benzyloxycarbonylleucyl-leucyl-leucine-aldehyde and Leukemia-Lymphoma--Adult-T-Cell

We have recently shown constitutive IkappaB kinase (IKK) activation and aberrant p52 expression in adult T cell leukemia (ATL) cells that do not express human T cell leukemia virus type I (HTLV-I) Tax, but the mechanism of IKK activation in these cells has remained unknown. Here, we demonstrate distinct regulation of IKK activity in ATL and HTLV-I-transformed T cells in response to protein synthesis inhibition or arsenite treatment. Protein synthesis inhibition for 4 h by cycloheximide (CHX) barely affects IKK activity in Tax-positive HTLV-I-transformed cells, while it diminishes IKK activity in Tax-negative ATL cells. Treatment of ATL cells with a proteasome inhibitor MG132 prior to protein synthesis inhibition reverses the inhibitory effect of CHX, and MG132 alone greatly enhances IKK activity. In addition, treatment of HTLV-I-transformed cells with arsenite for 1 h results in down-regulation of IKK activity without affecting Tax expression, while 8 h of arsenite treatment does not impair IKK activity in ATL cells. These results indicate that a labile protein sensitive to proteasome-dependent degradation governs IKK activation in ATL cells, and suggest a molecular mechanism of IKK activation in ATL cells distinct from that in HTLV-I-transformed T cells.

Topics: Arsenites; Cell Line, Transformed; Cell Line, Tumor; Cell Transformation, Viral; Cycloheximide; Enzyme Inhibitors; Human T-lymphotropic virus 1; Humans; I-kappa B Kinase; Leukemia-Lymphoma, Adult T-Cell; Leupeptins; Proteasome Endopeptidase Complex; Protein Serine-Threonine Kinases; Protein Synthesis Inhibitors; T-Lymphocytes

Cytokines, such as interleukin-2 (IL-2), activate intracellular signaling pathways via rapid tyrosine phosphorylation of their receptors, resulting in the activation of many genes involved in cell growth and survival. The deubiquitinating enzyme DUB-2 is induced in response to IL-2 but as yet its function has not been determined. The results of this study show that DUB-2 is expressed in human T-cell lymphotropic virus-I (HTLV-1)-transformed T cells that exhibit constitutive activation of the IL-2 JAK/STAT (signal transducers and activators of transcription) pathway, and when expressed in Ba/F3 cells DUB-2 markedly prolonged IL-2-induced STAT5 phosphorylation. Although DUB-2 did not enhance IL-2-mediated proliferation, when withdrawn from growth factor, cells expressing DUB-2 had sustained STAT5 phosphorylation and enhanced expression of IL-2-induced genes cis and c-myc. Moreover, DUB-2 expression markedly inhibited apoptosis induced by cytokine withdrawal allowing cells to survive. Taken together these data suggest that DUB-2 can enhance signaling through the JAK/STAT pathway, prolong lymphocyte survival, and, when constitutively expressed, may contribute to the activation of the JAK/STAT pathway observed in some transformed cells.

Topics: Apoptosis; Cell Line; Cell Line, Transformed; Cell Transformation, Viral; Cysteine Endopeptidases; DNA-Binding Proteins; Endopeptidases; Human T-lymphotropic virus 1; Humans; Immediate-Early Proteins; Interleukin-2; Leukemia-Lymphoma, Adult T-Cell; Leupeptins; Milk Proteins; Multienzyme Complexes; Phosphorylation; Proteasome Endopeptidase Complex; Signal Transduction; STAT5 Transcription Factor; T-Lymphocytes; Trans-Activators; Transcriptional Activation; Transfection; Ubiquitins