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Distinct functional constraints driving conservation of the cofilin N-terminal regulatory tail

ABSTRACT: Cofilin family proteins have essential roles in remodeling the cytoskeleton through filamentous actin depolymerization and severing. The short unstructured N-terminal region of cofilin is critical for actin binding and harbors the major site of inhibitory phosphorylation. Atypically for a disordered sequence, the N-terminal region is highly conserved, but specifics aspects driving this conservation are unclear. Here, we screened a library of 16,000 human cofilin N-terminal sequence variants for their capacity to support growth in S. cerevisiae in the presence or absence of the upstream regulator LIM kinase. Results from the screen and biochemical analysis of individual variants revealed distinct sequence requirements for actin binding and regulation by LIM kinase. LIM kinase recognition only partly explained sequence constraints on phosphoregulation, which were instead driven to a large extent by the capacity for phosphorylation to inactivate cofilin. We found remarkably loose sequence requirements for actin binding and phosphoinhibition, but collectively they restricted the N-terminus to sequences found in natural cofilins. Our results illustrate how a phosphorylation site can balance potentially competing sequence requirements for function and regulation.

ORGANISM(S): Saccharomyces cerevisiae

PROVIDER: GSE242403 | GEO | 2023/11/18

REPOSITORIES: GEO

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Project description:SMCs express plasminogen activator inhibitor-1 (PAI-1), which regulates SMC function and vascular remodeling. However, whether PAI-1 controls SMC cytoskeletal dynamics and stiffness is unknown, and the causal role of PAI-1 in arterial stiffening is undefined. SMCs from human coronary arteries and aortae of wild-type vs. PAI-1-deficient mice were cultured with or without PAI-039, a specific PAI-1 inhibitor, after which cell stiffness was measured by atomic force microscopy, filamentous actin structures were assessed by confocal microscopy, and the activities cofilin, LIM domain kinase 1 (LIMK), slingshot homolog 1 (SSH), and AMP-activated protein kinase (AMPK) were measured. RNA sequencing was performed to determine the effects of PAI-039 on SMC gene expression. Effects of PAI-039 on aortic stiffness were assessed by pulse wave velocity. PAI-039 significantly reduced intrinsic stiffness of human SMCs, which was accompanied by significant decreases in cytoplasmic actin filaments. Similar effects were observed in wild-type, but not in PAI-1-deficient SMCs. Mechanistically, PAI-039 significantly increased the activity of cofilin, an actin depolymerase, in SMCs expressing PAI-1, but not in PAI-1-deficient cells. PAI-039 had no significant effects on LIMK or SSH activity. RNA-sequencing analysis suggested that PAI-039 up-regulates AMPK signaling in SMCs, which was confirmed by western blotting. Inhibition of AMPK prevented activation of cofilin by PAI-039. In mice, PAI-039 significantly decreased aortic stiffness without significantly altering peri-aortic fibrosis. PAI-039 decreases intrinsic SMC stiffness by reducing cytoplasmic stress fiber content. These effects are mediated by AMPK-dependent activation of cofilin. PAI-039 also decreases aortic stiffness in vivo. These findings suggest that PAI-1 is an important regulator of the SMC cytoskeleton and that pharmacologic inhibition of PAI-1 has potential to treat cardiovascular diseases mediated by accelerated arterial stiffening.

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Distinct functional constraints driving conservation of the cofilin N-terminal regulatory tail

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