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Non-canonical role for the ataxia-telangiectasia-Rad3 pathway in STAT3 activation in human multiple myeloma cells
Lin Li1, Xiaoyan Hu1, Jewel Nkwocha1
1Division of Hematology/Oncology, Department of Medicine, Virginia Commonwealth University, P.O. Box 980035, Richmond, VA, 23298, USA.
Purpose:
The goal of this study was to characterize the relationship between ATR and STAT3 interactions in human multiple myeloma (MM) cells.
Methods:
Various MM cell lines, including IL-6-dependent cells were exposed to ATR inhibitors and effects on STAT3 Tyr705 and Ser727 were monitored by WB analysis and ImageStream analysis. Parallel studies examined induction of cell death, STAT3 DNA binding activity, and expression of STAT3 downstream targets (BCL-XL, MCL-1, c-MYC). Validation was obtained in ATR shRNA knock-down cells, and in cells ectopically expressing BCL-XL, MCL-1, or c-MYC. Analogous studies were performed in primary MM cells and in a MM xenograft model.
Results:
Multiple pharmacologic ATR inhibitors inhibited STAT3 Tyr705 (but not Ser727) phosphorylation at low uM concentrations and down-regulated BCL-XL, MCL-1, c-MYC in association with cell death induction. Compatible results were observed in ATR shRNA knock-down cells. Cell death induced by ATR inhibitors was significantly attenuated in cells ectopically expressing constitutively active STAT3, BCL-XL, MCL-1, or c-MYC. Concordant results were observed in primary human MM cells and in an in vivo MM xenograft model.
Conclusions:
Collectively, these findings argue for a non-canonical role for the ATR kinase in STAT3 activation in MM cells, and suggest that STAT3 inactivation contributes to the lethal actions of ATR inhibitors in MM.
Insights
ATR inhibitors reduce STAT3 activation and promote cell death in multiple myeloma (MM). This suggests ATR kinase plays a non-canonical role in STAT3 activation, offering new therapeutic strategies for MM.
Area of Science:
- Oncology
- Molecular Biology
- Cell Signaling
Background:
- Multiple myeloma (MM) is a hematologic malignancy characterized by uncontrolled plasma cell proliferation.
- Signal transducer and activator of transcription 3 (STAT3) is a key transcription factor implicated in MM pathogenesis and drug resistance.
- Ataxia telangiectasia and Rad3-related (ATR) kinase is a DNA damage response kinase, with its role in MM yet to be fully elucidated.
Purpose of the Study:
- To investigate the functional relationship between ATR kinase and STAT3 signaling in human multiple myeloma cells.
- To determine if ATR inhibition impacts STAT3 activation and downstream targets crucial for MM cell survival.
Main Methods:
- Utilized multiple myeloma cell lines and primary patient cells treated with ATR inhibitors.
- Monitored STAT3 phosphorylation (Tyr705 and Ser727) using Western blot and ImageStream analysis.
- Assessed cell death, STAT3 DNA binding, downstream target expression (BCL-XL, MCL-1, c-MYC), and validated findings in ATR knockdown and xenograft models.
Main Results:
- ATR inhibitors significantly reduced STAT3 Tyr705 phosphorylation and expression of BCL-XL, MCL-1, and c-MYC, leading to cell death.
- These effects were confirmed in ATR shRNA knockdown models and primary MM cells.
- Ectopic expression of activated STAT3 or its downstream targets attenuated ATR inhibitor-induced cell death, highlighting STAT3's role.
Conclusions:
- ATR kinase plays a non-canonical role in activating STAT3 signaling in multiple myeloma cells.
- STAT3 inactivation is a key mechanism contributing to the anti-myeloma effects of ATR inhibitors.
- Targeting the ATR-STAT3 axis presents a promising therapeutic strategy for multiple myeloma treatment.
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