[The interaction between CDX2 transcription factor and DDX5 RNA helicase]

Previously, our results of a two-hybrid screening essay allowed us to recognize p68 (DDX5) as a possible partner of CDX2. The recent part of research was carried out to confirm this interaction. We show the co-localization of these proteins in the nuclei of colon carcinoma cell line and of epithelium of villi. By means of GST-pulldown we reveal DDX5 as a part of a complex with CDX2. During the investigation of the effect of DDX5-CDX2 interaction upon beta-catenin-mediated transcription regulation we note that in each of three investigated cell lines Cdx2 acts as an activator of luciferase expression. In T98G and U20S cell lines we observe a partial decline of beta-catenin transcription enhancing effect while interacting with CDX2. In the cell systems studied, DDX5 acts as a weak repressor both solely and together with CDX2 and beta-catenin. Concerning the influence upon D1 cyclin promoter, we find that, depending on environment, CDX2 may either decline its transcription (U20S line) or raise it (T98G). Besides, PDGF reduces CDX2 activity both in activation and repression. When DDX5 and CDX2 are transfected in T98G cells together, the repressing activity of DDX5 is leveled with activation by Cdx2. In both cell lines the native DDX5 acts as a weak repressor of D1 cycline; PDGF treatment does no significant effect on its activity.