NF-kappaB p65-Dependent Transactivation of miRNA Genes following Cryptosporidium parvum Infection Stimulates Epithelial Cell Immune Responses

Abstract

Cryptosporidium parvum is a protozoan parasite that infects the gastrointestinal epithelium and causes diarrheal disease worldwide. Innate epithelial immune responses are key mediators of the host's defense to C. parvum. MicroRNAs (miRNAs) regulate gene expression at the posttranscriptional level and are involved in regulation of both innate and adaptive immune responses. Using an in vitro model of human cryptosporidiosis, we analyzed C. parvum-induced miRNA expression in biliary epithelial cells (i.e., cholangiocytes). Our results demonstrated differential alterations in the mature miRNA expression profile in cholangiocytes following C. parvum infection or lipopolysaccharide stimulation. Database analysis of C. parvum-upregulated miRNAs revealed potential NF-κB binding sites in the promoter elements of a subset of miRNA genes. We demonstrated that mir-125b-1, mir-21, mir-30b, and mir-23b-27b-24-1 cluster genes were transactivated through promoter binding of the NF-κB p65 subunit following C. parvum infection. In contrast, C. parvum transactivated mir-30c and mir-16 genes in cholangiocytes in a p65-independent manner. Importantly, functional inhibition of selected p65-dependent miRNAs in cholangiocytes increased C. parvum burden. Thus, we have identified a panel of miRNAs regulated through promoter binding of the NF-κB p65 subunit in human cholangiocytes in response to C. parvum infection, a process that may be relevant to the regulation of epithelial anti-microbial defense in general.

CFTR mediates bicarbonate-dependent activation of miR-125b in preimplantation embryo development

“…Interestingly, activation of NF-κB has been observed in early singlecell stage embryo and postulated to be required for the development of mouse embryos beyond the twocell stage [40]. More importantly, NF-κB can bind to the promoter element of miR-125b and upregulate its expression [20]. Therefore, we proposed that CFTRmediated HCO 3 − influx activates sAC, which in turns triggers PKA-dependent NF-κB activation, leading to upregulation of miR-125b expression.…”

“…The expression of miR-125b is also found in mouse preimplantation embryos although its exact role has not been eluciated [16]. Several proteins, including p53, have been reported to be the targets of miR-125b and mediate its action in various physiological and pathological events, including neuronal differentiation [12,17,18], immune response [19,20] and cancer [10,[21][22][23]. Particularly, p53 has been reported to mediate the effect of miR-125b on embryo development [15].…”

MicroRNAs in the regulation of TLR and RIG-I pathways

“…For the most part, primary miRNA transcription is dependent on the NF-kB transcription factor. 64,65 Additionally, TLR signals can negatively regulate miRNAs, including miR125b, let-7i and miR-98, [66][67][68] in certain cell types. Little is known about how TLR signals decrease miRNA expression, which most likely occurs through transcriptional repression or post-transcriptional destabilization of miRNA.…”

MicroRNA immunobiology: when microRNA chemists meet immunologists

“…For example, Toll-like receptors (TLRs) induce the expression of more than 20 miRNAs (including miR-21, miR-15b, miR-16, miR-23b, miR-27b, miR-30b, miR-30c, miR-125b, miR-146, miR-147 and miR-155), each of which selectively targets a specific group of mRNAs. [6][7][8][9][10] Thus, TLR-induced miR-146a turns off TLR response by degrading IRAK1 and TRAF6 mRNAs that are required for TLR signaling, and mediates lipopolysaccharide tolerance that is crucial for preventing septic shock 6,11 Similarly, TLR4-induced miR-21 blocks TLR4 response by targeting programmed cell death 4, a crucial transcriptional and translational regulator of TLR-induced gene expression 12 Knocking down either miR-146a or miR-21, or knocking out dicer, a gene that controls miRNA biogenesis, leads to hyper-activation of TLRs 6,9,12 Thus, besides the negative regulatory proteins of TLRs, 13 TLR-induced microRNAs represent a new class of negative feedback regulators essential for preventing deleterious inflammatory conditions induced by pathogens.…”

“…It is unknown how immune receptors selectively activate some miRNA genes but not others; once activated, it is unclear how miRNAs selectively control immune responses that induce them. TLRs can upregulate .20 miRNAs and downregulate .30 [6][7][8][9][10] As many of these miRNAs regulated by TLR signaling are also dysregulated in cancer, it is possible that miRNAs form a key link between inflammation and cancer and that the induction of specific miRNAs, including miR-21, by TLRs may be a key step in tumor genesis. Thus, interdisciplinary research will likely continue to be the engine of growth of this nascent field for years to come.…”