MRP5/ABCC5, A CONSERVED ABC TRANSPORTER, REGULATES METAZOAN HEME HOMEOSTASIS

Hemes are metalloporphyrins used by nearly all organisms as cofactors for proteins involved in respiration, binding and sensing gases, and as catalysts for various reactions. Despite extensive knowledge about heme biosynthesis and catabolism, the pathways for transporting heme between cells and within cells remain poorly understood. C. elegans serves as a unique animal model for uncovering these pathways, as it is unable to synthesize its own heme and depends on the uptake of dietary heme for growth and reproduction. Functional RNAi screens implicated mrp-5 as a potential heme transporter in C. elegans. This gene encodes a membrane-bound ABC transporter that localizes to the basolateral intestinal membrane and is required for worm growth and reproduction. Depletion of mrp-5 activates heme deprivation signals within the worm, protects worms from toxicity associated with a toxic heme analog, and results in worms accumulating the fluorescent heme analog, zinc mesoporphyrin IX, in intestinal cells. Taken together, these results indicate a defect in heme export from the intestine when MRP-5 activity is lost. Functional assays in yeast support the hypothesis that MRP-5 is capable of exporting heme across cell membranes, and that this function is conserved in the human ortholog. Knockdown of mrp5 in zebrafish embryos results in developmental defects and decreased blood formation, indicating that this transporter likely regulates heme homeostasis in vertebrates. Loss of Mrp5 in mammalian cells leads to decreased heme transport into the secretory pathway as measured by activity of a Golgi-targeted heme-dependent enzyme. Furthermore, macrophages from mice lacking Mrp5 are unable to activate a number of cellular responses when undergoing erythrophagocytosis, the process whereby the heme-iron in senescent red bloods is recycled. Altogether, our results implicate MRP-5 as a key heme transporter in C. elegans, and point to an evolutionarily conserved role for MRP5 proteins in regulating heme homeostasis

Involvement of the p62/NRF2 signal transduction pathway on erythrophagocytosis

This deposit is composed by the main article plus the supplementary materials of the publication.Erythrophagocytosis, the phagocytic removal of damaged red blood cells (RBC), and subsequent phagolysosome biogenesis are important processes in iron/heme metabolism and homeostasis. Phagolysosome biogenesis implies the interaction of nascent phagosomes with endocytic compartments and also autophagy effectors. Here, we report that besides recruitment of microtubule-associated protein-1-light chain 3 (LC3), additional autophagy machinery such as sequestosome 1 (p62) is also acquired by single-membrane phagosomes at very early stages of the phagocytic process and that its acquisition is very important to the outcome of the process. In bone marrow-derived macrophages (BMDM) silenced for p62, RBC degradation is inhibited. P62, is also required for nuclear translocation and activation of the transcription factor Nuclear factor E2-related Factor 2 (NRF2) during erythrophagocytosis. Deletion of the Nrf2 allele reduces p62 expression and compromises RBC degradation. In conclusion, we reveal that erythrophagocytosis relies on an interplay between p62 and NRF2, potentially acting as protective mechanism to maintain reactive oxygen species at basal levels and preserve macrophage homeostasis.Fundação para a Ciência e a Tecnologia grants: (HMSP-ICT/0024/2010, UID/Multi/04462/2013, SFRH/BD/62197/2009, SFRH/BD/90258/2012, SFRH /BD/51877/2012, SFRH/BD/52293/2013, PTDC/SAU-TOX/116627/2010, HMSP-ICT/0022/2010 ); European Union FEDER support: (COMPETE, QREN, PT2020 Partnership Agreement), ERC grant: (ERC-2011-AdG 294709-DAMAGECONTROL).info:eu-repo/semantics/publishedVersio

MicroRNA silencing of tumor suppressor DLC-1 promotes efficient hepatitis C virus replication in primary human hepatocytes

MicroRNAs (miRNAs) are approximately 22-nucleotide noncoding RNAs that constitute silencers of target gene expression. Aberrant expression of miRNA has been linked to a variety of cancers, including hepatocellular carcinoma (HCC). Hepatitis C virus (HCV) infection is considered a major cause of chronic liver disease and HCC, although the mechanism of virus infection-associated hepatocarcinogenesis remains unclear. We report a direct role of miRNAs induced in HCV-infected primary human hepatocytes that target the tumor suppressor gene DLC-1 (a Rho GTPase-activating protein), which is frequently deleted in HCC, and other solid human tumors. MicroRNA miR-141 that targets DLC-1 was accentuated in cells infected with HCV genotypes 1a, 1b, and 2a. We present several lines of evidence that efficient HCV replication requires miR-141-mediated suppression of DLC-1. An increase in miR-141 correlated with the inhibition of DLC-1 protein in HCV-infected cells. Depletion of miR-141 with oligonucleotides complementary to the miRNAs inhibited virus replication, whereas artificially increased levels of intracellular miR-141 enhanced HCV replication. HCV-infected hepatocytes showed enhanced cell proliferation that can be countered by overexpression of DLC-1. Conclusion: The collective results of this study suggest a novel mechanism of HCV infection-associated miRNA-mediated regulation of a tumor suppressor protein that has the ability to influence cell proliferation and HCV infection-mediated liver cancer. © 2010 American Association for the Study of Liver Diseases.link_to_subscribed_fulltex