Damaged microtubules can inactivate BCL-2 by means of the mTOR kinase

Rapamycin, a specific inhibitor of the serine/threonine mTOR kinase, markedly inhibited both cell growth and apoptosis in human B-cell lines. Besides arresting cells in G(1) by increasing p27(kip1), rapamycin tripled the cellular level of the BCL-2 protein. The activity was dose-dependent and specific for the p27(kip1) and BCL-2 proteins. Rapamycin did not affect bcl-2 mRNA although it increased cellular BCL-2 concentration by inhibiting phosphorylation, a mechanism initiating the decay process. To add new insight, we combined rapamycin treatment with treatment by taxol, which, by damaging microtubules, can phosphorylate BCL-2 and activate apoptosis. It was found that the mTOR kinase was activated in cells treated with taxol or with nocodazole although it was inhibited in cells pre-treated with rapamycin. BCL-2 phosphorylation, apoptosis and hyperdiploidy were also inhibited by rapamycin. In contrast, taxol-induced microtubule stabilization or metaphase synchronization were not inhibited by rapamycin. Taken together, these findings indicate that mTOR belongs to the enzymatic cascade that, starting from damaged microtubules, phosphorylates BCL-2. By regulating apoptosis, in addition to the control of a multitude of growth-related pathways, mTOR plays a nodal role in signaling G(1) and G(2)-M events

Inhibition of oxidative phosphorylation underlies the antiproliferative and proapoptotic effects of mofarotene (Ro 40-8757) in Burkitt's lymphoma cells

In the search for retinoids active against Burkitt's lymphoma (BL), we found that the arotinoid mofarotene (Ro 40-8757) induced strong antiproliferative and apoptotic responses in most established BL cell lines as well as in primary BL cells. Ro 40-8757-induced apoptosis is associated with mitochondrial membrane depolarization, activation of caspase-3 and -9, and enhanced production of reactive oxygen species. These effects were related to a transient drop in intracellular ATP content, probably favored by a downregulation of NADH dehydrogenase subunit-1, a component of the mitochondrial respiratory chain (MRC) Complex I. Inhibition of MRC with thenoyltrifluoroacetone suppressed both the ATP recovery and apoptosis, confirming that the effects of Ro 40-8757 are mediated by changes in mitochondrial function. Compared to EBV-negative lines, EBV-carrying BLs were more resistant to Ro 40-8757-induced apoptosis. EBV infection and ectopic LMP-1 expression increased the resistance of BL cells to Ro 40-8757-induced apoptosis, probably through bcl-2 upregulation. Finally, we also show that 2-methoxyoestradiol, an inhibitor of the scavenger enzymes superoxide dismutases, enhanced Ro 40-8757-mediated apoptosis. These findings provide the rationale for evaluating the clinical efficacy of Ro 40-8757 in BL patients and suggest that the combination of Ro 40-8757 with inhibitors of scavenger enzymes may be a promising therapeutic approach for this aggressive lymphoma

Retinoids irreversibly inhibit in vitro growth of Epstein-Barr virus-immortalized B lymphocytes.

