Actin directly interacts with phospholipase D, inhibiting its activity

Area of Science:

• Biochemistry
• Cell Biology
• Molecular Biology

Background:

• Mammalian phospholipase D (PLD) is crucial for signal transduction and cellular functions.
• Understanding PLD regulation is key to elucidating its diverse roles.

Purpose of the Study:

• To identify and characterize PLD-binding proteins, specifically focusing on beta-actin.
• To investigate the interaction between beta-actin and PLD isozymes (PLD1 and PLD2).
• To determine the regulatory role of beta-actin on PLD activity in conjunction with other factors like alpha-actinin and ARF1.

Main Methods:

• Peptide mass fingerprinting and MALDI-TOF MS to identify PLD2-binding proteins.
• Glutathione S-transferase (GST) fusion proteins to map beta-actin binding sites on PLD2.
• In vitro enzyme activity assays to assess beta-actin's inhibitory effects.
• In vitro binding assays to study competitive binding with alpha-actinin.
• Immunocytochemistry and co-immunoprecipitation to confirm in vivo interactions.

Main Results:

• Beta-actin was identified as a major direct binding protein of PLD2.
• A specific region (amino acids 613-723) of PLD2 was found essential for beta-actin binding.
• Beta-actin potently inhibited PLD2 activity, with an IC50 of 5 nM.
• Beta-actin could displace alpha-actinin binding to PLD2, indicating independent interactions.
• ADP-ribosylation factor 1 (ARF1) could enhance PLD2 activity despite beta-actin's inhibition.
• Beta-actin exhibited similar binding and inhibitory potencies for both PLD1 and PLD2.
• In vivo interactions between PLD1/PLD2 and actin were confirmed in cells.

Conclusions:

• Beta-actin is a significant regulator of PLD1 and PLD2 activity.
• Cytoskeletal proteins like beta-actin and alpha-actinin, along with ARF1, play a role in modulating PLD functions.
• These interactions are likely important for cytoskeleton-related cellular processes mediated by PLD.