Sublytic terminal complement attack on myotubes decreases the expression of mRNAs encoding muscle-specific proteins.
Activation of inflammatory and cytotoxic complement effectors that include the C5b-9 complex plays an important pathogenic role in myasthenia gravis, an inflammatory autoimmune disease of the muscle. Altered muscle-specific gene expression has been observed in experimental myasthenic rats. In this study, we have examined the effect of sublytic C5b-9 on myotubes differentiated from C2C12 myoblasts, by generating C5b-9 with C7-deficient serum with or without C7. Within 2 h, C7-deficient serum plus C7, compared with C7-deficient serum alone, induced markedly decreased levels of mRNAs encoding alpha-actin, troponin I slow twitch isoform, acetylcholine receptor alpha, and muscle aldolase A, whereas the heat shock protein 83 mRNA level remained constant, by northern analysis. Because the half-life of the acetylcholine receptor alpha was estimated to be > 8 h, the C5b-9 effect was, in part, due to enhanced mRNA decay. Because C5b-9 also induced c-jun mRNA and reduced the myoD mRNA level, a possible inhibition of muscle gene transcription by C5b-9 was examined in myotubes transfected with troponin promoter-luciferase gene constructs. Luciferase activity was reduced to 50% in response to C5b-9 at 2 h. Thus, C5b-9 appears to inhibit the muscle-specific gene expression by stimulating mRNA decay and by decreasing the transcription process. The data also indicate a possible pathogenic role of C5b-9 in immune-mediated inflammatory muscle disorders in which complement activation has been implicated.
Lang
T J
TJ
Department of Pathology, University of Maryland School of Medicine, Baltimore, USA.
Badea
T C
TC
Wade
R
R
Shin
M L
ML
D000818:Animals; D015152:Blotting, Northern; D002454:Cell Differentiation / Q000235:genetics; D002478:Cells, Cultured / Q000737:chemistry / Q000187:drug effects / Q000502:physiology; D015938:Complement Membrane Attack Complex / Q000737:chemistry / Q000494:pharmacology*; D005786:Gene Expression Regulation / Q000187:drug effects; D051379:Mice; D018485:Muscle Fibers, Skeletal / Q000166:cytology / Q000187:drug effects* / Q000502:physiology; D009124:Muscle Proteins / Q000235:genetics*; D011401:Promoter Regions, Genetic / Q000502:physiology; D011519:Proto-Oncogenes / Q000502:physiology; D012333:RNA, Messenger / Q000378:metabolism; D011950:Receptors, Cholinergic / Q000235:genetics; D014157:Transcription Factors / Q000235:genetics; D014158:Transcription, Genetic / Q000502:physiology; D019210:Troponin I / Q000737:chemistry / Q000235:genetics
D015938:Complement Membrane Attack Complex; D009124:Muscle Proteins; D012333:RNA, Messenger; D011950:Receptors, Cholinergic; D014157:Transcription Factors; D019210:Troponin I