Effects of the RAF/MEK/ERK and PI3K/AKT signal transduction pathways on the abrogation of cytokine-dependence and prevention of apoptosis in hematopoietic cells.

The Raf/MEK/ERK kinase cascade is pivotal in transmitting signals from membrane receptors to transcription factors that control gene expression culminating in the regulation of cell cycle progression. This cascade can prevent cell death through ERK2 and p90(Rsk) activation and phosphorylation of apoptotic and cell cycle regulatory proteins. The PI3K/Akt kinase cascade also controls apoptosis and can phosphorylate many apoptotic and cell cycle regulatory proteins. These pathways are interwoven as Akt can phosphorylate Raf and result in its inactivation, and Raf can be required for the antiapoptotic effects of Akt. In this study, the effects of activated Raf (Raf-1, A-Raf and B-Raf) and PI3K/Akt proteins on abrogation of cytokine dependence in FL5.12 hematopoietic cells were examined. Activated Raf, PI3K or Akt expression, by themselves, did not readily relieve cytokine dependence. The presence of activated Raf and PI3K/Akt increased the isolation of factor-independent cells from 400- to 2500-fold depending upon the particular combination examined. The individual effects of activated Raf and Akt on proliferation, apoptosis and autocrine growth factor synthesis were further examined with hormone-inducible constructs (Delta Raf-1:AR and Delta Akt:ER*(Myr(+)). Activation of either Raf or Akt hindered cell death; however, both proliferation and maximal synthesis of autocrine cytokines were dependent upon activation of both signaling pathways. The effects of small molecular weight inhibitors on DNA synthesis and cytokine gene expression were also examined. The PI3K inhibitor, LY294002, inhibited growth and cytokine gene expression. This effect could be synergistically increased by addition of the MEK inhibitor UO126. These cells will be useful in elucidating the interactions between Raf/MEK/ERK and PI3K/Akt cascades in proliferation, apoptosis, and leukemogenesis, as well as evaluating the efficacy of signal transduction inhibitors that target these cascades.

Fibroblastic, hematopoietic, and hormone responsive epithelial cell lines and culture conditions for elucidation of signal transduction and drug resistance pathways by gene transfer.

Elucidation of signal transduction pathways involved in proliferation, cell cycle progression and the regulation of apoptosis has shown great promise in the treatment of various diseases including neoplastic, inflammatory, autoimmune, immunodeficiency, arthritic and neurodegenerative disorders. By understanding how these signal transduction pathways function, chemotherapeutic targets may be identified which will suppress or eliminate the disease. This information may eventually be translated into therapy, which would either eliminate or safely contain the patient's disease. This chapter will focus on basic tissue culture techniques which are used to elucidate signal transduction pathways. Furthermore, this chapter will provide a general background for understanding how gene transfer techniques can be used to elucidate signal transduction pathways as well as various pitfalls commonly encountered with their usage.

Elucidation of signal transduction pathways by transfection of cells with modified oncogenes.

This chapter will focus on introduction of various wild type (WT) and mutant genes into cells by DNA transfection. Techniques for analysis of the inheritance, expression, and biological effects of the introduced genes will be described. Various strong and weak points about three different techniques of stable gene transfer, including calcium-phosphate DNA precipitation, transfection via liposomes, and transfection via electroporation, will be discussed.

Elucidation of signal transduction pathways by retroviral infection of cells with modified oncogenes.

This chapter will focus on understanding how various wild type (WT), dominant negative (DN), constitutively active (CA), and conditionally active (COND) oncogenes, as well as antisense (AS) genes contained in retroviral vectors may be used to elucidate signal transduction pathways. We will describe methods to introduce these genes into cells and subsequent analysis of inheritance, expression, and biological effects of the genes introduced. Furthermore, we will discuss various strong points about each of these different types of constructs, how they can be used to elucidate signal transduction, apoptotic, and drug resistance pathways as well as various pitfalls commonly encountered with their usage.