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Biomedical subjects

S P Jackson

Publications and source records attributed to S P Jackson.

At least 19 recordsLinked to original sources
PubMed2005

Human cell senescence as a DNA damage response.

It has been established that telomere-dependent replicative senescence of human fibroblasts is stress-dependent. First, it was shown that telomere shortening, which is a major contributor to telomere uncapping, is stress-dependent to a significant degree. Second, the signalling pathway connecting telomere uncapping and replicative senescence appears to be the same as the one that is activated by DNA damage: uncapped telomeres activate signalling cascades involving the protein kinases ATM, ATR and, possibly, DNA-PK. Furthermore, phosphorylation of histone H2A.X facilitates the formation of DNA damage foci around uncapped telomeres, and this in turn activates downstream kinases Chk1 and Chk2 and, eventually, p53. It appears that this signalling pathway has to be maintained in order to keep cells in a senescent state. Thus, cellular senescence can be regarded as a permanently maintained DNA damage response state. This suggests that antibodies against DNA damage foci components might be useful markers for senescent cells in vivo.

Cells, Cultured↗
PubMed2005

Patient attitudes to sternotomy and thoracotomy scars.

BACKGROUND: There are no data comparing patient attitudes to sternotomy and thoracotomy scars following surgery for congenital heart disease (CHD). METHODS: Two hundred and one patients with a scar from CHD surgery (105 sternotomy, 36 thoracotomy, and 60 both scars) had a structured interview to explore attitudes to their scar. RESULTS: Comparable proportions of each group reported that they did not like or hated their scar (23/105 [22 %] sternotomy, 9/36 [25 %] thoracotomy, 17/60 [28 %] both scars). Significantly more patients stated that they where embarrassed by and/or their choice of clothing was affected by a thoracotomy scar (20/36, 56 %) than those with a sternotomy scar (36/105, 34 %), p = 0.04. This was also seen when comparing sternotomy alone with both scars (36/105 [34 %] vs. 34/60 [57 %], p = 0.008). CONCLUSIONS: Adults who have undergone surgery for CHD are more likely to have a negative attitude to a thoracotomy than a sternotomy scar. Before a change in surgical approach is considered based on patient preferences, the acceptability and psychological impact of the different scars following surgery needs formal study.

Adult↗
PubMed2005

Exploiting the DNA repair defect in BRCA mutant cells in the design of new therapeutic strategies for cancer.

Individuals harboring germ-line mutations in the BRCA1 or BRCA2 genes are at highly elevated risk of a variety of cancers. Ten years of research has revealed roles for BRCA1 and BRCA2 in a wide variety of cellular processes. However, it seems likely that the function of these proteins in DNA repair is critically important in maintaining genome stability. Despite this increasing knowledge of the defects present in BRCA-deficient cells, BRCA mutation carriers developing cancer are still treated similarly to sporadic cases. Here we describe our efforts, based on understanding the DNA repair defects in BRCAdeficient cells, to define the optimal existing treatment for cancers arising in BRCA mutation carriers and, additionally, the development of novel therapeutic approaches. Finally, we discuss how therapies developed to treat BRCA mutant tumors might be applied to some sporadic cancers sharing similar specific defects in DNA repair.

Animals↗
PubMed2005

DNA damage responses at low radiation doses.

Increased cell killing after exposure to low acute doses of X rays (0-0.5 Gy) has been demonstrated in cells of a number of human tumor cell lines. The mechanisms underlying this effect have been assumed to be related to a threshold dose above which DNA repair efficiency or fidelity increases. We have used cells of two radioresistant human tumor cell lines, one that shows increased sensitivity to low radiation doses (T98G) and one that does not (U373), to investigate the DNA damage response at low doses in detail and to establish whether there is a discontinuous dose response or threshold in activation of any important mediators of this response. In the two cell lines studied, we found a sensitive, linear dose response in early signaling and transduction pathways between doses of 0.1 and 2 Gy with no evidence of a threshold dose. We demonstrate that ATM-dependent signaling events to downstream targets including TP53, CHK1 and CHK2 occur after doses as low as 0.2 Gy and that these events promote an effective damage response. Using chemical inhibition of specific DNA repair enzymes, we show that inhibition of DNA-PK-dependent end joining has relatively little effect at low (<1 Gy) doses in hyper-radiosensitive cells and that at these doses the influence of RAD51-mediated repair events may increase, based on high levels of RAD51/BRCA2 repair foci. These data do not support a threshold model for activation of DNA repair in hyper-radiosensitive cells but do suggest that the balance of repair enzyme activity may change at low doses.

