FAS-ACTIVATED SERINE THREONINE KINASE (FAST) PHOSPHORYLATES TIA-1 DURING FAS-MEDIATED APOPTOSIS

We have identified a serine/threonine kinase that is rapidly activated during Fas-mediated apoptosis. Fas-activated serine/threonine kinase (FAST) is phosphorylated on serine and threonine residues in Jurkat ce lls. In response to Fas ligation, it is rapidly dephosphorylated and c oncomitantly activated to phosphorylate TIA-1, a nuclear RNA-binding p rotein that has been implicated as an effector of apoptosis. Phosphory lation of TIA-1 precedes the onset of DNA fragmentation, suggesting a role in signaling downstream events in the apoptotic program. Our resu lts introduce FAST and TIA-1 as components of a molecular cascade invo lved in signaling Fas-mediated apoptosis.