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Fig. 14 Light-activated inhibition of miRNA function. An inhibitory oligonucleotide was intramolecularly linked
to a blocking strand with a photocleavable linker, inhibiting its ability to target miRNAs. Upon a brief irradiation
with UV light the linker is cleaved affording the activation of the antisense oligonucleotide. This construct was
proven to be effective in modulating miRNA-mediated developmental processes in C. elegans . Image adapted
with permission from Zheng G et al. (2012) ACS Chem Biol
catalytic ribozyme motifs. These oligonucleotide enzymes are
capable of cleaving RNA substrates in a sequence-specifi c fashion
leading to gene inactivation. DNAzymes are composed of a con-
served catalytic core with two fl anking regions that are capable of
binding an RNA-substrate sequence [ 64 ]. The binding and cleav-
ing actions of DNAzymes prove to be effi cient and specifi c inhibi-
tors of miRNA, with locked nucleic acid (LNA) modifi cations
enhancing the catalytic activity. This new class of antisense inhibi-
tors has been coined “antagomirzymes” [ 65 ].
Through in vitro assays antagomirzymes were found to cleave
specifi c miRNA targets with approximately 70 % of the miRNA
targets cleaved by the LNA-based analogs. The catalytic activity
was confi rmed via disruption of the catalytic domain, which eradi-
cated the ability of the antagomirzyme to inhibit miRNAs.
Moreover, an in vivo luciferase assay examined hsa-miR-372 and
hsa-miR-373 targets, with LNA antagomirzymes restoring the
reporter level by up to 80 %. In comparison, oligonucleotides with
a shuffl ed catalytic domain led to suppressed expression, again
highlighting the catalytic action of the antigomirzyme rather than
simply its binding ability. While both forms of antigomirzymes
effectively cleave miRNAs in vitro and in vivo, very high concen-
trations are required to be therapeutically useful. Future work in
this area requires the identifi cation of better cleavage sites within
miRNA targets and optimization of cellular delivery.
A fi nal mechanism to regulate RNAi within mammalian cells
involves a hybrid approach that engineers an RNA aptamer onto an
shRNA in order to modulate miRNA levels using a small-molecule
effector [ 66 ]. Researchers constructed an shRNA (targeting
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