Endogenous small RNAs (miRNAs)
regulate gene expression by mechanisms conserved
across metazoans. While the number of verified human
miRNAs is still expanding, only few have been
functionally annotated. To perform genetic screens
for novel functions of miRNAs we developed a library
of vectors expressing the majority of cloned human
miRNAs and created corresponding DNA barcode
arrays.
In a screen for miRNAs that cooperate
with oncogenes in cellular transformation we
identified miR-372 and miR-373, each permitting
proliferation and tumorigenesis of primary human
cells that harbor both oncogenic RAS and active wild
type p53. These miRNAs neutralize p53-mediated CDK2
inhibition, most likely through direct suppression
of the expression of the tumor-suppressor LATS2. We
demonstrate that these miRNAs are novel oncogenes
participating in the development of human testicular
germ cell tumors by numbing the p53 pathway, thus
allowing tumorigenic growth in the presence of wild
type p53.
In a a novel functional genetic
approach we identified miR-221 and miR-222
(miR-221&222) as potent regulators of p27Kip1, a
cell cycle inhibitor and tumor suppressor.
Interestingly, high miR-221 level appears in
signatures of poor prognosis cancers. Using
miRNA-inhibitors we demonstrated that certain cancer
cell lines require high activity of miR-221 for the
maintenance of low p27Kip1 levels and continuous
proliferation. We show that this interaction plays a
role in human glioblastoma development.
