1,381 research outputs found
Dissection of GnRH receptor-G protein coupling
Hypothalamic gonadotropin-releasing hormone (GnRH) (GnRH I) is the central
regulator of the mammalian reproductive system. Most vertebrates studied also
possess a second form of GnRH, GnRH II. GnRH I acts on its cognate G proteincoupled
receptor (GPCR) on pituitary gonadotropes and activates Gq/11-mediated
signalling pathways to stimulate the biosynthesis and the release of luteinising
hormone (LH) and follicle-stimulating hormone (FSH). Both GnRHs have also been
suggested to inhibit cellular proliferation, an action which has largely been proposed
to be mediated by the coupling of the receptor to Gi/o. However, the range of G
proteins activated by the GnRH receptor and the signalling cascades involved in
inducing antiproliferation remain controversial.
To delineate the G protein coupling selectivity of the mammalian GnRH receptor and
to identify the signalling pathways involved in GnRH I-mediated cell growth
inhibition, I examined the ability of the receptor to interact with Gq/11, Gi/o and Gs in
Gαq/11 knockout MEF cells. My results indicate that the receptor is unable to interact
with Gi/o but can signal through Gq/11. Additionally, my data do not support the
suggestion of GnRH receptor-Gs interaction. Furthermore, I show that the GnRH Iinduced
inhibition of cell growth is dependent on Gq/11, src and extracellular signal
regulated kinase (ERK) but is independent of the activity of protein kinase C (PKC),
Ca2+, jun-N-terminal kinase (JNK) or P38. Based on these findings and previous
research within our group, I propose a mechanism whereby GnRH I may induce
antiproliferation.
Previous studies from our laboratory suggest that the GnRH receptor can adopt
distinct active conformations in response to the binding of GnRH I and GnRH II.
These data thus account for our hypothesis of ligand-induced selective signalling
(LiSS). Given my previous results, I examined the ability of the GnRH receptor to
couple to G12/13. My work indicates that the receptor can directly activate G12/13 and
the downstream signalling cascades associated with this G protein family. Indeed, I
provide evidence, in several cellular backgrounds, to suggest that GnRH receptor-
G12/13-mediated signalling is involved in the regulation of GnRH-induced MAPK
activity, SRE-driven gene transcription and cytoskeletal reorganisation.
Furthermore, I propose a role for these G proteins in the transcriptional regulation of
LHβ and FSHβ. Finally, I confirm previous results from our laboratory indicating
that the GnRH receptor may interact with src Tyr kinase and show that GnRH I but
not GnRH II may, independently of Gq/11, stimulate the Tyr phosphorylation and thus
the activation of this protein. I propose that this differential signalling accounts for
the distinct effects of GnRH I and GnRH II on cellular morphology and SREpromoted
transcriptional activity.
The research presented within this thesis provides evidence to refute published
conclusions based on largely circumstantial experimental data, describes novel
GnRH receptor signalling pathways and offers support for the concept of LiSS. It
may assist in the development of new therapeutic compounds which selectively
target one GnRH-mediated signalling pathway while bypassing others
CORE and the Haldane Conjecture
The Contractor Renormalization group formalism (CORE) is a real-space
renormalization group method which is the Hamiltonian analogue of the Wilson
exact renormalization group equations. In an earlier paper\cite{QGAF} I showed
that the Contractor Renormalization group (CORE) method could be used to map a
theory of free quarks, and quarks interacting with gluons, into a generalized
frustrated Heisenberg antiferromagnet (HAF) and proposed using CORE methods to
study these theories. Since generalizations of HAF's exhibit all sorts of
subtle behavior which, from a continuum point of view, are related to
topological properties of the theory, it is important to know that CORE can be
used to extract this physics. In this paper I show that despite the folklore
which asserts that all real-space renormalization group schemes are necessarily
inaccurate, simple Contractor Renormalization group (CORE) computations can
give highly accurate results even if one only keeps a small number of states
per block and a few terms in the cluster expansion. In addition I argue that
even very simple CORE computations give a much better qualitative understanding
