Synthesis of TMV-specific RNAs and proteins at the early stage of infection in tobacco protoplasts: transient expression of the 30K protein and its mRNA

All four TMV-coded proteins (180K, 130K, 30K, and coat) and corresponding mRNAs were detected in TMV-infected protoplasts. The 30K protein and its mRNA were synthesized between 2 and 9 hr postinoculation, while the other proteins and their mRNAs (the CP mRNA, the genomic RNA) were synthesized continuously. The results indicated that the synthesis of the two subgenomic RNAs (the CP mRNA, the 30K protein mRNA) is regulated by different mechanisms.

Pre-clinical evaluation of a new orally-active CCK-2R antagonist, Z-360, in gastrointestinal cancer models

BACKGROUND

Gastrin has a role in gastrointestinal (GI) malignancy. This study provides pre-clinical evaluation of a novel, orally-active gastrin/cholecystokinin-2 receptor (CCK-2R) antagonist, Z-360.

METHODS

(125)I gastrin-17 (G17) displacement and G17-stimulated calcium assays were used in classical CCK-2R-transfected cell lines. Akt phosphorylation was assessed by Western blotting. Z-360 efficacy in vivo was evaluated in three human xenograft models, and microvessel density and apoptosis in these models were investigated by immunohistochemistry.

RESULTS

Z-360 inhibited (125)I G17 binding to cells expressing CCK-2R, and G17-stimulated signalling. Reduced Akt phosphorylation in an oesophageal cell-line treated with Z-360 was reversed by co-treatment with G17. Z-360 increased survival in a gastric ascites model (p=0.011) and decreased tumour growth in a hepatic metastasis model (81%, p=0.02). In an orthotopic pancreatic model, Z-360 combined with gemcitabine decreased final tumour weight compared to single agents (84%, p=0.002) and there was increased apoptosis and decreased microvessel density in ex vivo tumour tissue.

CONCLUSIONS

These results show that the orally-active CCK-2R antagonist, Z-360 has high sub-nM affinity for classical CCK-2R, is well tolerated in vivo and exerts an anti-tumour effect.

Taste bud contains both short-lived and long-lived cell populations

Taste bud cells undergo continual turnover even in adulthood, and their average lifespan has been estimated as approximately 10 days. However, it is not clear whether this figure can be applied to all the different cell types contained in a taste bud. Here, we describe the age and life cycle of taste bud cells in rat circumvallate papillae, and indicate that the lifespan is heterogeneous, ranging from 2 days to over 3 weeks. Taste bud cells were incorporated from the basal proliferative layer in 1-2 days after birth. After incorporation, approximately half of the cells were eliminated within 2-3 days, and the remaining half were maintained with gradual decrease, suggesting that there are at least two types of cells; short-lived cells and long-lived cells. Moreover, above 10% of the incorporated cells were maintained at 3 weeks. In order to gain information about the relationship between the cell functions and the cell age, we carried out double-labeling experiments using 5-bromo-2'-deoxyuridine and each of two markers for in situ hybridization: mammalian achaete-scute homolog 1 (Mash1) and phospholipase C beta 2 (PLCbeta2) as markers of early differentiation and functional taste signaling, respectively. Mash1 expression began immediately after the incorporation and reached a maximum at 5-6 days after birth. Fewer but distinct Mash1-positive cells were still observed after 3 weeks. PLCbeta2 expression was observed from day 5, reached a maximum at day 12, and continued over 3 weeks. Taken together, a taste bud contains both short-lived and long-lived cells: the short-lived cells are eliminated in a time course similar to the surrounding epithelial cells, and the long-lived cells including taste receptor cells have a lifespan longer than the previous estimation.

Life-threatening bleeding and acquired factor V deficiency associated with primary systemic amyloidosis

Acquired factor X deficiency has been described in patients with amyloidosis but acquired factor V deficiency is quite rare. We report here a case of life-threatening bleeding and acquired factor V deficiency associated with primary amyloidosis. A 50-year-old man who had no previous hemorrhagic diathesis was referred to our hospital because of recurrent epistaxis, gingival bleeding and hemospermia. The laboratory examination revealed that both the prothrombin time (PT) and the activated partial thromboplastin time (aPTT) were significantly prolonged, and factor V activities were markedly decreased to 14-39% of the normal value. Other coagulation factors such as fibrinogen, prothrombin, factor VII, factor VIII, factor IX and factor X were subnormal and normal. Transaminases were slightly elevated but serological tests of hepatitis B and hepatitis C were negative. Mild hepatosplenomegaly was noted without sign of liver cirrhosis. The PT and aPTT obtained 8 years ago when he received a cholecystectomy due to cholecystitis were both normal. Specific assays for the detection of factor V inhibitor were repeatedly performed but no factor V inhibitor was found. Furthermore, a significant recovery of the infused factor V was noted shortly after an intravenous administration of 5-10 U fresh frozen plasma, but it did not last more than 6 h. Melena, bleedings into the left shoulder and buttock, and finally mortal retroperitoneal hemorrhage developed despite repeated infusions of large amounts of fresh frozen plasma. Acquired factor V deficiency associated with primary amyloidosis was suspected but histological diagnosis was not obtained because of the severe bleeding tendency. Autopsy revealed hepatosplenomegaly and massive deposits of AL amyloid in the liver, spleen, heart and other parenchymal organs. Perivascular amyloid deposition and factor V deficiency are both thought to be the cause of the severe hemorrhagic tendency seen in this patient.

Primary culture of rat taste bud cells that retain molecular markers for taste buds and permit functional expression of foreign genes

Taste buds are constituted of several kinds of cells which have distinct characteristics and play different roles. In this study, we have established an in vitro culture system by optimizing the method for isolating the cells and by selecting culture media and reagents effective for cell viability and adhesion. As a result, the taste bud cells were adhesive and viable for over 3 days when cultured onto Matrigel-coated dishes in medium based on keratinocyte growth medium. The cells retained molecular markers for both the cytoskeleton and intracellular signaling such as cytokeratin 8 and phospholipase Cbeta2. In addition, three intracellular signaling molecules, gustducin, phospholipase Cbeta2, and inositol 1,4,5-trisphosphate receptor type 3, are expressed in the same correlation as those in vivo, although the ratio of signaling molecule-positive cells vs. total cells was somewhat lower in the culture than in vivo. Next, we tried several methods to introduce foreign genes into the cells, and obtained a greater than 90% efficiency of introduction using an adenovirus vector. Finally, we show that an exogenously expressed myc-tagged alpha1A-adrenoceptor sorts into the plasma membrane, and transduces a ligand-dependent signal resulting in intracellular [Ca(2+)] increase in about half of the infected cells. These results suggest that taste bud cells after 3 days of culture retain characteristic molecular markers, and may prove useful for describing the molecular and physiological features of taste bud cells, and that these cells can be further manipulated by adenovirus-mediated gene introduction.

