Sequential disassembly of myofibrils induced by myristate acetate in cultured myotubes.
The phorbol ester TPA induces the sequential disassembly of myofibrils. First the alpha-actin thin filaments are disrupted and then, hours later, the myosin heavy chain (MHC) thick filaments. TPA does not induce the disassembly of the beta- and gamma-actin thin filaments of stress fibers in presumptive myoblasts or fibroblasts, nor does it block the reemergence of stress fibers in 72-h myosacs that have been depleted of all myofibrillar molecules. There are differences in where, when, and how myofibrillar alpha-actin and MHC are degraded and eliminated from TPA-myosacs. Though the anisodiametric myotubes have begun to retract into isodiametric myosacs after 5 h in TPA, staining with anti-MHC reveals normal tandem A bands. In contrast, staining with mAb to muscle actin fails to reveal tandem I bands. Instead, both mAb to muscle actin and rhophalloidin brilliantly stain numerous disk-like bodies approximately 3.0 micron in diameter. These muscle actin bodies do not fuse with one another, nor do they costain with anti-MHC. All muscle actin bodies and/or molecules disappear in 36-h myosacs. The collapse of A bands is first initiated in 10-h myosacs. Their loss correlates with the appearance of immense, amorphous MHC patches. MHC patches range from a few micrometers to over 60 micron in size. They do not costain with antimuscle actin or rho-phalloidin. While diminishing in number and fluorescence intensity, MHC aggregates are present in 30% of the 72-h myosacs. Myosacs removed from TPA rapidly elongate, and after 48 h display normal newly assembled myofibrils. TPA reversibly blocks incorporation of [35S]methionine into myofibrillar alpha-actin, MHC, myosin light chains 1 and 2, the tropomyosins, and troponin C. It does not block the synthesis of beta- or gamma-actins, the nonmyofibrillar MHC or light chains, tubulin, vimentin, desmin, or most household molecules.
Lin
Z X
ZX
Department of Anatomy, School of Medicine, University of Pennsylvania, Philadelphia 19104-6058.
Eshelman
J R
JR
Forry-Schaudies
S
S
Duran
S
S
Lessard
J L
JL
Holtzer
H
H
D000199:Actins / Q000378:metabolism; D000818:Animals; D002478:Cells, Cultured; D002642:Chick Embryo; D009124:Muscle Proteins / Q000096:biosynthesis; D009132:Muscles / Q000166:cytology / Q000187:drug effects / Q000648:ultrastructure; D009210:Myofibrils / Q000187:drug effects / Q000648:ultrastructure*; D013755:Tetradecanoylphorbol Acetate / Q000494:pharmacology*
D000199:Actins; D009124:Muscle Proteins; D013755:Tetradecanoylphorbol Acetate