Ataxia Telangiectasia Mutated Proteins↗
PubMed2004

Life insurance and mortgage application in adults with congenital heart disease.

OBJECTIVE: To compare the outcome of life insurance and mortgage applications of adults with congenital heart disease (CHD) with controls and at different severities of CHD. METHODS: Two hundred and ninety-nine adult CHD patients underwent a questionnaire-based interview by a trained nurse. They were asked to give an identical questionnaire to a friend to act as a control. One hundred and seventy-seven controls replied. CHD patients were classified into three categories based on severity. Comparisons were made between matched controls and between different severities of CHD. RESULTS: Similar proportions of the CHD group (59%) had applied for life insurance as matched controls (56%). Compared to controls, significantly more of the adults with CHD who had applied for life insurance have been refused (34 vs 4%, P < 0.0001) or asked to pay extra (37 vs 6%, P = 0.0002). Mortgage application rate was also similar in both groups with more of the CHD patients refused than matched controls (20 vs 3%, P = 0.0004). These differences in both life insurance and mortgage remain significant when the cases and controls are matched by employment status and NYHA functional class. There was no significant difference in life insurance and mortgage application outcome between the groups of mild, significant and complex CHD. CONCLUSIONS: Adults with CHD are significantly more likely to have difficulty obtaining life insurance or a mortgage than controls. Refusal rates appear to be independent of the severity of CHD. This suggests that the label of CHD may have a negative impact despite the lesion being minor and that the outcome of an individual application is difficult to predict based on the severity of the CHD. The increasing numbers of adults with CHD suggest that this problem is likely to increase and needs to be addressed as it can have a major impact on the patient's quality of life.

Adult↗
PubMed2004

Phosphoinositide 3-kinases and the regulation of platelet function.

A clear understanding of the role of PI (phosphoinositide) 3-kinases in supporting the haemostatic function of platelets has been slow to evolve. In fact, insight into the roles of individual PI 3-kinase isoforms in platelet function remains rudimentary. However, based on in vitro studies using wortmannin and LY294002, there is evidence for an important role for PI 3-kinases in regulating a broad range of functional platelet responses, including primary platelet adhesion, cytoskeletal remodelling and platelet aggregation. One of the critical platelet responses involves affinity regulation of the major platelet integrin alphaIIbbeta3, the primary receptor mediating platelet aggregation and thrombus growth. The input signals regulating integrin alphaIIbbeta3 can be divided into three main groups: (1) G(q)-coupled receptors linked to the activation of PLCbeta (phospholipase Cbeta); (2) G(i)-coupled receptors linked to the regulation of adenylate cyclase and Rap1b; and (3) adhesion receptor signalling involving Src kinase-dependent activation of PLCgamma isoforms. PI 3-kinases have not been demonstrated to play a critical role in G(q)-dependent platelet activation; however, one or more PI 3-kinase isoforms appears to be important for G(i)-dependent activation of Rap1b and adhesion receptor activation of PLCgamma isoforms. Thus distinct co-operative PI 3-kinase signalling mechanisms appear to play an important role in regulating the adhesive function of integrin alphaIIbbeta3.

Animals↗
PubMed2003

The complex matter of DNA double-strand break detection.

To maintain genomic stability, despite constant exposure to agents that damage DNA, eukaryotic cells have developed elaborate and highly conserved pathways of DNA damage sensing, signalling and repair. In this review, we concentrate mainly on what we know about DNA damage sensing with particular reference to Lcd1p, a yeast protein that functions early in DNA damage signalling, and MDC1 (mediator of DNA damage checkpoint 1), a recently identified human protein that may be involved in recruiting the MRE11 complex to radiation-induced nuclear foci. We describe a model for the DNA damage response in which factors are recruited sequentially to sites of DNA damage to form complexes that can amplify the original signal and propagate it to the multitude of response pathways necessary for genome stability.

Adaptor Proteins, Signal Transducing↗
PubMed2003

Localized morphoea preceded by a pigmented purpuric dermatosis.

