Inhibition of miR-9 de-represses HuR and DICER1 and impairs Hodgkin lymphoma tumour outgrowth in vivo

Abstract

MicroRNAs are important regulators of gene expression in normal development and disease. miR-9 is overexpressed in several cancer forms, including brain tumours, hepatocellular carcinomas, breast cancer and Hodgkin lymphoma (HL). Here we demonstrated a relevance for miR-9 in HL pathogenesis and identified two new targets Dicer1 and HuR. HL is characterized by a massive infiltration of immune cells and fibroblasts in the tumour, whereas malignant cells represent only 1% of the tumour mass. These infiltrates provide important survival and growth signals to the tumour cells, and several lines of evidence indicate that they are essential for the persistence of HL. We show that inhibition of miR-9 leads to derepression of DICER and HuR, which in turn results in a decrease in cytokine production by HL cells followed by an impaired ability to attract normal inflammatory cells. Finally, inhibition of miR-9 by a systemically delivered antimiR-9 in a xenograft model of HL increases the protein levels of HuR and DICER1 and results in decreased tumour outgrowth, confirming that miR-9 actively participates in HL pathogenesis and points to miR-9 as a potential therapeutic target.Oncogene ( Keywords: miR-9; cytokines; Hodgkin lymphoma; HuR; DICER1 INTRODUCTIONChronic inflammation is a well-recognized cause of cancer and up to 25% of all cancers are thought to be induced by either chronic infections or autoimmune diseases. 1 Inflammation not only works as a tumour-promoting agent but also influences other steps of tumorigenesis by inducing DNA damage, angiogenesis, invasion and metastasis. 2 Hodgkin lymphoma (HL) is one of the most frequent lymphomas in the western world 3 and it can be divided in several subtypes based on the morphology, composition of the infiltrates and the phenotype of the immune cells. The nodular sclerosis subtype is the most common subtype of classical HL (cHL) and accounts for about 60--70% of the cHL cases, followed by mixed cellularity cHL accounting for 20--25%.cHL is an unusual B-cell malignancy in which the tumour cells represent only 1% of the tumour bulk, whereas the vast majority of the cells are a mixture of infiltrating immune cells and fibroblasts actively attracted via chemokine secretion by the malignant cells, the so-called Hodgkin and Reed --Sternberg cells. 3 Several lines of evidence indicate that the infiltrating cells are necessary for the survival of the HL cells by providing growth and survival signals, and protection from NK cells. 3,4 MicroRNAs (miRNAs) are small non-coding RNAs that regulate gene expression at the posttranscriptional level by base-pairing to target mRNAs and promoting transcript instability and/or translational repression. 5 Mature miRNAs derive from long hairpin precursors that are sequentially processed by the RNase-III-type enzymes DROSHA and DICER1, respectively. 5 miRNAs have been implicated in several physiological and pathological events and can act as both tumour suppressors and oncogenes. 6

MicroRNA 9-3p Targets β1 Integrin To Sensitize Claudin-Low Breast Cancer Cells to MEK Inhibition

“…This can be due to the relative abundance of a target mRNA, alternative polyadenylation sites resulting in the loss or gain of miRNA transcript binding sites, or mutation of miRNA binding sites (reviewed in reference 38). In fact, rather than being epigenetically silenced, mir-9 was shown to be overexpressed in Hodgkin's lymphoma (39), in lymphoma of the central nervous system (40), and in gastric cancer (41). In our screen, the miR-9-5p strand yielded a growth phenotype opposite that yielded by our synthetic enhancer hit, miR-9-3p.…”

The Role of Immune Modulatory MicroRNAs in Tumors

“…miRNA-9 is involved in the cellular differentiation [55] and aberrantly expressed in many cancer types breast cancer [56], colon cancer [57], nasopharyngeal carcinoma [58], and melanoma [59], suggesting that the decreased miRNA-9 expression is associated with tumor suppressor activity. In contrast, miRNA-9 expression is increased in brain cancer [60] and in Hodgkin's lymphoma [61], implying an oncomir potential. Furthermore, miRNA-9 has been shown to regulate the proliferation [56,[60][61][62] epithelial-mesenchymal transition (EMT), invasion and metastasis [62][63][64], apoptosis [56], tumor angiogenesis [63][64], and evasion of immune surveillance in many cancer types [54].…”

“…In contrast, miRNA-9 expression is increased in brain cancer [60] and in Hodgkin's lymphoma [61], implying an oncomir potential. Furthermore, miRNA-9 has been shown to regulate the proliferation [56,[60][61][62] epithelial-mesenchymal transition (EMT), invasion and metastasis [62][63][64], apoptosis [56], tumor angiogenesis [63][64], and evasion of immune surveillance in many cancer types [54]. Although the function of miRNA-9 in the classical MHC class I pathway has still to be characterized in extent, miRNA-9-mediated regulation of APM deficiencies might be at least partially responsible for the T cell-mediated immune escape.…”

Les multiples facettes d’un petit régulateur

“…Dans certains cas, miR-9 présente des propriétés oncogéniques (favorisant la progression tumorale), alors que dans d'autres, il se comporte comme un gène suppresseur de tumeurs (agissant contre la progression tumorale). Ainsi, miR-9 est fortement exprimé et participe au développement de lymphomes de Hodgkin [37], ou de certains cancers du sein [38], du col de l'utérus [39], du côlon [40] et de l'estomac [41]. Cette implication de miR-9 dans des cancers de tissus si variés est le signe que l'expression de miR-9 peut être associée à des états ou processus cellulaires généraux et non spécifiques des tissus neuraux.…”