LEF-1, a nuclear factor coordinating signaling inputs from wingless and decapentaplegic

wingless and decapentaplegic signal during endoderm induction in Drosophila to regulate expression of the homeotic gene Ultrabithorax. Here, we define a minimal wingless response sequence in the midgut enhancer of Ultrabithorax. We show that this sequence is recognized by the murine transcription factor LEF-1 (lymphocyte enhancer binding factor 1) in a ternary complex with armadillo protein, the cytoplasmic target of the wingless signaling pathway. In stable transformants, transcriptional stimulation of the Ultrabithorax enhancer by LEF-1 depends on armadillo. Furthermore, overexpression of LEF-1 bypasses the need for wingless signaling and causes phenotypes in the midgut, notum, and wing that mimic wingless hyperstimulation. Finally, efficient transcriptional stimulation by LEF-1 in the midgut depends also on the decapentaplegic response sequence and is limited spatially by decapentaplegic signaling. Thus, LEF-1 coordinates inputs from multiple positional signals, consistent with its architectural role in regulating the assembly of multiprotein enhancer complexes.

Characterization of a cDNA encoding a subunit of the rat brain rsec6/8 complex

Many proteins required for neurotransmission are homologous to proteins involved in the Golgi-to-plasma membrane stage of the yeast secretory pathway. A novel 17S complex composed of eight proteins including rsec6 and rsec8, the rat homologues of the yeast secretory proteins, Sec6p and Sec8p, has been identified in rat brain cytosol. Sec6p and Sec8p are components of a complex of at least seven proteins which are essential for secretion in yeast. While the complementary DNAs (cDNA) encoding rsec6 and rsec8 have been cloned [Ting et al. (1995) Proc. Natl. Acad. Sci. USA 92, 9613-9617], the other six components of the 17S complex remain undescribed. Using the peptide sequence obtained from p71, one of the subunits of the rat brain 17S complex, we isolated a full-length cDNA from a rat brain library. This cDNA is predicted to encode a hydrophilic protein of 82 kDa, similar in size to that observed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) for the endogenous rat brain rsec6/8 complex 71 kDa component. p71 contains domains of peptide sequence which display significant homology to regions of the tail domain of yeast type II myosin. Northern blot analysis of rat tissues indicates that messenger RNA transcripts of 3.1 and 4.4 kb encoding this protein are expressed broadly across several rat tissues in a pattern similar to that of rsec6 and rsec8 mRNA expression. A possible role for p71 as a point of interaction for proteins of the cytoskeleton and proteins involved in secretion is discussed.

Inhibition of angiogenesis in human glioblastomas by chromosome 10 induction of thrombospondin-1

Glioblastoma multiforme is distinguished from its less malignant astrocytoma precursors by intense angiogenesis and frequent loss of tumor suppressor genes on chromosome 10. Here we link these traits by showing that when a wild-type chromosome 10 was returned to any of three human glioblastoma cell lines U251, U87, or LG11, they lost their ability to form tumors in nude mice and switched to an antiangiogenic phenotype, as measured by the inhibition of capillary endothelial cell migration and of corneal neovascularization. This change in angiogenesis was directly due to the increased secretion of a potent inhibitor of angiogenesis, thrombospondin-1, because: (a) neutralizing thrombospondin completely relieved the inhibition; (b) the inhibitory activity of thrombospondin was not dependent on transforming growth factor beta; and (c) chromosome 10 introduction did not alter secreted inducing activity. The inducing activity was dependent on vascular endothelial cell growth factor and had an ED50 of 10 microg/ml in media conditioned by parental cells and 9-13 microg/ml in media conditioned by chromosome 10 revertants. Normal human astrocytes were also antiangiogenic due to secreted thrombospondin. The effect of chromosome 10 on thrombospondin production in vitro was reflected in patient material. Normal brain and lower grade astrocytomas known to retain chromosome 10 stained strongly for thrombospondin, but 12 of 13 glioblastomas, the majority of which lose chromosome 10, did not. These data indicate that the loss of tumor suppressors on chromosome 10 contributes to the aggressive malignancy of glioblastomas in part by releasing constraints on angiogenesis that are maintained by thrombospondin in lower grade tumors.

