RUNX2 controls human IPO8 basal transcription in Saos-2 cells.

Runt-related transcription factor 2 (RUNX2) is a vital regulatory factor that controls osteoblast-specific gene expression; however, RUNX2‑regulated genes in human mesenchymal stem cells (hMSCs) remain to be fully elucidated. In the present study, chromatin immunoprecipitation (ChIP)-on-chip analysis of RUNX2 in hMSCs demonstrated that importin 8 (IPO8) may be a novel target gene. The 5' flanking region of the IPO8 gene, which is ~3,300 bp in length, was cloned and inserted into the pGL3‑basic luciferase reporter vector. The results of dual luciferase reporter assays indicated that this segment possessed strong basal promoter activity. Furthermore, the RUNX2 binding site, which encompasses positions ‑496 to ‑501 bp, was required to achieve maximal IPO8 promoter activity in Saos‑2 human osteosarcoma cells. In addition, ChIP analysis indicated that RUNX2 uniquely binds to this specific IPO8 sequence motif. Cells with a knockdown in RUNX2 expression exhibited downregulated IPO8 transcription. Finally, synchronization of IPO8 and RUNX2 expression was observed in Saos‑2 cells cultured in osteoblast‑induction medium. Taken together, these results indicated that RUNX2 regulates IPO8 gene transcription, and may have a contributory role in osteoblast differentiation.