Skeletal muscle is the biggest of the human body’s tissues in physiological conditions. It has an important function as a secretory organ, as it releases more than a hundred myokines and other peptides during physical activity. One of the most important myokines, which is released from skeletal muscle during muscle contraction, is interleukin-6 (IL-6). It is involved in processes such as myogenesis and muscle hypertrophy. During myogenesis, myoblasts fuse into multinucleated myotubes, which later form mucle fibers. IL-6 has anti-inflammatory properties, as it inhibits expression of cytokines TNF and IL-1. IL-6 also stimulates secretion of anti-inflammatory cytokines, such as IL-10 and IL-1ra. It is also one of the phosphorylated proteins of the secretory pathway. The human genome encodes genes for kinases from family Fam20, which include Fam20A, Fam20B and Fam20C. Each of these kinases has a different function. Kinase Fam20C phosphorylates more than a hundred secreted proteins and is allosterically activated by interaction with pseudokinase Fam20A. Fam20C substrates are involved in many biologically important processes, such as biomineralization, metabolism of phosphates, cell adhesion and migration and heart function. Fam20B phosphorylates xylose residues in proteoglicans. All three kinases have a signal peptide, that directs them into the secretory pathway.
The purpose of this research was to determine the expression of kinase Fam20C and preusokinase Fam20A in primary human skeletal muscle cells and rat skeletal muscle cell line L6. Using a real-time polymerase chain reaction and Western blot, we showed that all three kinases are expressed in human and rat skeletal muscle cells. We demonstrated that differentiation of these cells in fact does have an effect on Fam20C and Fam20A expression. We also concluded that the pattern of Fam20B expression is different than the expression Fam20C and Fam20A.
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