Asbestos-related chest diseases: plain radiographic findings

In summary, there are a wide range of pulmonary manifestations seen in asbestos-exposed individuals from pleural and parenchymal fibrosis to pleural and parenchymal malignancy. The chest roentgenogram has assumed an important role in the detection and surveillance of asbestos-related pleural and parenchymal changes.

A retroviral-like metal binding motif in an aminoacyl-tRNA synthetase is important for tRNA recognition

The gag genes of retroviruses encode nucleocapsid proteins that package genomic RNA and are essential for viral infectivity. These RNA binding proteins have a Cys-Xaa2-Cys-Xaa4-His-Xaa4-Cys zinc binding motif that is distinct from the typical zinc-finger motif Cys-Xaa2-Cys-Xaa12-14-His-Xaa2-His that is found in some transcriptional activators. Escherichia coli alanyl-tRNA synthetase contains a zinc-binding Cys-Xaa2-Cys-Xaa6-His-Xaa2-His motif that resembles that of retroviral nucleic acid binding proteins. We show here that, for alanyl-tRNA synthetase, the metal bound at the retroviral-like metal binding motif is important specifically for tRNA recognition and not for amino acid activation. Moreover, the enzyme-tRNA interaction is strongly dependent on the geometry of metal coordination to the protein. These and additional experiments collectively suggest a role for the retroviral-like metal binding motif in RNA recognition and, further, raise the possibility that the protein-bound metal itself participates in an RNA interaction.

Evidence for a "cysteine-histidine box" metal-binding site in an Escherichia coli aminoacyl-tRNA synthetase

Escherichia coli alanyl-tRNA synthetase contains the sequence Cys-X2-Cys-X6-His-X2-His. This motif is distinct from the zinc fingers of DNA-binding proteins but has some similarity to the Cys-X2-Cys-X4-His-X4-Cys zinc-binding motif of retroviral gag proteins, where it has a role in RNA packaging. In Ala-tRNA synthetase, this sequence is located in an amino-terminal domain which has the site for docking the acceptor end of the tRNA near the bound aminoacyl adenylate and is immediately adjacent in the sequence to the location of a mutation that affects the specificity of tRNA recognition. We show here that Ala-tRNA synthetase contains approximately 1 mol of zinc/mol of polypeptide and that addition of the zinc chelator 1,10-phenanthroline inhibits its aminoacylation activity. Conservative mutations of specific cysteine or histidine residues in the "Cys-His box" destabilize and inactivate the enzyme, whereas mutations of intervening amino acids do not inactivate. The possibility that this motif can bind zinc (or cobalt) was demonstrated with a synthetic 22 amino acid peptide that is based on the sequence of the alanine enzyme. The peptide-cobalt complex has the spectral characteristics of tetrahedral coordination geometry. The results establish that the Cys-His box motif of Ala-tRNA synthetase has the potential to form a specific complex with zinc (at least in the context of a synthetic peptide analogue) and suggest that this motif is important for enzyme stability/activity.

Mutant aminoacyl-tRNA synthetase that compensates for a mutation in the major identity determinant of its tRNA

A single G3.U70 base pair in the acceptor helix is the major determinant for the identity of alanine transfer RNAs (Hou & Schimmel, 1988). Introduction of this base pair into foreign tRNA sequences confers alanine acceptance on them. Moreover, small RNA helices with as few as seven base pairs can be aminoacylated with alanine, provided that they encode the critical base pair (Francklyn & Schimmel, 1989). Alteration of G3.U70 to G3.C70 abolishes aminoacylation with alanine in vivo and in vitro. We describe here the mutagenesis and selection of a single point mutation in Escherichia coli Ala-tRNA synthetase that compensates for a G3.C70 mutation in tRNAAla. The mutation maps to a region previously implicated as proximal to the acceptor end of the bound tRNA. In contrast to the wild-type enzyme, the mutant charges small RNA helices that encode a G3.C70 base pair. However, the mutant enzyme retains specificity for alanine tRNA and can serve as the sole source of Ala-tRNA synthetase in vivo. The results demonstrate the capacity of an aminoacyl-tRNA synthetase to compensate through a single amino acid substitution for mutations in the major determinant of its cognate tRNA.

Supplemental emergent chest computed tomography in the management of blunt torso trauma

The efficacy of conventional chest X-ray (CXR) in comparison to chest computed tomography (CCT) in acutely injured blunt trauma patients was examined. Over a 21-month period, 50 patients underwent CXR and CCT according to a standard protocol, and their films and records were reviewed retrospectively. Hemo- and/or pneumothorax (HPTX) was noted in 12 patients (five by CXR, 12 by CCT). Pulmonary contusion (PC) was identified in ten patients (four by CXR, ten by CCT). Three additional false positive PC were diagnosed by CXR. Therapy changes based upon CCT findings occurred in seven of seven HPTX and five of six PC. The two imaging techniques were complementary in detecting fractures. Atelectasis was a common CCT finding (58% incidence). Chest X-ray is less sensitive than chest computed tomography in the detection of HPTX (42% vs. 100%) and PC (40% vs. 100%). Emergent chest computed tomography is recommended in stable patients with: 1) blunt high-energy torso trauma, 2) "cross-body" injury pattern, and/or 3) a mechanism of injury suggestive of chest trauma.

