Biomedical subjects

N McMahon

Publications and source records attributed to N McMahon.

7 recordsLinked to original sources

PubMed2000

Dimerization and N-terminal domain proximity underlie the function of the molecular chaperone heat shock protein 90.

Heat shock protein (hsp)90 functions in a complex chaperoning pathway where its activity is modulated by ATP and by interaction with several co-chaperones. One co-chaperone, p23, binds selectively to the ATP-bound state of hsp90. However, the isolated ATP-binding domain of hsp90 does not bind p23. In an effort to identify the p23-binding domain, we have constructed a series of hsp90 deletion mutants fused with glutathione-S-transferase (GST). Full-length GST-hsp90 is able to bind p23, and also, to chaperone assembly of progesterone receptor complexes. Truncations from the C terminus of GST-hsp90 reveal a C-terminal boundary for the p23-binding domain at approximately residue 490. This fragment contains, in order, the ATP-binding domain, a highly charged region, and 203 residues beyond the charged region. p23 binding is unaffected by deletion of the charged region, indicating that two noncontiguous regions of hsp90 are involved in p23 binding. These regions are only effective when hsp90 is in a dimeric state as shown by loss of p23 binding upon removal of GST or as shown by use of FK506-binding protein12-hsp90 constructs that form dimers and bind p23 only in the presence of a bivalent drug. Thus, p23 binding requires an hsp90 dimer with close proximity between N-terminal regions of hsp90 and a conformation specified by ATP.

Binding Sites↗

PubMed1998

The assembly of progesterone receptor-hsp90 complexes using purified proteins.

The progesterone receptor can be reconstituted into hsp90-containing complexes in vitro, and the resulting complexes are needed to maintain hormone binding activity. This process requires ATP/Mg2+, K+, and several axillary proteins. We have developed a defined system for the assembly of progesterone receptor complexes using purified proteins. Five proteins are needed to form complexes that are capable of maintaining hormone binding activity. These include hsp70 and its co-chaperone, hsp40, the hsp70/hsp90-binding protein, Hop, hsp90, and the hsp90-binding protein, p23. The proteins Hip and FKBP52 were not required for this in vitro process even though they have been observed in receptor complexes. Each of the five proteins showed a characteristic concentration dependence. Similar concentrations of hsp70, hsp90, and p23 were needed for optimal assembly, but hsp40 and Hop were effective at about 1/10 the concentration of the other proteins, suggesting that these two proteins act catalytically or are needed at levels similar to the receptor concentration. ATP was required for the functioning of both hsp70 and hsp90. The binding of hsp70 to the receptor requires hsp40 and about 10 microM ATP; however, hsp90 binding appears to occur subsequent to hsp70 binding and is optimal with 1 mM ATP. A three-step model is presented to describe the assembly process.

Animals↗

PubMed1998

Reflex vascular responses in the anesthetized dog to large rapid changes in carotid sinus pressure.

This study examined reflex vascular responses to large rapid increases and decreases in carotid sinus pressure to determine whether delayed or inappropriate vascular responses might be obtained that, if they occurred in people, could lead to hypotension during exposure to rapidly alternating gravitational forces. In chloralose-anesthetized open-chest dogs, a perfusion circuit controlled carotid sinus and thoracic aortic pressures and blood flows to both the vascularly isolated abdominal circulation and a hindlimb (perfusion pressure changes denoted resistance). When carotid pressure was increased and decreased over the range of 60-180 mmHg, the resulting reflex vasodilatation occurred significantly more rapidly than the vasoconstriction (P < 0.001). In the abdominal vascular bed, time constants for vasodilatation and vasoconstriction were 4.2 +/- 0.5 and 7.5 +/- 1.0 s, respectively. Decreases in carotid pressure in pulses of 10-s duration or less failed to elicit maximal vasoconstriction, whereas increases in carotid pressure lasting as little as 5 s did elicit maximal vasodilatation. "Square-wave" alternations in carotid pressure with periods of 10 s or less (5 s high, 5 s low) resulted in attenuation of the vasoconstriction, and at a 4-s period, both vascular beds remained almost maximally vasodilated throughout. The failure of vascular resistance to follow carotid pressure changes was not due to a failure of the response of sympathetic efferent activity, since the time constants for the reduction and increase in discharge were much shorter at 0.56 +/- 0.13 and 0.43 +/- 0.10 s, respectively. These results indicate that rapid changes in carotid pressure could result in inappropriate vasodilatation and hypotension and might, in some circumstances, such as in pilots flying high-performance aircraft, predispose to syncope.

