Muscle Develops a Specific Form of Small Heat Shock Protein Complex Composed of MKBP/HSPB2 and HSPB3 during Myogenic Differentiation

Abstract

Previously, we identified a new mammalian sHSP, MKBP, as a myotonic dystrophy protein kinase-binding protein, and suggested its important role in muscle maintenance (Suzuki, A., Sugiyama, Y., Hayashi, Y., Nyu-i, N., Yoshida, M., Nonaka, I., Ishiura, S., Arahata, K., and Ohno, S. (1998) J. Cell Biol. 140, 1113-1124). In this paper, we develop the former work by performing extensive characterization of five of the six sHSPs so far identified, that is, HSP27, ␣B-crystallin, p20, MKBP/ HSPB2, and HSPB3, omitting lens-specific ␣A-crystallin. Tissue distribution analysis revealed that although each sHSP shows differential constitutive expression in restricted tissues, tissues that express all five sHSPs are only muscle-related tissues. Especially, the expressions of HSPB3, identified for the first time as a 17-kDa protein in this paper, and MKBP/HSPB2 are distinctly specific to muscles. Moreover, these sHSPs form an oligomeric complex with an apparent molecular mass of 150 kDa that is completely independent of the oligomers formed by HSP27, ␣B-crystallin, and p20. The expressions of MKBP/HSPB2 and HSPB3 are induced during muscle differentiation under the control of MyoD, suggesting that the sHSP oligomer comprising MKBP/ HSPB2 and HSPB3 represents an additional system closely related to muscle function. The functional divergence among sHSPs in different oligomers is also demonstrated in several ways: 1) an interaction with myotonic dystrophy protein kinase, which has been suggested to be important for the maintenance of myofibril integrity, was observed only for MKBP/HSPB2; 2) a myotube-specific association with actin bundles was observed for HSP27 and ␣B-crystallin, but not for MKBP/ HSPB2; and 3) sHSPs whose mRNAs are induced by heat shock are ␣B-crystallin and HSP27. Taken together, the results suggest that muscle cells develop two kinds of stress response systems composed of diverged sHSP members, and that these systems work independently in muscle maintenance and differentiation.Heat shock and numerous other stress conditions lead to the rapid induction of several genes whose protein products, collectively called heat shock proteins (HSPs), 1 play protective roles in cell survival (1). Considering that muscles are frequently subjected to severe conditions caused by heat, oxidative, and mechanical stresses, especially during exercise (2), these HSPs may be especially important in this particular tissue. In fact, several HSPs, including HSP60, 70, and 90, have been shown to be induced after exhaustive exercise (3). In addition, the inducible isoform of HSP70 has been shown to be constitutively expressed in a certain type of skeletal muscle fiber (4), suggesting that muscle cells are chronically ready to respond to frequent stresses. However, there have been limited numbers of studies that focus on HSPs in muscle cells.HSPs with low molecular masses of 15-30 kDa are called small heat shock proteins (sHSPs); they commonly share a homologous sequence of about 80 amino acids called the "␣-crystallin domain" (5). Among ...

The response profiles of HSPA12A and TCTP from Mytilus galloprovincialis to pathogen and cadmium challenge

“…In the present study, the expression of MgTCTP mRNA was dominantly detected in muscle, which was different from previous report on Venerupis philippinarum TCTP [11]. It was suggested that MgTCTP perhaps played an important role in muscle maintenance of M. galloprovincialis, as this tissue was frequently affected by heat, oxidative and mechanical stress [31]. Additionally, the high expression level of MgHSPA12A and MgTCTP in gonad perhaps indicated an essential role in reproductive processes, which was in agreement with Kappé et al, who found that some sHSPs were specially expressed in human testis [32].…”

Small heat-shock proteins: important players in regulating cellular proteostasis

“…Moreover, as a result of their ubiquitous role in interacting with and stabilising a wide range of partially unfolded proteins against aggregation, sHsps are involved in many processes central to disease development and manifestation. These include cellular growth and differentiation [84,162,163]; interaction with cytoskeletal components such as actin and intermediate filaments [70,164,165]; and apoptosis [166]. Several of the sHsp family members (Hsp27, HSPB2, Hsp27, Hsp20 and Bc) have been attributed a protective role in the development of neurodegenerative and neuromuscular diseases, roles thought to be related to their abilities to both stabilise target proteins and to interact with cytoskeletal elements as the key features of these diseases are protein aggregation and defective axonal transport [70].…”

“…To-date, there is also evidence for the formation of hetero-oligomeric complexes between αA-and αBc [37,54], αAc and Hsp27 [81], HspB2 and HspB3 [84,85], αBc and Hsp20 [86] and Hsp27 and Hsp20 [82]. However, caution is required in interpreting work that has involved adding a bulky tag directly to the sHsps to measure sub-unit exchange (e.g.…”

Different anti-aggregation and pro-degradative functions of the members of the mammalian sHSP family in neurological disorders

“…maintaining myofibrillar integrity [25] HSPB4 (aAcrystallin) brain: not reported low in: sciatic nerve [2] none none n.a.…”

“…activation of DMPK [24]; maintaining myofibrillar integrity [25] HSPB3 (HSPL27) low in: cortex, cerebellum, spinal cord, sciatic nerve (RT qPCR) [1][2][3] high [4] high [4] n.a.…”