Characteristics, management, and outcomes of patients with hepatocellular carcinoma in Africa: a multicountry observational study from the Africa Liver Cancer Consortium.

BACKGROUND: Hepatocellular carcinoma is a leading cause of cancer-related death in Africa, but there is still no comprehensive description of the current status of its epidemiology in Africa. We therefore initiated an African hepatocellular carcinoma consortium aiming to describe the clinical presentation, management, and outcomes of patients with hepatocellular carcinoma in Africa. METHODS: We did a multicentre, multicountry, retrospective observational cohort study, inviting investigators from the African Network for Gastrointestinal and Liver Diseases to participate in the consortium to develop hepatocellular carcinoma research databases and biospecimen repositories. Participating institutions were from Cameroon, Egypt, Ethiopia, Ghana, Ivory Coast, Nigeria, Sudan, Tanzania, and Uganda. Clinical information-demographic characteristics, cause of disease, liver-related blood tests, tumour characteristics, treatments, last follow-up date, and survival status-for patients diagnosed with hepatocellular carcinoma between Aug 1, 2006, and April 1, 2016, were extracted from medical records by participating investigators. Because patients from Egypt showed differences in characteristics compared with patients from the other countries, we divided patients into two groups for analysis; Egypt versus other African countries. We undertook a multifactorial analysis using the Cox proportional hazards model to identify factors affecting survival (assessed from the time of diagnosis to last known follow-up or death). FINDINGS: We obtained information for 2566 patients at 21 tertiary referral centres (two in Egypt, nine in Nigeria, four in Ghana, and one each in the Ivory Coast, Cameroon, Sudan, Ethiopia, Tanzania, and Uganda). 1251 patients were from Egypt and 1315 were from the other African countries (491 from Ghana, 363 from Nigeria, 277 from Ivory Coast, 59 from Cameroon, 51 from Sudan, 33 from Ethiopia, 21 from Tanzania, and 20 from Uganda). The median age at which hepatocellular carcinoma was diagnosed significantly later in Egypt than the other African countries (58 years [IQR 53-63] vs 46 years [36-58]; p<0·0001). Hepatitis C virus was the leading cause of hepatocellular carcinoma in Egypt (1054 [84%] of 1251 patients), and hepatitis B virus was the leading cause in the other African countries (597 [55%] of 1082 patients). Substantially fewer patients received treatment specifically for hepatocellular carcinoma in the other African countries than in Egypt (43 [3%] of 1315 vs 956 [76%] of 1251; p<0·0001). Among patients with survival information (605 [48%] of 1251 in Egypt and 583 [44%] of 1315 in other African countries), median survival was shorter in the other African countries than in Egypt (2·5 months [95% CI 2·0-3·1] vs 10·9 months [9·6-12·0]; p<0·0001). Factors independently associated with poor survival were: being from an African countries other than Egypt (hazard ratio [HR] 1·59 [95% CI 1·13-2·20]; p=0·01), hepatic encephalopathy (2·81 [1·72-4·42]; p=0·0004), diameter of the largest tumour (1·07 per cm increase [1·04-1·11]; p<0·0001), log α-fetoprotein (1·10 per unit increase [1·02-1·20]; p=0·0188), Eastern Cooperative Oncology Group performance status 3-4 (2·92 [2·13-3·93]; p<0·0001) and no treatment (1·79 [1·44-2·22]; p<0·0001). INTERPRETATION: Characteristics of hepatocellular carcinoma differ between Egypt and other African countries. The proportion of patients receiving specific treatment in other African countries was low and their outcomes were extremely poor. Urgent efforts are needed to develop health policy strategies to decrease the burden of hepatocellular carcinoma in Africa. FUNDING: None.

A SNARE complex mediating fusion of late endosomes defines conserved properties of SNARE structure and function.

Sets of SNARE proteins mediate membrane fusion by assembling into core complexes. Multiple SNAREs are thought to function in different intracellular trafficking steps but it is often unclear which of the SNAREs cooperate in individual fusion reactions. We report that syntaxin 7, syntaxin 8, vti1b and endobrevin/VAMP-8 form a complex that functions in the fusion of late endosomes. Antibodies specific for each protein coprecipitate the complex, inhibit homotypic fusion of late endosomes in vitro and retard delivery of endocytosed epidermal growth factor to lysosomes. The purified proteins form core complexes with biochemical and biophysical properties remarkably similar to the neuronal core complex, although each of the four proteins carries a transmembrane domain and three have independently folded N-terminal domains. Substitution experiments, sequence and structural comparisons revealed that each protein occupies a unique position in the complex, with syntaxin 7 corresponding to syntaxin 1, and vti1b and syntaxin 8 corresponding to the N- and C-terminal domains of SNAP-25, respectively. We conclude that the structure of core complexes and their molecular mechanism in membrane fusion is highly conserved between distant SNAREs.

The R-SNARE endobrevin/VAMP-8 mediates homotypic fusion of early endosomes and late endosomes.

