Biomedical subjects
Publications and source records attributed to C Kay.
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In order to understand the dynamics of the endoplasmic reticulum (ER) luminal environment, we investigated the role of Ca(2+), Zn(2+), and ATP on conformational changes of calreticulin. Purified calreticulin was digested with trypsin in the presence or absence of Ca(2+), Zn(2+), and ATP. At low Ca(2+) concentration (<100 micrometer), calreticulin is rapidly and fully degraded by trypsin, indicating that under these conditions the protein is in a highly trypsin-susceptible conformation. Increasing Ca(2+) concentration up to 500 micrometer or 1 mm resulted in protection of the full-length calreticulin and in generation of the 27-kDa fragment highly resistant to trypsin digestion. The 27-kDa protease-resistant core of the protein represented the NH(2)-terminal half of calreticulin and was identified by its reactivity with specific antibodies and by NH(2)-terminal amino acid sequence analysis. Ca(2+)-dependent changes in calreticulin's sensitivity to proteolysis indicate that agonist-induced fluctuation in the free ER luminal Ca(2+) concentration may affect the protein conformation and function. Trypsin digestion of calreticulin in the presence of Zn(2+) resulted in the formation of a 17-kDa central protease-resistant core in the protein corresponding to the central region of the protein, indicating that under these conditions the N- and C-domains of the protein are in an extended conformation. Here we also show that calreticulin is an ATP-binding protein but that it does not contain detectable ATPase activity. Digestion of the protein with trypsin in the presence of Mg(2+)-ATP protects the full-length protein. These results indicate that calreticulin may undergo frequent, ion-induced conformation changes, which may affect its function and its ability to interact with other proteins in the lumen of the ER.
The thermodynamic stability and oligomerization status of the tumor suppressor p53 tetramerization domain have been studied experimentally and theoretically. A series of hydrophilic mutations at Met-340 and Leu-344 of human p53 were designed to disrupt the hydrophobic dimer-dimer interface of the tetrameric oligomerization domain of p53 (residues 325-355). Meanfield calculations of the free energy of the solvated mutants as a function of interdimer distance were compared with experimental data on the thermal stability and oligomeric state (tetramer, dimer, or equilibrium mixture of both) of each mutant. The calculations predicted a decreasing stability and oligomeric state for the following amino acids at residue 340: Met (tetramer) > Ser Asp, His, Gln, > Glu, Lys (dimer), whereas the experimental results showed the following order: Met (tetramer) > Ser > Gln > His, Lys > Asp, Glu (dimers). For residue 344, the calculated trend was Leu (tetramer) > Ala > Arg, Gln, Lys (dimer), and the experimental trend was Leu (tetramer) > Ala, Arg, Gln, Lys (dimer). The discrepancy for the lysine side chain at residue 340 is attributed to the dual nature of lysine, both hydrophobic and charged. The incorrect prediction of stability of the mutant with Asp at residue 340 is attributed to the fact that within the meanfield approach, we use the wild-type backbone configuration for all mutants, but low melting temperatures suggest a softening of the alpha-helices at the dimer-dimer interface. Overall, this initial application of meanfield theory toward a protein-solvent system is encouraging for the application of the theoretical model to more complex systems.
The effect of lipid association on the local environment of the two tryptophan residues of Locusta migratoria apolipophorin III (apoLp-III) has been studied. In the lipid-free state, Trp115 in helix 4 is buried in the hydrophobic interior of the helix bundle, while Trp130 is located in a loop connecting helices 4 and 5. Fluorescence spectroscopy of single Trp mutants revealed an emission maximum (lambda(max)) of 321 nm for apoLp-III-W@115 (excitation 280 nm) which red-shifted to 327 nm upon binding to dimyristoylphosphatidylcholine (DMPC). ApoLp-III-W@130 displayed a lambda(max) of 338 nm while interaction with DMPC resulted in a blue shift to 331 nm. Quenching studies with KI and acrylamide revealed decreased accessibility to Trp115 compared to Trp130, while lipid binding induced a decrease in quenching of Trp130. Aromatic circular dichroism (CD) spectra showed that Trp vibronic transitions at 278, 286, and 294 nm for lipid-free apoLp-III were caused by Trp115. Upon lipid association, aromatic extrema are reversed in sign, becoming entirely negative with both Trp residues contributing to the vibronic transitions, implying restriction in side-chain mobility of these residues. Thus, lambda(max), quencher accessibility, and aromatic CD analysis indicate that Trp115 is much less solvent-exposed than Trp130. Differences in fluorescence properties of these residues are minimized in the lipid-bound state, a result of relocation of Trp115 and Trp130 into the lipid milieu. Thus, in addition to the hydrophobic faces of apoLp-III amphipathic alpha-helices, the loop region containing Trp130 comes in close contact with DMPC.