Localized morphoea uncommonly occurs in a linear distribution and may present following trauma, although most cases are idiopathic. Pigmented purpuric dermatoses such as lichen aureus may also rarely occur in a linear distribution and have been associated with trauma. A middle-aged man is described who initially presented with lesions typical of lichen aureus in a linear distribution at a site exposed to chronic low-grade trauma. This eruption was transient and clinically underwent spontaneous complete resolution. Several months later he developed localized morphoea in an identical distribution. To our knowledge this is the first reported case of a pigmented purpuric dermatosis, presumably precipitated by trauma, evolving into linear morphoea.

Humans↗
PubMed2003

Signaling events underlying thrombus formation.

Recent in vivo studies have highlighted the dynamic and complex nature of platelet thrombus growth and the requirement for multiple adhesive receptor-ligand interactions in this process. In particular, the importance of von Willebrand factor (VWF) in promoting both primary adhesion and aggregation under high shear conditions is now well established. In general, the efficiency with which platelets adhere and aggregate at sites of vessel wall injury is dependent on the synergistic action of various adhesive and soluble agonist receptors, with the contribution of each of the individual receptors dependent on the prevailing blood flow conditions. In this review, we will discuss the major platelet adhesive interactions regulating platelet thrombus formation under high shear, with specific focus on the VWF (GPIb and integrin alphaIIbbeta3) and collagen receptors (GPVI and integrin alpha2beta1). We will also discuss the signaling mechanisms utilized by these receptors to induce platelet activation with specific emphasis on the role of cytosolic calcium flux in regulating platelet adhesion dynamics. The role of soluble agonists in promoting thrombus growth will be highlighted and a model to explain the synergistic requirement for adhesive and soluble stimuli for efficient platelet aggregation will be discussed.

Animals↗
PubMed2003

Characterization and consumer acceptance of three muscles from Hampshire x Rambouillet cross sheep expressing the callipyge phenotype.

Eight Hampshire x Rambouillet crossbred wethers expressing the callipyge phenotype and eight Hampshire x Rambouillet half-sibling wethers with a normal phenotype were slaughtered when they reached 59 kg. The supraspinatus (SPM), longissimus (LM), and semitendinosus (STM) muscles were analyzed to determine callipyge effects on calpain and calpastatin activities, sarcomere length, percentage of muscle fiber types, and muscle fiber areas. After 14 d of aging, chops were frozen until analyses for trained sensory panel evaluations, Warner-Bratzler shear force values, and consumer perceptions of tenderness, flavor, juiciness, and overall satisfaction of chops were conducted. Calpastatin activity was 57% greater (P < 0.05) and m-calpain activity was 33% greater (P < 0.05) in muscles from carcasses of callipyge than normal sheep. Sarcomeres were shorter (P < 0.001) in the LM than the SPM or STM, regardless of phenotype. Muscle fiber area was 76% larger (P < 0.05) in the LM of callipyge than normal sheep, but muscle fiber area was not affected (P > 0.05) by phenotype in the SPM or STM. Phenotype had no effect (P = 0.12) on the percentage of slow-twitch, oxidative fiber types in any of the three muscles. In STM and LM from callipyge lambs, the percentage of fast-twitch, oxidative/glycolytic fibers was lower (P < 0.05) and that of fast-twitch-glycolytic fibers was higher (P < 0.05) than in their normal counterparts. Phenotype did not affect (P = 0.90) the fiber type percentage in the SPM. Callipyge LM were less tender and normal LM were more tender than other chops (P < 0.05). Callipyge loin chops had higher Warner-Bratzler shear force values than other chops (P < 0.001). Consumers rated fewer (P < 0.05) callipyge loin and shoulder chops acceptable in juiciness, tenderness, and overall acceptability than normal chops, but phenotype did not affect (P > 0.05) consumer acceptability of leg chops. These results indicate that LM from Hampshire x Rambouillet sheep displaying the callipyge phenotype had higher calpastatin activity and were less tender than the LM from normal sheep. In addition, consumer perceptions indicated that only one in 10 leg chops, one in five shoulder chops, and one in four loin chops from callipyge sheep were unacceptable.

Animals↗
PubMed2001

DNA repair: how Ku makes ends meet.

The recently determined crystal structure of the Ku heterodimer, in both DNA-bound and unbound forms, has shed new light on the mechanism by which this protein fulfills its key role in the repair of DNA double-strand breaks.

