Specificity and Functionality of microRNA Inhibitors

Highly potent microRNA (miRNA) inhibitors are valuable tools for elucidating the roles of miRNAs and their targets. Although it is known that pairings between endogenous miRNAs and their natural targets in animals generally involve base pair mismatches, studies of how mismatches between endogenous miRNAs and artificial inhibitor targets might affect inhibitor specificity and functionality have been very limited. Using a Luciferase reporter system we have investigated the specicity of miRNA inhibitors. We first confirmed significant levels of cross-reactivity among the closely related let-7 family members. Subsequently,
a systematic study of mismatches incorporated into inhibitors of single-family-member miRNAs identified two regions that are important for overall inhibitor functionality. Our findings indicate that features important for natural miRNA target recognition also appear to be important for inhibitor specificity. Understanding the specificity of inhibitors allows for better interpretation of inhibitor activity in endogenous systems.