Mutations uncover a role for two magnesium ions in the catalytic mechanism of adenylyl cyclase

The recent determination of the crystal structure of adenylyl cyclase has elucidated many structural features that determine the regulatory properties of the enzyme. In addition, the characterization of adenylyl cyclase by mutagenic techniques and the identification of the binding site for P-site inhibitors have led to modeling studies that describe the ATP-binding site. Despite these advances, the catalytic mechanism of adenylyl cyclase remains uncertain, especially with respect to the role that magnesium ions may play in this process. We have identified four mutant mammalian adenylyl cyclases defective in their metal dependence, allowing us to further characterize the function of metal ions in the catalytic mechanism of this enzyme. The wild-type adenylyl cyclase shows a biphasic Mg2+ dose-response curve in which the high-affinity component displays cooperativity (Hill coefficient of 1.4). Two mutations (C441R and Y442H) reduce the affinity of the adenylyl cyclase for Mg2+ dramatically without affecting the binding of MgATP, suggesting that there is a metal requirement in addition to the ATP-bound Mg2+. The results of this study thus demonstrate multiple metal requirements of adenylyl cyclase and support the existence of a Mg2+ ion essential for catalysis and distinct from the ATP-bound ion. We propose that adenylyl cyclase employs a catalytic mechanism analogous to that of DNA polymerase, in which two key magnesium ions facilitate the nucleophilic attack of the 3'-hydroxyl group and the subsequent elimination of pyrophosphate.

Value of image subtraction in 3D gadolinium-enhanced MR angiography of the renal arteries

The objective of this study was to evaluate quantitatively and qualitatively the effect of image subtraction on the image quality of three-dimensional (3D) gadolinium-enhanced MR angiograms of the renal arteries. Breath-hold 3D gadolinium MR angiography (MRA) as well as conventional contrast angiography of the renal arteries was performed on 20 patients with suspected renovascular hypertension. MR angiograms were acquired before and during dynamic infusion of gadolinium-diethylenetriamine pentaacetic acid (Gd-DTPA). Contrast-enhanced images were compared with images that had undergone voxel-by-voxel signal intensity subtraction of contrast-enhanced data from precontrast data. One false positive finding for significant renal artery stenosis was recorded with MRA using conventional angiography as the gold standard. Image subtraction did not alter the diagnosis at MRA in any case. The mean contrast-to-noise ratio (CNR) was significantly higher (P < .05) on the subtraction MR angiograms compared to the nonsubtracted MR angiograms. There was no significant difference in the signal-to-noise ratio (SNR). Qualitative analysis revealed a significant improvement in image quality after image subtraction with respect to visualization of the distal renal arteries. In conclusion, image subtraction improves the quality of renal MRA in terms of both CNR and visualization of the distal renal arteries.

[Laparoscopic hernia surgery--status of minimal invasive techniques in a spectrum of surgical indications]

Endoscopic surgery led in the nineties to a discussion on surgical treatment of hernias. At the present time there are three groups of operative procedures: the conventional procedure--Shouldice, Bassini--the open tension-free procedure with implantation of a mesh--Lichtenstein, Gilbert-Rutkow--and the endoscopic procedure (predominantly transabdominal preperitoneal hernioplasty (TAPP) and total extraperitoneal hernioplasty (TEP)). The debate on the optimal therapy of hernias is understandable in view of the large number of hernia operations which are carried out. Numerous studies, some randomized, have demonstrated both the advantages and the disadvantages of the individual operative procedures. In addition to the recurrence rate and the complications, the cost factor and the associated socio-economic aspects of the particular operation play an increasingly important role in the decision on the method that should be used. In December 1995 some Austrian surgeons, who concerned themselves with problems of hernia repair already before the definitive introduction of laparoscopic hernia repair in today's surgery, came together on the occasion of a "Consensus Conference". During the meeting a summary of all relevant aspects of the complex of problems was worked out and summarized in a catalog of indications for the different operative interventions. The main statement was that the traditional open surgery, which can be performed under local anesthesia is indicated for an unilateral primary hernia. In case of an unclear finding at the contralateral side, as well as in case of a recurrent hernia, an endoscopic procedure is indicated. Meanwhile the Hernia Forum of Zürs ("Zürser Hernienforum") was founded. The function of this forum is the realization of a prospective randomized study for hernia repair in Austria.

