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STAT6 mediates interleukin-4 growth inhibition in human breast cancer cells
Jennifer L Gooch1, Barbara Christy, Douglas Yee
1Department of Medicine, Division of Oncology, University of Texas Health Science Center, San Antonio, TX 78284, USA.
Abstract:
In addition to acting as a hematopoietic growth factor, interleukin-4 (IL-4) inhibits growth of some transformed cells in vitro and in vivo. In this study, we show that insulin receptor substrate (IRS)-1, IRS-2, and signal transducer and activator of transcription 6 (STAT6) are phosphorylated following IL-4 treatment in MCF-7 breast cancer cells. STAT6 DNA binding is enhanced by IL-4 treatment. STAT6 activation occurs even after IRS-1 depletion, suggesting the two pathways are independent. To examine the role of STAT6 in IL-4-mediated growth inhibition and apoptosis, a full-length STAT6 cDNA was transfected into MCF-7 cells. Transient overexpression of STAT6 resulted in both cytoplasmic and nuclear expression of the protein, increased DNA binding in response to IL-4, and increased transactivation of an IL-4 responsive promoter. In STAT6-transfected cells, basal proliferation was reduced whereas apoptosis was increased. Finally, stable expression of STAT6 resulted in reduced foci formation compared to vector-transfected cells alone. These results suggest STAT6 is required for IL-4-mediated growth inhibition and induction of apoptosis in human breast cancer cells.
Insights
Interleukin-4 (IL-4) inhibits breast cancer cell growth by activating STAT6. This study demonstrates STAT6
Area of Science:
- Oncology
- Cell Biology
- Immunology
Background:
- Interleukin-4 (IL-4) exhibits dual roles, acting as a hematopoietic growth factor and inhibiting certain transformed cells.
- The molecular mechanisms underlying IL-4's anti-cancer effects, particularly in breast cancer, require further elucidation.
Purpose of the Study:
- To investigate the role of Signal Transducer and Activator of Transcription 6 (STAT6) in mediating IL-4's effects on MCF-7 breast cancer cells.
- To determine if STAT6 activation is dependent on Insulin Receptor Substrate (IRS)-1/IRS-2 pathways.
Main Methods:
- MCF-7 breast cancer cells were treated with IL-4.
- Phosphorylation of IRS-1, IRS-2, and STAT6 was assessed.
- STAT6 DNA binding activity and transactivation were measured.
- STAT6 was overexpressed transiently and stably via cDNA transfection.
- Cell proliferation, apoptosis, and foci formation were evaluated.
Main Results:
- IL-4 treatment induced phosphorylation of IRS-1, IRS-2, and STAT6 in MCF-7 cells.
- STAT6 activation and DNA binding were enhanced by IL-4, independent of IRS-1.
- Transient STAT6 overexpression increased IL-4 responsiveness and promoter transactivation.
- STAT6 overexpression reduced basal proliferation and increased apoptosis.
- Stable STAT6 expression led to decreased foci formation.
Conclusions:
- STAT6 is a key mediator of IL-4's growth inhibitory and pro-apoptotic effects in human breast cancer cells.
- STAT6 activation by IL-4 is crucial for suppressing cancer cell proliferation and inducing apoptosis.