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Combined Inhibition of p38MAPK and PIKfyve Synergistically Disrupts Autophagy to Selectively Target Cancer Cells
Constandina E O'Connell1, Alex Vassilev2
1National Institute of Child Health and Human Development, NIH, Bethesda, Maryland.
Abstract:
In nutrient-poor conditions, autophagy buffers metabolic stress and counteracts the effects of chemotherapy and radiation on cancer cells, which depend on autophagy for survival. However, clinical trials targeting autophagy have failed to produce successful anticancer treatments using currently available inhibitors. Recent studies have shown that PIKfyve kinase inhibitors disrupt lysosome function in autophagy and can selectively kill certain cancer cells. Analysis of biochemical changes caused by PIKfyve inhibition revealed that resistant cells contain significantly higher levels of cellular p38MAPK protein and phosphorylation. Expression of the lysosomal protein, lysosomal-associated membrane protein 2, carrying phosphomimetic mutations of the p38MAPK phosphorylation sites prevented all effects caused by PIKfyve inhibition-induced lysosome dysfunction. Thus, the activation of p38MAPK in response to PIKfyve inhibition revealed a novel compensatory role in maintaining lysosome function in autophagy. The functional cooperation between the cellular PIKfyve and p38MAPK pathways in regulating lysosome homeostasis was especially important in cancer cells. Combined inhibition of PIKfyve and p38MAPK activities synergistically blocked autophagy-mediated protein degradation, prevented cathepsin maturation, and markedly reduced the viability of multiple cancer cell types without affecting the viability of normal cells. Furthermore, combined PIKfyve and p38MAPK inhibitors synergistically reduced tumor growth in mice bearing xenografts of human colorectal adenocarcinoma, suggesting a novel way to target cancer cells by prolonged inhibition of autophagy using lower drug concentrations. SIGNIFICANCE: This study demonstrates that PIKfyve and p38MAPK cooperate to regulate lysosome homeostasis and their combined inhibition synergistically blocks autophagy to reduce cancer cell viability in vitro and in vivo.
Insights
Targeting cancer cells involves inhibiting PIKfyve and p38MAPK pathways. This dual inhibition disrupts autophagy, reduces cancer cell viability, and shrinks tumors, offering a new therapeutic strategy.
Area of Science:
- Cell Biology
- Cancer Research
- Molecular Biology
Background:
- Autophagy is crucial for cancer cell survival under nutrient-poor conditions.
- Current autophagy inhibitors have limited success in clinical cancer treatments.
- PIKfyve kinase inhibitors show potential by disrupting lysosome function and killing cancer cells.
Purpose of the Study:
- To investigate the compensatory mechanisms in cancer cells resistant to PIKfyve inhibition.
- To explore the functional cooperation between PIKfyve and p38MAPK pathways in regulating lysosome homeostasis.
- To evaluate the synergistic effect of combined PIKfyve and p38MAPK inhibition on cancer cell viability and tumor growth.
Main Methods:
- Analysis of biochemical changes in cancer cells upon PIKfyve inhibition.
- Investigating the role of p38MAPK protein levels and phosphorylation.
- Utilizing phosphomimetic mutations to study p38MAPK phosphorylation sites on lysosomal-associated membrane protein 2.
- Assessing the impact of combined PIKfyve and p38MAPK inhibition on autophagy, cathepsin maturation, and cell viability.
- Evaluating synergistic effects on tumor growth in mouse xenograft models.
Main Results:
- Resistant cancer cells exhibit elevated p38MAPK protein and phosphorylation.
- p38MAPK activation compensates for PIKfyve inhibition-induced lysosome dysfunction.
- Combined PIKfyve and p38MAPK inhibition synergistically blocks autophagy, prevents cathepsin maturation, and reduces cancer cell viability.
- Combined inhibition significantly reduces tumor growth in colorectal adenocarcinoma xenografts without affecting normal cells.
Conclusions:
- PIKfyve and p38MAPK pathways cooperate to maintain lysosome homeostasis, particularly in cancer cells.
- Combined inhibition of PIKfyve and p38MAPK offers a novel strategy to target cancer cells by blocking autophagy.
- This approach demonstrates synergistic efficacy in reducing cancer cell viability and tumor growth, suggesting potential for lower drug concentrations in therapy.
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