USP29 Deubiquitinates And Stabilizes Snail Protein And Ajuba Co-activates The Transcriptional Activity Of PPARγ And ERα

Metastasis is the master reason for the high mortality of gastric cancer patients.Snail protein is the critical transcriptional factor involved in EMT which is the primary way for cell migration and metastasis.The expression level of Snail is tightly controlled by its stability.Many ubiquitin ligases E3 mediate ubiquitinationproteasomal degradation of Snail protein,but Snail’s deubiquitnase(DUB)has rarely been reported.By extensive screening of members of the DUB family,we found that several DUBs can enhance Snail protein level,including USP13,USP28,USP29,USP37,OTUD6 A and DUB3.Among them,the effect of USP29 on Snail protein is the most significant in different cell lines.Our further study found that there is a direct interaction between Snail and USP29.In the nucleus,USP29 directly de-ubiquitinates Snail protein and inhibits Snail protein degradation.We also found that USP29 directly binds Snail’s phosphatases-SCP proteins,and promotes the binding of Snail to the SCP proteins,which provides another important mechanism for USP29 to stabilize Snail protein.Overexpression of USP29 in a variety of gastric cancer cells can promote cell EMT,cell migration and enhance chemoresistance.In contrast,the knocking-down of USP29 inhibited cell migration.By searching the online public database,we found that the expression of USP29,Snail and SCP in gastric cancer patients are negatively correlated with the survival rate,and these molecules may become new targets for the treatment of gastric cancer.The LIM protein Ajuba can act as a co-activator of various nuclear receptors such as PPAR? and ER?(13)However,the detailed mechanism of action remains unclear.Now,in our study about PPAR?,we found Ajuba forms a functional protein complex with histone acetyltransferase CBP/P300 and synergistically activates the transactivity of PPAR?.In addition,we also found that Ajuba can form homodimer and respectively bind to the PPAR?/RXR heterodimer by utilizing its EPSG motif.Similarly,we found that the main mechanism of Ajuba co-activating ER? is also forming a functional complex with CBP/P300.Ajuba promotes the association between ER? and CBP/P300 and enhances ER? acetylation,DNA-binding activity and transcriptional activity.In addition,we found DBC1 is another binding-protein forming the co-factors’ complex with Ajuba.The PreLIM and LIM domain of Ajuba interacts with DBC1 and CBP/P300,respectively.Ajuba bridges CBP/P300 and DBC1,which promotes the formation of a ternary-complex in activating ER? transactivity.Our research enriches the mechanism of PPAR? and ER? in regulating genes expression and provides new therapeutic targets for diseases such as breast cancer,diabetes and obesity.