[Trigeminal neuralgia with the offending artery transfixing the trigeminal nerve: a case report]

We report a rare case of a patient manifesting trigeminal neuralgia with the offending artery transfixing the trigeminal nerve. A 67-year-old woman was admitted with typical episodes of trigeminal neuralgia on the right side. Magnetic resonance angiograms revealed the right superior cerebellar artery (SCA) compressing the nerve. Through a retromastoid suboccipital craniotomy on the right side, the right SCA was found to compress the root entry zone (REZ) and then penetrate the portio major of the trigeminal nerve. The nerve was dissected parallel to the axis, 7 mm distally from the transfixing point to facilitate transposition of the SCA. In addition to anchoring the distal portion of the SCA to the tentrium, a prosthesis was interposed between the proximal portion and the pons to secure the decompression. The pain was completely relieved immediately after operation with no neurological deficit. Procedures, such as the longitudinal rhizotomy employed in this case, must be carried out for microcompression, in response to individual anatomical variations in neurovascular structures.

Effects of ebselen on cerebral ischemia and reperfusion evaluated by microdialysis

Since ebselen is known to have glutathione peroxidase-like activity and inhibitory effects on lipoxygenase and cyclo-oxygenase, we investigated its protective effects against cerebral ischemia in the rat using microdialysis. Ebselen was given through a gastric tube 30 min before occlusion in the experimental groups. Ischemia was induced using 4-vessel occlusion either transiently (20-min occlusion of the arteries followed by reperfusion), or over a prolonged period (120-min occlusion). Extracellular lactate, pyruvate and purine catabolites were sampled using microdialysis and measured by high performance liquid chromatography. During ischemia, the level of lactate, adenosine, inosine and hypoxanthine in the control group increased markedly. The lactate: pyruvate ratio increased during ischemia and decreased after reperfusion. Although the level of lactate and adenosine decreased immediately after reperfusion, those of inosine and hypoxanthine showed delayed decrease. Ebselen reduced the maximum values of lactate and purine catabolites significantly and markedly in transient ischemia. Although it reduced the values significantly in prolonged ischemia, the decrements were less marked than those in transient ischemia. Based on these results we consider ebselen to protect against ischemic metabolic changes and to accelerate the recovery during reperfusion.

Isolation and cloning of rat poly(ADP-ribose) glycohydrolase: presence of a potential nuclear export signal conserved in mammalian orthologs

Poly(ADP-ribose) glycohydrolase (Parg) is the main enzyme of poly(ADP-ribose) degradation. To understand its structure-and-function relationship, we purified Parg from rat testis 9,740-fold using an improved affinity column; the purified product was a 60 kDa protein. Based on the determined sequences of three peptide fragments, degenerated primers were synthesized and a Parg cDNA comprising 3,974 nucleotides, encoding a 109 kDa protein, was isolated. The 60 kDa Parg purified from rat testes corresponded to the C-terminal half of the 109 kDa deduced peptide. When recombinant rat Parg was expressed as a glutathione S-transferase fusion protein in Escherichia coli, Parg activity was observed for the full-length and C-terminal half proteins but not in for the N-terminal half protein. Taken together, these data indicate that the catalytic domain of Parg is located in the C-terminal half. Further, we newly identified the presence of a potential nuclear export signal in the N-terminal half in addition to the previously reported nuclear localization signals in rat and other mammalian Pargs. Northern blot analysis showed the ubiquitous expression of a single 4.0 kb Parg mRNA in various rat tissues. The findings suggest that the 60 kDa Parg is produced by post-transcriptional processing.

Role of Syk in Fc gamma receptor-coupled tyrosine phosphorylation of Cbl in a manner susceptible to inhibition by protein kinase C

Fcgamma receptors (FcgammaR) of guinea pig neutrophils were ligated and anti-Cbl immunoprecipitates prepared therefrom were assayed for the associated protein tyrosine kinase activity, which increased upon ligation of FcgammaR. The increases were overcome upon activation of cellular protein kinase C by simultaneous addition of phorbol 12-myristate 13-acetate (PMA) to the ligated cells. Syk proved to be the most important tyrosine kinase bound to Cbl that served as the major substrate; essentially no tyrosine phosphorylation occurred in the anti-Cbl immunoprecipitates prepared from the cell lysate that had been depleted of Syk by prior immunoprecipitation with anti-Syk antibodies. Exposure of the (32)P-labeled cells to PMA resulted in phosphorylation of cellular Cbl on serine residues. Thus, protein kinase C-induced serine phosphorylation of Cbl suppressed its tyrosine phosphorylation by Syk as a result of tyrosine kinase inhibition by unknown mechanisms, leading to inhibition of Cbl-mediated signaling such as phosphatidylinositol 3-kinase activation.

