title: SIX2 Effects on Wilms Tumor Biology.
abstract: Wilms tumor (WT) blastema retains gene expression profiles characteristic of the multipotent nephron progenitor pool, or cap mesenchyme (CM), in the developing kidney. As a result, WT blastema and the CM are believed to represent contextual analogues of one another. Sine oculis homeobox 2 (SIX2) is a transcription factor expressed specifically in the CM, provides a critical mechanism for CM self-renewal, and remains persistently active in WT blastema, although its purpose in this childhood malignancy remains unclear. We hypothesized that SIX2, analogous to its function in development, confers a survival pathway to blastema, the putative WT stem cell. To test its functional significance in WT biology, wild-type SIX2 was overexpressed in the human WT cell line, WiT49. After validating this model, SIX2 effects on anchorage-independent growth, proliferation, invasiveness, canonical WNT pathway signaling, and gene expression of specific WNT pathway participants were evaluated. Relative to controls, WiT49 cells overexpressing SIX2 showed significantly enhanced anchorage-independent growth and early-passage proliferation representing surrogates of cell survival. Interestingly, overexpression of SIX2 generally repressed TCF/LEF-dependent canonical WNT signaling, which activates and coordinates both differentiation and stem pathways, but significantly heightened canonical WNT signaling through the survivin promoter, a mechanism that exclusively maintains the stem state. In summary, when overexpressed in a human WT cell line, SIX2 enhances cell survival and appears to shift the balance in WNT/β-catenin signaling away from a differentiation path and toward a stem cell survival path.
authors.affiliation: Department of Pediatric Surgery, Vanderbilt University School of Medicine, Nashville, TN, USA.
authors.forename: Janene
authors.initials: J
authors.lastname: Pierce
authors.affiliation: Department of Pediatric Surgery, Vanderbilt University School of Medicine, Nashville, TN, USA.
authors.forename: Andrew J
authors.initials: AJ
authors.lastname: Murphy
authors.affiliation: Department of Pediatric Surgery, Vanderbilt University School of Medicine, Nashville, TN, USA.
authors.forename: Alexis
authors.initials: A
authors.lastname: Panzer
authors.affiliation: Department of Pediatric Surgery, Vanderbilt University School of Medicine, Nashville, TN, USA.
authors.forename: Christian
authors.initials: C
authors.lastname: de Caestecker
authors.affiliation: Department of Biostatistics, Vanderbilt University School of Medicine, Nashville, TN, USA.
authors.forename: Gregory D
authors.initials: GD
authors.lastname: Ayers
authors.affiliation: Department of Pediatric Surgery, Vanderbilt University School of Medicine, Nashville, TN, USA.
authors.forename: David
authors.initials: D
authors.lastname: Neblett
authors.affiliation: Departments of Medicine and Cell and Developmental Biology, Vanderbilt University School of Medicine, Nashville, TN, USA.
authors.forename: Kenyi
authors.initials: K
authors.lastname: Saito-Diaz
authors.affiliation: Departments of Medicine and Cell and Developmental Biology, Vanderbilt University School of Medicine, Nashville, TN, USA.
authors.forename: Mark
authors.initials: M
authors.lastname: de Caestecker
authors.affiliation: Department of Pediatric Surgery, Vanderbilt University School of Medicine, Nashville, TN, USA. Electronic address: harold.lovvorn@vanderbilt.edu.
authors.forename: Harold N
authors.initials: HN
authors.lastname: Lovvorn