Mammalian homologues of yeast vacuolar protein sorting (vps) genes implicated in Golgi-to-lysosome trafficking

Sec1p, Vps33p, Vps45p and Sly1p constitute a family of proteins implicated in vesicle trafficking at distinct stages of the yeast secretory pathway. Several mammalian homologues of Sec1p have been described, including n-sec1 which has been implicated in the regulation of synaptic vesicle docking at the nerve terminal. We have characterized cDNA clones encoding three additional mammalian homologues belonging to this family: r-vps33a and r-vps33b from rat, which are 30 and 26% identical to yeast Vps33p, respectively, and h-vps45 from human which is 38% identical to yeast Vps45p at the amino acid (aa) level. Phylogenetic analysis of 16 Sec1p-related proteins from several species is consistent with the hypothesis that the evolution of this gene family parallels the specialization of vesicle trafficking to distinct intracellular compartments. By Northern analysis, each of these genes is expressed in all tissues examined (brain, spleen, lung, liver, skeletal muscle, kidney, testis). While n-sec1 binds syntaxin 1a, 2, and 3, r-vps33a, r-vps33b and h-vps45 do not bind any of the known syntaxins. We propose that the three proteins bind as yet unidentified syntaxin homologues involved in vesicle trafficking between the Golgi apparatus, prelysosomal compartment(s), and the lysosome.

The mammalian brain rsec6/8 complex

rsec6 and rsec8 are two components of a 17S complex in mammalian brain that is homologous to the yeast 834 kDa Sec6/8/15 complex which is essential for exocytosis. Purification and partial amino acid sequencing of the mammalian rsec6/8 complex reveals that it is composed of eight novel proteins with a combined molecular weight of 743 kDa. The complex is broadly expressed in brain and displays a plasma membrane localization in nerve terminals. Membrane associated rsec6/8 complex coimmunoprecipitates with syntaxin, a plasma membrane protein critical for neurotransmission. These data suggest a role for the mammalian rsec6/8 complex in neurotransmitter release via interactions with the core vesicle docking and fusion apparatus.

Decreased bone mineral density in premenopausal patients with systemic lupus erythematosus

To study bone mineral density (BMD) in premenopausal adult female patients with systemic lupus erythematosus (SLE) and its relation with clinical parameters, 56 SLE patients (mean age 31 years, mean disease duration 6.3 years) and 15 normal controls were studied. BMD at the lumbar vertebrae (L2-L4) was measured by dual energy X-ray absorptiometry (DEXA). Classification of BMD was made according to the WHO criteria in 1994. Correlation between BMD and clinical parameters was calculated. It was found BMD in the SLE patients (0.942 +/- 0.136 g/cm2) was lower than in the control group (1.055 +/- 0.080 g/cm2) (P < 0.01). According to the WHO criteria, 17 patients (30%) had normal BMD, 22 patients (40%) had osteopenia and 17 patients (30%) had osteoporosis. BMD was inversely correlated with disease duration in SLE patients (p < 0.005). The minimal disease duration for a female SLE patient to develop osteopenia was 3.5 years. In conclusion, SLE patients have lower lumbar BMD than normal controls. SLE patients with longer disease duration have lower BMD. In order to achieve early prevention of osteoporosis, we suggest that female SLE patients with disease duration for more than 3.5 years should take a BMD examination.

Linkage of a fusion peptide to a CTL epitope from the nucleoprotein of measles virus enables incorporation into ISCOMs and induction of CTL responses following intranasal immunization

The introduction of soluble protein antigens into the endogenous processing pathway is a prerequisite for the efficient induction of MHC class-1 restricted cytotoxic T-lymphocytes (CTLs). Antigens incorporated into immunostimulating complexes (ISCOMs) containing lipids and Quil-A are able to induce CD8+ CTL responses in vivo. Furthermore, lipopeptides have also been used to raise peptide-specific CTLs and bypass the requirement for the use of an adjuvant. Although conventional ISCOM technology is in general restricted to the use of hydrophobic proteins or fatty acid-derivitized proteins or peptides, we have demonstrated that the linkage of a conserved paramyxovirus fusion peptide to a CTL epitope NP29 (residues 281-290 of measles virus nucleoprotein) resulted in the incorporation of this hydrophilic CTL epitope into ISCOMs and the in vivo priming of peptide specific CTLs following intranasal immunization. In addition, the fusion peptide-CTL epitope chimera was able to efficiently sensitise P815 target cells for lysis by nucleoprotein specific CTLs induced following immunization of mice with recombinant RAd-68 adenovirus, suggesting the efficient introduction of the peptide into the class-1 restricted antigen processing pathway. Furthermore, immunization of mice with this fusion peptide chimera in saline was able to prime an NP29-specific CTL response despite the absence of adjuvant.