[Microsurgical results of paraclinoid aneurysms of the internal carotid artery: microsurgery versus intravascular surgery]

Since paraclinoid aneurysms exhibit considerable variations in the surrounding skull base structures, some skill and experience are considered essential for their microsurgical treatment. On the other hand, intravascular coil embolization would be free from these extravascular factors. Fifty-two aneurysms in 48 patients were treated microsurgically. They were divided into an early series treated before 1995 and a late series treated after 1996. Three aneurysms in 3 patients were treated by intravascular surgery. Preoperative neuroimages, topographic anatomy and surgical results were compared retrospectively. The results in the microsurgical late series were better than those in the early series. While 89% of the patients exhibited excellent results with two patients left with partial visual field defect (7%) and one death (3%) in the early series, the rates in the late series were 95%, 5% and 0%, respectively. Complications and failure in neck clipping were considered to be due to such topography as, 1) C3 aneurysms extending into the anterior clinoid process, 2) multiple aneurysms, 3) ophthalmic artery originating near the dome, 4) atheroma or calcification at the neck, 5) marked medical shift of C2 segment, and 6) tight adhesion of the dural ring to the dome. Coil embolization was successful in two aneurysms, while it was given up in one. We currently propose that intravascular surgery is indicated for cases 1), 4), 5) and 6), and microsurgery would be more advantageous for cases where the neck is broad and where the topography concerning aneurysmal multiplicity or the branching site of the ophthalmic artery is not fully understood by preoperative imaging.

[Simulation study on parent artery occlusion therapy for basilar head giant aneurysms: hemodynamic efficacy of additional bypass on enhancing aneurysmal thrombosis]

Parent artery occlusion therapy has been used as an alternative for directly untreatable basilar head giant aneurysms. However, some aneurysms still require additional technique to further induce intraaneurysmal stagnation and thrombosis. Using a hydraulic model, half-life of the dye in the model aneurysm was measured as an index of the intraaneurysmal stagnation. The ratio of diameters (D1, D2) of the two posterior communicating arteries (PCom) is defined as diameter ratio (DR) (D1/D2, D1 < D2). Occlusion therapy was simulated in 4 different sites. The most distal site was at the distal BA (Type A) and the most proximal site at the bilateral VA (Type D). The additional technique investigated was bypass placement to the P2 segment of the posterior cerebral artery (PCA) on the smaller PCom side. The half-life was 2.5 +/- 0.2 (mean +/- 2SD) sec before occlusion. Occlusion therapy significantly increased the half-life depending on the occlusion site and DR values with the maximum values of infinite in Type A and 25 sec in Type D. Placement of the bypass decreased the tangential flow volume to the aneurysmal neck, and increased the time markedly in Types A and B, considerably in Type C and slightly in Type D. Parent artery occlusion therapy has been considered less beneficial for patients with a diameter ratio of less than 0.70 since aneurysmal stagnation depends on the diameter ratio. Bypass placement additional to the occlusion therapy is very useful in enhancing the aneurysmal stagnation, which would make those patients indicated for the therapy.

The posterior temporal artery as the recipient in superficial temporal artery to posterior cerebral artery bypass. Technical note

BACKGROUND

While superficial temporal artery (STA) to superior cerebellar artery (SCA) or STA to posterior cerebral artery (PCA) anastomosis has been used for rostral brain stem ischemia, it is reported not infrequently to be associated with serious complications. Although the inferior temporal artery has been proposed as a possible recipient artery for the STA, its advantage is not yet widely recognized.

CASE REPORT

A 42-year-old man presented with repeated loss of vision in the left visual field. Angiography disclosed occlusion in the proximal portion of the P2 segment of the right PCA. The second case was a 68-year-old man experiencing swallowing disturbance; the bilateral vertebral arteries were markedly stenotic. Since hemodynamic insufficiency was considered to be responsible for the patients' symptoms, STA-PCA anastomosis was performed using the posterior temporal artery (PTA) as the recipient. The postoperative courses were uneventful with good patency of the bypass.

