Identification of STAT3 as a specific substrate of breast tumor kinase

Breast tumor kinase (Brk) is a non-receptor tyrosine kinase distantly related to the Src family kinase. It is expressed in more than 60% of breast tumors, but the biological role of this kinase remains to be determined. Only a limited number of substates have been identified for Brk, and the link of Brk to tumorigenesis remains largely unknown. In this study, we provide evidence that the signal transducer and activator of transcription 3, STAT3, is a physiological target of Brk. Activation of STAT3 previously has been linked to oncogenesis, and results in this study demonstrate that STAT3 is tyrosine phosphorylated and transcriptionally activated in cells expressing endogenous Brk. Signal transducer and activator of transcription 3 is specifically targeted since other STAT members are not responsive to Brk expression. Signal transducer and activator of transcription 3 activation requires the catalytic activity of Brk, and expression of both STAT3 and Brk stimulate cellular proliferation. In addition, we have identified a negative regulator of Brk, the suppressor of cytokine signaling, SOCS3. The SOCS3 protein is known to block signaling mediated by cytokine receptors, and here we find that SOCS3 is able to repress the activity of the Brk non-receptor tyrosine kinase.

Structure and autoregulation of the insulin-like growth factor 1 receptor kinase

The insulin-like growth factor 1 (IGF1) receptor is closely related to the insulin receptor. However, the unique biological functions of IGF1 receptor make it a target for therapeutic intervention in human cancer. Using its isolated tyrosine kinase domain, we show that the IGF1 receptor is regulated by intermolecular autophosphorylation at three sites within the kinase activation loop. Steady-state kinetic analyses of the isolated phosphorylated forms of the IGF1 receptor kinase (IGF1RK) reveal that each autophosphorylation event increases enzyme turnover number and decreases Km for ATP and peptide. We have determined the 2.1 A-resolution crystal structure of the tris-phosphorylated form of IGF1RK in complex with an ATP analog and a specific peptide substrate. The structure of IGF1RK reveals how the enzyme recognizes peptides containing hydrophobic residues at the P+1 and P+3 positions and how autophosphorylation stabilizes the activation loop in a conformation that facilitates catalysis. Although the nucleotide binding cleft is conserved between IGF1RK and the insulin receptor kinase, sequence differences in the nearby interlobe linker could potentially be exploited for anticancer drug design.

Differential phosphorylation of IRS-1 by insulin and insulin-like growth factor I receptors in Chinese hamster ovary cells

Insulin receptor (IR) and insulin-like growth factor I receptor (IGF-IR) are closely related receptor tyrosine kinases. Despite their high degree of homology, recent evidence suggests that the two receptors have distinct biological roles. In several recent studies, the cytoplasmic tyrosine kinase domains of the two receptors have been shown to possess different signalling specificities. In this study, we examine the hypothesis that differential phosphorylation of insulin receptor substrate 1 (IRS-1) may contribute to these differences in signalling between the two receptors. Using Chinese hamster ovary (CHO) cells stably expressing human IR or IGF-IR and activated by their respective ligands, we show that there are differences between the two receptors with regard to the complement of SH2-containing proteins recruited to IRS-1. In particular, IGF-IR appears to couple IRS-1 preferentially to Grb2 whereas, in contrast, IR appears to couple IRS-1 preferentially to the p85 subunit of phosphatidyl inositol 3-kinase (PI3-kinase) and to Nck. The two receptors couple IRS-1 equally to the tyrosine phosphatase SHP2. We have also generated phosphospecific antibodies to three important tyrosine phosphorylation sites on IRS-1 (pY608, pY895 and pY1172). We used these antibodies to probe the phosphorylation status of these sites in intact CHO/IR and CHO/IGF-IR cells. In the case of pY608, these results also show evidence for differential phosphorylation of IRS-1 by the two receptors. Taken together, the results presented here support the notion that the cytoplasmic domains of IR and IGF-IR have differences in their intrinsic signalling potentials.

Inhibition of Src by direct interaction with protein phosphatase 2A

In this study, we report that Src kinase is inhibited by protein phosphatase 2A (PP2A), a serine/threonine phosphatase. We carried out experiments in vitro using purified PP2A (AC dimer) and full-length v-Src or truncated forms of v-Src. The inhibition of v-Src by PP2A is concentration- and time-dependent. Addition of okadaic acid, a PP2A phosphatase inhibitor, abolished the PP2A-dependent inhibition of v-Src. When experiments were carried out at 4 degrees C under conditions where PP2A activity is inhibited, Src activity was unaffected by the presence of PP2A, suggesting that PP2A binding alone is insufficient to block Src activity. These results imply that PP2A activity is essential for inhibition of v-Src. We also demonstrate that PP2A binds to the catalytic and the regulatory domains of v-Src.