Efficient binding to the MHC class I K(d) molecule of synthetic peptides in which the anchoring position 2 does not fit the consensus motif

Peptides eluted from the MHC class I K(d) molecule are generally nonamers that display a strong preference for Tyr in position 2 and Ile or Leu in position 9. We investigated the binding ability of several synthetic peptides which did not fit this consensus motif. In our peptides, Tyr(2) was substituted by other amino acids, i.e. LeU, Ile or Met. These peptides were variants of the 252-260 K(d)-restricted peptide SYIPSAEKI derived from the Plasmodium berghei circumsporozoite protein. They bound to purified K(d) molecules in vitro with intermediate affinity. One of them was tested for in vivo stimulation of T cells and induced a cytotoxic response. These results demonstrate the importance of binding motif refinement to discover new binding characteristics and new ligands such as low-affinity peptides.

A mammalian homologue of SLY1, a yeast gene required for transport from endoplasmic reticulum to Golgi

We characterized rat cDNAs that predict a protein, r-Sly1, which is similar to SLY1, a yeast protein that plays a critical role in endoplasmic reticulum to Golgi apparatus vesicle trafficking. The r-Sly1 gene is expressed in all tissues examined.

rSec6 and rSec8, mammalian homologs of yeast proteins essential for secretion

Many of the molecules necessary for neurotransmission are homologous to proteins involved in the Golgi-to-plasma membrane stage of the yeast secretory pathway. Of 15 genes known to be essential for the later stages of vesicle trafficking in yeast, 7 have no identified mammalian homologs. These include the yeast SEC6, SEC8, and SEC15 genes, whose products are constituents of a 19.5S particle that interacts with the GTP-binding protein Sec4p. Here we report the sequences of rSec6 and rSec8, rat homologs of Sec6p and Sec8p. The rSec6 cDNA is predicted to encode an 87-kDa protein with 22% amino acid identity to Sec6p, and the rSec8 cDNA is predicted to encode a 110-kDa protein which is 20% identical to Sec8p. Northern blot analysis indicates that rSec6 and rSec8 are expressed in similar tissues. Immunodetection reveals that rSec8 is part of a soluble 17S particle in brain. COS cell cotransfection studies demonstrate that rSec8 colocalizes with the GTP-binding protein Rab3a and syntaxin 1a, two proteins involved in synaptic vesicle docking and fusion at the presynaptic terminal. These data suggest that rSec8 is a component of a high molecular weight complex which may participate in the regulation of vesicle docking and fusion in brain.

The induction of respiratory syncytial virus-specific cytotoxic T-cell responses following immunization with a synthetic peptide containing a fusion peptide linked to a cytotoxic T lymphocyte epitope

Previously published work has shown that a cytotoxic T-cell epitope (CTL) representing residues 82-90 of the M2 protein of respiratory syncytial virus (RSV) is the target for a protective response against the virus. In this report, we demonstrate that a synthetic peptide representing residues 81-95, when covalently linked to a fusion peptide derived from the conserved N-terminal 19 residues of the F1 protein of measles virus efficiently primes RSV-specific CTLs in vivo following immunization without adjuvant.

Distinct domains of syntaxin are required for synaptic vesicle fusion complex formation and dissociation

Membrane fusion resulting in neurotransmitter secretion forms the basis of neural communication. Three multimeric complexes of the protein syntaxin are important in this process: syntaxin and n-sec1; syntaxin, VAMP, and SNAP-25; and syntaxin, VAMP, SNAP-25, alpha SNAP, and NSF (20S complex). In this report, we demonstrate that unique, yet overlapping, domains of syntaxin are required to form these complexes. The formation of higher order heteromultimers has a set of structural requirements distinct from those required for dimeric interactions. Dissociation of the 20S complex by NSF following ATP hydrolysis requires amino-terminal regions of syntaxin that are outside of the binding domains for the 20S constituent proteins. These data are consistent with the hypothesis that conformational changes in syntaxin, resulting from protein-protein interactions and ATP hydrolysis by NSF, mediate neurotransmitter release.