Endobrevin/VAMP-8 is an R-SNARE localized to endosomes, but it is unknown in which intracellular fusion step it operates. Using subcellular fractionation and quantitative immunogold electron microscopy, we found that endobrevin/VAMP-8 is present on all membranes known to communicate with early endosomes, including the plasma membrane, clathrin-coated pits, late endosomes, and membranes of the trans-Golgi network. Affinity-purified antibodies that block the ability of endobrevin/VAMP-8 to form SNARE core complexes potently inhibit homotypic fusion of both early and late endosomes in vitro. Fab fragments were as active as intact immunoglobulin Gs. Recombinant endobrevin/VAMP-8 inhibited both fusion reactions with similar potency. We conclude that endobrevin/VAMP-8 operates as an R-SNARE in the homotypic fusion of early and late endosomes.

Interactions between Spc2p and other components of the endoplasmic reticulum translocation sites of the yeast Saccharomyces cerevisiae.

In yeast, the endoplasmic reticulum membrane proteins Sec11p and Spc3p are essential for the cleavage of signal peptides of nascent polypeptide chains during their passage through translocation sites. Genetic and biochemical experiments demonstrate that Sec11p and Spc3p are tightly associated with two other proteins, Spc1p and Spc2p, whose functions are largely unknown. Using anti-Spc2p antibodies, we show here that this heterotetrameric complex associates with Sbh1p and Sbh2p, the beta-subunits of the Sec61p complex and the Ssh1p complex, respectively. Depletion of Spc2p decreased the enzymatic activity of the SPC in vitro, led to a loss of Spc1p, and led to a down-regulation of the amount of Sec11p and Spc3p in the endoplasmic reticulum. Moreover, the deletion of Spc2p also decreased the expression level of Sbh2p. These data implicate that Spc2p not only enhances the enzymatic activity of the SPC but also facilitates the interactions between different components of the translocation site.

The SNARE Vti1a-beta is localized to small synaptic vesicles and participates in a novel SNARE complex.

Specific soluble N-ethylmaleimide-sensitive factor attachment protein (SNAP) receptor (SNARE) proteins are required for different membrane transport steps. The SNARE Vti1a has been colocalized with Golgi markers and Vti1b with Golgi and the trans-Golgi network or endosomal markers in fibroblast cell lines. Here we study the distribution of Vti1a and Vti1b in brain. Vti1b was found in synaptic vesicles but was not enriched in this organelle. A brain-specific splice variant of Vti1a was identified that had an insertion of seven amino acid residues next to the putative SNARE-interacting helix. This Vti1a-beta was enriched in small synaptic vesicles and clathrin-coated vesicles isolated from nerve terminals. Vti1a-beta also copurified with the synaptic vesicle R-SNARE synaptobrevin during immunoisolation of synaptic vesicles and endosomes. Therefore, both synaptobrevin and Vti1a-beta are integral parts of synaptic vesicles throughout their life cycle. Vti1a-beta was part of a SNARE complex in nerve terminals, which bound N-ethylmaleimide-sensitive factor and alpha-SNAP. This SNARE complex was different from the exocytic SNARE complex because Vti1a-beta was not coimmunoprecipitated with syntaxin 1 or SNAP-25. These data suggest that Vti1a-beta does not function in exocytosis but in a separate SNARE complex in a membrane fusion step during recycling or biogenesis of synaptic vesicles.

Selective interaction of complexin with the neuronal SNARE complex. Determination of the binding regions.

Complexins are evolutionarily conserved proteins that specifically bind to soluble N-ethylmaleimide-sensitive factor attachment protein receptor (SNARE) complexes and thus may regulate SNARE function. Using purified proteins, we have performed a detailed analysis of the structure of complexin and of its interaction with SNARE proteins. NMR spectroscopy revealed that isolated complexins have no tertiary structure but contain an unusual alpha-helical middle domain of approximately 58 amino acids that overlaps with the most highly conserved region of the molecules. Complexins form a stable stoichiometric complex with the central domain of the ternary SNARE complex, whereas no binding was observed to monomeric SNAREs. Using a combination of limited proteolysis, deletion mutagenesis, and NMR spectroscopy, we found that the helical middle region of complexin is responsible for binding to the SNARE complex. Binding was highly sensitive to substitution of syntaxin 1 or synaptobrevin 2 with other SNARE homologs but less sensitive to substitution of SNAP-25. In addition, a stretch of 12 amino acids in the middle of the SNARE motif of syntaxin 1A was able to confer binding activity to the non-binding relative syntaxin 4. Furthermore, disassembly of ternary complexes is not affected by complexins. We conclude that complexins are specific ligands of the neuronal core complex that bind with a central alpha-helical domain, probably to the middle of the surface groove formed by synaptobrevin and syntaxin. Complexins may regulate the function of ternary complexes and control membrane fusion through this interaction.

Exocytotic mechanism studied by truncated and zero layer mutants of the C-terminus of SNAP-25.

