The speckling domain of the Wilms tumor suppressor WT1 overlaps with the transcriptional repression domain

Deletion of the Wilms' Tumor Suppressor Gene in the Cardiac Troponin-T Lineage Reveals Novel Functions of WT1 in Heart Development

Expression of Wilms’ tumor suppressor transcription factor (WT1) in the embryonic epicardium is essential for cardiac development, but its myocardial expression is little known. We have found that WT1 is expressed at low levels in 20–25% of the embryonic cardiomyocytes. Conditional ablation of WT1 using a cardiac troponin T driver (Tnnt2^Cre) caused abnormal sinus venosus and atrium development, lack of pectinate muscles, thin ventricular myocardium and, in some cases, interventricular septum and cardiac wall defects, ventricular diverticula and aneurisms. Coronary development was normal and there was not embryonic lethality, although survival of adult mutant mice was reduced probably due to perinatal mortality. Adult mutant mice showed electrocardiographic anomalies, including increased RR and QRS intervals, and decreased PR intervals. RNASeq analysis identified differential expression of 137 genes in the E13.5 mutant heart as compared to controls. GO functional enrichment analysis suggested that both calcium ion regulation and modulation of potassium channels are deeply altered in the mutant myocardium. In summary, together with its essential function in the embryonic epicardium, myocardial WT1 expression is also required for normal cardiac development.

Nuclear transport of Wilms' tumour protein Wt1 involves importins α and β

BACKGROUND/AIMS

Wilms' tumour protein, Wt1, is a zinc finger molecule, which is required for normal embryonic development. Mutations of the WT1 gene can give rise to childhood cancer of the kidneys. Different Wt1 isoforms exist, which function either as transcription factors or have a presumed role in mRNA processing. Previous studies suggested that Wt1 undergoes nucleocytoplasmic shuttling, and cytoplasmic Wt1 was higher in malignant than in normal cells. The aim of this study was to analyse the molecular pathways along which Wt1 shuttles between the cytoplasm and nucleus.

METHODS

Interaction of Wt1 protein with various importin α subtypes and importin β was assessed in pull-down assays and co-immunoprecipitation experiments. Nuclear localisation signals (NLS) were identified by combining site-directed mutagenesis with subcellular immunodetection of the transfected Wt1 variants.

RESULTS

Wt1(+/-KTS) proteins were found to interact with importin α1 and importin β in vitro and in living cells in vivo. A NLS that was necessary and sufficient for nuclear import could be mapped to the third Wt1 zinc finger. Mutation of this NLS strongly weakened binding of Wt1 to importins.

CONCLUSION

Nuclear translocation of Wilms' tumour protein involves importins α and β, and a NLS in the third zinc finger.