TECHNIQUE

Through a horizontally extended temporal craniotomy with the base of the temporal bone sufficiently drilled away, the inferior aspect of the temporal lobe was searched for a recipient artery for the STA. The anastomosis was performed with less difficulty and at a shallower level, by 20 mm in one case and by 10 mm in the other, than had we anastomosed it to the P2 segment of the PCA.

CONCLUSION

Anastomosis of the STA to the PTA is less complicated than anastomosis of the STA to the main branch of the PCA for the treatment of rostral brain stem ischemia.

A novel negative regulator molecule, Cho-1, is involved in the cytotoxicity by human natural killer cells but not in cytotoxic T lymphocytes

We previously reported the cytotoxic negative regulatory molecule, Cho-1, that was expressed on the cell surface of rat fetal fibroblast cells in the cytotoxicity by natural killer (NK) cells. This molecule was IFN-gamma-inducible, but appeared to be different from MHC class I. It was expressed on NK-resistant cells but not on NK-sensitive murine target cells such as YAC-1. In this paper, first we determined whether Cho-1 could also act as the negative regulatory molecule in a human NK-resistant HEPM line. Our data strongly suggested that Cho-1 could act as such a negative regulatory molecule in human NK cytotoxicity. The immunoprecipitates made with HEPM cell lysate and anti-MHC class I monoclonal antibody (mAb) did not react against anti-Cho-1 mAb, indicating that Cho-I was different from MHC class I. Second, an assessment was made as to whether or not this molecule is involved in the cytotoxicity of CD8 (+) cytotoxic T lymphocytes (CTL) against human autologous tumor cells. The data indicated that although this cell surface molecule was expressed on certain tumor lines, it was not involved in the cytotoxic mechanism of CTL. Thus, Cho-1 appeared to be the novel regulatory molecule in the NK cytotoxic mechanism.

Molecular remodeling of complement regulatory proteins for xenotransplantation

In pig-to-human discordant xenotransplantation, human complement is a major barrier against long survival of xenografts. Human complement regulatory proteins expressed on xenografts have been adapted as safeguards against host-induced hyperacute rejection of xenografts. For successful xenotransplantation, there have been many attempts to generate molecules with potent human complement regulatory activity but without activities related to harmful functions such as infection, immunosuppression and signal transduction devastating cellular homeostasis. Here, we summarize the strategy by which molecules for xenotransplantation should be designed and propose a GPI-anchored form of monomeric human C4bp as a candidate for efficient protection of swine xenografts from human complement attack.

Simulation of therapeutic parent artery occlusion for basilar head aneurysms. Hemodynamic effect of occlusion sites and diameters of collateral arteries

We simulated parent artery occlusion therapy for basilar head aneurysms to elucidate the hemodynamic changes induced by different occlusion sites and diameters of the posterior communicating arteries (PCom) as collateral pathways. A vascular model of the vertebrobasilar system with a basilar head aneurysm was constructed. Four types of occlusion were simulated: Basilar artery occlusion distal to (Type A), between (Type B) and proximal to (Type C) the superior cerebellar arteries, and bilateral vertebral artery occlusion (Type D). Glycerol solution was perfused into the model, and the half-life of the dye injected into the aneurysm was calculated and regarded as an index of stagnant flow in the aneurysm. The half-life was increased significantly and nonlinearly after parent artery occlusion, depending on the occlusion site and the ratio of two PCom diameters (diameter ratio). Intra-aneurysmal stagnation developed markedly in Type A and Type B in the diameter ratio higher than 0.70 and considerably in Type C in the ratio higher than 0.80. Additional P1 occlusion of the posterior cerebral artery enhanced the stagnation in Type A and B. Since the results are consistent with the published clinical data, the simulation study will be useful for speculating the efficacy of the therapeutic occlusion.

