title: Localization of the transmembrane proteoglycan syndecan-4 and its regulatory kinases in costameres of rat cardiomyocytes: a deconvolution microscopic study.
abstract: Syndecan-4 (syn-4), a transmembrane heparan sulfate-containing proteoglycan, is unique among the four members of the syndecan family in its specific cellular localization to complex cytoskeletal adhesion sites, i.e., focal adhesions. During early phenotypic redifferentiation of neonatal cardiomyocytes in culture, immunolocalization reveals syn-4 to be heavily concentrated in the perinuclear endoplasmic reticulum-Golgi region, with little found at the peripheral regions. Subsequently, syn-4 becomes localized to a cytoskeletal adhesion complex unique to striated muscle, the costamere. Soon after redifferentiation of myofibrils in cultured neonatal cardiomyocytes, syn-4 is present only in costameres, not in focal adhesions. In cultured adult cardiomyocytes, it is present in both costameres and focal adhesions-the latter in two distinct regions of the spread cardiomyocytes, reflecting localization with two types of actin-containing filaments. The fact that syn-4 is observed early in the costameric regions, as opposed to later in the focal adhesions, suggests that it may play an initial role in early adhesion/signal transduction mechanisms in close proximity to the contractile apparatus, as well as in transmission of contractile force to the collagenous extracellular matrix (ECM) which surrounds the cardiac myofibers in situ. With respect to possible regulatory mechanisms of syn-4, we localized syn-4 with both the epsilon isoform of protein kinase C and the tyrosine kinase pp60(csrc) in costameric regions. These findings suggest that syn-4 may not only play a role in cellular adhesion and contractile force transmission, it may also, through ser, thr, and tyr phosphorylation, be part of an interactive signal transduction mechanism in myocardial functioning via these adhesive cytoskeletal complexes.
authors.affiliation: Department of Pathology and Laboratory Medicine, University of Texas Medical School at Houston, Houston, Texas 77030, USA. w.b.van.winkle@uth.tmc.edu
authors.forename: W Barry
authors.initials: WB
authors.lastname: VanWinkle
authors.forename: Mark B
authors.initials: MB
authors.lastname: Snuggs
authors.forename: Eugenio L
authors.initials: EL
authors.lastname: De Hostos
authors.forename: L Maximilian
authors.initials: LM
authors.lastname: Buja
authors.forename: Anne
authors.initials: A
authors.lastname: Woods
authors.forename: John R
authors.initials: JR
authors.lastname: Couchman
mesh_terms: D000818:Animals; D000831:Animals, Newborn; D002454:Cell Differentiation / Q000502:physiology; D002462:Cell Membrane / Q000201:enzymology / Q000378:metabolism*; D002478:Cells, Cultured; D003599:Cytoskeleton / Q000378:metabolism / Q000648:ultrastructure; D005109:Extracellular Matrix / Q000378:metabolism / Q000648:ultrastructure; D022001:Focal Adhesions / Q000378:metabolism / Q000648:ultrastructure; D049452:Green Fluorescent Proteins; D007150:Immunohistochemistry; D007527:Isoenzymes / Q000378:metabolism; D008164:Luminescent Proteins; D008297:Male; D008562:Membrane Glycoproteins / Q000378:metabolism* / Q000648:ultrastructure; D018613:Microscopy, Confocal; D009119:Muscle Contraction / Q000502:physiology; D009206:Myocardium / Q000201:enzymology* / Q000648:ultrastructure; D032383:Myocytes, Cardiac / Q000201:enzymology* / Q000648:ultrastructure; D009210:Myofibrils / Q000378:metabolism / Q000648:ultrastructure; D011493:Protein Kinase C / Q000378:metabolism; D051744:Protein Kinase C-epsilon; D017434:Protein Structure, Tertiary / Q000502:physiology; D011509:Proteoglycans / Q000378:metabolism* / Q000648:ultrastructure; D016392:Proto-Oncogene Proteins pp60(c-src) / Q000378:metabolism; D051381:Rats; D017207:Rats, Sprague-Dawley; D015398:Signal Transduction / Q000502:physiology; D053671:Syndecan-4
chemical_list: D007527:Isoenzymes; D008164:Luminescent Proteins; D008562:Membrane Glycoproteins; D011509:Proteoglycans; C508307:Sdc4 protein, rat; D053671:Syndecan-4; D049452:Green Fluorescent Proteins; C497257:Prkce protein, rat; D016392:Proto-Oncogene Proteins pp60(c-src); D011493:Protein Kinase C; D051744:Protein Kinase C-epsilon