Published in Cancer Detection and Prevention 2001; 25(4):375-393.

Interactions between the P13K and Raf Signaling Pathways Can Result in the Transformation of Hematopoietic Cells

James A. McCubrey, PhD,a,b John T Lee, BS,a Linda S. Steelman, MA,a William L. Blalock, PhD,a Phillip W Moye, MS,a Fumin Chang, PhD,a Marianne Pearce, BS,a John G. Shelton, BS,a Martyn K. White, PhD,c Richard A. Franklin, PhD,a,b and Steven C. Pohnert, BSd

aDepartments of Microbiology and Immunology and dBiochemistry and bLeo Jenkins Cancer Center, Brody School of Medicine at East Carolina University, Greenville, NC, and cDepartment of Pathology, Anatomy and Cell Biology, Thomas Jefferson College of Medicine, Philadelphia, PA

Address all correspondence and reprint requests to: James A. McCubrey, PhD, Department of Microbiology and Immunology, Brody School of Medicine at East Carolina University. Brody Building 5N98C, Greenville, NC 27858.

ABSTRACT: The PI3K/Akt and Raf/MEK/ERK signal transduction cascades are pivotal in transmitting signals from membrane receptors to downstream targets that regulate apoptosis, gene expression, and cell growth. The abilities of activated P13K, Akt, Raf, and MEK proteins to abrogate the cytokine dependence of three different hematopoietic cell lines were determined. Activated P13K or Akt expression by themselves did not efficiently annul cytokine dependence. Raf and MEK could abrogate the cytokine dependence of murine FDC-PI and human TF-1 cells; however, the frequency of transformation was dependent on the particular oncogene examined, as more factor-independent cells were isolated after infection with activated retroviruses encoding A-Raf or RafI than were with MEK1 or B-Raf. Cytokine-independent ARaf-l-infected cells formed tumors on injection into immunocompromised mice, whereas cytokine-dependent cell lines did not, demonstrating the oncogenic effects of activation of the Raf/MEK/ERK pathway. Overexpression of the antiapoptotic Bcl-2 protein synergized with activation of the Raf/MEK/ERK cascade and increased the efficiency of transformation of FDC-PI and TF-l cells. In contrast to the results observed with FDC-PI and TF-l cells, the activated Raf genes did not relieve the cytokine dependence of murine FL5.12 cells. The abilities of the Raf and P13K pathways to interact and annul the cytokine dependence of FL5.12 cells were determined. The combination of Raf and either P13K or Akt expression relieved cytokine dependence of some FL5.12 cells, and the efficiency of transformation could be enhanced further by Bcl-2 or Bcl-XL overexpression. Thus, the antiapoptotic PI3KIAkt and Bcl-2/Bcl-XL proteins can interact with the growth-promoting Raf/MEK/ERK pathway and annul the cytokine dependence of certain hematopoietic cells. KEY WORDS: P13K, Akt. Raf, cytokines, hematopoietic cells, oncogenes, signal transduction.

KEY WORDS: Akt, Raf, Cytokines, hematopoietic cells, oncogenes, signal transduction.