Anesthesia, Intravenous↗

PubMed1997

Nucleotides and two functional states of hsp90.

Previous studies have demonstrated the ATP-dependent formation of a complex containing the heat shock protein hsp90, the unique hsp90 binding protein p23, and one of three high molecular weight immunophilins. In the present study, hsp90 and p23 are shown to form a complex that requires elevated temperature and ATP/Mg2+. Complex formation is strongly promoted by molybdate and by the nonionic detergent Nonidet P-40. ADP and the benzoquinone ansamycin, geldanamycin, are potent inhibitors of complex formation. The ATP-dependent process alters the state of hsp90, not p23, and influences the ability of hsp90 to bind to phenyl-Sepharose. Conversion of hsp90 to the ATP-bound state lowers its affinity for phenyl-Sepharose. These results show that hsp90 can exist in at least two functional states, one able to bind p23 and the other with a high affinity for hydrophobic resins. A model is presented where these states are dictated by the binding of either ATP or ADP.

Benzoquinones↗

PubMed1991

Single step selection of cis-diamminedichloroplatinum(II) resistant mutants from a human ovarian carcinoma cell line.

We have shown that cis diamminedichloroplatinum-(II) (DDP) resistant mutants can be isolated from the human ovarian carcinoma cell line A2780 using a single-step selection protocol with DDP. DDP resistant colonies were calculated to be present at a frequency of 1.7 x 10(-6)/viable cell using a fluctuation analysis. The mutational origin of these surviving colonies is inferred by the fact that their frequency is increased by treatment of the A2780 cells with the chemical mutagen ethyl methane-sulfonate, with a maximum frequency observed after a 3-day expression time. Independently isolated clones maintain, in the absence of selection, a DDP resistant phenotype up to 7-fold more resistant than the parental A2780 cells. The resistance modifiers aphidicolin and buthionine sulfoximine have no effect on the frequency of DDP resistant mutants. Therefore neither of these drugs appears to have an effect on increasing the sensitivity of DDP resistant mutants existing in a cell population prior to DDP exposure.

Aphidicolin↗

PubMed1984

Cotherapy: the need for positive pairing.

Therapists who are of the opinion that the cotherapy relationship has minimal therapeutic value, fail to understand the potential of this type of therapy. Cotherapy, in group psychotherapy, is a unique form of therapy with specific implications for therapeutic intervention. This paper will present three hypotheses developed from clinical observations which encourage a re-examination of traditional group perspectives. First, the authors believe that the development of the cotherapy relationship effects the development of group process. Second, the authors hypothesize that the pairing of the cotherapy relationship is paralleled by the pairing of group participants and finally that pairing in group psychotherapy is positive and can be utilized as an intervention technique. Although, traditionally, pairing has been viewed as an obstacle to group process, this paper presents the premise that pairing in group psychotherapy should be considered as a positive and necessary occurrence for cotherapy intervention. Six phases of cotherapy development are illustrated to show how the complex aspects of the cotherapy relationship impacts upon the developmental stages of group process. The clinical implications of this perspective may be the beginnings of new therapeutic horizons for cotherapists.

Female↗

PubMedDate not supplied

Repressive coping and blood lipids in men and women.

Studies have suggested that a repressive coping style, characterized by defensiveness against negative emotions, may be related to several adverse health outcomes. This study examined whether repressive coping is associated with blood lipids, and whether this association is influenced by age or sex. One hundred fourteen healthy adults completed the Marlowe-Crowne scale (MC) and the Bendig version of the Taylor Manifest Anxiety scale (TMAS) prior to having their blood drawn after an overnight fast. Hierarchical regression analyses showed a significant interaction of sex, MC, and TMAS on total cholesterol (F(1, 104) = 4.41, p < 0.05), after controlling for the influence of age, body mass index, and other main effects and interactions. Results showed that male repressors (high MC; low TMAS) had the highest cholesterol levels, while truly low anxious males (low MC; low TMAS) had the lowest levels. The opposite pattern was noted for women. There were no interactive effects of age and coping style on lipids. The results suggest that males who repress negative emotions may be at greater risk for atherosclerotic diseases.

Adaptation, Psychological↗