STAT5a activation mediates the epithelial to mesenchymal transition induced by oncogenic RhoA. Salvador Aznar Benitah 1 , Pilar F. Valerón 1 , Hallger Rui**, and Juan Carlos Lacal* *Instituto de Investigaciones Biomédicas, CSIC, Madrid, Spain, and ** Department of Pathology, Uniformed Services University of the Health Sciences, USA. KEY WORDS: RhoGTPases/ Oncogenes/ STAT5 Transcription factor/ JAK2/ Tyrosine kinases/ MEK1/ EM transition Running title: Activation of Stat5a by oncogenic RhoA (1) These authors contributed equally to this work (*) Corresponding author Instituto de Investigaciones Biomédicas, CSIC, Arturo Duperier 4, 28029 Madrid, Spain Ph. 34-91.585.4607 FAX 34-91. 585.4606 E-mail: jclacal@iib.uam.es Abstract The involvement of Rho GTPases in signal transduction pathways leading to transcription activation is one of the major roles of this family of GTPases. Thus, the identification of transcription factors regulated by Rho GTPases as well as the understanding of the mechanisms of their activation and its biological outcome is of great interest. We provide here evidence that Rho GTPases modulate Stat5a, a transcription MBC in Press, published on October 16, 2002 as 10.1091/mbc.E02-08-0454