Multiple intracranial metastases from a gastric gastrointestinal stromal tumor

Intracranial metastases are rare from gastrointestinal stromal tumor (GIST). We report a 60-year-old male with a history of stomach GIST who presented with ataxia 2.5 years after a partial gastrectomy. MRI revealed enhancing masses in the cerebellum and frontal lobe. A suboccipital craniotomy revealed metastatic GIST. With subsequent radiosurgical boost to the resection cavity and frontal lobe lesion, the patient is doing well 15 months postoperatively. To our knowledge, this is one of only a few reports on cerebral GIST metastases from the stomach.

Atypical pituitary adenoma with malignant features

Pituitary carcinoma is characterized by the presence of systemic or central nervous system metastases rather than malignant histological features, making it an anomaly amongst carcinomas. In contrast, aggressive or atypical pituitary adenomas often have a relatively bland histological appearance despite their malignant growth patterns. We now report a case of a 67-years-old male with a giant pituitary tumor with overt pathologic and phenotypic features of malignancy, but the absence of metastases, that evolved from a benign non-functioning gonadotroph macroadenoma treated 10 years earlier. This case represents the first report of a pituitary adenoma with overt malignant histology that does not meet criteria for classification as pituitary carcinoma, helping to complete the pathological spectrum of disease observed with pituitary tumors.

COPII-dependent export of cystic fibrosis transmembrane conductance regulator from the ER uses a di-acidic exit code

Cystic fibrosis (CF) is a childhood hereditary disease in which the most common mutant form of the CF transmembrane conductance regulator (CFTR) ΔF508 fails to exit the endoplasmic reticulum (ER). Export of wild-type CFTR from the ER requires the coat complex II (COPII) machinery, as it is sensitive to Sar1 mutants that disrupt normal coat assembly and disassembly. In contrast, COPII is not used to deliver CFTR to ER-associated degradation. We find that exit of wild-type CFTR from the ER is blocked by mutation of a consensus di-acidic ER exit motif present in the first nucleotide binding domain. Mutation of the code disrupts interaction with the COPII coat selection complex Sec23/Sec24. We propose that the di-acidic exit code plays a key role in linking CFTR to the COPII coat machinery and is the primary defect responsible for CF in ΔF508-expressing patients.

Statin-associated myopathy with normal creatine kinase levels

BACKGROUND

Muscle symptoms in patients who are treated with statins and have normal creatine kinase levels are not well understood.

OBJECTIVE

To report biopsy-confirmed myopathy and normal creatine kinase levels associated with statin use.

DESIGN

Case reports from preliminary analysis of an ongoing clinical trial.

SETTING

Clinical research center in a community hospital.

PATIENTS

Four patients with muscle symptoms that developed during statin therapy and reversed during placebo use.

MEASUREMENTS

1) Patients' ability to identify blinded statin therapy and 2) standard measures of functional capacity and muscle strength.

RESULTS

All four patients repeatedly distinguished blinded statin therapy from placebo. Strength testing confirmed weakness during statin therapy that reversed during placebo use. Muscle biopsies showed evidence of mitochondrial dysfunction, including abnormally increased lipid stores, fibers that did not stain for cytochrome oxidase activity, and ragged red fibers. These findings reversed in the three patients who had repeated biopsy when they were not receiving statins. Creatine kinase levels were normal in all four patients despite the presence of significant myopathy.

CONCLUSION

Some patients who develop muscle symptoms while receiving statin therapy have demonstrable weakness and histopathologic findings of myopathy despite normal serum creatine kinase levels.

