miR-155 is upregulated by HMGB1 in MEF-derived damage associated molecular pattern molecules [DAMPs]

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Micro-RNAs have emerged as important regulators of tumor biology¹. In particular Hsa-miR-155 is over-expressed in many human tumors including pancreatic, breast, colon and lung. We hypothesize that the source of hsa-miR-155 expression in tumors is derived from activated macrophages found in tumors. Human monocytes express hsa-miR-155 following stimulation with pathogen-associated molecular pattern molecules [PAMPs] such as LPS and polyIC, as well as the cytokines, TNFα and IFNβ. We investigated whether exposure of human monocytes to DAMPS could similarly induce expression of microRNA. Human PBMCs were stimulated with necrotic MEF cell lysates [+/-HMGB1], as a source of DAMPs. We observed reproducible increases in TNFα mRNA levels (after 8hrs) and secreted protein (after 24hrs). Interestingly, at early time points of 3 and 10hrs the levels of miR-155 were not increased in necrotic lysate-stimulated PBMCs, although in LPS-stimulated PBMCs the levels were increased 5 fold. Following 24hrs of stimulation only with HMGB1+ lysate, miR-155 expression was increased comparably to LPS, by about 3 fold. In order to assess expression of the downstream targets of miR-155 in human monocytes, we transfected pre-miR-155 into human primary monocytes (enriched following PBMC attachment). We observed about a 2000 fold increase (n=2) in the relative levels of mature hsa-miR-155 by real-time Taqman RT-PCR. We are currently assessing mRNA and protein levels of computational targets of miR-155, including TLR4, IKKϵ and CCR6.
 ¹Lotze MT, Yu Y. Cancer genomics: the unknown unknowns. Curr Opin Investig Drugs. 2006 Jun;7(6):497-500.