1
|
Ahamed F, Eppler N, Jones E, He L, Zhang Y. Small Heterodimer Partner Modulates Macrophage Differentiation during Innate Immune Response through the Regulation of Peroxisome Proliferator Activated Receptor Gamma, Mitogen-Activated Protein Kinase, and Nuclear Factor Kappa B Pathways. Biomedicines 2023; 11:2403. [PMID: 37760844 PMCID: PMC10525324 DOI: 10.3390/biomedicines11092403] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/25/2023] [Revised: 08/19/2023] [Accepted: 08/25/2023] [Indexed: 09/29/2023] Open
Abstract
Hepatic macrophages act as the liver's first line of defense against injury. Their differentiation into proinflammatory or anti-inflammatory subpopulations is a critical event that maintains a delicate balance between liver injury and repair. In our investigation, we explored the influence of the small heterodimer partner (SHP), a nuclear receptor primarily associated with metabolism, on macrophage differentiation during the innate immune response. During macrophage differentiation, we observed significant alterations in Shp mRNA expression. Deletion of Shp promoted M1 differentiation while interfering with M2 polarization. Conversely, overexpression of SHP resulted in increased expression of peroxisome proliferator activated receptor gamma (Pparg), a master regulator of anti-inflammatory macrophage differentiation, thereby inhibiting M1 differentiation. Upon lipopolysaccharide (LPS) injection, there was a notable increase in the proinflammatory M1-like macrophages, accompanied by exacerbated infiltration of monocyte-derived macrophages (MDMs) into the livers of Shp myeloid cell specific knockout (Shp-MKO). Concurrently, we observed significant induction of tumor necrosis factor alpha (Tnfa) and chemokine (C-C motif) ligand 2 (Ccl2) expression in LPS-treated Shp-MKO livers. Additionally, the mitogen-activated protein kinase (MAPK) and nuclear factor kappa B (NF-κB) pathways were activated in LPS-treated Shp-MKO livers. Consistently, both pathways were hindered in SHP overexpression macrophages. Finally, we demonstrated that SHP interacts with p65, thereby influencing macrophage immune repones. In summary, our study uncovered a previously unrecognized role of SHP in promoting anti-inflammatory macrophage differentiation during the innate immune response. This was achieved by SHP acting as a regulator for the Pparg, MAPK, and NF-κB pathways.
Collapse
Affiliation(s)
| | | | | | | | - Yuxia Zhang
- Department of Pharmacology, Toxicology and Therapeutics, University of Kansas Medical Center, MS 1018, 3901 Rainbow Boulevard, Kansas City, KS 66160, USA; (F.A.); (N.E.); (E.J.); (L.H.)
| |
Collapse
|
2
|
Sampson C, Wang Q, Otkur W, Zhao H, Lu Y, Liu X, Piao H. The roles of E3 ubiquitin ligases in cancer progression and targeted therapy. Clin Transl Med 2023; 13:e1204. [PMID: 36881608 PMCID: PMC9991012 DOI: 10.1002/ctm2.1204] [Citation(s) in RCA: 9] [Impact Index Per Article: 9.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/06/2022] [Revised: 02/07/2023] [Accepted: 02/13/2023] [Indexed: 03/08/2023] Open
Abstract
Ubiquitination is one of the most important post-translational modifications which plays a significant role in conserving the homeostasis of cellular proteins. In the ubiquitination process, ubiquitin is conjugated to target protein substrates for degradation, translocation or activation, dysregulation of which is linked to several diseases including various types of cancers. E3 ubiquitin ligases are regarded as the most influential ubiquitin enzyme owing to their ability to select, bind and recruit target substrates for ubiquitination. In particular, E3 ligases are pivotal in the cancer hallmarks pathways where they serve as tumour promoters or suppressors. The specificity of E3 ligases coupled with their implication in cancer hallmarks engendered the development of compounds that specifically target E3 ligases for cancer therapy. In this review, we highlight the role of E3 ligases in cancer hallmarks such as sustained proliferation via cell cycle progression, immune evasion and tumour promoting inflammation, and in the evasion of apoptosis. In addition, we summarise the application and the role of small compounds that target E3 ligases for cancer treatment along with the significance of targeting E3 ligases as potential cancer therapy.
