Nuclear speckle-associated protein Pnn/DRS binds to the transcriptional corepressor CtBP and relieves CtBP-mediated repression of the E-cadherin gene

Previously, we have shown that pinin/DRS (Pnn), a 140-kDa nuclear and cell adhesion-related phosphoprotein, is involved in the regulation of cell adhesion and modulation of the activity of multiple tumor suppressor genes. In the nucleus Pun is concentrated in the "nuclear speckles," zones of accumulation of transcriptional and mRNA splicing factors, where Pun is involved in mRNA processing. Alternatively, other roles of Pnn in gene regulation have not yet been established. By utilizing in vitro pull-down assays, in vivo interaction studies, and immunofluorescence in combination with overexpression and RNA interference experiments, we present evidence that Pun interacts with the known transcriptional corepressor CtBP1. As a consequence of this interaction Pun was capable of relieving the CtBP1-mediated repression of E-cadherin promoter activity. Our results suggest that the interaction of Pun with the corepressor CtBP1 may modulate repression of transcription by CtBP1. This interaction may reflect the existence of coupling factors involved in CtBP-mediated transcriptional regulation and mRNA processing events.