MicroRNAs (miRNAs) are ubiquitously expressed small, non-coding RNAs that negatively regulate
gene expression at a post-transcriptional level. So far, over 1000 miRNAs have been identified in human cells
and their diverse functions in normal cell homeostasis and many different diseases have been thoroughly
investigated during the past decade. MiR-29, one of the most interesting miRNA families in humans to date,
consists of three mature members miR-29a, miR-29b and miR-29c, which are encoded in two genetic clusters.
Members of this family have been shown to be silenced or down-regulated in many different types of cancer
and have subsequently been attributed predominantly tumor-suppressing properties, albeit exceptions have
been described where miR-29s have tumor-promoting functions. MiR-29 targets expression of diverse proteins
like collagens, transcription factors, methyltransferases and others, which may partake in abnormal migration,
invasion or proliferation of cells and may favor development of cancer. Furthermore, members of the miR-29
family can be activated by interferon signaling, which suggests a role in the immune system and in hostpathogen
interactions, especially in response to viral infections. In this review, we summarize current
knowledge on the genomic organization and regulation of the miR-29 family and we provide an overview of its
implication in cancer suppression and promotion as well as in host immune responses. The numerous
remarkable properties of these miRNAs and their often altered expression patterns might make the miR-29
family promising biomarkers and therapeutic targets for various diseases in future.