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Increased protein phosphorylation of cytoplasmic dynein results in impaired motor function
M T Runnegar1, X Wei, S F Hamm-Alvarez
1Department of Medicine, University of Southern California, 1985 Zonal Avenue, Los Angeles, CA 90089-9121, USA.
Abstract:
Inhibition of serine/threonine protein phosphatases in rat hepatocytes by okadaic acid and microcystin increased the phosphorylation of several components of the cytoplasmic dynein complex. UV light/vanadate cleavage and Western blot analysis revealed that two of these components with molecular masses of approx. 400 kDa and 74 kDa were dynein heavy- and intermediate-chains respectively. This increased phosphorylation resulted in inhibition of dynein ATPase activity, and reduced motor-dependent avidity of endosomal/lysosomal membranes for microtubules.
Insights
Inhibiting protein phosphatases in rat liver cells with toxins increased the phosphorylation of cytoplasmic dynein components. This impaired dynein motor function and microtubule binding.
Area of Science:
- Cell Biology
- Molecular Biology
- Biochemistry
Background:
- Cytoplasmic dynein is a crucial motor protein complex involved in intracellular transport.
- Protein phosphorylation regulates the activity of many cellular proteins, including motor proteins.
Purpose of the Study:
- To investigate the effect of serine/threonine protein phosphatase inhibition on cytoplasmic dynein function in rat hepatocytes.
- To identify specific dynein components affected by this inhibition and their functional consequences.
Main Methods:
- Rat hepatocytes were treated with okadaic acid and microcystin to inhibit protein phosphatases.
- UV light/vanadate cleavage and Western blot analysis were used to identify and quantify phosphorylated dynein components.
- Dynein ATPase activity and microtubule binding assays were performed to assess motor function.
Main Results:
- Inhibition of protein phosphatases led to increased phosphorylation of cytoplasmic dynein heavy and intermediate chains (approx. 400 kDa and 74 kDa).
- Increased phosphorylation resulted in the inhibition of dynein's ATPase activity.
- The motor-dependent binding of endosomal/lysosomal membranes to microtubules was reduced.
Conclusions:
- Serine/threonine protein phosphatase activity is critical for regulating cytoplasmic dynein function.
- Phosphorylation of dynein heavy and intermediate chains by these phosphatases is essential for maintaining dynein motor activity and microtubule association.
- Dysregulation of dynein phosphorylation can impair intracellular transport processes.