Wilms' tumorigenesis is altered by misexpression of the transcriptional co-activator, CITED1

Purpose: Wilms' tumors arise from arrested differentiation of renal progenitor cells. CITED1 is a transcriptional regulator that blocks the metanephric mesenchymal-to-epithelial conversion and is expressed in the blastema of both the developing kidney and Wilms' tumors. We hypothesized that alterations of CITED1-dependent signaling promote persistence of blastema and thereby subject these pluripotent cells to future oncogenic events. Methods: We used a retroviral delivery system to overexpress the full-length CITED I (F/L) protein and 2 deletion mutants lacking either of its known functional domains, Delta SID (Smad-4 Interacting Domain) and Delta CR2 (Conserved Region 2; the CITED1 transactivation domain), in a human Wilms' tumor cell line that endogenously expresses CITED1. In vitro effects on cellular proliferation and apoptosis were assayed. In vivo effects on tumorigenesis, growth, proliferation, and apoptosis were determined after heterotransplantation into immunodeficient mice (n = 15 per cell line). Results: In vitro, overexpression of CITED1-F/L significantly increased, whereas overexpression of the functionally inactivating mutant, CITED1-Delta CR2, significantly reduced cellular proliferation relative to the other lines (P <.0001). In vivo, Wilms' tumor incidence was significantly reduced in animals injected with cells overexpressing the mutant CITED1-Delta CR2 (7%) compared with CITED1-F/L (40%, P=.03) and CITED1-Delta SID (60%, P <.002). Similarly, mean tumor volume was least in the CITED1-Delta CR2 animals when compared with CITED1-F/L (P=.03) and CITED1-Delta SID animals (P <.005). Furthermore, the CITED1-Delta CR2 tumor showed the least cellular proliferation. Misexpression of CITED I did not affect apoptosis either in vitro or in vivo. Conclusions: Overexpression of CITED1 in a human Wilms' tumor cell line significantly increases proliferation in vitro, whereas mutation of its functionally critical transactivation domain (Delta CR2) significantly reduces proliferation. This mutation further perturbs tumorigenesis and tumor growth after heterotransplantation into immunodeficient mice. We speculate that overexpression of CITED1 promotes expansion of a rapidly proliferating population of blastema and thereby induces an unstable environment highly susceptible to future oncogenic events. (c) 2007 Elsevier Inc. All rights reserved.

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