L-JNKi1

This L-stereoisomer is a cell permeable JNK (c-Jun N-terminal kinase) inhibitor. For increased cell permeability the peptide was covalently linked to the 10 aa recognized by the TAT transporter. Neuroprotective agent for stroke. Inhibits the interaction between JNK (JNK-1, -2 and –3) and its substrate with the same IC₅₀ (in vitro IC₅₀ ~ 1µM), but is degraded more readily than the D-stereoisomer, thus requiring higher treatment concentrations in vitro and in vivo.

A protein inhibitor named IB1 has been described that competitively blocks the interaction between JNK and c-Jun, thereby inhibiting the signalling events downstream of JNK like c-Jun, ATF2 and ELK1 phosphorylation. To convert IB1 into cell-permeable inhibitors of JNK (JNKI peptides) the minimal 20 aa inhibitory sequence of IB1 was covalently linked to the 10 amino acids recognized by TAT transporter. The L-JNKI1 and the protease resistant D-JNKI1 peptides represent the only potent inhibitors that are specific for JNK (JNK1, JNK2 and JNK3). Different from chemical inhibitors that directly affect kinase activity e.g. by competing with the ATP-binding site of the protein kinase, JNKI1 rather inhibits the interaction between JNK and its substrate, resulting in a JNK K.O. phenotype. In contrast to pure diffusion the TAT-peptides are actively transported into cells, where they remain until their proteolytic degradation. They can be used for in vitro as well as for in vivo applications (IC50~1µM). D-JNKI1 is the only form found to be active on neuronal cells, probably due to a high level of proteolytic degradation of the L-stereoisomer (T. Borsello and C. Bonny; unpublished data).