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Biomedical subjects

Michael Howell

Publications and source records attributed to Michael Howell.

10 recordsLinked to original sources
PubMed2006

Smads orchestrate specific histone modifications and chromatin remodeling to activate transcription.

Smads are intracellular transducers for TGF-beta superfamily ligands, but little is known about the mechanism by which complexes of receptor-phosphorylated Smad2 and Smad4 regulate transcription. Using an in vitro transcription system, we have discovered that, unlike most transcription factors that are sufficient to recruit the basal transcription machinery and therefore activate transcription on both naked DNA and chromatin templates, the Smads only activate transcription from chromatin templates. We demonstrate that Smad2-mediated transcription requires the histone acetyltransferase, p300. Smad2-recruited p300 exhibits an altered substrate specificity, specifically acetylating nucleosomal histone H3 at lysines 9 and 18, and these modifications are also detected on an endogenous Smad2-dependent promoter in a ligand-induced manner. Furthermore, we show that endogenous Smad2 interacts with the SWI/SNF ATPase, Brg1, in a TGF-beta-dependent manner, and demonstrate that Brg1 is recruited to Smad2-dependent promoters and is specifically required for TGF-beta-induced expression of endogenous Smad2 target genes. Our data indicate that the Smads define a new class of transcription factors that absolutely require chromatin to assemble the basal transcription machinery and activate transcription.

Acetylation↗
PubMed2006

IL-31 is associated with cutaneous lymphocyte antigen-positive skin homing T cells in patients with atopic dermatitis.

BACKGROUND: IL-31 is a newly discovered T-cell cytokine that, when overexpressed in mice, results in pruritus and skin dermatitis resembling human atopic dermatitis (AD). OBJECTIVE: We sought to investigate the expression of IL-31 and IL-31 receptor A (IL-31RA) in skin biopsy specimens and peripheral blood cells from patients with AD and healthy individuals. METHODS: Expression of IL-31 and IL-31RA was evaluated in skin biopsy specimens from patients with AD and healthy individuals by means of immunohistochemistry and RT-PCR. IL-31 protein production by skin-homing cutaneous lymphocyte antigen (CLA)-positive T cells was also assessed. RESULTS: IL-31RA protein was expressed by keratinocytes and infiltrating macrophages in skin biopsy specimens from patients with AD. Comparisons between skin from patients with AD and healthy skin showed IL-31RA expression at higher levels on epidermal keratinocytes in AD samples. Infiltrating cells, more numerous in skin from patients with AD compared with that of healthy individuals, expressed IL31 mRNA. Histomorphometric analysis of these cells indicated they were of the lymphocytic lineage, with the majority of cells staining positive for CLA and CD3. IL31 mRNA and protein expression is largely restricted to CD45RO(+) (memory) CLA(+) T cells in peripheral blood of patients with AD and healthy volunteers. Moreover, circulating CLA(+) T cells from patients with AD, but not from patients with psoriasis, are capable of producing higher levels of IL-31 compared with CLA(+) T cells from healthy individuals. However, the average levels of IL-31 were not significantly different between patients with AD and healthy individuals. CONCLUSION: We provide evidence that IL-31 expression is associated with CLA(+) T cells and might contribute to the development of AD-induced skin inflammation and pruritus.

Adult↗
PubMed2006

Defects in yolk sac vasculogenesis, chorioallantoic fusion, and embryonic axis elongation in mice with targeted disruption of Yap65.

YAP is a multifunctional adapter protein and transcriptional coactivator with several binding partners well described in vitro and in cell culture. To explore in vivo requirements for YAP, we generated mice carrying a targeted disruption of the Yap gene. Homozygosity for the Yap(tm1Smil) allele (Yap-/-) caused developmental arrest around E8.5. Phenotypic characterization revealed a requirement for YAP in yolk sac vasculogenesis. Yolk sac endothelial and erythrocyte precursors were specified as shown by histology, PECAM1 immunostaining, and alpha globin expression. Nonetheless, development of an organized yolk sac vascular plexus failed in Yap-/- embryos. In striking contrast, vasculogenesis proceeded in both the allantois and the embryo proper. Mutant embryos showed patterned gene expression domains along the anteroposterior neuraxis, midline, and streak/tailbud. Despite this evidence of proper patterning and tissue specification, Yap-/- embryos showed developmental perturbations that included a notably shortened body axis, convoluted anterior neuroepithelium, caudal dysgenesis, and failure of chorioallantoic fusion. These results reveal a vital requirement for YAP in the developmental processes of yolk sac vasculogenesis, chorioallantoic attachment, and embryonic axis elongation.

