SALL4, a human homolog to Drosophila spalt, is a novel zinc finger transcriptional factor essential for development. We cloned SALL4 and its isoforms (SALL4A and SALL4B).

SALL1 is a member of the SAL gene family that encodes a group of putative developmental transcription factors. SALL1 plays a critical role during kidney development as mutations of the human SALL1 gene cause Townes-Brocks syndrome, which is associated with kidney malformation. Deletion of the mouse Sall1 gene results in renal agenesis or severe dysgenesis. To date, little is known about the molecular mechanisms controlling the regulation of SALL1 expression. This report describes the cloning and characterization of the human SALL1 gene promoter. Consensus binding sites were identified for several transcription factors, with multiple sites for WT1 and SIX1. In transient transfection assays, SALL1 promoter activity was higher in HEK-293 human kidney cells and COS-7 monkey kidney cells than in NIH-3T3 fibroblasts, consistent with its role in kidney development. Transcription from the SALL1 promoter was strikingly activated by the SIX1 protein. Utilizing a luciferase reporter gene assay, endogenous or exogenously added SIX1 activated the SALL1 promoter. Overexpression of SIX1 induced a significant increase in the endogenous SIX1 protein. In addition, co-expression of SIX1 and Eya1 resulted in a significant increase in the SALL1 promoter activity when compared with either SIX1 or Eya1 alone. Finally, we demonstrate that SIX1 was able to bind to the SALL1 promoter by retardation assays and that deletion of the putative element of SIX1 significantly diminishes the SALL1 promoter activity response to SIX1 stimulation. Our findings, when taken together, indicate that SALL1 is a likely target gene for SIX1 during kidney development.

SALL4, a gene homologous to the Drosophila homeotic spalt, is a zinc finger transcriptional factor essential for human development. In Drosophila, spalt is regulated by the Wnt signaling pathway, a pathway critical for hematopoietic self-renewal of stem cells. We cloned SALL4 and its isoforms (SALL4A and SALL4B). We used immunohistochemistry, to demonstrate that SALL4 was constitutively expressed in primary acute myeloid leukemia cells (French American British, FAB: M1 to M5, N=81). The SALL4 in RNA was quantitative in bone marrow cells derived from acute myeloid leukemia (AML) and compared to non-neoplastic hematopietic cells from a purified CD34 progenitor pool, normal bone marrow and peripheral blood by RT-PCR. SALL4 expression was present in the purified normal CD34+ cells, AML blasts, but absent in mature myeloid cells. We tested the leukemogenic potential of constitutive overexpression of SALL4 in a murine hematopoietic model. All transgenic mice overexpressing SALL4B using the CMV promoter developed hematopoietic disorders, including myelodysplastic (MDS)-like symptoms and an AML transformation that disseminated to peripheral tissues including the spleen, liver, kidney and lymph nodes. The myelodysplastic features in these transgenic mice were pathologically similar to human MDSs and manifested as ineffective myelopoiesis. Dysplatic features such as Pseudo-Pelger-Huet like atypical white cells, and increased immature cells were detectable in the transgenic mouse peripheral blood. A high level of apoptosis and increased immature cells were also evident in transgenic mouse marrows and day-7 colony-forming unit assays in vitro. Both SALL4A and SALL4B were able to bind to β-catenin in vitro and synergistically enhanced the Wnt/β-catenin signaling pathway in a reporter gene assay. Our data suggests that the constitutive expression of SALL4 is causal to the leukemic phenotype. Our model should provide a useful platform to analyze the interaction of SALL4 with Wnt/β-catenin pathway in leukemia stem cells.