A comparative study of three cranial sensory ganglia projecting into the oral cavity: in situ hybridization analyses of neurotrophin receptors and thermosensitive cation channels

Peripheral cranial sensory nerves projecting into the oral cavity receive food intake stimuli and transmit sensory signals to the central nervous system. To describe and compare the features of the cranial sensory ganglia that innervate the oral cavity, i.e., the trigeminal, petrosal, and geniculate ganglia (TG, PG, and GG, respectively), in situ hybridization was conducted using riboprobes for neurotrophin receptors (TrkA, TrkB, and TrkC), a neurotransmitter (substance P), and ion channels important for thermosensation (VR1 and TREK-1). In TG, all in six probes yielded positive signals to various extent in intensity and frequency. In addition, a strong correlation between the expression of VR1 and those of TrkA and substance P was observed as in the case of the dorsal root ganglia. In PG, positive signals to all six probes were also detected, and the correlation of expression was similar to that shown by TG. On the other hand, most cells in GG were positive to the TrkB probe, and a small number of cells were positive to the TrkC probe, but no significant signal was observed for the other four probes. These results indicate that TG and PG consist of cells that are heterogeneous in terms of neurotrophin requirement and somatosensory functions, and that GG seems to consist mainly of a homogeneous cell type, gustatory neurons. In conclusion, TG, PG, and GG, show gene expression characteristics intrinsic to the three ganglia. It is also concluded that TG and a portion of PG project several types of somatosensory nerves. This is consistent with the finding that GG and a portion of PG project gustatory nerves.

Both the N- and C-terminal chaperone sites of Hsp90 participate in protein refolding

Hsp90 is able to bind partially unfolded firefly luciferase and maintain it in a refoldable state; the subsequent successive action of the 20S proteasome activator PA28, Hsc70 and Hsp40 enables its refolding. Hsp90 possesses two chaperone sites in the N- and C-terminal domains that prevent the aggregation of denatured proteins. Here we show that both chaperone sites of Hsp90 are effective not only in capturing thermally denatured luciferase, but also in holding it in a state prerequisite for the successful refolding process mediated by PA28, Hsc70 and Hsp40. In contrast, the heat-induced activity of Hsp90 to bind chemically denature dihydrofolate reductase efficiently and prevent its rapid spontaneous refolding was detected in the N-terminal site of Hsp90 only, while the C-terminal site was without effect. Thus it is most likely that both the N- and C-terminal chaperone sites may contribute to Hsp90 function as holder chaperones, however, in a significantly distinct manner.

IP(3) receptor type 3 and PLCbeta2 are co-expressed with taste receptors T1R and T2R in rat taste bud cells

The Ca(2+) signaling cascade has been reported to be activated by many tastants in vertebrate taste systems. Recently we have shown that G(i2) and phospholipase Cbeta2 (PLCbeta2) are co-expressed in a subset of taste bud cells and are possibly involved in Ca(2+) triggering of taste signaling in rats. We report here that, as a component downstream of PLCbeta2, the type 3 isoform of the inositol 1,4,5-trisphosphate (IP(3)) receptor (IP(3)R3) is specifically expressed in the same cells as PLCbeta2 in rat taste buds. We also show that cells expressing rT2R9, a probable cycloheximide receptor, are included among PLCbeta2- and IP(3)R3-positive cells, as in the case of rT1R2, a different type of taste receptor. Our findings indicate that PLCbeta2 and IP(3)R3 co-localize together with G(i2) as downstream components of two different types of taste receptors, T1R and T2R, in taste bud cells.

Suppression of allergic reactions by royal jelly in association with the restoration of macrophage function and the improvement of Th1/Th2 cell responses

We studied the immunomodulatory effects of royal jelly (RJ), the principal food source of the queen honeybee. In this study, suppression of allergic reactions by RJ was investigated in DNP-KLH immunized mice (DNP-KLH mice). Oral administration of RJ (1 g/kg) to DNP-KLH mice significantly decreased the serum levels of antigen-specific Ig E and significantly inhibited DNP-KLH mediated-histamine release from mast cells, resulting in the suppression of immediate hypersensitivity reactions of ear skin. In DNP-KLH mice, IFN-gamma (Th1 cytokine) production from CD4+ T cells was suppressed and IL-4 (Th2 cytokine) production from CD4+ T cells was increased as compared to normal mice. On the other hand, RJ improved the balance of Th1/Th2 cell responses from Th2-dominant to Th1-dominant. RJ significantly increased GSH levels in macrophages from DNP-KLH mice. In addition, the administration of RJ to DNP-KLH mice increased IL-12 p40 mRNA expression and NO production, and decreased PG E2 production from macrophages as compared to untreated DNP-KLH mice. These results suggested that RJ suppressed antigen-specific Ig E production and histamine release from mast cells in association with the restoration of macrophage function and improvement of Th1/Th2 cell responses in DNP-KLH mice.

An actin-binding protein, CAP, is expressed in a subset of rat taste bud cells

Single cell cDNA libraries were constructed from taste bud cells of rat circumvallate papillae. Using three steps of screening, including differential hybridization, sequence analyses and in situ hybridization, a clone encoding a rat homolog of yeast adenylyl cyclase-associated protein (CAP) was identified to be highly expressed in a subset of taste bud cells.

Domain III of calpain is a ca2+-regulated phospholipid-binding domain

The X-ray structure of m-calpain shows that domain III of the large subunit is structurally related to C2 domains, Ca2+-regulated lipid binding modules in many enzymes. To address whether this structural similarity entails functional analogy, we have characterized recombinant domain III from rat micro- and m-calpain and Drosophila CALPB. In a Ca2+ overlay assay domain III displays a large capacity for Ca2+ binding, commensurable with that of domain IV, the principal Ca2+-binding domain of calpains. The amount of Ca2+ bound to domain III increases 2- to 10-fold upon the addition of liposomes containing 20-40% di- and triphosphoinositides. Conversely, phospholipid-binding in spin-column size-exclusion chromatography is significantly promoted by Ca2+, in a manner similar to known C2 domains. These results suggest that domain III might be the primary lipid binding site of calpain and may play a decisive role in orchestrating Ca2+- and lipid activation of the enzyme.

