The Ras branch of small GTPases: Ras family members don't fall far from the tree.

The Ras branch of the Ras superfamily consists of small GTPases most closely related to Ras and include the R-Ras, Rap, Ral, Rheb, Rin and Rit proteins. Although our understanding of Ras signaling and biology is now considerable, recent observations suggest that Ras function is more complex than previously believed. First, the three Ras proteins may not be functionally identical. Second, Ras function involves functional cross-talk with their close relatives.

Association of the protein kinases c-Bcr and Bcr-Abl with proteins of the 14-3-3 family.

In this study, a protein that interacts with sequences encoded by the first exon of the protein kinase Bcr was cloned. The Bcr-associated protein 1 (Bap-1) is a member of the 14-3-3 family of proteins. Bap-1 interacts with full-length c-Bcr and with the chimeric Bcr-Abl tyrosine kinase of Philadelphia chromosome (Ph1)-positive human leukemias. Bap-1 is a substrate for the Bcr serine-threonine kinase and is also phosphorylated on tyrosine by Bcr-Abl but not by c-Abl. Bap-1 may function in the regulation of c-Bcr and may contribute to the transforming activity of Bcr-Abl in vivo. 14-3-3 proteins are essential for cell proliferation and have a role in determining the timing of mitosis in yeast. Through direct binding to sequences present in Bcr and in other proteins implicated in signaling, the mammalian 14-3-3 proteins may link specific signaling protein components to mitogenic and cell-cycle control pathways.

Remarkable leukemogenic potency and quality of a constitutively active neurotrophin receptor, deltaTrkA.

Neurotrophins and their receptors play a key role in neurogenesis and survival. However, we and others have recently obtained evidence for a potential involvement of this receptor system in leukemia. To investigate mechanisms underlying the leukemogenic potential of activated neurotrophin receptor signaling, we analyzed in vivo leukemogenesis mediated by deltaTrkA, a mutant of TRKA (tropomyosin-related kinase A) isolated from a patient with acute myeloid leukemia (AML). Retroviral expression of deltaTrkA in myeloid 32D cells induced AML in syngeneic C3H/Hej mice (n=11/11, latency approximately 4 weeks). C57Bl/6J mice transplanted with deltaTrkA-transduced primary lineage negative (Lin-) bone marrow cells died of a transient polyclonal AML (n=7/15, latency of <12 days). Serial transplantation of AML cells did not re-induce this disease but rather acute lymphoblastic leukemia (ALL, latency >78 days). All primary recipients surviving the early AML developed clonal ALL or myeloid leukemia (latency >72 days) that required additional genetic lesions. PI3K and mTOR-raptor were identified as the crucial mediators of leukemic transformation, whereas STAT and MAP kinase signaling pathways were not activated. Thus, our findings reveal potent and unique transforming properties of altered neurotrophin receptor signaling in leukemogenesis, and encourage further analyses of neurotrophin receptors and downstream signaling events in hematological malignancies.

Identification and characterization of an activating TrkA deletion mutation in acute myeloid leukemia.

In this study, we utilized retroviral transfer of cDNA libraries in order to identify oncogenes that are expressed in acute myeloid leukemia (AML). From screens using two different cell types as targets for cellular transformation, a single cDNA encoding a variant of the TrkA protooncogene was isolated. The protein product of this protooncogene, TrkA, is a receptor tyrosine kinase for nerve growth factor. The isolated transforming cDNA encoded a TrkA protein that contains a 75-amino-acid deletion in the extracellular domain of the receptor and was named DeltaTrkA. DeltaTrkA readily transformed fibroblast and epithelial cell lines. The deletion resulted in activation of the tyrosine kinase domain leading to constitutive tyrosine phosphorylation of the protein. Expression of DeltaTrkA in cells led to the constitutive activation of intracellular signaling pathways that include Ras, extracellular signal-regulated kinase/mitogen-activated protein kinase, and Akt. Importantly, DeltaTrkA altered the apoptotic and growth properties of 32D myeloid progenitor cells, suggesting DeltaTrkA may have contributed to the development and/or maintenance of the myeloid leukemia from which it was isolated. Unlike Bcr-Abl, expression of DeltaTrkA did not activate Stat5 in these cells. We have detected expression of DeltaTrkA in the original AML sample by reverse transcriptase PCR and by Western blot analysis. While previous TrkA mutations identified from human tumors involved fusion to other proteins, this report is the initial demonstration that deletions within TrkA may play a role in human cancers. Finally, this report is the first to indicate mutations in TrkA may contribute to leukemogenesis.

