Ewing family
tumors (EFTs) are associated with a
chromosomal translocation resulting in a fusion of the amino-terminus of EWS with the
DNA-binding domain of an
ETS transcription factor. Although previous reports suggested that these chimeric
proteins would act as aberrant
transcription factors, their downstream targets have not been fully elucidated. To identify downstream targets of these EWS-ETS fusion
proteins, we introduced EWS-ETS fusion constructs into a human
fibrosarcoma cell line, HT-1080, by retroviral transduction. Here we report that the LAMB3 gene encoding the beta3 chain of basement membrane
protein laminin-5 is induced to a significantly higher level in cells expressing EWS-ETSs than in cells expressing normal ETSs. Additionally through use of an
antisense oligonucleotide for EWS-ERG in the W-ES EFT cell line,
laminin beta3
protein was reduced coordinately with EWS-ERG fusion
protein expression. Furthermore, we found small mRNAs were preferentially transcribed from the LAMB3 gene in EFT cell lines. Molecular cloning of the entire coding region shows that the alternative transcripts from different promoter(s) located within the intron 14, which encode small
proteins, likely are major products of the LAMB3 gene in EFT cells. We show that the small
isoforms conferred increased anchorage-independent proliferation to NIH3T3 cells. Together with previous studies showing that
laminin-5 is involved in the invasive and malignant phenotype of several
tumor types, our data suggest that the oncogenic effect of EWS-ETS may be mediated in part by upregulation of LAMB3 expression.