Abstract
Src protein tyrosine kinases (SFKs) are a family of nonreceptor tyrosine kinases that are localized beneath the plasma membrane and are activated during cell adhesion, migration, and elongation. Due to their involvement in the activation of signal transduction cascades, SFKs have been suggested to play important roles in the determination of cell polarity during cell extension and elongation. However, the mechanism underlying Src-mediated polarity formation remains unclear. The present study was performed to investigate the mechanisms underlying Src-induced cell polarity formation and cell elongation using Src knockout fibroblasts (SYFs) together with an inhibitor of Src. Normal and Src knockout fibroblasts were also transfected with a wild-type c-Src, dominant negative c-Src, or constitutively active c-Src gene to analyze the changes in cell morphology. SYF cells cultured on a glass substrate elongated symmetrically into spindle-shaped cells, with the formation of focal adhesions at both ends of the cells. When normal fibroblasts were treated with Src Inhibitor No. 5, a selective inhibitor of Src tyrosine kinases, they elongated into symmetrical spindle-shaped cells, similar to SYF cells. These results suggest that cell polarity during extension and elongation may be regulated by SFKs and that the expression and regulation of Src are important for the formation of polarity during cell elongation.
Highlights
Src family of protein tyrosine kinases (SFKs) consist of several proteins, i.e., Src, Fyn, Yes, Fgr, Lck, Hck, Blk, Lyn, Frk, and Yrk, that interact with the intracellular domains of growth factors/cytokine receptors, G proteincoupled receptors (GPCRs), and integrins [39,40,41,42]
Typical focal adhesions are formed at both ends of the cells, and many relatively small adhesive patch-like structures are observed at the center of the cells (Figure 1d, arrow; compare to Figure 1b for normal fibroblasts adhering to the coverslip)
Phosphotyrosine proteins are highly accumulated at the sites of focal adhesion in cells in culture, reflecting the involvement of these sites in signal transduction
Summary
Biomedicines 2021, 9, Cell polarity refers to the spatial, morphological, and structural asymmetry of cells and involves a characteristic spatial distribution of morphological, structural, and cellular components, i.e., the plasma membrane, cytoskeletal components, and sites of cell–cell adhesion (focal adhesions). Cell functions, such as transport, intracellular signaling, and mechanosensing, are dependent on the asymmetrical distribution of intracellular components. Epithelial cell polarity has an apical membrane–outer basal membrane orientation, and neural cell polarity is involved in the formation of two types of neurites, i.e., dendrites and axons [1]. Actin molecules switch between polymerization and depolymerization with the activation of Rho GTPases, a family of small
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