Molecular genetic analyses of c-Jun N-terminal kinases

To address the cellular function of JNK, a molecular genetic approach using gain-of-function JNK and targeted disruption of jnk genes was employed. Gain-of-function forms of two JNK1 isoforms JNK1α and JNK1β (MKK7-JNK1α and MKK7-JNK1β) were generated and stably expressed in Swiss 3T3 fibroblasts. To identify genes whose expression is regulated by these distinct gain-of-function JNK polypeptides, gene expression profiles were determined by oligonucleotide arrays. The expression of a panel of interferon-stimulated genes is selectively increased by gain-of-function JNK1β and is associated with increased resistance to killing by vesicular stomatitis virus. Additionally, the expression of MKK7-JNK1α selectively induced mild transformation and both gain-of-function JNK1α and JNK1β proteins affected cell viability in serum-restricted condition. Fibroblasts generated from the mice with targeted disruption of the jnk1 or jnk2 genes were also used to investigate the function of JNK. The gene expression profiles were obtained form cells lacking JNK1 or JNK2 proteins and compared with those of gain-of-function JNK-expressing cells. The examination of gene expression patterns revealed the role of JNK as a transcriptional repressor as well as a transcription activator. Notably, some genes were induced in both gain-of-function JNK-expressing cells and Jnk-deficient cells, which implicated a kinase-independent repressor function similar to that observed with yeast MAPK. These gene expressions may be repressed by inactive JNK and stimulated by activated JNK, indicating JNK may act as a transcriptional switch from repression to activation. In summary, isoform-specific functions of JNK in transcriptional activation and repression were revealed in this thesis and these studies increase the understanding of the complexity of JNK regulation in cell signaling.