Ataxin-3 Like (ATXN3L), A Member Of The Josephin Family Of Deubiquitinating Enzymes,Promotes Breast Cancer Proliferation By Deubiquitinating Kruppel-Like Factor 5(KLF5)

Kruppel sample factors(Kruppel-like the factors, KLFs) is a transcription factors family. (Human Kruppel-like factor 5) is an important member of the family of KLFs, which located at chromosome 13q21, encoding a 55 KDa protein which contains about 457 amino acids. In normal tissue, KLF5 extensively controls many important cellular processes,including proliferation, differentiation,movement, inflammation and pluripotency.Within the tumor associated process, KLF5 regulates a lot of gene expression. It can promote cell proliferation, cell cycle, survival, angiogenesis, and self-renewal of stem cell.The previous results showed that KLF5 is highly expressed,in ERα negative and undifferentiated breast cancer. KLF5 acts as an oncogene in breast cancer.It has been identified that KLF5 protein undergoes a variety of posttranslational modifications such as phosphorylation, acetylation, Ubiquitination and SUMOylation.Ubiquitin proteasome pathway (ubiquitin proteasome pathway, UPP) is an important regulation of protein function. Ubiquitination and deubiquitination keep a dynamic balance in the fine regulation of KLF5 protein level.Many important transcription factors, such as p53、c-Myc and β-catenin,are ubiquitinated and rapidly degradaded through the proteasome. There is is also the case for KLF5. Ceshi Chen et al, discovered that KLF5 was regulated by UPP and two key enzymes of E3 ubiquitin ligases WWP1 and SCFFbow7 target KLF5 for ubiquitin-mediated degradation. Protein ubiquitination is a reversible process.Deubiquitinase can remove ubiquitin modifications from the target protein. So far,three E3 ligases,such as ubiquitination:WWP1, SCFFbw7 and SMURF2,have been identified to ubiquitinate KLF5.However, the KLF5 DUB have yet to be identified. In this study,we aim to identify the KLF5 protein DUB which can regulate KLF5 protein stability and promote breast cancer.We obtained the following results:1. Knockdown of ATXN3L, a members of MJD family (Machado-Joseph diseases related enzymes) down-regulated KLF5 protein level and upregulated p21 and p27 expression level. On the contrary,ATXN3L overexpression upregulated the KLF5 level. Thus, ATXN3L can regulate the KLF5 protein stability.2. ATXN3L can interacted directly with KLF5,Both N-terminal and C-terminal of ATXN3L and N-terminal and C-terminal of KLF5 mediated the protein interaction between ATXN3L and KLF5.3. ATXN3L extended the half-life of KLF5 protein, ATXN3L increased KLF5 protein stability through deubiquitination of KLF5.The Josephin domain of ATXN3L is essential for KLF5 deubiquitination.4. In TNBC cell lines HCC1806 and SUM1315 cells, knockdown of ATXN3L inhibited breast cancer cell proliferation.We first identified that deubiquitinase ATXN3L increased the stability of KLF5, and KLF5 was a substrate of ATXN3L. ATXN3L maintained the stability of KLF5 protein through deubiquitination. ATXN3L can promoted breast cancer cell proliferation.This study provides new evidence for targeting KLF5 and also provides a new strategy for the treatment of breast tumor.