The effect and mechanism of oleanonic acid targeting TRAF1 in regulating Cullin NEDD8 modification

In the early stage of the project, it was found that natural pentacyclic triterpenes liquidambaric acid regulates the NEDD8 modification of Cullin2. This study aims to find more triterpenoid natural active molecules targeting Cullin family members and reveal its mechanism of action. Western blot was used to detect natural products that can significantly change the total protein NEDD8 modification and specific Cullin protein NEDD8 modification in cells; microscale thermophoresis (MST) was used to detect the direct binding of candidate small molecule oleanonic acid to TRAF family proteins, and the binding at the level of living cells was verified by cellular thermal shift assay (CETSA). Proximity ligation assay (PLA) was used to investigate the regulatory effect of oleanonic acid on the protein interaction between TNF receptor-associated factor 1 (TRAF1) and Cullin1 NEDD8 modified complex. Three pentacyclic triterpenoids were found to significantly inhibit NEDD8 modification in cells, among which oleanonic acid had the strongest effect on blocking NEDD8 modification. Different from the previous identification that liquidambaric acid regulates Cullin2/5, oleanonic acid can also specifically induce NEDD8-modified Cullin1 to transform into its unmodified form. And binding experiments showed that oleanonic acid could directly bind to TRAF1 at the level of cell lysate and living cells. Further mechanism studies found that oleanonic acid significantly changed the protein interaction between TRAF1 and Cullin1 NEDD8 modified complex. The above results indicate that oleanonic acid targets TRAF1 and regulates its interaction with NEDD8 modification complex to inhibit NEDD8 modification of Cullin.