The c-Jun NH(2)-terminal kinase (JNK) signal transduction pathway causes increased gene expression mediated, in part, by members of the activating transcription factor protein (AP1) group. JNK is therefore implicated in the regulation of cell growth and cancer. To test the role of JNK in Ras-induced tumor formation, we examined the effect of compound ablation of the ubiquitously expressed genes Jnk1 plus Jnk2. We report that JNK is required for Ras-induced transformation of p53-deficient primary cells in vitro. Moreover, JNK is required for lung tumor development caused by mutational activation of the endogenous KRas gene in vivo. Together, these data establish that JNK plays a key role in Ras-induced tumorigenesis.

The cJun NH(2)-terminal kinase (JNK) signal transduction pathway has been implicated in the growth of carcinogen-induced hepatocellular carcinoma. However, the mechanism that accounts for JNK-regulated tumor growth is unclear. Here we demonstrate that compound deficiency of the two ubiquitously expressed JNK isoforms (JNK1 and JNK2) in hepatocytes does not prevent hepatocellular carcinoma development. Indeed, JNK deficiency in hepatocytes increased the tumor burden. In contrast, compound JNK deficiency in hepatocytes and nonparenchymal cells reduced both hepatic inflammation and tumorigenesis. These data indicate that JNK plays a dual role in the development of hepatocellular carcinoma. JNK promotes an inflammatory hepatic environment that supports tumor development, but also functions in hepatocytes to reduce tumor development.

The cJun N-terminal kinase (JNK) signal transduction pathway is implicated in the regulation of neuronal function. JNK is encoded by three genes that play partially redundant roles. Here we report the creation of mice with targeted ablation of all three Jnk genes in neurons. Compound JNK-deficient neurons are dependent on autophagy for survival. This autophagic response is caused by FoxO-induced expression of Bnip3 that displaces the autophagic effector Beclin-1 from inactive Bcl-XL complexes. These data identify JNK as a potent negative regulator of FoxO-dependent autophagy in neurons.

The c-Jun NH(2)-terminal kinase (JNK) signaling pathway has been implicated in the development of tumor necrosis factor (TNF)-dependent hepatitis. JNK may play a critical role in hepatocytes during TNF-stimulated cell death in vivo. To test this hypothesis, we examined the phenotype of mice with compound disruption of the Jnk1 and Jnk2 genes. Mice with loss of JNK1/2 expression in hepatocytes exhibited no defects in the development of hepatitis compared with control mice, whereas mice with loss of JNK1/2 in the hematopoietic compartment exhibited a profound defect in hepatitis that was associated with markedly reduced expression of TNF-alpha. These data indicate that JNK is required for TNF-alpha expression but not for TNF-alpha-stimulated death of hepatocytes. Indeed, TNF-alpha induced similar hepatic damage in both mice with hepatocyte-specific JNK1/2 deficiency and control mice. These observations confirm a role for JNK in the development of hepatitis but identify hematopoietic cells as the site of the essential function of JNK.

A high-fat diet causes activation of the regulatory protein c-Jun NH2-terminal kinase 1 (JNK1) and triggers development of insulin resistance. JNK1 is therefore a potential target for therapeutic treatment of metabolic syndrome. We explored the mechanism of JNK1 signaling by engineering mice in which the Jnk1 gene was ablated selectively in adipose tissue. JNK1 deficiency in adipose tissue suppressed high-fat diet-induced insulin resistance in the liver. JNK1-dependent secretion of the inflammatory cytokine interleukin-6 by adipose tissue caused increased expression of liver SOCS3, a protein that induces hepatic insulin resistance. Thus, JNK1 activation in adipose tissue can cause insulin resistance in the liver.

The JNK signaling pathway is implicated in the regulation of the AP1 transcription factor and cell proliferation. Here, we examine the role of JNK by using conditional and chemical genetic alleles of the ubiquitously expressed murine genes that encode the isoforms JNK1 and JNK2. Our analysis demonstrates that JNK is not essential for proliferation. However, JNK is required for expression of the cJun and JunD components of the AP1 transcription factor, and JNK-deficient cells exhibit early p53-dependent senescence. These data demonstrate that JNK can act as a negative regulator of the p53 tumor suppressor.