Regulatory Factor X1-induced Down-regulation of Transforming Growth Factor β2 Transcription in Human Neuroblastoma Cells

Regulatory factor X (RFX) proteins are transcription factors. Seven mammalian RFX proteins have been identified. RFX1 is the prototype RFX. However, its biological functions are not known. Here, RFX1 overexpression reduced fetal bovine serum-stimulated proliferation of SH-SY5Y cells, a human neuroblastoma cell line. This inhibition is associated with decreased transforming growth factor β2 (TGFβ2) and phospho-extracellular signal-regulated kinase (ERK). Exogenous TGFβ2 increased cell proliferation and phospho-ERK in cells overexpressing RFX1. An anti-TGFβ2 antibody and PD98059, an ERK activation inhibitor, inhibited SH-SY5Y cell proliferation. TGF β2 promoter activity was decreased in cells overexpressing RFX1. Chromosome immunoprecipitation assay showed that RFX1 bound the TGF β2 promoter. RFX1 down-regulation increased TGFβ2 in SH-SY5Y and HCN-1A cells, a normal human neuronal cell line. More importantly, TGFβ2 concentrations were negatively correlated with RFX1 levels in human medulloblastoma tissues with a R 2 of 0.464. These results suggest that RFX1 reduces cell proliferation through inhibiting the TGFβ2-ERK signaling pathway. RFX1 blocks TGF β2 expression through its direct action on TGF β2 transcription. This effect also appears in human brain tumor tissues. Because TGF β is known to be involved in cancer development, our results provide initial evidence to suggest that RFX1 may play an important role in human tumor biology. Background: Biological functions of regulatory factor X1 (RFX1) are not clear. Results: RFX1 decreases transforming growth factor β2 ( TGF β2) transcription and exogenous TGFβ2 reverses the inhibitory effects of RFX1 on cell proliferation. Conclusion: RFX1 inhibits neuroblastoma cell proliferation through direct down-regulation of TGF β2 transcription. Significance: This might be the first evidence of RFX1 regulation of TGF β2 transcription and cell proliferation.