Functional antagonism between activin and osteogenic protein-1 in human embryonal carcinoma cells.
Activin A and osteogenic protein-1 (OP-1) exerted antagonistic effects on each other's responses on the human Tera-2 embryonal carcinoma cell line. OP-1 dose dependently inhibited activin A-induced activation of p3TP-Lux transcriptional reporter, containing part of the human plasminogen activator inhibitor-1 (PAI-1) promoter, while activin A inhibited OP-1-mediated alkaline phosphatase induction. Approximately equimolar concentrations of both growth factors resulted in 50% inhibition of the respective biological responses. Affinity cross-linking studies using 125I-activin A or 125I-OP-1 followed by receptor-immunoprecipitations revealed that both ligands bound to the activin type II receptor (ActR-II), but recruited different type I receptors. In addition, OP-1 competed with binding of 125I-activin A, and activin A competed with binding of 125I-OP-1 to ActR-II. Transient transfection studies showed that competition between activin A and OP-1 also occurred at the type I receptor (ActR-1) level; constitutively active (CA)-ActR-I inhibited CA-ActR-IB-mediated p3TP-Lux reporter induction. There was no competition between activin A and OP-1 for availability of Smad4, indicating that the concentration of this common signal transducer is not limiting for generating the observed biological responses. Overexpression of ActR-II abolished the inhibitory effect of OP-1 on activin A-induced p3TP-Lux activation and, surprisingly, led to OP-1-induced transcriptional reporter activity. Whereas the exact mechanism of competition is unclear, the role of ActR-II in the competition between activin A and OP-1 is discussed in light of the observed interference in downstream signaling by CA-ActR-I and CA-ActR-IB.
Piek
E
E
Department of Cell Biology, University of Nijmegen, The Netherlands.
Afrakhte
M
M
Sampath
K
K
van Zoelen
E J
EJ
Heldin
C H
CH
ten Dijke
P
P
D030201:Activin Receptors, Type I; D030301:Activin Receptors, Type II; D028341:Activins; D000469:Alkaline Phosphatase / Q000378:metabolism; D015152:Blotting, Northern; D055419:Bone Morphogenetic Protein 7; D019485:Bone Morphogenetic Proteins / Q000032:analysis / Q000235:genetics / Q000378:metabolism*; D004268:DNA-Binding Proteins / Q000235:genetics; D054278:Embryonal Carcinoma Stem Cells; D004789:Enzyme Activation / Q000502:physiology; D015971:Gene Expression Regulation, Enzymologic / Q000502:physiology; D015972:Gene Expression Regulation, Neoplastic / Q000502:physiology; D017930:Genes, Reporter; D006133:Growth Substances / Q000032:analysis / Q000235:genetics / Q000378:metabolism*; D006801:Humans; D007265:Inhibins / Q000032:analysis / Q000235:genetics / Q000378:metabolism*; D014411:Neoplastic Stem Cells / Q000737:chemistry / Q000201:enzymology*; D017395:Plasminogen Activator Inhibitor 1 / Q000235:genetics; D011401:Promoter Regions, Genetic / Q000502:physiology; D011485:Protein Binding / Q000502:physiology; D016755:Proto-Oncogene Proteins c-jun / Q000235:genetics; D012333:RNA, Messenger / Q000032:analysis; D017978:Receptors, Growth Factor / Q000378:metabolism; D051905:Smad6 Protein; D051906:Smad7 Protein; D015534:Trans-Activators / Q000235:genetics; D014158:Transcription, Genetic / Q000502:physiology; D016212:Transforming Growth Factor beta / Q000032:analysis / Q000235:genetics / Q000378:metabolism; D014407:Tumor Cells, Cultured / Q000737:chemistry / Q000201:enzymology
C525819:BMP7 protein, human; D055419:Bone Morphogenetic Protein 7; D019485:Bone Morphogenetic Proteins; D004268:DNA-Binding Proteins; D006133:Growth Substances; D017395:Plasminogen Activator Inhibitor 1; D016755:Proto-Oncogene Proteins c-jun; D012333:RNA, Messenger; D017978:Receptors, Growth Factor; C497802:SMAD6 protein, human; C497806:SMAD7 protein, human; D051905:Smad6 Protein; D051906:Smad7 Protein; D015534:Trans-Activators; D016212:Transforming Growth Factor beta; D028341:Activins; D007265:Inhibins; D030201:Activin Receptors, Type I; D030301:Activin Receptors, Type II; D000469:Alkaline Phosphatase