Type I antifreeze protein (AFP) from winter flounder is an alanine-rich, 37 amino acid, single alpha-helix that contains three 11 amino acid repeats (Thr-X(2)-Asx-X(7)), where X is generally Ala. The regularly spaced Thr, Asx and Leu residues lie on one face of the helix and have traditionally been thought to form hydrogen bonds and van der Waals interactions with the ice surface. Recently, substitution experiments have called into question the importance of Leu and Asn for ice-binding. Sequence alignments of five type I AFP isoforms show that Leu and Asn are not well conserved, whereas Ala residues adjacent to the Thr, at right angles to the Leu/Asn-rich face, are completely conserved. To investigate the role of these Ala residues, a series of Ala to Leu steric mutations was made at various points around the helix. All the substituted peptides were fully alpha-helical and remained as monomers in solution. Wild-type activity was retained in A19L and A20L. A17L, where the substitution lies adjacent to the Thr-rich face, had no detectable antifreeze activity. The nearby A21L substitution had 10% wild-type activity and demonstrated weak interactions with the ice surface. We propose a new ice-binding face for type I AFP that encompasses the conserved Ala-rich surface and adjacent Thr.
Casade Blue (CB), a fluorescent dye, was used to investigate the dynamics of interactions between endoplasmic reticulum (ER) lumenal chaperones including calreticulin, protein disulfide isomerase (PDI), and ERp57. PDI and ERp57 were labeled with CB, and subsequently, we show that the fluorescence intensity of the CB-conjugated proteins changes upon exposure to microenvironments of a different polarity. CD analysis of the purified proteins revealed that changes in the fluorescence intensity of CB-ERp57 and CB-PDI correspond to conformational changes in the proteins. Using this technique we demonstrate that PDI interacts with calreticulin at low Ca2+ concentration (below 100 microM), whereas the protein complex dissociates at >400 microM Ca2+. These are the Ca2+ concentrations reminiscent of Ca2+ levels found in empty or full ER Ca2+ stores. The N-domain of calreticulin interacts with PDI, but Ca2+ binding to the C-domain of the protein is responsible for Ca2+ sensitivity of the interaction. ERp57 also interacts with calreticulin through the N-domain of the protein. Initial interaction between these proteins is Ca2+-independent, but it is modulated by Ca2+ binding to the C-domain of calreticulin. We conclude that changes in ER lumenal Ca2+ concentration may be responsible for the regulation of protein-protein interactions. Calreticulin may play a role of Ca2+ "sensor" for ER chaperones via regulation of Ca2+-dependent formation and maintenance of structural and functional complexes between different proteins involved in a variety of steps during protein synthesis, folding, and post-translational modification.
OBJECTIVE: To describe the long term effects of the use of oral contraceptives on mortality. DESIGN: Cohort study with 25 year follow up. Details of oral contraceptive use and of morbidity and mortality were reported six monthly by general practitioners. 75% of the original cohort was "flagged" on the NHS central registers. SETTING: 1400 general practices throughout Britain. SUBJECTS: 46 000 women, half of whom were using oral contraceptives at recruitment in 1968-9. Median age at end of follow up was 49 years. MAIN OUTCOME MEASURES: Relative risks of death adjusted for age, parity, social class, and smoking. RESULTS: Over the 25 year follow up 1599 deaths were reported. Over the entire period of follow up the risk of death from all causes was similar in ever users and never users of oral contraceptives (relative risk=1.0, 95% confidence interval 0.9 to 1.1; P=0.7) and the risk of death for most specific causes did not differ significantly in the two groups. However, among current and recent (within 10 years) users the relative risk of death from ovarian cancer was 0.2 (0.1 to 0.8; P=0.01), from cervical cancer 2.5 (1.1 to 6.1; P=0.04), and from cerebrovascular disease 1.9 (1.2 to 3.1, P=0.009). By contrast, for women who had stopped use >/= 10 years previously there were no significant excesses or deficits either overall or for any specific cause of death. CONCLUSION: Oral contraceptives seem to have their main effect on mortality while they are being used and in the 10 years after use ceases. Ten or more years after use ceases mortality in past users is similar to that in never users.