Breakdown of Th cell immune responses and steroidogenic CYP11A1 expression in CD4+ T cells in a murine model implanted with B16 melanoma

The association between the balance of Th1/Th2 cell responses and CYP11A1 expression in CD4+ T cells was investigated in a murine model implanted with highly metastatic B16F10 melanoma cells (B16F10 mice). When 2 x 10(5) cells/mouse of B16F10 cells were inoculated into C57BL/6 mice, Th2 cell responses and pulmonary metastasis were increased. In addition, corticosterone levels in splenic tissue or serum and CYP11A1 mRNA expression (mRNA encoding cholesterol side-chain cleavage p450 enzyme) in CD4+ T cells were increased in these mice. When the anti-corticosterone drug aminoglutethimide (CYP11A1 inhibitor) was administered to B16F10 mice, corticosterone levels in splenic tissue or serum and CYP11A1 mRNA expression were decreased at 14 days after tumor inoculation. In addition, Th1 cell responses were restored and pulmonary metastasis was reduced by aminoglutethimide. These results indicated that the breakdown of Th cell responses and increase of pulmonary metastasis were due to an increase in steroidogenic CYP11A1 mRNA expression in CD4+ T cells. Moreover, it was suggested that promotion of CYP11A1 mRNA expression in Th2 cells was partially involved due to an increase in level of corticosterone in splenic tissue and the breakdown of Th cell responses locally in the splenic tissue, which then affected the maintenance of Th2 cell functions in the microenvironment of tumor-bearing mice.

Comprehensive study on G protein alpha-subunits in taste bud cells, with special reference to the occurrence of Galphai2 as a major Galpha species

Previous studies have identified many cDNA species that encode a variety of G protein alpha-subunits occurring in taste buds. These include the cDNA encoding a taste-bud-specific Galpha, gustducin (G(gust)). Here we carried out comprehensive analyses of Galpha species that occur in the taste buds of rat circumvallate papillae and also in their single cells isolated from the taste buds. Reverse transcriptase-polymerase chain reaction showed the presence of 10 kinds of Galpha cDNAs, including a splice variant of Galphas, among which G(gust), Galphas, Galphai2 and Galphai3 cDNAs were shown to be major species. In situ hybridization and immunohistochemistry showed that Galphai2, as well as G(gust), expressed in a subset of taste bud cells, and the frequency of Galphai2-expression appears to be higher than that of G(gust). Southern analyses of the amplified cDNA from single cells showed that each taste bud cell expresses multiple Galpha mRNA species. For example, some Galphai2-positive cells also express one or more other Galpha species, including Galphas, Galphai3 and G(gust), and there is no apparent correlation in expression among the three Galpha species.

Addition of signal leader sequences to the N-termini of olfactory receptor proteins enhances their expression in Xenopus oocytet

Several recent papers have reported the difficulties in expressing olfactory receptor proteins (ORs) in heterologous systems, and proposed that some sequences in ORs have negative effects on their efficient expression. To obtain an efficient expression system of ORs, we modified N-terminal sequences of ORs through the addition of exogenous sequences. Three kinds of sequences, designated as 5HT, V, and VL, were used. 5HT and V corresponded to the signal leader (SL) sequences of 5HT 3R and VIPR, respectively. VL corresponded to the first extracellular region of VIPR containing the SL sequence and three potential asparagine- (Asn-) linked glycosylation sites. The myc epitope was also added to the C-termini of the sequences. Several ORs including 17 of rat, GUST43 of rat, Y1 of medaka, FOR1-3 of pufferfish, 47E of carp, and ODR-10 of nematode were subjected to the modifications, and the RNAs encoding modified ORs were injected into Xenopus oocytes. The membrane fraction of the oocytes were analyzed by Western blotting to examine the expression of the proteins. In the cases of ORs modified with 5HT and V, only ODR-10 and 47E, both of which have more than two Asn-linked glycosylation sites in their extracellular regions, were detected as the bands of predicted molecular weights. On the other hand, most of the ORs modified with VL showed the bands of predicted molecular weights. These results suggest that SL sequences together with potential Asn-linked glycosylation sites have positive effects on the expression of ORs in heterologous systems.

Random expression of main and vomeronasal olfactory receptor genes in immature and mature olfactory epithelia of Fugu rubripes

Main olfactory receptor genes were isolated from a seawater fish, Fugu rubripes (pufferfish), and characterized. Two subfamilies of genes encoding seven transmembrane receptors were identified; one consists of five or more members, termed FOR1-1 to 5 of FOR1 subfamily, and the other appears to be a single copy gene, termed the FOR2 subfamily. FOR1 members show extremely high amino acid sequence similarities of about 95% to one another, and are distantly related to catfish-1 with the highest similarity of 37%. FOR2 shows 43% similarity to goldfish-A28. Phylogenically, both FOR members are categorized among pedigrees of the fish main olfactory receptor family outside the mammalian receptor family, although similarities between Fugu receptors and those of fresh-water fishes are lower than those among fresh-water fishes. In situ hybridization shows that both subfamilies of receptor genes are expressed randomly over the olfactory epithelium throughout all developmental stages, and no segregation of the signals was found. On the other hand, when three members of a vomeronasal olfactory receptor gene family, related to the Ca(2+)-sensing receptor, were used as probes, they were also randomly expressed over the same epithelium as the main olfactory receptors. This is in contrast to the expression profiles observed for zebrafish and goldfish, where the main or vomeronasal olfactory receptors are expressed in segregated patterns. It is thus suggested that the expression pattern of fish olfactory receptors varies depending on the species, although fish olfactory receptors are highly related to one another in their primary structures, and are phylogenically distinct from those of mammals.

Co-expression of calcium signaling components in vertebrate taste bud cells

In order to investigate the molecular mechanism of calcium signaling pathways common to the vertebrate gustatory systems, we have analyzed the expression of their molecular components. We first identified a phospholipase C (PLC) beta subtype expressed in the taste buds of pond loach (Misgurnus anguillicaudatus), designated DPLCbeta2, which is closely related to mammalian PLCbeta2 shown recently to be expressed in rat taste buds. The taste bud-specific expression of PLCbeta2 in a fish species as well as rat strongly suggests that PLCbeta2 mediates the tastant-induced second messenger response in taste buds, which is common to vertebrates. Next, we examined the correlation of gene expression of the candidate components leading to PLCbeta2 activation in rat circumvallate papillae, including G proteins, G(i2) and gustducin, and a G protein-coupled receptor, TR2. As a result, it was shown that the mRNAs for PLCbeta2 and G(i2) co-exist in the same cells, and PLCbeta2- and G(i2)-positive cells include both gustducin-positive cells and TR2-positive cells. However, no correlation was found between the expressions of TR2 and gustducin as reported previously. Our results thus indicate that a taste transduction pathway comprising TR2, G(i2) and PLCbeta2 occurs in a subset of taste cells.

