rottlerin and Leukemia-Lymphoma--Adult-T-Cell

Protein kinase C (PKC)-δ is a member of the PKC family. It has been implicated in tumor suppression as well as survival of various cancers. The aggressive malignancy of T lymphocytes known as adult T-cell leukemia (ATL) is associated with human T-cell leukemia virus type 1 (HTLV-1) infection. In this study, we show that HTLV-1-infected T cells are characterized by phosphorylation and nuclear translocation of PKC-δ. Expression of HTLV-1 regulatory protein Tax increased PKC-δ phosphorylation. Blockade of PKC-δ by rottlerin suppressed PKC-δ phosphorylation and inhibited cell viability in HTLV-1-infected T-cell lines and primary ATL cells. Rottlerin induced cell cycle arrest at the G1 phase and caspase-mediated apoptosis of HTLV-1-infected T cells. Rottlerin downregulated the expression of proteins involved in G1/S cell cycle transition, cyclin D2, CDK4 and 6, and c-Myc, resulting in dephosphorylation of retinoblastoma protein (pRb). Furthermore, rottlerin reduced the expression of important anti-apoptotic proteins (e.g., survivin, XIAP, Bcl-xL and c-FLIP) and Bcl-2 phosphorylation, and activated the pro-apoptotic protein Bax. Our results showed that permanent activation of nuclear factor-κB (NF-κB) by HTLV-1 Tax allows infected cells to escape cell cycle arrest and apoptosis and that PKC-δ mediates Tax-induced activation of NF-κB. Based on these findings, new therapies designed to target PKC-δ could be potentially useful in the treatment of ATL.

Topics: Acetophenones; Adult; Apoptosis; Benzopyrans; Cell Line, Tumor; Cell Proliferation; Enzyme Activation; Gene Products, tax; HTLV-I Infections; Human T-lymphotropic virus 1; Humans; Indoles; Leukemia-Lymphoma, Adult T-Cell; Maleimides; NF-kappa B; Phosphorylation; Protein Kinase C-delta; Protein Kinase Inhibitors; Signal Transduction

Macrophage-derived chemokine [CC chemokine ligand 22 (CCL22)] and thymus- and activation-regulated chemokine (CCL17) mediate cellular effects, principally by binding to their receptor CC chemokine receptor 4 (CCR4) and together, constitute a multifunctional chemokine/receptor system with homeostatic and inflammatory roles within the body. This study demonstrates that CCL22 and CCL17 stimulate pertussis toxin-sensitive elevation of intracellular calcium in the CEM leukemic T cell line and human peripheral blood-derived T helper type 2 (Th2) cells. Inhibition of phospholipase C (PLC) resulted in the abrogation of chemokine-mediated calcium mobilization. Chemokine-stimulated calcium responses were also abrogated completely by the inhibition of inositol 1,4,5-trisphosphate [Ins(1,4,5)P3] receptor-mediated calcium release. Chemotactic responses of CEM and human Th2 cells to CCL17 and CCL22 were similarly abrogated by inhibition of PLC and inhibition of novel, Ca2+-independent/diacylglycerol-dependent protein kinase C (PKC) isoforms. Inhibition of Ins(1,4,5)P3 receptor-mediated calcium release from intracellular stores had no effect on chemotactic responses to CCR4 ligands. Taken together, this study provides compelling evidence of an important role for PLC and diacylglycerol-dependent effector mechanisms (most likely involving novel PKC isoforms) in CCL17- and CCL22-stimulated, directional cell migration. In this regard, CCL22 stimulates phosphatidylinositol-3 kinase-independent phosphorylation of the novel delta isoform of PKC at threonine 505, situated within its activation loop--an event closely associated with increased catalytic activity.

Topics: Acetophenones; Benzopyrans; Calcium; Calcium Channels; Calcium Signaling; Catalytic Domain; Cell Line, Tumor; Chemokine CCL17; Chemokine CCL22; Chemokines, CC; Chemotaxis; Chromones; Diglycerides; Estrenes; Humans; Indoles; Inositol 1,4,5-Trisphosphate; Inositol 1,4,5-Trisphosphate Receptors; Leukemia-Lymphoma, Adult T-Cell; Morpholines; Pertussis Toxin; Phosphatidylinositol 3-Kinases; Phosphatidylinositol Diacylglycerol-Lyase; Phosphoinositide-3 Kinase Inhibitors; Phosphorylation; Phosphothreonine; Protein Processing, Post-Translational; Pyrroles; Pyrrolidinones; Receptors, CCR4; Receptors, Chemokine; Receptors, Cytoplasmic and Nuclear; Recombinant Fusion Proteins; T-Lymphocytes; Th2 Cells