decrease of AHR target gene expression, including in genes that control homeostasis and testis development. This suggests that gonadal AHR activation may affect the expression of gene networks that control sperm production and could be critical for fertility not just in Drosophila but also in humans. Finally, we found that the activation of the expression for some AHR target genes depends on the expression of testis-specific chaperone CG5017 in gonadal cells. Since CG5017 belongs to the nucleosome assembly protein (NAP) family and may participate in epigenetic regulation, we propose that this nucleotropic chaperone is essential to provide the human AHR with access to only the defined set of its target genes during spermatogenesis

Wild type and mutant antenna and leg in flies in normal conditions and following irradiation.

<p>Simultaneous combination of mutations at both <i>ss</i> and <i>CG5017</i> loci increases sensitivity to even low doses of X-ray radiation (1 and 10 R), which is manifested as an increase in the mutant phenotype (photographs within the red frame).</p

Wild type and mutant leg and antenna phenotypes.

<p>Micrographs show the normal morphology of the tarsal structures of the wild type <i>Canton S</i>, <i>ss^a40ahm</i> and <i>milkah-1</i> flies. Antennal structures of the <i>milkah-1</i> mutant flies do not show any difference from the wild type. The distal segment of the antenna – the arista - of the <i>ss^a40ahm</i> flies presents a certain thickening of the proximal end. The arista of the <i>ss^a40ahmmilkah-1</i> hybrid flies suffered homeotic transformation into an unsegmented tarsus. The tarsal structures of the <i>ss^a40ahmmilkah-1</i> hybrids show altered segment fusion.</p

Dynamics of acquisition and retention of conditioned courtship suppression in mutant males.

<p>Males from wild type <i>Canton S</i> (A-B), <i>milkah-1</i> (C–D), <i>ss^a40a</i> (E–F) and <i>ss^a40amilkah-1</i> (G–H) lines were tested. (A, C, E, G) – of tested males. (B, D, F, H) – of tested males. On the X-axis: time following training, in days; on the Y axis: – courtship index, – learning index, standard units. Open columns – of naive males, hatched columns – () of trained males. Each point represents 20 males. ** - or significantly lower than for wild type (two-sided randomization test, ) in similar condition; - in a test immediately following training or in a deferred test, significantly lower than the CI of naive males (two-sided randomization test, ); - in the delayed test significantly lower than in test immediately following training (two-sided randomization test,.</p

Effect of X-rays and pharmacological agents on Cyp6g1, GST-theta (CG1681) and ss mRNA expression.

<p>The relative level of expression of mRNA was measured using real-time PCR. A, B, C – level of mRNA expressed in <i>Canton S</i>, <i>ss^a40a</i> and <i>ss^aSc</i> flies respectively. As a control, we used RNA from flies, which have not been exposed to radiation (cont.). F, 5-HT – level of mRNA expressed in flies, grown on medium with added furazidin (F) and 5-hydroxytryptamine (5-HT), respectively; R – radiation dose in Roentgens; 1-10R, level of expressed mRNA of the genes under study in flies irradiated with a dose of 1-10 R. F1-10R, 5-HT1-10R – level of expressed mRNA of the genes under study in flies grown on medium with added F or 5-HT and radiated with 1-10 R, respectively. The bars show the level of mRNA expression. The error bars represent the standard error of the mean of triplicate experiments. * - P<0.05, compared to control group, - P<0.05, compared to F or 5-HT group.</p