Protein phosphatase 2A interacts with the Src kinase substrate p130(CAS)

In this study, we report that the Src substrate Cas (p130 Crk-associated substrate) associates with protein phosphatase 2A (PP2A), a serine/threonine phosphatase. We investigated this interaction in cells expressing a temperature-sensitive mutant form of v-Src. v-Src activation (by shifting cells from the nonpermissive to the permissive temperature) led to an increase in the tyrosine phosphorylation of v-Src and Cas, as well as in the association between v-Src and Cas. v-Src has previously been shown to bind to PP2A and to phosphorylate the catalytic subunit of PP2A, resulting in inhibition of phosphatase activity. We found that the association between v-Src and PP2A decreased as cells were shifted to the permissive temperature. In contrast, the levels of PP2A that co-immunoprecipitated with Cas increased when v-Src was activated. We obtained similar results in pull-down experiments with immobilized Microcystin, a PP2A inhibitor. Serine/threonine phosphorylation of Cas has previously been shown to occur in a cell cycle regulated matter. Treatment of NIH3T3 cells with okadaic acid, a PP2A inhibitor, augments the serine/threonine phosphorylation of Cas that occurs at mitosis. Furthermore, PP2A dephosphorylates serine residues on Cas in vitro. Taken together, our results suggest that PP2A may be involved in the cell cycle-specific dephosphorylation of Cas.

Reliability of soft-copy versus hard-copy interpretation of emergency department radiographs: a prototype study

OBJECTIVE

The purpose of this study was to compare the diagnostic reliability of hard-copy and soft-copy interpretation of radiographs obtained in the emergency department using a methodology for evaluating imaging systems when independent proof of the diagnosis is not available.

MATERIALS AND METHODS

We collected radiographs from a stratified sample of 100 patients seen in the emergency department. The images were obtained using computed radiography, and the digital images were printed on film and stored for display on a workstation. A group of seven experienced radiologists reported the cases using both film and the workstation display. The results were analyzed using mixture distribution analysis (MDA).

RESULTS

The reliability expressed as the percentage of agreement of a typical observer relative to the majority was computed from the MDA. The result was 90% for both hard copy and soft copy with bootstrap confidence intervals of 86-94%.

CONCLUSION

We conclude that, in the emergency department, soft-copy interpretation is as reliable as hard-copy interpretation. The strength of this conclusion depends on the validity of the MDA approach as well as the extent to which the observer sample and case sample are representative of the emergency department.

Progesterone receptor contains a proline-rich motif that directly interacts with SH3 domains and activates c-Src family tyrosine kinases

Steroid hormones have rapid nongenomic effects on cell-signaling pathways, but the receptor mechanisms responsible for this are not understood. We have identified a specific polyproline motif in the amino-terminal domain of conventional progesterone receptor (PR) that mediates direct progestin-dependent interaction of PR with SH3 domains of various cytoplasmic signaling molecules, including c-Src tyrosine kinases. Through this interaction, PR is a potent activator of Src kinases working by an SH3 domain displacement mechanism. By mutagenesis, we also show that rapid progestin-induced activation of Src and downstream MAP kinase in mammalian cells is dependent on PR-SH3 domain interaction, but not on the transcriptional activity of PR. Preliminary evidence for the biological significance of this PR signaling pathway through regulatory SH3 domains was shown with respect to an influence on progestin-induced growth arrest of breast epithelial cells and induction of Xenopus oocyte maturation.

Processive phosphorylation of p130Cas by Src depends on SH3-polyproline interactions

Many in vivo substrates of Src family tyrosine kinases possess sequences conforming to Src homology 2 and 3 (SH2 and SH3) domain-binding motifs. One such substrate is p130Cas, a protein that is hyperphosphorylated in v-Src transformed cells. Cas contains a substrate domain consisting of 15 potential tyrosine phosphorylation sites, C- and N-terminal polyproline regions fitting the consensus sequence for SH3 domain ligands, and a YDYV motif that binds the Src SH2 domain when phosphorylated. In an effort to understand the mechanisms of processive phosphorylation, we have explored the regions of Cas necessary for interaction with Src using the yeast two-hybrid system. Mutations in the SH2 domain-binding region of Cas or the Src SH2 domain have little effect in Cas-Src complex formation or phosphorylation. However, disruption of the C-terminal polyproline region of Cas completely abolishes interaction between the two proteins and results in impaired phosphorylation of Cas. Kinetic analyses using purified proteins indicated that multisite phosphorylation of Cas by Src follows a processive rather than a distributive mechanism. Furthermore, the kinetic studies show that there are two properties of the polyproline region of Cas that are important in enhancing substrate phosphorylation. First, the C-terminal polyproline serves to activate Src kinases through the process of SH3 domain displacement. Second, this region aids in anchoring the kinase to Cas to facilitate processive phosphorylation of the substrate domain. The two processes combine to ensure phosphorylation of Cas with high efficiency.

