• Toxicological Research
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• v.24 no.2
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• pp.93-100
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• 2008

Targeting protein kinases has been active area in drug discovery. The c-Jun N-terminal kinases(JNKs) have also been target for development of novel therapy in various diseases, since the roles of JNK signaling in pathological conditions were revealed in studies using jnk-deficient mice. Small molecule inhibitors and peptide inhibitors are identified for therapeutic intervention of JNK signaling pathway. SP-600125, an anthrapyrazole small molecule inhibitor for JNK with high potency and selectivity has been widely used for dissecting JNK signaling pathway. CC-401 is the first JNK inhibitor that went into clinical trial for inflammation and leukemia. Inhibitor for mixed lineage kinase (MLK), CEP-1347 also negatively regulates JNK signaling, and tried for potential use in Parkinson's disease. Cell-permeable peptide inhibitor D-JNKI-1 is being developed for the treatment of hearing loss. The current status of these JNK inhibitors and safety issue is discussed in the minireview.

• Archives of Pharmacal Research
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• v.26 no.12
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• pp.1055-1060
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• 2003

Lysophosphatidic acid (LPA) is a well-known mitogen in various cell types. However, we found that LPA inhibits melanocyte proliferation. Thus, we further investigated the possible signaling pathways involved in melanocyte growth inhibition. We first examined the regulation of the three major subfamilies of mitogen-activated protein (MAP) kinases and of the Akt pathway by LPA. The activations of extracellular signal-regulated protein kinase (ERK) and c-Jun N-terminal kinase (JNK) were observed in concert with the inhibition of melanocyte proliferation by LPA, whereas p38 MAP kinase and Akt were not influenced by LPA. However, the specific inhibition of the ERK or JNK pathways by PD98059 or D-JNKI1, respectively, did not restore the antiproliferative effect. We next examined changes in the expression of cell cycle related proteins. LPA decreased cyclin $D_1 and cyclin D_2$ levels but increased $p21^{WAF1/CIP1}$ (p21) and $p27^{KIP1}$ (p27) levels, which are known inhibitors of cyclin-dependent kinase. Flow cytometric analysis showed the inhibition of DNA synthesis by a reduction in the S phase and an increase in the $G_0/G_1$ phase of the cell cycle. Our results suggest that LPA induces cell cycle arrest by regulating the expressions of cell cycle related proteins.