Posterior parahepatic cyst as an incidental finding--review of 40 cases.

AIM: To describe the characteristic imaging features of the incidental, isolated posterior parahepatic cyst. METHODS: Out of 150 patients previously identified on computed tomography (CT) to have an incidental, isolated posterior parahepatic cyst, 40 patients had lesions that were large enough to be assessed for enhancement on CT and/or magnetic resonance imaging (MRI) and had at least 1 year of imaging follow-up. All available CT, MRI, and 2- [(18)F]-fluoro-2-deoxy-d-glucose (FDG) positron emission tomography (PET) examinations for these 40 patients were reviewed, and the lesions were assessed for size, attenuation, and location relative to the spine and right kidney. RESULTS: For the 40 patients reviewed, all parahepatic lesions were shown to be cysts by absence of identifiable enhancement on CT or MRI. Cysts ranged in size from 3mm to 2.5cm. Hounsfield unit (HU) measurements ranged from 12HU to 83HU. In the transverse plane, all cysts were located lateral to the lateral margin of the right kidney. In the craniocaudal dimension, all cysts were at or above the level of the right kidney, and all were located between the T11-12 and L1-2 vertebral levels. All cysts were stable on follow-up imaging with a mean duration of follow-up of 41 months. CONCLUSION: Isolated, indolent posterior parahepatic cysts have a characteristic appearance and location and demonstrate benign behaviour with stability on follow-up imaging. These cysts should be considered in the differential diagnosis for isolated parahepatic lesions, and the imaging features described here aid in the distinction of these cysts from other entities such as metastatic disease.

The transmembrane domain of the E5 oncoprotein contains functionally discrete helical faces.

The E5 protein of bovine papillomavirus is a 44-amino acid, Golgi-resident, type II transmembrane protein that efficiently transforms immortalized mouse fibroblasts. The transmembrane (TM) domain of E5 is not only critical for biological activity, it also regulates interactions with cellular targets including the platelet derived growth factor receptor (PDGF-R) and the 16-kDa subunit of the vacuolar proton ATPase (V-ATPase). In order to define the specific TM amino acids essential for E5 biological and biochemical activity, we performed scanning alanine mutagenesis on 25 of the 30 potential TM residues and genetically mapped discrete alpha-helical domains which separately regulated the ability of E5 to bind PDGF-R, activate PDGF-R, and to form oligomers. Alanine substitutions at positions 17, 21, and 24 (which lie on the same helical face) greatly inhibited E5 association with the PDGF-R, suggesting that this region comprises the receptor binding site. PDGF-R activation also mapped to a specific but broader domain in E5; mutant proteins with alanines on one helical face (positions 8, 9, 11, 16, 19, 22, and 23) continued to induce PDGF-R tyrosine phosphorylation, whereas mutant proteins with alanines on the opposite helical face (positions 7, 10, 13, 17, 18, 21, 24, and 25) did not, indicating that the latter helical face was critical for mediating receptor transphosphorylation. Interestingly, these "activation-defective" mutants segregated into two classes: 1) those that were unable to form dimers but that could still form higher order oligomers and transform cells, and 2) those that were defective for PDGF-R binding and were transformation-incompetent. These findings suggest that the ability of E5 to dimerize and to bind PDGF-R is important for receptor activation. However, since several transformation-competent E5 mutants were defective for binding and/or activating PDGF-R, it is apparent that E5 must have additional activities to mediate cell transformation. Finally, alanine substitutions also defined two separate helical faces critical for E5/E5 interactions (homodimer formation). Thus, our data identify distinct E5 helical faces that regulate homologous and heterologous intramembrane interactions and define two new classes of biologically active TM mutants.