Molecular heterogeneity and function of EWS-WT1 fusion transcripts in desmoplastic small round cell tumors.
Desmoplastic small round cell tumor (DSRCT) is a primitive sarcoma with a consistent cytogenetic abnormality, t(11;22)(p13;q12). This chromosomal translocation generates a chimeric transcript that is formed by fusion of the 5' region of the Ewing's sarcoma gene, EWS, with the 3' DNA-binding segment of WT1, the Wilms' tumor suppressor gene. We collected 14 DSRCT tumor samples and examined the hybrid transcripts. We identified: (a) combinatorial heterogeneity of EWS exons fused to WT1 including use of EWS exons 7, 8, and 9; (b) subpopulations of variant transcripts in 6 of 14 tumors characterized by aberrant splicing resulting in loss of EWS exon 6 or WT1 exon 9; (c) multiple cDNA products with large internal deletions; and (d) insertion of small stretches of heterologous DNA at the fusion site or exon splice region in transcripts from two tumors. Most of the splice variants were in-frame, and in vitro translated fusion proteins with intact DNA-binding motifs formed complexes with a WT1 response element in gel mobility assays. Each of the chimeric proteins retains the ability to bind to the GC and TC elements of the early transcription factor EGR-1 as well as WT1 consensus sequences. We present evidence that various EWS-WT1 proteins up-regulated EGR-1 promoter activity and that this up-regulation is specifically dependent upon the absence of the exon 9 KTS domain of WT1. The molecular diversity and functionality exhibited by these fusion transcripts may have significant biological implications for their transactivating and tumorigenic potential.
Liu
J
J
Department of Medicine and Pharmacology, Yale Cancer Center, Yale University School of Medicine and Veterans Affairs Connecticut Healthcare System, New Haven 06520, USA.
Nau
M M
MM
Yeh
J C
JC
Allegra
C J
CJ
Chu
E
E
Wright
J J
JJ
D000008:Abdominal Neoplasms / Q000235:genetics*; D000293:Adolescent; D000328:Adult; D001665:Binding Sites; D018288:Carcinoma, Small Cell / Q000235:genetics*; D002648:Child; D020740:Chimerin Proteins / Q000235:genetics; D018076:DNA, Complementary / Q000235:genetics / Q000378:metabolism; D004273:DNA, Neoplasm / Q000235:genetics / Q000378:metabolism; D004268:DNA-Binding Proteins / Q000235:genetics; D051766:Early Growth Response Protein 1; D005260:Female; D016162:Genes, Wilms Tumor / Q000235:genetics; D006801:Humans; D017874:Immediate-Early Proteins; D008297:Male; D015514:Oncogene Proteins, Fusion / Q000235:genetics / Q000378:metabolism / Q000502:physiology*; D011401:Promoter Regions, Genetic / Q000502:physiology; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D020133:Reverse Transcriptase Polymerase Chain Reaction; D012512:Sarcoma, Ewing / Q000235:genetics; D014157:Transcription Factors / Q000235:genetics; D015533:Transcriptional Activation / Q000502:physiology; D025721:WT1 Proteins; D016335:Zinc Fingers / Q000502:physiology
D020740:Chimerin Proteins; D018076:DNA, Complementary; D004273:DNA, Neoplasm; D004268:DNA-Binding Proteins; C497325:EGR1 protein, human; C106032:EWS1-WT1 fusion protein, human; D051766:Early Growth Response Protein 1; D017874:Immediate-Early Proteins; D015514:Oncogene Proteins, Fusion; D012333:RNA, Messenger; D014157:Transcription Factors; D025721:WT1 Proteins