MARCH2 suppresses odontoblast differentiation by polyubiquitinating PTPRD

Dentin, the main component of dental hard tissues, is produced by differentiated odontoblasts. How odontoblast differentiation is regulated remains understudied. Here, we screen that the expression of membrane-associated RING finger protein 2 (March2) is the highest among all March family members, with an increasing trend during odontoblast differentiation. In mouse incisors and molars, MARCH2 is moderately expressed in the undifferentiated dental papilla cells and strongly expressed in the odontoblasts. Knockdown and overexpression experiments demonstrate that MARCH2 inhibits odontoblastic differentiation of mouse dental papilla cells (mDPCs). Additionally, both March2 deficient mice and mice with odontoblast specific knockdown of March2 exhibit the phenotype of increased dentin thickness, accelerated dentin deposition as well as elevated expression levels of odontoblast markers compared with control littermates. Therefore, MARCH2 plays an inhibitory role in odontoblast differentiation. Mechanistically, MARCH2 interacts with protein tyrosine phosphatase receptor delta (PTPRD) and facilitates its K27-linked polyubiquitination and subsequent degradation, which is dependent on the ligase activity of MARCH2. The presence of MARCH2 promotes the translocation of PTPRD from the cell membrane to the lysosome, thereby enhancing its degradation via the lysosomal pathway. Further experiments show that knockdown of endogenous Ptprd impairs odontoblastic differentiation of mDPCs. Ptprd and March2 double knockdown in mDPCs apparently reversed the enhanced odontoblastic differentiation by knockdown of March2 alone, indicating that MARCH2 inhibits odontoblastic differentiation by promoting PTPRD degradation. This study unveils a novel mechanism where an E3 ubiquitin ligase regulates odontoblast differentiation through post-translational modification of a membrane protein, highlighting a promising direction for future exploration.