Wilms' tumorigenesis is altered by misexpression of the transcriptional co-activator, CITED1.
OBJECTIVE
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 CITED1 (F/L) protein and 2 deletion mutants lacking either of its known functional domains, deltaSID (Smad-4 Interacting Domain) and deltaCR2 (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-deltaCR2, 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-deltaCR2 (7%) compared with CITED1-F/L (40%, P = .03) and CITED1-deltaSID (60%, P < .002). Similarly, mean tumor volume was least in the CITED1-deltaCR2 animals when compared with CITED1-F/L (P = .03) and CITED1-deltaSID animals (P < .005). Furthermore, the CITED1-deltaCR2 tumor showed the least cellular proliferation. Misexpression of CITED1 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 (deltaCR2) 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.
Lovvorn
Harold N
HN
Department of Pediatric Surgery, Vanderbilt University School of Medicine, Nashville, TN 37232, USA. harold.lovvorn@vanderbilt.edu
Boyle
Scott
S
Shi
Genbin
G
Shyr
Yu
Y
Wills
Marcia L
ML
Perantoni
Alan O
AO
de Caestecker
Mark
M
D000818:Animals; D051017:Apoptosis Regulatory Proteins; D045744:Cell Line, Tumor; D018014:Gene Transfer Techniques; D006801:Humans; D051379:Mice; D009687:Nuclear Proteins / Q000235:genetics*; D015534:Trans-Activators; D014157:Transcription Factors / Q000235:genetics*; D009396:Wilms Tumor / Q000235:genetics*
D051017:Apoptosis Regulatory Proteins; C512688:CITED1 protein, human; D009687:Nuclear Proteins; D015534:Trans-Activators; D014157:Transcription Factors