Myeloproliferative Neoplasms: Molecular Drivers and Therapeutics.

Activating mutations in genes that drive neoplastic cell growth are numerous and widespread in cancer, and specific genetic alterations are associated with certain types of cancer. For example, classic myeloproliferative neoplasms (MPNs) are hematopoietic stem cell disorders that affect cells of the myeloid lineage, including erythrocytes, platelets, and granulocytes. An activating mutation in the JAK2 tyrosine kinase is prevalent in these diseases. In MPN patients that lack such a mutation, other genetic changes that lead to activation of the JAK2 signaling pathway are present, indicating deregulation of JAK2 signaling plays an etiological driving role in MPNs, a concept supported by significant evidence from in vivo experimental MPN systems. Thus, small molecules that inhibit JAK2 activity are ideal drugs to impede the progression of disease in MPN patients. However, even though JAK inhibitors provide significant symptomatic relief, they have failed as a remission-inducing therapy. Nonetheless, the progress made understanding the molecular etiology of MPNs since 2005 is significant and has provided insight for the development and testing of novel molecular targeted therapeutic approaches. The current understanding of driver mutations in MPNs and an overview of current and potential therapeutic strategies for MPN patients will be discussed.

The Bcr-Abl tyrosine kinase activates mitogenic signaling pathways and stimulates G1-to-S phase transition in hematopoietic cells.

Bcr-Abl is a constitutively active tyrosine kinase that is expressed in Philadelphia chromosome (Ph1)-positive human leukemias. Bcr-Abl has been shown to inhibit apoptosis and cause anchorage independent growth. However, its ability to activate mitogenic signaling pathways is controversial. Here we show that Bcr-Abl signaling prevents down-regulation of cyclin-dependent kinase activity and cell cycle arrest after growth factor deprivation of hematopoietic progenitor cells. Using an inducible system to regulate Bcr-Abl expression, we also demonstrate that Bcr-Abl expression is sufficient to induce G1-to-S phase transition, DNA synthesis, and activation of cyclin-dependent kinases in cells that were arrested in G0 by growth factor deprivation. Furthermore, Bcr-Abl activates Ras, Erk, and Jnk pathways as a primary consequence of expression. These data show that Bcr-Abl is one of a select group of oncogenes that is capable of both inhibiting apoptosis and deregulating cell proliferation. The combination of these activities is likely to be important for the progression of CML.

Analysis of function and regulation of proteins that mediate signal transduction by use of lipid-modified plasma membrane-targeting sequences.

It is now established that the function of many signaling molecules is controlled, in part, by regulation of subcellular localization. For example, the dynamic recruitment of normally cytosolic proteins to the plasma membrane, by activated Ras or activated receptor tyrosine kinases, facilitates their interaction with other membrane-associated components that participate in their full activation (e.g., Raf-1). Therefore, the creation of chimeric proteins that contain lipid-modified signaling sequences that direct membrane localization allows the generation of constitutively activated variants of such proteins. The amino-terminal myristoylation signal sequence of Src family proteins and the carboxy-terminal prenylation signal sequence of Ras proteins have been widely used to achieve this goal. Such membrane-targeted variants have proved to be valuable reagents in the study of the biochemical and biological properties of many signaling molecules.

[CT-guided biopsies of the axial skeleton. The approaches and results]. / CT-kontrollierte Biopsien des Achsenskeletts. Zugangswege und Ergebnisse.

The value of percutaneous CT-guided biopsies of the axial skeleton for establishing a diagnosis is determined from a series of 75 punctures in 74 patients in retrospect. Indications showed benign conditions to prevail over malignant lesions by a ratio of 1.6:1. Biopsy routes turned out to be strongly determined by regional anatomy allowing for a standardised procedure in each area. 64 out of 75 histological diagnoses were confirmed by open surgery (n = 17) or follow-up (n = 58) accounting for an accuracy of 85.3%. In 7 cases no definite diagnosis could be made from the sample and in 4 cases the diagnosis proved false although tissue cores could be obtained in each case. No serious or irreversible complications occurred. CT-guided punctures of the axial skeleton are considered a safe and highly accurate procedure to establish a definite diagnosis unless there is a primary indication for surgery or the need for decompression.

[The value of CT and MRT in the diagnosis of cartilage-forming tumors]. / Wertigkeit von CT und MRT in der Diagnostik knorpelbildender Tumoren.

