Micro(mi)RNAs are a large class of ~22-nucleotide non-coding RNA molecules that participate a major part in the regulation of gene expression in majority of the eukaryotes. Increasingly, they have been shown to play significant roles in a variety of cancers, in particular of those involving different blood cells [
1]. Marek's disease (MD), a naturally occurring CD4+ T-cell lymphoma in chickens induced by Marek's disease virus (MDV), is considered to be a very good model for herpesvirus-induced rapid-onset T-cell lymphomas [
2]. Recent studies on the miRNA expression profiles of a number of MDV-transformed chicken lymphoid cell lines have shown significant alterations in the expression of several host miRNAs compared to the normal chicken lymphocytes [
3]. One of the miRNAs that was consistently downregulated in a number of MDV-transformed chicken lymphoid cell lines is gga-miR-26a [
3]. Suppression of miR-26a has been demonstrated in a variety of human cancers also [
4‐
6] suggesting that miR-26a has potential tumour suppression functions, and its downregulation could be essential for transformation. This notion is supported from the roles of miR-26a in p53 tumour suppressor network [
7], as well as in the regulation of transformation-related targets such as cyclin D2, SMAD1, EZH2 and PTEN [
8,
9].
Antigen-specific T cell proliferation and immunological responses are dependent on the expression of several cytokine genes such as interleukin-2 (IL-2). IL-2 plays an important role in the development, differentiation and homeostasis of T cells, and IL-2 expression is dysregulated in diseases such as leukaemia, autoimmunity and pathogenesis of viral diseases [
10], including MD [
11]. As in mammals, the chicken IL-2 can modulate T-cell proliferation and cytotoxicity
in vitro and
in vivo [
12]. The mechanisms of transcriptional regulation of IL-2 promoters through activating transcription factors such as NFκB or AP-1 have been extensively studied [
13]. Negative regulation of IL-2 expression is also important both for maintaining the gene in an inactive state in resting cells and for repressing the gene after the activation. Compared to the studies on transactivation, the mechanisms involved in the negative regulation of IL-2 gene expression are less well studied. Although the roles of co-repressors and histone deacetylases in the transcriptional repression of IL-2 has been demonstrated [
14], it is also becoming clear that a number of miRNAs are also involved in shaping of the immune responses [
15,
16] at least in part through the regulation of cytokine genes [
17]. For example, miR-146a has been shown to modulate the adaptive immune responses by regulating the IL-2 expression in human T lymphocytes [
18]. However, chicken IL-2 is not a predicted target of gga-miR-146a
http://www.ebi.ac.uk/enright-srv/microcosm/htdocs/targets/. Although miR-26a has not been implicated in the regulation of IL-2, we examined whether miR-26a downregulation in MDV-transformed chicken lymphoma cell lines do affect IL-2 expression. We present the data suggesting that chicken IL-2 is a direct target of miR-26a, and its downregulation could affect IL-2 expression and signalling pathways in these transformed cells.