title: Inhibition of STAT3 signaling leads to apoptosis of leukemic large granular lymphocytes and decreased Mcl-1 expression.
abstract: Large granular lymphocyte (LGL) leukemia is characterized by the expansion of antigen-activated cytotoxic T lymphocytes. These leukemic cells are resistant to Fas-mediated apoptosis despite expressing high levels of Fas. We found that leukemic LGL from 19 patients displayed high levels of activated STAT3. Treatment of leukemic LGL with the JAK-selective tyrosine kinase inhibitor AG-490 induced apoptosis with a corresponding decrease in STAT-DNA binding activity. Moreover, using an antisense oligonucleotide approach to diminish STAT3 expression, we found that Fas sensitivity was restored in leukemic LGL. AG-490-induced apoptosis in leukemic LGL was independent of Bcl-xL or Bcl-2 expression. However, we found that the Bcl-2-family protein Mcl-1 was significantly reduced by AG-490 treatment. Activated STAT3 was shown to bind an SIE-related element in the murine mcl-1 promoter. Using a luciferase reporter assay, we demonstrated that v-src overexpression in NIH3T3 induced STAT3-dependent transcriptional activity from the mcl-1 promoter and increased endogenous Mcl-1 protein levels. We conclude that STAT3 activation contributed to accumulation of the leukemic LGL clones. These findings suggest that investigation should focus on novel strategies targeting STAT3 in the treatment of LGL leukemia.
authors.affiliation: Hematologic Malignancy Program, H. Lee Moffitt Cancer Center and Research Institute, 12902 Magnolia Drive, MRC, Room 2068 f and g, Tampa, Florida 33612, USA. burnetpk@moffitt.usf.edu
authors.forename: P K
authors.initials: PK
authors.lastname: Epling-Burnette
authors.forename: J H
authors.initials: JH
authors.lastname: Liu
authors.forename: R
authors.initials: R
authors.lastname: Catlett-Falcone
authors.forename: J
authors.initials: J
authors.lastname: Turkson
authors.forename: M
authors.initials: M
authors.lastname: Oshiro
authors.forename: R
authors.initials: R
authors.lastname: Kothapalli
authors.forename: Y
authors.initials: Y
authors.lastname: Li
authors.forename: J M
authors.initials: JM
authors.lastname: Wang
authors.forename: H F
authors.initials: HF
authors.lastname: Yang-Yen
authors.forename: J
authors.initials: J
authors.lastname: Karras
authors.forename: R
authors.initials: R
authors.lastname: Jove
authors.forename: T P
authors.initials: TP
authors.lastname: Loughran
mesh_terms: D017209:Apoptosis / Q000187:drug effects; D015153:Blotting, Western; D018414:CD8-Positive T-Lymphocytes / Q000187:drug effects / Q000502:physiology*; D002460:Cell Line; D004268:DNA-Binding Proteins / Q000037:antagonists & inhibitors* / Q000378:metabolism; D019281:Dimerization; D004791:Enzyme Inhibitors / Q000494:pharmacology; D005786:Gene Expression Regulation; D006801:Humans; D007938:Leukemia / Q000503:physiopathology*; D064549:Myeloid Cell Leukemia Sequence 1 Protein; D009363:Neoplasm Proteins / Q000096:biosynthesis* / Q000235:genetics; D015688:Oncogene Protein pp60(v-src); D010766:Phosphorylation; D019253:Proto-Oncogene Proteins c-bcl-2; D050796:STAT3 Transcription Factor; D015398:Signal Transduction; D015534:Trans-Activators / Q000037:antagonists & inhibitors* / Q000378:metabolism; D014407:Tumor Cells, Cultured; D020032:Tyrphostins / Q000494:pharmacology
chemical_list: D004268:DNA-Binding Proteins; D004791:Enzyme Inhibitors; D064549:Myeloid Cell Leukemia Sequence 1 Protein; D009363:Neoplasm Proteins; D019253:Proto-Oncogene Proteins c-bcl-2; D050796:STAT3 Transcription Factor; C494086:STAT3 protein, human; D015534:Trans-Activators; D020032:Tyrphostins; C095512:alpha-cyano-(3,4-dihydroxy)-N-benzylcinnamide; D015688:Oncogene Protein pp60(v-src)