Natural and synthetic retinoids have proved to be effective in the treatment and prevention of various human cancers. In the present study, we investigated the effect of retinoids on Epstein-Barr virus (EBV)-infected lymphoblastoid cell lines (LCLs), since these cells closely resemble those that give rise to EBV-related lymphoproliferative disorders in the immunosuppressed host. All six compounds tested inhibited LCL proliferation with no significant direct cytotoxicity, but 9-cis-retinoic acid (RA), 13-cis-RA, and all-trans-RA (ATRA) were markedly more efficacious than Ro40-8757, Ro13-6298, and etretinate. The antiproliferative action of the three most effective compounds was confirmed in a large panel of LCLs, thus appearing as a generalized phenomenon in these cells. LCL growth was irreversibly inhibited even after 2 days of treatment at drug concentrations corresponding to therapeutically achievable plasma levels. Retinoid-treated cells showed a marked downregulation of CD71 and a decreased S-phase compartment with a parallel accumulation in Gzero/ G1 phases. These cell cycle perturbations were associated with the upregulation of p27 Kip1, a nuclear protein that controls entrance and progression through the cell cycle by inhibiting several cyclin/cyclin-dependent kinase complexes. Unlike what is observed in other systems, the antiproliferative effect exerted by retinoids on LCLs was not due to the acquisition of a terminally differentiated status. In fact, retinoid-induced modifications of cell morphology, phenotype (downregulation of CD19, HLA-DR, and s-Ig, and increased expression of CD38 and c-Ig), and IgM production were late events, highly heterogeneous, and often slightly relevant, being therefore only partially indicative of a drug-related differentiative process. Moreover, EBV-encoded EBV nuclear antigen-2 and latent membrane protein-1 proteins were inconstantly downregulated by retinoids, indicating that their growth-inhibitory effect is not mediated by a direct modulation of viral latent antigen expression. The strong antiproliferative activity exerted by retinoids in our experimental model indicates that these compounds may represent a useful tool in the medical management of EBV-related lymphoproliferative disorders of immunosuppressed patients

Epstein-Barr virus strains with latent membrane protein-1 deletions: prevalence in the Italian population and high association with human immunodeficiency virus-related Hodgkin's disease.

Six Epstein-Barr virus (EBV)-related lymphoproliferative disorders were investigated to verify whether the EBV strain harbored by neoplastic cells had the same EBNA-2 and latent membrane protein-1 (LMP-1) DNA sequences of the virus carried by normal lymphocytes of the same patients. Within each case, the analysis of neoplastic lymph nodes, reactive lymphadenopathies, and/or EBV+ spontaneous lymphoblastoid cell lines gave concordant results with respect to type-specific EBNA-2 region and LMP-1 gene. In particular, five cases showed the same deletion in the 3' end of the LMP-1 gene in both normal and neoplastic cells. We also determined the prevalence of LMP-1 deletions in a large series of normal peripheral blood mononucleated cells (PBMCs) from Italian individuals. The analysis showed that 50% (9 of 18) of PBMCs from human immunodeficiency virus (HIV)-seronegative donors carried a 30-bp deletion in the C-terminal portion of the LMP-1 gene, whereas a nondeleted fragment was amplified in about 44% (8 of 18) of the cases. Only one sample (5.6%) showed the amplification of a full-length LMP-1 band together with a deleted fragment. Similarly, PBMCs from HIV-infected patients showed an almost equivalent prevalence of full-length (17 of 37, 46%) and deleted (16 of 37, 43.2%) LMP-1 fragments, whereas about 11% of samples (4 of 37) showed evidence of double infections. Of note, deletions in the LMP-1 gene were detected with similar prevalence values in EBV+ Hodgkin's disease (HD) (13 of 30, 43.3%) and non-Hodgkin's lymphoma (NHL) (2 of 5, 40%) cases from HIV-seronegative patients and in HIV-related, EBV+ NHLs (4 of 7, 57.1%). Conversely, a 30-bp LMP-1 deletion was found in 10 of 12 HIV-associated HD cases (83%), a prevalence significantly higher than that detected in HIV-unrelated HD (P = .01). These findings indicate that: (1) the same EBV strain carrying LMP-1 deletions is harbored by normal and neoplastic cells of patients with EBV+ disorders, ruling out that these mutations might result from immunoselection phenomena; (2) in the Italian population, the prevalence of LMP-1 deletion mutants is comparable to that of EBV strains with full-length LMP-1; (3) HIV-induced immunosuppression is not associated with an increased prevalence of LMP-1 deletions in PBMCs; and (4) HIV-related HD cases, but not those of HIV-seronegative Italian patients, are closely correlated with the presence of LMP-1 deletions, suggesting that infection with these strains may increase the risk of developing HD in the HIV setting