Involvement of protein phosphatase 2A in the interleukin-3-stimulated Jak2-Stat5 signaling pathway

In this study, we report that the tyrosine kinase, Janus kinase 2 (Jak2), associates with the serine/threonine protein phosphatase 2A (PP2A) in 32Dcl3 myeloid progenitor cells. The association between Jak2 and PP2A transiently increases following interleukin-3 (IL-3) stimulation and activation of Jak2. The catalytic subunit of PP2A is tyrosine phosphorylated by Jak2 in vitro and in vivo, resulting in inhibition of phosphatase activity. PP2A also associates with Stat5 in 32Dcl3 cells in an IL-3-dependent manner. Pretreatment of 32Dcl3 cells with okadaic acid (OA), an inhibitor of PP2A, resulted in increased tyrosine phosphorylation and nuclear translocation of Stat5. Our results suggest that PP2A plays a negative regulatory role in regulating the IL-3 signaling pathway via formation of complexes with Jak2 and Stat5.

Utility of high resolution computed tomography in predicting bronchiolitis obliterans syndrome following lung transplantation: preliminary findings

This study was undertaken to evaluate the efficacy of high resolution computed tomography (HRCT) in predicting the development of bronchiolitis obliterans syndrome (BOS) in lung transplant recipients. Fifty lung transplant patients who were clinically stable and without evidence of BOS were evaluated for the presence of four HRCT features reported to be associated with bronchiolitis obliterans: mosaic attenuation on inspiratory CT (mosaic perfusion), mosaic attenuation on expiratory CT (air trapping), bronchiectasis, and tree-in-bud opacities. CT exams were part of an annual surveillance process with the hope of predicting subsequent development of BOS. Diagnosis of BOS was made in 9 of 50 patients as indicated by a fall in FEV1 of greater than 20% of a stable baseline. None of the radiographic features associated with clinically established BOS were both sensitive and specific in the prediction of BOS. Air trapping demonstrated moderate sensitivity (56%, 5/9) and moderate specificity (76%, 35/46) for prediction of BOS in the year following the CT exam. Bronchiectasis, the most reliable indicator of the presence of BOS was a poor predictor of subsequent BOS with an 11% (1/9) sensitivity but had high specificity (96%, 44/46). No high resolution CT features accurately predicted the development of BOS.

Clustered pulmonary nodules: highly suggestive of benign disease

Thirty-one adult patients with a cluster of small, noncalcified, pulmonary nodules identified on chest computed tomography (CT) examinations were studied retrospectively. Pathology revealed an infectious/inflammatory etiology in all cases in which a surgical resection of the involved lung was performed. None of the patients in our study group showed evidence of malignancy in the region of a cluster of pulmonary nodules over the follow-up period. The authors conclude that an isolated cluster of small pulmonary nodules is strongly suggestive of benign disease. Although exceptions may rarely occur, most cases represent incidental infectious or inflammatory disease.

Investigating the substrate specificity of the HER2/Neu tyrosine kinase using peptide libraries

The product of the HER2/Neu oncogene is a receptor tyrosine kinase that is amplified in 25-30% of human primary breast tumors. In this project, we have isolated the HER2/Neu kinase from Sf9 cells infected with a baculovirus expression vector. We probed the substrate specificity of the HER2/Neu kinase using two peptide libraries: (1) a soluble peptide library containing three degenerate positions N-terminal to tyrosine; and (2) a bead-supported combinatorial library possessing six degenerate positions at P-1, P-2, P-3, P+1, P+2, and P+3. We identified four novel substrate sequences for HER2/Neu from the two peptide libraries. We synthesized these peptides as individual sequences and measured steady-state kinetic properties for phosphorylation by HER2/Neu. One of the peptides, AAEEIYAARRG, is the best synthetic peptide substrate reported to date for HER2/Neu. All of the sequences bear a resemblance to sites of autophosphorylation on HER2/Neu and related epidermal growth factor (EGF) receptor family tyrosine kinases.

A peptide model system for processive phosphorylation by Src family kinases

The Src homology 2 (SH2) and Src homology 3 (SH3) domains of Src family kinases are involved in substrate recognition in vivo. Many cellular substrates of Src kinases contain a large number of potential phosphorylation sites, and the SH2 and SH3 domains of Src are known to be required for phosphorylation of these substrates. In principle, Src could phosphorylate these substrates by either a processive mechanism, in which the enzyme remains bound to the peptide substrate during multiple phosphorylation events, or a nonprocessive (distributive) mechanism, where each phosphorylation requires a separate binding interaction between enzyme and substrate. Here we use a synthetic peptide system to demonstrate that Hck, a Src family kinase, can phosphorylate substrates containing an SH2 domain ligand by a processive mechanism. Hck catalyzes the phosphorylation of these sites in a defined order. Furthermore, we show that addition of an SH3 domain to a peptide can enhance its phosphorylation both by activating Hck and by increasing the affinity of the substrate. On the basis of our observations on the role of the SH2 and SH3 domains in substrate recognition, we present a model for substrate targeting in vivo.

