TRAF [TNF (tumour necrosis factor)-receptor-associated factor] 2 and 6 are essential adaptor proteins for the NF-κB (nuclear factor κB) signalling pathway, which play important roles in inflammation and immune response. Polyubiquitination of TRAF2 and TRAF6 is critical to their activities and functions in TNFα- and IL (interleukin)-1β-induced NF-κB activation. However, the regulation of TRAF2 and TRAF6 by deubiquitination remains incompletely understood. In the present study, we identified USP (ubiquitin-specific protease) 4 as a novel deubiquitinase targeting TRAF2 and TRAF6 for deubiquitination. We found that USP4 specifically interacts with TRAF2 and TRAF6, but not TRAF3. Moreover, USP4 associates with TRAF6 both in vitro and in vivo, independent of its deubiquitinase activity. The USP domain is responsible for USP4 to interact with TRAF6. Ectopic expression of USP4 inhibits the TRAF2- and TRAF6-stimulated NF-κB reporter gene and negatively regulates the TNFα-induced IκBα (inhibitor of NF-κBα) degradation and NF-κB activation. Knockdown of USP4 significantly increased TNFα-induced cytokine expression. Furthermore, we found that USP4 deubiquitinates both TRAF2 and TRAF6 in vivo and in vitro in a deubiquitinase activity-dependent manner. Importantly, the results of the present study showed that USP4 is a negative regulator of TNFα- and IL-1β-induced cancer cell migration. Taken together, the present study provides a novel insight into the regulation of the NF-κB signalling pathway and uncovers a previously unknown function of USP4 in cancer.
The proproliferative transcription factor KLF5 plays an important role in promoting cell proliferation and tumorigenesis. KLF5 is a short-lived protein that can be rapidly degraded through the ubiquitin-proteasome pathway in cancer cells. However, the mechanisms regulating protein stability remain poorly understood. In this study, the tumor suppressor Fbw7, a component of the SCF complex (SCF Fbw7 ) E3 ubiquitin ligase, specifically promoted the degradation and ubiquitination of KLF5 but had little effect on the stability of KLF4. Fbw7 interacted with KLF5 in a CDC4 phosphodegron (CPD)-dependent manner. Three CPDs were found in the KLF5 protein. Simultaneous mutation of these CPDs significantly abolished Fbw7-mediated ubiquitination and degradation. Furthermore, Fbw7 deficiency dramatically delayed KLF5 turnover and led to the accumulation of KLF5 protein in cancer cells. Glycogen synthase kinase-3 could phosphorylate and promote Fbw7-mediated KLF5 degradation. More importantly, Fbw7 negatively regulated the biological activity of KLF5 in gene regulation and cell proliferation. Taken together, these data indicate that Fbw7 is a key negative regulator controlling KLF5-mediated cell proliferation and suggest an additional mechanism linking the loss of Fbw7 function to tumorigenesis. Sp/Krüppel-like factor (KLF) 2 transcription factors are involved in various biological processes and human diseases (1, 2). KLF5 (also known as IKLF and BTEB2) is a basic KLF transcription factor that regulates cell proliferation and plays an important role in diverse physiological and pathological processes, including stemness, inflammation, and atherogenesis (3, 4). As a proproliferative factor, KLF5 also has essential functions in tumorigenesis (3). Increasing evidence indicates that KLF5 can function as an oncogenic protein by promoting cell proliferation in many cancers (5-10). For example, a high expression level of KLF5 correlates with a shorter survival time in breast cancer patients (11). Inhibition of KLF5 expression by pharmacological or genetic methods significantly reduces colorectal cancer cell proliferation (6, 12). However, under certain conditions, KLF5 can also act as a tumor suppressor in some cancers (13,14). The exact mechanisms underlying these apparently contradictory functions are not completely understood.The function of KLF5 is regulated at multiple levels. KLF5 transcription is regulated by several signaling molecules such as Wnt and lysophosphatidic acid (15,16). At the post-translational level, KLF5 function is modulated by phosphorylation, sumoylation, and acetylation (3). Phosphorylation of KLF5 by protein kinase C enhances its transactivation activity and its interaction with CBP (cAMP-responsive element-binding protein-binding protein) (17), whereas sumoylation regulates KLF5-mediated lipid metabolism and its subcellular localization (18,19).KLF5 is an unstable protein with a short half-life in cells. Its protein levels are regulated negatively by the ubiquitin-proteasome pathway (20). The E3 ubiquiti...
Rapid phenotypic changes in traits of adaptive significance are crucial for organisms to thrive in changing environments. How such phenotypic variation is achieved rapidly, despite limited genetic variation in species that experience a genetic bottleneck is unknown.Capsella rubella, an annual and inbreeding forb (Brassicaceae), is a great system for studying this basic question. Its distribution is wider than those of its congeneric species, despite an extreme genetic bottleneck event that severely diminished its genetic variation. Here, we demonstrate that transposable elements (TEs) are an important source of genetic variation that could account for its high phenotypic diversity. TEs are (i) highly enriched inC. rubellacompared with its outcrossing sister speciesCapsella grandiflora, and (ii) 4.2% of polymorphic TEs inC. rubellaare associated with variation in the expression levels of their adjacent genes. Furthermore, we show that frequent TE insertions atFLOWERING LOCUS C (FLC)in natural populations ofC. rubellacould explain 12.5% of the natural variation in flowering time, a key life history trait correlated with fitness and adaptation. In particular, we show that a recent TE insertion at the 3′ UTR ofFLCaffects mRNA stability, which results in reducing its steady-state expression levels, to promote the onset of flowering. Our results highlight that TE insertions can drive rapid phenotypic variation, which could potentially help with adaptation to changing environments in a species with limited standing genetic variation.
