Destabilization of Krüppel-Like Factor 4 Protein in Response to Serum Stimulation Involves the Ubiquitin-Proteasome Pathway

Abstract

Although the zinc finger transcription factor Krüppel-like factor 4 (KLF4) has been shown to be a negative regulator of cell proliferation, the mechanisms underlying the posttranslational modification of KLF4, especially at the level of protein degradation, are poorly understood. Here, we show that KLF4 protein levels in quiescent cells were high, but decreased rapidly as cells entered the proliferating stage following serum stimulation. This decrease was partially reversed by pretreatment with MG132, a proteasome inhibitor. Moreover, KLF4 was an unstable protein that underwent rapid turnover, and exhibited a relatively short half-life (t 1/2 f120 minutes). To investigate the involvement of the ubiquitin-proteasome pathway in the regulation of the stability of KLF4, HCT116 cells were treated with proteasome inhibitors. Our results showed that, following lactacystin treatment, levels of endogenous KLF4 increased in a time-and dose-dependent manners. Using a cell-free system, in vitro-translated 35 S-labeled KLF4 protein was degraded by protein extracts prepared from exponentially growing HCT116 cells in the presence of ATP. These effects were prevented by pretreatment with MG132 or replacement of ATP with ATP-;-S, a nonhydrolyzable analogue of ATP, suggesting that ATP is required for KLF4 degradation by the 26S proteasome. In addition, KLF4 was subject to ubiquitination when cells were treated with the proteasome inhibitor or transfected with exogenous ubiquitin. Collectively, these results indicate that destabilization of KLF4 following serum stimulation is mediated, at least in part, through a ubiquitinproteasome pathway. (Cancer Res 2005; 65(22): 10394-400)

KLF4 Modulates Expression of IL-6 in Dendritic Cells via Both Promoter Activation and Epigenetic Modification

“…: (25)(26)(27)(28)(29)(30)(31)(32). Because of its known role as a transcription factor, we sought to systematically determine how it interacted with the IL-6 promoter.…”

A Small Ubiquitin-related Modifier-interacting Motif Functions as the Transcriptional Activation Domain of Krüppel-like Factor 4

“…Cycloheximide Chase Assay-The cycloheximide chase assay was performed as described (81,82). Briefly, HEK293T cells were transfected with either pCMV-Myc-KLF4 or pCMVMyc-KLF4-K275R, treated with 100 g/ml cycloheximide, and lysed at the indicated time points.…”

RETRACTED ARTICLE: Regulation of estrogen receptor signaling in breast carcinogenesis and breast cancer therapy

“…The oncogenic effect of KLF4 has been reported in breast and squamous cell carcinoma [243][244][245][246][247], while its tumor suppression role was reported in various types of cancers such as colon cancer [248,249]. It was demonstrated that KLF4 is a fast turnover protein, whose turnover-half life is governed by the ubiquitin-proteasome system [250,251]. Several e3 ligases such as APC/CDH1 and CUL2/vHL have been linked to the turnover of KLF4 in response to different signaling [224,252].…”