Skeletal muscle expression of the adhesion-GPCR CD97: CD97 deletion induces an abnormal structure of the sarcoplasmatic reticulum but does not impair skeletal muscle function.

Tatiana Zyryanova,Gabriela Aust,Rick Schneider,Doreen Sittig,Christiane Kerner,Jochen Neuhaus,Henrik Ruffert,Claudia Gebhardt,Volker Adams,Karla Punkt,Jörg Hamann,Stefan Glasmacher,Pierre Hepp,Laszlo Csernoch

doi:10.1371/journal.pone.0100513

Tatiana Zyryanova, Gabriela Aust + Show 12 more

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https://doi.org/10.1371/journal.pone.0100513

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Abstract

CD97 is a widely expressed adhesion class G-protein-coupled receptor (aGPCR). Here, we investigated the presence of CD97 in normal and malignant human skeletal muscle as well as the ultrastructural and functional consequences of CD97 deficiency in mice. In normal human skeletal muscle, CD97 was expressed at the peripheral sarcolemma of all myofibers, as revealed by immunostaining of tissue sections and surface labeling of single myocytes using flow cytometry. In muscle cross-sections, an intracellular polygonal, honeycomb-like CD97-staining pattern, typical for molecules located in the T-tubule or sarcoplasmatic reticulum (SR), was additionally found. CD97 co-localized with SR Ca2+-ATPase (SERCA), a constituent of the longitudinal SR, but not with the receptors for dihydropyridine (DHPR) or ryanodine (RYR), located in the T-tubule and terminal SR, respectively. Intracellular expression of CD97 was higher in slow-twitch compared to most fast-twitch myofibers. In rhabdomyosarcomas, CD97 was strongly upregulated and in part more N-glycosylated compared to normal skeletal muscle. All tumors were strongly CD97-positive, independent of the underlying histological subtype, suggesting high sensitivity of CD97 for this tumor. Ultrastructural analysis of murine skeletal myofibers confirmed the location of CD97 in the SR. CD97 knock-out mice had a dilated SR, resulting in a partial increase in triad diameter yet not affecting the T-tubule, sarcomeric, and mitochondrial structure. Despite these obvious ultrastructural changes, intracellular Ca2+ release from single myofibers, force generation and fatigability of isolated soleus muscles, and wheel-running capacity of mice were not affected by the lack of CD97. We conclude that CD97 is located in the SR and at the peripheral sarcolemma of human and murine skeletal muscle, where its absence affects the structure of the SR without impairing skeletal muscle function.

Highlights

CD97 is a member of the adhesion-class of G-protein coupled receptor, which are non-canonical seven-transmembrane (7TM) molecules with essential roles in planar cell and tissue polarity, development, tumorigenesis, and immunity [1,2]. aGPCRs possess a unique structure with an unusual, large extracellular part containing various protein domains and a juxtamembranous GPCR autoproteolysis-inducing (GAIN) domain [2]
To examine which fiber type more strongly expresses CD97, skeletal muscles were co-stained for CD97 together with myosin heavy chain (MHC) and sarco(endo)plasmatic reticulum Ca2+-adenosine triphosphatase (ATPase) (SERCAs)
We report here that normal human and murine skeletal muscles express the aGPCR CD97

Summary

Introduction

CD97 is a member of the adhesion-class of G-protein coupled receptor (aGPCR), which are non-canonical seven-transmembrane (7TM) molecules with essential roles in planar cell and tissue polarity, development, tumorigenesis, and immunity [1,2]. aGPCRs possess a unique structure with an unusual, large extracellular part containing various protein domains and a juxtamembranous GPCR autoproteolysis-inducing (GAIN) domain [2]. AGPCRs possess a unique structure with an unusual, large extracellular part containing various protein domains and a juxtamembranous GPCR autoproteolysis-inducing (GAIN) domain [2]. The GAIN domain facilitates cleavage into an extracellular N-terminal fragment (NTF) and a C-terminal fragment (CTF) containing the 7TM and the intracellular domain (ICD). Both fragments, i.e. the NTF and CTF, remain noncovalently associated during expression at the cell surface [3,4]. CD97 is one of the most widely distributed aGPCRs, expressed by all leukocytes and various normal and malignant epithelial cells [5,6,7,8,9]. CD97 is upregulated in several carcinomas, where it probably increases tumor cell migration [6,8,17]

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