Estrogen causes degradation of KLF5 by inducing the E3 ubiquitin ligase EFP in ER-positive breast cancer cells

• Type of Material: Article
• Authors: Ke-Wen Zhao, Emory University; Deepa Sikriwal, Emory University; Xueyuan Dong, Emory University; Peng Guo, Emory University; Xiaodong Sun, Emory University; Jin-Tang Dong, Emory University
• Language: English
• Date: 2011-05-04
• Publisher: Portland Press
• Publication Version: Author Accepted Manuscript (After Peer Review)
• Copyright Statement: © The Authors Journal compilation © 2011 Biochemical Society
• Final Published Version (URL): http://www.biochemj.org/bj/437/0323/bj4370323.htm
• Title of Journal or Parent Work: Biochemical Journal
• ISSN: 0264-6021
• Volume: 437
• Issue: 2
• Start Page: 323
• End Page: 333
• Grant/Funding Information: This work was supported by the National Institute of Health/National Cancer Institute through grant R01 CA087921 and grant from Shanghai Municipal Education Commission (11ZZ106).
• Keywords: ER; breast cancer; EFP; KLF5; estrogen
• Research Categories: Health Sciences, Oncology; Chemistry, Biochemistry

Abstract

Krüppel-like factor 5 (KLF5) is a multifunctional transcription factor involved in cell proliferation, differentiation and carcinogenesis. In addition to frequent inactivation in different types of human cancers including breast cancer, KLF5 has been identified as an essential co-factor for the TGF-β tumor suppressor. In our previous study demonstrating a negative regulation of ER (estrogen receptor alpha) function by KLF5 in breast cancer cells, we noticed that estrogen reduced the protein level of KLF5. In this study, we tested whether and how estrogen-ER signaling regulates KLF5 protein. We found that estrogen caused the degradation of KLF5 protein, and the degradation was sensitive to proteasome inhibitors but not other inhibitors. The estrogen-inducible E3 ligase EFP was identified as a key player in estrogen-mediated degradation of KLF5, as knockdown and over-expression of EFP increased and decreased KLF5 protein levels respectively, and the decrease continued even when protein synthesis was blocked. EFP-mediated degradation impaired the function of KLF5 in gene transcription. While only unubiquitinated EFP interacted with KLF5, overexpression of EFP appeared to prevent the ubiquitination of KLF5 while resulting in heavy ubiquitination of the E3 itself. Furthermore, ubiquitination of EFP interrupted its interaction with KLF5. Although the mechanism for how EFP degrades KLF5 remains to be determined, these results suggest that estrogen causes the degradation of KLF5 protein by inducing the expression of EFP in ER-positive breast cancer cells.