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AXL receptor signalling suppresses p53 in melanoma through stabilization of the MDMX-MDM2 complex
Anna de Polo1, Zhongling Luo1,2, Casimiro Gerarduzzi1
1John B. Little Center for Radiation Sciences, Harvard T.H. Chan School of Public Health, Boston, MA 02115, USA.
Abstract:
Deregulation of the tyrosine kinase signalling is often associated with tumour progression and drug resistance, but its underlying mechanisms are only partly understood. In this study, we investigated the effects of the receptor tyrosine kinase AXL on the stability of the MDMX-MDM2 heterocomplex and the activity of p53 in melanoma cells. Our data demonstrated that AXL overexpression or activation through growth arrest-specific 6 (Gas6) ligand stimulation increases MDMX and MDM2 protein levels and decreases p53 activity. Upon activation, AXL stabilizes MDMX through a post-translational modification that involves phosphorylation of MDMX on the phosphosite Ser314, leading to increased affinity between MDMX and MDM2 and favouring MDMX nuclear translocation. Ser314 phosphorylation can also protect MDMX from MDM2-mediated degradation, leading to stabilization of the MDMX-MDM2 complex. We identified CDK4/6 and p38 MAPK as the two kinases mediating AXL-induced modulation of the MDMX-MDM2 complex, and demonstrated that suppression of AXL, either through siRNA silencing or pharmacological inhibition, increases expression levels of p53 target genes P21, MDM2, and PUMA, improves p53 pathway response to chemotherapy, and sensitizes cells to both Cisplatin and Vemurafenib. Our findings offer an insight into a novel signalling axis linking AXL to p53 and provide a potentially druggable pathway to restore p53 function in melanoma.
Insights
The receptor tyrosine kinase AXL stabilizes the MDMX-MDM2 complex, inhibiting p53 activity in melanoma. Suppressing AXL restores p53 function and sensitizes cancer cells to chemotherapy.
Area of Science:
- Oncology
- Molecular Biology
- Signal Transduction
Background:
- Deregulation of tyrosine kinase signaling pathways, including AXL, is implicated in cancer progression and therapeutic resistance.
- The interplay between receptor tyrosine kinases, MDMX-MDM2 complex stability, and p53 tumor suppressor activity is not fully elucidated.
- Melanoma pathogenesis involves complex signaling networks that can be targeted for therapeutic intervention.
Purpose of the Study:
- To investigate the role of the receptor tyrosine kinase AXL in regulating the MDMX-MDM2 heterocomplex stability and p53 activity in melanoma cells.
- To identify the molecular mechanisms by which AXL influences MDMX-MDM2 complex dynamics and p53 function.
- To evaluate the therapeutic potential of targeting the AXL signaling axis for melanoma treatment.
Main Methods:
- Utilized AXL overexpression and growth arrest-specific 6 (Gas6) stimulation to assess effects on MDMX, MDM2, and p53.
- Investigated post-translational modifications of MDMX, including phosphorylation at Ser314, using biochemical assays.
- Employed siRNA silencing and pharmacological inhibitors targeting AXL, CDK4/6, and p38 MAPK.
- Assessed p53 pathway activation and response to chemotherapy agents like Cisplatin and Vemurafenib.
Main Results:
- AXL activation by Gas6 increased MDMX and MDM2 protein levels, concurrently decreasing p53 activity.
- AXL stabilized MDMX via Ser314 phosphorylation, enhancing MDMX-MDM2 affinity and nuclear translocation, while protecting MDMX from degradation.
- CDK4/6 and p38 MAPK were identified as key kinases mediating AXL's effects on the MDMX-MDM2 complex.
- AXL suppression (siRNA or inhibitors) upregulated p53 target genes (P21, MDM2, PUMA), enhanced p53 response to chemotherapy, and sensitized melanoma cells to Cisplatin and Vemurafenib.
Conclusions:
- AXL signaling directly impacts MDMX-MDM2 complex stability and p53 tumor suppressor activity in melanoma.
- AXL-mediated phosphorylation of MDMX at Ser314 is a critical mechanism for complex stabilization and p53 inhibition.
- Targeting the AXL-MDMX-MDM2 axis represents a promising therapeutic strategy to restore p53 function and overcome drug resistance in melanoma.
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