The highly conserved SNARE proteins, SNAP-25, syntaxin and synaptobrevin, form a tight ternary complex, which is essential for exocytosis. Crystallization of this complex revealed a four-helix bundle with an unusual hydrophilic layer (zero layer) in its center. In order to evaluate the role of this layer in different kinetic components of secretion, we used the Semliki Forest virus (SFV) system to infect adrenal chromaffin cells with SNAP-25 Q174L, a point mutant in the zero layer. Using combined flash photolysis of caged calcium and membrane capacitance measurements, we investigated its effect on the exocytotic burst and sustained phase of exocytosis with high time resolution. Cells expressing SNAP-25 Q174L displayed a selective reduction in the sustained phase, while the two components of the exocytotic burst remained unaffected. Furthermore, the exocytotic response to the second flash was significantly reduced, indicating a decrease in refilling kinetics. We therefore conclude that the zero layer is critical for the formation of SNARE complexes, but that it plays no role in the dynamic equilibrium between the two exocytosis-competent vesicle pools.

Identification of SNAREs involved in regulated exocytosis in the pancreatic acinar cell.

The molecular basis of exocytotic membrane fusion in the pancreatic acinar cell was investigated using an in vitro assay that measures both zymogen granule-plasma membrane fusion and granule-granule fusion. These two fusion events were differentially sensitive to Ca(2+), suggesting that they are controlled by different Ca(2+)-sensing mechanisms. Botulinum neurotoxin C (BoNT/C) treatment of the plasma membranes caused cleavage of syntaxin 2, the apical isoform of this Q-SNARE, but did not affect syntaxin 4, the basolateral isoform. BoNT/C also cleaved syntaxin 3, the zymogen granule isoform. BoNT/C treatment of plasma membranes abolished granule-plasma membrane fusion, whereas toxin treatment of the granules reduced granule-plasma membrane fusion and abolished granule-granule fusion. Tetanus toxin cleaved granule-associated synaptobrevin 2 but caused only a small reduction in both granule-plasma membrane fusion and granule-granule fusion. Our results indicate that syntaxin 2 is the isoform that mediates fusion between zymogen granules and the apical plasma membrane of the acinar cell. Syntaxin 3 mediates granule-granule fusion, which might be involved in compound exocytosis. In contrast, the major R-SNARE on the zymogen granule remains to be identified.

Mixed and non-cognate SNARE complexes. Characterization of assembly and biophysical properties.

Assembly of soluble N-ethylmaleimide-sensitive fusion attachment protein receptor (SNARE) proteins between two opposing membranes is thought to be the key event that initiates membrane fusion. Many new SNARE proteins have recently been localized to distinct intracellular compartments, supporting the view that sets of specific SNAREs are specialized for distinct trafficking steps. We have now investigated whether other SNAREs can form complexes with components of the synaptic SNARE complex including synaptobrevin/VAMP 2, SNAP-25, and syntaxin 1. When the Q-SNAREs syntaxin 2, 3, and 4, and the R-SNARE endobrevin/VAMP 8 were used in various combinations, heat-resistant complexes were formed. Limited proteolysis revealed that these complexes contained a protease-resistant core similar to that of the synaptic complex. All complexes were disassembled by the ATPase N-ethylmaleimide-sensitive fusion protein and its cofactor alpha-SNAP. Circular dichroism spectroscopy showed that major conformational changes occur during assembly, which are associated with induction of structure from unstructured monomers. Furthermore, no preference for synaptobrevin was observed during the assembly of the synaptic complex when endobrevin/VAMP 8 was present in equal concentrations. We conclude that cognate and non-cognate SNARE complexes are very similar with respect to biophysical properties, assembly, and disassembly, suggesting that specificity of membrane fusion in intracellular membrane traffic is not due to intrinsic specificity of SNARE pairing.

Detection of 100% of the CFTR mutations in 63 CF families from Tyrol.

We identified 100% of the CFTR gene mutations, including three novel mutations, in 126 unrelated cystic fibrosis chromosomes from Tyrol, Austria. The frequency of the major mutation deltaF508 (74.6%) was not significantly different in Tyrolian CF-patients than in patients from Bavaria (71.0%) and Middle- and Northern Germany (71.9%), but was significantly higher than in patients from Styria (58.1%) or Northern Italy (47.6%). Interestingly, the distribution of the next most frequent mutations, R1162X (8.7%) 2183AA-->G, 2789+5G-->A and G542X (2.4% each), was more similar to the distribution of these mutations among CF-patients from Northern Italy than to those from Styria, Bavaria or Middle- and Northern Germany. Nine further mutations occurred once or twice. One of these, the missense mutation M1101K, is rare worldwide but very frequent in the Hutterite brethren, a small founder population which came from Southern Austria to Northern America. Three other different mutations (deltaL453, 1874insT and 4108delT) were present in single Tyrolian families and have not been described before. The identification of 100% of CFTR gene mutations in a particular CF population demonstrates the power of genetic analysis for the diagnosis and counselling of CF families in this restricted geographical area of Austria. Our study provides evidence for a closer genetic relation between CF patients from Tyrol and those from Bavaria or Middle- and Northern Germany as well as Northern Italy, than between CF patients from the two Austrian states Tyrol and Styria.