Distribution of thrombi in acute lower extremity deep venous thrombosis: implications for sonography and CT and MR venography

OBJECTIVE

Our objective was to determine the typical distribution of thrombi in acute lower extremity deep venous thrombosis as a means of evaluating the validity of imaging techniques that only include the common femoral and popliteal veins, but not the superficial femoral vein.

MATERIALS AND METHODS

The results of 2704 lower extremity venous sonograms, obtained in 2026 consecutive patients over a 4-year interval, were reviewed retrospectively. The distribution of acute deep venous thromboses across various lower extremity venous segments was analyzed for this population, which consisted of both symptomatic and asymptomatic patients.

RESULTS

Of 2704 lower extremities studied with duplex sonography, acute deep venous thrombosis was identified in 269 (9.9%). Of these 269 cases, acute deep venous thrombosis was isolated to the superficial femoral vein in 60 (22.3%). The remaining 209 cases (77.7%) showed thrombus that extended into the common femoral or popliteal veins (or both).

CONCLUSION

An abbreviated imaging study that evaluates only the common femoral and popliteal veins would fail to identify more than 20% of lower extremity acute deep venous thromboses in a population like ours. Although evaluation of the superficial femoral vein requires additional time and resources, evaluation of this segment may prevent a substantial number of thrombi from being missed.

CT findings in patients with esophagitis

OBJECTIVE

The purpose of our study was to determine the CT findings in patients with esophagitis.

MATERIALS AND METHODS

A search of medical and radiology files revealed 29 patients with esophagitis in whom thoracic CT was performed within 1 month of the diagnosis. The CT scans were reviewed retrospectively for esophageal wall thickening, a target sign, or other abnormalities. The thickness of the esophageal wall was also measured on CT in these 29 patients and compared with a control group of 85 patients.

RESULTS

We found that 16 patients (55%) with esophagitis had abnormal findings on CT, including a thickened esophageal wall (using 5 mm as the threshold for wall thickening) in all 16 (55%) and a target sign in five (17%). The overall mean esophageal wall thickness was 4.7 mm (standard deviation [SD], 2 mm; 95% confidence interval [CI], 0.7-8.7 mm) in patients with esophagitis versus a mean wall thickness of 2.9 mm (SD, 0.8 mm; 95% CI, 1.3-4.5 mm) in controls (p <.001). Using the same 5-mm threshold for wall thickening, we found that only three (4%) of 85 controls had a thickened esophageal wall on CT.

CONCLUSION

The majority of patients with esophagitis had abnormalities on CT, including a thickened esophageal wall (> or =5 mm) in 55% and a target sign in 17%. Although barium studies and endoscopy are more sensitive modalities for detecting this condition, the CT finding of a relatively long segment of circumferential esophageal wall thickening, with or without a target sign, should suggest the diagnosis of esophagitis in the proper clinical setting.

The substrate specificity of the catalytic domain of Abl plays an important role in directing phosphorylation of the adaptor protein Crk

c-Abl preferentially phosphorylates peptide substrates that contain proline at the P+3 site (relative to the phosphorylated tyrosine). We previously described a mutant form of the Abl catalytic domain (Y569W) with altered substrate specificity at the P+3 position, as measured using synthetic peptides. In this study, we examine the phosphorylation of Crk, a protein substrate of Abl that is phosphorylated in the sequence Tyr221-Ala-Gln-Pro. In vitro, phosphorylation of Crk by Y569W Abl is greatly reduced relative to wild-type Abl. Overexpression of Y569W mutant Abl in 293T kidney cells produces a similar overall pattern of tyrosine phosphorylation as wild-type Abl, indicating that not all cellular proteins depend on Pro at P+3 for Abl recognition. However, phosphorylation of Crk by Y569W Abl in these cells is markedly reduced relative to wild-type Abl. A truncated form of Abl lacking the C-terminal polyproline region is not able to phosphorylate Crk in these assay conditions. Thus, proper phosphorylation of Crk by Abl depends not only on the interaction of the Crk SH3 domain with the Abl polyproline region, but also on the recognition of amino acids surrounding tyrosine by the Abl catalytic domain.