Selectivity of cell cycle regulation of glucocorticoid receptor function

The restricted expression of some genes to distinct stages of the cell cycle is often brought about through alterations in the activity and/or abundance of specific transcription factors. Many cells have been shown to be unresponsive to glucocorticoid hormone action during the G2 phase of the mammalian cell cycle, suggesting that some activities of the glucocorticoid receptor (GR), a ligand-activated transcription factor, are subjected to cell cycle control. We show here that GR insensitivity in G2 is selective, affecting receptor-mediated transactivation from a simple glucocorticoid response element, but not repression from a composite glucocorticoid response element. Since glucocorticoid-dependent down-regulation of GR protein levels is also unaffected in G2, distinct activities of the receptor that participate in this homologous down-regulation must be operating as effectively in G2-synchronized cells as in asynchronous cells. Finally, the phosphorylation state of the GR is altered in G2-synchronized cells reflecting, in part, both site-specific phosphorylation and dephosphorylation events. These results suggest that, while GR may be a target for cell cycle regulated kinases and phosphatases, the resulting changes in receptor phosphorylation have an impact only on selected GR functions.

Specificity and regulation of a synaptic vesicle docking complex

Synaptic vesicles are proposed to dock at the presynaptic plasma membrane through the interaction of two integral membrane proteins of synaptic vesicles, VAMP and synaptotagmin, and two plasma membrane proteins, syntaxin and SNAP-25. We have characterized the binding properties of these proteins and observed SNAP-25 potentiation of VAMP 2 binding to syntaxins 1a and 4 but not syntaxins 2 or 3. n-sec1, a neuron-specific syntaxin-binding protein, bound syntaxin with nanomolar affinity, forming a complex that is distinct from the previously identified 7S and 20S syntaxin-containing complexes. This suggests that syntaxin exists in at least three states: bound to n-sec1, in a 7S particle, and in a 20S particle. Recombinant n-sec1 inhibited VAMP or SNAP-25 binding to syntaxin. We propose that the specific associations of VAMP, SNAP-25, and syntaxin mediate vesicle docking and that a syntaxin/n-sec1 complex precedes and/or regulates formation of these complexes.

Glucose metabolism in photoreceptor outer segments. Its role in phototransduction and in NADPH-requiring reactions

Glucose metabolism in the photoreceptor rod outer segment produces both ATP (GTP) and NADPH to support phototransduction and NADPH-requiring processes in this organelle. Glycolysis in isolated bovine rod outer segments produces 44.0 +/- 6.4 nmol of ATP/min/mg of protein or 5.7 mM ATP/min. This rate of ATP production is more than sufficient to maintain the basal rate of cGMP synthesis (0.86 mM cGMP/min) in the dark requiring 1.7 mM ATP/min. Following photoexcitation, the 4.5-fold increase in the turnover of cGMP requires an ATP synthesis rate of up to 7.7 mM ATP/min (Ames, A., Walseth, T. F., Heyman, R. A., Barad, M., Graeff, R. M., and Goldberg, N. D. (1986) J. Biol. Chem. 261, 13034-13042). Under these conditions the rate of ATP production by glycolysis as measured in isolated rod outer segments is not sufficient for the regeneration of cGMP. Additional energy is most likely provided by the phosphocreatine shuttle which transports high energy phosphate groups in the form of creatine phosphate from the rod inner segment to the rod outer segment for conversion to ATP. The hexose monophosphate pathway in bovine rod outer segments can produce up to 39.8 +/- 2.2 nmol of NADPH/min/mg of protein. This rate of NADPH production is sufficient to support both the reduction of retinal to retinol (1.2 +/- 0.2 nmol of NADPH/min/mg of protein) following the photobleaching of rhodopsin and glutathione reduction (1.1 +/- 0.1 nmol of NADPH/min/mg of protein) for the protection of rod outer segments from oxidative damage. These studies provide insight into the contribution of anaerobic glycolysis and the hexose monophosphate pathway in providing energy and nucleotides for phototransduction and other outer segment processes.

