Abstract 5612: Evidence for Posttranscriptional Control of Individual Members of the miR-17–92 Cluster
MicroRNAs (miRs) are small noncoding RNAs that regulate gene expression by binding to the cellular transcript leading to translational repression or degradation of the target mRNA. The miR-17–92 cluster encodes miR-17, miR-18a, miR-19a, miR-20a, miR-19b and miR-92a. Several members of the miR-17–92 cluster regulate angiogenesis and inhibition of miR-92a was recently shown to enhance recovery after ischemia in animal models. Because all members of the miR-17–92 cluster are under the control of the same promoter and are transcribed by one primary transcript, the mature miRs are expected to be regulated similarly. However, when we assessed the expression of the individual miRs in different cell types using a microRNA array, specific miRs were enriched. In HUVEC, miR-19b (51±3), miR-20a (13±1) and miR-92a (11±0.5) were highly expressed, whereas in CD34+ hematopoietic progenitor cells, miR-17 (27±3), miR-19b (88±13), miR-20a (94±19) were expressed at highest levels. MiR-18a expression was similar in both cell types (1.6±0.1 versus 1.8±0.1) indicating that specific members of the cluster are selectively processed or stabilized. To determine the regulation of the individual mature miRs in endothelial cells, HUVEC were incubated under hypoxia. Whereas the primary miR-17–92 cluster was not regulated, the mature forms of miR-19a (257+145%, 72h) and miR-92a (246±72%, 72h) were increased although with a different time course. Likewise, the individual members of the miR-17–92 cluster were significantly up-regulated after induction of hind limb ischemia (miR-92a: 4-fold; maximum at day 2) and miR-19a (6-fold; maximum at day 3), whereas miR-18a was not significantly regulated. In summary, these data provide first evidence for the posttranscriptional regulation of the miR-17–92 cluster, which controls neovascularization. Ongoing studies aim at identifying miR binding proteins in order to further characterize the mechanisms underlying the posttranscriptional regulation of the miR-17–92 cluster.