Evidence that the root of the tree of life is not within the Archaea

The Archaea occupy uncommon and extreme habitats around the world. They manufacture unusual compounds, utilize novel metabolic pathways, and contain many unique genes. Many suspect, due to their novel properties, that the root of the tree of life may be within the Archaea, although there is little direct evidence for this root. Here, using gene insertions and deletions found within protein synthesis factors present in all prokaryotes and eukaryotes, we present statistically significant evidence that the root of life is outside the Archaea.     

Skin layer-specific transcriptional profiles in normal and recessive yellow (Mc1re/Mc1re) mice

The melanocortin 1 receptor (Mc1r) plays a central role in cutaneous biology, but is expressed at very low levels by a small fraction of cells in the skin. In humans, loss-of-function MC1R mutations cause fair skin, freckling, red hair, and increased predisposition to melanoma; in mice, Mc1r loss-of-function is responsible for the recessive yellow mutation, associated with pheomelanic hair and a decreased number of epidermal melanocytes. To better understand how Mc1r signaling affects different cutaneous phenotypes, we examined large-scale patterns of gene expression in different skin components (whole epidermal sheets, basal epidermal cells and whole skins) of neonatal (P2.5) normal and recessive yellow mice, starting with a 26K mouse cDNA microarray. From c. 17 000 genes whose levels could be accurately measured in neonatal skin, we identified 883, 2097 and 552 genes that were uniquely expressed in the suprabasal epidermis, basal epidermis and dermis, respectively; specific biologic roles could be assigned for each class. Comparison of normal and recessive yellow mice revealed 69 differentially expressed genes, of which the majority had not been previously implicated in Mc1r signaling. Surprisingly, many of the Mc1r-dependent genes are expressed in cells other than melanocytes, even though Mc1r expression in the skin is confined almost exclusively to epidermal melanocytes. These results reveal new targets for Mc1r signaling, and point to a previously unappreciated role for a Mc1r-dependent paracrine effect of melanocytes on other components of the skin.     

Potentiation of TRPV3 channel function by unsaturated fatty acids

Transient receptor potential vanilloid (TRPV) channels are polymodal detectors of multiple environmental factors, including temperature, pH, and pressure. Inflammatory mediators enhance TRPV function through multiple signaling pathways. The lipoxygenase and epoxygenase products of arachidonic acid (AA) metabolism have been shown to directly activate TRPV1 and TRPV4, respectively. TRPV3 is a thermosensitive channel with an intermediate temperature threshold of 31-39 degrees C. We have previously shown that TRPV3 is activated by 2-aminoethoxydiphenyl borate (2APB). Here we show that AA and other unsaturated fatty acids directly potentiate 2APB-induced responses of TRPV3 expressed in HEK293 cells, Xenopus oocytes, and mouse keratinocytes. The AA-induced potentiation is observed in intracellular Ca2+ measurement, whole-cell and two-electrode voltage clamp studies, as well as single channel recordings of excised inside-out and outside-out patches. The fatty acid-induced potentiation is not blocked by inhibitors of protein kinase C and thus differs from that induced by the kinase. The potentiation does not require AA metabolism but is rather mimicked by non-metabolizable analogs of AA. These results suggest a novel mechanism regulating the TRPV3 response to inflammation, which differs from TRPV1 and TRPV4, and involves a direct action of free fatty acids on the channel.     

Myostatin induces cachexia by activating the ubiquitin proteolytic system through an NF-kappaB-independent, FoxO1-dependent mechanism

Myostatin, a transforming growth factor-beta (TGF-beta) super-family member, has been well characterized as a negative regulator of muscle growth and development. Myostatin has been implicated in several forms of muscle wasting including the severe cachexia observed as a result of conditions such as AIDS and liver cirrhosis. Here we show that Myostatin induces cachexia by a mechanism independent of NF-kappaB. Myostatin treatment resulted in a reduction in both myotube number and size in vitro, as well as a loss in body mass in vivo. Furthermore, the expression of the myogenic genes myoD and pax3 was reduced, while NF-kappaB (the p65 subunit) localization and expression remained unchanged. In addition, promoter analysis has confirmed Myostatin inhibition of myoD and pax3. An increase in the expression of genes involved in ubiquitin-mediated proteolysis is observed during many forms of muscle wasting. Hence we analyzed the effect of Myostatin treatment on proteolytic gene expression. The ubiquitin associated genes atrogin-1, MuRF-1, and E214k were upregulated following Myostatin treatment. We analyzed how Myostatin may be signaling to induce cachexia. Myostatin signaling reversed the IGF-1/PI3K/AKT hypertrophy pathway by inhibiting AKT phosphorylation thereby increasing the levels of active FoxO1, allowing for increased expression of atrophy-related genes. Therefore, our results suggest that Myostatin induces cachexia through an NF-kappaB-independent mechanism. Furthermore, increased Myostatin levels appear to antagonize hypertrophy signaling through regulation of the AKT-FoxO1 pathway.     