Pancreatic cancer has traditionally been difficult to diagnose. There are now numerous diagnostic tests that can visualize these tumors early when they are small and determine which cases are the most likely to be unresectable. The principal tests, including spiral CT, MR imaging, endoscopic ultrasound, and laparoscopy, have advantages and disadvantages. The purpose of this article is to review each technique, and try to come up with a recommended approach to evaluating the patient with pancreatic malignancy.
Recently two germline mutations in the oligomerization domain of p53 have been identified in patients with Li-Fraumeni and Li-Fraumeni-like Syndromes. We have used biophysical and biochemical methods to characterize these two mutants in order to better understand their functional defects and the role of the p53 oligomerization domain (residues 325-355) in oncogenesis. We find that residues 310-360 of the L344P mutant are monomeric, apparently unfolded and cannot interact with wild-type (WT) p53. The full length L344P protein is unable to bind sequence specifically to DNA and is therefore an inactive, but not a dominant negative mutant. R337C, on the other hand, can form dimers and tetramers, can hetero-oligomerize with WTp53 and can bind to a p53 consensus element. However, the thermal stability of R337C is much lower than that of WTp53 and at physiological temperatures more than half of this mutant is less than tetrameric. Thus, the R337C mutant retains some functional activity yet leads to a predisposition to cancer, suggesting that even partial inactivation of p53 oligomerization is sufficient for accelerated tumour progression.
BACKGROUND: Use of tacrolimus (FK506), a potent immunosuppressive agent, has been reported to have a 10-20% incidence of insulin-dependent diabetes mellitus (IDDM) in adults, but the incidence of IDDM in pediatric renal transplant recipients treated with this agent is unknown. In this article, we report our single-center experience with FK506-induced IDDM in children. METHODS: Five consecutive living related donor pediatric renal transplants were reviewed retrospectively. RESULTS: All five patients developed IDDM lasting longer than 6 months. Mean follow-up time was 18.6 months. CONCLUSIONS: Pediatric patients may be at high risk for developing FK506-induced IDDM.
A retrospective review of over-anticoagulated patients with critical international normalized ratios (INRs) was undertaken in a large outpatient laboratory. In the six-month study period, 85 prothrombin times (PTs) were identified with an INR of > or = 6.0, an overall incidence of elevated PTs of 0.2% or two per 1,000 INR tests. Complete follow-up data was available on 65 patients. When compared to an age- and gender-matched control group without INR > or = 6.0, high-INR patients were significantly more likely to manifest the presence of alcoholism or liver disease, to have been anticoagulated for less than six months, to have experienced more frequent warfarin dosage changes, and to have had the addition of a medication known to interact with warfarin. In the high-INR group, a likely cause for the specific critical INR was identified in 44 patients (68%). Drug interactions followed by compliance problems were the most common factors identified. The 13 patients (20%) who received vitamin K therapy experienced no difference in the clinical outcome compared with those managed conservatively. Conservative management of critically high INR values appeared to be as efficacious as intervention with vitamin K therapy.
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PURPOSE: To evaluate a magnetic resonance (MR) technique for depicting the kidneys and urinary tract. MATERIALS AND METHODS: Fourteen patients with urinary tract obstruction and 20 without obstructions were examined with a modified, heavily T2-weighted fast spin-echo pulse sequence (MR urography). In addition, six healthy volunteers underwent modified MR urography with intravenous administration of furosemide and ureteral compression prior to imaging. RESULTS: MR urography provided high-resolution images of the kidneys and urinary tract in all patients with obstruction with intact collecting systems. Anatomic anomalies were depicted in two patients. Intraluminal neoplasia was well demonstrated in both obstructed and nonobstructed systems (n = 4). Furosemide-enhanced MR urography provided fine anatomic and functional detail of both the kidneys and urinary tract (n = 6). CONCLUSION: MR urography may provide an alternative to more conventional urinary tract imaging techniques. It does not require ionizing radiation or iodinated contrast material. When combined with furosemide and ureteral compression, MR urography provides fine detail and reflects function.