Acyltransferases↗
PubMed2005

A blueprint for a sepsis protocol.

Despite numerous advances in medicine, sepsis remains an unconquered challenge. Although outcomes have improved slightly over decades, the unacceptably high mortality rate of 30%-50% for severe sepsis and septic shock continues. However, after years of unsuccessful clinical trials, several investigations over the last few years have reported survival benefit in the treatment of sepsis. Physicians now have several proven therapies to treat sepsis, but have yet to implement them on a widespread, systematic basis. This led 11 international professional societies spanning multiple specialties and continents to come together to create the Surviving Sepsis Campaign. The product of their work is an international effort organized to improve care of patients with sepsis and includes consensus, evidence-based guidelines for care that improves survival in septic patients, and an action plan for change. Given the clear role of early identification and treatment in stopping the sepsis cascade, therapy must start early in the emergency department (ED) and continue throughout the hospital course. The first of the recommendations by the Surviving Sepsis Campaign is the aggressive resuscitation strategy of early goal-directed therapy (EGDT). EGDT is reported to reduce absolute mortality by a staggering 16%. The use of recombinant activated protein C was demonstrated to confer a 6% absolute survival benefit. Steroid supplementation in adrenal insufficiency produced a 10% benefit. Additionally, early and appropriate use of antibiotics remains a cornerstone of therapy. Although no randomized trial will be performed, the effects are undisputed. Finally, although predominantly intensive care unit therapies, tight glucose control and low-tidal-volume ventilation strategies have also led to improved survival. Armed with these new therapies, the medical community must rise to this call to action. Clinicians must change the approach to this disease, as well as the way the septic patient is viewed. Although complex and challenging, these therapies must be brought to the patient's bedside. We propose and describe the Multiple Urgent Sepsis Therapies (MUST) protocol as a practical way to implement a comprehensive treatment plan using available evidence-based therapies.

Anti-Infective Agents↗
PubMed2004

Heterogeneous nuclear ribonuclear protein U associates with YAP and regulates its co-activation of Bax transcription.

Although initially described as a cytosolic scaffolding protein, YAP (Yes-associated protein of 65 kDa) is known to associate with multiple transcription factors in the nucleus. Using affinity chromatography and mass spectrometry, we show that YAP interacts with heterogeneous nuclear ribonuclear protein U (hnRNP U), an RNA- and DNA-binding protein enriched in the nuclear matrix that also plays a role in the regulation of gene expression. hnRNP U interacts specifically with the proline-rich amino terminus of YAP, a region of YAP that is not found in the related protein TAZ. Although hnRNP U and YAP localize to both the nucleus and the cytoplasm, YAP does not translocate to the nucleus in an hnRNP U-dependent manner. Furthermore, hnRNP U and YAP only interact in the nucleus, suggesting that the association between the two proteins is regulated. Co-expression of hnRNP U attenuates the ability of YAP to increase the activity of a p73-driven Bax-luciferase reporter plasmid. In contrast, hnRNP U has no effect when co-expressed with a truncated YAP protein lacking the hnRNP U-binding site. Because YAP is distinguished from the homologue TAZ by its proline-rich amino terminus, the YAP-hnRNP U interaction may uniquely regulate the nuclear function(s) of YAP. The YAP-hnRNP U interaction provides another mechanism of YAP transcriptional regulation.

Amino Acid Sequence↗
PubMed2004

Recognition of phosphorylated-Smad2-containing complexes by a novel Smad interaction motif.

