MiR-124 regulates osteoblast differentiation through GSK-3ß in ankylosing spondylitis.

OBJECTIVE: Ankylosing spondylitis (AS) is a spastic and spinal joint disease with the characteristic of pathological ossification. Bioinformatics analysis demonstrated that there is a complementary binding site between microRNA-124 (miR-124) and the 3'-UTR of glycogen synthase kinase-3ß (GSK-3ß) mRNA. We aimed to investigate the role of miR-124 in regulating GSK-3ß expression, Wnt/ß-catenin pathway activity, and osteoblast differentiation of spinal ligament fibroblasts. PATIENTS AND METHODS: The ligament tissues of AS and the femoral neck fracture patients were collected. MiR-124 and GSK-3ß mRNA expressions were detected by using quantitative Real-time PCR (qRT-PCR). GSK-3ß and ß-catenin protein expressions were detected by using Western blot. Ligament fibroblasts were isolated and induced to differentiate into osteoblasts. Alizarin red S staining (ARS) was used to identify osteoblast differentiation. Expressions of miR-124, GSK-3ß, ß-catenin, Osterix, and runt-related transcription factor 2 (RUNX2) were detected during differentiation. The cells were divided into two groups as agomiR-normal control (NC) transfection group and agomir miR-124 transfection group. Alkaline phosphatase (ALP) activity and Alizarin Red S staining were detected. RESULTS: MiR-124 and ß-catenin expressions in the ligament of AS patients increased, while GSK-3ß level reduced compared with control. MiR-124, ß-catenin, Osterix, and RUNX2 expressions gradually elevated, whereas GSK-3ß level gradually declined following increased osteoblasts differentiation. Antagomir miR-124 transfection significantly up-regulated the expression of GSK-3ß in osteoblast differentiation, significantly decreased the expression of ß-catenin, Osterix, and RUNX2, and significantly inhibited osteoblast differentiation. CONCLUSIONS: MiR-124 decreased and GSK-3ß elevated in AS ligament tissue. Down-regulation of miR-124 expression enhanced GSK-3ß expression, weakened Wnt/ß-catenin pathway activity, and inhibited the differentiation of ligament fibroblasts into osteoblasts.

Phosphorylation of eukaryotic protein synthesis initiation factor 4E at Ser-209.

Initiation factor 4E (eIF-4E) binds to the m7GTP-containing cap of eukaryotic mRNA and facilitates the entry of mRNA into the initiation cycle of protein synthesis. eIF-4E is a phosphoprotein, and the phosphorylated form binds to mRNA caps 3-4-fold more tightly than the nonphosphorylated form. A previous study indicated that the major phosphorylation site was Ser-53 (Rychlik, W., Russ, M. A., and Rhoads, R. E. (1987) J. Biol. Chem. 262, 10434-10437). In the present study, we synthesized the phosphopeptide expected to result from tryptic digestion of eIF-4E, O-phosphoseryllysine. Surprisingly, the tryptic and synthetic phosphopeptides did not comigrate electrophoretically. Accordingly, we redetermined the phosphorylation site by isolating a chymotryptic phosphopeptide on reverse phase high performance liquid chromatography. The peptide was sequenced by Edman degradation and corresponded to 198QSHADTATKSGSTTKNRF215. The site of phosphorylation was determined to be Ser-209 by four methods: the increase in the ratio of dehydroalanine to serine derivatives during Edman degradation, the release of 32P, the further digestion of the chymotryptic phosphopeptide with trypsin, Glu-C, and Asp-N, and site-directed mutagenesis of eIF-4E cDNA. The S209A variant was not phosphorylated in a rabbit reticulocyte lysate system, whereas the wild-type, S53A, and S207A variants were. This site falls within the consensus sequence for phosphorylation by protein kinase C.