The IGF-I receptor gene promoter is a molecular target for the Ewing's sarcoma-Wilms' tumor 1 fusion protein.
Desmoplastic small round cell tumor (DSRCT) is an abdominal malignancy in children which is characterized by a recurrent chromosomal translocation, t(11;22)(p13;q12). This rearrangement results in the fusion of the ubiquitously expressed EWS1 gene to the Wilms' tumor suppressor (WT1) gene. The chimeric protein contains the N-terminal domain of EWS1 fused to the DNA-binding domain of WT1, including zinc fingers 2-4. Because WT1 has been shown previously to bind and repress the insulin-like growth factor I (IGF-I-R) promoter, we investigated whether this promoter is, in addition, a target for the aberrant EWS/WT1 transcription factor. EWS/WT1 activated the IGF-I-R promoter approximately 340%, whereas a fusion protein containing a three-amino acid insert (KTS) between zinc fingers 3 and 4 had no effect. On the other hand, expression vectors encoding either WT1 or EWS1 reduced the activity of the promoter to 46 and 58% of control values, respectively. Results of gel shift assays indicate that the binding affinity of EWS/WT1 to a fragment of the 5'-flanking region of the receptor promoter was higher than the affinity of WT1 itself. Consistent with the results of functional assays, the binding of EWS/WT1(+KTS) was significantly reduced. Due to the central role of the IGF-I-R in tumorigenesis, activation of the receptor promoter by EWS/WT1 may constitute a potential mechanism for the etiology and/or progression of DSRCT.
Karnieli
E
E
Section on Molecular and Cellular Physiology, Diabetes Branch, NIDDK, National Institutes of Health, Bethesda, Maryland 20892, USA.
Werner
H
H
Rauscher
F J
FJ
Benjamin
L E
LE
LeRoith
D
D
D001483:Base Sequence; D002460:Cell Line; D002471:Cell Transformation, Neoplastic; D004247:DNA; D006801:Humans; D008969:Molecular Sequence Data; D011401:Promoter Regions, Genetic; D017526:Receptor, IGF Type 1 / Q000235:genetics*; D011993:Recombinant Fusion Proteins / Q000235:genetics*; D012512:Sarcoma, Ewing / Q000235:genetics*; D014158:Transcription, Genetic; D009396:Wilms Tumor / Q000235:genetics*
D011993:Recombinant Fusion Proteins; D004247:DNA; D017526:Receptor, IGF Type 1