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Opposing effects of PML and PML/RAR alpha on STAT3 activity
Akira Kawasaki1, Itaru Matsumura, Yoshihisa Kataoka
1Department of Hematology and Oncology, Osaka University Graduate School of Medicine, Suita, Japan.
Abstract:
Promyelocytic leukemia protein PML acts as a tumor suppressor, whereas its chimeric mutant promyelocytic leukemia/retinoic acid receptor alpha (PML/RAR alpha) causes acute promyelocytic leukemia (APL). Because PML has been shown to form transcription-regulatory complexes with various molecules, we speculated that PML and/or PML/RAR alpha might affect signal transducer and activator of transcription 3 (STAT3) activity, which plays a crucial role in granulocyte colony-stimulating factor (G-CSF)-induced growth and survival of myeloid cells. In luciferase assays, PML inhibited STAT3 activity in NIH3T3, 293T, HepG2, and 32D cells. PML formed a complex with STAT3 through B-box and COOH terminal regions in vitro and in vivo, thereby inhibiting its DNA binding activity. Although PML/RAR alpha did not interact with STAT3, it dissociated PML from STAT3 and restored its activity suppressed by PML. To assess the biologic significance of these findings, we introduced PML and PML/RAR alpha into interleukin-3 (IL-3)-dependent Ba/F3 cells expressing the chimeric receptor composed of extracellular domain of G-CSF-R and cytoplasmic domain of gp130, in which gp130-mediated growth is essentially dependent on STAT3 activity. Neither PML nor PML/RAR alpha affected IL-3-dependent growth of these clones. By contrast, gp130-mediated growth was abrogated by PML, whereas it was enhanced by PML/RAR alpha. These results reveal new functions of PML and PML/RAR alpha and suggest that dysregulated STAT3 activity by PML/RAR alpha may participate in the pathogenesis of APL.
Insights
Promyelocytic leukemia protein PML suppresses STAT3 activity, while its mutant PML/RAR alpha disrupts this, potentially driving acute promyelocytic leukemia (APL) pathogenesis by dysregulating STAT3 signaling in myeloid cells.
Area of Science:
- Molecular Biology
- Oncology
- Cell Signaling
Background:
- Promyelocytic leukemia protein (PML) functions as a tumor suppressor.
- The chimeric mutant PML/RAR alpha is implicated in acute promyelocytic leukemia (APL) development.
- Signal transducer and activator of transcription 3 (STAT3) is critical for myeloid cell growth and survival, particularly in response to granulocyte colony-stimulating factor (G-CSF).
Purpose of the Study:
- To investigate the impact of PML and PML/RAR alpha on STAT3 activity.
- To elucidate the molecular mechanisms underlying PML and PML/RAR alpha interactions with STAT3.
- To assess the biological significance of these interactions in cellular growth and survival.
Main Methods:
- Luciferase assays were employed to measure STAT3 activity in various cell lines (NIH3T3, 293T, HepG2, 32D).
- In vitro and in vivo co-immunoprecipitation assays were used to detect complex formation between PML and STAT3.
- Ba/F3 cells expressing a chimeric G-CSF-R/gp130 receptor were utilized to study the effects of PML and PML/RAR alpha on STAT3-dependent growth.
Main Results:
- PML inhibited STAT3 activity by forming a complex with STAT3, thereby reducing its DNA binding.
- PML/RAR alpha did not directly interact with STAT3 but dissociated PML from STAT3, restoring STAT3 activity.
- In gp130-mediated growth assays, PML abrogated growth, while PML/RAR alpha enhanced it, indicating STAT3 pathway modulation.
Conclusions:
- PML directly inhibits STAT3 activity through physical complex formation.
- PML/RAR alpha disrupts the PML-STAT3 interaction, leading to STAT3 activation.
- Dysregulated STAT3 activity by PML/RAR alpha may contribute to the pathogenesis of acute promyelocytic leukemia.