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The PTEN Tumor Suppressor Forms Homodimers in Solution
Frank Heinrich1, Srinivas Chakravarthy2, Hirsh Nanda1
1Department of Physics, Carnegie Mellon University, Pittsburgh, PA 15213, USA; NIST Center for Neutron Research, National Institute of Standards and Technology, Gaithersburg, MD 20899, USA.
Abstract:
As the phosphoinositol-3-kinase antagonist in the PI3K pathway, the PTEN tumor suppressor exerts phosphatase activity on diacylphosphatidylinositol triphosphate in the plasma membrane. Even partial loss of this activity enhances tumorigenesis, but a mechanistic basis for this aspect of PTEN physiology has not yet been established. It was recently proposed that PTEN mutations have dominant-negative effects in cancer via PTEN dimers. We show that PTEN forms homodimers in vitro, and determine a structural model of the complex from SAXS and Rosetta docking studies. Our findings shed new light on the cellular control mechanism of PTEN activity. Phosphorylation of the unstructured C-terminal tail of PTEN reduces PTEN activity, and this result was interpreted as a blockage of the PTEN membrane binding interface through this tail. The results presented here instead suggest that the C-terminal tail functions in stabilizing the homodimer, and that tail phosphorylation interferes with this stabilization.
Insights
The tumor suppressor PTEN forms homodimers, and its C-terminal tail stabilizes this structure. Tail phosphorylation reduces PTEN activity by disrupting homodimerization, offering new insights into cancer mechanisms.
Area of Science:
- Molecular Biology
- Biochemistry
- Cancer Research
Background:
- PTEN acts as a tumor suppressor by antagonizing the PI3K pathway.
- Loss of PTEN phosphatase activity promotes tumorigenesis.
- PTEN's role in dimerization and its regulation are not fully understood.
Purpose of the Study:
- To investigate the role of PTEN dimerization in its tumor suppressor function.
- To elucidate the structural basis of PTEN homodimerization.
- To understand how PTEN C-terminal tail phosphorylation affects its activity and dimerization.
Main Methods:
- In vitro PTEN homodimerization assays.
- Small-angle X-ray scattering (SAXS) for structural analysis.
- Rosetta docking for computational modeling.
Main Results:
- PTEN forms stable homodimers in vitro.
- A structural model of the PTEN homodimer was determined.
- PTEN C-terminal tail phosphorylation destabilizes the homodimer, reducing PTEN activity.
Conclusions:
- PTEN homodimerization is a key aspect of its cellular function.
- The C-terminal tail is crucial for stabilizing PTEN homodimers.
- Phosphorylation of the C-terminal tail regulates PTEN activity by disrupting homodimerization, not by blocking membrane binding.
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