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 Facto r-P (TGF-P) is thought to be mediated by the same molecules (Smad2/3 and Sm ad4). Although differentiation of murine erythroleukemia F5-5.fl cells is i nduced by activin, it is not induced by TGF-beta, suggesting that at some p oint TGF-beta signaling is defective. The aim of this study was to investig ate the unresponsiveness of F5-5.fl cells to TGF-beta. Design: 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 a ffected 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) w ere 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, sugge sting that neither activins nor BMPs are produced in F5-5.fl cells. The exp ression of both type 1 (ALK-4/ActRIB) and type II (ActRII) receptors for ac tivin was detected in F5-5.fl cells. In contrast, while the expression of t ype I receptor for TGF-beta (ALK-5/T beta RI) was detected, that of type TI receptor (T beta RII) 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.