Non-conventional trafficking of the cystic fibrosis transmembrane conductance regulator through the early secretory pathway

The mechanism(s) of cystic fibrosis transmembrane conductance regulator (CFTR) trafficking from the endoplasmic reticulum (ER) through the Golgi apparatus, the step impaired in individuals afflicted with the prevalent CFTR-DeltaF508 mutation leading to cystic fibrosis, is largely unknown. Recent morphological observations suggested that CFTR is largely absent from the Golgi in situ (Bannykh, S. I., Bannykh, G. I., Fish, K. N., Moyer, B. D., Riordan, J. R., and Balch, W. E. (2000) Traffic 1, 852-870), raising the possibility of a novel trafficking pathway through the early secretory pathway. We now report that export of CFTR from the ER is regulated by the conventional coat protein complex II (COPII) in all cell types tested. Remarkably, in a cell type-specific manner, processing of CFTR from the core-glycosylated (band B) ER form to the complex-glycosylated (band C) isoform followed a non-conventional pathway that was insensitive to dominant negative Arf1, Rab1a/Rab2 GTPases, or the SNAp REceptor (SNARE) component syntaxin 5, all of which block the conventional trafficking pathway from the ER to the Golgi. Moreover, CFTR transport through the non-conventional pathway was potently blocked by overexpression of the late endosomal target-SNARE syntaxin 13, suggesting that recycling through a late Golgi/endosomal system was a prerequisite for CFTR maturation. We conclude that CFTR transport in the early secretory pathway can involve a novel pathway between the ER and late Golgi/endosomal compartments that may influence developmental expression of CFTR on the cell surface in polarized epithelial cells.

The Sar1 GTPase coordinates biosynthetic cargo selection with endoplasmic reticulum export site assembly

Cargo selection and export from the endoplasmic reticulum is mediated by the COPII coat machinery that includes the small GTPase Sar1 and the Sec23/24 and Sec13/31 complexes. We have analyzed the sequential events regulated by purified Sar1 and COPII coat complexes during synchronized export of cargo from the ER in vitro. We find that activation of Sar1 alone, in the absence of other cytosolic components, leads to the formation of ER-derived tubular domains that resemble ER transitional elements that initiate cargo selection. These Sar1-generated tubular domains were shown to be transient, functional intermediates in ER to Golgi transport in vitro. By following cargo export in live cells, we show that ER export in vivo is also characterized by the formation of dynamic tubular structures. Our results demonstrate an unanticipated and novel role for Sar1 in linking cargo selection with ER morphogenesis through the generation of transitional tubular ER export sites.

Fetal obstructive uropathy: patterns of renal pathology

Fetal obstructive uropathy (FOU) is characterized by obstruction of the urethra, renal anomalies, ureterovesical dilatation, oligohydramnios, cryptorchidism, and abdominal muscle wall changes. The main objective of the present study was to better understand the relationship between FOU and renal pathology using a series of 15 male autopsy cases. A total of 11 cases with patent anus and 4 with imperforate anus were analyzed. Of the first group, most cases showed obstruction at the level of prostatic urethra. Seven cases showed obstruction at the level of the prostatic urethra and histologic study revealed scarring and partial or complete absence of the prostate, while in the remaining four cases the prostate was present. Of the cases with imperforate anus, two showed obstruction at the level of prostatic urethra, one showed posterior urethral valves, and one was obstructed at the proximal urethra. In all cases the kidneys showed mixed (dysplastic and cystic) changes with no significant differences between the two groups. An inverse correlation was observed between degree of renal dysplasia and gestational age, whereas the opposite was true for cystic changes. Distal and collecting tubules were more intensely immunoreactive to the anti-cytokeratin antibody when compared to proximal tubules. Moreover, anti-cytokeratin immunoreactivity was more prominent in tubules displaying cystic dilatation. DNA fragmentation analysis of renal tissue revealed a higher apoptosis of mesenchymal and tubular cells in the FOU cases, compared to gestational aged-matched controls. These results suggest that renal anomalies in FOU might be related to the gestational age at which the injury occurred and to the duration of the obstruction.

A di-acidic (DXE) code directs concentration of cargo during export from the endoplasmic reticulum

Efficient export of vesicular stomatitis virus glycoprotein (VSV-G), a type I transmembrane protein, from the endoplasmic reticulum requires a di-acidic code (DXE) located in the cytosolic carboxyl-terminal tail (Nishimura, N., and Balch, W. E. (1997) Science 277, 556-558). Mutation of the DXE code by mutation to AXA did not prevent VSV-G recruitment to pre-budding complexes formed in the presence of the activated form of the Sar1 and the Sec23/24 complex, components of the COPII budding machinery. However, the signal was required at a subsequent concentration step preceding vesicle fission. By using green fluorescence protein-tagged VSV-G to image movement in a single cell, we found that VSV-G lacking the DXE code fails to be concentrated into COPII vesicles. As a result, the normal 5-10-fold increase in the steady-state concentration of VSV-G in downstream pre-Golgi intermediates and Golgi compartments was lost. These results demonstrate for the first time that inactivation of the DXE signal uncouples early cargo selection steps from concentration into COPII vesicles. We propose that two sequential steps are required for efficient export from the endoplasmic reticulum.

