Truncated STAT proteins are prevalent at relapse of acute myeloid leukemia

Signal transducer and activator of transcription (STAT) proteins are implicated in the control of cell survival., proliferation and differentiation in response to hematopoietic cytokines. C-terminally truncated STAT isoforms (STAT beta), as opposed to the full length form (STAT alpha), have a competitive or even transdominant negative effect on gene induction mediated by the STAT pathway. We have previously demonstrated that while constitutively active STAT proteins were detected in ten of 36 (28%) for STAT3 and eight of 36 (22%) for STAT5 in pretreatment samples from newly diagnosed acute myeloid leukemia (AML) patients, a significantly larger fraction of samples [21 of 27 (78%)] expressed STAT beta proteins. To determine whether STAT beta expression was maintained or increased after relapse in AML, we compared STAT activity and isoform expression at diagnosis and at relapse in 17 patients. In this selected group, constitutively active STAT3 was detected in 13 of 17 (76%) AML samples at diagnosis but was detected in only four of these patients at relapse, Constitutively active STAT5 was detected in three of 17 (18%) AML samples at diagnosis; but only two at relapse. In contrast. STAT beta protein expression was observed in 12 of the 17 pretreatment samples (71%) and in 16 of 17 samples at relapse. Only one patient did not express STAT beta at relapse. Our results suggest that STAT beta isoform expression, rather than level of constitutive activity, may be involved in disease progression in AML. (C) 2001 Elsevier Science Ltd. All rights reserved.