The vinculin/sarcomeric-alpha-actinin/alpha-actin nexus in cultured cardiac myocytes.
Experiments are described supporting the proposition that the assembly of stress fibers in non-muscle cells and the assembly of myofibrils in cardiac cells share conserved mechanisms. Double staining with a battery of labeled antibodies against membrane-associated proteins, myofibrillar proteins, and stress fiber proteins reveals the following: (a) dissociated, cultured cardiac myocytes reconstitute intercalated discs consisting of adherens junctions (AJs) and desmosomes at sites of cell-cell contact and sub-sarcolemmal adhesion plaques (SAPs) at sites of cell-substrate contact; (b) each AJ or SAP associates proximally with a striated myofibril, and conversely every striated myofibril is capped at either end by an AJ or a SAP; (C) the invariant association between a given myofibril and its SAP is especially prominent at the earliest stages of myofibrillogenesis; nascent myofibrils are capped by oppositely oriented SAPs; (d) the insertion of nascent myofibrils into AJs or into SAPs invariably involves vinculin, alpha-actin, and sarcomeric alpha-actinin (s-alpha-actinin); (e) AJs are positive for A-CAM but negative for talin and integrin; SAPs lack A-CAM but are positive for talin and integrin; (f) in cardiac cells all alpha-actinin-containing structures invariably are positive for the sarcomeric isoform, alpha-actin and related sarcomeric proteins; they lack non-s-alpha-actinin, gamma-actin, and caldesmon; (g) in fibroblasts all alpha-actinin-containing structures are positive for the non-sarcomeric isoform, gamma-actin, and related non-sarcomeric proteins, including caldesmon; and (h) myocytes differ from all other types of adherent cultured cells in that they do not assemble authentic stress fibers; instead they assemble stress fiber-like structures of linearly aligned I-Z-I-like complexes consisting exclusively of sarcomeric proteins.
Lu
M H
MH
Department of Anatomy, University of Pennsylvania Medical School, Philadelphia 19104-6058.
DiLullo
C
C
Schultheiss
T
T
Holtzer
S
S
Murray
J M
JM
Choi
J
J
Fischman
D A
DA
Holtzer
H
H
D000185:Actinin / Q000378:metabolism*; D000199:Actins / Q000378:metabolism*; D000818:Animals; D015152:Blotting, Northern; D002148:Calmodulin-Binding Proteins / Q000378:metabolism; D002478:Cells, Cultured; D002642:Chick Embryo; D016023:Integrins / Q000378:metabolism; D008856:Microscopy, Fluorescence; D009206:Myocardium / Q000378:metabolism*; D012518:Sarcomeres / Q000378:metabolism*; D016608:Talin / Q000378:metabolism; D016596:Vinculin / Q000378:metabolism*
D000199:Actins; D002148:Calmodulin-Binding Proteins; D016023:Integrins; D016608:Talin; D000185:Actinin; D016596:Vinculin