RESUMEN
The human herpesvirus 8 (HHV8/KSHV), along with certain other herpesviruses, encodes a gene with cyclin homology. Although the functional significance of the encoded cyclin is not clear at present, various lines of evidence propose a role for this cyclin in latently infected cells and possibly in the induction of tumors that arise in HHV8-infected individuals. We provide evidence here that the cyclin protein is expressed in HHV8 positive primary effusion lymphoma (PEL)-derived cell lines and that its level of expression varies greatly between different lines. Our analysis indicates that the level of cyclin protein expression in different PEL cell lines may correlate with the level of transcript expression during latency but not in cells induced to undergo lytic replication. In highly expressing BC-3 cells the cyclin is complexed with cdk6, cdk4, cdk2, and cdk5 under both latent and lytic conditions, although subtle changes in the level of cdk association are seen after induction of the lytic cycle. Altogether our findings support the notion that the cyclin is a latency-associated gene product expressed in PEL tumor cells. They furthermore indicate that after lytic cycle induction, the level of cyclin transcript expression may not be a reliable indicator for the level of cyclin protein expression.
Asunto(s)
Ciclinas/genética , Herpesvirus Humano 8/genética , Linfoma de Células B/virología , Proteínas Virales/genética , Anticuerpos Antivirales/química , Antígenos Virales/genética , Antígenos Virales/inmunología , Quinasas Ciclina-Dependientes/metabolismo , Ciclinas/biosíntesis , Ciclinas/inmunología , Herpesvirus Humano 8/enzimología , Humanos , Linfoma de Células B/química , ARN Mensajero/metabolismo , Células Tumorales Cultivadas , Proteínas Virales/biosíntesisRESUMEN
Cyclins are known effectors of cellular proliferation. While originally considered as the product of cellular genes, it is now clear that representatives of this class of proteins can be encoded by certain viruses. One of these viruses is HHV-8, a gamma herpesvirus implicated as a causative agent of Kaposi's Sarcoma and lymphomas in humans. The significance of the virally encoded cyclin proteins in viral propagation is as yet unclear. However, the fact that deregulation of cellular cyclin expression is a known event in tumour development suggests that the virally encoded cyclins could be part of a mechanism utilised by these viruses to induce tumour formation.
Asunto(s)
Ciclinas/fisiología , Herpesvirus Humano 8/genética , Animales , Quinasas Ciclina-Dependientes/fisiología , Ciclinas/genética , Humanos , Neoplasias/etiologíaRESUMEN
Infection of human B cells with Epstein-Barr virus (EBV) results in activation of the cell cycle and cell growth. To interpret the mechanisms by which EBV activates the cell, we have assayed many proteins involved in control of the G0 and G1 phases of the cell cycle and regulation of apoptosis. In EBV infection most of the changes, including the early induction of cyclin D2, are dependent on expression of EBV genes, but an alteration in the E2F-4 profile was partly independent of viral gene expression, presumably occurring in response to signal transduction activated when the virus binds to its receptor, CD21. By comparing the expression of genes controlling apoptosis, including those encoding several members of the BCL-2 family of proteins, the known relative resistance of EBV-immortalized B-cell lines to apoptosis induced by low serum was found to correlate with expression of both BCL-2 and A20. A20 can be regulated by the NF-kappaB transcription factor, which is known to be activated by the EBV LMP-1 protein. Quantitative assays demonstrated a direct temporal relationship between LMP-1 protein levels and active NF-kappaB during the time course of infection.
Asunto(s)
Apoptosis , Linfocitos B/virología , Herpesvirus Humano 4/fisiología , Linfocitos B/fisiología , Ciclo Celular , Línea Celular , Ciclina D2 , Ciclinas/biosíntesis , Proteínas de Unión al ADN/biosíntesis , Factor de Transcripción E2F4 , Antígenos Nucleares del Virus de Epstein-Barr/fisiología , Humanos , FN-kappa B/metabolismo , Proteínas Proto-Oncogénicas/análisis , Proteínas Proto-Oncogénicas c-bcl-2/análisis , Factores de Transcripción/biosíntesis , Proteínas de la Matriz Viral/biosíntesis , Proteína X Asociada a bcl-2RESUMEN
The exposure of Epstein-Barr virus immortalised B cells (LCLs) to the genotoxic effects of gamma irradiation causes a decreased proliferation of the cells. The early events in this process have been investigated here. The induction of p53 expression correlates with a cell cycle arrest in the G1 and G2/M phases of the cell cycle within 24 h of exposure. The molecular mechanism governing the decreased proliferation appears to involve the induction of the cyclin dependent kinase (cdk) inhibitor p21CIP1 and its functional association with cdk2.
