Telomere-independent Rap1 is an IKK adaptor and regulates NF-κB-dependent gene expression
Laboratory of NFkappaB Signaling, Proteos, Singapore 138673, Singapore. Nature Cell Biology
(Impact Factor: 19.68).
08/2010; 12(8):758-67. DOI: 10.1038/ncb2080
We describe a genome-wide gain-of-function screen for regulators of NF-kappaB, and identify Rap1 (Trf2IP), as an essential modulator of NF-kappaB-mediated pathways. NF-kappaB is induced by ectopic expression of Rap1, whereas its activity is inhibited by Rap1 depletion. In addition to localizing on telomeres, mammalian Rap1 forms a complex with IKKs (IkappaB kinases), and is crucial for the ability of IKKs to be recruited to, and phosphorylate, the p65 subunit of NF-kappaB to make it transcriptionally competent. Rap1-mutant mice display defective NF-kappaB activation and are resistant to endotoxic shock. Furthermore, levels of Rap1 are positively regulated by NF-kappaB, and human breast cancers with NF-kappaB hyperactivity show elevated levels of cytoplasmic Rap1. Similar to inhibiting NF-kappaB, knockdown of Rap1 sensitizes breast cancer cells to apoptosis. These results identify the first cytoplasmic role of Rap1 and provide a mechanism through which it regulates an important signalling cascade in mammals, independent of its ability to regulate telomere function.
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Available from: Brendan O'Brien
- "Additional roles for TERF2IP include prevention of non-homologous end joining  and homology-directed repair , protection from obesity via regulation of metabolic genes  and regulation of senescence . Additionally, TERF2IP associates with iκB kinases in the cytoplasm and regulates NF-κB modulated gene expression . "
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ABSTRACT: Telomeres are specialized nucleoprotein structures that protect chromosomal ends from degradation. These structures progressively shorten during cellular division and can signal replicative senescence below a critical length. Telomere length is predominantly maintained by the enzyme telomerase. Significant decreases in telomere length and telomerase activity are associated with a host of chronic diseases; conversely their maintenance underpins the optimal function of the adaptive immune system. Habitual physical activity is associated with longer leukocyte telomere length; however, the precise mechanisms are unclear. Potential hypotheses include regulation of telomeric gene transcription and/or microRNAs (miRNAs). We investigated the acute exercise-induced response of telomeric genes and miRNAs in twenty-two healthy males (mean age = 24.1±1.55 years). Participants undertook 30 minutes of treadmill running at 80% of peak oxygen uptake. Blood samples were taken before exercise, immediately post-exercise and 60 minutes post-exercise. Total RNA from white blood cells was submitted to miRNA arrays and telomere extension mRNA array. Results were individually validated in white blood cells and sorted T cell lymphocyte subsets using quantitative real-time PCR (qPCR). Telomerase reverse transcriptase (TERT) mRNA (P = 0.001) and sirtuin-6 (SIRT6) (P<0.05) mRNA expression were upregulated in white blood cells after exercise. Fifty-six miRNAs were also differentially regulated post-exercise (FDR <0.05). In silico analysis identified four miRNAs (miR-186, miR-181, miR-15a and miR-96) that potentially targeted telomeric gene mRNA. The four miRNAs exhibited significant upregulation 60 minutes post-exercise (P<0.001). Telomeric repeat binding factor 2, interacting protein (TERF2IP) was identified as a potential binding target for miR-186 and miR-96 and demonstrated concomitant downregulation (P<0.01) at the corresponding time point. Intense cardiorespiratory exercise was sufficient to differentially regulate key telomeric genes and miRNAs in white blood cells. These results may provide a mechanistic insight into telomere homeostasis and improved immune function and physical health.
Available from: Ranjodh Sandhu
- "At the insect stage, FAIRE and MNase digestion results indicated that TbRAP1 depletion affects chromatin structure mildly at many loci throughout the genome, which is much broader than we previously anticipated. In both yeast and mammalian cells, RAP1 homologs have been found to locate at non-telomeric regions and act as transcription regulators (45–49), and yeast RAP1 has been found to help determine genome-wide chromatin structure (50). We previously observed that some TbRAP1 appears to localize at loci other than telomeres (23). "
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ABSTRACT: Trypanosoma brucei causes human African trypanosomiasis and regularly switches its major surface antigen variant surface glycoprotein (VSG)
to evade mammalian host immune responses at the bloodstream form (BF) stage. Monoallelic expression of BF Expression Site
(BES)-linked VSGs and silencing of metacyclic VSGs (mVSGs) in BF cells are essential for antigenic variation, whereas silencing of both BES-linked and mVSGs in the procyclic form (PF) cells is important for cell survival in the midgut of its insect vector. We have previously shown
that silencing BES-linked VSGs in BF cells depends on TbRAP1. We now show that TbRAP1 silences both BES-linked and mVSGs at both BF and PF stages. The strength of TbRAP1-mediated BES-linked VSG silencing is stronger in the PF cells than that in BF cells. In addition, Formaldehyde-Assisted Isolation of Regulatory Elements
analysis and MNase digestion demonstrated that depletion of TbRAP1 in PF cells led to a chromatin structure change, which is significantly stronger at the subtelomeric VSG loci than at chromosome internal loci. On the contrary, no significant chromatin structure changes were detected on depletion
of TbRAP1 in BF cells. Our observations indicate that TbRAP1 helps to determine the chromatin structure at the insect stage, which likely contributes to its strong silencing effect
Available from: Juana M Flores
- "By generating a whole-body Rap1-deficient mouse model, we show here that the mammalian telomere-binding protein RAP1 is dispensable for mouse development and adult viability, in contrast to that previously reported by Teo et al. (2010) and in agreement with Sfeir et al. (2010). In agreement with our previous findings that RAP1 binds throughout chromosome arms (Martinez et al., 2010), we find a role for RAP1 in the transcriptional regulation of pathways involved in postnatal cellular energy metabolism. "
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ABSTRACT: RAP1 is part of shelterin, the protective complex at telomeres. RAP1 also binds along chromosome arms, where it is proposed to regulate gene expression. To investigate the nontelomeric roles of RAP1 in vivo, we generated a RAP1 whole-body knockout mouse. These mice show early onset of obesity, which is more severe in females than in males. Rap1-deficient mice show accumulation of abdominal fat, hepatic steatosis, and high-fasting plasma levels of insulin, glucose, cholesterol, and alanine aminotransferase. Gene expression analyses of liver and visceral white fat from Rap1-deficient mice before the onset of obesity show deregulation of metabolic programs, including fatty acid, glucose metabolism, and PPARα signaling. We identify Pparα and Pgc1α as key factors affected by Rap1 deletion in the liver. We show that RAP1 binds to Pparα and Pgc1α loci and modulates their transcription. These findings reveal a role for a telomere-binding protein in the regulation of metabolism.
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