INHIBITION OF CELLULAR PROLIFERATION BY THE WILMS-TUMOR SUPPRESSOR WT1 REQUIRES ASSOCIATION WITH THE INDUCIBLE CHAPERONE HSP70

The Wilms tumor suppressor WT1 encodes a zinc finger transcription fac tor that is expressed in glomerular podocytes during a narrow window i n kidney development. By immunoprecipitation and protein microsequenci ng analysis, we have identified a major cellular protein associated wi th endogenous WT1 to be the inducible chaperone Hsp70, WT1 and Hsp70 a re physically associated in embryonic rat kidney cells, in primary Wil ms turner specimens and in cultured sells with inducible expression of WT1. Colocalization of WT1 and Hsp70 is evident within podocytes of t he developing kidney, and Hsp70 is recruited to the characteristic sub nuclear clusters that contain WT1. The amino-terminal transactivation domain of WT1 is required for binding to Hsp70, and expression of that domain itself is sufficient to induce expression of Hsp70 through the heat shock element (HSE). Substitution of a heterologous Hsp70-bindin g domain derived from human DNAJ is sufficient to restore the function al properties of a WT1 protein with an amino-terminal deletion, an eff ect that is abrogated by a point mutation in DNAJ that reduces binding to Hsp70. These observations indicate that Hsp70 is an important cofa ctor for the function of WT1, and suggest a potential role for this ch aperone during kidney differentiation.