Vol. 297, Issue 3, 868-875, June 2001

Involvement of Protein Kinase C- in Signal Transduction of Thrombopoietin in Enhancement of Interleukin-3-Dependent Proliferation of Primitive Hematopoietic Progenitors

Noriyuki Shiroshita , Manabu Musashi , Keisuke Sakurada , Kazuhiro Kimura, Yuzo Tsuda, Shuichi Ota, Hiroshi Iwasaki, Tamotsu Miyazaki, Takashi Kato, Hiroshi Miyazaki, Akihiro Shimosaka and Masahiro Asaka

Third Department of Internal Medicine, Hokkaido University School of Medicine (N.S., M.M., K.S., Y.T., S.O., T.M., M.A.); Health Administration Center, Hokkaido University (M.M., K.S.); Department of Biomedical Science, Graduate School of Veterinary Medicine (K.K.), Hokkaido University; Sapporo Kosei Hospital (N.S., H.I.), Sapporo, Japan; and Kirin Brewery Co., Ltd., Tokyo, Japan (T.K., H.M., A.S.)

We studied the effect of thrombopoietin (TPO) on interleukin-3 (IL-3)-dependent bone marrow cell colony formation of mice to clarify the role of protein kinase C (PKC) in the signal transduction of TPO for the proliferation of primitive hematopoietic progenitors. TPO alone hardly yielded colonies. However, TPO in combination with IL-3 increased colony numbers synergistically from 2- to 4-fold, compared with those supported by IL-3 alone. Serial observation of colony development showed that TPO may hasten the appearance of colonies by shortening the dormant period (G₀) of primitive progenitors. Immunocytochemical studies on PKC isoforms in progenitor cells stimulated with TPO have revealed that the expression pattern of PKC- is changed, but not that of PKC-, -, -, -, or -. Selective PKC inhibitors, such as calphostin C and GF 109203X, and PKC--specific translocation inhibitor peptide abrogated the enhancing effect of TPO on IL-3-dependent colony formation and the changes in the intracellular expression pattern of PKC-. These data taken together suggest that TPO has a direct effect on primitive progenitors and enhances IL-3-dependent colony formation, at least partly through the activation of PKC-.