|Budget Amount *help
¥14,600,000 (Direct Cost: ¥14,600,000)
Fiscal Year 2002: ¥4,200,000 (Direct Cost: ¥4,200,000)
Fiscal Year 2001: ¥10,400,000 (Direct Cost: ¥10,400,000)
Interleukin 3 (IL3) and erythropoietin (Epo) are hematppoietic growth factors that regulate the growth and differentiation of hematopoietic progenitor cells through activation of their specific receptors expressed on the cell surface. Their receptors transduce the intracellular signals by activating receptor-associated tyrosine kinases, mainly Jak2 and Lyn, and thereby inducing tyrosine phosphorylation of various signaling molecules including the receptors themselves. In the current research project, we have found that CrkL, an adapter protein implicated in pathogenesis of chronic myelogenous leukemia, is recruited to the EpoR, possibly through interaction between the CrkL SH2 domain and phosphorylated Y-460 in the EpoR cytoplasmic domain, and undergoes tyrosine phosphorylation by receptor-associated Lyn in Epo-stimulated hematopoietic cells. Through its interaction with C3G, a guanine nucleotide exchange factor for fP the Ras family GTPases, CrkL was found to mediate Epo-induced activation of Ras and Rap1. By using various mutants of these GTPases and'other signaling molecules, we have also found that the activation of Rap1 is involved in stimulation of VLA-4 and VLA-5 integrin-mediated adhesion of hematopoietic cells. It was further indicated that phospholipase C-γ, known to be activated by the EpoR, may also mediate the Epo-induced Rapl activation through generation of its second messengers. We have also found that Rac, a member of the Rho family small GTPases, is activated by Epo as well as IL3 stimulation in hematopoietic cells and may play a role in activation of the Erk/Elk-1 signaling pathway. Rac was also found to be activated by outside-in signaling from VLA-4 through signaling mechanisms involving CrkL. Furthermore, hematopoietic cell adhesion mediated by VLA-4 was found to induce tyrosine phosphorylation of the hematopoietic cytokine receptors in a manner dependent on Jak2 activation.