ABSTRACT
STAT5 fulfills essential roles in hematopoietic stem cell (HSC) self-renewal and chronic myeloid leukemia (CML), a prototypical stem cell malignancy. However, the specific contributions of the two related genes STAT5A and STAT5B have not been determined. In this study, we used a RNAi-based strategy to establish participation of these genes to CML disease and persistence following targeted therapy. We showed that STAT5A/STAT5B double-knockdown triggers CML cell apoptosis and suppresses both normal and CML HSC long-term clonogenic potential. STAT5A and STAT5B exhibited similar prosurvival activity, but STAT5A attenuation alone was ineffective at impairing growth of normal and CML CD34(+) cells isolated at diagnosis. In contrast, STAT5A attenuation was sufficient to enhance basal oxidative stress and DNA damage of normal CD34(+) and CML cells. Furthermore, it weakened the ability to manage exogenous oxidative stress, increased p53 (TRP53)/CHK-2 (CHEK2) stress pathway activation, and enhanced prolyl hydroxylase domain (PHD)-3 (EGLN3) mRNA expression. Only STAT5A and its transactivation domain-deficient mutant STAT5AΔ749 specifically rescued these activities. STAT5A attenuation was also active at inhibiting growth of CML CD34(+) cells from patients with acquired resistance to imatinib. Our findings show that STAT5A has a selective role in contributing to stress resistance through unconventional mechanisms, offering new opportunities to eradicate the most primitive and tyrosine kinase inhibitor-resistant CML cells with an additional potential to eradicate persistent stem cell populations.
Subject(s)
Drug Resistance, Neoplasm , Leukemia, Myelogenous, Chronic, BCR-ABL Positive/metabolism , Neoplastic Stem Cells/metabolism , Oxidative Stress , Protein Kinase Inhibitors/pharmacology , STAT5 Transcription Factor/metabolism , Tumor Suppressor Proteins/metabolism , Apoptosis , Benzamides/pharmacology , Blotting, Western , Cell Proliferation , Fluorescent Antibody Technique , Hematopoietic Stem Cells/cytology , Hematopoietic Stem Cells/drug effects , Hematopoietic Stem Cells/metabolism , Humans , Hydrogen Peroxide/pharmacology , Imatinib Mesylate , Immunoenzyme Techniques , Leukemia, Myelogenous, Chronic, BCR-ABL Positive/drug therapy , Leukemia, Myelogenous, Chronic, BCR-ABL Positive/pathology , Neoplastic Stem Cells/drug effects , Neoplastic Stem Cells/pathology , Piperazines/pharmacology , Pyrimidines/pharmacology , RNA, Messenger/genetics , RNA, Small Interfering/genetics , Real-Time Polymerase Chain Reaction , Reverse Transcriptase Polymerase Chain Reaction , STAT5 Transcription Factor/antagonists & inhibitors , STAT5 Transcription Factor/genetics , Tumor Suppressor Proteins/antagonists & inhibitors , Tumor Suppressor Proteins/geneticsSubject(s)
Antigens, CD34/immunology , Gene Products, nef/physiology , PPAR gamma/physiology , Simian Acquired Immunodeficiency Syndrome/physiopathology , Animals , Gene Expression Regulation , Macaca , STAT5 Transcription Factor/genetics , Simian Acquired Immunodeficiency Syndrome/genetics , Simian Acquired Immunodeficiency Syndrome/immunologyABSTRACT
Infection of primates by HIV-1 and SIV induces multiple hematological abnormalities of central hematopoietic origin. Although these defects greatly contribute to the pathophysiology of HIV-1 infection, the molecular basis for altered BM function remains unknown. Here we show that when cynomolgus macaques were infected with SIV, the multipotent potential of their hematopoietic progenitor cells was lost, and this correlated with downregulation of STAT5A and STAT5B expression. However, forced expression of STAT5B entirely rescued the multipotent potential of the hematopoietic progenitor cells. In addition, an accessory viral protein required for efficient SIV and HIV replication and pathogenicity, "Negative factor" (Nef), was essential for SIV-mediated impairment of the multipotent potential of hematopoietic progenitors ex vivo and in vivo. This newly uncovered property of Nef was both conserved between HIV-1 and SIV strains and entirely dependent upon the presence of PPARgamma in targeted cells. Further, PPARgamma agonists mimicked Nef activity by inhibiting STAT5A and STAT5B expression and hampering the functionality of hematopoietic progenitors both ex vivo and in vivo. These findings have extended the role of Nef in the pathogenicity of HIV-1 and SIV and reveal a pivotal role for the PPARgamma/STAT5 pathway in the regulation of early hematopoiesis. This study may provide a basis for investigating the potential therapeutic benefits of PPARgamma antagonists in both patients with AIDS and individuals with hematopoietic disorders.
