Position-dependent alternative splicing activity revealed by global profiling of alternative splicing events regulated by PTB (Exon array)

To gain global insights into the role of the well-known repressive splicing regulator PTB we analyzed the consequences of PTB knockdown in HeLa cells using high-density oliogonucleotide splice-sensitive microarrays. The major class of identified PTB-regulated splicing event was PTB-repressed cassette exons, but there was also a substantial number of PTB-activated splicing events. PTB repressed and activated exons showed a distinct arrangement of motifs with pyrimidine-rich motif enrichment within and upstream of repressed exons, but downstream of activated exons. The N-terminal half of PTB was sufficient to activate splicing when recruited downstream of a PTB-activated exon. Moreover, insertion of an upstream pyrimidine tract was sufficient to convert a PTBactivated to a PTB-repressed exon. Our results demonstrate that PTB, an archetypal splicing repressor, has variable splicing activity that predictably depends upon its binding location with respect to target exons. Target was prepared from 6 biological replicates of PTB/nPTB knockdown and 6 control mock knockdowns from HeLa S3 cell line and hybridized to the Affymetrix Human Exon 1.0 ST Array. Two groups of three replicates each were collected at two different times.