Heparan sulfate chain valency controls syndecan-4 function in cell adhesion.
Fibroblasts null for the transmembrane proteoglycan, syndecan-4, have an altered actin cytoskeleton, compared with matching wild-type cells. They do not organize alpha-smooth muscle actin into bundles, but will do so when full-length syndecan-4 is re-expressed. This requires the central V region of the core protein cytoplasmic domain, though not interactions with PDZ proteins. A second key requirement is multiple heparan sulfate chains. Mutant syndecan-4 with no chains, or only one chain, failed to restore the wild-type phenotype, whereas those expressing two or three were competent. However, clustering of one-chain syndecan-4 forms with antibodies overcame the block, indicating that valency of interactions with ligands is a key component of syndecan-4 function. Measurements of focal contact/adhesion size and focal adhesion kinase phosphorylation correlated with syndecan-4 status and alpha-smooth muscle actin organization, being reduced where syndecan-4 function was compromised by a lack of multiple heparan sulfate chains.
Gopal
Sandeep
S
Department of Biomedical Sciences, University of Copenhagen, 2200 Copenhagen N, Denmark.
Bober
Adam
A
Whiteford
James R
JR
Multhaupt
Hinke A B
HA
Yoneda
Atsuko
A
Couchman
John R
JR
D000199:Actins / Q000378:metabolism*; D000595:Amino Acid Sequence; D000818:Animals; D015153:Blotting, Western; D019556:COS Cells; D002448:Cell Adhesion; D002478:Cells, Cultured; D002522:Chlorocebus aethiops; D003599:Cytoskeleton / Q000378:metabolism; D004622:Embryo, Mammalian / Q000166:cytology / Q000378:metabolism; D005347:Fibroblasts / Q000378:metabolism*; D005353:Fibronectins / Q000378:metabolism; D051416:Focal Adhesion Protein-Tyrosine Kinases / Q000378:metabolism; D006497:Heparan Sulfate / Q000502:physiology*; D006801:Humans; D051379:Mice; D018345:Mice, Knockout; D008856:Microscopy, Fluorescence; D008969:Molecular Sequence Data; D010766:Phosphorylation; D011509:Proteoglycans / Q000378:metabolism; D053671:Syndecan-4 / Q000502:physiology*
D000199:Actins; D005353:Fibronectins; D051416:Focal Adhesion Protein-Tyrosine Kinases; D006497:Heparan Sulfate; D011509:Proteoglycans; D053671:Syndecan-4; C544013:alpha-smooth muscle actin, mouse