Neurotransmitter release from semi-intact synaptosomes

We have developed a secretion assay composed of semi-intact synaptosomes from which transmitter release is optimally evoked by micromolar Ca2+ in the presence of cytosol. Transmitter release from this preparation reconstitutes known characteristics of regulated exocytosis and is accompanied by a marked decrease in synaptic vesicles. The assay is useful in characterizing the components known to be involved in transmitter release, and should also facilitate the identification of additional factors that are important for this process.

Differential regulation of exocytosis by calcium and CAPS in semi-intact synaptosomes

Using a novel approach to measure exocytosis in vitro from semi-intact synaptosomes, we establish that the Ca2+-dependent release of glutamate requires cytosolic factors for mobilization from the reserve pool. The cytosolic activity for glutamate release was not satisfied by CAPS, a soluble component required for norepinephrine (NE) release. Moreover, the CAPS-independent glutamate release from synaptic vesicles (SVs) was 200-fold less sensitive to Ca2+ than that required for dense core vesicles (DCVs). The differential regulation of exocytosis by CAPS, Ca2+, and potential novel cytosolic factor(s) suggests that the docking and fusion machinery controlling DCVs has diverged from that regulating glutamate-containing SVs.

Cargo selection by the COPII budding machinery during export from the ER

Cargo is selectively exported from the ER in COPII vesicles. To analyze the role of COPII in selective transport from the ER, we have purified components of the mammalian COPII complex from rat liver cytosol and then analyzed their role in cargo selection and ER export. The purified mammalian Sec23-24 complex is composed of an 85-kD (Sec23) protein and a 120-kD (Sec24) protein. Although the Sec23-24 complex or the monomeric Sec23 subunit were found to be the minimal cytosolic components recruited to membranes after the activation of Sar1, the addition of the mammalian Sec13-31 complex is required to complete budding. To define possible protein interactions between cargo and coat components, we recruited either glutathione-S-transferase (GST)-tagged Sar1 or GST- Sec23 to ER microsomes. Subsequently, we solubilized and reisolated the tagged subunits using glutathione-Sepharose beads to probe for interactions with cargo. We find that activated Sar1 in combination with either Sec23 or the Sec23-24 complex is necessary and sufficient to recover with high efficiency the type 1 transmembrane cargo protein vesicular stomatitis virus glycoprotein in a detergent-soluble prebudding protein complex that excludes ER resident proteins. Supplementing these minimal cargo recruitment conditions with the mammalian Sec13-31 complex leads to export of the selected cargo into COPII vesicles. The ability of cargo to interact with a partial COPII coat demonstrates that these proteins initiate cargo sorting on the ER membrane before budding and establishes the role of GTPase-dependent coat recruitment in cargo selection.

Role of vesicle-associated syntaxin 5 in the assembly of pre-Golgi intermediates

Syntaxins are thought to function during vesicular transport as receptors on the target membrane and to contribute to the specificity of membrane docking and fusion by interacting with vesicle-associated receptors. Here, syntaxin 5 (Syn5) was shown to be an integral component of endoplasmic reticulum-derived transport vesicles. This pool, but not the target, Golgi-associated Syn5 pool, was essential for the assembly of vesicular-tubular pre-Golgi intermediates and the delivery of cargo to the Golgi. The requirement for vesicle-associated Syn5 in transport suggests a reevaluation of the basis for operation of the early secretory pathway.

