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Thyroid hormone induces activation of mitogen-activated protein kinase in cultured cells
H Y Lin1, F B Davis, J K Gordinier
1Division of Molecular and Cellular Medicine, Department of Medicine, Albany Medical College, Albany, New York 12208, USA.
Abstract:
Thyroid hormone [L-thyroxine (T4)] rapidly induced phosphorylation and nuclear translocation (activation) of mitogen-activated protein kinase (MAPK) in HeLa and CV-1 cells in the absence of cytokine or growth factor. A pertussis toxin-sensitive and guanosine 5'-O-(3-thiotriphosphate)-sensitive cell surface mechanism responsive to T4 and agarose-T4, suggesting a G protein-coupled receptor, was implicated. Cells depleted of MAPK or treated with MAPK pathway inhibitors showed reduced activation of MAPK and of the signal transducer and activator of transcription STAT1alpha by T4; they also showed reduced T4 potentiation of the antiviral action of interferon-gamma (IFN-gamma). T4 treatment caused tyrosine-phosphorylated MAPK-STAT1alpha nuclear complex formation and enhanced Ser-727 phosphorylation of STAT1alpha, in the presence or absence of IFN-gamma. STAT1alpha-deficient cells transfected with STAT1alpha containing an alanine-for-serine substitution at residue 727 (STAT1alphaA727) showed minimal T4-stimulated STAT1alpha activation. IFN-gamma induced the antiviral state in cells containing wild-type STAT1alpha (STAT1alphawt) or STAT1alphaA727; T4 potentiated IFN-gamma action in STAT1alphawt cells but not in STAT1alphaA727 cells. T4-directed STAT1alpha Ser-727 phosphorylation is MAPK mediated and results in potentiated STAT1alpha activation and enhanced IFN-gamma activity.
Insights
Thyroid hormone (T4) activates the MAPK pathway, which is crucial for STAT1alpha activation and enhancing antiviral responses. This T4-mediated signaling involves a G protein-coupled receptor and potentiates interferon-gamma activity.
Area of Science:
- Cellular signaling pathways
- Endocrinology
- Molecular biology
Background:
- Thyroid hormone (T4) plays a critical role in cellular regulation.
- The precise mechanisms by which T4 exerts its non-genomic effects are not fully understood.
- Mitogen-activated protein kinase (MAPK) and Signal Transducer and Activator of Transcription 1-alpha (STAT1alpha) are key signaling molecules.
Purpose of the Study:
- To investigate the role of MAPK and STAT1alpha in T4-induced cellular responses.
- To elucidate the signaling pathway initiated by T4.
- To determine how T4 modulates the antiviral activity of interferon-gamma (IFN-gamma).
Main Methods:
- Utilized HeLa and CV-1 cell lines.
- Employed MAPK pathway inhibitors and MAPK-depleted cells.
- Investigated STAT1alpha phosphorylation and nuclear translocation.
- Assessed the potentiation of IFN-gamma antiviral activity.
- Used site-directed mutagenesis of STAT1alpha (STAT1alphaA727).
Main Results:
- T4 rapidly induced MAPK phosphorylation and nuclear translocation via a pertussis toxin-sensitive, G protein-coupled receptor-like mechanism.
- MAPK activation was essential for T4-induced STAT1alpha activation and potentiation of IFN-gamma antiviral activity.
- T4 treatment led to the formation of a tyrosine-phosphorylated MAPK-STAT1alpha nuclear complex.
- T4-induced STAT1alpha Ser-727 phosphorylation, mediated by MAPK, was critical for enhanced STAT1alpha activation and IFN-gamma potentiation.
Conclusions:
- T4 activates MAPK signaling through a cell surface receptor, leading to STAT1alpha activation.
- MAPK-mediated phosphorylation of STAT1alpha at Ser-727 is a key step in T4's non-genomic effects.
- T4 enhances cellular antiviral responses by potentiating IFN-gamma activity via the MAPK-STAT1alpha pathway.