Decreased Dicer expression elicits DNA damage and up-regulation of MICA and MICB

Abstract

RNA interference (RNAi) acts constitutively to silence the innate immune response, and innate immunity genes are misregulated in Dicer-deficient Caenorhabditis elegans. Here, we show that inhibition of Dicer expression by RNAi in human cells up-regulates major histocompatibility complex class I–related molecules A and B (MICA and MICB). MICA and MICB are innate immune system ligands for the NKG2D receptor expressed by natural killer cells and activated CD8(+)T cells. We reveal that knockdown of Dicer elicits DNA damage. Up-regulation of MICA and MICB by Dicer knockdown is prevented by pharmacologic or genetic inhibition of DNA damage pathway components, including ataxia telangiectasia mutated (ATM) kinase, ATM- and Rad3-related kinase, or checkpoint kinase 1. Therefore we conclude that up-regulation of MICA and MICB is the result of DNA damage response activation caused by Dicer knockdown. Our results suggest that RNAi is indirectly linked to the human innate immune system via the DNA damage pathway.

Phospho-ΔNp63α is a key regulator of the cisplatin-induced microRNAome in cancer cells

“…To test the effect of DICER1 on miRNA expression in HNSCC cells after CIS exposure, we used scrambled siRNA (5 0 -AATTCTCCGAACGTGTCACGT-3 0 ) and DICER1 siRNA (5 0 -AAGGCTTACCTTCTCCAGGCT-3 0 ) obtained from Dharmacon (Lafayette, CO, USA), as previously described. 40 To maximally inhibit DICER1 expression and keep the cells at optimal density, DNp63a cells were transfected with two rounds of DICER1 siRNA or scrambled siRNA (each at 100 nM). Cells were split 48 h after the first round of DICER1 siRNAs transfection and were transfected again with the same siRNAs for another 24 h along with exposure to Con or 10 mg/ml CIS.…”

Dicer-regulated microRNAs 222 and 339 promote resistance of cancer cells to cytotoxic T-lymphocytes by down-regulation of ICAM-1

“…S6), Dicer (ex 5Ϫ/Ϫ) cells exhibited greater sensitivity to NK cell-mediated lysis. However, a recent study indicated that inhibition of Dicer leads to up-regulation of ligands for the NKG2D receptor, MICA, and MICB via DNA damage (36). Hence, a variety of immunological mechanisms may operate in increased susceptibility of Dicer (ex5 Ϫ/Ϫ) cells against immune surveillance.…”

Dicer Regulates the Expression of Major Histocompatibility Complex (MHC) Class I Chain-Related Genes A and B

“…Immunostaining assays for the phosphorylated form of histone H2AX ( -H2AX), a widely used marker for double-strand DNA breaks (Foster ER. & Downs JA., 2005), and for the replication protein A 70 (RPA70), a protein that becomes phosphorylated and forms intranuclear foci upon exposure of cells to DNA damage (Zou Y. et al, 2006), revealed that a much higher percentage of Dicer knockdown cells display intense -H2AX foci and RPA foci compared to control cells (Tang KF. et al, 2008b).…”

“…Decreased Dicer expression elicits DNA damage (Mudhasani R. et al, 2008;Peng JC. & Karpen GH., 2009;Tang KF. et al, 2008b).…”

“…DNA damage induces upregulation of NKG2D ligands (including MICA and MICB). Some components of the DNA damage checkpoints, including ATM and ATR (two proteins involved in DNA damage detection), and Chk1 (a protein that transduces the DNA damage signal to effector proteins), are essential for the up-regulation of NKG2D ligands (Gasser S. et al, 2005;Tang KF. et al, 2008b).…”