Involvement of Ras/Raf/AP-1 in BMP-4 signaling during Xenopus embryonic development.
Previously, we elucidated the role of bone morphogenetic protein 4 (BMP-4) in the dorsal-ventral patterning of the Xenopus embryo by using a dominant negative mutant of the BMP-4 receptor (DN-BR). The present paper describes the involvement of Ras, Raf, and activator protein 1 (AP-1) in BMP-4 signaling during Xenopus embryonic development. The AP-1 activity was determined by injecting an AP-1-dependent luciferase reporter gene into two-cell-stage Xenopus embryos and measuring the luciferase activity at various developmental stages. We found that injection of BMP-4 mRNA increased AP-1 activity, whereas injection of DN-BR mRNA inhibited AP-1 activity. Similar inhibitory effects were seen with injection of mRNAs encoding dominant negative mutants of c-Ha-Ras, c-Raf, or c-Jun. These results suggest that the endogenous AP-1 activity is regulated by BMP-4/Ras/Raf/Jun signals. We next investigated the effects of Ras/Raf/AP-1 signals on the biological functions of BMP-4. DN-BR-induced dorsalization of the embryo, revealed by the formation of a secondary body axis or dorsalization of the ventral mesoderm explant analyzed by histological and molecular criteria, was significantly reversed by coinjection of [Val12]Ha-Ras, c-Raf, or c-Jun mRNA. Furthermore, the BMP-4-stimulated erythroid differentiation in the ventral mesoderm was substantially inhibited by coinjection with the dominant negative c-Ha-Ras, c-Raf, or c-Jun mutant. Our results suggest the involvement of Ras/Raf/AP-1 in the BMP-4 signaling pathway.
Xu
R H
RH
Laboratory of Biochemical Physiology, National Cancer Institute-Frederick Cancer Research and Development Center, MD 21702-1201, USA.
Dong
Z
Z
Maeno
M
M
Kim
J
J
Suzuki
A
A
Ueno
N
N
Sredni
D
D
Colburn
N H
NH
Kung
H F
HF
D000818:Animals; D019485:Bone Morphogenetic Proteins; D004627:Embryonic Induction; D004920:Erythropoiesis / Q000502:physiology; D008648:Mesoderm; D008954:Models, Biological; D009154:Mutation; D017346:Protein Serine-Threonine Kinases / Q000235:genetics / Q000378:metabolism; D011506:Proteins / Q000378:metabolism*; D011518:Proto-Oncogene Proteins / Q000235:genetics / Q000378:metabolism*; D016755:Proto-Oncogene Proteins c-jun / Q000235:genetics / Q000378:metabolism; D019908:Proto-Oncogene Proteins c-raf; D016283:Proto-Oncogene Proteins p21(ras) / Q000235:genetics / Q000378:metabolism; D015398:Signal Transduction; D016378:Tissue Transplantation; D018808:Transcription Factor AP-1 / Q000235:genetics / Q000378:metabolism*; D014981:Xenopus / Q000196:embryology*
D019485:Bone Morphogenetic Proteins; D011506:Proteins; D011518:Proto-Oncogene Proteins; D016755:Proto-Oncogene Proteins c-jun; D018808:Transcription Factor AP-1; D017346:Protein Serine-Threonine Kinases; D019908:Proto-Oncogene Proteins c-raf; D016283:Proto-Oncogene Proteins p21(ras)