Setting up an efficient and reliable screening method for novel c-Jun N-terminal kinase substrates

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The c-Jun N-terminal kinase (JNK), also known as the stress activated protein kinase (SAPK), forms a family of serine-threonine kinases that can be efficiently activated by both mitogenic and apoptotic signals. Moreover in various cases JNK activation has been shown to have both preventative and causative roles in apoptosis. Thus far the best characterized target of JNK is c-Jun, which forms a part of the transcription factor AP-1. It is a well established fact that the activation of JNKs in the cell will lead to the phosphorylation of Ser63 and Ser73 at the c-Jun activation domain. This in turn results in the transcriptional activation of the AP-1 responsive genes. We show here that, in some cancer cell lines, JNK activation does not always correlate with AP-1 activation. This lack of AP-1 activation is also associated with the lack of the phosphorylation of c-Jun. We have been testing two different 'substrate screening systems' in order to find novel, relevant JNK substrates from these cancer cells.