Synthetic peptide model of an essential region of an aminoacyl-tRNA synthetase

A 40 amino acid sequence of the unsolved structure of Escherichia coli alanine-tRNA synthetase is essential for tRNA binding and encodes an immunological determinant that cross-reacts with antibodies raised against a eukaryote (insect Bombyx mori) alanine enzyme. The secondary structure of this sequence is predicted to be an amphiphilic alpha-helix that includes one aspartyl and eight glutamyl side chain carboxyl groups. The antibody reactivity and the conformation of a synthetic peptide model of this region (Glu346 to Ser385) were investigated. In addition, double Arg----Gln and Leu----Ala substitutions were separately placed in the enzyme on the hydrophilic and hydrophobic face, respectively, of the predicted helix. These mutations conserve the polar/nonpolar character of each face and retain the potential for helix formation. Circular dichroism spectra of the synthetic peptide model demonstrate the potential for amphiphilic helix formation for the segment from Glu346 to Ser385. The behavior of the mutations in the enzyme, together with earlier data and immunological assays presented here, suggests that one face of the putative helix is an antigenic region of the surface of the enzyme where it contributes to the interaction with alanine tRNA and that the specific sequence of the helix is an important determinant of enzyme stability.

Cryptococcal pulmonary infection in patients with AIDS: radiographic appearance

The clinical, laboratory, and radiographic findings in seven patients with acquired immunodeficiency syndrome (AIDS) and cryptococcal pulmonary infections were reviewed. The infection was most commonly seen on radiographs as lymphadenopathy, interstitial infiltrates, or both. Interstitial infiltrates were commonly nodular. Large nodules or alveolar infiltrates, the most common findings at presentation in both immunocompetent patients and immunocompromised patients without AIDS, were not present in our series. Isolated pleural effusion was seen as the only radiographic finding in one case. Meningitis was present in six of seven cases and was neurologically silent in five of six cases. Cryptococcal pneumonia in AIDS patients should prompt a search for neurologically silent cryptococcal meningitis.

Bowler-hat sign: a simple principle for differentiating polyps from diverticula

The bowler-hat sign has been described both with colonic polyps and with diverticula. The authors describe a simple principle for evaluating a bowler-hat sign in order to determine whether it is caused by a polyp or a diverticulum. If the bowler hat points toward the center of the long axis of the bowel, it represents an intraluminal structure (ie, a polyp). If, however, it points away from the center of the long axis of the bowel, it represents an extraluminal structure (ie, a diverticulum). Only if the bowler hat is located in the midline or is directly parallel to the long axis of the bowel is it impossible to classify the abnormality as a polyp or a diverticulum. The value of this principle was confirmed with both a radiographic model and a blinded review of radiographs from 37 cases demonstrating the bowler-hat sign. When a bowler hat is present on a double-contrast barium enema examination, use of this principle provides a simple and objective means of differentiating a polyp from a diverticulum.

Purification of recombinant pp60v-src protein tyrosine kinase and phosphorylation of peptides with different secondary structure preference

The expression of the transforming gene product of Rous sarcoma virus (pp60v-src) in Saccharomyces cerevisiae has recently been reported (Kornbluth et al., 1987; Brugge et al., 1987). To carry out biochemical and structural studies of this enzyme, a facile purification was developed. The purification was accomplished in four chromatographic steps: Q-Sepharose, Affi-Gel Blue, phosphoagarose, and hydroxylapatite chromatography. The tyrosine kinase was isolated in milligram quantities as two highly active proteolytic fragments (52 and 54 kDa). Three model tyrosine kinase substrates with propensities to adopt helical or omega-loop conformations were synthesized and characterized. The peptides were based on the sites of phosphorylation of pp60v-src, lipocortin I, and lipocortin II. Circular dichroism spectroscopy was used to study the conformation of the helix-forming peptides in 50 mM Tris and in 50% trifluoroethanol/Tris. Peptide 1, which was designed to form an amphiphilic alpha-helix, displayed 24.2% helicity in buffer and 40.2% helicity in 50% TFE/buffer. Similar experiments for peptide 3, the other helix former, showed a lower helicity (8.1% helical and 26.0% helical in buffer and in 50% TFE/buffer, respectively). All three peptides were shown to be substrates for the recombinant tyrosine kinase. Kinetic measurements using high-voltage paper electrophoresis indicated that the helix-forming peptides exhibited low KM values (approximately 450 microM) for the purified src gene product, consistent with the notion that elements of secondary structure may be important in substrate recognition by tyrosine kinases.

