Ewing tumors that do not overexpress BMI-1 are a distinct molecular subclass with variant biology: a report from the Children's Oncology Group.
OBJECTIVE
Ewing sarcoma family tumors (ESFT) are aggressive tumors of putative stem cell origin for which prognostic biomarkers and novel treatments are needed. In several human cancers, high expression of the polycomb protein BMI-1 is associated with poor outcome. We have assessed the potential clinical significance of BMI-1 expression level in ESFT.


METHODS
BMI-1 expression was assessed in 130 tumors by immunostaining and associations with clinical features and outcome determined. The molecular signatures of BMI-1-low and BMI-1-high tumors were compared using microarrays and differentially activated canonical pathways identified by gene-specific enrichment analysis. Automated quantitative analysis of phosphoproteins was used to assess relative levels of pathway activation. Sensitivity to IGF1-R inhibition was determined using MTS [3-(4,5-dimethylthiazol-2-yl)-5-(3-carboxymethoxyphenyl)-2-(4-sulfophenyl)-2H-tetrazolium] assays.


RESULTS
BMI-1 is overexpressed by the vast majority of ESFTs. However, in 20% of cases, BMI-1 levels are low to undetectable. Significantly, although clinical presentation and outcome were similar between BMI-1-high and BMI-1-low tumors, whole genome expression array analysis showed marked differences in their respective gene expression profiles. Gene-specific enrichment analysis identified that several cancer-associated canonical biological pathways, including IGF1, mTOR, and WNT, are significantly downregulated in BMI-1-low compared with BMI-1-high tumors. Consistent with these in vivo data, the response to IGF1-R inhibition in vitro was diminished in BMI-1-low compared with BMI-1-high ESFT cells.


CONCLUSIONS
ESFT that do not overexpress BMI-1 represent a novel subclass with a distinct molecular profile and altered activation of and dependence on cancer-associated biological pathways.
Division of Hematology-Oncology, The Saban Research Institute, Childrens Hospital Los Angeles, Los Angeles, California, USA.
Aaron
A
Cooper
John
J
van Doorninck
Lingyun
L
Ji
Darren
D
Russell
Marc
M
Ladanyi
Hiroyuki
H
Shimada
Mark
M
Krailo
Richard B
RB
Womer
Jessie Hao-ru
JH
Hsu
Dafydd
D
Thomas
Timothy J
TJ
Triche
Richard
R
Sposto
Elizabeth R
ER
Lawlor
D000293:Adolescent; D000328:Adult; D045744:Cell Line, Tumor; D002648:Child; D002675:Child, Preschool; D005260:Female; D015972:Gene Expression Regulation, Neoplastic; D006801:Humans; D007223:Infant; D007231:Infant, Newborn; D008297:Male; D008875:Middle Aged; D009687:Nuclear Proteins / Q000235:genetics*; D010641:Phenotype; D063150:Polycomb Repressive Complex 1; D011379:Prognosis; D011518:Proto-Oncogene Proteins / Q000235:genetics*; D012333:RNA, Messenger / Q000235:genetics; D017526:Receptor, IGF Type 1 / Q000037:antagonists & inhibitors / Q000378:metabolism; D012097:Repressor Proteins / Q000235:genetics*; D020133:Reverse Transcriptase Polymerase Chain Reaction; D012512:Sarcoma, Ewing / Q000145:classification* / Q000175:diagnosis / Q000235:genetics*; D055815:Young Adult
C069077:BMI1 protein, human; D009687:Nuclear Proteins; D011518:Proto-Oncogene Proteins; D012333:RNA, Messenger; D012097:Repressor Proteins; D063150:Polycomb Repressive Complex 1; D017526:Receptor, IGF Type 1