Inhibition of STAT3 signaling leads to apoptosis of leukemic large granular lymphocytes and decreased Mcl-1 expression
P.K. Epling-Burnette, … , Richard Jove, Thomas P. Loughran Jr.
P.K. Epling-Burnette, … , Richard Jove, Thomas P. Loughran Jr.
Published February 1, 2001
Citation Information: J Clin Invest. 2001;107(3):351-362. https://doi.org/10.1172/JCI9940.
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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

P.K. Epling-Burnette, Jin Hong Liu, Robyn Catlett-Falcone, James Turkson, Marc Oshiro, Ravi Kothapalli, Yongxiang Li, Ju-Ming Wang, Hsin-Fang Yang-Yen, James Karras, Richard Jove, Thomas P. Loughran Jr.

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Figure 1

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Activation of STAT3 and STAT1 in leukemic LGLs. (a) EMSA with nuclear ex...
Activation of STAT3 and STAT1 in leukemic LGLs. (a) EMSA with nuclear extracts from PBMCs of normal donors (NL), from normal donors activated for 7 days with PHA + IL-2 (NL-AC), and from patients with LGL leukemia (LGL). Cytoplasmic extracts from each sample were run on an SDS-PAGE gel and blotted for expression of STAT3. (b) EMSA supershift or blocking experiments with untreated (lanes 1, 4, 7, 10, and 13), anti-STAT1–preincubated (lanes 2, 5, 8, 11, and 14), and anti-STAT3–preincubated (lanes 3, 6, 9, 12, and 15) reaction mixtures. (c) Western blot analysis of whole-cell extracts for phosphorylated STAT3, total STAT3, and β-actin. (d) EMSA for STAT5-DNA–binding activity with activated normal and leukemic LGLs (10024-AC) used as a positive control. The relative migration of STAT3:3 homodimers (ST3:3), STAT1:3 heterodimers (ST1:3), and STAT1:1 homodimers (ST1:1) is shown in a and b. (d) STAT5:5 homodimers (ST5:5) and STAT1:1 homodimers (ST1:1) are indicated. WB, Western blot.