RNAi mediated gene silencing of ITPA using a targeted nanocarrier: Apoptosis induction in SKBR3 cancer cells.

A pure nucleotide pool is required for high-fidelity DNA replication and prevention of carcinogenesis in living cells. Human inosine triphosphatase (ITPase), encoded by the ITPA gene, plays a critical role in maintaining the purity of the cellular nucleotide pool by excluding nucleotides that enhance mutagenesis. ITPase is a nucleoside triphosphate pyrophosphatase that hydrolyzes the non-canonical nucleotides inosine triphosphate (ITP) and xanthine triphosphate (XTP). The monophosphate products of ITPase reactions are subsequently excluded from the nucleotide pool and the improper substitution of ITP and XTP into DNA and RNA is prevented. Previous studies show that deficiency in ITPA can suppress cellular growth and enhance DNA instability. In this study, we evaluated the influence of effective ITPA down-regulation on the induction of apoptosis in a human cancer cell line using folate-single wall nanotubes (SWNT) as a targeted nanocarrier. We assessed whether SWNT enhances IPTA-siRNA transfection efficiency in cancer cells using folate as a homing device. Since folate receptor is considerably overexpressed in cancer cells, conjugation of SWNTs to folate could enhance their cancer-specific penetrance. We found that nanocarrier mediated ITPA-siRNA transfection into SKBR3 cells caused significant reduction of ITPA mRNA expression level and complete down-regulation of the ITPase protein product. The silencing of ITPA led to promotion of apoptosis in SWNT-treated SKBR3 cancer cells.

Sex-specific and developmental expression of Dmrt genes in the starlet sea anemone, Nematostella vectensis.

BACKGROUND: The molecular mechanisms underlying sex determination and differentiation in animals are incredibly diverse. The Dmrt (doublesex and mab-3 related transcription factor) gene family is an evolutionary ancient group of transcription factors dating to the ancestor of metazoans that are, in part, involved in sex determination and differentiation in numerous bilaterian animals and thus represents a potentially conserved mechanism for differentiating males and females dating to the protostome-deuterostome ancestor. Recently, the diversity of this gene family throughout animals has been described, but the expression and potential function for Dmrt genes is not well understood outside the bilaterians. RESULTS: Here, we report sex- and developmental-specific expression of all 11 Dmrts in the starlet sea anemone Nematostella vectensis. Nine out of the eleven Dmrts showed significant differences in developmental expression, with the highest expression typically in the adult stage and, in some cases, with little or no expression measured during embryogenesis. When expression was compared in females and males, seven of the eleven Dmrt genes had significant differences in expression with higher expression in males than in females for six of the genes. Lastly, expressions of two Dmrt genes with differential expression in each sex are located in the mesenteries and into the pharynx in polyps. CONCLUSIONS: Our results show that the phylogenetic diversity of Dmrt genes in N. vectensis is matched by an equally diverse pattern of expression during development and in each sex. This dynamic expression suggests multiple functions for Dmrt genes likely present in early diverging metazoans. Detailed functional analyses of individual genes will inform hypotheses regarding the antiquity of function for these transcription factors.

Testing models of the APC tumor suppressor/ß-catenin interaction reshapes our view of the destruction complex in Wnt signaling.

The Wnt pathway is a conserved signal transduction pathway that contributes to normal development and adult homeostasis, but is also misregulated in human diseases such as cancer. The tumor suppressor adenomatous polyposis coli (APC) is an essential negative regulator of Wnt signaling inactivated in >80% of colorectal cancers. APC participates in a multiprotein "destruction complex" that targets the proto-oncogene ß-catenin for ubiquitin-mediated proteolysis; however, the mechanistic role of APC in the destruction complex remains unknown. Several models of APC function have recently been proposed, many of which have emphasized the importance of phosphorylation of high-affinity ß-catenin-binding sites [20-amino-acid repeats (20Rs)] on APC. Here we test these models by generating a Drosophila APC2 mutant lacking all ß-catenin-binding 20Rs and performing functional studies in human colon cancer cell lines and Drosophila embryos. Our results are inconsistent with current models, as we find that ß-catenin binding to the 20Rs of APC is not required for destruction complex activity. In addition, we generate an APC2 mutant lacking all ß-catenin-binding sites (including the 15Rs) and find that a direct ß-catenin/APC interaction is also not essential for ß-catenin destruction, although it increases destruction complex efficiency in certain developmental contexts. Overall, our findings support a model whereby ß-catenin-binding sites on APC do not provide a critical mechanistic function per se, but rather dock ß-catenin in the destruction complex to increase the efficiency of ß-catenin destruction. Furthermore, in Drosophila embryos expressing some APC2 mutant transgenes we observe a separation of ß-catenin destruction and Wg/Wnt signaling outputs and suggest that cytoplasmic retention of ß-catenin likely accounts for this difference.

Regulation of Wnt signaling by the tumor suppressor adenomatous polyposis coli does not require the ability to enter the nucleus or a particular cytoplasmic localization.

Wnt signaling plays key roles in development and disease. The tumor suppressor adenomatous polyposis coli (APC) is an essential negative regulator of Wnt signaling. Its best-characterized role is as part of the destruction complex, targeting the Wnt effector ß-catenin (ßcat) for phosphorylation and ultimate destruction, but several studies suggested APC also may act in the nucleus at promoters of Wnt-responsive genes or to shuttle ßcat out for destruction. Even in its role in the destruction complex, APC's mechanism of action remains mysterious. We have suggested APC positions the destruction complex at the appropriate subcellular location, facilitating ßcat destruction. In this study, we directly tested APC's proposed roles in the nucleus or in precisely localizing the destruction complex by generating a series of APC2 variants to which we added tags relocalizing otherwise wild-type APC to different cytoplasmic locations. We tested these for function in human colon cancer cells and Drosophila embryos. Strikingly, all rescue Wnt regulation and down-regulate Wnt target genes in colon cancer cells, and most restore Wnt regulation in Drosophila embryos null for both fly APCs. These data suggest that APC2 does not have to shuttle into the nucleus or localize to a particular subcellular location to regulate Wnt signaling.