Accuracy in the assessment of lesion extension, specificity for histologic type and tumour status were reviewed in MRI and CT scans of 27 chondrosarcomas, 18 osteochondromas and 10 enchondromas and compared with the results obtained by plain radiography. No significant differences in the description of the lesion were found in chondrosarcomas and enchondromas between MRI and CT. In osteochondromas cartilage caps smaller than 5 mm and isodense to muscle were missed or not adequately delineated in CT. The specificity for the primary benign and malignant forms was equally high for CT and plain films, while MRI implies a much lower specificity due to the low sensitivity for matrix mineralisations. The criteria for malignant transformation of osteochondromas are visualised to better advantage by MRI. Solid ossified and small unmineralised recurrences of chondrosarcomas are detected by MRI with a higher sensitivity and specificity than by CT.

[Radiomorphologic classification of central chondrosarcomas]. / Radiomorphologische Klassifikation zentraler Chondrosarkome.

A retrospective study of 50 exostotic chondrosarcomas of the trunk reveals statistically significant correlations of histological grading and growth pattern as well as bone destruction pattern as general hallmarks of the degree of malignancy. No correlation between presence and type of matrix mineralisations was found. A radiomorphological classification derived from the CT appearance of mineralisations allows a distinction of 5 types that are important for diagnostic specificity and recurrence detection. MRI provides sensitive detection of early local recurrences due to high-contrast display of chondroid tissue irrespective of mineralisations. However, the specificity is low.

[Magnetic resonance tomography of the orbit using surface coils. Study technic, anatomy and initial clinical experience]. / Kernspintomographie der Orbita mit Oberflächenspulen. Untersuchungstechnik, Anatomie und erste klinische Erfahrungen.

MRI of the orbit is strongly improved by the use of surface coils due to a higher signal-to-noise ratio. Oblique views without moving the patient present the optic nerve in full length on one slice. First experience with a small number of cases demonstrates normal anatomy and lesions in detail only at T1-weighted pulse sequences. Losses in contrast variation and detail accuracy are caused by movements of the eyeballs. Edge artifacts due to chemical shifting impair the image quality. So far there are no pointers towards tissue-specific signal intensity behaviour. Procedure and most favourable parameters at 1 tesla are given.

[MRT and CT of diaphragmatic lipomas]. / MRT und CT bei Zwerchfell-Lipomen.

The radiological appearance of 6 posterior epidiaphragmatic fatty tissue masses in MRI and CT is reported. The differential diagnostic considerations of lipoma, herniation or dystopia and the value of imaging techniques are discussed.

[Radiological diagnosis of intraosseous lipoma]. / Aspekte der radiologischen Diagnostik des intraossären Lipoms.

Intraosseous lipomas exhibit a very characteristic radiological appearance. Diagnosis can be derived exclusively from x-ray examinations if a sharply defined cystic lesion with dense central sclerosis and fat-equivalent CT values is detected. When the latter criterion is not markedly pronounced the occurrence of a lipoma-derived, e.g. myxomatous, process can be discussed.

[Diagnostic value and interpretation of imaging bone densitometry based on quantitative CT]. / Aussagefähigkeit und Interpretation der bildgebenden Osteodensitometrie am Beispiel der quantitativen CT.

Quantitative CT of the axial skeleton (aQCT) may serve as an example of the evaluation and interpretation of bone densitometric data as it is the only state-of-the-art technique with valid longitudinal observations. The value of bone density measurements in interindividual cross sections refers to a grading derived from a representative reference population and provides an evaluation of fracture risk. The presence and rate of any bone loss can only be evaluated in an intraindividual longitudinal follow-up. Adequate follow-up for trabecular bone requires at least 3 to 5 years intervals to discriminate between different loss rates. Bone losses induced by steroid therapy or immobilisation may have faster kinetics apparent within months; bone density increase due to hormone substitution may be significant after one to two years. Morphological data allow critical evaluation of the quantitative measurements, eliminating false values and differentiating between rarefying and destructive osteopenia.

[MRT of the hypophysis: spin echo 2D or gradient echo 3D?]. / MRT der Hypophyse: Spinecho 2D oder Gradientenecho 3D?

Diagnostic efficacy of T1-weighted 3D gradient-echo and 2D spin-echo pulse sequences in the detection of adenomas were evaluated in a ROC study of 50 patients. Sensitivity, specificity and accuracy did not differ significantly, but in direct comparison gradient-echo received a clear lower rating due to susceptibility artifacts, lower signal-to-noise ratio, and inferior periglandular contrasts. Additional lesions could not be reliably detected in gradient-echo imaging at 1 mm slice thickness. A substitution of 2D spin-echo imaging by gradient-echo sequences cannot be recommended at present.