Very young patient with peculiar squamous cell carcinoma of the lung

A 20-year-old man with squamous cell carcinoma of the lung is described. Histology of the open lung biopsy specimen revealed squamous cell carcinoma with definite keratinization. Interestingly, the tumor cells were characterized by partial expression of CD34 antigen and neuroendocrine differentiation. The diagnosis was delayed in this case because of his young age. This delayed diagnosis resulted in rapid progression and short survival time. In our review of 667 cases of lung cancers at Okayama University Hospital, only 3 (0.4%) of them were under 30 years of age and also showed advanced stage and very poor prognosis. It is important to take note of lung cancer as a differential diagnosis to detect early-stage lung cancer in young patients when they present with abnormal shadow on chest radiograph.

An immunomodulatory arabinomannan extracted from Mycobacterium tuberculosis, Z-100, restores the balance of Th1/Th2 cell responses in tumor bearing mice

The regulatory effect of Z-100 on the balance of Th1/Th2 cell responses in BALB/c mice bearing Meth-A fibrosarcoma was investigated. In tumor bearing mice, Th1 cytokine production (IL-2, IFN-gamma) are suppressed and Th2 cytokine production (IL-4, IL-10) are increased, as compared with those of normal mice. The administration of Z-100 (10 mg/kg) to tumor bearing mice restored the balance of Th1/Th2 cell responses from Th2 dominant state to the normal state. This regulatory effect of Z-100 was eliminated by depletion of adherent cells from splenocytes derived from tumor bearing mice, and by the treatment with 2-ClAdo (a macrophage inhibitor). Similarly, this regulatory effect was diminished by the treatment with anti-IL-12 mAb and anti-IFN-gamma mAb. In addition, the IL-12 p40 mRNA expression in splenic adherent cells and IFN-gamma mRNA expression in CD4+ T cells were increased by the administration of Z-100 to tumor bearing mice. These results suggested that Z-100 restored the balance of Th1/Th2 cell responses to the normal one in tumor bearing mice through the activation of macrophages and up-regulation of IL-12 production from macrophages and IFN-gamma production from CD4+ T cells.

Two subfamilies of olfactory receptor genes in medaka fish, Oryzias latipes: genomic organization and differential expression in olfactory epithelium

We cloned and characterized two subfamilies of olfatory receptor (OR) genes from medaka fish (Oryzias latipes). Southern blot analysis showed that each of the two subfamilies, designated as subfamilies Y and E, consists of about five members, as usually observed for other vertebrate ORs. Analyses of the genomic clones encoding these members revealed that two members of subfamily Y and four members of subfamily E are tandemly reiterated in 15 and 22 kbp regions of the medaka genome, respectively. The members of each subfamily show very similar amino acid sequences, with similarities greater than 70%. However, the similarities to the sequences of other vertebrate ORs are lower. Members of subfamily Y show amino acid sequence similarities of ca. 30% to other fish ORs, including subfamily E members, as well as to mammalian ORs. On the other hand, members of subfamily E show sequence similarities of ca. 50% to other fish ORs and ca. 30% to mammalian ORs. Phylogenic analyses of various fish ORs, including medaka, catfish, and zebrafish ORs, indicate that the primary structures of fish ORs are diverse compared with those of mammalian ORs, which consist of much larger numbers of members. The expression patterns of subfamilies Y and E genes in the olfactory epithelium of adult medaka fish were examined by in situ hybridization, showing that the frequency of positive signals is different between the two subfamilies: about 2% of the olfactory neurons are positive to probes for members of subfamily Y, while less than 1% are positive to probes for members of subfamily E. These results indicate that each subfamily is under different transcriptional control.

Morphological changes and detachment of adherent cells induced by p122, a GTPase-activating protein for Rho

We recently cloned a novel signaling molecule, p122, that shows a GTPase-activating activity specific for Rho and the ability to enhance the phosphatidylinositol 4,5-bisphosphate-hydrolyzing activity of phospholipase C delta1 in vitro. Here we analyzed the in vivo function of p122. Microinjection of the GTPase-activating domain of p122 suppressed the formation of stress fibers and focal adhesions induced by lysophosphatidic acid, suggesting a GTPase-activating activity for Rho as in in vitro. Transfection of p122 also induced the disassembly of stress fibers and the morphological rounding of various adherent cells. Analyses using deletion and point mutants demonstrated that the GTPase-activating domain of p122 is responsible for the morphological changes and detachment and that arginine residues at positions 668 and 710 and a lysine residue at position 706 in the GTPase-activating domain are essential. Using Fluo-3-based Ca2+ microscopy, we found that p122 evoked a rapid elevation of intracellular Ca2+ levels, suggesting that p122 stimulates the phosphatidylinositol 4, 5-bisphosphate-hydrolyzing activity of phospholipase C delta1. These results demonstrate that p122 synergistically functions as a GTPase-activating protein specific for Rho and an activator of phospholipase C delta1 in vivo and induces morphological changes and detachment through cytoskeletal reorganization.

A gustatory cyclic nucleotide-gated channels CNGgust, is expressed in the retina

Cyclic nucleotide-gated (CNG) channels are essential proteins that contribute to the intracellular signal transduction of the senses of sight and smell. Recently, we found a novel CNG channel (CNGgust) in rat taste buds, and demonstrated its possible involvement in taste signal transduction. In the present study, we used RT-PCR and immunostaining to prove that this gustatory CNG channel is expressed in the outer segments of rat cone photoreceptor cells. The study strongly suggests that the senses of taste and sight share, at least in part, a common signal transduction pathway.

Molecular cloning and taste bud-specific expression of a novel cyclic nucleotide-gated channel

Cyclic nucleotide-gated (CNG) channels serve as downstream targets of signaling pathways in vertebrate photoreceptor cells and olfactory sensory neurons. For taste signaling as well, a great deal of information is available predicting the presence of a CNG channel, but no report has been presented on its molecular entity. Here we report on molecular cloning and functional expression of a taste bud-specific CNG channel tentatively named CNGgust. Reverse transcriptase polymerase chain reaction (RT-PCR) primers were synthesized according to some amino acid sequences generally conserved in many CNG channels. RT-PCR was conducted using rat circumvallate papillary mRNA-derived cDNA as a template to obtain positive clones. A corresponding genomic DNA clone was then obtained by screening from a genomic DNA library. Dissecting the entire structure of this gene, we found that the encoding protein had an amino acid sequence similarity of 80% to each of retina and olfactory CNG channels. It was also found by immunostaining with a specific antibody that this gustatory CNG channel (CNGgust) is localized in the tongue and also expressed specifically on the pore side of each taste bud in the circumvallate papillae. Electrophysiological experiments demonstrated that CNGgust resided in a functional state. All these data suggest that CNGgust may be involved in taste signal transduction in sensory cells.

