RESUMO
The anaphase-promoting complex/cyclosome (APC/C) is a conserved ubiquitin ligase controlling mitosis and G1 phase of the cell cycle. The APC/C is activated by two regulatory subunits Cdc20 (APC/C(Cdc20)) and Cdh1 (APC/C(Cdh1)) to target securin, mitotic cyclins and other cell cycle regulatory proteins. Cdc20 is essential for sister chromatid separation at the meta- to anaphase transition in yeast, drosophila and perhaps mouse embryos. However, whether Cdc20 is essential for mitotic control of human somatic cells is uncertain. Therefore, we used a lentiviral vector-mediated inducible RNA interference (RNAi) system to generate strong downregulation of Cdc20 expression in clonal cells to further elucidate the role of human Cdc20. Here we show, that even an almost complete knockdown of Cdc20 below the detection limit in western blots does neither cause a mitotic block nor significant stabilization of the APC/C(Cdc20) substrates cyclin B and securin. Thus, there may be redundant mechanisms of mitotic control in the human somatic cell cycle.
Assuntos
Proteínas de Ciclo Celular/metabolismo , Técnicas de Silenciamento de Genes , Mitose/fisiologia , Complexos Ubiquitina-Proteína Ligase/metabolismo , Ciclossomo-Complexo Promotor de Anáfase , Animais , Proteínas Cdc20 , Ciclo Celular/fisiologia , Proteínas de Ciclo Celular/genética , Ciclina B/genética , Ciclina B/metabolismo , Genes cdc , Humanos , Camundongos , Proteínas de Neoplasias/genética , Proteínas de Neoplasias/metabolismo , Interferência de RNA , Securina , Complexos Ubiquitina-Proteína Ligase/genéticaRESUMO
Approximately 50% of all cancer patients develop cachexia, a paraneoplastic syndrome that is characterized by wasting of adipose tissue and skeletal muscle mass. Cytokines, including TNF-alpha, interleukins-1, -6, and interferon-A are known mediators of the cachectic process. The latter however represent only one of many imbalanced systems in cancer cachexia. The aim of this study was to further delineate the pathogenesis of cachexia by molecular profiling. Human renal cancer xenografts that do and do not induce cachexia in mice were used as disease models. Cachexia-associated gene expression was studied on Human Genome U95 Affymetrix arrays and revealed several new genes such as TNF-alpha ligand superfamily protein, interferon-A treatment inducible protein, and DKFZ5641I1922. The expression of the IL-8 gene was also elevated in cachexia inducing xenografts (CIX). At the protein level, TNF-alpha was found expressed only in CIX, whereas IL-1 and IL-6 were not cachexia specific. Levels of parathyroid hormone-related protein were elevated in CIX and accompanied by hypercalcemia. COX-2 and prostaglandin E2 were also found to be over expressed. By using the COX-2 inhibitors rofecoxib and nimesulide, we were able to delay tumor-mediated wasting in vivo. Overall, our results suggest that cachexia is a multigenetic disease that will require complex combinations of drugs for an effective therapeutic intervention.