Animals↗
PubMed2001

Identification of a conserved archaeal RNA polymerase subunit contacted by the basal transcription factor TFB.

Archaea possess two general transcription factors that are required to recruit RNA polymerase (RNAP) to promoters in vitro. These are TBP, the TATA-box-binding protein and TFB, the archaeal homologue of TFIIB. Thus, the archaeal and eucaryal transcription machineries are fundamentally related. In both RNAP II and archaeal transcription systems, direct contacts between TFB/TFIIB and the RNAP have been demonstrated to mediate recruitment of the polymerase to the promoter. However the subunit(s) directly contacted by these factors has not been identified. Using systematic yeast two-hybrid and biochemical analyses we have identified an interaction between the N-terminal domain of TFB and an evolutionarily conserved subunit of the RNA polymerase, RpoK. Intriguingly, homologues of RpoK are found in all three nuclear RNA polymerases (Rpb6) and also in the bacterial RNA polymerase (omega-subunit).

Amino Acid Sequence↗
PubMed2001

Phenotype changes resulting in high-affinity binding of von Willebrand factor to recombinant glycoprotein Ib-IX: analysis of the platelet-type von Willebrand disease mutations.

To maintain hemostasis under shear conditions, there must be an interaction between the platelet glycoprotein (GP) Ib-IX receptor and the plasma ligand von Willebrand factor (vWf). In platelet-type von Willebrand disease (Pt-vWD), hemostasis is compromised. Two mutations in the GPIbalpha polypeptide chain have been identified in these patients-a glycine-233 to valine change and a methionine-239 to valine change. For this investigation, these mutant proteins have been expressed in a Chinese hamster ovary cell model system. Ligand-binding studies were performed at various concentrations of ristocetin, and adhesion assays were performed under flow conditions. The Pt-vWD mutations resulted in a gain-of-function receptor. vWf binding was increased at all concentrations of ristocetin examined, and adhesion on a vWf matrix was enhanced in terms of cell tethering, slower rolling velocity, and decreased detachment with increasing shear rate. Two other mutations were also introduced into the GPIbalpha chain. One mutation, encompassing both the Pt-vWD mutations, created an increase in the hydrophobicity of this region. The second mutation, involving a valine-234 to glycine change, decreased the hydrophobicity of this region. Both mutations also resulted in a gain-of-function receptor, with the double mutation producing a hyperreactive receptor for vWf. These data further support the hypothesis that ligand binding is regulated by conformational changes in the amino-terminal region of GPIbalpha, thereby influencing the stability of the GPIbalpha-vWf interaction.

Animals↗
PubMed2001

The yeast Xrs2 complex functions in S phase checkpoint regulation.

The Nbs1 complex is an evolutionarily conserved multisubunit nuclease composed of the Mre11, Rad50, and Nbs1 proteins. Hypomorphic mutations in the NBS1 or MRE11 genes in humans result in conditions characterized by DNA damage sensitivity, cell cycle checkpoint deficiency, and high cancer incidence. The equivalent complex in the yeast Saccharomyces cerevisiae (Xrs2p complex) has been implicated in DNA double-strand break repair and in telomere length regulation. Here, we find that xrs2Delta, mre11Delta, and rad50Delta mutants are markedly defective in the initiation of the intra-S phase checkpoint in response to DNA damage. Furthermore, the absence of a functional Xrs2p complex leads to sensitivity to deoxynucleotide depletion and to an inability to efficiently slow down cell cycle progression in response to hydroxyurea. The checkpoint appears to require the nuclease activity of Mre11p and its defect is associated with the abrogation of the Tel1p/Mec1p signaling pathway. Notably, DNA damage induces phosphorylation of both Xrs2p and Mre11p in a Tel1p-dependent manner. These results indicate that the Tel1p/ATM signaling pathway is conserved from yeast to humans and suggest that the Xrs2p/Nbs1 complexes act as signal modifiers.

Bleomycin↗
PubMed2001

Platelet endothelial cell adhesion molecule-1 is a negative regulator of platelet-collagen interactions.