Transforming growth factor beta (TGF-beta) superfamily members signal via complexes of activated Smads, comprising phosphorylated receptor-regulated Smads, such as Smad2 and Smad3, and Smad4. These complexes are recruited to DNA by specific transcription factors. The forkhead/winged-helix transcription factors, XFast-1/XFoxH1a and XFast-3/XFoxH1b, bind an activated Smad heterotrimer comprising two Smad2s and one Smad4. Here we identify a novel Smad2 interaction motif, the Fast/FoxH1 motif (FM), present in all known Fast/FoxH1 family members, N-terminal to the common Smad interaction motif (SIM). The FM is necessary and sufficient to bind active Smad2/Smad4 complexes. The FM differs from the SIM since it discriminates between Smad2 and Smad3, and moreover only binds phosphorylated Smad2 in the context of activated Smad complexes. It is the first Smad interaction motif with this property. Site-directed mutagenesis indicates that the binding site for the FM on a Smad2/Smad4 heterotrimer is a hydrophobic pocket that incorporates the Smad/Smad interface. We demonstrate that the presence of an FM and SIM in the Fast/FoxH1 proteins allows them to compete efficiently for activated Smad2/Smad4 complexes with transcription factors such as Mixer that only contain a SIM. This establishes a hierarchy of Smad-interacting transcription factors, determined by their affinity for active Smad complexes.

Amino Acid Motifs↗
PubMed2003

Matrix-assisted laser desorption/ionization directed nano-electrospray ionization tandem mass spectrometric analysis for protein identification.

In those cases where the information obtained by peptide mass fingerprinting or matrix-assisted laser desorption/ionization tandem mass spectrometry (MALDI-MS/MS) is not sufficient for unambiguous protein identification, nano-electrospray ionization (nano-ESI) and/or electrospray ionization tandem mass spectrometry (ESI-MS/MS) analysis must be performed. The sensitivity of nano-ESI/MS, however, is lower than that of MALDI-MS, especially at very low analyte concentrations and/or in the presence of contaminants, such as salt and detergents. Moreover, to perform ESI-MS/MS, the peptide masses of the precursor ions must be known. The approach described in this paper, MALDI-directed nano-ESI-MS/MS, makes use of information obtained from the more sensitive MALDI-MS experiments in order to direct subsequent nano-ESI-MS/MS experiments. Peptide molecular ions found in the MALDI-MS analysis are then selected, as their (+2) precursor ions, for nano-ESI-MS/MS sequencing, even though these ions cannot be detected in the ESI-MS spectra. This method, originally proposed by Tempst et al. (Anal. Chem. 2000, 72: 777-790), has been extended to provide better sensitivity and shorter analysis times; also, a comparison with liquid chromatography/tandem mass spectrometry (LC/MS/MS) has been performed. These experiments, performed using quadrupole time-of-flight instruments equipped with commercially available nano-ESI sources, have allowed the unambiguous identification of in-gel digested proteins at levels below their ESI-MS detection limits, even in the presence of salts and detergents.

Nanotechnology↗
PubMed2002

A novel Xenopus Smad-interacting forkhead transcription factor (XFast-3) cooperates with XFast-1 in regulating gastrulation movements.

In early Xenopus embryos, the prototypical XFast-1/Smad2/Smad4 complex ARF1 is induced at the Mix.2 ARE by activin overexpression. We have characterised ARF2, a related, but much more abundant, complex formed during gastrulation in response to endogenous TGFbeta family members and we have identified a novel Fast family member, XFast-3, as its transcription factor component. Endogenous ARF2 efficiently competes out ARF1 at early gastrulation, due to the ability of XFast-3 to interact with activated Smads with much higher affinity than XFast-1. We demonstrate that ARF1 and ARF2 are activated by distinct TGFbeta family members. Using morpholino antisense oligonucleotides to deplete levels of the constituent transcription factors XFast-1 and XFast-3 specifically, we demonstrate an important role for ARF1 and ARF2 in early Xenopus embryos in controlling the convergent extension movements of gastrulation.

3T3 Cells↗