No abstract

Drug resistance is a major cause of cancer treatment failure, with multidrug resistance (MDR) being the most serious, whereby cancer cells display cross-resistance to structurally and functionally unrelated drugs. MDR is caused by overexpression of the efflux transporters P-glycoprotein (P-gp) and multidrug resistance-associated protein 1 (MRP1). These transporters act to maintain sublethal intracellular drug concentrations within the cancer cell, making the population treatment unresponsive. Recently, we discovered a novel nongenetic basis to MDR whereby microparticles (MPs) transfer P-gp intercellularly from MDR donor cells to drug-sensitive recipient cells. MPs isolated from MDR leukemia and breast cancer cells were cocultured with their drug-sensitive counterparts. P-gp transfer was assessed by direct immunolabeling, and acquired transcripts and regulatory microRNAs by quantitative real-time PCR. We show that MDR MPs incorporate nucleic acids; MPs change recipient cells' transcriptional environment to reflect donor MDR phenotype, and distinct pathways exist among cancers of different origin that may be dependent on donor cells' ABCB1 overexpression. We demonstrate that this pathway exists for both hematological and nonhematological malignancies. By conferring MDR and "retemplating" the transcriptional landscape of recipient cells, MPs provide a novel pathway, having implications in the dissemination and acquisition of deleterious traits in clinical oncology.

BackgroundMicroparticles (MPs) are membrane vesicles which are released from normal and malignant cells following a process of budding and detachment from donor cells. MPs contain surface antigens, proteins and genetic material and serve as vectors of intercellular communication. MPs comprise the major source of systemic RNA including microRNA (miRNA), the aberrant expression of which appears to be associated with stage, progression and spread of many cancers. Our previous study showed that MPs carry both transcripts and miRNAs associated with the acquisition of multidrug resistance in cancer.ResultsHerein, we expand on our previous finding and demonstrate that MPs carry the transcripts of the membrane vesiculation machinery (floppase and scramblase) as well as nucleic acids encoding the enzymes essential for microRNA biogenesis (Drosha, Dicer and Argonaute). We also demonstrate using microarray miRNA profiling analysis, the selective packaging of miRNAs (miR-1228*, miR-1246, miR-1308, miR-149*, miR-455-3p, miR-638 and miR-923) within the MP cargo upon release from the donor cells.ConclusionsThese miRNAs are present in both haematological and non-haematological cancer cells and are involved in pathways implicated in cancer pathogenesis, membrane vesiculation and cascades regulated by ABC transporters. Our recent findings reinforce our earlier reports that MP transfer ‘re-templates’ recipient cells so as to reflect donor cell traits. We now demonstrate that this process is likely to occur via a process of selective packaging of nucleic acid species, including regulatory nucleic acids upon MP vesiculation. These findings have significant implications in understanding the cellular basis governing the intercellular acquisition and dominance of deleterious traits in cancers.

Metabolic disorders in HIV-infected patients, especially those receiving highly active antiretroviral therapy (HAART) regimens containing protease inhibitors, are associated with insulin resistance. These metabolic disorders include fat redistribution, diabetes, and hypertriglyceridemia. Thiazolidinediones (TZDs) are used to treat patients with diabetes secondary to insulin resistance, and TZDs are being studied in HAART-related metabolic disorders. We studied the effects of TZDs (peroxisome proliferator-activated receptor-gamma [PPARgamma] agonists) and a PPARalpha agonist on HIV replication and TNFalpha production in peripheral blood mononuclear cells (PBMCs) acutely infected with HIV-1, in a chronically infected monoblastoid cell line (U1) and in alveolar macrophages (AMs) from HIV-infected subjects and uninfected controls. Rosiglitazone, ciglitazone, troglitazone, and PgJ (PPARgamma agonists) as well as fenofibrate (PPARalpha agonist) inhibited HIV replication in both PBMCs and U1 cells. These agents also inhibited TNFalpha production, but the magnitude of TNFalpha inhibition was not directly correlated with the quantitative decreases in HIV replication. In AMs, ciglitazone, rosiglitazone, and troglitazone reduced TNFalpha production. We hypothesize that alterations in mitogen-activated protein kinase signaling pathways have contemporaneous and interrelated effects on HIV replication, cytokine production, and lipid metabolism. Modulation of these pathways using PPAR agonists may improve the metabolic alterations during HAART in conjunction with desirable decreases in HIV replication and TNFalpha production.