A ROLE FOR JUN-N-TERMINAL KINASE IN ANOIKIS - SUPPRESSION BY BCL-2 AND CRMA

The disruption of interactions between extracellular matrix and specif ic cognate integrins triggers apoptosis in epithelial cells, in a proc ess termed ''anoikis.'' To understand anoikis, the connections between epithelial cell integrin signaling and the apoptosis-regulatory prote ins are being explored. We report herein that early after detachment f rom matrix, epithelial cells activate Jun-N-Terminal Kinases (JNKs; al ternatively known as Stress-activated Protein Kinases), which are also activated by other apoptotic stimuli. The activity of this pathway wa s required for anoikis. Another early response to cell suspension was the activation of the ICE-related cysteine protease, ICE/LAP3; this ac tivation and anoikis were suppressed by the ICE-protease inhibitor, cr mA. The overexpression of bcl-2 suppressed ICE/LAP3 activation as well . Surprisingly, bcl-2 and crmA attenuated the activation of JNKs follo wing cell suspension, suggesting that the JNK pathway is regulated dir ectly or indirectly by proteolysis. In addition, the blockage of the J NK pathway attenuated the activation of ICE/LAP3, suggesting a positiv e feedback loop between the ICE and JNK systems. These results indicat e the following sequence of information flow in anoikis: integrins-->b cl-2/bax-->(ICE-proteases <----> JNK)-->apoptosis. Cell-cell interacti ons, which were previously shown to sensitize cells to anoikis, caused bcl-2 mRNA to be downregulated, a permissive event for downstream apo ptotic signaling.