Collapse
Affiliation(s)
- Chibuzo Sampson
- CAS Key Laboratory of Separation Science for Analytical ChemistryDalian Institute of Chemical PhysicsChinese Academy of SciencesDalianChina
- University of Chinese Academy of SciencesBeijingChina
| | - Qiuping Wang
- CAS Key Laboratory of Separation Science for Analytical ChemistryDalian Institute of Chemical PhysicsChinese Academy of SciencesDalianChina
| | - Wuxiyar Otkur
- CAS Key Laboratory of Separation Science for Analytical ChemistryDalian Institute of Chemical PhysicsChinese Academy of SciencesDalianChina
| | - Haifeng Zhao
- Department of OrthopedicsDalian Second People's HospitalDalianChina
| | - Yun Lu
- CAS Key Laboratory of Separation Science for Analytical ChemistryDalian Institute of Chemical PhysicsChinese Academy of SciencesDalianChina
- Department of StomatologyDalian Medical UniversityDalianChina
| | - Xiaolong Liu
- CAS Key Laboratory of Separation Science for Analytical ChemistryDalian Institute of Chemical PhysicsChinese Academy of SciencesDalianChina
| | - Hai‐long Piao
- CAS Key Laboratory of Separation Science for Analytical ChemistryDalian Institute of Chemical PhysicsChinese Academy of SciencesDalianChina
- University of Chinese Academy of SciencesBeijingChina
| |
Collapse
|
3
|
Abstract
Human T-cell leukemia virus type 1 (HTLV-1) was discovered in 1980 as the first, and to date, the only retrovirus that causes human cancer. While HTLV-1 infection is generally asymptomatic, 3-5% of infected individuals develop a T cell neoplasm known as adult T cell leukemia/lymphoma (ATL) decades after infection. Since its discovery, HTLV-1 has served as a model for understanding retroviral oncogenesis, transcriptional regulation, cellular signal transduction, and cell-associated viral infection and spread. Much of the initial research was focused on the viral trans-activator/oncoprotein, Tax. Over the past decade, the study of HTLV-1 has entered the genomic era. With the development of new systems for studying HTLV-1 infection and pathogenesis, the completion of the whole genome, exome and transcriptome sequencing analyses of ATL, and the discovery of HBZ as another HTLV-1 oncogene, many established concepts about how HTLV-1 infects, persists and causes disease have undergone substantial revision. This chapter seeks to integrate our current understanding of the mechanisms of action of Tax and HBZ with the comprehensive genomic information of ATL to provide an overview of how HTLV-1 infects, replicates and causes leukemia.
Collapse
|
4
|
Guo Y, Li R, Tan Z, Shi J, Fu Y, Song Y, Zhu M, Zhang L, Huang J. E3 ubiquitin ligase ASB8 negatively regulates interferon via regulating TBK1/IKKi homeostasis. Mol Immunol 2020; 121:195-203. [DOI: 10.1016/j.molimm.2020.03.011] [Citation(s) in RCA: 11] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/02/2019] [Revised: 02/17/2020] [Accepted: 03/18/2020] [Indexed: 12/29/2022]
|
5
|
The Superimposed Deubiquitination Effect of OTULIN and Porcine Reproductive and Respiratory Syndrome Virus (PRRSV) Nsp11 Promotes Multiplication of PRRSV. J Virol 2018; 92:JVI.00175-18. [PMID: 29444948 DOI: 10.1128/jvi.00175-18] [Citation(s) in RCA: 23] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/08/2018] [Accepted: 02/12/2018] [Indexed: 02/06/2023] Open
Abstract
