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A novel pool of protein phosphatase 2A is associated with microtubules and is regulated during the cell cycle
E Sontag1, V Nunbhakdi-Craig, G S Bloom
1Department of Pharmacology, University of Texas Southwestern Medical Center, Dallas 75235-9041.
Abstract:
Immunofluorescence microscopy revealed the presence of protein phosphatase 2A (PP2A) on microtubules in neuronal and nonneuronal cells. Interphase and mitotic spindle microtubules, as well as centrosomes, were all labeled with antibodies against individual PP2A subunits, showing that the AB alpha C holoenzyme is associated with microtubules. Biochemical analysis showed that PP2A could be reversibly bound to microtubules in vitro and that approximately 75% of the PP2A in cytosolic extracts could interact with microtubules. The activity of microtubule-associated PP2A was differentially regulated during the cell cycle. Enzymatic activity was high during S phase and intermediate during G1, while the activity in G2 and M was 20-fold lower than during S phase. The amount of microtubule-bound PP2A remained constant throughout the cell cycle, implying that cell cycle regulation of its enzymatic activity involves factors other than microtubules. These results raise the possibility that PP2A regulates cell cycle-dependent microtubule functions, such as karyokinesis and membrane transport.
Insights
Protein phosphatase 2A (PP2A) binds to microtubules in cells. Its activity changes during the cell cycle, suggesting PP2A regulates microtubule functions in cell division and transport.
Area of Science:
- Cell Biology
- Molecular Biology
- Biochemistry
Background:
- Protein phosphatase 2A (PP2A) is a key regulator of cellular processes.
- Microtubules are essential components of the cytoskeleton involved in cell division and transport.
- The localization and regulation of PP2A in relation to microtubules are not fully understood.
Purpose of the Study:
- To investigate the association of PP2A with microtubules in neuronal and nonneuronal cells.
- To determine the cell cycle-dependent regulation of microtubule-associated PP2A activity.
- To explore the functional implications of PP2A-microtubule interaction.
Main Methods:
- Immunofluorescence microscopy to visualize PP2A localization on microtubules and centrosomes.
- Biochemical assays to assess PP2A binding to microtubules in vitro.
- Enzymatic activity assays of PP2A across different cell cycle phases.
Main Results:
- PP2A holoenzyme (AB alpha C) is localized on interphase and mitotic spindle microtubules and centrosomes.
- Approximately 75% of cytosolic PP2A can reversibly bind to microtubules.
- Microtubule-bound PP2A enzymatic activity is highest in S phase and significantly lower in G2/M phases, while PP2A levels on microtubules remain constant.
- Cell cycle regulation of PP2A activity is independent of microtubule binding levels.
Conclusions:
- PP2A is a microtubule-associated protein with cell cycle-regulated enzymatic activity.
- The findings suggest PP2A plays a role in regulating cell cycle-dependent microtubule functions.
- Potential roles in karyokinesis and membrane transport are proposed, warranting further investigation.