Rapid nucleolytic degradation of the small cytoplasmic Y RNAs during apoptosis

We have investigated the fate of the RNA components of small ribonucleoprot ein particles in apoptotic cells. We show that the cytoplasmic Ro ribonucle oprotein-associated Y RNAs are specifically and rapidly degraded during apo ptosis via a caspase-dependent mechanism. This is the first study describin g the selective degradation of a specific class of small structural RNA mol ecules in apoptotic cells. Cleavage and subsequent truncation of Y RNAs was observed upon exposure of cells to a variety of apoptotic stimuli and were found to be inhibited by Bcl-2, zinc, and several caspase inhibitors, Thes e results indicate that apoptotic degradation of Y RNAs is dependent on cas pase activation, which suggests that the nucleolytic activity responsible f or Y RNA degradation is activated downstream of the caspase cascade. The Y RNA degradation products remain bound by the Ro60 protein and in part also by the La protein, the only two proteins known to be stably associated with intact Ro ribonucleoprotein particles. The size of the Y RNA degradation p roducts is consistent with the protection from degradation of the most high ly conserved region of the Y RNAs by the bound Ro60 and La proteins. Our re sults indicate that the rapid abrogation of the yet unknown function of Y R NAs might be an early step in the systemic deactivation of the dying cell.