Linear ubiquitination plays an important role in the regulation of the immune response by regulating nuclear factor κB (NF-κB). The linear ubiquitination-specific deubiquitinase ovarian tumor domain deubiquitinase with linear linkage specificity (OTULIN) can control the immune signaling transduction pathway by restricting the Met1-linked ubiquitination process. In our study, the porcine OTLLIN gene was cloned and deubiquitin functions were detected in a porcine reproductive and respiratory syndrome virus (PRRSV)-infected-cell model. PRRSV infection promotes the expression of the OTULIN gene; in turn, overexpression of OTULIN contributes to PRRSV proliferation. There is negative regulation of innate immunity with OTULIN during viral infection. The cooperative effects of swine OTULIN and PRRSV Nsp11 potentiate the ability to reduce levels of cellular protein ubiquitin associated with innate immunity. Importantly, PRRSV Nsp11 recruits OTULIN through a nonenzymatic combination to enhance its ability to remove linear ubiquitination targeting NEMO, resulting in a superimposed effect that inhibits the production of type I interferons (IFNs). Our report presents a new model of virus utilization of the ubiquitin-protease system in vivo from the perspective of the viral proteins that interact with cell deubiquitination enzymes, providing new ideas for prevention and control of PRRSV.IMPORTANCE Deubiquitination effects of swine OTULIN were identified. The interaction between porcine OTULIN and PRRSV Nsp11 is dependent on the OTU domain. PRRSV Nsp11 recruits OTULIN through a nonenzymatic combination to promote removal of linear ubiquitination targeting NEMO, resulting in a superimposed effect that inhibits the production of type I IFNs.
Collapse
|
6
|
Zhang J, Lei Z, Huang Z, Zhang X, Zhou Y, Luo Z, Zeng W, Su J, Peng C, Chen X. Epigallocatechin-3-gallate(EGCG) suppresses melanoma cell growth and metastasis by targeting TRAF6 activity. Oncotarget 2018; 7:79557-79571. [PMID: 27791197 PMCID: PMC5346735 DOI: 10.18632/oncotarget.12836] [Citation(s) in RCA: 59] [Impact Index Per Article: 9.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/24/2016] [Accepted: 10/07/2016] [Indexed: 11/30/2022] Open
Abstract
TRAF6 (TNF Receptor-Associated Factor 6) is an E3 ubiquitin ligase that contains a Ring domain, induces K63-linked polyubiquitination, and plays a critical role in signaling transduction. Our previous results demonstrated that TRAF6 is overexpressed in melanoma and that TRAF6 knockdown dramatically attenuates tumor cell growth and metastasis. In this study, we found that EGCG can directly bind to TRAF6, and a computational model of the interaction between EGCG and TRAF6 revealed that EGCG probably interacts with TRAF6 at the residues of Gln54, Gly55, Asp57 ILe72, Cys73 and Lys96. Among these amino acids, mutation of Gln54, Asp57, ILe72 in TRAF6 could destroy EGCG bound to TRAF6, furthermore, our results demonstrated that EGCG significantly attenuates interaction between TRAF6 and UBC13(E2) and suppresses TRAF6 E3 ubiquitin ligase activity in vivo and in vitro. Additionally, the phosphorylation of IκBα, p-TAK1 expression are decreased and the nuclear translocation of p65 and p50 is blocked by treatment with EGCG, leading to inactivation of the NF-κB pathway. Moreover, EGCG significantly inhibits cell growth as well as the migration and invasion of melanoma cells. Taken together, these findings show that EGCG is a novel E3 ubiquitin ligase inhibitor that could be used to target TRAF6 for chemotherapy or the prevention of melanoma.
