title: Interferon γ is a STAT1-dependent direct inducer of BCL6 expression in imatinib-treated chronic myeloid leukemia cells.
abstract: B-cell CLL/lymphoma 6 (BCL6) exerts oncogenic effects in several human hematopoietic malignancies including chronic myeloid leukemia (CML), where BCL6 expression was shown to be essential for CML stem cell survival and self-renewal during imatinib mesylate (IM) treatment. As several lines of evidence suggest that interferon γ (IFNγ) production in CML patients might have a central role in the response to tyrosine kinase inhibitor (TKI) therapy, we analyzed if IFNγ modulates BCL6 expression in CML cells. Although separate IFNγ or IM treatment only slightly upregulated BCL6 expression, combined treatment induced remarkable BCL6 upregulation in CML lines and primary human CD34+ CML stem cells. We proved that during combined treatment, inhibition of constitutive signal transducer and activator of transcription (STAT) 5 activation by IM allowed the specific enhancement of the STAT1 dependent, direct upregulation of BCL6 by IFNγ in CML cells. By using colony-forming assay, we found that IFNγ enhanced the ex vivo colony or cluster-forming capacity of human CML stem cells in the absence or presence of IM, respectively. Furthermore, inhibition of the transcriptional repressor function of BCL6 in the presence of IM and IFNγ almost completely blocked the cluster formation of human CML stem cells. On the other hand, by using small interfering RNA knockdown of BCL6, we demonstrated that in an IM-treated CML line the antiapoptotic effect of IFNγ was independent of BCL6 upregulation. We found that IFNγ also upregulated several antiapoptotic members of the BCL2 and BIRC gene families in CML cells, including the long isoform of MCL1, which proved to be essential for the antiapoptotic effect of IFNγ in an IM-treated CML line. Our results suggest that combination of TKIs with BCL6 and MCL1 inhibitors may potentially lead to the complete eradication of CML stem cells.
authors.affiliation: Department of Microbiology, Tumor and Cell Biology, Karolinska Institutet, Stockholm, Sweden.
authors.forename: H S
authors.initials: HS
authors.lastname: Madapura
authors.affiliation: Department of Microbiology, Tumor and Cell Biology, Karolinska Institutet, Stockholm, Sweden.
authors.forename: N
authors.initials: N
authors.lastname: Nagy
authors.affiliation: Department of Women's and Children's Health, Karolinska Institutet, Stockholm, Sweden.
authors.forename: D
authors.initials: D
authors.lastname: Ujvari
authors.affiliation: Department of Microbiology, Tumor and Cell Biology, Karolinska Institutet, Stockholm, Sweden.
authors.forename: T
authors.initials: T
authors.lastname: Kallas
authors.affiliation: Department of Microbiology, Tumor and Cell Biology, Karolinska Institutet, Stockholm, Sweden.
authors.forename: M C L
authors.initials: MCL
authors.lastname: Kröhnke
authors.affiliation: Department of Microbiology, Tumor and Cell Biology, Karolinska Institutet, Stockholm, Sweden.
authors.forename: S
authors.initials: S
authors.lastname: Amu
authors.affiliation: Division of Hematology, Department of Medicine, Karolinska University Hospital Solna and Karolinska Institutet, Stockholm, Sweden.
authors.forename: M
authors.initials: M
authors.lastname: Björkholm
authors.affiliation: Division of Hematology, Department of Medicine, Karolinska University Hospital Solna and Karolinska Institutet, Stockholm, Sweden.
authors.forename: L
authors.initials: L
authors.lastname: Stenke
authors.affiliation: Department of Experimental Therapeutics, The University of Texas M. D. Anderson Cancer Center, Houston, TX, USA.
authors.forename: P K
authors.initials: PK
authors.lastname: Mandal
authors.affiliation: Department of Experimental Therapeutics, The University of Texas M. D. Anderson Cancer Center, Houston, TX, USA.
authors.forename: J S
authors.initials: JS
authors.lastname: McMurray
authors.affiliation: Department of Microbiology, Tumor and Cell Biology, Karolinska Institutet, Stockholm, Sweden.
authors.forename: M
authors.initials: M
authors.lastname: Keszei
authors.affiliation: Department of Microbiology, Tumor and Cell Biology, Karolinska Institutet, Stockholm, Sweden.
authors.forename: L S
authors.initials: LS
authors.lastname: Westerberg
authors.affiliation: Department of Pharmaceutical Sciences, University of Maryland School of Pharmacy, Baltimore, MD, USA.
authors.forename: H
authors.initials: H
authors.lastname: Cheng
authors.affiliation: Department of Pharmaceutical Sciences, University of Maryland School of Pharmacy, Baltimore, MD, USA.
authors.forename: F
authors.initials: F
authors.lastname: Xue
authors.affiliation: Department of Microbiology, Tumor and Cell Biology, Karolinska Institutet, Stockholm, Sweden.
authors.forename: G
authors.initials: G
authors.lastname: Klein
authors.affiliation: Department of Microbiology, Tumor and Cell Biology, Karolinska Institutet, Stockholm, Sweden.
authors.forename: E
authors.initials: E
authors.lastname: Klein
authors.affiliation: Department of Microbiology, Tumor and Cell Biology, Karolinska Institutet, Stockholm, Sweden.|Department of Women's and Children's Health, Karolinska Institutet, Stockholm, Sweden.
authors.forename: D
authors.initials: D
authors.lastname: Salamon
mesh_terms: D018952:Antigens, CD34 / Q000378:metabolism; D045744:Cell Line, Tumor; D006801:Humans; D000068877:Imatinib Mesylate / Q000494:pharmacology / Q000627:therapeutic use*; D007371:Interferon-gamma / Q000494:pharmacology / Q000627:therapeutic use*; D007937:Leukapheresis; D015466:Leukemia, Myeloid, Chronic-Phase / Q000188:drug therapy* / Q000378:metabolism; D064549:Myeloid Cell Leukemia Sequence 1 Protein / Q000378:metabolism; D014411:Neoplastic Stem Cells / Q000187:drug effects; D051616:Neuronal Apoptosis-Inhibitory Protein / Q000187:drug effects / Q000378:metabolism; D011518:Proto-Oncogene Proteins / Q000235:genetics / Q000378:metabolism*; D034741:RNA, Small Interfering / Q000235:genetics / Q000378:metabolism; D012097:Repressor Proteins / Q000235:genetics / Q000378:metabolism*; D050794:STAT1 Transcription Factor / Q000235:genetics / Q000378:metabolism*; D050799:STAT5 Transcription Factor / Q000235:genetics / Q000378:metabolism; D051025:bcl-Associated Death Protein / Q000187:drug effects / Q000378:metabolism
chemical_list: D018952:Antigens, CD34; C411984:BCOR protein, human; C579095:MCL1 protein, human; D064549:Myeloid Cell Leukemia Sequence 1 Protein; C496800:NAIP protein, human; D051616:Neuronal Apoptosis-Inhibitory Protein; D011518:Proto-Oncogene Proteins; D034741:RNA, Small Interfering; D012097:Repressor Proteins; D050794:STAT1 Transcription Factor; C494079:STAT1 protein, human; D050799:STAT5 Transcription Factor; D051025:bcl-Associated Death Protein; D007371:Interferon-gamma; D000068877:Imatinib Mesylate