mRNA expression of type I and type II receptors for activin, transforming growth factor-beta, and bone morphogenetic protein in the murine erythroleukemic cell line, F5-5.fl.
OBJECTIVE
Intracellular signaling of activin and transforming growth factor-beta (TGF-beta) is thought to be mediated by the same molecules (Smad2/3 and Smad4). Although differentiation of murine erythroleukemia F5-5.fl cells is induced by activin, it is not induced by TGF-beta, suggesting that at some point TGF-beta signaling is defective. The aim of this study was to investigate the unresponsiveness of F5-5.fl cells to TGF-beta.


METHODS
mRNA expression of ligands, receptors, and signal mediators for the TGF-beta family was examined in F5-5.fl cells using RT-PCR.


RESULTS
Activin induced erythrodifferentiation of F5-5.fl cells in a dose-dependent manner. Neither TGF-beta1 nor bone morphogenetic protein (BMP)-4 affected the differentiation of F5-5.fl cells in the presence or absence of activin. Although mRNAs of TGF-betas (TGF-beta1, TGF-beta2 and TGF-beta3) were detected, those of inhibin/activin (alpha-, betaA- and betaB-subunits) and BMPs (BMP-2, BMP-4 and BMP-7) could not be detected in the cells, suggesting that neither activins nor BMPs are produced in F5-5.fl cells. The expression of both type I (ALK-4/ActRIB) and type II (ActRII) receptors for activin was detected in F5-5.fl cells. In contrast, while the expression of type I receptor for TGF-beta (ALK-5/TbetaRI) was detected, that of type II receptor (TbetaRII) was not. The mRNA of all Smads examined was detected in F5-5.fl cells.


CONCLUSIONS
A defect in the type II receptor might cause unresponsiveness to TGF-beta in F5-5.fl cells. An erythrodifferentiation assay using F5-5.fl cells would be useful for measuring net activin activity because it would not be necessary to consider endogenous activins and BMPs.
Machida
H
H
Laboratory Animal Research Center, RIKEN, 2-1 Hirosawa, Wako, Saitama, 351-0198 Japan.
Ogawa
K
K
Funaba
M
M
Mizutani
T
T
Tsujimoto
M
M
D030201:Activin Receptors, Type I; D030301:Activin Receptors, Type II; D000818:Animals; D019485:Bone Morphogenetic Proteins / Q000096:biosynthesis*; D002454:Cell Differentiation / Q000187:drug effects; D007202:Indicators and Reagents; D004915:Leukemia, Erythroblastic, Acute / Q000378:metabolism*; D008024:Ligands; D051379:Mice; D012333:RNA, Messenger / Q000096:biosynthesis*; D017978:Receptors, Growth Factor / Q000096:biosynthesis*; D020133:Reverse Transcriptase Polymerase Chain Reaction; D015398:Signal Transduction / Q000502:physiology; D016212:Transforming Growth Factor beta / Q000096:biosynthesis*; D014407:Tumor Cells, Cultured
D019485:Bone Morphogenetic Proteins; D007202:Indicators and Reagents; D008024:Ligands; D012333:RNA, Messenger; D017978:Receptors, Growth Factor; D016212:Transforming Growth Factor beta; D030201:Activin Receptors, Type I; D030301:Activin Receptors, Type II