Asunto(s)
Linfocitos B/efectos de la radiación , Quinasas CDC2-CDC28 , Ciclo Celular/efectos de la radiación , Quinasas Ciclina-Dependientes/fisiología , Rayos gamma , Proteínas Serina-Treonina Quinasas/fisiología , Apoptosis , Linfocitos B/citología , Linfocitos B/enzimología , Línea Celular Transformada , Transformación Celular Viral , Quinasa 2 Dependiente de la Ciclina , Inhibidor p21 de las Quinasas Dependientes de la Ciclina , Ciclinas/biosíntesis , Ciclinas/fisiología , Represión Enzimática , Herpesvirus Humano 4/fisiología , Humanos , Proteína p53 Supresora de Tumor/biosíntesisRESUMEN
Infection of human primary B-lymphocytes with Epstein-Barr virus (EBV) drives quiescent cells into continual proliferation and results in the outgrowth of immortal cell lines. This requires re-programming of the mechanisms that, in the absence of appropriate antigenic stimulation, normally prevent the proliferation of B-lymphocytes. Since the Retinoblastoma protein (pRb) and its relatives, p107 and p130, play critical roles in controlling the mammalian cell division cycle, we have investigated the expression and phosphorylation status of these proteins following EBV immortalisation of primary B-lymphocytes. In this report, we show that EBV drives the hyperphosphorylation of pRb. This is achieved by a strategy involving the altered expression of several components of the signal transduction pathway that normally regulates the phosphorylation status of pRb, including the up regulation of a number of cyclins and cyclin-dependent kinases and the down regulation of a subset of cyclin-dependent kinase inhibitors. The net result is the formation of active cyclin-dependent kinase complexes that are capable of phosphorylating and inactivating pRb. The results presented here identify the activation of a normal signal transduction pathway as an important component of the strategy used by EBV to drive cell proliferation.
Asunto(s)
Linfocitos B/virología , Proteínas de Ciclo Celular , Herpesvirus Humano 4/fisiología , Proteínas , Proteína de Retinoblastoma/metabolismo , Proteínas Supresoras de Tumor , Proteínas Portadoras/metabolismo , Línea Celular Transformada , Inhibidor p16 de la Quinasa Dependiente de Ciclina , Inhibidor p27 de las Quinasas Dependientes de la Ciclina , Ciclinas/metabolismo , Herpesvirus Humano 4/genética , Humanos , Proteínas Asociadas a Microtúbulos/metabolismo , Proteínas Nucleares/metabolismo , Fosfoproteínas/metabolismo , Fosforilación , Proteína p107 Similar a la del Retinoblastoma , Proteína p130 Similar a la del Retinoblastoma , Regulación hacia ArribaRESUMEN
This study investigated the change in 1000-m simulated rowing performance in two matched groups of 19 competitive rowers following a 5-day period of supplementation with placebo (CON group) or creatine at a dose equivalent to 0.25 g creatine monohydrate per kilogram of body mass (BM) (EXP group). Creatine uptake was calculated from the difference between the amount fed and the amount recovered in urine during each 24-h period of supplementation. Total creatine uptake for the EXP group over the 5-day period of supplementation averaged 34.9 +/- 10.9 g (range 20.1-54.9 g), which equated to 3.54 +/- 0.93 mmol kg BM-1. The estimated creatine uptake into muscle was 38.1 +/- 10.0 (range 22.6-56.6) mmol kg dry weight-1 for these subjects. After supplementation with placebo, the CON group showed no change in 1000-m rowing performance (214.0 +/- 30.9 vs 214.1 +/- 31.5 s; P = 0.88). Of these subjects, 7 decreased and 10 increased their performance times (range - 3.1 to 2.7%). By contrast, 16 of the 19 subjects in the EXP group improved their performance times. The mean improvement in rowing performance for the EXP group was 2.3 s (211.0 +/- 21.5 vs 208.7 +/- 21.8 s; P < 0.001), an overall improvement of just over 1% (range - 0.4 to 3.4%). We conclude that in competitive rowers, a 5-day period of creatine supplementation was effective in raising whole-body creatine stores, the magnitude of which provided a positive, though statistically non-significant (r = 0.426, P = 0.088), relationship with 1000-m rowing performance.