No abstract

20030 Background: The relation between apoptosis-related molecules and chemosensitivity has been extensively studied. In recent years, attention has shifted to a new family of inhibitor of apoptosis proteins (IAPs). XIAP (X- linked inhibitor of apoptosis) is the most versatile and potent member of the IAP family. To date, the overexpression of XIAP has been detected in various cancers. XAF1 (X-linked inhibitor of apoptosis associated factor 1) is a new protein identified for its ability to interact with XIAP. Neither XIAP nor XAF1 or XIAP/XAF1 mRNA expression have been studied in bladder cancer patients. Methods: The expression of XIAP and XAF1 mRNA was analyzed by a real time quantitative fluorogenic PCR method in a group of 17 patients with locally advanced bladder cancer treated with a combination of neoadjuvant Gemcitabine and Cisplatin. The prognostic significance of XIAP and XAF1 mRNA expression and the correlation with several clinicopathological variables was evaluated. Results: XIAP and XAF1 mRNA expression was detected in all 17 (100%) case samples. The levels of XIAP mRNA expression showed a moderate variation among samples. In contrast, XAF1 and XIAP/XAF1 mRNA levels showed significant variation among samples. Bivariate correlation analyses revealed a significant positive Spearman direct correlation coefficient between the XIAP expression and the pathological response. No significant correlation was found for XAF1 expression as well as for the XIAP/XAF1 ratio and clinical and pathological response. Conclusions: This is first study to address the role of XIAP, its negative regulator XAF1, and the XIAP/XAF1 ratio in bladder cancer patients. The positive correlation between the XIAP mRNA expression and the pathological response is in line with a previous study from our group in which a correlation was found between XIAP expression and survival. All these observations point to a complex role of XIAP in tumor biology. XAF1 mRNA expression in bladder carcinomas did not achieve significance as an independent predictive and prognostic factor in a bivariate analysis. Further studies are necessary in order to better assess a possible clinical value for XIAP and XAF1 as predictive and prognostic markers in cancer patients. No significant financial relationships to disclose.

BARD1 (BRCA1-Associated Ring Domain 1) was originally identified in a yeast-two-hybrid (Y2H) screen as a binding partner of BRCA1. The functional heterodimer BRCA1/BARD1 is required for several of the cellular and tumor-suppressor functions of BRCA1. Both proteins interact through the N-terminal RING domain to form a heterodimeric E3 ubiquitin ligase that constitutes the major catalytic activity of the BRCA1-BARD1 complex. BARD1 is also associated to p53-mediated apoptosis, in a BRCA1-independent manner. The carboxy terminus of BRCA1 is highly acidic and contains two tandem BRCA1 C-terminal (BRCT) domains, which are characteristic of members of a large superfamily of proteins involved in DNA repair and cell cycle checkpoint control. These domains are protein-protein interacting regions that mediate the association with a number of other proteins with a role in DNA replication, DNA damage repair pathway, transcription, cell cycle control, and ubiquitination. Although several BRCA1-interacting proteins were reported, few proteins were described to interact with BARD1. In order to identify putative interaction-proteins with BARD1 C-terminal region we performed a Y2H assay using BARD1 BRCT tandem domain (aa 554-777) to screen a human testis cDNA library. We identified, among other hits, a cDNA coding for BCCIP (BRCA2 and CDKN1A Interacting Protein) C-terminal region. BCCIP is known for its involvement in DNA damage repair and the cell cycle control. BCCIP interacts with BRCA2, and both proteins are important for RAD51 focus formation after ionizing radiation and homologous recombination (HR) repair of double-strand-breaks (DSBs). BCCIP enhances the p21 suppression activity towards CDK2, and BCCIP downregulation reduces p21 expression by abrogating p53 transcription activity. We confirmed BCCIP/BARD1 interaction by pull-down and co-immunoprecipitation (co-IP) analysis of ectopically expressed BARD1 and BCCIP. We also identified the constitutive BCCIP/BARD1 complex in human cells by co-IP assays. Interestingly the BCCIP observed in complex with BARD1 corresponds to a mono-ubiquitinated form, suggesting that BCCIP may be a putative natural target for BRCA1/BARD1 heterodimer E3 ubiquitin ligase. BRCA1 participation in a multicomponent complex with BCCIP is under investigation. In order to assess the biological significance of the interaction between BCCIP and BARD1 we are investigating its role in DNA damage repair, cell cycle control and apoptosis. We are also evaluating the BCCIP protein interaction network using a tandem affinity purification approach. Citation Format: Joao Séllos, Thales C. Nepomuceno, Renato S. Carvalho, Guilherme Suarez-Kurtz, Alvaro N.A. Monteiro, Marcelo A. Carvalho. Characterization of BCCIP as a novel BARD1 interaction partner. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 632. doi:10.1158/1538-7445.AM2013-632

Apoptosis is a phenomenon of cellular degeneration highly conserved evolutionarily, being observed not only during development, but also associated with a number of diseases. Apoptosis is regulated by a complex set of proteins and accomplished by biochemical mechanisms that act to initiate and complete the destruction of the cell. Recently, typical biochemical and morphological changes associated to cell death were correlated with other vital cellular events, such as proliferation and differentiation. Despite the general tendency to treat apoptosis and cell differentiation as the result of different signaling pathways, several studies have shown that there is a high degree of morphological similarity between these events. The molecules involved in the regulation of apoptosis-like processes of differentiation have not been fully described. Since the main endogenous inhibitor of caspase-3 is the protein XIAP, which in turn is regulated by XAF1, we analyzed the expression of these proteins in the context of differentiation of different cell lines. The objective of this study was to evaluate the activation pathways of cell death in the process of monocytic/macrophage differentiation. We have observed that the expression of XAF1 protein decreases during monocytic/macrophage differentiation of HL60 cell line induced by PMA, but levels of its mRNA do not change. Interestingly, we have found that HL60 cell lines overexpressing either Bcl-XL or Bcl-2 cell lines have decreased expression of XAF1 due to methylation of its promoter. Also, besides rendering cells resistant to apoptosis as expected, HL60 cells overexpressing either Bcl-XL or Bcl-2 were more prone to differentiate by PMA treatment than parental cells. The correlation between high levels of mRNA expression of Bcl-2 with low expression of XAF1 mRNA was also observed in the analysis of samples from patients with follicular lymphoma retrieved from Oncomine database (www.oncomine.com). These results demonstrate the differential activation of pathways of cell death in monocytic / macrophagic differentiation, suggesting that a descrease in XAF1 expression is a necessary event during this process. Furthemore, our results reveal a transcriptional regulatory loop exerted by Bcl-2 family of proteins that had not yet been described. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr 195. doi:10.1158/1538-7445.AM2011-195