An isolated WT1 interacting protein having the amino acid sequence as set forth in SEQ ID NO: 2, or an isolated protein that has an amino acid sequence in which one or a plurality of amino acids have been substituted, deleted, inserted, and/or added is functionally equivalent to the protein having the amino acid sequence as set forth in SEQ ID NO: 2; and comprises the amino acid sequence from Glu at position 449 to Met at position 541 in SEQ ID NO: 2.