Interferon-γ-induced activation of Signal Transducer and Activator of Transcription 1 (STAT1) up-regulates the tumor suppressing microRNA-29 family in melanoma cells

Abstract

BackgroundThe type-II-cytokine IFN-γ is a pivotal player in innate immune responses but also assumes functions in controlling tumor cell growth by orchestrating cellular responses against neoplastic cells. The role of IFN-γ in melanoma is not fully understood: it is a well-known growth inhibitor of melanoma cells in vitro. On the other hand, IFN-γ may also facilitate melanoma progression. While interferon-regulated genes encoding proteins have been intensively studied since decades, the contribution of miRNAs to effects mediated by interferons is an emerging area of research.We recently described a distinct and dynamic regulation of a whole panel of microRNAs (miRNAs) after IFN-γ-stimulation. The aim of this study was to analyze the transcriptional regulation of miR-29 family members in detail, identify potential interesting target genes and thus further elucidate a potential signaling pathway IFN-γ → Jak→ P-STAT1 → miR-29 → miR-29 target genes and its implication for melanoma growth.ResultsHere we show that IFN-γ induces STAT1-dependently a profound up-regulation of the miR-29 primary cluster pri-29a~b-1 in melanoma cell lines. Furthermore, expression levels of pri-29a~b-1 and mature miR-29a and miR-29b were elevated while the pri-29b-2~c cluster was almost undetectable. We observed an inverse correlation between miR-29a/b expression and the proliferation rate of various melanoma cell lines. This finding could be corroborated in cells transfected with either miR-29 mimics or inhibitors. The IFN-γ-induced G1-arrest of melanoma cells involves down-regulation of CDK6, which we proved to be a direct target of miR-29 in these cells. Compared to nevi and normal skin, and metastatic melanoma samples, miR-29a and miR-29b levels were found strikingly elevated in certain patient samples derived from primary melanoma.ConclusionsOur findings reveal that the miR-29a/b1 cluster is to be included in the group of IFN- and STAT-regulated genes. The up-regulated miR-29 family members may act as effectors of cytokine signalling in melanoma and other cancer cells as well as in the immune system.

miR-29b Mediates NF-κB Signaling in KRAS-Induced Non–Small Cell Lung Cancers

“…Tumor DNA was analyzed for KRAS and EGFR mutations by pyrosequencing or Sanger sequencing as described previously (21). Copy numbers of the miR-29b loci were assessed by qPCR using primer pairs encompassing a region from the pre-miRNA (22) relative to the autosomal reference gene GAPDH (QT02504271, Qiagen). The ethical board of the Inselspital Bern approved the study as part of the general approval for research on formalin FFPE (KEK#200/2014).…”

The role of miR-29 family members in malignant hematopoiesis

“…It was shown that interferon γ induces STAT1 dependent increase of the primary cluster pri-miR-29a/b-1, and hence the expression of miR-29a and miR-29b, while the level of pri-miR29b-2/c remains undetectable. In this case the increased miR-29a and miR-29b expression results in diminished expression of CDK6, ultimately leading to the cell cycle arrest in the G1 phase of melanoma cells 14 . It was found that during myogenesis is miR-29 the target gene of the NF-κB-YY1 signaling pathway.…”

“…This effect is mediated by two TCF/LEF binding sites within the proximal promoter and is necessary for osteoblast differentiation 13 . Recent study unveiled the ability of interferon γ to regulate the pri-miR-29a/b-1 cluster expression in melanoma 14 . Interferons are cytokines that modulate the natural immune response, however, they also have strong anti-proliferative activity.…”

microRNA-29b: an Emerging Player in Human Cancer

“…miR-29b plays an important role in oxLDL-mediated methylation of matrix metalloproteinase-2 (MMP-2)/ MMP-9 genes (Chen et al, 2011). (3)At the transcriptional level, the miR-29b cluster is involved in the group of interferon (IFN)-and signal transducers and activators of transcription (STAT)-regulated genes (Schmitt et al, 2012). The miR-29b promoter contains three GATA3-binding sites.…”