Identification of taste-tissue-specific cDNA clones from a subtraction cDNA library of rat circumvallate and foliate papillae

To identify genes specifically expressed in taste tissues, we constructed a subtraction cDNA library of epithelium of rat circumvallate and foliate papillae and carried out differential screening of this library. Dot blot analysis showed 46 out of 88 clones obtained by this method to be expressed in the epithelium of papillae. The cDNA inserts in these clones were sequenced and analyzed for similarity to entries the GenBank database. About 54.3% of the clones were known sequences, including the sequences of ebnerin, cytokeratin 18, and Na+,K+-ATPase, that were shown by in situ hybridization to be expressed in the circumvallate papillae. About 41.3% of the papillae-specific clones had no significant similarity to known sequences and are candidates for novel taste bud-specific marker genes.

Identification of two alpha-subunit species of GTP-binding proteins, Galpha15 and Galphaq, expressed in rat taste buds

We cloned cDNAs for two G protein alpha-subunits belonging to the Galphaq family, each capable of activating PLCbeta, from rat tongue. One is a Galphaq in the narrow sense, and the other, termed rat Galpha15, is a rat counterpart of mouse Galpha15, sharing an amino acid sequence similarity of 94%. RT-PCR and Northern blot analysis demonstrated that rat Galpha15 and Galphaq were distinctly expressed in tongue epithelia containing taste buds. Immunostaining also showed that rat Galpha15, together with the Galphaq, was localized mainly in taste buds. These studies suggest the possibility that these two Galpha proteins function for taste signal transduction in sensory cells.

Functional expression and enzymatic properties of two Sitophilus zeamais cysteine proteinases showing different autolytic processing profiles in vitro

To characterize in more detail the cathepsin L-like cysteine proteinases from Sitophilus zeamais (SCPs) cloned in our previous study [Matsumoto et al. (1997) J. Biochem. 121, 464-476], we established a system for their functional expression and purification using a glutathione S-transferase (GST) fusion gene vector from Escherichia coli. The proenzyme forms of two representative SCPs, proSCPc1 and proSCPg3, were expressed as GST-fusion proteins and purified on a glutathione Sepharose column. GST-proSCPc1 undergoes autoproteolytic cleavage into the mature form efficiently at acidic pH, and exhibits significant proteolytic activity toward various substrates including hemoglobin and Z-Phe-Arg-MCA. The enzymatic characteristics of the activated form of SCPc1 are similar to those of mammalian cathepsin L, but its pH optimum for the hydrolysis of hemoglobin is significantly lower. The other proSCP, GST-proSCPg3, which has a shorter COOH-terminal domain than SCPc1, undergoes almost no autolytic processing and shows only very slight proteolytic activity, although the other enzymatic characteristics of GST-proSCPg3 are similar to those of GST-proSCPc1.

Z-100, a polysaccharide-rich preparation extracted from the human type Mycobacterium tuberculosis, improves the resistance of Meth-A tumor-bearing mice to endogenous septic infection

The effect of Z-100, an immunomodulatory arabinomannan extracted from Mycobacterium tuberculosis, on cecal ligation and puncture (CLP)-induced sepsis in mice bearing Meth-A fibrosarcoma was investigated. When normal BALB/c mice were subjected to the CLP procedure, their mortality rate was 17%. On the other hand, an increased mortality was observed in tumor-bearing mice subjected to CLP 10 days after tumor inoculation, and then all mice died when tumor-bearing mice were subjected to CLP 20 days after tumor inoculation. However, the increased percent mortality was decreased by 50% when these mice were injected intraperitoneally with a 10 mg/kg dose of Z-100. When splenocytes (5 x 10(7) cells), obtained from Meth-A tumor-bearing mice 20 days after tumor inoculation, were transferred intravenously to normal mice (recipient mice), mortality of these recipient mice were increased by 62% as compared with that of the control (22%). However, no increased mortality (25%) was observed in recipient mice which were transferred with splenocytes from tumor-bearing mice injected intraperitoneally with Z-100 (10 mg/kg). In addition, suppressor cell activity was demonstrated in splenocytes from Meth-A tumor-bearing mice at 20 days after tumor inoculation using one-way mixed lymphocyte reaction. However, the suppressor cell activity was significantly decreased by the intraperitoneal administration of a 10 mg/kg dose of Z-100 (p < 0.01). The increase of mortality in recipient mice by adoptive transfer of mononuclear cells (MNCs) from tumor-bearing mice was not detected when these MNCs were treated with anti-Thy 1.2 monoclonal antibody (mAb), anti-Lyt 2.2 mAb or anti-CD11b mAb, but an increase was seen with anti-Lyt 1.2 mAb or anti-immunoglobulin antiserum treated MNCs. These results suggest that the suppressor cells affect the mortality of CLP-induced sepsis and Z-100 may have a therapeutic activity against opportunistic infections in immunocompromised hosts through the regulation of suppressor T-cells.

Identification of endogenous substrates for Drosophila calpain from a salt-extracted fraction of Drosophila ovaries

Drosophila calpain (Dm-calpain) produced in Escherichia coli has a distinct Ca2+-dependent activity. By using a recombinant Dm-calpain, we searched for its substrates occurring in Drosophila ovaries, where Dm-calpain is expressed. Among a number of major proteins, several proteins in a salt-extracted fraction were selectively degraded by Dm-calpain in a Ca2+-dependent manner. The major substrates were identified by microsequencing the lysylendopeptidase-digested proteins. Three ribosomal proteins, the L5, L7, and L8 subunits of the 60S ribosome, were found to be potential Dm-calpain substrates. In addition, the alpha subunit of elongation factor-1 (EF-1alpha), a multi-functional protein involved in both protein synthesis and cytoskeletal regulation, was shown to be cleaved by Dm-calpain into several distinct fragments when expressed as a GST-fusion protein. Endogenous EF-1alpha in ovary extracts was also shown by western blot analysis to be similarly degraded. These observations suggest that Dm-calpain may regulate protein synthesis and cytoskeletal structure through its degradative or processing activity.