Collapse
Affiliation(s)
- Jianglin Zhang
- The Department of Dermatology, Xiangya Hospital, Central South University, Changsha, Hunan, China.,Hunan Key Laboratory of Skin Cancer and Psoriasis, Xiangya Hospital, Central South University, Changsha, Hunan, China
| | - Zhou Lei
- The Department of Dermatology, Xiangya Hospital, Central South University, Changsha, Hunan, China.,Hunan Key Laboratory of Skin Cancer and Psoriasis, Xiangya Hospital, Central South University, Changsha, Hunan, China
| | - Zunnan Huang
- Key Laboratory for Medical Molecular Diagnostics of Guangdong Province, Dongguan Scientific Research Center, Guangdong Medical University, Dongguan, Guangdong, China
| | - Xu Zhang
- The Department of Dermatology, Xiangya Hospital, Central South University, Changsha, Hunan, China.,Hunan Key Laboratory of Skin Cancer and Psoriasis, Xiangya Hospital, Central South University, Changsha, Hunan, China
| | - Youyou Zhou
- The Department of Dermatology, Xiangya Hospital, Central South University, Changsha, Hunan, China.,Hunan Key Laboratory of Skin Cancer and Psoriasis, Xiangya Hospital, Central South University, Changsha, Hunan, China
| | - Zhongling Luo
- The Department of Dermatology, Xiangya Hospital, Central South University, Changsha, Hunan, China.,Hunan Key Laboratory of Skin Cancer and Psoriasis, Xiangya Hospital, Central South University, Changsha, Hunan, China
| | - Weiqi Zeng
- The Department of Dermatology, Xiangya Hospital, Central South University, Changsha, Hunan, China.,Hunan Key Laboratory of Skin Cancer and Psoriasis, Xiangya Hospital, Central South University, Changsha, Hunan, China
| | - Juan Su
- The Department of Dermatology, Xiangya Hospital, Central South University, Changsha, Hunan, China.,Hunan Key Laboratory of Skin Cancer and Psoriasis, Xiangya Hospital, Central South University, Changsha, Hunan, China
| | - Cong Peng
- The Department of Dermatology, Xiangya Hospital, Central South University, Changsha, Hunan, China.,Hunan Key Laboratory of Skin Cancer and Psoriasis, Xiangya Hospital, Central South University, Changsha, Hunan, China
| | - Xiang Chen
- The Department of Dermatology, Xiangya Hospital, Central South University, Changsha, Hunan, China.,Hunan Key Laboratory of Skin Cancer and Psoriasis, Xiangya Hospital, Central South University, Changsha, Hunan, China
| |
Collapse
|
7
|
Dwane L, Gallagher WM, Ní Chonghaile T, O'Connor DP. The Emerging Role of Non-traditional Ubiquitination in Oncogenic Pathways. J Biol Chem 2017; 292:3543-3551. [PMID: 28154183 DOI: 10.1074/jbc.r116.755694] [Citation(s) in RCA: 38] [Impact Index Per Article: 5.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/19/2022] Open
Abstract
The addition of ubiquitin to a target protein has long been implicated in the process of degradation and is the primary mediator of protein turnover in the cell. Recently, however, many non-proteolytic functions of ubiquitination have emerged as key regulators of cellular homeostasis. In this review, we will describe the various non-traditional functions of ubiquitination, with particular focus on how they can be used as signaling entities in cancer formation and progression. Elaboration of this topic can lead to a better understanding of oncogenic mechanisms, as well as the discovery of novel druggable proteins within the ubiquitin pathway.
Collapse
Affiliation(s)
- Lisa Dwane
- From Molecular and Cellular Therapeutics and
| | - William M Gallagher
- the Cancer Biology and Therapeutics Laboratory, UCD School of Biomolecular and Biomedical Science, UCD Conway Institute of Biomolecular and Biomedical Research, University College Dublin, Dublin 4, Ireland
| | - Tríona Ní Chonghaile
- the Department of Physiology and Medical Physics, Royal College of Surgeons in Ireland, 123 St. Stephen's Green, Dublin 2, Ireland and
| | | |
Collapse
|
8
|
