ANALYSIS OF SYNERGISM BETWEEN STEM-CELL FACTOR AND GRANULOCYTE-MACROPHAGE COLONY-STIMULATING FACTOR ON HUMAN MEGAKARYOBLASTIC CELLS - AN INCREASE IN TYROSINE PHOSPHORYLATION OF 145 KDA SUBUNIT OF C-KIT IN 2-FACTOR COMBINATION

In normal hematopoiesis, stem cell factor (SCF) stimulates survival, p roliferation and differentiation of hematopoietic progenitors. Althoug h SCF acts synergistically with a variety of cytokines, the mechanism of growth factor-cooperation remains to be determined. To analyze the synergism between SCF and granulocyte-macrophage colony-stimulating fa ctor (GM-CSF), we established a new megakaryoblastic cell line, HML-2, by culture in the presence of both SCF and GM-CSF. While SCF alone or GM-CSF alone supported modest cell growth, SCF and GM-CSF together in duced substantial growth of this cell line. SCF alone tyrosine-phospho rylated several bands including the 145 kDa subunit of c-kit, GM-CSF a lone did not cause the tyrosine phosphorylation of the 145 kDa subunit , but markedly up-regulated the expression of the 145 kDa subunit of c -kit. The combination of SCF and GM-CSF resulted in a synergistic incr ease in tyrosine phosphorylation of the 145 kDa subunit of c-kit. Seve ral proliferation inhibitors which removed the two-factor interaction on the growth of the HML-2 cells down-regulated the 145 kDa subunit of c-kit. Thus, a synergistic increase in tyrosine phosphorylation of th e 145 kDa subunit of c-kit may be one possible mechanism underlying th e cooperation of SCF and GM-CSF on the HML-2 cell growth, (C) 1997 Els evier Science Ltd. All rights reserved.