STAT5 activation by BCR-Abl contributes to transformation of K562 leukemiacells

Signal transducers and activators of transcription (STATs) belong to a fami ly of transcription factors that were originally identified as mediators of cytokine-induced gene expression. Recent evidence, however, has shown that certain members of the STAT family, including STAT3, are also involved in cellular transformation. Here we show that STAT5 also plays a role in cellu lar transformation by the BCR-Abl oncogene. In BCR-Abl transformed K562 cel ls, STAT5A and 5B are constitutively phosphorylated on tyro sine and are tr anscriptionally active. Moreover, expression of a dominant negative form of STAT5 shows that active STAT5 is necessary for the growth in soft agar of these cells. These results show that besides STAT3, STAT5 can also be invol ved in cellular transformation. (C) 1999 by The American Society of Hematol ogy.