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Cancers 2015, 7(1), 503-537; doi:10.3390/cancers7010503

Stat5 Exerts Distinct, Vital Functions in the Cytoplasm and Nucleus of Bcr-Abl+ K562 and Jak2(V617F)+ HEL Leukemia Cells

1
Georg-Speyer-Haus, Institute for Tumor Biology and Experimental Therapy, Frankfurt am Main 60596, Germany
2
Ganymed Pharmaceuticals AG, Mainz 55131, Germany
3
Boston Children's Hospital, Division of Hematology/Oncology, Boston, MA 02115, USA
4
Ludwig Boltzmann Institute for Cancer Research (LBI-CR), Vienna 1090, Austria
*
Author to whom correspondence should be addressed.
Academic Editor: James Turkson
Received: 16 December 2014 / Revised: 9 March 2015 / Accepted: 12 March 2015 / Published: 19 March 2015
(This article belongs to the Special Issue STAT3 Signalling in Cancer: Friend or Foe)
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Abstract

Signal transducers and activators of transcription (Stats) play central roles in the conversion of extracellular signals, e.g., cytokines, hormones and growth factors, into tissue and cell type specific gene expression patterns. In normal cells, their signaling potential is strictly limited in extent and duration. The persistent activation of Stat3 or Stat5 is found in many human tumor cells and contributes to their growth and survival. Stat5 activation plays a pivotal role in nearly all hematological malignancies and occurs downstream of oncogenic kinases, e.g., Bcr-Abl in chronic myeloid leukemias (CML) and Jak2(V617F) in other myeloproliferative diseases (MPD). We defined the mechanisms through which Stat5 affects growth and survival of K562 cells, representative of Bcr-Abl positive CML, and HEL cells, representative for Jak2(V617F) positive acute erythroid leukemia. In our experiments we suppressed the protein expression levels of Stat5a and Stat5b through shRNA mediated downregulation and demonstrated the dependence of cell survival on the presence of Stat5. Alternatively, we interfered with the functional capacities of the Stat5 protein through the interaction with a Stat5 specific peptide ligand. This ligand is a Stat5 specific peptide aptamer construct which comprises a 12mer peptide integrated into a modified thioredoxin scaffold, S5-DBD-PA. The peptide sequence specifically recognizes the DNA binding domain (DBD) of Stat5. Complex formation of S5-DBD-PA with Stat5 causes a strong reduction of P-Stat5 in the nuclear fraction of Bcr-Abl-transformed K562 cells and a suppression of Stat5 target genes. Distinct Stat5 mediated survival mechanisms were detected in K562 and Jak2(V617F)-transformed HEL cells. Stat5 is activated in the nuclear and cytosolic compartments of K562 cells and the S5-DBD-PA inhibitor most likely affects the viability of Bcr-Abl+ K562 cells through the inhibition of canonical Stat5 induced target gene transcription. In HEL cells, Stat5 is predominantly present in the cytoplasm and the survival of the Jak2(V617F)+ HEL cells is impeded through the inhibition of the cytoplasmic functions of Stat5. View Full-Text
Keywords: peptide aptamer (PA); signal transducer and activator of transcription 5 (Stat5); RNA interference (RNAi); protein/lentiviral transduction; chronic myeloid leukemia (CML); human erythroid leukemia (HEL); Bcr-Abl; Jak2(V617F); canonical/non-canonical peptide aptamer (PA); signal transducer and activator of transcription 5 (Stat5); RNA interference (RNAi); protein/lentiviral transduction; chronic myeloid leukemia (CML); human erythroid leukemia (HEL); Bcr-Abl; Jak2(V617F); canonical/non-canonical
This is an open access article distributed under the Creative Commons Attribution License which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. (CC BY 4.0).

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MDPI and ACS Style

Weber, A.; Borghouts, C.; Brendel, C.; Moriggl, R.; Delis, N.; Brill, B.; Vafaizadeh, V.; Groner, B. Stat5 Exerts Distinct, Vital Functions in the Cytoplasm and Nucleus of Bcr-Abl+ K562 and Jak2(V617F)+ HEL Leukemia Cells. Cancers 2015, 7, 503-537.

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