The Wilms tumor suppressor Wt1 promotes cell adhesion through transcriptional activation of the α4integrin gene

Cell-matrix interaction through specific adhesion molecules is a critical step during organ development. In addition, down-regulation of cell adhesion receptors may promote tumor invasion and metastasis. We show here that the Wilms tumor suppressor Wt1, which is necessary for normal development of the epicardium, coronary vessels, genitourinary system, and other tissues, activates transcription of the alpha 4integrin gene. Binding of the Wt1(-KTS) form, which is transcriptionally active, to the proximal alpha 4integrin promoter was demonstrated by electrophoretic mobility shift assay and chromatin immunoprecipitation. A reporter construct harboring similar to 1.9 kb of the human alpha 4integrin gene promoter was activated significantly by transient co-transfection of a Wt1(-KTS) expression plasmid. Introducing mutations in two identified Wt1(-KTS) binding motifs in the proximal promoter of the alpha 4integrin gene abrogated this stimulatory effect. Endogenous alpha 4integrin transcripts were increased more than 3-fold in human embryonic kidney 293 cells with stable expression of the Wt1(-KTS) protein. Wt1-overexpressing cells showed augmented adhesion to the alpha 4integrin ligand vascular cell adhesion molecule-1 that was abolished upon incubation with an inhibitory alpha 4integrin antibody. Double immunofluorescent staining revealed co-localization of Wt1 and alpha 4integrin in the developing epicardium of mouse embryos. Cardiac expression of alpha 4integrin was reduced significantly in embryos with a homozygous Wt1 defect (Wt1(-/-)). These findings demonstrate that Wt1 can support cell adhesion through enhanced expression of alpha 4integrin. This transcriptional activation of the alpha 4integrin gene by Wt1(-KTS) might contribute to normal formation of the epicardium and other tissues in the developing embryo.