BACKGROUND: Recent guidelines recommend that patients with obvious acute myocardial infarction receive thrombolysis, unless contraindicated, within 60-90 minutes of summoning assistance. If this target is to be achieved, an increasing number of general practitioners are likely to be involved in the administration of thrombolytic agents. AIM: This study aimed to assess the practicality and safety of thrombolysis with anistreplase when given by general practitioners. METHOD: An observational study was conducted in 805 general practices throughout the United Kingdom. Between March 1991 and September 1992, a total of 3383 patients with a clinical diagnosis of myocardial infarction were recruited--888 by 344 general practitioners who wished to include anistreplase in their management of myocardial infarction ('user' group) and 2495 by 776 general practitioners who did not wish to use anistreplase but who were willing to provide information about their cases ('comparison' group). RESULTS: More than half the patients were seen within two hours of onset of symptoms. A high frequency of contra-indications to thrombolysis, diagnostic uncertainty, and other, mainly practical, reasons limited the number of occasions on which anistreplase was administered. Thus, only 310 patients were given anistreplase in the community. The general practitioners in the study used anistreplase safely. Their diagnostic accuracy was high (of the 310 patients given anistreplase 69% had a definite, possible or probably myocardial infarction, 4% a definite non-cardiac diagnosis), the number of patients given anistreplase in spite of a documented contraindication was small (seven patients), and the doctors appeared to be aware of potential bleeding problems associated with thrombolysis. In all cases, the complications of acute myocardial infarction appeared to be managed appropriately. CONCLUSION: General practitioners can use anistreplase both appropriately and safely in the early management of acute myocardial infarction. Recognized contraindications to thrombolysis and practicalities of diagnosis and drug administration may, however, limit the number of occasions on which anistreplase is used.
The binding of epidermal growth factor (EGF) or an EGF-like growth factor to the EGF receptor is the initial event which leads to receptor activation, and consequently the induction of cell growth. In order to study this binding interaction in detail, we produced the extracellular domain of the EGF receptor (EGFR) using the baculovirus expression system. Affinity-labeling and Western-blot analyses revealed that the baculovirus-infected insect cells secrete active EGFR extracellular domain relatively efficiently, however a significant amount of inactive EGFR extracellular domain is retained within the cells. The apparent dissociation constant (Kd) of the secreted EGFR extracellular domain for EGF and transforming growth factor alpha (TGF-alpha), as determined using an immobilized receptor binding assay, was approximately 200 nM. Interestingly, this Kd value is 30-40-fold lower than that of the full-length EGFR derived from detergent-solubilized A431 cell membranes. The stoichiometry of binding of the EGFR extracellular domain to EGF and TGF-alpha was examined by band-shift analysis on non-denaturing PAGE and was estimated to be 1:1. We have also shown, using sedimentation equilibrium analysis, that ligand binding induces significant dimerization of the EGFR extracellular domain. Finally, we carried out site-specific mutagenesis on the EGFR extracellular domain in order to define the ligand-binding region. We identified amino acid residues which are close to the binding site since they are common to the epitopes of several ligand-competitive monoclonal antibodies. However, these residues do not contribute directly to ligand binding since the affinity of the mutated EGFR extracellular domain for EGF and TGF-alpha was unaffected.
In a previous report, we described that tumor necrosis factor (TNF) and granulocyte-macrophage colony-stimulating factor (GM-CSF) synergistically enhanced the development of dendritic cell (DC) progeny from early stem cells and that there is a common monocyte-DC progenitor cell. Low levels of DC were obtained with GM-CSF alone, and TNF by itself failed to induce stem cell development. Here, we investigate mechanisms by which TNF and GM-CSF institute increases in DC, and how these same molecules support later stages of DC differentiation. We show that TNF is required as the first signal, that there is upregulation of GM-CSF receptors (GM-CSFRs), and that TNF inhibits the differentiation of colony-forming units-granulocyte. High levels of GM-CSFR were always associated with conditions yielding a large number of DC, and a kinetic analysis showed a close ontogenic relationship between DC and GM-CSFR levels. The addition of anti-GM-CSF or anti-TNF antibodies blocked synergistic responses related to DC development, including high levels of GM-CSFRs. Anti-GM-CSF was the most potent inhibitor of proliferation (80%) and macrophage, DC, and polymorphonuclear (PMN) cell development. With polyclonal anti-TNF, inhibition was less (35%), and there was a shift from myelomonocytic and DC to PMN progeny. Our results support the concept that receptor upregulation is an important mechanism for growth factor synergy. Our data also indicate that the opposing effects of TNF on hematopoiesis contribute to the selection of the DC pathway and emphasize the importance of GM-CSFRs not only in initiated DC development, but also in controlling DC viability and function.
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