Phagocytosis in Myeloid Inflammatory Cells miR-24, miR-30b, and miR-142-3p Regulate

Micro-RNAs (miRNAs) are small noncoding RNAs that regulate various biological pathways. As their role in phagocytosis remains poorly understood, we investigated their impact on phagocytosis in myeloid inflammatory cells. Seven miRNAs (miR-24,-30b,-101, 142-3p,-652-3p,-652-5p, and-1275) that were differentially expressed during monocyte to macrophage (Mw) and monocyte to dendritic cell (DC) differentiation were screened for their potential role in phagocytosis. Among these, overexpression of miR-24, miR-30b, and miR-142-3p in human monocyte-derived Mw, DC, monocytes, and PBMCs significantly attenuate phagocytosis of Escherichia coli and Staphylococcus aureus, as well as the secretion of inflammatory mediators, including TNF-a, IL-6, and IL-12p40. miRNA-mediated changes in cytokine profiles were observed at transcriptional and/or posttranscriptional levels and importantly exhibit miRNA-specific impact. To examine the underlying mechanism, we monitored the expression of phagocytosis pathway-associated genes and identified several genes that were altered in Mw and DC transfected with miR-24, miR-30b, and miR-142-3p mimics. Some of these genes with altered expression also harbor putative miRNA binding sites. We show that miR-142-3p directly regulates protein kinase Ca (PKCa), a key gene involved in phagocytosis. Interestingly, miR-142-3p and PKCa exhibit antagonistic expression during Mw and DC differentiation. Short interfering RNA-mediated knockdown of PKCa in Mw leads to reduced bacterial uptake, further highlighting the role of the gene in phagocytosis. Overall, these results demonstrate that miR-24, miR-30b, and miR-142-3p regulate phagocytosis and associated cytokine production in myeloid inflammatory cells through modulation of various genes involved in the pathway. M onocytes, macrophages (Mw), and dendritic cells (DC) are myeloid inflammatory cells capable of recognizing a plethora of microorganisms via conserved pathogen-recognition receptors. Ligation of these pathogen-recognition receptors results in a pattern of altered gene expression that enhances pathogen recognition, uptake, and removal (1, 2). This response is fine-tuned by various factors, including the class of pathogen present, the local cytokine milieu, concomitant signaling via damage-associated molecular patterns (3), as well as site-specific mechanisms of immune regulation. Critical for innate immunity and host survival is the ability of myeloid inflammatory cells to engulf microorganisms, activate antimicrobial functions, and degrade, process, and present foreign Ag to the adaptive immune system. Each type of myeloid inflam-matory cell has a role for which it is best evolved. For example, whereas Mw are the most potent at killing engulfed microorganisms, DC are most effective at presenting Ag to lymphocytes (2, 4). In monocytes, phagocytosis induces autocrine and paracrine signaling that influences local monocyte differentiation, monocyte production in the bone …