Genetic selection of mammalian adenylyl cyclases insensitive to stimulation by Gsalpha

We describe the development of a genetic system allowing for the isolation of mutant mammalian adenylyl cyclases defective in their responses to G protein subunits, thus allowing for the identification of structural elements within the cyclase that are responsible for the recognition of these regulators. Expression of mammalian type V adenylyl cyclase in a cyclase-deleted yeast strain can conditionally complement the lethal phenotype of this strain. Type V adenylyl cyclase-expressing yeast grow only when the cyclase is activated by coexpression of Gsalpha or addition of forskolin to the medium; however, growth arrest is observed in the presence of both activators or under basal conditions. Utilizing this genetic system, we have isolated 25 adenylyl cyclase mutants defective in their response to Gsalpha. Sequence analysis and biochemical characterization of these mutants have identified residues in both cytoplasmic domains of the cyclase that are involved in the specific binding of and regulation by Gsalpha.

The presence of chorionic gonadotrophin beta subunit in normal cyclic human endometrium

The aim of the present study was to determine whether human endometrial cells are able to secrete beta-chorionic gonadotrophin (betaCG). Immunohistochemical studies and in-situ hybridization were performed in order to provide evidence for the occurrence of betaCG in the normal endometrium in 15 patients in the proliferative phase, two patients in the periovulatory phase and 13 patients in the secretory phase. Neither immunohistochemical nor hybridization reactions could be recognized during the proliferative phase. In contrast, both protein and betaCG mRNA were observed in the glandular cells of the endometrium during the secretory phase. The results were supported by Western blotting of secretory phase endometrium extracts and the assessment of the functional secretory capacity of primary endometrium cultures. In comparison with cultured and separated cell fractions, tissue extracts showed a higher betaCG, indicating a regulatory interaction. In conclusion, betaCG can be demonstrated in normal human cyclic endometrium, suggesting a paracrine role in endometrial physiology.

The type 1 receptor (CD120a) is the high-affinity receptor for soluble tumor necrosis factor

Tumor necrosis factor (TNF) can induce a variety of cellular responses at low picomolar concentrations. This is in apparent conflict with the published dissociation constants for TNF binding to TNF receptors in the order of 100-500 pM. To elucidate the mechanisms underlying the outstanding cellular sensitivity to TNF, we determined the binding characteristics of TNF to both human TNF receptors at 37 degrees C. Calculation of the dissociation constant (Kd) from the association and dissociation rate constants determined at 37 degrees C revealed a remarkable high affinity for TNF binding to the 60-kDa TNF type 1 receptor (TNF-R1; Kd = 1.9 x 10(-11) M) and a significantly lower affinity for the 80-kDa TNF type 2 receptor (TNF-R2; Kd = 4.2 x 10(-10) M). The high affinity determined for TNF-R1 is mainly caused by the marked stability of ligand-receptor complexes in contrast to the transient interaction of soluble TNF with TNF-R2. These data can readily explain the predominant role of TNF-R1 in induction of cellular responses by soluble TNF and suggest the stability of the TNF-TNF receptor complexes as a rationale for their differential signaling capability. In accordance with this reasoning, the lower signaling capability of homotrimeric lymphotoxin, compared with TNF, correlates with a lower stability of the lymphotoxin-TNF-R1 complex at 37 degrees C.

[Fate of the calcium-dense proximal fragment in scaphoid fracture]

A cohort study with retrolective and prolective collection of data was carried out 49 of 99 patients with scaphoid fractures, initially treated by plaster cast immobilization and having developed a proximal fragment with increased bone density were studied. More than half of these patients had a good or excellent result according to the modified score of Green and O'Brien 29 of 49 proximal fragments with increased bone density returned to normal density: 45 of 49 showed bony union, and 35 of 49 showed no signs of posttraumatic arthrosis. The appearance of stripes with increased bone density in plain X-rays indicated a problem in the process of fracture healing; the clinical interpretation, however, was difficult. Four patients were treated by percutaneous canulated screw (Streli). These fractures showed bony union, the fragment with increased bone density returned to normal in three of four patients. All of these patients had some remaining clinical problems.

