Up-regulation of a novel integrin alpha-chain (alpha mt) on human fetal myotubes.
Integrin expression and distribution was studied in cloned human fetal G6 myoblasts and myotubes. Immunoprecipitation of beta 1 integrins from surface iodinated and metabolically labeled G6 cells typically showed a five-fold induction of a beta 1 integrin associated protein upon differentiation. Under non-reducing conditions this beta 1 associated protein migrated as 145 kD. No such beta 1 associated protein was observed in the myogenic L8 rat cell line, before or after differentiation. The beta 1 integrin associated cell surface protein present in G6 myotubes remained associated with the beta 1 subunit in the presence of 1% Triton X-100 and 0.5 M NaCl. Like integrin alpha-chains, the protein dissociated from the beta 1 integrin subunit at low pH. Immunoprecipitation of G6 myotubes further indicated the presence of alpha 1, alpha 3, alpha 5, and alpha v integrins, and small amounts of alpha 4 and alpha 6 integrins. Immunodepletion with integrin alpha-chain antibodies to alpha 1, alpha 3, alpha 4, alpha 5, alpha 6, and alpha v integrin chains could not deplete the beta 1 integrin associated protein, indicating that it did not interact with any of these known integrin heterodimers. Upon treatment with reducing agents, the beta 1 integrin associated protein migrated in SDS-PAGE as a 155 kD protein. The decreased mobility in SDS-PAGE upon reduction is a feature shared with alpha 1, alpha 2, and alpha 9 integrin alpha-chains. Antibodies to alpha 1 immunoprecipitated an integrin heterodimer distinct from the 155 kD protein.(ABSTRACT TRUNCATED AT 250 WORDS)
Gullberg
D
D
Department of Animal Physiology, Uppsala University, Sweden.
Velling
T
T
Sjöberg
G
G
Sejersen
T
T
D002454:Cell Differentiation / Q000502:physiology; D002478:Cells, Cultured / Q000166:cytology / Q000502:physiology; D003429:Cross Reactions; D004591:Electrophoresis, Polyacrylamide Gel; D005333:Fetus / Q000502:physiology*; D005455:Fluorescent Antibody Technique; D018507:Gene Expression Regulation, Developmental / Q000502:physiology; D006801:Humans; D007150:Immunohistochemistry; D019012:Integrin beta1 / Q000235:genetics / Q000276:immunology / Q000648:ultrastructure*; D009132:Muscles / Q000166:cytology / Q000196:embryology* / Q000502:physiology; D011233:Precipitin Tests; D012333:RNA, Messenger / Q000032:analysis; D015854:Up-Regulation / Q000502:physiology
D019012:Integrin beta1; D012333:RNA, Messenger