Our most recent studies focus on understanding how aberrant expression of the Raf/MEK/MAP kinase cascade can transform hematopoietic, breast and prostate cells. Raf is a key serine-threonine protein kinase which exerts its effects on the transmission of growth and anti-apoptotic messages. These signals can be initiated after receptor ligation and are transmitted to members of the MAP kinase cascade that subsequently activate transcription factors controlling gene expression. Raf is a member of a multigene family which includes: Raf-1, A-Raf and B-Raf. The roles that individual Raf kinases play in the regulation of normal and malignant hematopoietic cell growth are not clear. Our studies have shown that all three Raf kinases are functionally present in human hematopoietic cells and their aberrant expression can result in abrogation of cytokine-dependency. Differences in the levels of Raf and downstream kinase activities were observed between cytokine-dependent and Raf-responsive Raf:ER-infected cells as estradiol-responsive cells expressed more Raf, MEK and activated MAPK activity than the GM-CSF-dependent Raf:ER-infected dependent cells. Abrogation of cytokine-dependency by the activated Raf:ER proteins was associated with autocrine growth factor synthesis which was sufficient to promote the growth of uninfected TF-1 cells. The expression of the p21Cip1 cell cycle arrest protein is being examined in these cells. Raf has been shown to induce the expression of p21Cip1 which then results in cell cycle arrest. It appears that one of the consequences of transformation to Raf-responsive growth is a lack of induction of p21Cip1. The consequences of the alteration in p21Cip1 expression on the tumorigenicity of the cells is being examined. In summary, these observations indicate that the aberrant expression of certain activated Raf:ER oncoproteins can alter the cytokine-dependency of hematopoietic TF-1 cells. These cells will be useful in evaluating the roles of the individual Raf oncoproteins in cytokine-mediated signal transduction, cell cycle progression, regulation of apoptosis and differentiation. Moreover these Raf-infected cells may be important in the evaluation of the efficacy of novel anticancer drugs designed to inhibit Raf and downstream signal transduction molecules.

Blalock W.L., Pearce M., Steelman L. S., Franklin R. A., McCarthy S. A., Cherwinski H., McMahon M and McCubrey J.A. (2000). A conditionally-active form of MEK1 results in autocrine transformation of human and mouse hematopoeitic cells. Oncogene 19: 526-536.

Hoyle P.E., Moye P. W., Steelman L. S., Blalock W. L., Franklin R. A., Pearce M., Cherwinski H., Bosch E., McMahon M and McCubrey J. A. (2000) Differential abilities of the Raf family of protein kinases to abrogate cytokine-dependency and prevent apoptosis in murine hematopoietic cells by a MEK1-dependent mechanism. Leukemia 14: 642-656.

Blalock WL., Moye PW, Chang F, Pearce M, Steelman LS, McMahon M and McCubrey JA. (2000) Combined Effects of Aberrant MEK1 Activity and BCL2 Overexpression on Relieving the Cytokine-Dependency of Human and Murine Hematopoietic Cells. Leukemia 14: 1080-1096.

Moye, PW, Blalock WL, Hoyle PE, Chang F, Franklin RA, Weinstein-Oppenheimer C, Pearce M, Steelman L, McMahon M and McCubrey JA. (2000). Synergy Between Raf and BCL2 in Abrogating the Cytokine-Dependency of Hematopoietic Cells. Leukemia 14: 1060-1079.

Chang F and McCubrey JA. (2001) p21^Cip1 induced by Raf is associated with increased Cdk4 activity in hematopoietic cells. Oncogene 20: 4353-4364.

Weinstein-Oppenheimer CR, Henríquez-Roldán CF, Davis J, Navolanic PM, Saleh OA, Steelman LS, Franklin RA, Robinson PJ, McMahon M and McCubrey JA. (2001). Role of the Raf signal transduction cascade in the in vitro resistance to the anticancer drug doxorubicin. Clinical Cancer Research. 7: 2892-2907.

Weinstein-Oppenheimer CR, Burrows C, Steelman LS, McCubrey JA. (2002). The Effects of β-Estradiol on Raf Activity, Cell Cycle Progression and Growth Factor Synthesis in the MCF-7 Breast Cancer Cell Line. Cancer Biology & Therapy 1: 254-260.

Chang F, Steelman LS and McCubrey, JA (2002). Raf-Induced Cell Cycle Progression in Human TF-1 Hematopoietic Cells. Cell Cycle 1: 220-227.

Lee JT Jr and McCubrey JA. (2002). Targeting the Raf kinase cascade in cancer therapy-Novel molecular targets and therapeutic strategies. Expert Opinions Therapeutic Targets 6: 659-678.

Davis JM, Weinstein-Oppenheimer CR, Steelman LS, Navolanic PN, Hu W, Konopleva M, Blagosklonny MV, and McCubrey JA. (2003). Raf-1 and Bcl-2 Induce Distinct and Common Pathways Which Contribute to Breast Cancer Drug Resistance. Clinical Cancer Research. 9: 1161-1170.

Navolanic PM, Steelman LS and McCubrey JA (2003). EGFR family signaling and its association with breast cancer development and resistance to chemotherapy. Int. J. Oncol. 22: 237-252.

Shelton JG, Steelman LS, Lee JT, Knapp SL, Blalock WL, Moye PM, Franklin RA, Pohnert SC, Mizra AM, McMahon M, and McCubrey JA (2003). Effects of the Raf/MEK/ERK and PI3K signal transduction pathways on the abrogation of cytokine dependence and prevention of apoptosis in hematopoietic cells. Oncogene 24: 2478-2492.

Blalock WL, Steelman LS, Shelton JG, Moye PW, Lee JT, Franklin RA, Mirza A, McMahon M, White MK, and McCubrey JA. (2003). Requirement for the PI3K/Akt Pathway in MEK1-Mediated Growth and Prevention of Apoptosis: Identification of an Achilles Heel in Leukemia. Leukemia 17: 1058-1067.

Shelton JG, Moye PW, Steelman LS, Blalock WL, Lee JT, Franklin RA, McMahon M and McCubrey JA. (2003). Differential effects of kinase cascade inhibitors on neoplastic and cytokine-mediated cell proliferation. Leukemia 17: 1765-1782.