RAPID REDUCTION OF MESSENGER-RNA CODING FOR 2'-5'-OLIGOADENYLATE SYNTHETASE IN RAT PHEOCHROMOCYTOMA PC12 CELLS DURING APOPTOSIS

Apoptosis is a form of physiological cell death, characterized by DNA fragmentation, which often depends on RNA and protein synthesis. Becau se cellular RNA is also degraded during apoptosis we studied the role of the 2'-5'-oligoadenylate (2-5A) synthetase in this process. The pro duct of the synthetase, 2-5A, stimulates endoribonuclease-L-mediated c ontrolled RNA degradation. Here we show that apoptosis is induced in r at pheochromocytoma PC12 cells by tributyltin (TBT) at low concentrati ons (1 nM); already 5-10 min. after addition of this compound DNA frag mentation resulting in a stepladder-like gel pattern was observed. The level of mRNA coding for 2-5A synthetase was determined using a clone d cDNA from rats. Sequence analyses of the rat 2-5A synthetase (M(r) 4 0-46,000) revealed high homology to other members of class I synthetas e cloned from mouse and human. Applying the rat cDNA as a probe we fou nd that parallel with degradation of DNA the level of mRNA coding for 2-5A synthetase decreased; already 7.5 min. after induction of apoptos is by TBT the amount of 2-5A synthetase mRNA was reduced by 60%. This finding indicates that this enzyme is among those mRNAs which are degr aded during apoptosis and it suggests that 2-5A synthetase, which is i nvolved in the antiviral response of cells and most likely in the cont rol of cell growth and differentiation, does not play an active role d uring this process.