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J. Cell Biol.,
Volume 145, Number 1, April 5, 1999 153-165
* Howard Hughes Medical Institute, Department of Physiology and Biophysics, Department of Neurology, University of Iowa
College of Medicine, Iowa City, Iowa 52242; The dystrophin-glycoprotein complex (DGC)
is a multisubunit complex that spans the muscle plasma
membrane and forms a link between the F-actin cytoskeleton and the extracellular matrix. The proteins of
the DGC are structurally organized into distinct subcomplexes, and genetic mutations in many individual
components are manifested as muscular dystrophy. We
recently identified a unique tetraspan-like dystrophin-associated protein, which we have named sarcospan
(SPN) for its multiple sarcolemma spanning domains
(Crosbie, R.H., J. Heighway, D.P. Venzke, J.C. Lee, and K.P. Campbell. 1997. J. Biol. Chem. 272:31221-31224).
To probe molecular associations of SPN within the
DGC, we investigated SPN expression in normal muscle as a baseline for comparison to SPN's expression in
animal models of muscular dystrophy. We show that, in
addition to its sarcolemma localization, SPN is enriched at the myotendinous junction (MTJ) and neuromuscular junction (NMJ), where it is a component of both the
dystrophin- and utrophin-glycoprotein complexes. We
demonstrate that SPN is preferentially associated with
the sarcoglycan (SG) subcomplex, and this interaction
is critical for stable localization of SPN to the sarcolemma, NMJ, and MTJ. Our experiments indicate that
assembly of the SG subcomplex is a prerequisite for
targeting SPN to the sarcolemma. In addition, the SG-
SPN subcomplex functions to stabilize Department of Pediatrics and Department of Anatomy and Neurobiology,
Washington University School of Medicine, St. Louis, Missouri 63110; and § Department of Human Genetics, University of
Michigan, Ann Arbor, Michigan 48109
-dystroglycan
to the muscle plasma membrane. Taken together, our
data provide important information about assembly
and function of the SG-SPN subcomplex.
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