Giam CZ, Semmes OJ. HTLV-1 Infection and Adult T-Cell Leukemia/Lymphoma-A Tale of Two Proteins: Tax and HBZ. Viruses 2016; 8:v8060161. [PMID: 27322308 PMCID: PMC4926181 DOI: 10.3390/v8060161] [Citation(s) in RCA: 99] [Impact Index Per Article: 12.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/30/2016] [Revised: 05/31/2016] [Accepted: 06/01/2016] [Indexed: 12/19/2022] Open
Abstract
HTLV-1 (Human T-cell lymphotropic virus type 1) is a complex human delta retrovirus that currently infects 10–20 million people worldwide. While HTLV-1 infection is generally asymptomatic, 3%–5% of infected individuals develop a highly malignant and intractable T-cell neoplasm known as adult T-cell leukemia/lymphoma (ATL) decades after infection. How HTLV-1 infection progresses to ATL is not well understood. Two viral regulatory proteins, Tax and HTLV-1 basic zipper protein (HBZ), encoded by the sense and antisense viral transcripts, respectively, are thought to play indispensable roles in the oncogenic process of ATL. This review focuses on the roles of Tax and HBZ in viral replication, persistence, and oncogenesis. Special emphasis is directed towards recent literature on the mechanisms of action of these two proteins and the roles of Tax and HBZ in influencing the outcomes of HTLV-1 infection including senescence induction, viral latency and persistence, genome instability, cell proliferation, and ATL development. Attempts are made to integrate results from cell-based studies of HTLV-1 infection and studies of HTLV-1 proviral integration site preference, clonality, and clonal expansion based on high throughput DNA sequencing. Recent data showing that Tax hijacks key mediators of DNA double-strand break repair signaling—the ubiquitin E3 ligase, ring finger protein 8 (RNF8) and the ubiquitin E2 conjugating enzyme (UBC13)—to activate the canonical nuclear factor kappa-light-chain-enhancer of activated B-cells (NF-κB) and other signaling pathways will be discussed. A perspective on how the Tax-RNF8 signaling axis might impact genomic instability and how Tax may collaborate with HBZ to drive oncogenesis is provided.
Collapse
Affiliation(s)
- Chou-Zen Giam
- Department of Microbiology and Immunology, Uniformed Services University of the Health Sciences, 4301 Jones Bridge Rd., Bethesda, MD 20814, USA.
| | - Oliver John Semmes
- Department of Microbiology and Molecular Cell Biology, The Leroy T. Canoles Jr Cancer Research Center, Eastern Virginia Medical School, Norfolk, VA 23501, USA.
| |
Collapse
|
9
|
The class II transactivator (CIITA) is regulated by post-translational modification cross-talk between ERK1/2 phosphorylation, mono-ubiquitination and Lys63 ubiquitination. Biosci Rep 2015; 35:BSR20150091. [PMID: 26181363 PMCID: PMC4613680 DOI: 10.1042/bsr20150091] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/13/2015] [Accepted: 06/11/2015] [Indexed: 02/01/2023] Open
Abstract
The class II transactivator (CIITA) is known as the master regulator for the major histocompatibility class II (MHC II) molecules. CIITA is dynamically regulated through a series of intricate post-translational modifications (PTMs). CIITA's role is to initiate transcription of MHC II genes, which are responsible for presenting extracellular antigen to CD4(+) T-cells. In the present study, we identified extracellular signal-regulated kinase (ERK)1/2 as the kinase responsible for phosphorylating the regulatory site, Ser(280), which leads to increased levels of mono-ubiquitination and an overall increase in MHC II activity. Further, we identify that CIITA is also modified by Lys(63)-linked ubiquitination. Lys(63) ubiquitinated CIITA is concentrated in the cytoplasm and following activation of ERK1/2, CIITA phosphorylation occurs and Lys=ubiquitinated CIITA translocates to the nucleus. CIITA ubiquitination and phosphorylation perfectly demonstrates how CIITA location and activity is regulated through PTM cross-talk. Identifying CIITA PTMs and understanding how they mediate CIITA regulation is necessary due to the critical role CIITA has in the initiation of the adaptive immune response.
