Abrogation of cytokine dependency in hematopoietic cells by Raf and PI3K/Akt

Cancer is the second leading cause of death in the United States. Leukemia is a cancer characterized by the uncontrolled proliferation of hematopoietic cells. This uncontrolled proliferation of hematopoietic cells is often the result of increased activity of signaling proteins.; The abilities of three activated signaling molecules (Raf, PI3K, and Akt) to abrogate cytokine-dependency were examined in these studies. Introduction of active forms of Raf-l, PI3K, or Akt did not allow for uncontrolled growth of FL5.12 cells, although in previous studies by our laboratory Raf-1 did promote uncontrolled growth of other hematopoietic cell lines. Raf-1 stimulation resulted in activation of PI3K and Akt. This is the first report of Raf pathway activating PI3K/Akt, although PI3K/Akt has been known to alter Raf signaling.; The ability of the Raf and PI3K/Akt pathways to interact was further examined by introduction of activated Raf and PI3K or Akt into hematopoietic cells. Cells infected with either Raf and PI3K or Raf and Akt resulted in the abrogation of cytokine dependency in these cells. Loss of cytokine dependency is often associated with uncontrolled cell growth. Cells that became factor-independent had elevated Raf levels. Factor-independence also altered cell morphology. Cells that were cytokine independent also expressed GM-CSF mRNA and protein. The functional role of GM-CSF production in these cells was confirmed as an event involved in the abrogation of cytokine dependency.; Small molecular weight pharmaceutical inhibitors were used to further elucidate the interaction between the Raf and PI3K/Akt pathways. All inhibitors examined decreased proliferation of IL-3 stimulated cells. Conversely, inhibition of Raf, MEK1, and PI3K decreased proliferation of cells growing in response to activated Raf and Akt. Similarly, Raf, MEK1, and PI3K inhibitors altered Raf expression. Use of these inhibitors further implicated that cross-talk between pathways in growth and prevention of apoptosis.; Leukemia is the uncontrolled growth of hematopoietic cells. Two separate pathways (Raf and PI3K/Akt) can interact to promote uncontrolled cell growth and possibly give rise to leukemia. The Raf pathway for the first time was demonstrated to activate the PI3K/Akt pathway.