Taste buds have a cyclic nucleotide-activated channel, CNGgust

Cyclic nucleotide-gated (CNG) channels have been characterized as important factors involved in physiological processes including sensory reception for vision and olfaction. The possibility thus exists that a certain CNG channel functions in gustation as well. In the present study, we carried out reverse transcription-polymerase chain reaction and genomic DNA cloning and characterized a CNG channel (CNGgust) as a cyclic nucleotide-activated species expressed in rat tongue epithelial tissues where taste reception takes place. Several types of 5'-rapid amplification of cDNA ends clones of CNGgust cDNA were obtained with various 5'-terminal sequences. As the CNGgust gene was a single copy, the formation of such CNGgust variants should result from alternative splicing. The encoded protein was homologous to known vertebrate CNG channels with 50-80% similarities in amino acid sequence, and particularly homologous to bovine testis CNG channel and human cone CNG channel with 82% similarities. CNGgust was functional when expressed in human embryonic kidney cells, where it opened upon the addition of cGMP or cAMP. Immunohistochemical analysis using an antibody raised against a CNGgust peptide demonstrated the channel to be localized on the pore side of each taste bud in the circumvallate papillae, with no signal observed for degenerated taste buds after denervation of the glossopharyngeal nerve. All these results, together with the indication that cyclic nucleotides play a role gustatory signaling pathway(s), strongly suggest the involvement of CNGgust in taste signal transduction.

Site-specific de-N-glycosylation of diglycosylated ovalbumin in hen oviduct by endogenous peptide: N-glycanase as a quality control system for newly synthesized proteins

Hen ovalbumin (OVA) is known to exist as a singly N-glycosylated form with a glycan chain on Asn-292 in egg white. Previous studies showed that di-N-glycosylated form of OVA [Di-OVA; CHO-Asn-292/CHO-Asn-311 (CHO, N-glycan chain)], which has two N-glycan chains on Asn-292 and Asn-311, was expressed only transiently in hen oviduct. Di-OVA was not found in egg white, suggesting that this form cannot be secreted normally and may possibly be converted to mono-N-glycosylated OVA (CHO-Asn-292/Asp-311) by the action of peptide:N-glycanase (PNGase) during synthesis and secretion. In this study, we have identified the putative PNGase activity in the homogenate of hen oviduct, purified 1,000-fold, and designated as PNGase HO. We examined the reactivity of Di-OVA to PNGase HO and found that this enzyme site-specifically cleaved off the glycan chain at Asn-311 to convert Di-OVA into the mono-N-glycosylated form (CHO-Asn-292/Asp-311). In contrast, this enzyme was found not to act on the mono-N-glycosylated OVA (CHO-Asn-292/Asn-311) found in egg white when it was tested as a substrate. The present findings support our view that de-N-glycosylation catalyzed by PNGase may be involved in quality control of newly synthesized proteins by converting its diglycosylated form into the mono-N-glycosylated form that can be secreted. However, the alternative possibility that de-N-glycosylation may trigger cytosolic degradation of the aberrantly glycosylated glycoprotein cannot be ruled out.

Characterization of a gene family encoding cysteine proteinases of Sitophilus zeamais (maize weevil), and analysis of the protein distribution in various tissues including alimentary tract and germ cells

We have identified and characterized a gene family comprising at least four genes encoding cathepsin L-like cysteine proteinases (SCPs) in Sitophilus zeamais, Coleoptera. A cDNA clone corresponding to a major mRNA species of the gene family in adult insects codes for a cysteine proteinase (CP) of 338 amino acid residues, and two genomic clones code for similar CPs of 331 residues whose COOH-terminal structures are seven amino acids shorter. These three SCPs show high sequence similarity to one another as well as to other insect and mammalian cathepsin L-like proteinases. A polyclonal antibody raised against bacterially expressed SCP was used as a probe to examine the molecular forms and distribution of the enzyme. SCP exists in both proenzyme and mature forms in larvae, pupae, and adults, and the proenzyme converts in vitro into the mature form at acidic pH. Immunohistochemical analysis showed that SCP is present in several tissues including alimentary organs and germ cells. In alimentary organs, SCP is distributed in the gastric caeca, but not the midgut. SCP is also present in genital organs, especially in oocytes and nurse cells, where it exists at high levels. These results indicate that SCP plays a variety of physiological roles including a role in food digestion.

Immunological analysis of two calpain-like Ca2+-dependent proteinases from lobster striated muscles: relationship to mammalian and Drosophila calpains

Lobster skeletal muscles contain four Ca2+-dependent cysteine proteinases (CDPs I, IIa, IIb, and III) that degrade myofibrillar proteins. Lobster CDPs share many properties with calpains from vertebrate tissues, but differ in native mass and subunit composition. Recently, cDNAs encoding a calpain-like protein (Dm-calpain; 91.5 or 94 kDa) have been isolated from fruit fly, Drosophila melanogaster. To further clarify the relationship between invertebrate CDPs and mammalian calpains, antibodies specific for mu-, m-, p94 (nCL-1), and Dm-calpains and lobster CDP IIb (native M(r) 195,000, subunit M(r) 95,000) were used in immunoblots to test for antigenic cross-reactivity. No common epitopes were found between CDP IIb and vertebrate calpains. However, polyclonal antibodies to CDP IIb cross-reacted strongly with a C-terminal 70-kDa portion of Dm-calpain expressed in Escherichia coli. Conversely, polyclonal antibodies to Dm-calpain recognized CDP IIb. A second CDP, CDP IIa (native M(r) 125,000), was partially purified from lobster muscle; enzyme activity coeluted with a 60-kDa polypeptide using anion-exchange chromatography. The 60-kDa protein reacted with a polyclonal antibody raised against a 20-amino acid peptide sequence found around the catalytic cysteine residue of mu- and m-calpains, but not with antibodies raised against other regions of mu- or m-calpain or with the anti-CDP IIb antibody. These results suggest that (1) the CDP IIb is the homolog of Drosophila calpain in crustaceans and (2) the active site regions of CDP IIa and mu- and m-calpains are similar.

Hepatocellular carcinoma cells resist necrosis during anoxia by preventing phospholipase-mediated calpain activation

Although hepatocellular carcinoma (HCC) cells are more resistant to anoxic injury than normal hepatocytes, the mechanisms responsible for this differential sensitivity remain obscure. Because enhanced calpain protease activity contributes to hepatocyte necrosis, we tested the hypothesis that HCC cells resist anoxia by preventing calpain activation. Cell viability in two rat HCC cell lines (N1S1 and McA-RH7777 cells) was fourfold greater compared to rat hepatocytes after 4 h of anoxia. Although calpain activity increased twofold in rat hepatocytes during anoxia, no increase in calpain activity occurred in HCC cells. Western and Northern blot analysis revealed greater or equivalent expression of calpains and calpastatin in HCC cells compared to hepatocytes. Because increases in cytosolic free Ca++ (Cai++) and phospholipid degradation products regulate calpains in vitro, we measured Cai++ and phospholipid degradation. Ca++i did not change in any cell types during 60 min of anoxia. In contrast, phospholipid degradation was fourfold greater in hepatocytes compared to HCC cells. Melittin, a phospholipase A2 activator, increased calpain activity and cell necrosis in all cell types; melittin-induced cell necrosis was ameliorated by a calpain protease inhibitor. In summary, these data demonstrate for the first time 1) calpain activation without a measureable increase in Ca++i, 2) phospholipase-mediated calpain activation in hepatocytes and HCC cells, and 3) the adaptive mechanism responsible for the resistance of HCC cells to anoxia-an inhibition of phospholipid-mediated calpain activation. Interruption of phospholipase-mediated calpain activation may be a therapeutic strategy for preventing anoxic cell injury.

