Ubiquitin-proteasome degradation of KLF5 transcription factor in cancer and untransformed epithelial cells

Department of Oncology and Hematology, Winship Cancer Institute, Emory University School of Medicine, 1365-C Clifton Road, Atlanta, GA, USA.
Oncogene (Impact Factor: 8.46). 06/2005; 24(20):3319-27. DOI: 10.1038/sj.onc.1208497
Source: PubMed


Ubiquitin-mediated proteolysis plays a central role in controlling intracellular levels of essential regulatory molecules such as p53, cyclins, myc, BRCA1, HIF-1alpha, etc. The Kruppel-like factor 5 (KLF5) transcription factor regulates biological processes involved in carcinogenesis, angiogenesis, and smooth muscle cell differentiation. In carcinogenesis, KLF5's role has been indicated by frequent genetic deletion as well as functional studies. Here we show that KLF5 is an unstable protein with a short half-life. Destruction of KLF5 was prevented by each of the proteasome-specific inhibitors tested but not by an inhibitor for trypsin-like proteases and cysteine proteases or by a lysosome inhibitor in epithelial cells. Furthermore, KLF5 underwent ubiquitination, and deletion of a 56-amino-acid sequence adjacent to a known transactivation domain of KLF5 significantly reduced its ubiquitination and degradation. Interestingly, cancer cells appeared to be more active in KLF5 degradation than untransformed epithelial cells, yet their proteasome activity was not higher. These results suggest that KLF5 protein is degraded at least in part through ubiquitination-proteasome pathway, which may have become hyperactive for KLF5 in cancer cells.

