Abnormal intracellular kinetics of cell-cycle-dependent proteins in lymphocytes from patients infected with human immunodeficiency virus: a novel biologic link between immune activation, accelerated T-cell turnover, and high levels of apoptosis

Abstract

Human immunodeficiency virus (HIV)-infection is characterized by loss of CD4؉ T cells associated with high levels of immune activation, T-cell proliferation, and lymphocyte apoptosis. To investigate the role of intrinsic perturbations of cellcycle control in the immunopathogenesis of acquired immunodeficiency syndrome (AIDS), we studied the expression of cellcycle-dependent proteins in lymphocytes from HIV-infected patients. Cyclin B1 expression, Nucleolar Organizer Regions (NORs) number, and NORs area of distribution were all consistently increased in HIV-infected patients, but returned to normal after effective antiretroviral therapy, suggesting that viral replication is directly implicated in the genesis of the observed changes. Analysis of cyclin B1 intracellular turnover showed that the increased cyclin B1 expression is (1) caused by defective degradation in the presence of normal rates of synthesis, and (2) is temporally associated with decreased levels of ubiquitination. After in vitro activation of lymphocytes from healthy individuals, cyclin B1 and cdc25 expression and ubiquitination, p34 cdc2 activity, NORs morphology, and C23/nucleolin localization showed a 72-to 96-hour cyclic pattern that led to a biologic state similar to baseline. On the contrary, complex but consistent changes of the same indices followed activation of T lymphocytes from HIVinfected patients, resulting in a 5-fold increase in apoptosis. Overall, our data indicate that a profound dysregulation of cellcycle control is present in lymphocytes from HIV-infected patients. This finding may provide a novel biologic link between immune activation, accelerated lymphocyte turnover, and increased apoptosis during HIV infection. IntroductionHuman immunodeficiency virus (HIV)-infection induces a progressive depletion of CD4 ϩ T lymphocytes and high susceptibility to opportunistic infections. 1 The mechanisms of HIV-induced CD4 ϩ T-cell loss include the virus-mediated killing of infected cells as well as the death of uninfected bystander cells. 1,2 Among the indirect mechanisms that have been implicated in the lymphocyte depletion of patients with acquired immunodeficiency syndrome (AIDS), increased level of apoptosis may be significant. In HIV-infected patients, increased susceptibility to apoptotic cell death has been shown in CD4 ϩ and CD8 ϩ T lymphocytes and appears to be correlated with the general state of immune activation. [3][4][5][6] Interestingly, both increased propensity to apoptosis and overall levels of immune activation are reversed by the institution of effective anti-HIV therapy. 7,8 It is therefore likely that an abnormal relationship between T-cell activation/proliferation and occurrence of apoptosis may play a significant role in the lymphocyte depletion in the HIV-infected patient. 9,10 Lymphocyte activation in response to extrinsic signals ultimately results in either progression through the cell cycle, or activation of proapoptotic pathway(s). 11,12 Although influenced by many factors, the fate of activated T cells is e...

Repression of IRF-4 target genes in human T cell leukemia virus-1 infection

“…The pathways involved in g-radiation-induced apoptosis were p53-independent and therefore cyclin B1 is believed to be the critical component of this type of apoptosis. Another recent study has demonstrated that an increase in cyclin B1 expression in HIV-1 infected patient-samples leads to increased apoptosis of these cells (Cannavo et al, 2001). Thus, a decrease in cyclin B1 by IRF-4 may also prevent apoptosis in HTLV-1 infected cells as well as inhibit the mitotic checkpoint activities (Figure 7).…”

Mechanisms of apoptosis induction by the HIV-1 envelope

“…Thus, cyclin B has been found to be overexpressed in circulating T lymphocytes from HIV-1 carriers, and this upregulation disappears upon successful antiretroviral therapy. 71,72 Similarly, mTOR and the phosphoneoepitope indicating phosphorylation of p53 on serine 15 were found to be overexpressed among a fraction of peripheral blood mononuclear cells, correlating with viral load, 55,62 as well as with the frequency of cells expressing tissue transglutaminase-2, a marker of preapoptosis. 73 Highly active antiretroviral therapy (HAART) corrected the abnormally high mTOR and p53S15P levels of the patients.…”

Apoptosis in SIV infection

“…Cytokines, in contrast, prevented both the apoptotic phenotype and the cell death by preserving mitochondrial membrane potential staining for the argyrophilic Nucleolar Organizing Regions (AgNOR) and the subcellular localization of nucleolin in confocal microscopy. [122][123][124][125][126][127] Importantly, the HIV-associated cell cycle dysregulation is exacerbated by in vitro treatment with mitogens and appears to be correlated with induction of T-cell apoptosis; 122,123,126 however, these cell cycle perturbations and apoptosis are reduced after exogenous administration of IL-2 in vitro. 122 In mitogen-activated lymphocytes from HIV-infected patients, the inappropriate activation of the cyclin B1/p34 cdc2 kinase complex is temporally associated with increased threonine phosphorylation, augmented fragmentation, and prominent extranuclear and cell surface localization of nucleolin.…”