Lipopolysaccharide stimulates HepG2 human hepatoma cells in the presence of lipopolysaccharide-binding protein via CD14

Lipopolysaccharide (LPS)-binding protein (LBP), an opsonin for activation of macrophages by bacterial LPS, is synthesized in hepatocytes and is known to be an acute phase protein. Recently, cytokine-induced production of LBP was reported to increase 10-fold in hepatocytes isolated from LPS-treated rats, compared with those from normal rats. However, the mechanism by which the LPS treatment enhances the effect of cytokines remains to be clarified. In the present study, we examined whether LPS alone or an LPS/LBP complex directly stimulates the hepatocytes, leading to acceleration of the cytokine-induced LBP production. HepG2 cells (a human hepatoma cell line) were shown to express CD14, a glycosylphosphatidylinositol-anchored LPS receptor, by both RT/PCR and flow cytometric analyses. An LPS/LBP complex was an effective stimulator for LBP and CD14 production in HepG2 cells, but stimulation of the cells with either LPS or LBP alone did not significantly accelerate the production of these proteins. The findings were confirmed by semiquantitative RT/PCR analysis of mRNA levels of LBP and CD14 in HepG2 cells after stimulation with LPS alone and an LPS/LBP complex. In addition, two monoclonal antibodies (mAbs) to CD14 (3C10 and MEM-18) inhibited LPS/LBP-induced cellular responses of HepG2 cells. Furthermore, prestimulation of HepG2 cells with LPS/LBP augmented cytokine-induced production and gene expression of LBP and CD14. All these findings suggest that an LPS/LBP complex, but not free LPS, stimulates HepG2 cells via CD14 leading to increased basal and cytokine-induced LBP and CD14 production.

Effect of mutations at the residues R25, D27, P69, and N70 of B95a-MCP on receptor activities for the measles viruses Nagahata wild-type strain and CAM vaccine strain

Human membrane cofactor protein (MCP, CD46) is a regulator of complement activation and also serves as a receptor for measles virus (MV). We recently isolated an MCP homolog from B95a, an Epstein-Barr virus-transformed marmoset B-lymphoblastoid cell line, which is 76% identical to human-MCP. B95a-MCP acts as an MV receptor for CAM, a vaccine strain of MV, but not for Nagahata, wild-type MV strain. The four residues in human-MCP (Asp27, Lys29, Arg69, and Asp70) are reportedly MV binding sites, and these are changed in B95a-MCP (Glu27, Asp29, Pro69, and Asn70). In the present study, we constructed B95a-MCP mutants by replacing the four residues with those in human-MCP, and tested whether the Chinese hamster ovary (CHO) transfectants expressing B95a-MCP mutants become susceptible to the Nagahata strain. The CHO transfectants expressing B95a-MCP mutants formed syncytium with the CAM strain but not with the Nagahata strain. The binding of the hemagglutinin (H) of MV with B95a-MCP mutants was observed with the CAM strain but not with the Nagahata strain. These results suggest that the failure of B95a-MCP as the MV receptor for the Nagahata strain is not due simply to the natural mutations at these four residues. The critical residues for MV binding in an MCP molecule seem to differ depending upon the structure of the MV H protein.

Spontaneous dissecting pseudoaneurysm of the extracranial internal carotid artery: endovascular treatment with a palmaz stent

SUMMARY

This case illustrates the usefulness of an endovascular stent to treat a pseudoaneurysm of the cervical internal carotid artery. A 46-year-old male patient presented with a spontaneous dissection of the cervical internal carotid artery. After failing conservative therapy, he was treated by endovascular placement of a Palmaz stent at level of the pseudoaneurysm and dissection. Immediate obliteration of pseudoaneurysm was achieved, and patency of the internal carotid artery was maintained. The patient sustained no neurological complications and the stenosis of treated carotid artery did not occur during the 6-month follow-up period. For internal carotid artery dissection, stent placement seems to be a reasonable therapeutic alternative to direct surgery.