Atherosclerosis-prone branch regions in human aorta: microarchitecture and cell composition of intima

The microarchitecture and cell composition of intima were studied at the macroscopically unaffected branch regions of human thoracic aorta using en face preparations, scanning and transmission electron microscopy, and immunohistochemistry. The endothelial lining showed a heterogeneous pattern and altered morphology including the areas of deendothelialization covered with platelets and dilated intercellular clefts. Leukocyte adhesion, accumulation of subendothelial macrophages and lymphocytes were characteristic of proximal and lateral zones, while the flow divider showed no significant accumulation of blood cells. Smooth muscle cells (SMCs) on the flow divider were elongated, in a contractile state, contacted side-by-side and did not contain lipid inclusions. In the lateral and proximal zones, intima appeared to be a network of stellate SMCs which were in contact through their processes. Most of the SMCs were in a synthetic state and many of them contained small lipid droplets. The number of procollagen I positive cells and the volume of extracellular components were most significant at the lateral zones rather than at the flow divider. We did not observe any difference in the rate of proliferation. Our results suggest that the intimal layer at the lateral and proximal zones has some distinct structural peculiarities, which provoke the development of initial atherosclerotic lesions at these sites. Such an intimal structure is probably caused by different flow patterns at these zone. However, only the totality of different morphological features exhibited in the area of altered vascular wall shear stress may be considered as a prerequisite for atherosclerotic lesions.

Regulation of constitutive exocytic transport by membrane receptors. A biochemical and morphometric study

Biochemical and morphometric approaches were combined to examine whether constitutive secretory transport might be controlled by plasma membrane receptors, as this possibility would have significant physiological implications. Indeed, IgE receptor stimulation in rat basophilic leukemia cells potently increased the rate of transport of soluble pulse-labeled 35S-sulfated glycosaminoglycans from distal Golgi compartments to the cell surface. This effect was largely protein kinase C (PKC)-dependent. Direct activation of PKC also stimulated constitutive transport of glycosaminoglycans, as indicated by the use of agonistic and antagonistic PKC ligands. PKC ligands also had potent, but different, effects on the exocytic transport from distal Golgi compartments to the plasma membrane of a membrane-bound protein (vesicular stomatitis virus glycoprotein), which was slightly stimulated by activators and profoundly suppressed by inhibitors of PKC. Morphological analysis showed impressive changes of the organelles of the secretory pathway in response to IgE receptor stimulation and to direct PKC activation (enhanced number of buds and vesicles originating from the endoplasmic reticulum and Golgi and increase in surface and volume of Golgi compartments), suggestive of an overall activation of exocytic movements. These results show that rapid and large changes in constitutive transport fluxes and in the morphology of the exocytic apparatus can be induced by membrane receptors (as well as by direct PKC stimulation).

The morphology of valves and valve-like structures in the canine and feline thoracic duct

The microanatomy and ultrastructure of the feline and canine thoracic duct and afferent lymphatics were studied by scanning and transmission electron microscopy. We found that the lymphatic vessels were always terminated by ostial valves of two shapes, crescent- and navicular-like, in a ratio of 4:1. Specific regulatory structures along the free edges of the valves, including marginal thickenings and buttresses, are described. The tissue and cellular organization of the valve endothelium showed distinct peculiarities, particularly in the orientation and shape of the cells and their microrelief. We found that valvular endothelial cells, especially ¿tip cells¿, which are situated in unfavourable lymphodynamic conditions, were characterized by an increased volume density of intermediate (probably vimentin-based) filaments, suggesting an accommodative mechanism involving such filaments.

Regeneration of the endothelium in the canine and feline thoracic duct

Recent improvements in microsurgical techniques on lymphatic vessels facilitated the treatment of lymphoedema. But it is becoming clear that a successful treatment of lymphatic disease has to be based on knowledge of ongoing processes. Particularly, one of the important and unclear issue is cellular mechanisms of lymphatic regeneration. The regeneration of endothelial and the smooth muscle cells of the thoracic duct has been experimentally tested in vivo. The canine and feline thoracic duct was cryo-injured using 3 mm-based copper rod. Damaged endothelial cells remained attached to the substrate and lost unthrombogenecy within 48 hr. Adjacent EC restored the defect within 3 days by migration and proliferation. We observed that on the first day, the endothelial monolayer included some elongated multinuclear cells with blind silver lines whereas, on the third day, they were replaced by a population of smaller ECs with numerous mitoses. Organization of the monolayer was restituted within 7 days. The newly formed endothelium was similar to regenerating endothelium of arteries. In general, the clot that appeared at the zone of injury on the second day was dissolved by the third day. Occasionally, the dense polymorphic clot adhered to the wall and caused a delay in reendothelisation. Complete restitution of the tunica media which involved migration and proliferation mechanisms accompanied the endothelium regeneration.

