The absence of fragile X mental retardation protein (FMRP) causes fragile X syndrome (FXS), which is the leading cause of hereditary mental retardation. Fragile X-related protein 1 (FXR1P), which plays an important role in normal muscle development, is one of the two autosomal paralogs of FMRP. To understand the functions of FXR1P, we screened FXR1P-interacting proteins by using a yeast two-hybrid system. The fragile X-related gene 1 (FXR1) was fused to pGBKT7 and then used as the bait to screen the human fetal brain cDNA library. The screening results revealed 10 FXR1P-interacting proteins including Bcl-2-associated transcription factor 1 (BTF). The interaction between FXR1P and BTF was confirmed by using both b-galactosidase assay and growth test in selective media. Co-immunoprecipitation assay in mammalian cells was also carried out to confirm the FXR1P/BTF interaction. Moreover, we confirmed that BTF co-localized with FXR1P in the cytoplasm around the nucleus in rat vascular smooth muscle cells by using confocal fluorescence microscopy. These results provide clues to elucidate the relationship between FXR1P and FXS.

FragileXsyndrome(FXS)isageneticmentalretardationdisease,withincidencesecondonlytotrisomy21syndrome.FragileXmentalretardationprotein(FMRP),isthecausativefactorofFXSandencodedbytheFragileXmentalretardation1(FMR1) gene,whichiswidelyexpressedincellsofthenerve,muscle,andtestes.FragileXrelatedprotein1(FXR1P)isencodedbya homologousgeneto FMR1---FragileXrelatedgene1( FXR1)andcaninteractwithproteinsandRNAs.Manyillnesseswere involvedinthealteredexpressionof FXR1.TounderstandthebiologicaleffectoftheinteractionbetweenFXR1PandCMAS,we constructedaFXR1 overexpressionvectorandinvestigateditsexpressioninPC12(theratpheochromocytoma)cellsandVSMC (vascularsmoothmusclecell)andtheeffectoftheoverexpressiononcellmorphologyandseveralcellprocessesrelatedto CMP-N-acetylneuraminicacidsynthetase(CMAS)activity.Wedemonstratethattheoverexpressionof FXR1 genecanincreaseactivity ofCMASinPC12cellsandprovideacertaindegreegrowthprotectionforthatcells.Thus,itsuggestsFXR1Pisatissue-specific regulatortoaltertheconcentrationofGM1inPC12cells,butnotinVSMC.