Role of Ezrin in maintaining balance between cortical actin and stress fibers

Behera, Amrutamaya (2021) Role of Ezrin in maintaining balance between cortical actin and stress fibers. Masters thesis, Indian Institute of Science Education and Research Kolkata.

	Text (MS Dissertation of Amrutamaya Behera (16MS081)) 16MS081_Thesis_file.pdf - Submitted Version Restricted to Repository staff only Download (3MB)
	Text 16MS081_Thesis_file.pdf Download (3MB)

Abstract

Ezrin is key to regulation of both membrane and cortical tension. By linking filamentous actin with membrane proteins, it helps forming various cellular structures like filopodia, growth cones, microvilli, lamellipodia, contractile furrow etc. These structures are crucial to cellular processes like migration, endocytosis and exocytosis, division etc. These developments happen through regulation of both membrane and cortical tension. Hence ezrin is crucial to tension regulation. It is known that ezrin organizes actin networks and forms above mentioned cellular growth structures. Also, it is reported that phosphorylating ezrin at specific site enhances rate of various cellular processes. Not only at cytoplasmic level, even in its inactive form ezrin can affect gene regulation and have a notable impact. Therefore, ezrin has a bigger role in all of these. Traction force is the force generated by actomyosin interaction and actin polymerization. This is transmitted to extracellular matrix, ECM, through stress fibers via focal adhesions which are local gathering of ECM proteins, membrane receptors and various cytoplasmic proteins. It varies from 1 to few nN depending on cell type. Cell cortex is known to be regulated not only in round spherical cells but also in well spread cells, by various physical properties like cell spread area, cell volume, and traction force too. It is reported that decreasing spread area increases cortical thickness and increasing traction force decreases cortical thickness. This happens via change of myosin II turnover rate, enhanced expression of cofilin and rate of actin polymerization. This elucidates the actin dynamics in MCA is regulated in response to change in spread area and traction force. We also observed in our lab that inhibiting ezrin increases traction forces. This implies strengthening of stress fiber. Thus, it compels us to ask further if ezrin plays an important role in regulation of actin dynamics and how. Hypothetically, is it achieved by redistribution of actin between stress fiber and cortical actin pool? To answer these questions, we inhibit ezrin by Ezrin inhibitor in CHO cells and to quantitate change in actin distribution we add Life-act mCherry fluorophore to fixed cells after inhibition of ezrin with keeping a control group added with same dye. Then observing the change in actin distribution in both stress fiber and cortex region we show that ezrin regulates stress fiber formation and cortical actin distribution through membrane tension modulation.

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