Ceramides are bioactive sphingolipids, which are composed of sphingoid bases carrying acyl chains of various lengths. Ceramides are synthesized by a family of six ceramide synthases (CerS) in ...mammals, which produce ceramides with different N-linked acyl chains. Increased ceramide levels are known to contribute to the development of obesity and insulin resistance. Recently, it has been demonstrated that the ceramide acylation pattern is of particular importance for an organism to maintain energy homeostasis. However, which of the CerS family members are involved in this process is not yet completely known. Using newly developed CerS5 knock-out mice, we show here that CerS5 is essential to maintain cellular C16:0 sphingolipid pools in lung, spleen, muscle, liver, and white adipose tissue. Glycerophospholipid levels in CerS5-deficient mice were not altered. We found a strong impact of CerS5-dependent ceramide synthesis in white adipose tissue after high fat diet feeding. In skeletal muscle, liver, and spleen, C16:0-ceramide levels were altered independent of feeding conditions. The loss of CerS5 is associated with reduced weight gain and improved systemic health, including maintenance of glucose homeostasis and reduced white adipose tissue inflammation after high fat diet challenge. Our findings indicate that reduction of endogenous C16:0-ceramide by genetic inhibition of CerS5 is sufficient to ameliorate obesity and its comorbidities.
Myc family proteins promote cancer by inducing widespread changes in gene expression. Their rapid turnover by the ubiquitin–proteasome pathway is regulated through phosphorylation of Myc Box I and ...ubiquitination by the E3 ubiquitin ligase SCFFbxW7. However, N-Myc protein (the product of the MYCN oncogene) is stabilized in neuroblastoma by the protein kinase Aurora-A in a manner that is sensitive to certain Aurora-A–selective inhibitors. Here we identify a direct interaction between the catalytic domain of Aurora-A and a site flanking Myc Box I that also binds SCFFbxW7. We determined the crystal structure of the complex between Aurora-A and this region of N-Myc to 1.72-Å resolution. The structure indicates that the conformation of Aurora-A induced by compounds such as alisertib and CD532 is not compatible with the binding of N-Myc, explaining the activity of these compounds in neuroblastoma cells and providing a rational basis for the design of cancer therapeutics optimized for destabilization of the complex. We also propose a model for the stabilization mechanism in which binding to Aurora-A alters how N-Myc interacts with SCFFbxW7 to disfavor the generation of Lys48-linked polyubiquitin chains.
Amplification of MYCN is a driver mutation in a subset of human neuroendocrine tumors, including neuroblastoma. No small molecules that target N-Myc, the protein encoded by MYCN, are clinically ...available. N-Myc forms a complex with the Aurora-A kinase, which protects N-Myc from proteasomal degradation. Although stabilization of N-Myc does not require the catalytic activity of Aurora-A, we show here that two Aurora-A inhibitors, MLN8054 and MLN8237, disrupt the Aurora-A/N-Myc complex and promote degradation of N-Myc mediated by the Fbxw7 ubiquitin ligase. Disruption of the Aurora-A/N-Myc complex inhibits N-Myc-dependent transcription, correlating with tumor regression and prolonged survival in a mouse model of MYCN-driven neuroblastoma. We conclude that Aurora-A is an accessible target that makes destabilization of N-Myc a viable therapeutic strategy.
•Aurora-A-specific inhibitors disrupt the Aurora-A/N-Myc complex•Inhibitors trigger proteasomal degradation of N-Myc via Fbxw7 ubiquitin ligase•Inhibitors revert N-Myc-dependent gene expression in a mouse model of neuroblastoma•Inhibitors induce tumor regression and extend survival in this model
MYC proteins bind globally to active promoters and promote transcriptional elongation by RNA polymerase II (Pol II). To identify effector proteins that mediate this function, we performed mass ...spectrometry on N-MYC complexes in neuroblastoma cells. The analysis shows that N-MYC forms complexes with TFIIIC, TOP2A, and RAD21, a subunit of cohesin. N-MYC and TFIIIC bind to overlapping sites in thousands of Pol II promoters and intergenic regions. TFIIIC promotes association of RAD21 with N-MYC target sites and is required for N-MYC-dependent promoter escape and pause release of Pol II. Aurora-A competes with binding of TFIIIC and RAD21 to N-MYC in vitro and antagonizes association of TOP2A, TFIIIC, and RAD21 with N-MYC during S phase, blocking N-MYC-dependent release of Pol II from the promoter. Inhibition of Aurora-A in S phase restores RAD21 and TFIIIC binding to chromatin and partially restores N-MYC-dependent transcriptional elongation. We propose that complex formation with Aurora-A controls N-MYC function during the cell cycle.