Type Iγ phosphatidylinositol phosphate kinase (PIPKIγ), a phospholipid kinase generating PIP2, is positively expressed in breast cancer tissues, which correlates intimately with the progression of patients. However, little is known about the expression level of PIPKIγ in patients with other cancer types as well as their underlying regulation mechanisms. Here, we report that PIPKIγ is highly expressed in lung cancer tissues and its expression level is critical for lung cancer cell proliferation, which may serve as a prognostic marker for lung cancer patients. Meanwhile, we show that E3 ubiquitin ligase Smurf1 directly interacts with PIPKIγ and targets PIPKIγ for ubiquitination and degradation in lung cancer cells. Also, we discover that Smurf1 directly binds to the kinase domain of PIPKIγ via its C2 domain while Lysine 255 in PIPKIγ acts as the major ubiquitin acceptor site for Smurf1. In addition, we demonstrate that the phosphorylation mimicking mutant of Smurf1, Smurf1 T306D, prevents PIPKIγi2 from ubiquitination and subsequent degradation similar to the effect of forskolin-potentiated cAMP formation, suggesting that Thr306 in Smurf1 is critical for its phosphorylation by PKA. Moreover, PKA-Smurf1-PIPKIγ signal transduction takes a significant part in lung cancer cell growth and in vivo tumorigenesis. Thus, we propose that the PKA-Smurf1-PIPKIγ pathway has an important role in pulmonary tumorigenesis and imposes substantial clinical impact on development of novel diagnostic markers and therapeutic targets for lung cancer treatment.
Flowering time is an adaptive life history trait. , a close relative of and a young species, displays extensive variation for flowering time but low standing genetic variation due to an extreme bottleneck event, providing an excellent opportunity to understand how phenotypic diversity can occur with a limited initial gene pool. Here, we demonstrate that common allelic variation and parallel evolution at the locus confer variation in flowering time in We show that two overlapping deletions in the 5' untranslated region (UTR) of , which are associated with local changes in chromatin conformation and histone modifications, reduce its expression levels and promote flowering. We further show that these two pervasive variants originated independently in natural populations after speciation and spread to an intermediate frequency, suggesting a role of this parallel -regulatory change in adaptive evolution. Our results provide an example of how parallel mutations in the same 5' UTR region can shape phenotypic evolution in plants.
Background: It was unknown whether human -arrestin 2 could be SUMOylated. Results: Human -arrestin 2 is SUMOylated on Lys-295. SUMOylation attenuates -arrestin 2 inhibition of IL-1R/TRAF6 signaling. Conclusion: SUMOylation attenuates human -arrestin 2 inhibition of TRAF6 and IL-1R signaling. Significance: We show SUMOylation as a novel mechanism in regulation of -arrestin 2-mediated IL-1R-TRAF6 signaling.
Polymorphisms of CYP19A1 may be related to the increased risk of lung cancer; in particular, haplotype ACA may contribute to lung-cancer progression in nonsmokers. Further validation with larger populations is required.
Background: Colon cancer is a top lethal cancer in man and women worldwide and drug resistance is the major cause of cancer-related death. Combinational therapy and drug delivery with nanoparticles have been shown to effectively overcome drug resistance in many cancers. We previously reported that nanoemulsion (NE) loaded paclitaxel (PTX) and BEZ235 could synergistically inhibit colon cancer cell growth. Purpose: To investigate whether NE loaded PTX and BEZ235 can overcome drug resistance and synergistically inhibit drug-resistant colon cancer cell growth in vitro and in vivo. Methods: The in vitro treatment effect on cell viability was assayed using CCK8 kit, cell morphological change was detected by β-tubulin immunofluorescence staining, drug resistancerelated proteins were analyzed by Western blotting, and in vivo tumor growth test was performed in nude mice xeno-transplanted with 2 drug-resistant colon cancer cell lines HCT116-LOHP and HT29-DDP. Results: Both cell lines were sensitive to PTX but relatively insensitive to BEZ235. PTX combined with BEZ235 synergistically inhibited the proliferation of both cell lines. Nanoemulsion loaded PTX (NE-PTX) reduced the IC50 of PTX to approximately 2/5 of free PTX, indicating a high inhibitory efficacy of NE-PTX. When NE-PTX combined with a low concentration of BEZ235 (50 nM), the IC50 was decreased to approximately 2/3 of free PTX. Moreover, NE-PTX+BEZ235 treatment increased apoptosis, decreased Pgp and ABCC1 expression, and reduced tumor weights compared to the single drug treatment and the control group. These results suggest that nanoemulsion loaded PTX+BEZ235 can overcome drug resistance and improve the inhibitory effect on cancer cell proliferation and tumor growth. Conclusion: Our study thus provides a possible new approach to treat colon cancer patients with drug resistance.
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