Apoptotic susceptibility of @entity5 cells selected for XXXX resistance: gene expression profiling, functional analysis, and molecular interaction mapping.

@entity588 @entity5 @entity4404 @entity900 @entity2307 @entity584 @entity2533 @entity9800 @entity866 @entity105 @entity1835 @entity4357 @entity8293
To study the molecular mechanisms by which drug resistance develops, we compared DU145 humanprostate @entity5 cells with a subline selected for resistance to @entity9800 . Differences in gene expression level were assessed by hybridizing the two cell types against each other using quadruplicate "Oncochip" cDNA microarrays that included 1648 @entity5 -related genes. Expression levels differing by a factor of >1.5 were detected for 181 of the genes. These differences were judged statistically reliable on the basis of a stratum-adjusted Kruskal-Wallis test, after taking into account a dye-dependent variable. The 181 expression-altered genes included a larger than expected number of the "apoptosis-related" genes (P = 0.04). To assess whether this observation reflected a generalized resistance of RCO.1 to apoptosis, we exposed the cells to a range of stresses ( @entity900 , @entity866 , UV, ionizing radiation, and serum starvation) and found greatly reduced apoptotic responses for RC0.1 (relative to DU145) using flow cytometric @entity4404 and terminal deoxynucleotidyl transferase-mediated nick end labeling assays. We next examined the apoptosis-related genes in the context of a molecular interaction map and found expression differences in the direction "expected" on the basis of the apoptosis-resistance of RC0.1 for @entity1835 , @entity8293 , and genes that signal via the Akt pathway. Exposure of the cells to @entity2307 , an inhibitor of the Akt effector @entity4357 3-kinase, provided functional support for involvement of the Akt pathway. However, closer examination of the molecular interaction map revealed a paradox: many of the expression differences observed for apoptosis-related genes were in the direction "contrary" to that expected given the resistance of RC0.1. The map indicated that most of these unexpected expression differences were associated with genes involved in the @entity2533 pathways. Overall, the patterns that emerged suggested a two-step model for the selection process that led to resistance in RC0.1 cells. The first hypothesized step would involve a decrease in apoptotic susceptibility through changes in the apoptosis-control machinery associated with the @entity588 and caspase gene families, and also in antiapoptotic pathways operating through @entity584 . The second step would involve changes in multifunctional upstream genes (including some genes in the nuclear factor kappa B and @entity2533 pathways) that can facilitate apoptosis but that would also tend to contribute to cell proliferation in the presence of drug. Thus, we propose that a downstream blockade of apoptosis was "permissive" for the selection of upstream pathway changes that would otherwise have induced apoptosis. This model is analogous to one suggested previously for the relationship between oncogene function and apoptosis in @entity105 .