of the physics than naive renormalization group methods. In particular I show
that the simplest CORE computation yields a first principles understanding of
how the famous Haldane conjecture works for the case of the spin-1/2 and spin-1
HAF.Comment: 36 pages, 4 figures, 5 tables, latex; extensive additions to conten
The novel histone deacetylase inhibitor, AR-42, inhibits gp130/Stat3 pathway and induces apoptosis and cell cycle arrest in multiple myeloma cells
Multiple myeloma (MM) remains incurable with current therapy, indicating the need for continued development of novel therapeutic agents. We evaluated the activity of a novel phenylbutyrate-derived histone deacetylase inhibitor, AR-42, in primary human myeloma cells and cell lines. AR-42 was cytotoxic to MM cells at a mean LC(50) of 0.18 ± 0.06 μmol/l at 48 hr and induced apoptosis with cleavage of caspases 8, 9 and 3, with cell death largely prevented by caspase inhibition. AR-42 downregulated the expression of gp130 and inhibited activation of STAT3, with minimal effects on the PI3K/Akt and MAPK pathways, indicating a predominant effect on the gp130/STAT-3 pathway. AR-42 also inhibited interleukin (IL)-6-induced STAT3 activation, which could not be overcome by exogenous IL-6. AR-42 also downregulated the expression of STAT3-regulated targets, including Bcl-xL and cyclin D1. Overexpression of Bcl-xL by a lentivirus construct partly protected against cell death induced by AR-42. The cyclin dependent kinase inhibitors, p16 and p21, were also significantly induced by AR-42, which together with a decrease in cyclin D1, resulted in G(1) and G(2) cell cycle arrest. In conclusion, AR-42 has potent cytotoxicity against MM cells mainly through gp130/STAT-3 pathway. The results provide rationale for clinical investigation of AR-42 in MM
Detection of the Entropy of the Intergalactic Medium: Accretion Shocks in Clusters, Adiabatic Cores in Groups
The thermodynamics of the diffuse, X-ray emitting gas in clusters of galaxies
is linked to the entropy level of the intra cluster medium. In particular,
models that successfully reproduce the properties of local X-ray clusters and
groups require the presence of a minimum value for the entropy in the center of
X-ray halos. Such a minimum entropy is most likely generated by
non-gravitational processes, in order to produce the observed break in
self-similarity of the scaling relations of X-ray halos. At present there is no
consensus on the level, the source or the time evolution of this excess
entropy. In this paper we describe a strategy to investigate the physics of the
heating processes acting in groups and clusters. We show that the best way to
extract information from the local data is the observation of the entropy
profile at large radii in nearby X-ray halos (z~0.1), both at the upper and
lower extremes of the cluster mass scale. The spatially and spectrally resolved
observation of such X-ray halos provides information on the mechanism of the
heating. We demonstrate how measurements of the size of constant entropy
(adiabatic) cores in clusters and groups can directly constrain heating models,
and the minimum entropy value. We also consider two specific experiments: the
detection of the shock fronts expected at the virial boundary of rich clusters,
and the detection of the isentropic, low surface-brightness emission extending
to radii larger than the virial ones in low mass clusters and groups. Such
observations will be a crucial probe of both the physics of clusters and the
relationship of non-gravitational processes to the thermodynamics of the
intergalactic medium.Comment: ApJ accepted, 31 pages including 8 figures. Important material added;
references update
Trends and Opportunities in Tick-Borne Disease Geography
Tick-borne diseases are a growing problem in many parts of the world, and their surveillance and control touch on challenging issues in medical entomology, agricultural health, veterinary medicine, and biosecurity. Spatial approaches can be used to synthesize the data generated by integrative One Health surveillance systems, and help stakeholders, managers, and medical geographers understand the current and future distribution of risk. Here, we performed a systematic review of over 8,000 studies and identified a total of 303 scientific publications that map tick-borne diseases using data on vectors, pathogens, and hosts (including wildlife, livestock, and human cases). We find that the