Structural mechanism for STI-571 inhibition of abelson tyrosine kinase

The inadvertent activation of the Abelson tyrosine kinase (Abl) causes chronic myelogenous leukemia (CML). A small-molecule inhibitor of Abl (STI-571) is effective in the treatment of CML. We report the crystal structure of the catalytic domain of Abl, complexed to a variant of STI-571. Critical to the binding of STI-571 is the adoption by the kinase of an inactive conformation, in which a centrally located "activation loop" is not phosphorylated. The conformation of this loop is distinct from that in active protein kinases, as well as in the inactive form of the closely related Src kinases. These results suggest that compounds that exploit the distinctive inactivation mechanisms of individual protein kinases can achieve both high affinity and high specificity.

Improving SH3 domain ligand selectivity using a non-natural scaffold

BACKGROUND

Src homology 3 (SH3) domains bind sequences bearing the consensus motif PxxP (where P is proline and x is any amino acid), wherein domain specificity is mediated largely by sequences flanking the PxxP core. This specificity is limited, however, as most SH3 domains show high ligand cross-reactivity. We have recently shown that diverse N-substituted residues (peptoids) can replace the prolines in the PxxP motif, yielding a new source of ligand specificity.

RESULTS

We have tested the effects of combining multiple peptoid substitutions with specific flanking sequences on ligand affinity and specificity. We show that by varying these different elements, a ligand can be selectively tuned to target a single SH3 domain in a test set. In addition, we show that by making multiple peptoid substitutions, high-affinity ligands can be generated that completely lack the canonical PxxP motif. The resulting ligands can potently disrupt natural SH3-mediated interactions.

CONCLUSIONS

Peptide-peptoid hybrid scaffolds yield SH3 ligands with markedly improved domain selectivity, overcoming one of the principal challenges in designing inhibitors against these domains. These compounds represent important leads in the search for orthogonal inhibitors of SH3 domains, and can serve as tools for the dissection of complex signaling pathways.

Reciprocal regulation of Hck activity by phosphorylation of Tyr(527) and Tyr(416). Effect of introducing a high affinity intramolecular SH2 ligand

The Src family tyrosine kinase Hck possesses two phosphorylation sites, Tyr(527) and Tyr(416), that affect the catalytic activity in opposite ways. When phosphorylated, Tyr(527) and residues C-terminal to it are involved in an inhibitory intramolecular interaction with the SH2 domain. However, this sequence does not conform to the sequence of the high affinity SH2 ligand, pYEEI. We mutated this sequence to YEEI and show that this mutant form of Hck cannot be activated by exogenous SH2 ligands. The SH3 domain of Hck is also involved in an inhibitory interaction with the catalytic domain. The SH3 ligand Nef binds to and activates YEEI-Hck mutant in a similar manner to wild-type Hck, indicating that disrupting the SH3 interaction overrides the strengthened SH2 interaction. The other phosphorylation site, Tyr(416), is the autophosphorylation site in the activation loop. Phosphorylation of Tyr(416) is required for Hck activation. We mutated this residue to alanine and characterized its catalytic activity. The Y416A mutant shows a higher K(m) value for peptide and a lower V(max) than autophosphorylated wild-type Hck. We also present evidence for cross-talk between the activation loop and the intramolecular binding of the SH2 and SH3 domains.

Acute biliary disease: initial CT and follow-up US versus initial US and follow-up CT

PURPOSE

To evaluate the utility of ultrasonography (US) versus that of computed tomography (CT) for assessment of acute biliary disease.

MATERIALS AND METHODS

Radiologic reports and clinical charts were reviewed in all patients who underwent US and CT within 48 hours of each other for evaluation of acute right upper quadrant pain. Radiologic findings and clinical outcome were correlated.

RESULTS

CT was the initial imaging study in 57 patients, and CT findings resulted in underdiagnosis or misdiagnosis of acute biliary disease in eight of 11 patients. Follow-up US results were suggestive of the correct diagnosis and provided additional clinical information in seven of these eight patients. US findings resulted in altered clinical treatment in six of 11 patients with acute biliary disease. US was the initial study in 66 patients, and US findings were suggestive of biliary disease or the correct diagnosis in seven of seven patients with acute biliary disease. Follow-up CT did not result in changes in clinical treatment in any patient with acute biliary disease.

CONCLUSION

Initial US is better than initial CT in patients suspected of having acute biliary disease. Follow-up CT provides no additional information regarding the biliary system, and its use should be limited to those patients with a wider differential diagnosis or with confusing clinical symptoms and signs.