A wild-type Japanese measles virus strain inducing predominant early down-regulation of CD46

Down-regulation of CD46 secondary to stimulation with measles virus (MV) was investigated using CD46-positive cell lines and Japanese wild-type MV strains. The cells used were simian cell lines B95a and Vero in which MV strains have been adapted to be amplified, and Chinese hamster ovary (CHO) cell transfectants expressing human CD46 with (CHO(tail+)) or without (CHO(tail-)) the cytoplasmic tail. Of four Vero-adapted and three B95a-adapted MV strains, one Vero-adapted strain named Khono (KO), down-regulated CD46 within 60 min (early down-regulation) in all cell lines examined except Vero. No strains other than Toyoshima (TY), which induced early down-regulation only in CHO(tail+) cells, induced early down-regulation of CD46 in any combination. On the other hand, conventional down-regulation of CD46 was observed 24 h post-MV inoculation (late down-regulation) when cell lines used were adapted to MV strains. Thus, we concluded that there are two modes of CD46 down-regulation by MV and the unique strain KO markedly induces early down-regulation. Also, the CD46 homologue of B95a, which fails to act as a MV receptor, is down-regulated concomitantly with MV replication (>24 h) in cells principally by competent virus strains.

Asymptomatic familial cerebral aneurysms

PURPOSE

We evaluated the prevalence and features of cerebral aneurysms in the family members of people with asymptomatic aneurysms among 8680 participants undergoing magnetic resonance angiography.

METHODS

Of the 8680 participants, 380 had family histories of aneurysms and 8300 did not. The prevalence and features of asymptomatic aneurysms were compared in these two subgroups. In addition, the prevalence in all living first- or second-degree relatives was evaluated in 20 families.

RESULTS

The prevalence of asymptomatic aneurysms was 7.0% (606 of 8680 participants) overall and 10.5% (40 of 380 participants) and 6.8% (566 of 8300 participants) in the subgroups with and without family histories of aneurysms, respectively. The prevalence in the female participants with family histories of aneurysms (12.3%, 28 of 228 participants) was higher than that in the male participants with family histories of aneurysms (7.9%, 12 of 152 participants) (P < 0.0001). Compared with the entire group, this subgroup more commonly showed aneurysms situated at the junction of the internal carotid and posterior communicating arteries (P < 0.0005) and at the middle cerebral artery (P < 0.0001). The prevalence of aneurysms in 115 members of the 20 families was 33.9%. Although the members of 14 families with aneurysmal subarachnoid hemorrhage showed higher prevalence of ruptured and asymptomatic aneurysms (42.1%) than did the members of 6 families with only asymptomatic aneurysms (17.9%), the former had very low prevalence of asymptomatic aneurysms.

CONCLUSION

The prevalence of aneurysms is significantly elevated in family members of people with asymptomatic aneurysms. It is suggested that familial asymptomatic aneurysms are more likely to rupture in families having members with aneurysmal subarachnoid hemorrhage than in those without.

Surgical treatment of distal cervical internal carotid artery aneurysm

We report on a 55-year-old male with an internal carotid artery aneurysm at the level of the second cervical vertebra. Since ant-coagulation therapy failed to prevent the ischemic attack, aneurysmectomy with arterial reconstruction was performed. Vertical mandibular osteotomy allowed a wide working space in deep operative field. This technique is considered to be useful in surgery for aneurysms of the extracranial distal internal carotid artery.

Magnetic resonance angiographic source images for depicting topography and surgical planning for middle cerebral artery aneurysms: technique application

PURPOSE

To evaluate the usefulness of magnetic resonance (MR) angiographic source images for determining the feasibility of M1 segment control via the distal approach in pterional craniotomy for middle cerebral artery (MCA) aneurysms.

METHODS

MR angiographic source and conventional angiographic source images were obtained in 40 patients with MCA aneurysms. Each aneurysm was treated surgically using a pterional craniotomy. We initially approached the aneurysm distally. When this was judged inappropriate, the approach was altered to proximally. We compared the topography based on these angiograms to that confirmed during surgery.

RESULTS

MR angiographic source images visualized the aneurysm, the M1 and M2 segments of the MCA, the insula, and the frontal and temporal opercula in all 40 patients. In 22 (55%) of them, the distal portion of the M1 segment was recognized from the posterolateral perspective between the aneurysmal neck and the insular surface. These aneurysms were successfully clipped via the distal approach after definite proximal control of the MCA was obtained.

CONCLUSIONS

It was concluded that MR angiographic source images have a distinguishing feature in defining cerebral tissue-vascular relationships and that they are useful in the surgical planning for MCA aneurysms.

