Role of the Polypyrimidine Tract Binding Protein on CD44 Alternative Splicing in Breast Cancer

摘要

The cytogenetic and nuclear changes that occur during tumor progression in the breast have been well documented, but the causes of these alterations are poorly understood. Changes in estrogen receptor status, loss of responsiveness to conventional chemotherapy, gain in metastatic potential, accumulation of PNCs, and differential splicing of numerous genes are examples of changes seen in breast cancer cells during tumor progression. Thus far, a strong connection between the splicing machinery and these subtle, yet significant, changes in gene expression has yet to be documented. Likely candidates are the alternative splicing factors most notably the Polypyrimidine Tract Binding Protein (PTB) . PTB is a known repressor of exon definition. During breast cancer progression, we believe, the ability of PTB's ability to repress exons is altered. In order to understand the changes in PTB function as cancer cells de-differentiate, a clear understanding of PTB mechanism must be attained. We are using the regulation of FGF-R2 exon IIIb as a model system to study PTB mediated exon repression. Thus far, we have mapped numerous binding sites for PTB and found them to be important in the repression of this exon. Furthermore overexpression of PTB and heterologous recruitment of PTB result in the repression of this exon. RNAi mediated PTB depletion results in the increase in exon IIIb inclusion.