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Available from: Keith D Wilkinson, Nov 17, 2014
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    • "KLF4 undergoes ubiquitination resulting in rapid degradation through the proteasome pathway in HCT116 cancer cells after stimulation with serum [8]. Likewise, the expression level of KLF5 is reportedly regulated by ubiquitin-dependent proteosomal degradation [9]. KLF4 and KLF5 interact with the SUMO E3 ligase PIAS1. "
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    ABSTRACT: Tumor necrosis factor α (TNFα) plays an essential role in the regulation of vascular smooth muscle cell (VSMC) phenotype. In the present study, we provide evidence that krüppel-like factor 5 (KLF5) plays an essential role in TNFα-induced phenotypic conversion of VSMCs. Ectopic expression of KLF5 completely blocked phenotypic conversion of VSMCs from synthetic to contractile type. In addition, stimulation of VSMCs with TNFα facilitated expression of KLF5, whereas expression of smooth muscle marker genes such as SM22α and smooth muscle actin (SMA) was significantly down-regulated. TNFα significantly enhanced the promoter activity of KLF5 as well as mRNA level, which is significantly suppressed by the inhibition of the MAPK pathway. Silencing of KLF5 suppressed TNFα-induced phenotypic conversion of VSMCs, whereas overexpression of KLF5 stimulated phenotypic conversion of VSMCs and facilitated the loss of angiotensin II (AngII)-dependent contraction. Finally, overexpression of KLF5 significantly attenuated the promoter activity of SM22α and SMA. Therefore, we suggest that TNFα-dependent induction of KLF5 may play an essential role in phenotypic modulation of VSMCs. Copyright © 2015. Published by Elsevier Inc.
    Biochemical and Biophysical Research Communications 06/2015; 463(4). DOI:10.1016/j.bbrc.2015.06.123 · 2.30 Impact Factor
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    • "The deletion is exclusively hemizygous, causing the haploinsufficiency of KLF5 during cancer development [10] [11] [12]. In addition, KLF5 protein is degraded by the ubiquitin proteasome pathway, and one E3 ubiquitin ligase that degrades KLF5, WWP1, is amplified and overexpressed in human prostate and breast cancers, causing excessive protein degradation and functional insufficiency of KLF5 [13] [14] [15]. These findings indicate that KLF5 is frequently inactivated during human carcinogenesis and thus could be a tumor suppressor gene, and some functional studies indeed support a tumor suppressor function of KLF5. "
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    ABSTRACT: Krüppel-like factor 5 (KLF5) regulates multiple biologic processes. Its function in tumorigenesis appears contradictory though, showing both tumor suppressor and tumor promoting activities. In this study, we examined whether and how Klf5 functions in prostatic tumorigenesis using mice with prostate-specific deletion of Klf5 and phosphatase and tensin homolog (Pten), both of which are frequently inactivated in human prostate cancer. Histologic analysis demonstrated that when one Pten allele was deleted, which causes mouse prostatic intraepithelial neoplasia (mPIN), Klf5 deletion accelerated the emergence and progression of mPIN. When both Pten alleles were deleted, which causes prostate cancer, Klf5 deletion promoted tumor growth, increased cell proliferation, and caused more severe morphologic and molecular alterations. Homozygous deletion of Klf5 was more effective than hemizygous deletion. Unexpectedly, while Pten deletion alone expanded basal cell population in a tumor as reported, Klf5 deletion in the Pten-null background clearly reduced basal cell population while expanding luminal cell population. Global gene expression profiling, pathway analysis, and experimental validation indicate that multiple mechanisms could mediate the tumor-promoting effect of Klf5 deletion, including the up-regulation of epidermal growth factor and its downstream signaling molecules AKT and ERK and the inactivation of the p15 cell cycle inhibitor. KLF5 also appears to cooperate with several transcription factors, including CREB1, Sp1, Myc, ER and AR, to regulate gene expression. These findings validate the tumor suppressor function of KLF5. They also yield a mouse model that shares two common genetic alterations with human prostate cancer—mutation/deletion of Pten and deletion of Klf5.
    Neoplasia (New York, N.Y.) 11/2014; 16(11). DOI:10.1016/j.neo.2014.09.006 · 4.25 Impact Factor
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    • "Not only is the KLF5 gene haploinsufficient [8], KLF5 protein is also sensitive to degradation mediated by the ubiquitin-proteasome pathway in epithelial cells [23], [24], [51], which indicates that the expression level of KLF5 is important for its proper function. Lack of more dramatic phenotypic alterations in prostates with the knockout of one Klf5 allele could be due to a fine-tuned regulation of Klf5 expression. "
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    ABSTRACT: KLF5 is a basic transcription factor that regulates multiple biological processes. While it was identified as a putative tumor suppressor in prostate cancer, likely due to its function as an effector of TGF-β in the inhibition of cell proliferation, KLF5 is unacetylated and promotes cell proliferation in the absence of TGF-β. In this study, we evaluated the expression and function of KLF5 in prostatic epithelial homeostasis and tumorigenesis using mouse prostates and human prostate epithelial cells in 3-D culture. Histological and molecular analyses demonstrated that unacetylated-Klf5 was expressed in basal or undifferentiated cells, whereas acetylated-Klf5 was expressed primarily in luminal and/or differentiated cells. Androgen depletion via castration increased both the level of Klf5 expression and the number of Klf5-positive cells in the remaining prostate. Functionally, knockdown of KLF5 in the human RWPE-1 prostate cell line decreased the number of spheres formed in 3-D culture. In addition, knockout of Klf5 in prostate epithelial cells, mediated by probasin promoter-driven Cre expression, did not cause neoplasia but promoted cell proliferation and induced hyperplasia when one Klf5 allele was knocked out. Knockout of both Klf5 alleles however, caused apoptosis rather than cell proliferation in the epithelium. In castrated mice, knockout of Klf5 resulted in more severe shrinkage of the prostate. These results suggest that KLF5 plays a role in the proliferation and differentiation of prostatic epithelial cells, yet loss of KLF5 alone is insufficient to induce malignant transformation in epithelial cells.
    PLoS ONE 06/2013; 8(6):e65538. DOI:10.1371/journal.pone.0065538 · 3.23 Impact Factor
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