Most existing chemotherapeutics lack adequate specificity for transformed cells and therefore have high rates of collateral damage to normal tissue. Moreover, such therapies often depend on p53 to induce cell death and are ineffective on the large number of human cancers that have lost p53 function. The discovery of novel p53-independent cancer therapies is therefore of significant interest. The Chicken Anemia Virus protein Apoptin selectively induces apoptosis in transformed cells in a p53-independent manner while leaving normal primary cells unaffected. This selectivity is thought to be largely due to cell type-specific localization: in primary cells Apoptin is cytoplasmic, whereas in transformed cells the protein localizes to the nucleus. The basis for this cell type-specific localization remains to be determined. In this study, Apoptin is revealed to be a nucleo-cytoplasmic shuttling protein whose localization is mediated by an N-terminal nuclear export signal (NES) and a C-terminal nuclear localization signal (NLS). Both signals are required for cell type-specific localization, as Apoptin fragments containing either the NES or NLS fail to localize differently between transformed and primary cells. Significantly, cell type-specific localization can be rescued in trans by co-expression of the two separate fragments, which are able to interact through an Apoptin multimerization domain. Interestingly, this multimerization domain overlaps with the NES suggesting that these two activities may be functionally coupled in cytoplasmic retention in primary cell types. Factors present in transformed cells induce localization of Apoptin to the nucleus where a biochemically distinct, more soluble form of the protein exists. Using affinity-purification and mass spectroscopy it was found that, specifically in transformed cells, Apoptin is associated with APC1, a subunit of the anaphase-promoting complex/cyclosome (APC/C). The APC/C is required to establish a mitotic cell-cycle checkpoint, and its inhibition results in G2/M arrest and apoptosis. Expression of wild type Apoptin in transformed cells inhibits APC/C function and induces G2/M arrest and apoptosis, whereas Apoptin mutants that are unable to associate with APC1 have no effect. In p53 null cells, ablation of APC1 by RNA interference induces a G2/M arrest and apoptosis analogous to that observed following Apoptin expression. Furthermore, Apoptin was found to induce the formation of PML bodies and to recruit APC/C subunits to these nuclear structures suggesting a mechanism involving sequestration and subsequent inhibition of the APC/C. Thus, the results of this study clarify Apoptin cell type-specific localization behavior and explain the ability of Apoptin to induce apoptosis in transformed cells in the absence of p53. This study advances a newly emerging field of viral mechanisms of apoptosis involving G2/M arrest and APC/C modulation. The resultant p53-independent apoptosis suggests that the APC/C may be an attractive target for the development of anti-cancer drugs.

Made available in DSpace on 2016-12-08T16:24:22Z (GMT). No. of bitstreams: 1 PGCA15MA178.pdf: 1072214 bytes, checksum: 2feb2bb4cea985aa369f44b04592defd (MD5) Previous issue date: 2015-08-14 / Chicken anemia virus (CAV) is an important virus that belongs to Circoviridae family, Gyrovirus genre, known to lead to significant losses in poultry, the viruses can cause immunosuppression and disease especially in young birds. CAV was the only virus of this family known to infect chickens by 2011, after the discovery of a new virus, the Avian Gyrovirus type 2 (AGV2). According to the literature, AGV2 is closely related to CAV, as well as being widely distributed in chickens in Brazil and other countries, but its pathogenic potential is unknown and studies on molecular epidemiology are still scarce. The present study aimed to detect CAV (Nested-PCR), and AGV2 (PCR) on DNA extracted from samples of thymus tissue of broiler chickens housed on two states of southern Brazil. In addition, perform phylogenetic analysis of AGV2 positive samples. Results showed that of 180 birds tested, 105 (58.33%) were positive for CAV and 39 (21.67%) positive for AGV2. On the positive material for AGV2 were selected eleven amplicons for sequencing and phylogenetic analysis, where it became clear that there were no differences among the samples. The sequences obtained were compared with samples from other countries, many of these detected in humans (HGyV). It was not possible in the present work, observe correlation between geographical distribution and genetic variability among most samples AGV2 now studied / O vírus da anemia das galinhas (CAV) é um importante vírus pertencente a família Circoviridae, gênero Girovirus, conhecido por levar a perdas significativas na avicultura, este vírus pode causar imunossupressão e doença principalmente em aves jovens. O CAV era o único vírus desta família conhecido por infectar galinhas até 2011, após a descoberta de um novo vírus, o Girovírus Aviário tipo 2 (AGV2). Segundo consta na literatura, o AGV2 está estreitamente relacionado ao CAV, além de estar amplamente distribuído em frangos no Brasil e em outros países, mas seu potencial patogênico ainda é desconhecido e trabalhos sobre sua epidemiologia molecular ainda são bastante escassos. Assim, o presente trabalho teve por objetivo realizar a detecção de CAV (Nested-PCR), e AGV2 (PCR) em amostras de DNA extraídas de tecido do timo, de aves alojadas em plantéis de frango de corte de dois estados da região Sul do Brasil. Além disso, realizar a análise filogenética de amostras positivas para AGV2. Os resultados apontaram que das 180 aves testadas 105 (58,33%)foram positivas para CAV e 39 (21,67%) positivas para AGV2. Do material positivo para AGV2 foram selecionados onze amplicons para sequenciamento e análise filogenética, onde foi possível evidenciar que não houve diferenças entre o material analisado. As sequências obtidas foram comparadas com amostras provenientes de outros países, muitas destas detectadas em humanos (HGyV), não tendo sido possível, no presente trabalho, observar correlação entre distribuição geográfica e variabilidade genética entre a maioria das amostras de AGV2 ora estudadas