Aberrant Overexpression of the Wilms Tumor Gene (WT1) in Human Leukemia

Abstract

To clarify whether the expression of the WT1 gene in leukemic cells is aberrant or merely reflects that in normal counterparts, the expression levels of the WT1 gene were quantitated for normal hematopoietic progenitor cells. Bone marrow (BM) and umbilical cord blood (CB) cells were fluorescence-activated cell sorting (FACS)-sorted into CD34+ and CD34− cell populations, and the CD34+ cells into nine subsets (CD34+CD33−, CD34+CD33+, CD34+CD38−, CD34+CD38+, CD34+HLA-DR−, CD34+HLA-DR+, CD34+c-kithigh, CD34+c-kitlow, and CD34+c-kit−) according to the expression levels of CD34, CD33, CD38, HLA-DR, and c-kit. Moreover, acute myeloid leukemic cells were also FACS-sorted into four populations (CD34+CD33−, CD34+CD33+, CD34− CD33+, and CD34− CD33−). FACS-sorted normal hematopoietic progenitor and leukemic cells and FACS-unsorted leukemic cells were examined for the WT1 expression by quantitative reverse transcriptase-polymerase chain reaction. The WT1 expression in the CD34+ and CD34− cell populations and in the nine CD34+ subsets of BM and CB was at either very low (1.0 to 2.4 × 10−2) or undetectable (<10−2) levels (the WT1 expression level of K562 cells was defined as 1.0), whereas the average levels of WT1 expression in FACS-sorted and -unsorted leukemic cells were 2.4 to 9.3 × 10−1. Thus, the WT1 expression levels in normal hematopoietic progenitor cells were at least 10 times less than those in leukemic cells. Therefore, we could not find any normal counterparts of BM or CB that expressed the WT1 at levels comparable with those in leukemic cells. These results indicate an aberrant overexpression of the WT1 gene in leukemic cells and imply the involvement of this gene in human leukemogenesis.

Fluorescent 5′‐exonuclease assay for the absolute quantification of Wilms' tumour gene (WT1) mRNA: implications for monitoring human leukaemias

“…Supporting earlier investigations, significant WT 1 overexpression in leukaemia of myeloid origin has been confirmed by several groups and expression levels in normal haemopoiesis turned out to be restricted to early progenitor cells (Brieger et al, 1994;Inoue et al, 1997). However, while there is little doubt concerning aberrant WT1 expression in leukaemias, the physiological significance of the role of WT1 has long been questioned.…”

“…In contrast, the occurrence of aberrant WT1 expression has been shown by several groups in all types of leukaemias (Miwa et al, 1992;Miyagi et al, 1993;Inoue et al, 1997). Moreover, some investigators found varying expression levels in different FAB subtypes, suggesting that WT1 expression may be more apparent in less differentiated subtypes (Miwa et al, 1992;Brieger et al, 1995;Pritchard-Jones & King-Underwood, 1997).…”

Prognostic significance of quantitative analysis of WT1 gene transcripts by competitive reverse transcription polymerase chain reaction in acute leukaemia

“…Data regarding the expression of WT1 on normal haemopoietic progenitors are somewhat conflicting (Baird & Simmons, 1997;Inoue et al, 1997;Maurer et al, 1997;Patmasiriwat et al, 1999). This discrepancy appears to result from the variable sensitivities of the different methodologies used to detect the WT1 transcript.…”

“…Thus, by quantitative analysis, we have shown WT1 expression to be at least 10 times lower in some normal progenitors compared with leukaemic cells, similar to previously reported results. (Inoue et al, 1996(Inoue et al, , 1997. Several studies (Brieger et al, 1994;Schmid et al, 1997) using a qualitative assay for WT1 in AML found no correlation between WT1 expression at diagnosis and achievement of CR, whereas Bergmann et al (1997) have shown a tendency towards a higher CR rate in patients with low-level expression of WT1 mRNA using a semiquantitative technique.…”

WT1 gene expression: an excellent tool for monitoring minimal residual disease in 70% of acute myeloid leukaemia patients – results from a single‐centre study

“…Although the altered WT1 expression in AML seems inherent to the leukaemic blasts (Menssen et al, 1995;Inoue et al, 1997) the role of WT1 in leukaemogenesis has yet to be established. In an effort to validate the use of WT1 as a quantitative marker for the leukaemic blasts we performed parallel longitudinal studies of WT1 and a fusion transcript found by multiplex PCR in 18 patients.…”