A feedback loop between RUNX2 and the E3 ligase SMURF1 in regulation of differentiation of human dental pulp stem cells.

INTRODUCTION Runt-related transcription factor 2 (RUNX2) is a transcription factor that is indispensable for bone and tooth development. Smad ubiquitylation regulatory factor-1 (SMURF1) promotes RUNX2 degradation and negatively regulates osteoblast differentiation, whereas RUNX2 activates SMURF1 transcription in osteoblasts. However, the relationship between RUNX2 and SMURF1 in tooth development is unknown. This study aimed to evaluate the potential relationship between RUNX2 and SMURF1 in human dental pulp stem cells (hDPSCs). METHODS RUNX2 or SMURF1 expression was silenced in hDPSCs by lentiviral transduction of short hairpin RNA . The relationship between RUNX2 and SMURF1 expression was analyzed using quantitative polymerase chain reaction, Western blotting, dual luciferase reporter assays, and chromatin immunoprecipitation. The effect of the interplay between RUNX2 and SMURF1 on the odontoblastic differentiation of hDPSCs was examined in SMURF1-deficient hDPSCs. RESULTS The inhibition of SMURF1 in hDPSCs significantly increased RUNX2 at the protein level that was associated with decreased RUNX2 ubiquitination but did not affect RUNX2 messenger RNA expression. On the other hand, depletion of RUNX2 in hDPSCs decreased SMURF1 at both the protein and messenger RNA levels. A RUNX2-binding motif at -308 bp of the SMURF1 promoter functioned in RUNX2-mediated SMURF1 expression. Moreover, the expression levels of RUNX2 were associated with SMURF1 levels during odontoblastic differentiation. Significantly, the knockdown of SMURF1 up-regulated RUNX2 expression and down-regulated dentin sialophosphoprotein and dental matrix protein-1 expression in odontoblastic differentiation. CONCLUSIONS These results reveal the regulatory circuit between RUNX2 and SMURF1 controls RUNX2 expression and regulates odntoblastic differentiation in hDPSCs.