title: Stem cell antigen-1 is necessary for cell-cycle withdrawal and myoblast differentiation in C2C12 cells.
abstract: Extracellular signaling pathways regulating myoblast differentiation and cell-cycle withdrawal are not completely understood. Stem cell antigen-1 (Sca-1/Ly-6A/E) is a glycosylphosphatidylinositol-anchored membrane protein known for its role in T-cell activation, and recently described as a marker for regeneration-competent myoblasts. We previously determined that expression of Sca-1/Ly-6A is transiently upregulated during myocyte cell-cycle withdrawal; however, a specific function for Sca-1 in myogenesis has not been described. Here, we show that Sca-1 expression on the surface of a subpopulation of differentiating C2C12 myoblasts is maximal at the time of cell-cycle withdrawal, and that blocking Sca-1 with monoclonal antibodies or downregulating Sca-1 expression by antisense both promotes proliferation and inhibits myotube formation. Downregulating Sca-1 expression derepresses Fyn at the time of myoblast cell-cycle withdrawal, and dominant-negative and constitutively active Fyn mutants rescue and recapitulate the Sca-1 antisense phenotype, respectively. This suggests a Fyn-mediated mechanism for Sca-1 action. Thus, we demonstrate an unprecedented role for Sca-1 in early myogenesis in C2C12 cells, and propose a novel pathway from the myoblast cell surface to intracellular signaling networks controlling proliferation versus differentiation in mammalian muscle. These findings suggest that, beyond its role as a marker for muscle progenitors, Sca-1 may be an important therapeutic target for promoting muscle regeneration.
authors.affiliation: Cardiovascular Research Institute, University of California, San Francisco, CA 94143, USA.
authors.forename: Conrad L
authors.initials: CL
authors.lastname: Epting
authors.forename: Javier E
authors.initials: JE
authors.lastname: López
authors.forename: Xun
authors.initials: X
authors.lastname: Shen
authors.forename: Liansen
authors.initials: L
authors.lastname: Liu
authors.forename: James
authors.initials: J
authors.lastname: Bristow
authors.forename: Harold S
authors.initials: HS
authors.lastname: Bernstein
mesh_terms: D000818:Animals; D000911:Antibodies, Monoclonal / Q000737:chemistry; D000945:Antigens, Differentiation, T-Lymphocyte / Q000502:physiology*; D000950:Antigens, Ly / Q000096:biosynthesis / Q000235:genetics* / Q000502:physiology*; D001973:Bromodeoxyuridine / Q000494:pharmacology; D002453:Cell Cycle; D002454:Cell Differentiation; D002460:Cell Line; D002462:Cell Membrane / Q000378:metabolism; D049109:Cell Proliferation; D004396:Coloring Agents / Q000494:pharmacology; D004305:Dose-Response Relationship, Drug; D015536:Down-Regulation; D005434:Flow Cytometry; D005799:Genes, Dominant; D005822:Genetic Vectors; D017261:Glycosylphosphatidylinositols / Q000378:metabolism; D015151:Immunoblotting; D008565:Membrane Proteins / Q000096:biosynthesis / Q000235:genetics* / Q000502:physiology*; D051379:Mice; D008810:Mice, Inbred C57BL; D032342:Muscle Cells / Q000166:cytology; D018482:Muscle, Skeletal / Q000166:cytology; D009132:Muscles / Q000166:cytology / Q000502:physiology; D009154:Mutation; D032446:Myoblasts / Q000166:cytology* / Q000378:metabolism; D016376:Oligonucleotides, Antisense / Q000737:chemistry; D010641:Phenotype; D011518:Proto-Oncogene Proteins / Q000378:metabolism; D051076:Proto-Oncogene Proteins c-fyn; D012038:Regeneration; D015398:Signal Transduction; D013234:Stem Cells / Q000166:cytology / Q000378:metabolism; D013997:Time Factors; D014162:Transfection; D015854:Up-Regulation; D019061:src-Family Kinases / Q000378:metabolism
chemical_list: D000911:Antibodies, Monoclonal; D000945:Antigens, Differentiation, T-Lymphocyte; D000950:Antigens, Ly; D004396:Coloring Agents; D017261:Glycosylphosphatidylinositols; C074650:Ly6a protein, mouse; D008565:Membrane Proteins; D016376:Oligonucleotides, Antisense; D011518:Proto-Oncogene Proteins; C494960:Fyn protein, mouse; D051076:Proto-Oncogene Proteins c-fyn; D019061:src-Family Kinases; D001973:Bromodeoxyuridine