J Biol Chem, Vol. 273, Issue 27, 16787-16791, July 3, 1998

Involvement of Ras in Bruton's Tyrosine Kinase-mediated JNK Activation

Jianbei Deng, Yuko Kawakami, Stephen E. Hartman, Takaya Satoh, and Toshiaki Kawakami

From the Division of Allergy, La Jolla Institute for Allergy and Immunology, San Diego, California 92121 and the  Faculty of Bioscience and Biotechnology, Tokyo Institute of Technology, 4259 Nagatsuta-cho, Midori-ku, Yokohama 226-8501, Japan

Defects in Bruton's tyrosine kinase (Btk) result in B cell immunodeficiencies in humans and mice. Recent studies showed that Btk is required for maximal activation of JNK, a family of stress-activated protein kinases, induced by several extracellular stimuli including interleukin (IL)-3. On the other hand, IL-3-induced JNK activation is dependent on Ras. In the present study we have investigated whether Ras is involved in Btk-mediated JNK activation in BaF3 mouse pro-B cells. Overexpression of wild-type Btk protein in these cells enhanced JNK activation upon IL-3 stimulation, whereas expression of kinase-dead Btk partially suppressed JNK activation. Induced expression of the dominant negative Ras(N17) in the cells overexpressing wild-type Btk suppressed JNK activation. Importantly, overexpression of Btk enhanced the level of the GTP-bound, active form of Ras in response to IL-3 stimulation. Btk overexpression also increased the Shc-Grb2 association induced by IL-3 stimulation. Expression of either N17Ras or V12Ras did not impose any effects on Btk kinase activity. These data collectively indicate that Ras plays a role of an intermediary signaling protein in Btk-mediated JNK activation induced by the IL-3 signaling pathway.