Kunihiro Matsumoto

TAK1 Mediates the Ceramide Signaling to Stress-activated Protein Kinase/c-Jun N-terminal Kinase

Ceramide has been proposed as a second messenger molecule implicated in a variety of biological processes. It has recently been reported that ceramide activates stress-activated protein kinase (SAPK, also known as c-Jun NH2-terminal kinase JNK), a subfamily member of mitogen-activated protein kinase superfamily molecules and that the ceramide/SAPK/JNK signaling pathway is required for stress-induced apoptosis. However, the molecular mechanism by which ceramide induces SAPK/JNK activation is unknown. Here we show that TAK1, a member of the mitogen-activated protein kinase kinase kinase family, is activated by treatment of cells with agents and stresses that induce an increase in ceramide. Ceramide itself stimulated the kinase activity of TAK1. Expression of a constitutively active form of TAK1 resulted in activation of SAPK/JNK and SEK1/MKK4, a direct activator of SAPK/JNK. Furthermore, expression of a kinase-negative form of TAK1 interfered with the activation of SAPK/JNK induced by ceramide. These results indicate that TAK1 may function as a mediator of ceramide signaling to SAPK/JNK activation.

Distinct Domains of Mouse Dishevelled Are Responsible for the c-Jun N-terminal Kinase/Stress-activated Protein Kinase Activation and the Axis Formation in Vertebrates

Recent studies have shown thatDrosophila Dishevelled (Dsh), an essential component of thewingless signal transduction, is also involved in planar polarity signaling through the c-Jun N-terminal kinase (JNK)/stress-activated protein kinase (SAPK) pathway inDrosophila. Here, we show that expression of a mouse homolog of Dsh (mDvl-1) in NIH3T3 cells activates JNK/SAPK, and its activator MKK7. A C-terminal half of mDvl-1 which contains the DEP domain was sufficient for the activation of JNK/SAPK, whereas an N-terminal half of mDvl-1 as well as the DEP domain is required for stimulation of the TCF/LEF-1-dependent transcriptional activation, a β-catenin-dependent process. A single amino acid substitution (Met for Lys) within the DEP domain (mDvl-1 (KM)) abolished the JNK/SAPK-activating activity of mDvl-1, but did not affect the activity to activate the LEF-1-dependent transcription. Ectopic expression of mDvl-1 (KM) or an N-terminal half of mDvl-1, but not the C-terminal, was able to induce secondary axis inXenopus embryos. Because the secondary axis formation is dependent on the Wnt/β-catenin signaling pathway, these results suggest that distinct domains of mDvl-1 are responsible for the two downstream signaling pathways, the β-catenin pathway and the JNK/SAPK pathway in vertebrates.

Suppurative arthritis of the temporomandibular joint: Report of a case with special reference to arthroscopic observations

A case of suppurative arthritis of the temporomandibular joint (TMJ) in a 43-year-old man is reported. Arthroscopic findings are briefly described. Arthroscopy led to the correct diagnosis and treatment, with a complication-free outcome.