Phosphorothioate Antisense Oligonucleotides Bind P-Body Proteins and Mediate P-Body Assembly

Antisense oligonucleotides (ASOs) regulate gene expression by binding to complementary target RNA, and ASOs can be designed to take advantage of a growing array of post RNA binding molecular mechanisms. Intracellular trafficking of ASOs influences their efficacy. We have identified a number of membrane-less structures in the nucleus, nucleolus, and cytoplasm where phosphorothioate-modified ASOs (PS-ASOs) accumulate and have shown that PS-ASOs can induce the formation of new nuclear structures such as PS-bodies and paraspeckle-like structures. In this study, we report that PS-ASOs can localize to cytoplasmic processing bodies (P-bodies) and increase the number of P-bodies in cells. The antisense activity of PS-ASOs was not affected by the absence of essential P-body assembly proteins DDX6 and LSm14A. Moreover, the effects of PS-ASOs on P-body assembly were independent of their antisense activities. The phosphorothioate modification stabilizes the association between ASOs and cellular proteins and is essential for the P-body localization of ASOs. Since PS-ASOs bind to major P-body components, PS-ASOs may serve as scaffolds for P-body formation. Taken together, these results indicate that interactions of PS-ASO with proteins, rather than antisense activities, are essential for the dynamic interplay between PS-ASOs and P-bodies.