Protein kinase CK2 inhibitor 4,5,6,7-tetrabromobenzotriazole (TBB) induces apoptosis and caspase-dependent degradation of haematopoietic lineage cell-specific protein 1 (HS1) in Jurkat cells

incubation of Jurkat cells with 4,5,6,7-tetrabromobenzotriazole (TBB), a specific inhibitor of protein kinase CK2, induces dose and time-dependent apoptosis as judged by several criteria. TBB-promoted apoptosis is preceded by inhibition of Ser/Thr phosphorylation of haematopoietic lineage cell-specific protein I (HS1 and is accompanied by caspase-dependent fragmentation of the same protein. Both effects are also observable if apoptosis is promoted by anti-Fas antibodies and by etoposide. Moreover, in vitro experiments show that HSI, once phosphorylated by CK2, becomes refractory to cleavage by caspase-3. These findings, in conjunction with similar data in the literature concerning two other CK2 protein substrates, Bid and Max, suggest that CK2 may play a general anti-apoptotic role through the generation of phosphorylated sites conferring resistance to caspase cleavage.