Downregulation and forced expression of EWS-Fli1 fusion gene results in changes in the expression of G1 regulatory genes

Chromosomal translocation t(11;22)(q24:q12) is detected in approximately 90% of tumours of the Ewing family (ET). This translocation results in EWS-Fli1 gene fusion which produces a EWS-Fli1 fusion protein acting as an aberrant transcriptional activator. We previously reported that the inhibition of EWS-Fli1 expression caused the G(0)/G(1) arrest of ET cells. We, therefore, hypothesized that EWS-Fli1 may affect the expression of G(1) regulatory genes. Downregulation of EWS-Fli1 fusion proteins was observed 48 hours after the treatment with EWS-Fli1 antisense oligonucleotides. The expressions of G(1) cyclins, cyclin D1 and cyclin E, were markedly decreased in parallel with the reduction of EWS-Fli1 iusion protein. On the other hand, the expression of p21 and p27, which are important cyclin-dependent kinase inhibitors (CKls) for G(1)-S transition, was dramatically increased after the treatment with EWS-Fli1 antisense oligonucleotides, RT-PCR analysis showed that alteration of the expressions of the cyclins and CKls occurred at the mRNA level. Furthermore, transfection of EWS-Fli1 cDNA to NIH3T3 caused transformation of the cells and induction of the expression of cyclin D1 and E, Clinical samples of ET also showed a high level of expression of cyclin D1 mRNA, whereas mRNAs for p21 and p27 were not detected in the samples. These findings strongly suggest that the G(1)-S regulatory genes may be involved in downstream of EWS-Fli1 transcription factor, and that the unbalanced expression of G(1)-S regulatory factors caused by EWS-Fli1 may lead to the tumorigenesis of ET. (C) 2001 Cancer Research Campaign http://www.bjcancer.com.