The functional importance of platelet endothelial cell adhesion molecule-1 (PECAM-1/CD31) in platelets is unclear. Because PECAM-1 represents a newly assigned immunoglobulin-ITIM superfamily member expressed on the surface of platelets, it was hypothesized that it may play an important regulatory role in modulating ITAM-bearing receptors such as collagen (GP)VI receptor and FcgammaRIIA. To examine the functional role of PECAM-1 in regulating platelet-collagen interactions, 2 different approaches were applied using recombinant human PECAM-1-immunoglobulin chimeras and platelets derived from PECAM-1-deficient mice. Stimulation of platelets by collagen-, (GP)VI-selective agonist, collagen-related peptide (CRP)-, and PECAM-1-immunoglobulin chimera induced tyrosine phosphorylation of PECAM-1 in a time- and dose-dependent manner. Activation of PECAM-1 directly through the addition of soluble wild-type PECAM-1-immunoglobulin chimera, but not mutant K89A PECAM-1-immunoglobulin chimera that prevents homophilic binding, was found to inhibit collagen- and CRP-induced platelet aggregation. PECAM-1-deficient platelets displayed enhanced platelet aggregation and secretion responses on stimulation with collagen and CRP, though the response to thrombin was unaffected. Under conditions of flow, human platelet thrombus formation on a collagen matrix was reduced in a dose-dependent manner by human PECAM-1-immunoglobulin chimera. Platelets derived from PECAM-1-deficient mice form larger thrombi when perfused over a collagen matrix under flow at a shear rate of 1800 seconds(-1) compared to wild-type mice. Collectively, these results indicate that PECAM-1 serves as a physiological negative regulator of platelet-collagen interactions that may function to negatively limit growth of platelet thrombi on collagen surfaces.

Animals↗
PubMed2001

Effects of DNA nonhomologous end-joining factors on telomere length and chromosomal stability in mammalian cells.

DNA repair by nonhomologous end-joining (NHEJ) relies on the Ku70:Ku80 heterodimer in species ranging from yeast to man. In Saccharomyces cerevisiae and Schizosaccharomyces pombe, Ku also controls telomere functions. Here, we show that Ku70, Ku80, and DNA-PKcs, with which Ku interacts, associate in vivo with telomeric DNA in several human cell types, and we show that these associations are not significantly affected by DNA-damaging agents. We also demonstrate that inactivation of Ku80 or Ku70 in the mouse yields telomeric shortening in various primary cell types at different developmental stages. By contrast, telomere length is not altered in cells impaired in XRCC4 or DNA ligase IV, two other NHEJ components. We also observe higher genomic instability in Ku-deficient cells than in XRCC4-null cells. This suggests that chromosomal instability of Ku-deficient cells results from a combination of compromised telomere stability and defective NHEJ.

Animals↗
PubMed2001

Cleavage of the Bloom's syndrome gene product during apoptosis by caspase-3 results in an impaired interaction with topoisomerase IIIalpha.

In higher eukaryotes, the integration of signals triggered in response to certain types of stress can result in programmed cell death. Central to these events is the sequential activation of a cascade of proteinases known as caspases. The final activated effector caspases of this cascade digest a number of cellular proteins, in some cases increasing their enzymatic activity, in others destroying their function. Of the proteins shown to be targets for caspase-mediated proteolysis, a surprisingly large proportion are proteins involved in the signalling or repair of DNA damage. Here we investigate whether BLM, the product of the gene mutated in Bloom's syndrome, a human autosomal disease characterised by cancer predisposition and sunlight sensitivity, is cleaved during apoptosis. BLM interacts with topoisomerase IIIalpha and has been proposed to play an important role in maintaining genomic integrity through its roles in DNA repair and replication. We show that BLM is cleaved during apoptosis by caspase-3 and reveal that the main cleavage site is located at the junction between the N-terminal and central helicase domains of BLM. Proteolytic cleavage by caspase-3 produces a 120 kDa fragment, which contains the intact helicase domain and three smaller fragments, the relative amounts of which depend on time of incubation with caspase-3. The 120 kDa fragment retains the helicase activity of the intact BLM protein. However, its interaction with topoisomerase IIIalpha is severely impaired. Since the BLM-topoisomerase interaction is believed to be necessary for many of the replication and recombination functions of BLM, we suggest that caspase-3 cleavage of BLM could alter the localisation and/or function of BLM and that these changes may be important in the process of apoptosis.

Adenosine Triphosphatases↗