18. Involvement of Protein Kinase C in Radiation-Induced Apoptosis Signaling Pathways in Murine Thymic Lymphoma Cells (3SBH5 Cells)

Tetsuo Nakajima, Osami Yukawa, Chihiro Azuma*, Harumi Ohyama, Bing Wang, Shuji Kojima*, Isamu Hayata and Hiroko Hama-Inaba
(*Science University of Tokyo)

Keywords: murine thymic lymphoma, protein kinase C, apoptosis, radiosensitivity, Raf-1

Radiation-induced apoptosis is known to be important for understanding the mechanism of radiosensitivity. It is widely accepted that protein kinase C (PKC) participates in the regulation of radiation-induced apoptosis. However, the PKC function remains obscure in the mechanism of radiosensitivity. Using 3SBH5 cells, one of the radiation sensitive murine thymic lymphoma cells were used to assess involvement of PKC in radiation-induced apoptosis regulation. 3SBH5 cells are quite sensitive to X-rays and undergo apoptosis shortly after X-ray-irradiation. PMA (phorbol 12-myristate 13-acetate), an activator of PKC, blocked the radiation-induced apoptosis in 3SBH5 cells. In contrast, chelerythrine, a PKC inhibitor, enhanced the radiation-induced apoptosis, as did Gö6976, a classical PKC (cPKC) specific inhibitor, for irradiation with 0.5Gy. These results imply that cPKC contributes to the balance between cell survival and death through radiation-induced activation of cPKC. Furthermore, irradiation alone had no effect on the distribution of PKC subtypes in 3SBH5 cells. This suggests that the radiation-induced cPKC activation is not caused by translocation of PKC molecules. On the other hand, although it was demonstrated that cPKC is associated with an anti-Raf-1 antibody-recognized protein in 3SBH5 cells, Raf1 Kinase Inhibitor I, one of the Raf1 kinase inhibitors, had no effect on the radiation-induced apoptosis. The anti-apoptotic function of cPKC in the radiation-induced apoptosis is under investigation by exploring cPKC-associated proteins. This function of cPKC may offer a clue to understanding radiosensitivity and radiation-induced adaptive response.