ANALYSIS OF ETV6 AND ETV6-AML1 PROTEINS IN ACUTE LYMPHOBLASTIC-LEUKEMIA

The t(12;21) is a recurring chromosomal abnormality in acute lymphobla stic leukaemias (ALLs) which results in the production of an ETV6-AML1 fusion gene. The association between t(12;21) and the deletion of the untranslocated allele of ETV6 is among the most frequent abnormalitie s observed in B-lineage ALLs in children. In order to study the protei ns encoded by ETV6 and ETV6-AML1, we raised polyclonal antibodies dire cted against a recombinant peptide corresponding to the junctional reg ion of ETV6-AML1. Cell lysates from various leukaemic cell lines, and from children with B- and T-lineage ALLs, wee studied by Western blot. Two isoforms of ETV6 protein were detected in normal bone marrow cell s and in leukaemic cells without 12p alteration: a major form (apparen t m.w. 63 kD) and a minor one (apparent m.w. 53 kD). In the REH cell l ine, which expresses the ETV6-AML1 fusion transcript and no normal ETV 6 mRNA, the ETV6 isoforms were absent and two new bands were detected corresponding to ETV6-AML1 protein products (apparent m.w. 95 and 105 kD). A similar pattern was obtained with blast cells from patients wit h a t(12;21) and a deletion of ETV6. In two patients with a t(12;21) b ut no deletion of ETV6, four bands were detected corresponding to both the normal ETV6 and ETV6-AML1 proteins, suggesting that in these case s the second ETV6 allele was not inactivated. Surprisingly, the expres sion pattern of ETV6 differed widely from patient to patient. In three out of 13 patients without t(12;21), the relative intensity of the ba nds corresponding to ETV6 isoforms in blast cells from patients was co mpletely different from normal cells, with a marked predominance of th e 53 kD isoform. The pattern of ETV6 expression was normal in bone mar row from the same patients during remission. These finding suggest tha t ETV6 abnormalities are not restricted to patients with translocation s or deletions involving this gene.