ARPC5L is a subunit of the Arp2/3 complex, a seven-protein assembly that nucleates branched actin filament networks 1. As a component of this complex, ARPC5L participates in actin polymerization regulation essential for cellular processes including cell migration, immune responses, and mechanotransduction. ARPC5L exists as an isoform of ARPC5 (67% identical) 2, and these paralogs have distinct functional roles. ARPC5L-containing complexes demonstrate superior actin assembly kinetics and slower filament disassembly compared to ARPC5-containing complexes 1, with structural differences in the N-terminal region contributing to this enhanced activity 3. In CD4 T cells, ARPC5L specifically drives nuclear actin polymerization upon T cell receptor activation 4. ARPC5L functions in macrophage migration and bacterial restriction 5, and its expression promotes single-cell migration in breast cancer models when combined with PI 3-kinase activation 6. ARPC5L also mediates cellular stiffness sensing through talin 1 interactions, contributing to tissue mechanical homeostasis 7. Unlike ARPC5, which shows non-redundant roles in development and immune function 2, ARPC5L functions as a specialized isoform for specific physiological contexts requiring enhanced actin nucleation capacity.