ABSTRACT
The mitogen-activated protein kinase (MAPK) (also called extracellular signal-regulated kinase [ERK]) pathway has been implicated in malignant transformation and in the regulation of cellular growth and proliferation of several tumor types, but its expression and function in Hodgkin disease (HD) are unknown. We report here that the active phosphorylated form of MAPK/ERK is aberrantly expressed in cultured and primary HD cells. Inhibition of the upstream MAPK kinase (also called MEK) by the small molecule UO126 inhibited the phosphorylation of ERK and demonstrated a dose- and time-dependent antiproliferative activity in HD cell lines. UO126 modulated the levels of several intracellular proteins including B-cell lymphoma protein 2 (Bcl-2), myeloid cell leukemia-1 (Mcl-1) and caspase 8 homolog FLICE-inhibitory protein (cFLIP), and induced G2M cell-cycle arrest or apoptosis. Furthermore, UO126 potentiated the activity of apoliprotein 2/tumor necrosis factor-related apoptosis-inducing ligand (APO2L/TRAIL) and chemotherapy-induced cell death. Activation of CD30, CD40, and receptor activator of nuclear kappabeta (RANK) receptors in HD cells by their respective ligands increased ERK phosphorylation above the basal level and promoted HD cell survival. UO126 inhibited basal and ligand-induced ERK phosphorylation, and inhibited ligand-induced cell survival of HD cell lines. These findings provide a proof-of-principle that inhibition of the MEK/ERK pathway may have therapeutic value in HD.
Subject(s)
Hodgkin Disease/metabolism , MAP Kinase Signaling System/physiology , Mitogen-Activated Protein Kinase Kinases/metabolism , Mitogen-Activated Protein Kinases/metabolism , Antineoplastic Agents/pharmacology , Apoptosis Regulatory Proteins , Butadienes/pharmacology , CD40 Antigens , Cell Division , Cell Survival , Enzyme Inhibitors/pharmacology , Glycoproteins , Hodgkin Disease/pathology , Humans , Ki-1 Antigen , Lymph Nodes/pathology , Membrane Glycoproteins/metabolism , Mitogen-Activated Protein Kinase Kinases/antagonists & inhibitors , Mitogen-Activated Protein Kinases/physiology , Nitriles/pharmacology , Osteoprotegerin , Phosphorylation , Receptors, Cytoplasmic and Nuclear , Receptors, Tumor Necrosis Factor , TNF-Related Apoptosis-Inducing Ligand , Tumor Cells, Cultured , Tumor Necrosis Factor-alpha/metabolismABSTRACT
In acute myeloid leukaemia (AML), cell kinetic quiescence has been postulated to contribute to drug resistance. As the anti-apoptotic genes Bcl-2 and Bcl-X(L) have been implicated in cell cycle regulation, we investigated the expression of these genes in non-proliferating (Q) and proliferating (P) AML and normal CD34+ progenitor cells. Using reverse transcription polymerase chain reaction, Bcl-X(L) and Bcl-2 were overexpressed in Q versus P AML cells, whereas no difference in Bcl-XS and Bax expression was found. Furthermore, the Bcl-X(L)/X(S) but not the Bcl-2/Bax ratio was higher in Q AML compared with normal CD34+ Q cells (P = 0.001). An inverse correlation between Bcl-2 expression of leukaemic Q cells and their ability to enter the cell cycle was found. Treatment with all-trans retinoic acid (ATRA) reduced Bcl-2 and Bcl-X(L) expression in the leukaemic Q cells, and enhanced their chemosensitivity to cytosine arabinoside (ara-C). These findings demonstrate overexpression of the anti-apoptotic proteins Bcl-X(L) and Bcl-2 in quiescent CD34+ AML cells and suggest their involvement in the chemoresistance. The observed inverse correlation between Bcl-2 and proliferation suggests a role for Bcl-2 in the cell cycle regulation of AML. These findings could be used in the development of therapies that selectively induce apoptosis in quiescent leukaemic progenitor cells.
