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

Yuki Sugiyama,Atsushi Suzuki,Masaru Kishikawa,Rika Akutsu,Tomonori Hirose,Mary M.Y Waye,Stephan K.W Tsui,Shosei Yoshida,Shigeo Ohno

doi:10.1074/jbc.275.2.1095

Yuki Sugiyama, Atsushi Suzuki + Show 7 more

Open Access

https://doi.org/10.1074/jbc.275.2.1095

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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, alphaB-crystallin, p20, MKBP/HSPB2, and HSPB3, omitting lens-specific alphaA-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, alphaB-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 alphaB-crystallin, but not for MKBP/HSPB2; and 3) sHSPs whose mRNAs are induced by heat shock are alphaB-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.

Highlights

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
The functional divergence among sHSPs in different oligomers is 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
Identification of a Novel sHSP with a Molecular Mass of 17 kDa Corresponding to HSPB3 cDNA—Among the six members of the mammalian sHSP family so far reported, HSPL27 is the only one that has not been identified at the protein level [27]

Summary

Introduction

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. Northern blot and RT-PCR analysis of the total RNA from differentiating C2C12 cells at the indicated times reveal the following features of sHSP expression (Fig. 4, a and c): 1) the amount of HSP27 mRNA remains unchanged during differentiation; 2) the mRNA for ␣B-crystallin is upregulated in conjunction with the induction of myogenin mRNA; 3) the mRNAs for MKBP/HSPB2 and HSPB3 are induced at a later stage of differentiation; and 4) the amount of p20 mRNA decreases somewhat during differentiation.

Results

Conclusion