Evidence for involvement of two isoforms of Syk protein-tyrosine kinase in signal transduction through the high affinity IgE receptor on rat basophilic leukemia cells

Recent evidence suggests a critical role for Syk in mast cell activation upon high affinity IgE receptor (FcepsilonRI) aggregation. A rat basophilic leukemia cell line, RBL-2H3, expresses similar levels of two Syk isoforms that differ with respect to the presence of a 23-amino acid insert within the "linker" region located between the second Src homology 2 and the catalytic domain. Although they exhibit comparable intrinsic enzymatic activity, functional differences between the two isoforms are unknown. Here we report that the deleted Syk isoform can mediate signal transduction in RBL-2H3 cells. Aggregation of chimeric kinase, consisting of either form of Syk fused to the transmembrane and extracellular domains of guinea pig type II IgG Fc receptor, on RBL transfectants resulted in degranulation, release of leukotrienes, and enhanced gene expression of tumor necrosis factor-alpha. The chimeras as well as phospholipase C-gamma1 and Vav became tyrosine-phosphorylated upon aggregation of chimeras. We also found that both Syk isoforms from transiently transfected COS-7 cells were capable of binding to phosphorylated FcepsilonRI, and their kinase activities were similarly up-regulated in the presence of tyrosine-phosphorylated synthetic peptides based on the sequence of the gamma subunit of FcepsilonRI. Thus, these results establish that both isoforms of Syk can mediate signal transduction in mast cells and suggest that the 23-amino acid insert in the linker region of Syk may not be obligatory for FcepsilonRI signaling.

A monomeric human C4b-binding protein (C4bp) more efficiently inactivates C3b than natural C4bp: participation of C-terminal domains in factor I-cofactor activity

We designed a cDNA construct encoding an artificial membrane molecule consisting of all 8 short consensus repeats (SCRs) of human monomeric C4b-binding protein (C4bp) followed by DAF's GPI anchor, named mC4bp, and expressed the protein on swine endothelial cells (SEC). At the same level of expression, mC4bp protected host cells as effectively as DAF, the most potent complement (C) regulator on the membrane. This result was unexpected from the reported functional properties of natural multimeric C4bp. Here, we investigated the mechanism whereby mC4bp has potent cell-protective activity. Our results were as follows: (1) mC4bp serves more efficiently as a methylamine-treated C3 (C3ma)-inactivating factor I-cofactor than natural C4bp and as efficiently as MCP as a methylamine-treated (C4ma)-inactivating cofactor by fluid-phase cofactor assay: (2) the potency of C3ma inactivation by mC4bp and factor I is quite high compared to those of other cofactors: (3)blocking studies using mAbs against C4bp suggested that both the 48 kDa N-terminal fragment and the C-terminal domain near the portion responsible for bundle formation participate in the high C3ma-inactivating capacity of mC4bp. Thus, acquiring high C3ma-inactivating capacity secondary to monomeric alteration leads to high C regulatory activity of mC4bp. These results infer that mC4bp differs from C4bp in its potent factor I-cofactor activity and is a good candidate as a safeguard against hyperacute rejection of xenografts.

Structural and functional properties of complement-activating protein M161Ag, a Mycoplasma fermentans gene product that induces cytokine production by human monocytes

Human malignant cells are targeted by homologous complement C3b if they express M161Ag, a 43-kDa protein with C3-activating property. cDNA of M161Ag cloned from human leukemia cell lines predicted M161Ag as a novel secretory protein comprised of 428 amino acids including 5 amino acids encoded by TGA codons (Matsumoto M., Takeda, J., Inoue, N., Hara, T., Hatanaka, M., Takahashi, K., Nagasawa, S., Akedo, H., and Seya, T. (1997) Nat. Med. 3, 1266-1270), although the origin of this gene was obscure. Here we clarified this point through genomic and biochemical analysis: 1) 5'-UT and genomic sequences represented the prokaryote promoter and ribosomal binding site; 2) the TGA codons in M161Ag cDNA were translated not into selenocysteines but into tryptophans; 3) M161Ag anchored onto the membrane secondary to its N-terminal palmitoylation like prokaryote lipoproteins; 4) genomic and cDNA clones of M161Ag were highly homologous to Mycoplasma fermentans gene encoding P48, a monocytic differentiation/activation factor, recently released in the data base, although the resultant proteins were different in the amino acid sequences. Additionally, purified soluble M161Ag efficiently provoked IL-1beta, tumor necrosis factor alpha, and IL-6 like P48, and further IL-10 and IL-12 in human peripheral blood monocytes. Thus, M161Ag originates from M. fermentans, and latently infected M. fermentans allows human cells to produce M161Ag. The liberated protein serves as a potent modulator of innate and cellular immune responses via its complement-activating and cytokine-producing activities.