Autonomous folding of a C-terminal inhibitory fragment of Escherichia coli isoleucine-tRNA synthetase

We previously reported that C-terminal fragments of Escherichia coli Ile-tRNA synthetase, a monomeric enzyme of 939 amino acids, act as dominant negative inhibitors of the wild-type enzyme in vivo and in vitro. Our experiments suggested that it is possible to block the functional assembly of a monomeric protein by interfering with the folding pathway. We postulated that the inhibitory C-terminal fragments fold autonomously, and in the presence of full-length Ile-tRNA synthetase, trap the N-terminal portion of polypeptide in an unproductive complex. Here, we report the results of experiments aimed at understanding the mechanism of dominant negative inhibition. We have carried out biophysical experiments on fragment 585-939 of Ile-tRNA synthetase, which we previously determined to be the minimal inhibitory unit. Circular dichroism and fluorescence spectroscopy indicate that this fragment forms a compact and stable structure in solution. The secondary structure of this fragment is predominantly alpha-helical, consistent with the crystal structure of Ile-tRNA synthetase from another organism. The C-terminal fragment is capable of forming native-like secondary and tertiary structure after refolding from guanidine HCl. Taken together, the results are consistent with the hypothesis that the inhibitory fragment of Ile-tRNA synthetase forms an independent folding unit.

Identification of residues involved in v-Src substrate recognition by site-directed mutagenesis

To study the role of the catalytic domain in v-Src substrate specificity, we engineered three site-directed mutants (Leu-472 to Tyr or Trp and Thr-429 to Met). The mutant forms of Src were expressed in Sf9 cells and purified. We analyzed the substrate specificities of wild-type v-Src and the mutants using two series of peptides that varied at residues C-terminal to tyrosine. The peptides contained either the YMTM motif found in insulin receptor substrate-1 (IRS-1) or the YGEF motif identified from peptide library experiments to be the optimal sequence for Src. Mutations at positions Leu-472 or Thr-429 caused changes in substrate specificity at positions P+1 and P+3 (i.e. one or three residues C-terminal to tyrosine). This was particularly evident in the case of the L-472W mutant, which had pronounced alterations in its preferences at the P+1 position. The results suggest that residue Leu-472 plays a role in P+1 substrate recognition by Src. We discuss the results in the light of recent work on the roles of the SH2, SH3 and catalytic domains of Src in substrate specificity.

Cross-sectional imaging of Kikuchi disease

PURPOSE

The purpose of this work was to characterize the cross-sectional imaging features of Kikuchi disease.

METHOD

A search of our hospital records yielded three patients with pathologically proven Kikuchi disease. CT, MR, and ultrasound examinations of these patients were reviewed to characterize the imaging features of Kikuchi disease.

RESULTS

MRI of the neck in one patient, CT of the chest and abdomen in another, and CT and MRI of the abdomen in the third demonstrated uniformly enhancing small lymph nodes in larger than normal numbers in the submandibular, axillary, gastrohepatic, celiac, periportal, paraaortic, retrocrural, mesenteric, and inguinal regions. Lymph node diameter was usually <10 mm and was always <18 mm.

CONCLUSION

Many small clustered lymph nodes may be a characteristic imaging feature of Kikuchi disease. The abdominal extent of disease may be underreported if cross-sectional imaging is not performed.

Advanced emphysema: preoperative chest radiographic findings as predictors of outcome following lung volume reduction surgery

PURPOSE

To determine whether preoperative chest radiographic findings alone can reliably predict which patients will achieve the best functional outcome of lung volume reduction surgery.

MATERIALS AND METHODS

The preoperative chest radiographs obtained in 57 patients who had undergone lung volume reduction surgery were retrospectively scored by five blinded readers for severity and distribution of emphysema, evidence of lung compression, disease heterogeneity, and other features. Comparisons were made with the 3-6-month postoperative functional outcome for each patient.

RESULTS

High disease heterogeneity (score > 2) and unequivocal lung compression (score 1) both were 100% predictive of a favorable outcome (FEV1 increase, > or = 30%). Low heterogeneity (score < 1) was 94% predictive of an unfavorable outcome (FEV1 increase < 30%), as was a lack of lung compression, which was 92% predictive of an unfavorable outcome. These two features also correlated with an improved 6-minute walk test result, although this correlation was weaker.

CONCLUSION

Chest radiography alone may be sufficient for initial screening. High disease heterogeneity and lung compression on chest radiographs are highly predictive of a favorable functional outcome.

Thickening of the diaphragm: a new computed tomography sign of diaphragm injury

Computed tomography examination is becoming a standard method of evaluating injury in blunt trauma. This report describes a previously unreported computed tomography sign of diaphragmatic injury. A retrospective review of imaging findings was performed on eight patients with surgically proven traumatic diaphragmatic rupture. Thickening of the diaphragm was present on computed tomography in six of eight patients with surgically proven diaphragm rupture. Two patients demonstrated previously established computed tomography signs of diaphragm rupture and two patients had no findings to suggest diaphragm injury. Diaphragm thickening is associated with diaphragm rupture and may be a useful diagnostic sign in the evaluation of patients with blunt trauma.

