Abstract
The membrane skeleton of mature erythrocyte is formed during erythroid differentiation. Fluid shear stress is one of the main factors that promote embryonic hematopoiesis, however, its effects on erythroid differentiation and cytoskeleton remodeling are unclear. Erythrocyte tropomodulin of 41 kDa (E-Tmod41) caps the pointed end of actin filament (F-actin) and is critical for the formation of hexagonal topology of erythrocyte membrane skeleton. Our study focused on the regulation of E-Tmod41 and its role in F-actin cytoskeleton remodeling during erythroid differentiation induced by fluid shear stress. Mouse erythroleukemia (MEL) cells and embryonic erythroblasts were subjected to fluid shear stress (5 dyn/cm2) and erythroid differentiation was induced in both cells. F-actin content and E-Tmod41 expression were significantly increased in MEL cells after shearing. E-Tmod41 overexpression resulted in a significant increase in F-actin content, while the knockdown of E-Tmod41 generated the opposite result. An E-Tmod 3’UTR targeting miRNA, miR-23b-3p, was found suppressed by shear stress. When miR-23b-3p level was overexpressed / inhibited, both E-Tmod41 protein level and F-actin content were reduced / augmented. Furthermore, among the two alternative promoters of E-Tmod, PE0 (upstream of exon 0), which mainly drives the expression of E-Tmod41, was found activated by shear stress. In conclusion, our results suggest that fluid shear stress could induce erythroid differentiation and F-actin cytoskeleton remodeling. It upregulates E-Tmod41 expression through miR-23b-3p suppression and PE0 promoter activation, which, in turn, contributes to F-actin cytoskeleton remodeling.
Highlights
The membrane skeleton is the basis of erythrocyte morphology and deformability
Quantitative RT-PCR data showed that markers for erythroid differentiation, Hbb-b1, glycophorin A (GYPA), and GATA1, were all significantly upregulated by both shear stress and dimethyl sulphoxide (DMSO) (Fig 1C–1E)
These data indicate that, it was less competent than DMSO, fluid shear stress induced the erythroid differentiation in Mouse erythroleukemia (MEL) cells
Summary
The membrane skeleton is the basis of erythrocyte morphology and deformability It is the hexagonal lattice structure formed by 6 spectrin tetramers connecting to the short actin filaments at the junctional complex. The short actin filaments or protofilaments in the junctional complexes have the constant length of ~35–37 nm, which plays important roles in keeping the hexagonal structure and the mechanical property of the membrane skeleton. As a TM-binding protein and the only capping protein at the pointed end in erythrocytes, E-Tmod plays a critical role in restricting the length of the short actin filament (F-actin) [1]. A short E-Tmod isoform of 29 kDa (E-Tmod29) was discovered [6] It lacks the N-terminal actin-binding domain but retains the C-terminal actin-binding domain. It may be due to the wide range of expression and the weak capping activity of U-Tmod [9]
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