The genetic hallmark of Ewing's sarcoma family of tumours (ET) is the presence of the translocation t(11;22)(q24;q12), which creates the ET fusion gene, leading to cellular transformation. Five human γ-glutamyl transpeptidase (γ-GT) genes are located near the chromosomal translocation in ET. γ-GT is a major enzyme involved in glutathione homoeostasis. Five human cell lines representative of primary or metastatic tumours were investigated to study whether γ-GT alterations could occur at the chromosomal breaks and rearrangements in ET. As shown by enzymic assays and FACS analyses, all ET cell lines consistently expressed a functional γ-GT which however did not discriminate steps of ET progression. As shown previously [Sancéau, Hiscott, Delattre and Wietzerbin (2000) Oncogene 19, 3372–3383], ET cells respond to the antiproliferative effects of interferons (IFNs) type I (α and β) and to a much less degree to IFN type II (γ). IFN-α and -β arrested cells in the S-phase of the cell cycle. We found an enhancement of γ-GT mRNA species with IFN-α and -β by reverse transcriptase—PCR analyses. This is reflected by up-regulation of γ-GT protein, which coincides with the increase in γ-GT-specific enzymic activity. Similarly, IFNs up-regulate the levels of γ-GT in another IFN-responsive B cell line. Whether this up-regulation of γ-GT by IFNs is of physiological relevance to cell behaviour remains to be studied.

Abbreviations used: ET, Ewing's sarcoma family of tumours; EWS, Ewing's sarcoma gene; IFN, interferon; γ-Glu-pNA, l-γ-glutamyl-p-nitroanilide; γ-GT, γ-glutamyl transpeptidase; RT, reverse transcriptase; STAT, signal transduction and activators of transcription; SF, specific fluorescence density.

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