Dlx3 Ubiquitination by Nuclear Mdm2 Is Essential for Dentinogenesis in Mice

Area of Science:

• Oral Biology
• Molecular Biology
• Biochemistry

Background:

• Dentin formation relies on odontoblasts, which synthesize the dentin matrix.
• The E3 ubiquitin ligase murine double minute 2 (Mdm2) was previously shown in vitro to promote odontoblast differentiation.
• The in vivo role of Mdm2 in odontoblast differentiation and dentinogenesis remained unclear.

Purpose of the Study:

• To investigate the in vivo function of Mdm2 in odontoblast differentiation and dentin formation.
• To elucidate the molecular mechanism by which Mdm2 regulates these processes.

Main Methods:

• Utilized Dmp1-Cre;Mdm2 conditional knockout mice.
• Employed histological and molecular biological analyses.
• Investigated Mdm2-p53 interactions using Nutlin-3a inhibitor.
• Performed in situ proximity ligation assay (PLA) and domain deletion studies.

Main Results:

• Mdm2 deletion in odontoblasts impaired differentiation and dentin formation.
• Mdm2's role in dentinogenesis was found to be p53-independent in vivo.
• Mdm2 interacted with and ubiquitinated Dlx3 in the odontoblast nucleus.
• Dlx3 facilitated nuclear translocation of Mdm2, which then ubiquitinated Dlx3, enhancing odontoblast differentiation and Dspp promoter activity.

Conclusions:

• Nuclear Mdm2 is essential for odontoblast differentiation and dentin formation in vivo.
• Mdm2 mediates Dlx3 ubiquitination, which is critical for Dlx3's transcriptional activity on Dspp.
• This interaction is independent of the p53 pathway, contrary to previous in vitro findings.