Phosphorylation of Heat Shock Protein 27 is Increased by Cast Immobilization and by Serum-free Starvation in Skeletal Muscles

Abstract

[Purpose] Cast immobilization- and cell starvation-induced loss of muscle mass are closely associated with a dramatic reduction in the structural muscle proteins. Heat shock proteins are molecular chaperones that are constitutively expressed in several eukaryotic cells and have been shown to protect against various stressors. However, the changes in the phosphorylation of atrophy-related heat shock protein 27 (HSP27) are still poorly understood in skeletal muscles. In this study, we examine whether or not phosphorylation of HSP27 is changed in the skeletal muscles after cast immobilization and serum-free starvation with low glucose in a time-dependent manner. [Methods] We undertook a HSP27 expression and high-resolution differential proteomic analysis in skeletal muscles. Furthermore, we used western blotting to examine protein expression and phosphorylation of HSP27 in atrophied gastrocnemius muscle strips and L6 myoblasts. [Results] Cast immobilization and starvation significantly upregulated the phosphorylation of HSP27 in a time-dependent manner, respectively. [Conclusion] Our results suggest that cast immobilization- and serum-free starvation-induced atrophy may be in part related to changes in the phosphorylation of HSP27 in rat skeletal muscles.

Keywords: Cast immobilization and serum-free starvation; Heat shock protein 27; Muscle atrophy.

Fig. 1.

Changes in phosphorylation of HSP27 and schematic representation of cellular response caused by cast immobilization and serum-free starvation with a low concentration of glucose in skeletal muscles. Proteomic (A) and immunoblotting (B) analysis in cast-immobilized skeletal muscle. 2DE and 1DE, two- and one-dimensional gel electrophoresis; HSP27, heat shock protein 27; PS, peptide sequence; R, arginine (Arg); V, valine (Val); P, proline (Pro); F, phenylalanine (Phe); S, serine (Ser); L, leucine (Leu); D, aspartic acid (Asp); Q, glutamine (Gln); A, alanine (Ala); G, glycine (Gly); N, asparagine (Asn); H, histidine (His); E, glutamic acid (Glu); T, threonine (Thr); K, lysine (Lys); I, isoleucine (Ile); FBS, fetal bovine serum; d, days; h, hours; p, phosphorylated protein; HSF, heat shock transcription factor; HSE, heat shock response element; HSPs, heat shock proteins (Kim et al.1⁾).