Abstract
Micro-RNA (miR) 199b-5p targets Hes1 in medulloblastoma, one of the downstream effectors of both the canonical Notch and noncanonical Sonic Hedgehog pathways. In medulloblastoma patients, expression of miR-199b-5p is significantly decreased in metastatic cases, thus suggesting a downregulation mechanism. We studied this mechanism, which is mediated mostly by Hes1 and epigenetic promoter modifications. The miR-199b-5p promoter region was characterized, which identified a Hes1 binding site, thus demonstrating a negative feedback loop of regulation. MiR-199b-5p was shown to be downregulated in several medulloblastoma cell lines and in tumors by epigenetic methylation of a cytosine-phosphate-guanine island upstream of the miR-199b-5p promoter. Furthermore, the cluster of differention (CD) carbohydrate antigen CD15, a marker of medulloblastoma tumor-propagating cells, is an additional direct target of miR-199b-5p. Most importantly, regulation of miR-199b-5p expression in these CD15+/CD133+ tumor-propagating cells was influenced by only Hes1 expression and not by any epigenetic mechanism of regulation. Moreover, reverse-phase protein array analysis showed both the Akt and extracellular-signal-regulated kinase pathways as being mainly negatively regulated by miR-199b-5p expression in several medulloblastoma cell lines and in primary cell cultures. We present here the finely tuned regulation of miR-199b-5p in medulloblastoma, underlining its crucial role by its additional targeting of CD15.