AF10-dependent transcription is enhanced by its interaction with FLRG.
BACKGROUND
FLRG (follistatin-related gene) is a secreted glycoprotein which is very similar to follistatin. As observed for follistatin, FLRG is involved in the regulation of various biological processes through its binding to members of the TGFbeta (transforming growth factor beta) superfamily, activin, BMPs (bone morphogenetic proteins) and myostatin. Unlike follistatin, FLRG has been found to be both secreted and localized within the nucleus of many FLRG-producing cells, suggesting the existence of specific intracellular functions of the protein.


RESULTS
In order to analyse the function of the nuclear form of FLRG, we performed a yeast two-hybrid screen, in which we identified AF10 [ALL1 (acute lymphoblastic leukaemia) fused gene from chromosome 10], a translocation partner of the MLL (mixed-lineage leukaemia) oncogene in human leukaemia, as a FLRG-interacting protein. This interaction was confirmed by far-Western-blot analysis and co-immunoprecipitation with transfected COS-7 cells. The N-terminal region of AF10, including the PHD (plant homeodomain), is sufficient to mediate this interaction, and has been shown to be involved in AF10 homo-oligomerization. By immunoprecipitation experiments, we showed that FLRG enhances the homo-oligomerization of AF10. Functional studies demonstrated that FLRG enhances the transactivation properties of the AF10 protein fused to Gal4 DNA-binding domains in transient transfection assays.


CONCLUSIONS
Our present study provides novel insights into the function of the nuclear form of the FLRG protein, which is revealed as a novel regulator of transcription. The nuclear isoform of FLRG lacks an intrinsic transactivation domain, but enhances AF10-mediated transcription, probably through promoting the homo-oligomerization of AF10, thus facilitating the recruitment of co-activators.
Forissier
Stéphanie
S
Inserm, U590, Centre Léon Bérard, Université Lyon 1, Lyon, F-69003, France.
Razanajaona
Diane
D
Ay
Anne-Sophie
AS
Martel
Sylvie
S
Bartholin
Laurent
L
Rimokh
Ruth
R
D000818:Animals; D019556:COS Cells; D002467:Cell Nucleus / Q000378:metabolism; D002522:Chlorocebus aethiops; D038702:Follistatin-Related Proteins / Q000235:genetics / Q000378:metabolism*; D017930:Genes, Reporter; D006367:HeLa Cells; D006801:Humans; D020033:Protein Isoforms / Q000235:genetics / Q000378:metabolism*; D020836:Protein Structure, Quaternary; D017434:Protein Structure, Tertiary; D011993:Recombinant Fusion Proteins / Q000235:genetics / Q000378:metabolism; D014157:Transcription Factors / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D014158:Transcription, Genetic; D015533:Transcriptional Activation; D020798:Two-Hybrid System Techniques
D038702:Follistatin-Related Proteins; C092513:MLLT10 protein, human; D020033:Protein Isoforms; D011993:Recombinant Fusion Proteins; D014157:Transcription Factors