A WT1 antisense oligonucleotide inhibits proliferation and induces apoptosis in myeloid leukaemia cell lines

The response of the CML-BC cell line, K562, the myelomonocytic cell line MM6 and the promyelocytic leukaemia cell line HL-60, to a 15 mer WT1 antisense oligonucleotide, targeted to the translation initiation site of the WT1 mRNA was examined. K562 cells exposed to 0.4 mu M antisense oligonucleotide showed markedly reduced proliferation which was associated with reduced cell viability. Sense, scrambled and mutant antisense oligonucleotides had no effect on the proliferation of K562 cells. MM6 cells exposed to 0.4 mu M antisense oligonucleotide also showed significantly reduced cellular proliferation which was also accompanied by loss of cell viability. In the K562 and MM6 antisense cultures that exhibited reduced cell viability, both DNA fragmentation and morphological features consistent with apoptosis could be identified. In contrast the growth of HL-60 cells was unaffected by exposure to oligonucleotide. In each of the cell WT1 antisense oligonucleotide abrogated WT1 protein expression, and analysis of WT1 coding sequence in these cells showed that no oncogenic point mutations in the gene were present. We propose therefore that in some myeloid leukaemia cell lines, the expression of a normal WT1 protein is necessary for cell proliferation and that it plays a role in maintaining the viability of some leukaemia cells.