Export of protein from the endoplasmic reticulum is regulated by a diacylglycerol/phorbol ester binding protein

The export of vesicular stomatitis virus glycoprotein (VSV-G) from the endoplasmic reticulum (ER) involves sorting and concentration, and has been proposed to require the function of heterotrimeric G proteins. To begin to identify the basic elements of a potential signaling pathway involved in vesicle assembly, we have examined whether protein kinase C (PKC) is required for ER to Golgi transport. Calphostin C, a specific inhibitor of the highly conserved cysteine-rich C6H2 motif present in the regulatory domain of PKC was found to be a potent inhibitor of export of VSV-G and vesicle budding from the ER in vivo and in vitro (IC50 approximately 60 nM). In contrast, the diacylglycerol analog phorbol 12-myristate 13-acetate, which activates PKC, enhanced the migration of VSV-G from the ER to pre-Golgi intermediates. Neither reagent had detectable effects on the oligomerization of VSV-G prior to export nor perturbed transport of protein between compartments of the Golgi stack. In contrast to the striking effects of calphostin C, reagents that inhibit the function of the catalytic domain of PKC (including the general kinase inhibitor staurosporine, as well as the more specific inhibitors H-7, H-8, pseudosubstrate inhibitor, or chelerythrine) did not inhibit export from the ER. Export was also insensitive to down-regulation of various PKC isoforms. These results suggest that a novel protein containing the conserved C6H2 motif may serve as a potential link in a signaling pathway regulating vesicle budding from the ER.

Stimulation of endogenous ADP-ribosylation by brefeldin A

Brefeldin A (BFA) is a fungal metabolite that exerts profound and generally inhibitory actions on membrane transport. At least some of the BFA effects are due to inhibition of the GDP-GTP exchange on the ADP-ribosylation factor (ARF) catalyzed by membrane protein(s). ARF activation is likely to be a key event in the association of non-clathrin coat components, including ARF itself, onto transport organelles. ARF, in addition to participating in membrane transport, is known to function as a cofactor in the enzymatic activity of cholera toxin, a bacterial ADP-ribosyltransferase. In this study we have examined whether BFA, in addition to inhibiting membrane transport, might affect endogenous ADP-ribosylation in eukaryotic cells. Two cytosolic proteins of 38 and 50 kDa were enzymatically ADP-ribosylated in the presence of BFA in cellular extracts. The 38-kDa substrate was tentatively identified as the glycolytic enzyme glyceraldehyde-3-phosphate dehydrogenase. The BFA-binding components mediating inhibition of membrane traffic and stimulation of ADP-ribosylation appear to have the same ligand specificity. These data demonstrate the existence of a BFA-sensitive mono(ADP-ribosyl)transferase that may play a role in membrane movements.

The tunica media of the thoracic duct contains a heterogeneous population of muscle cells

The three-dimensional cyto-architecture and ultrastructure of cells composing the different regions of the tunica media of canine and feline thoracic ducts (ThD) were investigated by scanning and transmission electron microscopy. The tunica media of the intervalvular regions consists of 2-4 layers of circulatory oriented ribbon-like smooth muscle cells (SMCs) of the contractile phenotype. Spot-like membrane contacts similar to gap junctions were observed between SMCs. In the parietal part of the valve's sinus (PPVS), modified SMCs containing large lipid droplets were found. Occasionally, in the upper thoracic part of the ThD in the PPVS, we observed cardiomyocyte-like cells (CMLCs) arranged as circularly oriented bundles. Frequent interdigitation contacts were formed between SMCs and CMLCs, suggesting a possible involvement of the latter cell type in pacemakers activity in the ThD.