Abstract 195: Cell death pathway activation during monocytic / macrophagic differentiation of hematopoietic tumor cell lines

Abstract

Abstract 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