Magnetosome vesicles are present before magnetite formation, and MamA is required for their activation

Bacterial magnetosomes are intracellular compartments that house highly ordered magnetite crystals. By using Magnetospirillum sp. AMB-1 as a model system, we show that magnetosome vesicles exist in the absence of magnetite, biomineralization of magnetite proceeds simultaneously in multiple vesicles, and biomineralization proceeds from the same location in each vesicle. The magnetosome-associated protein, MamA, is required for the formation of functional magnetosome vesicles and displays a dynamic subcellular localization throughout the growth cycle of magnetotactic bacteria. Together, these results suggest that the magnetosome precisely coordinates magnetite biomineralization and can serve as a model system for the study of organelle biogenesis in noneukaryotic cells

The tumor suppressor miR-642a-5p targets Wilms tumor 1 gene and cell-cycle progression in prostate cancer

RNA-based therapeutics are emerging as innovative options for cancer treatment, with microRNAs being attractive targets for therapy development. We previously implicated microRNA-642a-5p (miR-642a-5p) as a tumor suppressor in prostate cancer (PCa), and here we characterize its mode of action, using 22Rv1 PCa cells. In an in vivo xenograft tumor model, miR-642a-5p induced a significant decrease in tumor growth, compared to negative control. Using RNA-Sequencing, we identified gene targets of miR-642a-5p which were enriched for gene sets controlling cell cycle; downregulated genes included Wilms Tumor 1 gene (WT1), NUAK1, RASSF3 and SKP2; and upregulated genes included IGFBP3 and GPS2. Analysis of PCa patient datasets showed a higher expression of WT1, NUAK1, RASSF3 and SKP2; and a lower expression of GPS2 and IGFBP3 in PCa tissue compared to non-malignant prostate tissue. We confirmed the prostatic oncogene WT1, as a direct target of miR-642a-5p, and treatment of 22Rv1 and LNCaP PCa cells with WT1 siRNA or a small molecule inhibitor of WT1 reduced cell proliferation. Taken together, these data provide insight into the molecular mechanisms by which miR-642a-5p acts as a tumor suppressor in PCa, an effect partially mediated by regulating genes involved in cell cycle control; and restoration of miR-642-5p in PCa could represent a novel therapeutic approach

Post-transcriptional regulation of the breast cancer susceptibility gene BRCA1 by Hu Antigen-R

BRCA1 is a breast cancer susceptibility gene that is down-regulated in the majority of cases of sporadic breast cancer. In tumours with reduced BRCA1 protein expression, there can be a concomitant reduction in mRNA level, or no change, suggesting that disruption of multiple different regulatory processes may contribute to BRCA1 down-regulation. Despite this, efforts to date have chiefly focussed on transcriptional and epigenetic regulation of the gene, whilst post-transcriptional processes that regulate the dynamics of the BRCA1 transcript, such as decay, localisation and translation efficiency, are poorly understood. Post-transcriptional regulation of gene expression is often mediated by RNA-binding proteins (RNA-BPs) that recognise sequence motifs in the untranslated regions (UTRs) of certain mRNAs, and recruit, or shield them from macromolecular complexes involved in RNA metabolism, such as the translation apparatus and the exosome. Primary and secondary structure analysis of the BRCA1 3'UTR sequence revealed two predicted binding sites for the RNA-BP Hu-antigen R (HuR), known to regulate the stability and translation efficiency of other transcripts, including COX-2, TNF-α and TP53. Interestingly, HuR is frequently over-expressed in sporadic breast cancer. We present the results of RNA-protein-binding assays showing that HuR interacts directly with synthetic RNA probes containing one of the predicted HuR-binding sites in the BRCA1 3'UTR, and immunoprecipitation studies showing that this interaction occurs endogenously in human mammary epithelial cell lines. Over-expression of HuR conferred a reduction in BRCA1 protein expression, and the BRCA1 3'UTR sequence was sufficient for down-regulation of a luciferase reporter gene in cells expressing ectopic HuR. Experiments addressing the mechanism underlying the change in BRCA1 expression in HuR over-expressing cells, including reporter assays, mRNA and protein stability assays, suggest that the mechanism of regulation is post-transcriptional. Current and future work is aimed at understanding the relationship between HuR and BRCA1 in breast cancer