[The morphological analysis of the vertebral spongiosa in quantitative CT]. / Morphologische Analyse der Wirbelkörperspongiosa in der quantitativen CT.

The diagnostic ranking of trabecular morphology for the evaluation of osteoporosis in quantitative CT (QCT) is presented. 5 patterns of cancellous bone correlating with trabecular density may be discerned. However, these patterns may indicate osteoporotic changes in particular cases only, by confluent rarefactions if the density is still within the normal range. There is neither a predictive value for the degree of spontaneous or therapy-induced bone loss, nor for therapy response. The trabecular appearances remain unchanged in short term even under strong quantitative changes and are therefore of no value for follow-up.

[The MR tomographic findings in cranial manifestations of neurofibromatosis]. / MR-tomographische Befunde kranialer Manifestationen der Neurofibromatose.

Twelve patients with central neurofibromatosis underwent MR examination of the head. Among these, chiasma glioma was the most common CNS tumour (6/12). Seven patients had multifocal areas of increased T2-signal without mass effect predominantly involving the region of the basal ganglia. No corresponding CT abnormalities were present. These lesions may represent multifocal dysplasia and seem to be characteristic of central neurofibromatosis.

[MR-Cholangiopancreatography as a single-shot projection: techniques and results of 200 examinations]. / MR-Cholangiopankreatikographie als Einzelschussprojektion: Erfahrungen und Ergebnisse bei 200 Untersuchungen.

PURPOSE: Evaluation of utility and value of a selective projection technique for bile and pancreatic ducts in MRI. MATERIAL AND METHODS: 200 patient examinations of the pancreaticobiliary duct system using a turbo-SE pulse sequence in "single-shot" technique were evaluated in retrospect concerning anatomic display and diagnostic accuracy compared to surgery, ERCP, i.v. cholangiography, ultrasound and clinical course. RESULTS: Non-dilated ducts allowed visualisation of gallbladders in 78%, common bile ducts in 97%, cystic ducts in 80%, intrahepatic main ducts in 71% and pancreatic main ducts in 69%. When dilatation was present, all common bile, intrahepatic main and pancreatic ducts were visible. Display of cystic ducts and gallbladders with a detection rate of 69 and 85%, respectively, did not improve. Sensitivities for diagnosing papillary stenoses (n = 6), pancreatic ductal stenoses and dilatation (n = 13), compressions and dilatations of the biliary tree (n = 33) as well as for one choledochal cyst were 100%. Choledocholithiasis could correctly be predicted in 11/15 cases (73%), cholecystolithiasis in 71/120 cases (59%). CONCLUSION: "Single-shot" MR-cholangiopancreatography is a fast and non-invasive modality which can replace i.v. cholangiography and restrict the indication for ERCP to therapeutic indications and problem cases.

[A comparison between digital luminescence radiography and conventional myelography]. / Vergleich zwischen digitaler Lumineszenzradiographie und konventioneller Myelographie.

The potential of digital luminescence radiography in replacing conventional myelography was analyzed using ROC methodology. 95 conventional (CR), digital (DR) and edge enhanced digital (EDR) myelograms (49 disk herniations, 46 normal) were read independently by 5 radiologists; and a ROC analysis was performed. Higher confidence levels were used in making both correct and incorrect diagnoses with DR and EDR than with CR. However, no statistically significant differences between AUC (area under the curve) values obtained with the different techniques, were noted. The separate analysis of cervical and lumbar myelograms showed no significant differences between the different techniques. With DR and EDR, the sensitivity of 4 of 5 readers was somewhat higher in the lumbar but lower in the cervical region than with CR. Replacement of conventional by digital luminescence myelography seems possible; however, some decrease of sensitivity in the cervical region must be accepted.

[The place of magnetic resonance tomography in the diagnosis of diseases of the shoulder joint]. / Stellenwert der Magnetresonanztomographie in der Diagnostik von Schultergelenkerkrankungen.

In a prospective study 43 patients with shoulder pain were examined by sonography and MRI. The findings were controlled by plain radiography, arthrography, and CT arthrography. Joint effusions and humeral head defects were equally identified by MR and sonography. In the diagnosis of labrum lesions, rotator cuff lesions, subacromial spurs, and synovial inflammatory disease sonography was not as accurate as MR. A special MR scoring system improved the diagnosis of an impingement syndrome.