CD46 (membrane cofactor protein of complement, measles virus receptor): structural and functional divergence among species (review)

Human CD46 was identified as a complement regulator and was later shown to be a measles virus receptor. The ubiquitous distribution profile of CD46 accounted for systemic measles infection and general protection of host tissue/organs from autologous complement. A similar ubiquitous distribution was observed for swine and simian CD46 homologues based upon subsequent cDNA cloning and Northern analysis, reinforcing the roles of CD46. In contrast, recent cDNA cloning and distribution analyses of murine and guinea-pig CD46 revealed the predominant expression of these rodent CD46 homologues in the testis, especially in mature testicular germ cells. These results do not support the established functions of human CD46 but support the hypothesis that CD46 on sperm serves as a fertilization-related adhesion molecule toward eggs. Here, we review the structure, function and distribution of human CD46 and discuss the possible differences between human CD46 and its homologues recently cloned from a variety of non-human primates and other animals.

The mechanism by which proteolysis enhances the ligand-binding activity of guinea pig type II Fc receptor for IgG (FcgammaRIIB)

We have previously shown that the ligand-binding activity of type II Fc receptor for IgG (FcgammaRIIB) on guinea pig peripheral blood polymorphonuclear leukocytes is very low and dramatically increases after treatment of the cells with proteolytic enzymes. In the present study, we analyzed the mechanism of this augmentation. We found that the protease treatment failed to enhance the binding of monomeric IgG to FcgammaRIIB, increased the binding of small immune complexes (IC) prepared under antigen-excess conditions only modestly, but markedly enhanced the binding of large IC prepared under antibody-excess conditions. These results suggest that proteolysis increases the ligand-binding avidity but not the intrinsic affinity of FcgammaRIIB. Confocal laser scanning microscopy revealed that the mobility of FcgammaRIIB on the cell surface was increased after protease treatment. In addition, transfection experiments indicated that the effect of proteolysis on IC binding to CHO cells expressing guinea pig FcgammaRIIB was strongly dependent on the receptor density. Finally, we demonstrated that the transmembrane and cytoplasmic domains of FcgammaRIIB were not involved in the proteolysis-induced augmentation of IC binding. Together our results suggest that the mobility of FcgammaRIIB, which may be restricted due to the association of the ectodomain of the receptor with unknown membrane proteins, is enhanced by proteolysis, allowing the receptors to bind multivalent ligands more readily and hence with higher avidity.

Post-translational modification and intracellular localization of a splice product of CD46 cloned from human testis: role of the intracellular domains in O-glycosylation

We obtained a unique CD46 cDNA, STc/CY4, from the human testis, the predicted amino acid sequence of which suggested the presence of a novel isoform of CD46. This message was present predominantly in the testis, and the predicted isoform possessed a short (11 amino acids) transmembrane section (TM) and an unidentified cytoplasmic tail (CY). When expressed in Chinese hamster ovary (CHO) cells, this CD46 isoform underwent no O-glycosylation and was mostly retained in the endoplasmic reticulum. This unusual behaviour of the new isoform was due in part to the short TM and the unusual sequences of the CY. The molecular mass of this isoform was 42,000, approximately 20,000 smaller than conventional CD46. These properties of the STc/CY4 isoform were similar to those of sperm CD46. The only difference between sperm CD46 and the STc/CY4 isoform expressed on CHO cells was that only the latter possessed N-linked sugars of high mannose types. Since the STc/CY4 isoform may behave like sperm CD46 in cellular localization and post-translational modification, studies of sperm-egg interassociation were performed using hamster eggs and CHO cell clones expressing various isoforms including the STc/CY4. Rosette formation was seen most effectively between hamster eggs and STc/CY4-expressing CHO cells. These results infer that O-glycosylation perturbs CD46-mediated sperm-binding to eggs and thus sperm CD46 lacking O-linked sugars can serve as an adhesion molecule. The possible role of CD46 in fertilization and the structural differences between sperm and conventional CD46 are discussed.