No abstract

Acute myeloid leukemia (AML) is a deadly hematologic malignancy characterized by the uncontrolled growth of immature myeloid cells. Over the past several decades, we have learned a tremendous amount regarding the genetic aberrations that govern disease development in AML. Among these are genes that encode noncoding RNAs, including the microRNA (miRNA) family. miRNAs are evolutionarily conserved small noncoding RNAs that display important physiological effects through their posttranscriptional regulation of messenger RNA targets. Over the past decade, studies have identified miRNAs as playing a role in nearly all aspects of AML disease development, including cellular proliferation, survival, and differentiation. These observations have led to the study of miRNAs as biomarkers of disease, and efforts to therapeutically manipulate miRNAs to improve disease outcome in AML are ongoing. Although much has been learned regarding the importance of miRNAs in AML disease initiation and progression, there are many unanswered questions and emerging facets of miRNA biology that add complexity to their roles in AML. Moving forward, answers to these questions will provide a greater level of understanding of miRNA biology and critical insights into the many translational applications for these small regulatory RNAs in AML.

Zinc pyrithione (ZPT) is an antimicrobial material with widespread use in antidandruff shampoos and antifouling paints. Despite decades of commercial use, there is little understanding of its antimicrobial mechanism of action. We used a combination of genome-wide approaches (yeast deletion mutants and microarrays) and traditional methods (gene constructs and atomic emission) to characterize the activity of ZPT against a model yeast, Saccharomyces cerevisiae. ZPT acts through an increase in cellular copper levels that leads to loss of activity of iron-sulfur cluster-containing proteins. ZPT was also found to mediate growth inhibition through an increase in copper in the scalp fungus Malassezia globosa. A model is presented in which pyrithione acts as a copper ionophore, enabling copper to enter cells and distribute across intracellular membranes. This is the first report of a metalligand complex that inhibits fungal growth by increasing the cellular level of a different metal.Fungi have an essential role in causing dandruff, a scalp disease affecting Ͼ40% of the world's adult population (36). Zinc pyrithione (ZPT) is an antimicrobial compound that has been used since the 1960s in antidandruff shampoos (36) and in antifouling paints (37). In dandruff subjects, ZPT treatment reduces the amount of fungus on the scalp and stops dandruff flaking (6). Despite billions of human scalp treatments for over 4 decades, little is known of the mechanism by which ZPT inhibits fungal growth.Malassezia globosa and M. restricta are the two most common fungi on scalp (15). Despite a recent description of the genome sequences of these two species (42), study of Malassezia is challenging due to the absence of transformation methods and available mutants. Several attempts have been made to characterize the mode of action of ZPT against model fungi. ZPT has been reported to inhibit transport by membrane depolarization (5, 11). However, efficacy was reported only with doses of at least 100 M, whereas microbial growth inhibition is observed at much lower ZPT doses. Pyrithione is a well-known zinc ionophore that causes increased zinc levels within mammalian cells (1,18,27). High intracellular zinc levels can inhibit microbial growth, likely due to zinc binding to intracellular proteins and resulting in mismetallation (31). Yasokawa et al. (43) recently used transcriptional analysis of ZPT-treated Saccharomyces cerevisiae to suggest that ZPT causes iron starvation. They further showed that an iron salt lowered the antiyeast activity of ZPT, suggesting that iron starvation is a key component of ZPT's mechanism of action.In this communication, we confirm the observation by Yasokawa et al. (43) that ZPT increases transcription of the iron regulon: however, we ascribe that increase not to a transcriptional response to low iron concentrations but rather to a decrease in the activity of iron-sulfur (Fe-S) cluster-containing proteins. We show that ZPT-mediated growth inhibition is due to increased copper uptake and that copper inactivates key F...

Mitoferrin1 is

Extracellular vesicles, including exosomes, have recently been implicated as novel mediators of immune cell communication in mammals. However, roles for endogenously produced exosomes in regulating immune cell functions in vivo are just beginning to be identified. Here, we demonstrate that Rab27a and Rab27b double knockout (Rab27DKO) mice that are deficient in exosome secretion have a chronic, low-grade inflammatory phenotype characterized by elevated inflammatory cytokines and myeloproliferation. Upon further investigation, we found that some of these phenotypes could be complemented by WT hematopoietic cells or administration of exosomes produced by GM-CSF expanded bone marrow cells. Additionally, chronically inflamed Rab27DKO mice had a blunted response to bacterial LPS, resembling endotoxin tolerance. This defect was rescued by bone marrow exosomes from WT but not miR-155−/− cells suggesting that uptake of miR-155-containing exosomes is important for a proper LPS response. Further, we found that SHIP1 and IRAK-M, direct targets of miR-155 that are known negative regulators of the LPS response, were elevated in Rab27DKO mice and decreased following treatment with WT but not miR-155−/− exosomes. Together, our study finds that Rab27-dependent exosome production contributes to homeostasis within the hematopoietic system and appropriate responsiveness to inflammatory stimuli.