SIX2 and CITED1, markers of nephronic progenitor self-renewal, remain active in primitive elements of Wilms' tumor.
OBJECTIVE
SIX2 and CITED1 are transcriptional regulators that specify self-renewing nephronic progenitor cells of the embryonic kidney. We hypothesized that SIX2, which promotes and maintains this stem cell population, and CITED1 remain active in Wilms' tumor (WT).


METHODS
To evaluate expression domains and the pathogenic significance of SIX2 and CITED1 across WT, the Children's Oncology Group provided 40 WT specimens of stages I to IV (n = 10 per stage), which were enriched for unfavorable histology (n = 20) and treatment failure (relapse or death, n = 20). SIX2 and CITED1 protein expression was evaluated qualitatively (immunohistochemistry) and quantitatively (Western blot, or WB). Gene transcription was estimated using quantitative real-time polymerase chain reaction (qRT-PCR).


RESULTS
SIX2 was visualized by immunohistochemistry in 36 (94.7%) of 38 specimens. Protein and messenger RNA expression of SIX2 were quantitatively similar across all stages of disease (P = .48 WB; P = 0.38 qPCR), in favorable or unfavorable histology (P = 0.51 WB; P = 0.58 qPCR), and in treatment failure or success (P = 0.86 WB; P = 0.49 qPCR). Although CITED1 expression paralleled SIX2 qualitatively, no quantitative correlation between SIX2 and CITED1 expression was observed (Spearman correlation coefficient, 0.28; P = 0.08). As in the fetal kidney, overlapping, but also distinct, WT cellular expression domains were observed between SIX2 and CITED1.


CONCLUSIONS
SIX2 and CITED1 remain active across all disease characteristics of WT. Activity of these genes in WT potentially identifies a population of self-renewing cancer cells that exhibit an embryonic, stemlike phenotype. Taken together, these transcriptional regulators may be fundamental to WT cellular self-renewal and may represent targets for novel therapies that promote terminal differentiation.
Department of Pediatric Surgery, Monroe Carell Jr Children's Hospital at Vanderbilt, Nashville, Tennessee, USA. andrew.j.murphy@vanderbilt.edu
Andrew J
AJ
Murphy
Janene
J
Pierce
Christian
C
de Caestecker
Chase
C
Taylor
James R
JR
Anderson
Alan O
AO
Perantoni
Mark P
MP
de Caestecker
Harold N
HN
Lovvorn
D051017:Apoptosis Regulatory Proteins; D014408:Biomarkers, Tumor; D015153:Blotting, Western; D002467:Cell Nucleus / Q000378:metabolism; D003600:Cytosol / Q000378:metabolism; D015972:Gene Expression Regulation, Neoplastic; D018398:Homeodomain Proteins / Q000096:biosynthesis* / Q000235:genetics; D006801:Humans; D007124:Immunoenzyme Techniques; D007668:Kidney / Q000196:embryology / Q000378:metabolism; D007680:Kidney Neoplasms / Q000378:metabolism* / Q000473:pathology; D008856:Microscopy, Fluorescence; D009363:Neoplasm Proteins / Q000096:biosynthesis* / Q000235:genetics; D014411:Neoplastic Stem Cells / Q000378:metabolism* / Q000473:pathology; D009399:Nephrons / Q000378:metabolism* / Q000473:pathology; D009419:Nerve Tissue Proteins / Q000096:biosynthesis* / Q000235:genetics; D009687:Nuclear Proteins / Q000096:biosynthesis* / Q000235:genetics; D011379:Prognosis; D012333:RNA, Messenger / Q000096:biosynthesis; D012334:RNA, Neoplasm / Q000096:biosynthesis; D020133:Reverse Transcriptase Polymerase Chain Reaction; D016037:Single-Blind Method; D015534:Trans-Activators; D014157:Transcription Factors / Q000096:biosynthesis* / Q000235:genetics; D009396:Wilms Tumor / Q000378:metabolism* / Q000473:pathology
D051017:Apoptosis Regulatory Proteins; D014408:Biomarkers, Tumor; C512688:CITED1 protein, human; D018398:Homeodomain Proteins; D009363:Neoplasm Proteins; D009419:Nerve Tissue Proteins; D009687:Nuclear Proteins; D012333:RNA, Messenger; D012334:RNA, Neoplasm; C484762:SIX2 protein, human; D015534:Trans-Activators; D014157:Transcription Factors