field is growing rapidly, with the major Ixodes-borne diseases (Lyme disease and tick-borne encephalitis in particular) giving way to monitoring efforts that encompass a broader range of threats. We find a tremendous diversity of methods used to map tick-borne disease, but also find major gaps: data on the enzootic cycle of tick-borne pathogens is severely underutilized, and mapping efforts are mostly limited to Europe and North America. We suggest that future work can readily apply available methods to track the distributions of tick-borne diseases in Africa and Asia, following a One Health approach that combines medical and veterinary surveillance for maximum impact
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IQGAP1 and IQGAP2 are Reciprocally Altered in Hepatocellular Carcinoma
<p>Abstract</p> <p>Background</p> <p>IQGAP1 and IQGAP2 are homologous members of the IQGAP family of scaffold proteins. Accumulating evidence implicates IQGAPs in tumorigenesis. We recently reported that IQGAP2 deficiency leads to the development of hepatocellular carcinoma (HCC) in mice. In the current study we extend these findings, and investigate IQGAP1 and IQGAP2 expression in human HCC.</p> <p>Methods</p> <p>IQGAP1 and IQGAP2 protein expression was assessed by Western blotting and immunohistochemistry. IQGAP mRNA was measured by quantitative RT-PCR. The methylation status of the <it>Iqgap2 </it>promoter was determined by pyrosequencing of bisulfite-treated genomic DNA.</p> <p>Results</p> <p>IQGAP1 and IQGAP2 expression was reciprocally altered in 6/6 liver cancer cell lines. Similarly, immunohistochemical staining of 82 HCC samples showed that IQGAP2 protein expression was reduced in 64/82 (78.0%), while IQGAP1 was present in 69/82 (84.1%). No IQGAP1 staining was detected in 23/28 (82.1%) normal livers, 4/4 (100.0%) hepatic adenomas and 23/23 (100.0%) cirrhosis cases, while IQGAP2 was increased in 22/28 (78.6%), 4/4 (100.0%) and 23/23 (100.0%), respectively. Although the <it>Iqgap2 </it>promoter was not hypermethylated in HCC at any of the 25 CpG sites studied (N = 17), IQGAP2 mRNA levels were significantly lower in HCC specimens (N = 23) than normal livers (N = 6).</p> <p>Conclusions</p> <p>We conclude that increased IQGAP1 and/or decreased IQGAP2 contribute to the pathogenesis of human HCC. Furthermore, downregulation of IQGAP2 in HCC occurs independently of hypermethylation of the <it>Iqgap2 </it>promoter. Immunostaining of IQGAP1 and IQGAP2 may aid in the diagnosis of HCC, and their pharmacologic modulation may represent a novel therapeutic strategy for the treatment of liver cancer.</p
The z=5 Quasar Luminosity Function from SDSS Stripe 82
We present a measurement of the Type I quasar luminosity function at z=5
using a large sample of spectroscopically confirmed quasars selected from
optical imaging data. We measure the bright end (M_1450<-26) with Sloan Digital
Sky Survey (SDSS) data covering ~6000 deg^2, then extend to lower luminosities
(M_1450<-24) with newly discovered, faint z~5 quasars selected from 235 deg^2
of deep, coadded imaging in the SDSS Stripe 82 region (the celestial equator in
the Southern Galactic Cap). The faint sample includes 14 quasars with spectra
obtained as ancillary science targets in the SDSS-III Baryon Oscillation
Spectroscopic Survey (BOSS), and 59 quasars observed at the MMT and Magellan
telescopes. We construct a well-defined sample of 4.7<z<5.1 quasars that is
highly complete, with 73 spectroscopic identifications out of 92 candidates.
Our color selection method is also highly efficient: of the 73 spectra
obtained, 71 are high redshift quasars. These observations reach below the
break in the luminosity function (M_1450* ~ -27). The bright end slope is steep
(beta <~ -4), with a constraint of beta < -3.1 at 95% confidence. The break
luminosity appears to evolve strongly at high redshift, providing an
explanation for the flattening of the bright end slope reported previously. We
find a factor of ~2 greater decrease in the number density of luminous quasars
(M_1450<-26) from z=5 to z=6 than from z=4 to z=5, suggesting a more rapid
decline in quasar activity at high redshift than found in previous surveys. Our
model for the quasar luminosity function predicts that quasars generate ~30% of
the ionizing photons required to keep the universe ionized at z=5.Comment: 29 pages, 22 figures, ApJ accepted (updated to published version
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