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•N-MYC forms complexes with TFIIIC, RAD21, and TOP2A•TFIIIC recruits RAD21 and is required for N-MYC-dependent pause release of Pol II•Aurora-A displaces TFIIIC, TOP2A, and RAD21 from N-MYC during S phase•Aurora-A inhibits pause release of Pol II during S phase
Büchel et al. demonstrate that N-MYC forms complexes with TFIIIC, TOP2A, and RAD21. Aurora-A competes with TFIIIC and RAD21 for binding to N-MYC, and Aurora-A displaces the three proteins from N-MYC during S phase. As consequence, N-MYC-dependent pause release is inhibited during S phase, preventing activation of the ATR checkpoint kinase.
In the 1970s and 1980s, important transitions took place in Germany in both migration and labor market policies. The so-called recruitment of 'guest-workers' came to an end, and the patterns of ...cross-border movement changed significantly - and with them the ways unions as well as migrant organizations articulated their political claims. Taking these aspects into account, I examine union strategies concerning migrant workers' interests. I discuss how migration challenged and changed the agenda of local trade unions in terms of content and processes. This paper puts forth the hypothesis that local trade union organizations could react to such challenges by broadening or narrowing their agenda. I draw on material gained from empirical research on trade unions and migrant organizations in Hamburg. Analyzing insights from qualitative interviews and primary sources, I discuss trade union activities regarding the inclusion of migrants, collective bargaining, and labor market policies, as well as migrants' access to social and political rights. I also present initiatives against racism both within and outside of trade unions.
When it comes to analysing exploitative and unfree labour, most research refers to “othering” or “race”. Race is often treated as a given category rather than a social phenomenon that needs ...explanation. In this article, I draw attention to the question of how racism is preserved, reproduced and changed within and through unfree labour relations. I do this by discussing the conceptual interlinkages between unfree labour, migration and racism. While the role of migration policies should not be underestimated, this should be accompanied by an analytical account of their racist background and outcomes. Based on this I present a framework for the analysis of racism as it relates to unfree labour and migration. I draw attention to three different levels of analysis (historico-structural, discursive-symbolic and everyday practices) and the interrelations between them. For empirical illustrations, I draw on my research on modern slave labour in two production sectors in Brazil: charcoal and clothing. I discuss the empirical findings with regard to three analytical problems in the analysis of unfree labour and racism: the impact of generalising knowledge on (future) migrant workers; the role and responsibility of global production networks; and the need to critically reflect on initiatives and policies aimed at the eradication of unfree labour.
KEYWORDS: labour migration; unfree labour; racism; Brazil; workers’ rights
Migrationspolitik Carstensen, Anne Lisa
Kölner Zeitschrift für Soziologie und Sozialpsychologie,
09/2018, Letnik:
70, Številka:
3
Journal Article, Book Review
MYC is an unstable protein, and its turnover is controlled by the ubiquitin system. Ubiquitination enhances MYC-dependent transactivation, but the underlying mechanism remains unresolved. Here we ...show that MYC proteasomal turnover is dispensable for loading of RNA polymerase II (RNAPII). In contrast, MYC turnover is essential for recruitment of TRRAP, histone acetylation, and binding of BRD4 and P-TEFb to target promoters, leading to phosphorylation of RNAPII and transcriptional elongation. In the absence of histone acetylation and P-TEFb recruitment, MYC associates with the PAF1 complex (PAF1C) through a conserved domain in the MYC amino terminus (“MYC box I”). Depletion of the PAF1C subunit CDC73 enhances expression of MYC target genes, suggesting that the MYC/PAF1C complex can inhibit transcription. Because several ubiquitin ligases bind to MYC via the same domain (“MYC box II”) that interacts with TRRAP, we propose that degradation of MYC limits the accumulation of MYC/PAF1C complexes during transcriptional activation.
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•Proteasomal turnover of MYC is required for its transcriptional activity•Stabilized MYC interacts with the elongation factor complex PAF1C•The MYC-PAF1C complex inhibits transcription•Turnover of MYC promotes histone acetylation and the transfer of PAF1C onto RNAPII
Jaenicke et al. demonstrate that MYC degradation promotes histone acetylation and transfer of elongation factors to RNA polymerase II. This mechanism limits the accumulation of inhibitory intermediates during transcriptional activation and stimulates transcriptional elongation.
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