Modification of alternative splicing of Bcl-x Pre-mRNA in prostate and breast cancer cells - Analysis of apoptosis and cell death

There is ample evidence that deregulation of apoptosis results in the devel opment, progression, and/or maintenance of cancer. Since many apoptotic reg ulatory genes (e.g. bcl-x) code for alternatively spliced protein variants with opposing functions, the manipulation of alternative splicing presents a unique way of regulating the apoptotic response. Here we have targeted ol igonucleotides antisense to the 5'-splice site of bcl-x(L), an anti-apoptot ic gene that is overexpressed in various cancers, and shifted the splicing pattern of Bcl-x pre-mRNA from Bcl-x(L) to Bcl-x(S), a pro-apoptotic splice variant. This approach induced significant apoptosis in PC-3 prostate canc er cells. In contrast, the same olgonucleotide treatment elicited a much we aker apoptotic response in MCF-7 breast cancer cells. Moreover, although th e shift in Bcl-x pre-mRNA splicing inhibited colony formation in both cell lines, this effect was much less pronounced in MCF-7 cells. These differenc es in responses to oligonucleotide treatment were analyzed in the context o f expression of Bcl-x(L), Bcl-x(S), and Bcl-2 proteins. The results indicat e that despite the presence of Bcl-x pre-mRNA in a number of cell types, th e effects of modification of its splicing by antisense oligonucleotides var y depending on the expression profile of the treated cells.