Obesity is closely associated with insulin resistance and establishes the leading risk factor for type 2 diabetes mellitus, yet the molecular mechanisms of this association are poorly understood. The c-Jun amino-terminal kinases (JNKs) can interfere with insulin action in cultured cells and are activated by inflammatory cytokines and free fatty acids, molecules that have been implicated in the development of type 2 diabetes. Here we show that JNK activity is abnormally elevated in obesity. Furthermore, an absence of JNK1 results in decreased adiposity, significantly improved insulin sensitivity and enhanced insulin receptor signalling capacity in two different models of mouse obesity. Thus, JNK is a crucial mediator of obesity and insulin resistance and a potential target for therapeutics.

The c-Jun N-terminal kinases (JNKs) are key regulators of inflammation and interfere with insulin action in cultured cells and whole animals. Obesity increases total JNK activity, and JNK1, but not JNK2, deficiency results in reduced adiposity and improved insulin sensitivity. Interestingly, a higher-than-normal level of JNK activation is observed in Jnk2 ؊/؊ mice, particularly in the liver, indicating an interaction between the isoforms that might have masked the metabolic activity of JNK2 in isolated mutant mice. To address the role of the JNK2 isoform in metabolic homeostasis, we intercrossed Jnk1 ؊/؊ and Jnk2 ؊/؊ mice and examined body weight and glucose metabolism in the resulting mutant allele combinations. Among all of the viable genotypes examined, we observed only reduced body weight and increased insulin sensitivity in Jnk1 ؊/؊ and Jnk1 ؉/؊ Jnk2 ؊/؊ mice. These two groups of mice also exhibited reduced total JNK activity and cytokine expression in liver tissue compared with all other genotypes examined. These data indicate that the JNK2 isoform is also involved in metabolic regulation, but its function is not obvious when JNK1 is fully expressed because of regulatory crosstalk between the two isoforms.diabetes ͉ fatty liver ͉ metabolic syndrome ͉ inflammation ͉ stress

A protein, which facilitates assembly of a nucleosome-like structure in vitro, was previously partially purified from mouse FM3A cells [Ishimi, Y. et al. (1 983) J . Biochem. (Tokyo) 94,735 -7441. The protein has been purified to approximately 80 from FM3A cells by using histone-Sepharose column chromatography. It sedimented at 4.6 S and had a molecular mass of 53kDa. A preincubation of core histones with the 53-kDa peptide before DNA addition was necessary for the nucleosome assembly. The 53-kDa peptide bound to core histones and formed a 12-S complex. This complex contained stoichiometrical amounts of the 53-kDa peptide and core histones, and the core histones in this complex were composed of equal amounts of H2A, H2B, H3 and H4 histones. The nucleosomes were assembled by adding pBR322 DNA to the 12-S complex. When mononucleosome DNA and core histones were mixed in the presence of the 53-kDa peptide, formation of a 10.5-S complex was observed. The complex contained DNA and core histones in equal amounts, while no 53-kDa peptide was detected in the complex.From above results it is suggested that the 53-kDa peptide facilitates nucleosome assembly by mediating formation of histone octarner and transferring it to DNA. Rat antibody against the 53-kDa peptide did not bind to nucleoplasmin from Xenopus eggs. The relationship between the 53-kDa peptide and nucleoplasmin is discussed.In eukaryotic cells, chromatin consists of a repeating unit called a 'nucleosome', which contains about 200 base-pairs of DNA, two molecules each of H2A, H2B, H3 and H4 histones, and one molecule of HI histone [1,2]. In many mammalian cells almost all core histones (H2A, H2B, H3, H4) are synthesized at S phase and their synthesis is coupled with DNA synthesis [3 -51. However, basal histone synthesis is observed also at GI phase in some cells [6], and mouse lymphoma cell synthesizes core histones at G I phase at the same level as S phase [7,8].As to the mode of deposition of newly synthesized histone on DNA, several confusing results have been presented. From the observation of the group of Weintraub [9-111, it is suggested that new histones are bound to the lagging strand of replicated DNA and they are assembled conservatively into an octamer. On the other hand, Jackson et al. [12,13] indicated that new H3 and H4 histones were bound to replicating DNA, while new H2A and H2B histones were deposited on nonreplicating DNA rather than the replicating DNA. There are several reports indicating that new histones are distributed equally to both daughter strands [14,15]. In any case it is not well examined whether new histones are bound to DNA by a single step as an octamer or by multiple steps.There are several factors which facilitatc nucleosome assembly in t'itro at physiological ionic strength. Nucleoplasmin (29 kDa), which has been discovered in Xenopus eggs by Laskey et al. [I 6,171, facilitate nucleosome assembly by the interaction with core histones. Experiments using its fluorescent antibody suggested that it exists in mammalian cells [...

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An activity which facilitates assembly of nucleosome-like structures in vitro at physiological ionic strength was detected both in human HeLa S3 cells and mouse FM3A cells. The assembly protein was purified from FM3A cells by fractionation with ammonium sulfate, DEAE-cellulose, phosphocellulose, Sephadex G-150 column chromatography, and sucrose gradient centrifugation. In the sucrose gradient, the activity was detected at 5S and the active fraction contained three peptides of 59,000, 65,000, and 102,000 daltons. When core histones were mixed with these peptides, the 59,000 peptide sedimented at the 6S and 10S positions, where the histones co-sedimented. The 6S fraction contained H2A, H2B, and A24 proteins, and the 10S fraction contained four kinds of core histones in equal amounts. Nucleosomes were formed by mixing DNA with the 10S fraction, but were not formed with the 6S fraction. The nucleosome structure assembled was assessed using the sensitivity to micrococcal nuclease.

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