Collapse
|
10
|
Tomar D, Singh R. TRIM family proteins: emerging class of RING E3 ligases as regulator of NF-κB pathway. Biol Cell 2014; 107:22-40. [DOI: 10.1111/boc.201400046] [Citation(s) in RCA: 67] [Impact Index Per Article: 6.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/09/2014] [Accepted: 10/06/2014] [Indexed: 12/22/2022]
Affiliation(s)
- Dhanendra Tomar
- Department of Cell Biology; School of Biological Sciences and Biotechnology; Indian Institute of Advanced Research; Gandhinagar India
| | - Rajesh Singh
- Department of Biochemistry; Faculty of Science; The M.S. University of Baroda; Vadodara 390 002 Gujarat India
| |
Collapse
|
11
|
Tomar D, Singh R. TRIM13 regulates ubiquitination and turnover of NEMO to suppress TNF induced NF-κB activation. Cell Signal 2014; 26:2606-13. [PMID: 25152375 DOI: 10.1016/j.cellsig.2014.08.008] [Citation(s) in RCA: 26] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/07/2014] [Accepted: 08/17/2014] [Indexed: 10/24/2022]
Abstract
The NF-κB family of transcription factors is activated in response to various intracellular or extracellular stimuli and its dysregulation leads to pathological conditions like infection, cancer, neurodegenerative disorders. The post-translational modification by ubiquitination regulates various steps of NF-κB pathway. In the current study, we have described the role of TRIM13, an endoplasmic reticulum (ER) membrane anchored E3 ligase in regulation of NF-κB. The expression of TRIM13 represses TNF induced NF-κB while the knockdown has the opposite effect. The E3 ligase activity and ER localization is essential for NF-κB suppression whereas TRIM13 regulated autophagy is not essential. TRIM13 interacts with NEMO and modulates its ubiquitination and turnover, hence may regulate IKK complex activity. TRIM13 mediated NF-κB repression is essential for negative regulation of clonogenic ability of the cells. This study for the first time demonstrated the role of TRIM13, ER resident RING E3 ligase as a novel regulator of NEMO ubiquitination, negative regulator of NF-κB signaling and its role as a tumor suppressor.
Collapse
Affiliation(s)
- Dhanendra Tomar
- Department of Cell Biology, School of Biological Sciences and Biotechnology, Indian Institute of Advanced Research, Gandhinagar, India
| | - Rajesh Singh
- Department of Cell Biology, School of Biological Sciences and Biotechnology, Indian Institute of Advanced Research, Gandhinagar, India.
| |
Collapse
|
12
|
HTLV-1 tax-induced rapid senescence is driven by the transcriptional activity of NF-κB and depends on chronically activated IKKα and p65/RelA. J Virol 2012; 86:9474-83. [PMID: 22740410 DOI: 10.1128/jvi.00158-12] [Citation(s) in RCA: 27] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/08/2023] Open
Abstract
The HTLV-1 oncoprotein Tax is a potent activator of classical and alternative NF-κB pathways and is thought to promote cell proliferation and transformation via NF-κB activation. We showed recently that hyperactivation of NF-κB by Tax triggers a cellular senescence response (H. Zhi et al., PLoS Pathog. 7:e1002025, 2011). Inhibition of NF-κB activation by expression of I-κBα superrepressor or by small hairpin RNA (shRNA)-mediated knockdown of p65/RelA rescues cells from Tax-induced rapid senescence (Tax-IRS). Here we demonstrate that Tax-IRS is driven by the transcriptional activity of NF-κB. Knockdown of IKKγ, the primary Tax target, by shRNAs abrogated Tax-mediated activation of both classical and alternative NF-κB pathways and rendered knockdown cells resistant to Tax-IRS. Consistent with a critical role of IKKα in the transcriptional activity of NF-κB, IKKα deficiency drastically decreased NF-κB trans-activation by Tax, although it only modestly reduced Tax-mediated I-κBα degradation and NF-κB nuclear localization. In contrast, although IKKβ knockdown attenuated Tax-induced NF-κB transcriptional activation, the residual NF-κB activation in IKKβ-deficient cells was sufficient to trigger Tax-IRS. Importantly, the phenotypes of NIK and TAK1 knockdown were similar to those of IKKα and IKKβ knockdown, respectively. Finally, double knockdown of RelB and p100 had a minor effect on senescence induction by Tax. These data suggest that Tax, through its interaction with IKKγ, helps recruit NIK and TAK1 for IKKα and IKKβ activation, respectively. In the presence of Tax, the delineation between the classical and alternative NF-κB pathways becomes obscured. The senescence checkpoint triggered by Tax is driven by the transcriptional activity of NF-κB, which depends on activated IKKα and p65/RelA.
Collapse
|