ODAM controls epithelial attachment via an integrin/ARHGEF5/RhoA signaling axis

Objective: During tooth development, the odontogenic ameloblast-associated protein (ODAM) is localized in cytoplasm, nucleus, and extracellular matrix. Of the identified proteins that interact with ODAM using protoarray, ARHGER5 was physiologically relevant in RhoA pathway and implicated in the control of epithelial cell motility. Rho GTPases regulate actin and focal adhesion dynamics in cells. During amelogenesis, ameloblasts undergo dramatic cytoskeletal changes, being regulated by Rho GTPases, and then the RhoA protein level is up-regulated. To investigate the function of ODAM in epithelial attachment, we ascertained the regulation of RhoA signaling by ODAM during tooth development.

Method: In order to assess the relationship of ODAM, ARHGEF5, and RhoA, we investigated the interaction among them, the RhoA activity by integrin signaling and ODAM, the regulation of ODAM by integrin signal, and the clinical study in patients with periodontitis by immunoprecipitation assay, western blot, RT-PCR, ELISA, and so on.

Result: ODAM, ARHGEF5, and RhoA exhibited similar patterns of expression during ameloblast differentiation. ODAM interacted with ARHGEF5 and then induced RhoA activity and the expression of downstream factors, such as ROCK and PI3K. In dental epithelial cells, ODAM regulates cell morphology and adhesion by actin rearrangement. ODAM activity increased through integrin a_vb₃ and a_vb₆ in the presence of fibronectin. Fibronectin-integrin-ODAM-ARHGEF5 complex could activate RhoA pathway. In integrin a_vb₆knockout mice, ODAM expression was inhibited after corresponding RhoA downregulation. Also, actin fiber did not arrange regularly compared with wild type. ODAM expressed in normal junctional epithelium(JE) and gingival fluid of periodontitis patients, but not detected in JE of periodontitis patients.

Conclusion: These findings suggest that ODAM controls epithelial attachment and has important roles in the progression of periodontitis via integrin-ARHGEF5-RhoA signaling pathway.