Engineering the substrate specificity of the Abl tyrosine kinase

c-Abl is a non-receptor tyrosine kinase that is involved in a variety of signaling pathways. Activated forms of c-Abl are associated with some forms of human leukemia. Presently, no high resolution structure of the tyrosine kinase domain of Abl is available. We have developed a structural homology model of the catalytic domain of Abl based on the crystal structure of the insulin receptor tyrosine kinase. Using this model as a guide, we selected residues near the active site predicted to play a role in peptide/protein substrate recognition. We expressed and purified 15 mutant forms of Abl with single amino acid substitutions at these positions and tested their peptide substrate specificity. We report here the identification of seven residues involved in recognition of the P-1, P+1, and P+3 positions of bound peptide substrate. Mutations in these residues cause distinct changes in substrate specificity. The results suggest features of Abl substrate recognition that may be relevant to related tyrosine kinases.

The right inferior supraazygous recess: a cause of upper esophageal pseudomass on double-contrast esophagography

OBJECTIVE

Our purpose was to characterize the radiographic features of a pseudomass impression on the upper thoracic esophagus, to determine the frequency of such a pseudomass both on double-contrast esophagography and on CT, and to elucidate the anatomic basis for this finding.

MATERIALS AND METHODS

Our study group consisted of 135 patients whose double-contrast esophagograms were reviewed retrospectively for the presence or absence of an extrinsic indentation on the right posterolateral wall of the upper thoracic esophagus. In another patient group, 50 CT scans of the chest were also reviewed for the presence or absence of a prominent right inferior supraazygous recess and an associated indentation on the upper thoracic esophagus.

RESULTS

Thirteen (9.6%) of the 135 barium studies revealed a smooth, gently sloping indentation on the right posterolateral wall of the upper thoracic esophagus. The indentations ranged from 5 to 10 cm in length and extended inferiorly from the thoracic inlet to or just below the aortic arch. Twenty-four (48%) of the 50 CT scans revealed a prominent right inferior supraazygous recess projecting behind the esophagus. In five cases (10%), this recess also caused a smooth indentation on the upper thoracic esophagus.

CONCLUSION

A pseudomass impression was seen on double-contrast radiography as a smooth, gently sloping indentation on the right posterolateral wall of the upper thoracic esophagus in approximately 10% of patients. The indentation probably represents a normal anatomic variant (i.e., an unusually prominent right inferior supraazygous recess) that should not be mistaken for adenopathy or other masses in the mediastinum impinging on the esophagus.

Intramolecular regulatory interactions in the Src family kinase Hck probed by mutagenesis of a conserved tryptophan residue

Intramolecular interactions between the Src homology domains (SH2 and SH3) and the catalytic domains of Src family kinases result in repression of catalytic activity. The crystal structure of the Src family kinase Hck, with its regulatory domains intact, has been solved. It predicts that a conserved residue, Trp260, at the end of the linker between the SH2 and the catalytic domains plays an important role in regulation by the SH3 and SH2 domains. We have mutated this residue and compared the activities of C-terminally phosphorylated wild type Hck and W260A Hck. The W260A mutant has a higher specific activity than wild type Hck. The W260A mutant requires autophosphorylation at Tyr416 for full activity, but it is not activated by ligand binding to the SH3 or SH2 domains. This mutation also changes the accessibility of the SH2 and SH3 domains to their cognate peptide ligands. Our results indicate that Trp260 plays a critical role in the coupling of the regulatory domains to the catalytic domain, as well as in positioning the ligand binding surfaces.

Thoracic CT in the intensive care unit: assessment of clinical usefulness

PURPOSE

To determine the clinical usefulness of thoracic computed tomography (CT) in patients in a general intensive care unit (ICU).

MATERIALS AND METHODS

Images obtained in 108 consecutive thoracic CT examinations and the associated bedside chest radiographs and medical records in 85 patients (55 men, 30 women; age range, 19-92 years) in the ICU of an institution were retrospectively reviewed. CT findings were compared with concurrent bedside chest radiographic findings. The clinical importance of each CT finding was determined by reviewing the clinical record.

RESULTS

Of the 232 chest radiographic findings, 199 (86%) were confirmed at CT; when disagreement about mild congestive heart failure was excluded, there was a 93% agreement (199 of 213 findings). However, only CT demonstrated 250 (52%) of the 482 total findings (232 + 250 findings). Although many of these new findings were not clinically important, 32 (30%) of the 108 CT examinations had at least one new clinically important finding. These important new findings most often were (a) abscesses or postoperative fluid collections in the mediastinum, chest wall, or retroperitoneum; (b) malignancies that were detected, staged, or evaluated; (c) unsuspected pneumonia; or (d) pleural effusions. The CT findings resulted in changes in clinical management in 24 (22%) of the 108 examinations.