[Risk assessment in ovarian hyperstimulation syndrome (OHS) using the machine learning system (Decision Master) in 155 in-vitro fertilisations and embryo-transfer (IVF/ET) cycles with a long stimulation protocol]

In 155 selected IVF/ET cycles stimulated with the long protocol 25 cycles with severe OHS are included which turned up later on (purposely overrepresented). An inductive machine learning program is described both in informatics and medical essentials. It is tested whether there exists an algorithm for ruling out the above-mentioned complication in the follicular phase of the same cycle already. By cross validation 89% of the OHS could be predicted and proven by practical rules using hormone and ultrasound values to avoid similar events in ongoing or further cycles.

Protein kinase C alters the responsiveness of adenylyl cyclases to G protein alpha and betagamma subunits

The ability of protein kinase C (PKC) to regulate the responsiveness of adenylyl cyclase to different activators was assessed. Membranes prepared from Sf9 cells infected with recombinant baculoviruses encoding either type II or IV adenylyl cyclase were incubated with recombinant PKCalpha (purified from Sf9 cells), and the effects on adenylyl cyclase activity were measured after reconstitution with Gsalpha, Gbetagamma, or forskolin. PKCalpha treatment of type II adenylyl cyclase leads to increases in basal, forskolin-stimulated, and betagamma-stimulated activities and greater sensitivity to stimulation by Gsalpha. Paradoxically, most of the betagamma potentiation of Gsalpha-stimulated activity is eliminated by pretreatment with PKCalpha. By contrast, treatment of type IV adenylyl cyclase with PKCalpha has little effect on the basal, forskolin-stimulated, or betagamma-stimulated activities but markedly reduces the Gsalpha-stimulated and betagamma-potentiated activity of this isoform. These studies demonstrate that protein kinases can alter both the activity of adenylyl cyclase isoforms and their responsiveness to G protein regulation, thereby altering the ability of adenylyl cyclases to integrate signals derived from multiple hormonal inputs.

The breast mucin MUCI as a novel adhesion ligand for endothelial intercellular adhesion molecule 1 in breast cancer

The MUC 1 mucin is expressed on normal breast epithelium and in 90% of breast cancers. We report here that tumor-associated MUC1 is a ligand for intercellular adhesion molecule 1 (ICAM-1). Antibodies to ICAM-1 and to MUC1 inhibited adhesion of human and transfected mouse MUC1-positive cell lines to human umbilical vein endothelial cell monolayers and immobilized recombinant human ICAM-1-immunoglobulin fusion protein. Purified MUC1 pretreatment of recombinant human ICAM-1 was an equally effective inhibitor of adhesion. The interaction between MUC1 and ICAM-1 may be critical to the process of bloodborne metastases in breast cancer.

Retrospective failure analysis in laparoscopic hernia repair possible because of routine videodocumentation

BACKGROUND

Studies performed to date show that laparoscopic hernia repair is superior to conventional procedures with regard to postoperative pain, complications, and duration of inability to work.

METHODS

From August 1, 1992, to February 16, 1995, we performed 245 laparoscopic hernia procedures on 224 patients utilizing a transabdominal preperitoneal polypropylene mesh-plasty (TAPP).

RESULTS

We observed in the first 100 patients a total of 21 postoperative complications in 20 patients (21%). We observed 3 hernia occurrences (3%) in this group. Due to careful video documentation of all procedures, retrospective analysis of operative failure was possible. Working on the complications occurring resulted in a modification of the procedure, leading to a standardization of the operative technique and to a rigorous reduction in the number of complications and recurrences.

CONCLUSIONS

Video-assisted retrospective failure analysis is consequently an effective method to use to optimize the results of minimal invasive hernia repair.

Tachocomb used in endoscopic surgery

BACKGROUND

Diffuse bleeding from parenchymatous organs or bleeding of the lung both in conventional and endoscopic surgery has to this day been treated with the usual methods - coagulation, tamponade, or oversewing.

METHODS

With the development by the pharmaceutical industry of a collagen fleece coated with fibrin glue (Tachocomb), an additional method of hemostasis became available.

