The 2 '-5 ' oligoadenylate/RNase L/RNase L inhibitor pathway regulates both MyoD mRNA stability and muscle cell differentiation

The 2'-5' oligoadenylate (2-5A)/RNase L pathway is one of the enzymatic pat hways induced by interferon. RNase L is a latent endoribonuclease which is activated by 2-5A and inhibited by a specific protein known as RLI (RNase L inhibitor). This system has an important role in regulating viral infectio n. Additionally variations in RNase L activity have been observed during ce ll growth and differentiation but the significance of the 2-5A/RNase L/RLI pathway in these latter processes is not known. To determine the roles of R Nase L and RLI in muscle differentiation, C2 mouse myoblasts were transfect ed with sense and antisense RLI cDNA constructs. Importantly, the overexpre ssion of RLI in C2 cells was associated with diminished RNase L activity, a n increased level of MyoD mRNA, and accelerated kinetics of muscle differen tiation. Inversely, transfection of the RLI antisense construct was associa ted with increased RNase L activity, a diminished level of MyoD mRNA, and d elayed differentiation. In agreement with these data, MyoD mRNA levels were also decreased in C2 cells transfected with an inducible RNase L construct . The effect of RNase L activity on MyoD mRNA levels was relatively specifi c because expression of several other mRNAs was not altered in C2 transfect ants. Therefore, RNase L is directly involved in myoblast differentiation, probably through its role in regulating MyoD stability. This is the first i dentification of a potential mRNA target for RNase L.