beta-catenin: molecular plasticity and drug design.

The protein beta-catenin is an essential component of intercellular junctions and the Wnt growth factor signaling pathway. In many cancers, mutation of Wnt pathway components leads to activation of oncogenes by the beta-catenin-Tcf transcription factor complex. This complex is therefore an attractive target for anti-cancer drugs, but any such compound must selectively interfere with the beta-catenin-Tcf complex without disrupting other essential interactions of beta-catenin. Recent structural and biochemical studies have probed the molecular basis of ligand interaction by beta-catenin, and highlighted the possibilities and challenges of designing inhibitors of the beta-catenin-Tcf complex.

Abnormal cerebral activation associated with a motor task in Tourette syndrome.

BACKGROUND AND PURPOSE: In Gilles de la Tourette syndrome, PET scanning and EEG suggest an abnormal organization of the sensorimotor cortex and basal ganglia. The purpose of this study was to use functional MR imaging to study activation in the sensorimotor cortex in patients with Tourette syndrome. METHODS: From echo-planar images acquired during intermittent performance of a finger-tapping task, the location of activated pixels was determined by means of conventional signal processing methods. In five patients with Tourette syndrome and five healthy volunteers, the number of activated pixels in the sensorimotor cortices and supplementary motor areas were counted. The area over which the activation was distributed was calculated. RESULTS: In the five patients, the average number of pixels activated during the finger-tapping task in the sensorimoter cortices and supplementary motor area (69.4 pixels) exceeded that in the volunteers (49.2 pixels). The difference was significant. The area over which the pixels was distributed was significantly larger (25.4 vs 13.8 cm2). CONCLUSION: Motor function is organized differently in patients with Tourette syndrome than in healthy subjects.

Crystal structure of the hCASK PDZ domain reveals the structural basis of class II PDZ domain target recognition.

PDZ domain containing proteins assist formation of cell-cell junctions and localization of membrane protein receptors and ion channels. PDZ domains interact with the C-terminal residues of a particular target membrane protein. Based on their binding specificities and sequence homologies, PDZ domains fall into two classes. The first crystal structure of a class II PDZ domain, that of hCASK, has been solved by multi-wavelength anomalous dispersion phasing. Complex formation with the C-terminus of a neighboring non-crystallographically related PDZ domain reveals interactions between hCASK and its ligand. Class II PDZ domains differ from class I domains by formation of a second hydrophobic binding pocket. The C-terminal carboxylate binding loop of the PDZ domain is structurally conserved in both classes suggesting a generalized carboxylate binding motif (h-Gly-h) where h is a hydrophobic residue.

Understanding the brain stem.

This article highlights features of brain anatomy that are important to know in interpreting magnetic resonance images. This article concentrates on the names of some brain stem structures, the three-dimensional appearance of six important tracts, and the location of cranial nerve nuclei.

Cortical activation response to acoustic echo planar scanner noise.

PURPOSE: Our goal was to determine the distribution of auditory and language cortex activation in response to acoustic echo planar scanner noise with functional MRI (fMRI). METHOD: Acoustic scanner noise and spoken text, reproduced on high output cassette tape, were separately delivered at equivalent intensities to six normal hearing adult volunteers through earphones during fMRI data acquisition. In nine other subjects, taped scanner noise was delivered in five successive iterations of the task to assess the consistency of cortical activation to the noise stimulus. Gyri of the auditory and language system were divided into 10 different subregions for analysis of cortical activation. The number of activated pixels and proportion of volunteers activating each cortical subregion were determined using a cross-correlation analysis. RESULTS: Cortical activation to taped acoustic scanner noise was present within the transverse temporal gyrus (primary auditory cortex) in all subjects, but activation was highly variable between subjects in auditory association and language relevant cortex. Auditory association cortex activation was seen in the planum polari, planum temporali, and middle temporal gyrus/superior temporal sulcus regions in one-half to two-thirds of the volunteers. There was no significant difference in the distribution of cortical activation within individual subjects across five successive iterations of the scanner noise task. Listening to spoken text consistently activated primary and association auditory cortex bilaterally as well as language relevant cortex in some cases. The mean number of activated pixels was significantly greater for text listening than acoustic scanner noise in auditory association and language relevant cortical subregions (p < 0.01), although the distribution of activity was similar between the two tasks. CONCLUSION: This preliminary investigation suggests that the complex sounds produced by the echo planar pulse sequence can activate relatively large regions of auditory and language cortex bilaterally, with the extent of activation outside the primary auditory cortex being variable between subjects. However, the distribution of activation within individual subjects was relatively constant across several iterations of the scanner noise stimulus.