RESULTS

The positive results obtained with the fibrin-coated collagen fleece in conventional surgery encouraged us to employ it when performing endoscopic operations. Especially with laparoscopic cholecystectomies, but also in other endoscopic operations, the application of Tachocomb has proved very successful. Nevertheless, the method of applying Tachocomb was not adequate, and limited its use, which made it necessary for us to develop an application system for endoscopic use.

CONCLUSIONS

The application system, which consists of a fan as the Tachocomb carrier and a mounting support, worked well during the first tests. In order to confirm this, clinical studies will now be carried out.

[Tubular differentiated stomach carcinoma of the (Ming) infiltrating type]

Gastric carcinoma of the infiltrative type (according to Ming) occasionally shows adenomatous differentiation only. Over the past 18 years, we have observed 23 cases of this tumour type, accounting for 3.6% of all surgically treated gastric carcinomas. Macroscopically they were classified as Borrmann IV or III, while histologically most of them were well differentiated. Histologically, these tumours retained the pre-existing structures of the stomach, most readily observable at the tunica muscularis propria; a pronounced desmoplasia was also characteristic, particularly in the submucosal and subserosal layers. In all cases the tumour tissue spread inside lymphatic vessels. All but 2 cases with metastatically involved lymph nodes, often small, showed infiltration of the lymph node sinus; in three quarters of cases the serosa was infiltrated by the tumour. Significant findings among the patients under observation for extended periods included bilateral ovarian metastases in 4 of 5 women examined and tumour recurrence at the anastomosis in 6 of 9 patients in whom Billroth II operation had been performed. The mean survival time of 16 patients was 14.9 months. Owing to the diffuse type of tumour growth, extensive surgery is recommended as in cases of signet ring cell cancer. The high incidence of small lymph node metastases from this type of tumour should also be taken in account preoperative staging. Preoperative diagnosis of this tumour subtype is difficult, because histological criteria alone do not allow clear identification. Close cooperation with clinical investigators is necessary, and intraoperative assessment of the tumour--including frozen section of necessary--in particular is of the utmost importance.

[Preoperative axillary ultrasound in breast carcinoma: value of the method in routine clinical practice]

AIM

To evaluate the significance of routinely performed preoperative axillary sonography in breast cancer patients.

METHOD

191 patients with surgical treated breast cancer were analysed retrospectively. 74 patients of these had an axillary sonography done by 5 different examiners.

RESULTS

For detecting lymph node metastases sensitivity was 68.2% in all T-stages and 50% in T1-stages with a specificity of 100%. Classification of the axillary status (positive or negative for lymph node metastases) is possible in 90.5% for all T-stages and 94.9% for T1-stages. Microscopic and small lymph node metastases are missed by ultrasound. Compared to axillary palpation, sonography is better.

CONCLUSION

Preoperative axillary sonography is an useful diagnostic method even when done routinely. If further criteria are considered, axillary dissection could be avoided in some patients.

[Value of preoperative axilla ultrasound in breast carcinoma]

Preoperative axillary sonography is a superior method in predicting axillary lymph node status than clinical examination in patients with breast cancer. However, the results depend on the skills and care of the examiner, metastases less than 3-5 mm are hardly visible.

[The normal CT and ultrasonic findings after a laparoscopic inguinal hernia operation]

Common surgery has been revolutionised by minimal invasive surgery in a very short period of time. Laparoscopic operations of inguinal hernias are routinely done by many surgeons. For interpreting correctly postoperative complications with radiological techniques it is necessary to know the sonographical and CT changes of the normal postoperative situs. For evaluating these changes 23 patients without symptoms were examined between the first and third postoperative day. Typical sonographic findings are high echogenicity of the hernial orifice (17x) and echo-lucent thickening of the spermatic cord. The surgical clips and fleece and CO2 bubbles could not be detected by ultrasound. Using CT we found free peritoneal fluid collection (2x), streaky thickenings in the area of operation (20x), oedema at the hernial orifice (19x), residual CO2 bubbles (22x), thickening of the spermatic cord (22x) and visualisation of the surgical clips. The surgical fleece was invisible in all patients.