Review coordinated by Life Science Editors Foundation
Reviewed by: Dr. Angela Andersen, Life Science Editors Foundation & Life Science Editors.
Potential Conflicts of Interest: None.
PUNCHLINE:
A stress-responsive p38 signaling pathway in choanoflagellates reveals deep evolutionary conservation of cellular stress adaptation mechanisms—functionally linking unicellular and multicellular stress responses.
BACKGROUND:
Cells across all domains of life must sense and respond to environmental stress, and kinase signaling pathways play a critical role in mediating these responses. In animals, p38 mitogen-activated protein kinase (MAPK) is a well-known regulator of stress responses, cell proliferation, and differentiation. However, its evolutionary origins remain unclear.
Choanoflagellates—the closest living relatives of animals—provide a unique window into the early evolution of signaling pathways before multicellularity. While previous studies have identified kinase homologs in choanoflagellates, their functional roles have been difficult to study due to limited genetic tools. This study uses high-throughput small-molecule screening and CRISPR-based gene editing in Salpingoeca rosetta to systematically dissect p38 kinase signaling in response to environmental stress.
Questions Addressed:
How do kinases regulate stress responses in choanoflagellates?
Can human kinase inhibitors be repurposed to probe kinase function in choanoflagellates?
SUMMARY:
This study functionally characterizes a stress-responsive p38 kinase pathway in choanoflagellates, demonstrating that kinase signaling in unicellular organisms plays a key role in environmental stress adaptation. Using a high-throughput screen of 1,255 human kinase inhibitors, the authors identified 95 compounds that disrupt S. rosetta proliferation. By focusing on sorafenib, a known human kinase inhibitor, they discovered that p38 kinase in S. rosetta is activated by heat shock and other stressors, revealing an ancient and conserved function for this pathway.
Key Results
1. Kinase Inhibitor Screening Identifies Regulators of S. rosetta Proliferation
A comprehensive kinase inhibitor screen was conducted using 1,255 human kinase inhibitors. 95 inhibitors significantly affected S. rosetta cell growth, suggesting deep conservation of kinase function between choanoflagellates and animals. The library covered all major kinase families, and flow cytometry and imaging validated inhibitor effects.
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Sorafenib Inhibits p38 Kinase and Blocks Stress-Induced Phosphorylation S. rosetta p38 kinase was identified as a sorafenib target, supporting its role in stress signaling. Heat shock increases p38 phosphorylation, but this activation is blocked by sorafenib, confirming a conserved stress-responsive pathway. p38 kinases in S. rosetta share critical catalytic residues with human p38, further supporting functional conservation.
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p38 Activation is Stress-Specific and Not Required for Proliferation
While p38 is activated by heat shock and oxidative stress, its inhibition does not prevent S. rosetta proliferation. CRISPR knockout of p38 (Sr-p38¹⁻¹⁵) confirmed that p38 activation is required for stress response but not cell division.
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p38 Kinase Function Precedes Multicellularity
The study reveals that p38’s role in stress adaptation predates animals, suggesting that stress responses were critical for early eukaryotic evolution. p38 homologs are present across choanoflagellates, reinforcing its ancient function.
STRENGTHS:
Bridges a Functional Gap in Evolutionary Biology. This study moves beyond comparative genomics by functionally testing kinase signaling in a unicellular organism, shedding light on the ancestral origins of stress pathways.
High-Throughput Chemical Genetics as a Tool for Evolutionary Biology. Using human kinase inhibitors to probe choanoflagellate signaling is an innovative approach that extends the power of small-molecule screening beyond traditional model organisms.
p38 MAPK as a Conserved Stress Sensor. The discovery that choanoflagellates use p38 signaling to respond to stress suggests that stress adaptation mechanisms evolved before multicellularity—a key insight into early eukaryotic evolution.
Biomedical and Biotechnological Implications. Understanding how stress signaling evolved could have implications for drug targeting in diseases like cancer and neurodegeneration, where kinase dysregulation plays a role.
FUTURE WORK:
• Does This Apply to Other Kinases?
• How Does p38 Interact with Other Stress Pathways?
• Do other unicellular relatives of animals use p38 for stress signaling?
• How does p38 respond to other environmental stressors (e.g., salinity, bacterial signals)?
FINAL TAKEAWAY:
This study functionally validates a stress-responsive p38 signaling pathway in choanoflagellates, providing compelling evidence that key elements of stress adaptation predate multicellularity. Beyond evolutionary implications, this work pioneers the use of kinase inhibitors to probe non-model organisms, opening up new avenues for studying the origins of complex cellular regulation.