| Co-Investigator(Kenkyū-buntansha) |
KITAYAMA Hitoshi Osaka University Hospital, Medical Staff, 医学系研究科, 医員
IKEDA Hirokazu Guraduate School of Medicine, Osaka University Assistant Professor, 医学系研究科, 助手 (10311755)
MATSUMURA Itaru Guraduate School of Medicine, Osaka University Assistant Professor, 医学系研究科, 助手 (00294083)
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| Research Abstract |
The c-kit receptor tyrosine kinase (KIT) and its ligand, stem cell factor (SCF) transduce crucial signals in hematopoietic cells. We revealed that two point mutations, Val559→Gly (G559) mutation in the juxtamembrane domain and Asp814→Val (V814) mutation in the kinase domain, lead to constitutive and oncogenic activation of KIT. In order to determine as to which portion of mutant KITs is indispensable for receptor dimerization or self-association in the absence of SCF, we have constructed a series of deletion and chimeric mutants of KIT, including the extracellular domain truncated type KIT and chimeric type KIT in which extracellular and transmembrane domains are replaced by src myristylation signal peptide. By using murine interleukin (IL)-3-dependent Ba/F3 cells that were subjected to transfection of various c-kit genes, we showed that the constituvely activating mutations at both the juxtamembrane and kinase domains of KIT may not necessarily require their extracellular and transmem
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brane domains for their formation of receptor self-association, and that the receptor self-association of mutant KIT may be important for activation of downstream effectors that are required for factor-independent growth and tumorigenicity.
In addition to the SCF/KIT system, thrombopoietin (TPO)/c-mpl system also plays a fundamental role in hematopoiesis. In an effort to clarify the mechanisms of TPO-induced proliferation and differentiation, c-mpl was introduced into human IL-3-dependent F-36P cells. F-36P-mpl cells were found to proliferate and differentiate at a high rate into mature megakaryocytes in response to TPO. By using dominant-negative (dn) forms of STATs and ras, it was suggested that TPO-induced proliferation may be mediated through activation of STAT5 and ras, and that prolonged ras activation may be involved in TPO-induced megakaryocytic differentiation. Furthermore, we found that STAT5, in addition to ras signaling, appeared to mediate transcriptional regulation of cyclin D1 during cytokine-dependent growth in hematopoietic cells. Less
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