Sphingosine 1-phosphate (S1P) participates in migration of bone marrow (BM)-derived mesenchymal stem cells (BMSCs) toward damaged liver via upregulation of S1P receptor 3 (S1PR3) during mouse liver fibrogenesis. But, the molecular mechanism is still unclear. HuR, as an RNA-binding protein, regulates tumor cell motility. Here, we examined the role of HuR in migration of human BMSCs (hBMSCs) in liver fibrosis. Results showed that HuR messenger RNA (mRNA) level was increased in human or mouse fibrotic livers, and correlated with S1PR3 mRNA expression. Using immunofluorescence, we found that HuR mainly localized in the nuclei of hepatocytes and non-parenchymal cells in normal livers. However, in fibrotic livers, we detected an increased HuR cytoplasmic localization in non-parenchymal cells. In chimeric mice of BM cell-labeled by EGFP, significant numbers of EGFP-positive cells (BM origin) were positive for HuR in fibrotic areas. Meanwhile, HuR-positive cells were also positive for α-SMA (myofibroblasts). In vitro, S1P induced hBMSCs migration via S1PR3 upregulation. HuR involved in S1P-induced hBMSCs migration and increased stabilization of S1PR3 mRNA via competing with miR-30e. RNA immunoprecipitation showed that HuR interacted with S1PR3 mRNA 3'UTR. Moreover, S1P resulted in phosphorylation and cytoplasmic translocation of HuR via S1PR3 and p38MAPK. Furthermore, we transplanted EGFP+ BMSCs with or without HuR small interfering RNA (siRNA) into carbon tetrachloride-treated mice and found that knockdown of HuR inhibited the migration of BMSCs toward injured livers by flow cytometric analysis in vivo. We identified a positive feedback regulation mechanism between HuR and S1PR3 in S1P-induced BMSCs migration. HuR participates in upregulation of S1PR3 induced by S1P. S1P results in phosphorylation and translocation of HuR via S1PR3. Our results provide a new regulatory manner to the mechanism of liver fibrogenesis.
Key message: HuR expression and cytoplasmic localization were increased in fibrotic livers. S1P induced migration of human bone marrow Mesenchymal Stem Cells via S1PR3 and HuR. HuR regulated S1PR3 mRNA expression by binding with S1PR3 mRNA 3'UTR. S1P induced HuR phosphorylation and cytoplasmic translocation via S1PR3. HuR regulated S1PR3 expression by competing with miR-30e.
Keywords: HuR; Human mesenchymal stem cells; Liver fibrosis; Sphingosine 1-phosphate; Sphingosine 1-phosphate receptor.