GUST27 and closely related G-protein-coupled receptors are localized in taste buds together with Gi-protein alpha-subunit

Gustatory, like olfactory signalling is probably mediated by seven-transmembrane receptors and coupling GTP-binding proteins (G proteins). We investigated the expression of a subset of these receptors and the Gi protein alpha-subunit by using their specific antibodies. Based on our previous finding that the mRNA for GUST27, one of these receptors, is expressed in rat lingual epithelia, we first prepared an antibody to the synthetic nonapeptide, H-Ser-Tyr-Ser-Gln-Ile-Ala-Ser-Ser-Leu-OH, which corresponds to the third intracellular domain of GUST27 and also to those of a subset of related receptors whose occurrence can be predicted by PCR. Immunohistochemical studies with rat circumvallate papillae indicated that the anti-GUST27 antibody reacted with many of the taste buds examined, with strong signals appearing in particular taste cells. We then carried out a similar immunohistochemical experiment with an antibody to the Gi protein alpha-subunit and found that this subunit is also expressed in taste buds as demonstrated in the case of gustducin and transducin. Taken together, these results strongly suggest that GUST27 and closely related receptors, as well as Gi alpha proteins, are involved in intracellular taste signal transduction.

Hepatocellular carcinoma cells resist necrosis during anoxia by preventing phospholipase-mediated calpain activation

Although hepatocellular carcinoma (HCC) cells are more resistant to anoxic injury than normal hepatocytes, the mechanisms responsible for this differential sensitivity remain obscure. Because enhanced calpain protease activity contributes to hepatocyte necrosis, we tested the hypothesis that HCC cells resist anoxia by preventing calpain activation. Cell viability in two rat HCC cell lines (N1S1 and McA-RH7777 cells) was fourfold greater compared to rat hepatocytes after 4 h of anoxia. Although calpain activity increased twofold in rat hepatocytes during anoxia, no increase in calpain activity occurred in HCC cells. Western and Northern blot analysis revealed greater or equivalent expression of calpains and calpastatin in HCC cells compared to hepatocytes. Because increases in cytosolic free Ca++ (Cai++) and phospholipid degradation products regulate calpains in vitro, we measured Cai++ and phospholipid degradation. Ca++i did not change in any cell types during 60 min of anoxia. In contrast, phospholipid degradation was fourfold greater in hepatocytes compared to HCC cells. Melittin, a phospholipase A2 activator, increased calpain activity and cell necrosis in all cell types; melittin-induced cell necrosis was ameliorated by a calpain protease inhibitor. In summary, these data demonstrate for the first time 1) calpain activation without a measureable increase in Ca++i, 2) phospholipase-mediated calpain activation in hepatocytes and HCC cells, and 3) the adaptive mechanism responsible for the resistance of HCC cells to anoxia-an inhibition of phospholipid-mediated calpain activation. Interruption of phospholipase-mediated calpain activation may be a therapeutic strategy for preventing anoxic cell injury.

A water channel closely related to rat brain aquaporin 4 is expressed in acid- and pepsinogen-secretory cells of human stomach

We isolated a cDNA clone encoding a water channel protein, aquaporin ( AQP), from human stomach. The encoded protein consisted of 323 amino acid residues, containing six putative transmembrane domains. The protein was designated human aquaporin 4 (hAQP4) because of its 94% sequence similarity to rat brain AQP4. Expression of hAQP4 cRNA in Xenopus oocytes resulted in a significant increase in osmotic water permeability, indicating that this protein functions as a water channel. Northern blot analysis demonstrated a strong signal of hAQP4 mRNA in brain, lung, and skeletal muscle as well as in stomach. Immunohistochemical experiments with human stomach tissues showed that hAQP4 as a protein is expressed mainly in cells located in the glandular portion of the fundic mucosa. These include chief cells which secrete pepsinogen and parietal cells which secrete hydrochloric acid. These results strongly indicate that hAQP4 is a principal factor involved in the osmotic regulation of pepsinogen and acid secretion in the stomach.

Molecular cloning and functional expression of the alpha1A-adrenoceptor of Medaka fish, Oryzias latipes

A genomic DNA encoding a subtype adrenoceptor (AR) was cloned from Medaka fish, Oryzias latipes, using an oligonucleotide probe corresponding to the consensus sequence of mammalian alpha-AR and beta-AR. The gene spans at least 9kbp, and the coding region consists of two exons split by an intron of 7.2 kbp located at the same position as those of mammalian alpha1B-AR genes. The gene encodes 470 amino acid residues, the sequence of which shows the highest similarity to that of mammalian alpha1A-AR (61%) and significant but lower similarities to other alpha-AR and beta-AR proteins (31-45%), indicating that the gene encodes a Medaka homolog of alpha1A-AR. To characterize the encoded protein, the mRNA was synthesized in vitro and injected into Xenopus oocytes. As a result, the oocytes responded to 100 nM epinephrine evoking a Ca2 + -dependent C1- current in the order of microamperes, which was not observed for oocytes injected with water alone. The response was reversibly inhibited by an alpha1-selective antagonist, WB4101 (2-[2,6-dimethoxphenoxyethyl]aminomethyl)-1,4-benzodioxane). Similar experiments using several adrenergic agonists revealed that Medaka alpha1A-AR responds to the following agonists in the order: epinephrine > or = (-)norepinephrine > oxymetazoline > or = methoxamine, which is similar to the responses of rat alpha1A receptor expressed in COS cells. The results indicate that fish contains adrenoceptor systems similar to those of mammals in terms of primary structure and pharmacological properties.

