Liprin-α controls stress fiber formation by binding to mDia and regulating its membrane localization

Area of Science:

• Cell Biology
• Molecular Biology
• Biochemistry

Background:

• Actin cytoskeleton regulation is vital for cell morphology and migration.
• mDia proteins are Rho GTPase-downstream actin nucleators essential for forming unbranched actin filaments.
• The precise mechanisms controlling mDia activity within cells are not fully understood.

Purpose of the Study:

• To identify proteins that bind to mDia and elucidate their regulatory role.
• To investigate the interaction between Liprin-alpha and mDia.
• To determine how Liprin-alpha binding affects mDia localization and activity.

Main Methods:

• Co-immunoprecipitation to identify mDia-binding proteins.
• Analysis of protein-protein interaction domains (Liprin-alpha central region, mDia DID and DD domains).
• Cell-based assays involving overexpression of Liprin-alpha fragments and RNA interference (RNAi) for Liprin-alpha depletion.
• Biochemical assays to assess binding affinities and competition with mDia autoregulatory domain (DAD).

Main Results:

• Liprin-alpha was identified as an mDia-binding protein.
• The interaction involves Liprin-alpha's central region and mDia's N-terminal Dia-inhibitory domain (DID) and dimerization domain (DD).
• Liprin-alpha competes with mDia's autoregulatory domain (DAD) for DID binding, preferring the open conformation of mDia.
• Overexpression of a Liprin-alpha fragment reduced mDia's plasma membrane localization and attenuated Rho-mDia-mediated stress fiber formation.
• Liprin-alpha depletion enhanced mDia's membrane fraction and promoted actin stress fiber formation.

Conclusions:

• Liprin-alpha negatively regulates mDia activity.
• Liprin-alpha binding to the DID-DD region of mDia displaces it from the plasma membrane, thereby inhibiting its nucleating function.
• This mechanism provides new insights into the spatial and temporal control of the actin cytoskeleton.