UC Riverside

Beta-arrestins are adaptor proteins that can scaffold a number of signaling proteins to promote localized activity within the cell. Downstream of some GPCRs, β-arrestins can promote activation of the actin filament severing protein, cofilin, through two mechanisms: one involving inhibition of LIM Kinase (LIMK) which negatively regulates cofilin activity through phosphorylation on serine 3. The mechanism by which β-arrestin-1 regulates LIMK activity has not been elucidated; however, it has been shown to be important for cell migration downstream of protease-activate-receptor-2 (PAR-2), dendritic spine formation and opioid receptor function. Here my work demonstrate that β-arrestin-1 directly binds both cofilin and LIMK, and inhibits LIMK activity directly and investigate the mechanism by which inhibition of kinase activity occurs. Using serial truncations and site-directed mutagenesis, I identify crucial residues for cofilin and LIMK interaction within amino acids 1-99 of β-arrestin-1 and show that charged residues at 50 and 51 are crucial for binding to LIMK and R51 is required for LIMK inhibition, PAR2 stimulated cofilin dephosphorylation and cell migration. Additionally, our work reveals that amino acids 1-99 aminos of β-arrestin-1 bind both cofilin and LIMK with a higher apparent affinity than the full length and blocks PAR2-stimulated cofilin dephosphorylaton in HEK293 cells, suggesting it functions as a selective dominant negative β-arrestin-1, inhibiting specifically the cofilin pathway. Thus, residues in the N-terminus of β-arrestin-1 are involved in LIMK inhibition and cofilin activation and this, in turn, is important for cell migration downstream of PAR-2.