Functional MR activation correlated with intraoperative cortical mapping.

PURPOSE: To evaluate the spatial specificity of functional MR imaging by comparing it with intraoperative electrocortical mapping. METHODS: Functional MR imaging was performed in 28 patients before awake craniotomy and intraoperative electrocortical mapping. Activation was mapped for finger movement, lip movement, tongue movement, word generation, and counting paradigms. During surgery, finger movement, lip movement, tongue movement, counting, and/or speaking were mapped. The functional images and the photographic recordings of the brain functions mapped during surgery were converted to bit maps and coregistered by a computer program. The distance between the intraoperatively mapped function site and the MR activation site for a comparable function was measured. RESULTS: Forty-six functions were recorded on MR images and intraoperative maps. In 100% of correlations, the intraoperative site and the MR activation site were within 20 mm; in 87% of correlations they were within 10 mm. For each paradigm, 67% or more of the intraoperative stimulation maps correlated within 10 mm of the MR activation site. CONCLUSIONS: For the tasks used in this study, the activation site on functional MR images correlated well with the site at which intraoperative stimulation identified function.

Normal MR imaging anatomy of the elbow.

This article discusses the normal, clinically relevant MR imaging anatomy of the elbow. A compartmental approach is utilized to help simplify this anatomically complex region. Imaging techniques, common anatomic variants, and imaging pitfalls are also briefly discussed.

MR imaging of lumbar spondylolysis: the importance of ancillary observations.

OBJECTIVE: The purpose of this study was to determine the frequency of characteristic ancillary MR findings in patients with lumbar spondylolysis. MATERIALS AND METHODS: The radiology reports and clinical records of 64 patients (16 female, 48 male; 12-77 years old) with 66 levels of lumbar spondylolysis who had undergone MR imaging were retrospectively reviewed. Spondylolysis was established by conventional radiography in all 64 patients and by CT in 18 patients. The proportion of patients with spondylolysis in whom sagittal MR images showed ancillary findings of an increased sagittal diameter of the spinal canal, reactive marrow changes in the pedicle, or abnormal wedging of the posterior aspect of the vertebral body was retrospectively determined. This proportion was then compared with the proportion of patients in whom spondylolysis was correctly diagnosed by the initial interpreters of the MR images, who used only direct visualization of defects of the pars interarticularis to make the diagnosis. RESULTS: Twenty (30%) of 66 levels of lumbar spondylolysis were misdiagnosed when the MR images were initially interpreted using direct visualization of defects of the pars interarticularis. An increased sagittal diameter of the spinal canal was the most common ancillary observation, occurring at 60 of 66 levels of lumbar spondylolysis. This finding was present in all patients with grade II, III, or IV spondylolisthesis, in 95% of patients with grade I spondylolisthesis; and in 77% of patients with no anterolisthesis. Thirty-two (48%) of 66 lumbar levels showed wedging of the posterior aspect of the vertebral body, which correlated significantly with the grade of spondylolisthesis. Reactive marrow changes in the pedicle distinct from normal adjacent levels were seen on MR images in 24(36%) of 66 levels of lumbar spondylolysis. On MR images, 97% of all levels of lumbar spondylolysis yielded one or more ancillary observations, including all 20 of the cases originally misdiagnosed. CONCLUSION: The combined use of ancillary observations and direct visualization of pars interarticularis defects makes MR imaging effective in revealing lumbar spondylolysis.

Functional MR of the primary auditory cortex: an analysis of pure tone activation and tone discrimination.

