The Wilms’ tumor gene WT1-GFP knock-in mouse reveals the dynamic regulation of WT1 expression in normal and leukemic hematopoiesis

Abstract

The Wilms' tumor gene WT1 is overexpressed in most of human leukemias regardless of disease subtypes. To characterize the expression pattern of WT1 during normal and neoplastic hematopoiesis, we generated a knock-in reporter green fluorescent protein (GFP) mouse (WT1 GFP/ þ ) and assayed for WT1 expression in normal and leukemic hematopoietic cells. In normal hematopoietic cells, WT1 was expressed in none of the long-term (LT) hematopoietic stem cells (HSC) and very few (o1%) of the multipotent progenitor cells. In contrast, in murine leukemias induced by acute myeloid leukemia 1 (AML1)/ ETO þ TEL/PDGFbR or BCR/ABL, WT1 was expressed in 40.5 or 38.9% of immature c-kit þ lin À Sca-1 þ (KLS) cells, which contained a subset, but not all, of transplantable leukemic stem cells (LSCs). WT1 expression was minimal in normal fetal liver HSCs and mobilized HSCs, both of which are stimulated for proliferation. In addition, overexpression of WT1 in HSCs did not result in proliferation or expansion of HSCs and their progeny in vivo. Thus, the mechanism by which expansion of WT1-expressing cells occurs in leukemia remains unclear. Nevertheless, our results demonstrate that the WT1 GFP/ þ mouse is a powerful tool for analyzing WT1-expressing cells, and they highlight the potential of WT1, as a specific therapeutic target that is expressed in LSCs but not in normal HSCs.

The Wilms’ tumour suppressor Wt1 is a major regulator of tumour angiogenesis and progression

“…To determine whether Wt1-expressing cells similarly contribute to tumour vessels and stroma in mice, we induced syngenic B16F10 tumours (mouse melanoma cell line) in Wt1-GFP knock-in animals 16 (Supplementary Table 1). Immunostaining revealed association of green fluorescent protein (GFP) with vessels and cells in the tumour stroma proving that Wt1-positive cells from the host invade the tumour.…”

“…Both Cre lines were backcrossed four times with C57BL6. Alternatively, Tie2-CreERT2;Wt1 lox mice were crossed with Wt1 GFP mice 16 to generate Tie2-CreERT2;Wt1 lox/GFP animals. Wt1CreERT2;mTmG animals were generated by crossing Wt1CreERT2 (ref.…”

Targeting survival cascades induced by activation of Ras/Raf/MEK/ERK, PI3K/PTEN/Akt/mTOR and Jak/STAT pathways for effective leukemia therapy

“…176 In normal hematopoietic stem cells, WT1 was not detected at high levels in long-term hematopoietic stem cells or in multipotent progenitor cells. In contrast, in AML1-ETO þ TEL-PDGFRbR or BCR-ABL murine leukemias, WT1 was expressed in approximately 50% of the transplantable leukemic stem cells.…”

“…In contrast, in AML1-ETO þ TEL-PDGFRbR or BCR-ABL murine leukemias, WT1 was expressed in approximately 50% of the transplantable leukemic stem cells. 176 Hence the WT1 protein may be a target for the successful treatment of leukemic stem cells.…”

Deregulation of the Wilms' tumour gene 1 protein (WT1) by BCR/ABL1 mediates resistance to imatinib in human leukaemia cells

“…3,4 In normal haematopoietic cells, WT1 is highly expressed in a subset of progenitors. [5][6][7][8][9][10] Analysis of lineage potential of haematopoietic progenitors from knockout mice demonstrates that WT1 is not critical for haematopoiesis, at least not in mice, 11 although murine progenitors lacking WT1 are less competitive during haematopoietic reconstitution in vivo, 12 suggesting positive effects of WT1 on proliferation and/or survival of haematopoietic cells.…”