Syndecan-4 distribution during the differentiation of satellite cells isolated from soleus muscle treated by phorbol ester and calphostin C.

It was shown that syndecans have a potential role in muscle development. We focused this study on the role of syndecan-4 distribution and phosphorylation during the differentiation of satellite cells isolated from Soleus muscle. Syndecans are cell surface heparan sulfate proteoglycans (HSPGs) that bind numerous ligands through their HS glycosaminoglycan chains (GAG). They play a role in cell-extracellular matrix and cell-cell adhesion, signal transduction and the targeting of growth factors and other molecules to the cell surface. Syndecan-4 acts as a co-receptor or, along with integrins, is localized to the cell membrane of focal contacts. Syndecan-4 participates in the organization of the structure of focal contacts reacting with extracellular matrix molecules. The interaction of syndecan-4 with protein kinase C (PKC) isoforms is the main mechanism regulating its distribution in cells. Our current study focused on the role of the distribution of syndecan-4, and its interactions with PKC isoforms during the differentiation of activated satellite cells. We used the PKC activator TPA (12-O-tetradecanoyl phorbol 13-acetate) and the PKC inhibitor Calphostin C (Cal C). We concluded that syndecan-4 was important not only in the activation of satellite cells, but also in myoblast differentiation. During our research, we observed the presence of syndecan-4 and changes in its location over the course of that process. We also showed that TPA and Cal C treatment had an influence on the subcellular distribution of syndecan-4, but there was no influence on myoblast differentiation. We speculated that the reason for changes after TPA treatment was the interactions with activated PKC alpha, which provoked syndecan-4/PKC alpha complex translocation to integrins. We also supposed that Cal C treatment inhibited PKC delta activity and probably induced PKC lpha association to syndecan-4, and syndecan-4 translocation to integrins.