RAAIJ A.J.M. オランダ国立発生生物学研究所, 上級研究員
SHOJI Hiroki Kagawa Medical University, Research Associate, 助手 (10263873)
NAKAMURA Takanori Kagawa Medicla University, Professor, 教授 (70183887)
EIJNDENーVAN オランダ国立発生生物学研究所, 上級研究員
EIJNDEN-VAN RAAIJ A.J.M. Netherlands Institute for Developmental Biology, Staff Scientist
|Budget Amount *help
¥2,400,000 (Direct Cost : ¥2,400,000)
Fiscal Year 1997 : ¥2,400,000 (Direct Cost : ¥2,400,000)
Activin belonging to the TGF-beta superfamily binds to and signals through a receptor complex comprising two transmembrane serine/threonine kinases, called type I and type II.So far, two type II (ActR-IIA,-IIB) and two type I (ActRA-IA,IB) activin receptors have been cloned from mammalian sources. In this study, we attempted to elucidate the role of type I receptors in activin signaling for growth, differentiation and apoptosis, and obtained following results.
(1) We established stable HS-72 transfectants overexpressing ActR-IA or ActR-IB by the electroporation procedure. Overexpression of ActR-IA suppressed activin-induced cell-cycle arrest in the G1 phase caused by inhibition of retinoblastoma protein phosphorylation through induction of p21, a cyclin-dependent kinase inhibitor, and subsequent apoptosis. In contrast, HS-72 clones that overexpressed ActR-IB significantly facilitated activin induced apoptosis. These results indicate that ActRA-IA and ActR-IB are distinct from each other
in activin signal transduction.
(2) Follistain (activin-binding protein) was found to promote the binding of activin to cell surface heparan sulfate. When the cells were incubated with ^<125>I-activin in the presence of follistatin, significant degradation of activin was observed.This activin degradation was abolished by heparan sulfate, chloroquine, and lysosomal protease inhibitors. These results indicate that cell-associated follistain accelerates the uptake of activin into cells, leading to increased degradation by lysosomal enzymes, and thus plays a role in the activin clearance system.
(3) In order to understand the role of follistain-related protein (FRP) in Xenopus embryogenesis, we carried out whole mount in situ hybridization. FRP expression was found to start at stage 10 of Xenopus embryos in the organizer region, suggesting that like follistatin, FRP functions as a organizer factor. The FRP expression in the notochord and floor plate was observed at the neural stage through the tailbud stage, suggesting its role in induction of neural structures. Less