Isoform specific function of calpain 2 in regulating membrane protrusion.

Area of Science:

• Cell Biology
• Biochemistry
• Molecular Biology

Background:

• Calpains are known to regulate cell migration by affecting focal adhesion and rear retraction.
• The specific role of calpains in membrane protrusion dynamics remains less understood.

Purpose of the Study:

• To investigate the role of calpains, specifically calpain 4, 1, and 2, in modulating membrane protrusion activity in fibroblasts.
• To elucidate the isoform-specific functions of calpain 1 and calpain 2 in lamellipodial dynamics.

Main Methods:

• Utilized an immortalized Capn4(-/-) fibroblast cell line to observe morphological and migratory defects.
• Employed small interfering RNAs (siRNAs) to knockdown calpain 1 and calpain 2 expression in fibroblasts.
• Analyzed cell morphology, membrane protrusion activity, lamellipodial extension kinetics, and protein substrate cleavage.

Main Results:

• Capn4(-/-) fibroblasts exhibited altered morphology with increased thin membrane projections and transient membrane activity, alongside impaired lamellipodial extension.
• Calpain 2 knockdown cells mirrored these phenotypes, showing protrusive morphology and altered protrusion kinetics, unlike calpain 1 knockdown cells.
• Calpain 2 was identified as the key isoform responsible for cleaving cytoskeletal and focal adhesion proteins including FAK, paxillin, spectrin, and talin.

Conclusions:

• Calpain 2 plays a critical role in limiting membrane protrusions and regulating lamellipodial dynamics at the leading edge of migrating cells.
• These findings reveal a novel function for calpain 2 in controlling cell protrusion and migration.
• Calpain 2's proteolytic activity on specific substrates is crucial for its function in cell migration.