Modulation of the acetylation state of histones plays a pivotal role in the regulation of gene expression. Histone deacetylases (HDACs) catalyze the removal of acetyl groups from lysines near the N termini of histones. This reaction promotes the condensation of chromatin, leading to repression of transcription. HDAC deregulation has been linked to several types of cancer, suggesting a potential use for HDAC inhibitors in oncology. Here we describe the first crystal structures of a human HDAC: the structures of human HDAC8 complexed with four structurally diverse hydroxamate inhibitors. This work sheds light on the catalytic mechanism of the HDACs, and on differences in substrate specificity across the HDAC family. The structure also suggests how phosphorylation of Ser39 affects HDAC8 activity.

Patten recognition receptors, which recognize pathogens or components of injured cells (danger), trigger activation of the innate immune system. Whether and how the host distinguishes between danger- versus pathogen-associated molecular patterns remains unresolved. We report that CD24-deficient mice exhibit increased susceptibility to danger- but not pathogen-associated molecular patterns. CD24 associates with high mobility group box 1 (HMGB1), heat shock protein 70 (HSP70) and heat shock protein 90 (HSP90), negatively regulates their stimulatory activity and inhibits nuclear factor-kappa B (NF-κB) activation. This occurs at least in part through CD24 association with Siglec-10 in humans or Siglec-G in mice. Our results reveal that the CD24-Siglec G pathway protects the host against a lethal response to pathological cell death and discriminates danger- versus pathogen-associated molecular patterns.

SUMMARY Anti-HER2/neu antibody therapy is reported to mediate tumor regression by interrupting oncogenic signals and/or inducing FcR-mediated cytotoxicity. Here, we demonstrate that the mechanisms of tumor regression by this therapy also require the adaptive immune response. Activation of innate immunity and T cells, initiated by antibody treatment, was necessary. Intriguingly, the addition of chemotherapeutic drugs, while capable of enhancing the reduction of tumor burden, could abrogate antibody-initiated immunity leading to decreased resistance to re-challenge or earlier relapse. Increased influx of both innate and adaptive immune cells into the tumor microenvironment by a selected immunotherapy further enhanced subsequent antibody-induced immunity, leading to increased tumor eradication and resistance to re-challenge. Therefore, this study proposes a model and strategy for anti-HER2/neu antibody-mediated tumor clearance.

Proprotein convertase subtilisin/kexin type 9 (PCSK9) regulates serum LDL cholesterol (LDL-C) by interacting with the LDL receptor (LDLR) and is an attractive therapeutic target for LDL-C lowering. We have generated a neutralizing anti-PCSK9 antibody, mAb1, that binds to an epitope on PCSK9 adjacent to the region required for LDLR interaction. In vitro, mAb1 inhibits PCSK9 binding to the LDLR and attenuates PCSK9-mediated reduction in LDLR protein levels, thereby increasing LDL uptake. A combination of mAb1 with a statin increases LDLR levels in HepG2 cells more than either treatment alone. In wild-type mice, mAb1 increases hepatic LDLR protein levels Ϸ2-fold and lowers total serum cholesterol by up to 36%: this effect is not observed in LDLR ؊/؊ mice. In cynomolgus monkeys, a single injection of mAb1 reduces serum LDL-C by 80%, and a significant decrease is maintained for 10 days. We conclude that anti-PCSK9 antibodies may be effective therapeutics for treating hypercholesterolemia.antibody ͉ LDL-C ͉ LDLR ͉ PCSK9 ͉ hypercholesterolemia P roprotein convertase subtilisin/kexin type 9 (PCSK9) has been implicated as an important regulator of LDL metabolism (1, 2). Human genetic studies provide strong validation for the role of PCSK9 in modulating LDL cholesterol (LDL-C) levels and the incidence of coronary heart disease (CHD) in man. Gain-of-function (GOF) mutations in the PCSK9 gene are associated with elevated serum LDL-C levels (Ͼ300 mg/dL) and premature CHD (3), whereas loss-of-function (LOF) mutations are associated with low serum LDL-C (Յ100 mg/dL) (4). Strikingly, subjects harboring the heterozygous LOF mutations exhibited an 88% reduction in the incidence of CHD over a 15-year period relative to noncarriers of the mutations (5). Moreover, despite a complete loss of PCSK9 and serum LDL-C of Ͻ20 mg/dL, the 2 subjects carrying compound heterozygote LOF mutations appear healthy (6, 7).PCSK9 belongs to the subtilisin family of serine proteases and consists of a prodomain, catalytic domain, and C-terminal V domain (8). Expressed highly in the liver, PCSK9 is secreted after autocatalytic cleavage of its zymogen form (1). The prodomain remains noncovalently associated with the catalytic domain and seems to inhibit further proteolytic enzyme activity (8, 9). Secreted PCSK9 modulates LDL-C levels by posttranslational downregulation of hepatic LDL receptor (LDLR) protein (1). The precise mechanism is unknown, but a direct interaction between repeat A of the LDLR EGF homology domain and the PCSK9 catalytic domain is required (10, 11). Proteolytic cleavage of the LDLR by PCSK9 does not occur (12, 13); rather, the PCSK9:LDLR complex is endocytosed and directed to the endosome/lysosome compartment for degradation (14, 15). Current understanding of the LDLR pathway asserts that apolipoprotein B (apoB) and E (apoE) containing lipoprotein particles endocytosed with the LDLR are transported to the acidic environment of the endosome, where they dissociate from the receptor and are subsequently catabolized in lysosomes, while t...

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We report the design and total chemical synthesis of "synthetic erythropoiesis protein" (SEP), a 51-kilodalton protein-polymer construct consisting of a 166-amino-acid polypeptide chain and two covalently attached, branched, and monodisperse polymer moieties that are negatively charged. The ability to control the chemistry allowed us to synthesize a macromolecule of precisely defined covalent structure. SEP was homogeneous as shown by high-resolution analytical techniques, with a mass of 50,825 +/-10 daltons by electrospray mass spectrometry, and with a pI of 5.0. In cell and animal assays for erythropoiesis, SEP displayed potent biological activity and had significantly prolonged duration of action in vivo. These chemical methods are a powerful tool in the rational design of protein constructs with potential therapeutic applications.

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As a testament to the importance of CD24, researchers with diverse interests, including adaptive immunity, inflammation, autoimmune diseases and cancer, have encountered CD24. CD24 is overexpressed in many cancers and appears oncogenic. In the adaptive immune response, CD24 is a redundant costimulatory molecule in costimulation-rich lymphoid organs but is essential in selected target organs tested, such as brain and skin. More recent studies suggest it may have a role in discriminating danger and pathogen-associated molecular patterns by dendritic cells. The biology of CD24 is intriguing but poorly understood. Here we summarize the major findings associated with CD24 to stimulate new ideas for further research that may reveal the underlying link among the diverse processes mediated by CD24.