leupeptins and Lymphoma--Primary-Effusion

Primary effusion lymphoma (PEL) is a rare subtype of non-Hodgkin's B-cell lymphoma and is caused by Kaposi's sarcoma-associated herpesvirus (KSHV) in immunosuppressed patients. PEL is an aggressive lymphoma and is frequently resistant to conventional chemotherapies. Sulforaphane (SFN), a natural compound found in cruciferous vegetables and broccoli sprouts, modulates signaling pathways and epigenetic gene expression. However, the anti-proliferative effects of SFN on PEL cells and the underlying mechanisms have not been identified. Here, we found that SFN decreased the viability of KSHV-infected PEL cells compared to KSHV-uninfected B-lymphoma cells. The anti-proliferative effects of SFN on PEL cells were mediated by apoptosis with activating caspases. In addition, SFN inhibited the phosphorylation of p38 mitogen-activated protein kinase (p38MAPK) and AKT in PEL cells. We also showed that p38MAPK and AKT inhibitors reduced PEL cell growth. The constitutive and/or transient activation of p38MAPK and AKT signaling are necessary for the survival and proliferation of PEL cells. Our data and previous literature indicate that SFN represses the phosphorylation of p38MAPK and AKT, which results in PEL cell apoptosis. Moreover, we investigated whether MG132 or sangivamycin (Sangi) in combination with SFN potentiated the cytotoxic effects of SFN on PEL cells. Compared to treatment with SFN alone, the addition of MG132 or Sangi enhanced the cytotoxic activity of SFN in a synergistic manner. In conclusion, the anti-proliferative effects of SFN indicate its potential as a new substance for the treatment of PEL.

Topics: Antineoplastic Agents; Apoptosis; Cell Line, Tumor; Cell Survival; Drug Synergism; Humans; Isothiocyanates; Leupeptins; Lymphoma, Primary Effusion; p38 Mitogen-Activated Protein Kinases; Phosphorylation; Proto-Oncogene Proteins c-akt; Pyrimidine Nucleosides; Sulfoxides

Primary effusion lymphoma (PEL) is an aggressive neoplasm caused by Kaposi's sarcoma-associated herpesvirus (KSHV). This study provides evidence that proteasomal activity is required for both survival of PEL cells stably harboring the KSHV genome and viral replication of KSHV. We evaluated the cytotoxic effects of proteasome inhibitors on PEL cells. The proteasome inhibitors MG132, lactacystin, and proteasome inhibitor I dramatically inhibited cell proliferation and induced apoptosis of PEL cells through the accumulation of p21 and p27. Furthermore, proteasome inhibitors induced the stabilization of NF-κB inhibitory molecule (IκBα) and suppressed the transcriptional activity of NF-κB in PEL cells. The NF-κB specific inhibitor BAY11-7082 also induced apoptosis in PEL cells. The constitutive activation of NF-κB signaling is essential for the survival and growth of B cell lymphoma cells, including PEL cells. NF-κB signaling is upregulated by proteasome-dependent degradation of IκBα. The suppression of NF-κB signaling by proteasome inhibitors may contribute to the induction of apoptosis in PEL cells. In addition, proteasome activity is required for KSHV replication in KSHV latently infected PEL cells. MG132 reduced the production of progeny virus from PEL cells at low concentrations, which do not affect PEL cell growth. These findings suggest that proteasome inhibitors may represent a novel strategy for the treatment of KSHV infection and KSHV-associated lymphomas.

Topics: Acetylcysteine; Antineoplastic Agents; Apoptosis; Cell Line, Tumor; Cysteine Proteinase Inhibitors; Herpesvirus 8, Human; Humans; Leupeptins; Lymphoma, Primary Effusion; NF-kappa B; Nitriles; Oligopeptides; Proteasome Inhibitors; Sulfones; Virus Replication

Primary effusion lymphoma (PEL) is an incurable, aggressive B-cell malignancy that develops rapid resistance to conventional chemotherapy. MG-132, a proteasome inhibitor, suppresses cell proliferation and induces apoptosis in several PEL cell lines. Treatment of PEL cells with MG-132 results in downregulation of S-phase kinase protein 2 (SKP2) and accumulation of p27Kip1. Furthermore, MG-132 treatment of PEL cells causes Bax conformational changes, leading to loss of mitochondrial membrane potential and release of cytochrome c to the cytosole. Such cytochrome c release results in sequential activation of caspases and apoptosis, while pretreatment of PEL cells with universal inhibitor of caspases, z-VAD-fmk prevents cell death induced by MG-132. Finally, our data demonstrated in PEL cells that MG-132 downregulates the expression of inhibitor of apoptosis proteins XIAP, cIAP1 and survivin. Altogether, these findings suggest that MG-132 is a potent inducer of apoptosis of PEL cells via downregulation of SKP2 leading to accumulation of p27Kip1, resulting in cell cycle arrest and apoptosis and strongly suggest that targeting the proteasomal pathway may provide a novel therapeutic approach for the treatment of PEL.

Topics: Amino Acid Chloromethyl Ketones; Antineoplastic Agents; Apoptosis; Cell Cycle; Cell Line, Tumor; Cyclin-Dependent Kinase Inhibitor p27; Cytochromes c; Gene Expression Regulation, Neoplastic; Humans; Inhibitor of Apoptosis Proteins; Leupeptins; Lymphoma, Primary Effusion; Microtubule-Associated Proteins; S-Phase Kinase-Associated Proteins; Survivin; X-Linked Inhibitor of Apoptosis Protein