CONCLUSION

CT of the thorax is clinically useful in selected situation in patients in ICUs.

Mycobacterial infection in immunocompromised patients

Mycobacterial infection, including both tuberculosis and nontuberculous mycobacterial infection, is an important cause of morbidity and mortality in immunocompromised patients, particularly those who are infected with the human immunodeficiency virus. When these patients have active tuberculosis, apical, often cavitary, opacities characteristic of postprimary tuberculosis remain among the more common radiographic presentations. However, unusual radiographic manifestations of tuberculosis are more common in immunocompromised patients than in the general population. Nontuberculous mycobacterial infection in immunocompromised patients is frequently hematogenously disseminated, and the appearance on chest radiography is varied. Among patients infected with the human immunodeficiency virus, unifocal or multifocal alveolar infiltrates and mediastinal lymphadenopathy are the most common manifestations.

Phosphorylation and activation of cGMP-dependent protein kinase by Src

Using information obtained from experiments with peptide substrates of v-Src, a motif within the cGMP-binding domain of cGMP-dependent protein kinase (cGK) was identified as a potential phosphorylation site for v-Src. Here we show that the purified Ialpha isozyme of cGK is phosphorylated stoichiometrically and in a time-dependent manner by purified Src in vitro. The kinase activity of cGK is elevated approximately 4-fold (relative to autophosphorylated cGK) or 10-fold (relative to unphosphorylated cGK) upon tyrosine phosphorylation by Src. Phosphorylation of cGK by v-Src produces modest effects on the cGMP-binding properties and dissociation rates of cGK, and reduces the kact for cGMP. We hypothesize that the mechanism of activation may involve coupling of the cGMP binding domain to the catalytic domain.

Reperfusion edema after thromboendarterectomy: radiographic patterns of disease

In patients with chronic pulmonary embolism, pulmonary thromboendarterectomy may result in a unique form of noncardiogenic pulmonary edema termed reperfusion edema. This report reviews the authors' experience after pulmonary thromboendarterectomy with particular emphasis on the radiographic manifestations of reperfusion edema. The clinical and radiographic record of 25 patients who underwent pulmonary thromboendarterectomy at the University of Pennsylvania from 1985 through 1995 were reviewed. The zonal distribution of radiographic opacity, time to maximal opacity, and the time to clearance of reperfusion edema were determined. The relationship of these radiographic manifestations to clinical severity of disease and clinical outcome was examined. Reperfusion edema, characterized by patchy bilateral perihilar alveolar opacities, occurred in all but one patient. There is a lower lung zone predominance of opacities, but in individual cases, striking unilateral or haphazard arrangements of opacities may be seen. In this small sample of patients, no association between preoperative pulmonary arterial pressures and radiographic appearance or clinical outcome was found. However, severity of radiographic opacities, as measured by the extent of involved lung, correlated with disease severity, as measured by time to extubation and time to discharge. Pneumonia, defined as a radiographic opacity that evolves discordantly with the reperfusion edema opacities, occurred in 20% of cases. Reperfusion edema is a common consequence of pulmonary thromboendarterectomy. The severity of radiographic manifestations and clinical severity of disease are related. This characteristically appears as perihilar alveolar opacities.

Enhanced phosphorylation of Src family kinase substrates containing SH2 domain binding sites

Src family protein-tyrosine kinases possess several modular domains important for regulation of catalytic activity and interaction with potential substrates. Here, we explore interactions between the SH2 domain of Hck, a Src family kinase, and substrates containing SH2 domain-binding sites. We have synthesized a series of peptide substrates containing a high affinity SH2 domain binding site, (phospho)Tyr-Glu-Glu-Ile. We show that the presence of this sequence in a peptide results in a dramatic increase in the phosphorylation rate of a second tyrosine located at the N terminus. Enhanced phosphorylation is not a consequence of stimulation of enzymatic activity by C-terminal tail displacement but is imparted instead by a 10-fold reduction in the Km of the phosphotyrosine-containing peptide when compared with a control. The isolated catalytic domain of the non-receptor tyrosine kinase Abl does not show a preference for the pYEEI motif-containing peptide; however, the preference is restored when the SH2 domain of Src is introduced into Abl. Furthermore, enhanced phosphorylation is dependent on the distance between SH2 domain-binding site and phosphorylatable tyrosine, with the minimum distance requirement being seven amino acids. Reversing the orientation of the pYEEI motif with respect to the substrate sequence decreases phosphorylation by down-regulated Hck, but both orientations are utilized equally well by activated Hck. We discuss the possible implications of these results for processive phosphorylation of substrates in vivo by Src family kinases.