PURPOSE: To use functional MR imaging to measure the effect of frequency (pitch), intensity (loudness), and complexity of auditory stimuli on activation in the primary and secondary auditory cortexes. METHODS: Multiplanar echo-planar images were acquired in healthy subjects with normal hearing to whom auditory stimuli were presented intermittently. Functional images were processed from the echo-planar images with conventional postprocessing methods. The stimuli included pure tones with a single frequency and intensity, pure tones with the frequency stepped between 1,000, 2,000, 3,000, or 4,000 Hz, and spoken text. The pixels activated by each task in the transverse temporal gyrus (TTG) and the auditory association areas were tabulated. RESULTS: The pure tone task activated the TTG. The 1,000-Hz tone activated significantly more pixels in the TTG than did the 4,000-Hz tone. The 4,000-Hz tone activated pixels primarily in the medial TTG, whereas the 1,000-Hz tone activated more pixels in the lateral TTG. Higher intensity tones activated significantly more pixels than did lower intensity tones at the same frequency. The stepped tones activated more pixels than the pure tones, but the difference was not significant. The text task produced significantly more activation than did the pure tones in the TTG and in the auditory association areas. The more complex tasks (stepped tones and listening to text) tended to activate more pixels in the left hemisphere than in the right, whereas the simpler tasks activated similar numbers of pixels in each hemisphere. CONCLUSION: Auditory stimuli activate the TTG and the association areas. Activation in the primary auditory cortex depends on frequency, intensity, and complexity of the auditory stimulus. Activation of the auditory association areas requires more complex auditory stimuli, such as the stepped tone task or text reading.

Synthesis and cytotoxic action of 3,5-isoxazolidinediones and 2-isoxazolin-5-ones in murine and human tumors.

The 3,5-isoxazolidinediones and 2-isoxazolin-5-ones demonstrated potent cytotoxicity against the growth of human Tmolt3 T cell leukemia, murine P388 and L1210 leukemias, as well as human HeLa-S3 uterine carcinoma and glioma tumor cell growth. The specificity of the 3,5-isoxazolidinedione and 2-isoxazoline-5-one derivatives as cytotoxic agents varied with the histological type of tumor cell. Selected compounds were active against solid HeLa uterine. KB nasopharynx, skin A431, SW-480 adenocarcinoma, osteosarcoma and glioma growth. Selected compounds demonstrated in vivo antineoplastic activity against Ehrlich ascites carcinoma growth. In L-1210 leukemia cells, the agents blocked DNA and protein synthesis at 25, 50 and 100 microM over 60 min. The agents were effective in reducing rate limiting enzymes in the de novo purine and pyrimidine pathways. In addition they suppressed dihydrofolate reductase and ribonucleoside reductase activities with moderate inhibition of DNA and RNA polymerase activities. DNA itself was not a target of the agents.

Two competing pathways for self-splicing by group II introns: a quantitative analysis of in vitro reaction rates and products.

Self-splicing group II introns are found in bacteria and in the organellar genes in plants, fungi, and yeast. The mechanism for the first step of splicing is generally believed to involve attack of a specific intronic 2'-hydroxyl group on a phosphodiester linkage at the 5'-splice site, resulting in the formation of a lariat intron species. In this paper, we present kinetic and enzymatic evidence that in vitro there are two distinct pathways for group II intron self-splicing: one involves 2'-OH attack and another involves attack of water or hydroxide. These two pathways occur in parallel under all reaction conditions, although either can dominate in the presence of particular salts or protein cofactors. Both pathways are followed by a successful second step of splicing, and either pathway can be highly efficient. We find that the hydrolytic pathway prevails under physiological ionic conditions, while branching predominates at molar concentrations of ammonium ion. The intron is observed to adopt two major active conformations. In order to quantify their individual reaction rates, we applied a mechanistic model describing biphasic parallel kinetic behavior. Kinetic analysis throughout the investigation reveals that there is no coupling between the unproductive "spliced-exon-reopening" reaction (SER) and hydrolysis during the first step of splicing. Conditions that stimulate branching can promote the SER reaction just as efficiently as conditions that stimulate the hydrolytic pathway. Although there is little evidence that it exists in vivo, a hydrolytic splicing pathway for group II introns has important implications for the translation of intron-encoded proteins and the inhibition of intron migration into new genomic positions.