Lfc subcellular localization and activity is controlled by αv-class integrin

Area of Science:

• Cell Biology
• Molecular Biology
• Biochemistry

Background:

• Integrins, such as αvβ3 and α5β1, bind fibronectin (FN) and mediate cellular responses.
• These integrins influence cell morphology and motility through Rho GTPases.
• The specific mechanisms linking FN-binding integrins to RhoA activation require further elucidation.

Purpose of the Study:

• To investigate the role of fibronectin (FN)-binding integrins, specifically αvβ3 and α5β1, in controlling RhoA signaling.
• To identify the downstream effectors and molecular mechanisms involved in integrin-mediated RhoA activation.
• To determine the integrin-specific regulation of cellular responses like stress fiber formation and focal adhesion maturation.

Main Methods:

• Utilized cell culture models to study integrin signaling pathways.
• Employed techniques to assess RhoA activation, stress fiber formation, and focal adhesion dynamics.
• Investigated the interaction of Lfc (GEF-H1) with microtubules and its phosphorylation status.
• Performed gene silencing experiments to evaluate the necessity of Lfc in FN-αvβ3 signaling.

Main Results:

• FN-bound αvβ3 integrin, but not α5β1, induced Lfc dissociation from microtubules (MTs), activating RhoA.
• Lfc depletion diminished RhoA activity, stress fiber formation, and focal adhesion (FA) size, identifying Lfc as a key downstream mediator.
• A kinase cascade involving MARK2 and MARK3 phosphorylated Lfc, with site S151 being critical for Lfc localization and activity.
• These findings highlight an integrin-specific orchestration of Lfc and RhoA activation in FN-adherent cells.

Conclusions:

• FN-bound αvβ3 integrin specifically activates RhoA signaling through the dissociation and activation of the RhoA GEF Lfc from microtubules.
• Lfc is a crucial downstream effector of FN-αvβ3 signaling, regulating RhoA activity, stress fiber assembly, and focal adhesion maturation.
• The MARK2/MARK3-mediated phosphorylation of Lfc, particularly at S151, is a key regulatory step in this integrin-specific pathway.