Title :
Mixed Lineage Leukemia 5 (
MLL5 ) Protein Stability Is Cooperatively Regulated by
O-GlcNac Transferase (
OGT ) and Ubiquitin Specific
Protease 7 (
USP7 )
Abstract :
- Mixed lineage leukemia 5 ( MLL5 ) protein is a trithorax family histone 3 lysine 4 ( H3K4 ) methyltransferase that regulates diverse biological processes, including cell cycle progression, hematopoiesis and cancer
- The mechanisms by which MLL5 protein stability is regulated have remained unclear to date
- Here, we showed that MLL5 protein stability is cooperatively regulated by O-GlcNAc transferase ( OGT ) and ubiquitin-specific protease 7 7 (USP7 )
- Depletion of OGT in cells led to a decrease in the MLL5 protein level through ubiquitin/ proteasome-dependent proteolytic degradation, whereas ectopic expression of OGT protein suppressed MLL5 ubiquitylation
- We further identified deubiquitinase USP7 as a novel MLL5-associated protein using mass spectrometry
- USP7 stabilized the MLL5 protein through direct binding and deubiquitylation
- Loss of USP7 induced degradation of MLL5 protein
- Conversely, overexpression of USP7 , but not a catalytically inactive USP7 mutant, led to decreased ubiquitylation and increased MLL5 stability
- Co-immunoprecipitation and co-immunostaining assays revealed that MLL5 , OGT and USP7 interact with each other to form a stable ternary complex that is predominantly located in the nucleus
- In addition, upregulation of MLL5 expression was correlated with increased expression of OGT and USP7 in human primary cervical adenocarcinomas
- Our results collectively reveal a novel molecular mechanism underlying regulation of MLL5 protein stability and provide new insights into the functional interplay among O-GlcNAc transferase , deubiquitinase and histone methyltransferase