Whole-lung tomography in urologic malignancy

The place of whole-lung tomography in urologic malignancy has not been established. We reviewed 88 cases of known or suspected urologic malignancy in which tomography was used. Most patients had renal, bladder, or testicular tumors. Of the 68 patients with negative screening chest roentgenograms, all but 2 had negative tomograms. One of these 2 patients had a normal chest film (the other had extrapulmonary metastasis), and he did not have the renal carcinoma initially suspected. Tomography discovered no metastases from urologic malignancy that was not already known about from the screening x-ray film. In 20 cases with a positive screening x-ray film, tomography was of limited value. It cleared two suspicious chest films and added information on extent of metastatic involvement in three. We conclude that whole-lung tomography adds little information not available by chest roentgenogram in our selected population, and with a negative screening chest film no additional chest study is needed.

Pulmonary edema as a complication of interleukin-2 therapy

Eight patients underwent IV bolus therapy with recombinant interleukin-2 (Cetus Corporation, Emeryville, CA) for treatment of metastatic melanoma or renal cell carcinoma. The patients were randomized to receive interleukin-2 alone or interleukin-2 in combination with lymphokine-activated killer cells. Radiographs showed pulmonary edema in five of the eight patients. The changes ranged from mild interstitial edema (two patients) to frank pulmonary edema (three patients). The edema generally resolved within 4 days after the termination of therapy (four patients), however, one patient developed edema and arrhythmias approximately 7 days after interleukin-2 therapy ended. Seven of the eight patients had either cardiac arrythmias or angina. The mechanisms that contribute to the pathogenesis of these cardiac complications with interleukin-2 therapy remain unclear. The development of pulmonary edema is thought to be caused by capillary leakage and cardiac pulmonary edema due to cardiac toxicity of the drug. The radiologic appearances of these types of pulmonary edema were indistinguishable from one another and from other causes of pulmonary edema. Our study shows that interleukin-2 can cause pulmonary edema, cardiac arrhythmias, and unstable angina. The severity of these conditions is unrelated to dose.

Cavitary pulmonary metastases in angiosarcoma. Diagnosis by transthoracic needle aspiration

An unusual case of cavitary pulmonary metastases from an angiosarcoma of the scalp is described. Transthoracic needle aspiration biopsy of one of the cavitary nodules was successful in establishing the diagnosis.

Recurrent esophageal carcinoma at thoracotomy incisions: diagnostic contributions of CT

Three cases of surgical implantation of esophageal carcinoma during esophagogastrectomy are presented. The CT and radiographic appearance is demonstrated. A possible etiology and method for decreasing the risk of surgical spread of tumor are discussed.

Pulmonary hypertension complicating portal hypertension: findings on chest radiographs

Pulmonary hypertension is a rare but well-established complication of portal hypertension with a prevalence of 0.73% in one large autopsy series. In this report, we review the findings on chest radiographs in eight patients with this complication. Portal hypertension in these patients was evidenced by the presence of esophageal varices and/or ascites. The causes of portal hypertension were liver cirrhosis in seven patients and portal venous thrombosis in one patient. Pulmonary hypertension was established by right heart catheterization and pressure measurement. Qualitative assessment of the radiographs showed that four patients had the classic findings of pulmonary hypertension including prominent central pulmonary arteries and right ventricular enlargement, three had subtle abnormalities, and one had only cardiomegaly. Measurements of the width of the right descending pulmonary artery and the pulmonary lobar diameter/transverse thoracic diameter ratio were made in five of the patients in whom postero-anterior radiographs were available. The results confirmed our qualitative analysis, although they did not establish the diagnosis in borderline cases. We also observed that pulmonary vascular redistribution to the upper lobes was present in four patients, a finding that has been reported in patients with other causes of pulmonary hypertension. We conclude that the possibility of pulmonary hypertension should be raised in patients with portal hypertension, even when only subtle chest radiographic findings are present to suggest that diagnosis.

Pulmonary sarcoidosis in the older patient: conventional radiographic features

The clinical and radiographic findings in 29 patients presenting with pulmonary sarcoidosis after the age of 50 years were reviewed. Fifty-nine percent (17 patients) had atypical findings at presentation. The atypical patterns at radiography included mediastinal adenopathy alone or in combination with unilateral hilar adenopathy (n = 8), solitary or multiple pulmonary masses (n = 3), and atelectasis (n = 3). Five patients had extrathoracic tumors at the time that the diagnosis of pulmonary sarcoidosis was made, which confused the diagnosis at radiography. An enhanced awareness of the atypical patterns of sarcoidosis in the older patient may facilitate the diagnostic process.