Abstract

The actin cytoskeleton powers membrane deformation during many cellular processes, such as migration, morphogenesis, and endocytosis [1, 2]. Phosphoinositides regulate activities of many actin-binding proteins (ABPs), including profilin, cofilin, Dia2, N-WASP, ezrin, and moesin [3]; however, underlying molecular mechanisms have remained elusive. Here, we applied a combination of biophysical assays [4,5] and atomistic molecular dynamics simulations to uncover the molecular principles by which ABPs interact with phosphoinositide-containing membranes. Our results reveal that ABPs show large differences in the affinities and dynamics of membrane interactions and in the ranges of phosphoinositide densities that they sense [6].

In the second half of my talk, I will briefly provide evidence that adherens junctions of epithelial cells harbor lamellipodia-like, dynamic actin-based membrane protrusions. A membrane-remodeling BAR domain protein [7] together with ABPs promote the formation of these membrane protrusions that contribute to the integrity of cell–cell junctions in epithelial monolayers [Senju et al., submitted]. These results elucidate physiological relevancies of the membrane-ABPs interactions, and membrane-interaction mechanisms of ABPs evolved to precisely fulfil their specific cellular functions in cytoskeletal dynamics.

Acknowledgement

My visit is supported by Okayama University to promote international networks and collaborations between Europe and Japan.

References

[1] Senju Y, Lappalainen P. Regulation of actin dynamics by PI(4,5)P2 in cell migration and endocytosis. Curr Opin Cell Biol. 2019 Feb;56:7-13.

[2] Senju Y, Miyata H. The role of actomyosin contractility in the formation and dynamics of actin bundles during fibroblast spreading. J Biochem. 2009 Feb;145(2):137-50.

[3] Senju Y, Tsai FC. A biophysical perspective of the regulatory mechanisms of ezrin/radixin/moesin proteins. Biophys Rev. 2022 Jan 28;14(1):199-208.

[4] Senju Y, Lappalainen P, Zhao H. Liposome Co-sedimentation and Co-flotation Assays to Study Lipid-Protein Interactions. Methods Mol Biol. 2021;2251:195-204.

[5] Senju Y, Zhao H. Fluorescence Assays to Study Membrane Penetration of Proteins. Methods Mol Biol. 2021;2251:215-223.

[6] Senju Y, Kalimeri M, Koskela EV, Somerharju P, Zhao H, Vattulainen I, Lappalainen P. Mechanistic principles underlying regulation of the actin cytoskeleton by phosphoinositides. Proc Natl Acad Sci U S A. 2017 Oct 24;114(43):E8977-E8986.

[7] Tsai FC, Henderson JM, Jarin Z, Kremneva E, Senju Y, Pernier J, Mikhajlov O, Manzi J, Kogan K, Le Clainche C, Voth GA, Lappalainen P, Bassereau P. Activated I-BAR IRSp53 clustering controls the formation of VASP-actin-based membrane protrusions. Sci Adv. 2022 Oct 14;8(41):eabp8677.