A cascade of degradative hydrolase activity contributes to hepatocyte necrosis during anoxia

Calpain proteases contribute to hepatocyte necrosis during anoxia. Our aim was to ascertain the mechanism causing calpain activation during anoxia. In rat hepatocytes, a twofold increase in calpain activity occurred despite the lack of an increase in cytosolic Ca2+ concentration ([Ca2+]i). The increase in calpain activity was not associated with an increase in calpain mRNA or a decrease in calpastatin mRNA expression. Because phospholipid degradation products generated by phospholipases can activate calpains at physiological [Ca2+]i, we determined the effect of phospholipase inhibitors and activators on calpain activity. Pretreatment of hepatocytes with fluphenazine, a phospholipase inhibitor, decreased calpain activation and improved cell survival. Melittin, a phospholipase A2 activator, increased calpain activity and potentiated cell killing. Finally, phospholipid degradation preceded the increase in calpain activity. Thus the enhanced calpain activity occurring in hepatocytes during anoxia 1) is regulated at the posttranslational level and 2) appears to be dependent on phospholipase activity. These data suggest a novel cascade for degradative hydrolase activity during hepatocyte necrosis by anoxia with phospholipase-mediated activation of calpains.

Effect of Z-100, an immunomodulator extracted from human type tubercle bacilli, on the pulmonary metastases of Lewis lung carcinoma in attempt to regulate suppressor T cells and suppressor factor, IL-4

In the present study, anti-metastatic effect of Z-100 on the spontaneous pulmonary metastases of Lewis lung carcinoma (3LL) was examined in an attempt to regulate suppressor T cells. When Z-100 (10 mg/kg) was daily injected i.p. after 3LL inoculation, survival rate of these mice was increased significantly (p < 0.05). In addition, the number of pulmonary metastatic colonies of 3LL in Z-100-treated mice were significantly decreased by 38% at 21 days, as compared with that of control mice (p < 0.05). Along with the decrease of pulmonary metastases, suppressor cell activity was also gradually reduced in these mice, as compared with that of control mice. When splenic suppressor cells (5 x 10(7) cells) from 3LL-bearing mice were adoptively transferred into normal mice (recipients) just before inoculation of 3LL, the development of pulmonary metastases in recipients was significantly accelerated. However, splenocytes from 3LL-bearing mice treated with Z-100 did not affect the development of pulmonary metastasis. The potential to accelerate the metastasis of splenic mononuclear cells from 3LL-bearing mice was decreased significantly by the treatment with anti-Thy 1.2 monoclonal antibody (mAb), anti-Lyt 2.2 mAb or anti-CD 11b mAb followed by complement. IL-4 activity in the sera of 3LL-bearing mice was detected 15 days after tumor inoculation (13 pg/ml) and gradually increased (18 pg/ml) 20 days after tumor inoculation. However, when Z-100 (10 mg/kg) was daily injected i.p., IL-4 activity in sera was decreased significantly, and the IL-4 activity was not detected in these mice on day 20. These results suggest that Z-100 could inhibit the pulmonary metastases in 3LL-bearing mice through the inhibition of suppressor T cell activity and a possible candidate of its effector molecule, IL-4.

Three-dimensional volume visualization of the in vivo human ocular lens showing localization of the cataract

An in vivo human lens containing a cataract has been visualized by volume rendering a transformed series of 60 rotated Scheimpflug digital images. The data set was obtained by rotating the Scheimpflug camera about the optic axis of the lens in 3-degree increments. The set of 60 Scheimpflug digital images were mathematically transformed into a new data set in which the images are oriented perpendicular to the optic axis of the eye. The transformed set of optical sections were first aligned to correct for eye movements during the data collection process, then rendered into a three-dimensional volume reconstruction with volume-rendering computer graphics techniques. The viewpoint and the transparency of the volume rendered in vivo human lens were varied in order to observe volume opacities in various regions of the lens. To help visualize lens opacities, the intensity of light scattering was pseudocolor-coded as an integral part of the three-dimensional volume rendering. Three-dimensional, pseudocolored volume rendering of the in vivo human ocular lens represents a new technique to visualize in vivo human cataracts.

Molecular cloning of a fish gene encoding a novel seven-transmembrane receptor related distantly to catecholamine, histamine, and serotonin receptors

A genomic DNA fragment encoding a G protein-coupled seven-transmembrane receptor was isolated from Medaka fish, Oryzias latipes. The encoded protein is similar in sequence to other receptors including catecholamine, histamine and serotonin receptors. However, the similarity is much lower than those among members of these receptor subfamilies, thus suggesting this seven-transmembrane receptor to be an orphan receptor whose ligand has not yet been identified. Genomic Southern blot analysis suggested that the fish genome contains additional receptor genes related to the isolated gene, indicating that this novel receptor, possibly with its related receptors, might constitute a novel subfamily of the seven-transmembrane receptor superfamily.

Cloning of cDNA and genomic DNA encoding fibroblast growth factor receptor-4 of Xenopus laevis

We have isolated and characterized the cDNA and genomic DNA encoding fibroblast growth factor receptor-4 of Xenopus laevis (XFGFR-4). The gene encompassing the total coding sequence spans about 10 kb, consists of 17 exons, and has an organization very similar to those of mammalian genes encoding FGFR-1 and -2, except that the XFGFR-4 gene does not contain an alternative exon for the third immunoglobulin-like domain nor an internal poly(A)-addition site. Thus, XFGFR-4 appears not to generate multiple forms of mRNA, as are identified for the mammalian FGFR-1, -2 and -3 genes. The amino-acid sequence of XFGFR-4 shows high homology to other vertebrate FGFR-4 species, but the similarity was significantly lower than in the cases of FGFR-1 and -2. Northern blot analysis showed the XFGFR-4 mRNA to occur throughout X. laevis early embryogenesis in a profile different from those of X. laevis FGFR-1 and -2.

A dual functional signal mediator showing RhoGAP and phospholipase C-delta stimulating activities

We have cloned a novel regulator protein, p122, in the PLC-delta signalling pathway by screening a rat brain expression library with antiserum raised against purified phospholipase C-delta 1 (PLC-delta 1). This novel p122-RhoGAP binds to PLC-delta 1 and activates the phosphatidylinositol 4,5-bisphosphate (PIP2) hydrolyzing activity of PLC-delta 1. As suggested by the deduced amino acid sequence, this regulator protein shows a similarity to the GTPase activating protein (GAP) homology region of Bcr and possesses GAP activity for RhoA, but not for Rac1; no guanine nucleotide exchange activity for RhoA and Rac1 was detected. These findings suggest that this novel RhoGAP is involved in the Rho signalling pathway, probably downstream of Rho activation, and mediates the stimulation of PLC-delta, which leads to actin-related cytoskeletal changes through the hydrolysis of PIP2, which binds to actin binding proteins such as gelsolin and profilin.