Structure of pyrimidine 5'-nucleotidase type 1. Insight into mechanism of action and inhibition during lead poisoning

Eukaryotic pyrimidine 5'-nucleotidase type 1 (P5N-1) catalyzes dephosphorylation of pyrimidine 5'-mononucleotides. Deficiency of P5N-1 activity in red blood cells results in nonspherocytic hemolytic anemia. The enzyme deficiency is either familial or can be acquired through lead poisoning. We present the crystal structure of mouse P5N-1 refined to 2.35 A resolution. The mouse P5N-1 has a 92% sequence identity to its human counterpart. The structure revealed that P5N-1 adopts a fold similar to enzymes of the haloacid dehydrogenase superfamily. The active site of this enzyme is structurally highly similar to those of phosphoserine phosphatases. We propose a catalytic mechanism for P5N-1 that is also similar to that of phosphoserine phosphatases and provide experimental evidence for the mechanism in the form of structures of several reaction cycle states, including: 1) P5N-1 with bound Mg(II) at 2.25 A, 2) phosphoenzyme intermediate analog at 2.30 A, 3) product-transition complex analog at 2.35 A, and 4) product complex at 2.1A resolution with phosphate bound in the active site. Furthermore the structure of Pb(II)-inhibited P5N-1 (at 2.35 A) revealed that Pb(II) binds within the active site in a way that compromises function of the cationic cavity, which is required for the recognition and binding of the phosphate group of nucleotides.     

A missense mutation in the seven-transmembrane domain of the human Ca2+ receptor converts a negative allosteric modulator into a positive allosteric modulator

G protein-coupled receptors (GPCRs) are the most common targets of drug action. Allosteric modulators bind to the seven-transmembrane domain of family 3 GPCRs and offer enhanced selectivity over orthosteric ligands that bind to the large extracellular N terminus. We characterize a novel negative allosteric modulator of the human Ca(2+) receptor, Compound 1, that retains activity against the E837A mutant that lacks a response to previously described positive and negative modulators. A related compound, JKJ05, acts as a negative allosteric modulator on the wild type receptor but as a positive modulator on the E837A mutant receptor. This positive modulation critically depends on the primary amine in JKJ05, which appears to interact with acidic residue Glu(767) in our model of the seven-transmembrane domain of the receptor. Our results suggest the need for identification of possible genetic variation in the allosteric site of therapeutically targeted GPCRs.     

Regulation of integrin activity by MIA

MIA (melanoma inhibitory activity) has been identified as a small protein secreted from malignant melanoma cells, which interacts with extracellular matrix proteins including fibronectin. Here, we show that MIA negatively regulates the activity of the mitogen-activated protein kinase pathway in malignant melanoma. Using far Western blotting and co-immunoprecipitation we searched for MIA-binding cell surface proteins. We found that MIA interacts with integrin alpha4beta1 and alpha5beta1, leading to down-regulation of integrin activity and reduction of mitogen-activated protein kinase signaling. These findings also suggest that MIA may play a role in tumor progression and the spread of malignant melanomas via mediating detachment of cells from extracellular matrix molecules by modulating integrin activity. Inhibiting MIA functions in vivo may therefore provide a novel therapeutic strategy for metastatic melanoma disease.     

CD8+ IL-17-producing T cells are important in effector functions for the elicitation of contact hypersensitivity responses

Allergen-induced contact hypersensitivity (CHS) is a T cell-mediated delayed-type immune response which has been considered to be primarily mediated by CD8+ T cytotoxic type I (Tc1) cells. IFN-gamma, the prototype Tc1 (Th1) cytokine, has been implicated as the primary inflammatory cytokine for CHS. In this study, we demonstrate that neutralization of IL-17 rather than IFN-gamma suppresses the elicitation of CHS. The suppression does not result from inhibition of the proliferation of allergen-activated T cells. Allergen sensitization induces the development of distinct CD8+ T cell subpopulations that produce IFN-gamma or IL-17. Although CD8+ IL-17-producing cells are stimulated by IL-23, they are inhibited by IL-12, a prototypical stimulator of IFN-gamma-producing Tc1 cells. This indicates that CD8+ IL-17-producing cells are distinct from Tc1 cells and are important in effector functions at the elicitation of CHS. These studies provide insights into a novel mechanism for CHS.