n-Sec1: a neural-specific syntaxin-binding protein

We have identified n-Sec1, a rat brain homolog of the yeast Sec1p protein that participates in the constitutive secretory pathway between the Golgi apparatus and the plasma membrane. The rat brain cDNA is predicted to encode a 68-kDa protein with 65% amino acid identity to Drosophila rop, 59% identity to Caenorhabditis elegans unc-18, and 27% identity to Saccharomyces cerevisiae Sec1p. By RNA blot analysis, n-Sec1 mRNA expression is neural-specific. An anti-peptide antiserum directed against the n-Sec1 carboxyl terminus detects a 68-kDa protein in rat brain cytosol and membranes, but not in peripheral tissues. In the presence of syntaxin 1a, a plasma membrane protein implicated in synaptic vesicle docking, n-Sec1 becomes membrane-associated. n-Sec1 binds to syntaxin 1a, 2, and 3 fusion proteins coupled to agarose beads, but not to syntaxin 4 fusion protein or beads coupled to a variety of other proteins. These findings indicate that n-Sec1 is a neural-specific, syntaxin-binding protein that may participate in the regulation of synaptic vesicle docking and fusion.

Differential diagnosis of extrahepatic biliary atresia from neonatal hepatitis: a prospective study

The clinical presentations of cholestasis in infancy caused by neonatal hepatitis and biliary atresia are very similar. Diagnosis may be difficult on many occasions, but the surgical treatment of biliary atresia should be performed as early as possible. We established a 3-day workup protocol for the differential diagnosis of biliary atresia and neonatal hepatitis and compared the diagnostic accuracy, sensitivity, specificity, and predictive values of various methods. One hundred and twenty-six infants, including 84 with neonatal hepatitis (age, 65.1 +/- 24.1 days) and 42 with biliary atresia (age, 60.3 +/- 31.1 days), were studied prospectively from July 1982 to December 1990. The diagnostic accuracy of various methods was as follows: liver histology, 96.8%; color of duodenal juice, 91.6%; peak radioisotope count in duodenal juice, 84.2%; ultrasonographic examination of the hepatobiliary system, 80.2%; and persistence of clay-colored stool, 80.2%. After stepwise logistic regression, the diagnostic methods of significance were liver biopsy, color of duodenal juice, abdominal ultrasonography, and stool color. However, stool color and the onset of jaundice could not differentiate severe neonatal hepatitis from biliary atresia. The diagnostic methods of significance then were liver biopsy and duodenal juice color. With this 3-day protocol, no biliary atresia was missed although four cases of neonatal hepatitis were misdiagnosed, resulting in unnecessary laparotomy; we found an overall diagnostic accuracy of 96.8%. We conclude that this 3-day diagnostic protocol is very helpful in the differential diagnosis of neonatal hepatitis and biliary atresia. Liver histologic examination is the most reliable single test for the differential diagnosis.

Carcinoma of the ampulla of Vater: long-term survival after surgical treatment

Ninety-one patients were identified as having carcinoma arising from the ampulla of Vater. Radical pancreaticoduodenectomy, using either a standard or pylorus-preserving method, was performed in 69 consecutive patients over a 30-year period. Frequent clinical findings included jaundice (84%), a weight loss of more than 10% of the body weight (75%), abdominal pain (59%), chills and fever (52%), pruritus (48%) and a palpable gallbladder (38%). Acute pancreatitis was present in 10%. Postoperative mortality was 11.6%. Surgical mortality was 23.1% from 1962 to 1971 and 12.5% from 1972 to 1981, but was reduced to 6.3% from 1982 to 1991. Surgical mortality was primarily due to pancreaticojejunostomy leaks. The five-year survival rate was 52% and the 10-year rate was 50%. Radical pancreaticoduodenectomy for ampullary carcinoma has a low mortality and should remain the procedure of choice for ampullary carcinoma.

Patterns of hepatitis B virus DNA integration in liver tissue of children with chronic infections

Although an integration of hepatitis B virus (HBV) DNA in children with chronic HBV infection has been documented at early phases of the disease, the incidence of this process is not known. Therefore we examined nine liver DNA specimens from chronic HBV carriers ages 5-14 years and one sample from a neonate delivered of a carrier mother, in order to determine the HBV DNA patterns of these patients at different ages and phases of chronic infection. The integrated HBV DNA was detected by Southern blot hybridization and analyzed by molecular cloning. Southern blot showed a smear pattern of HBV DNA integration in four of six chronic hepatitis patients (ages 5-14), as well as in one asymptomatic carrier (age 12). Multiple and random integrations occurred during chronic infections in childhood. The neonate did not, however, show signs of any integrations, suggesting that integration starts after HBV multiplication. A band pattern that suggested clonal growth of integrated liver cells was found in a chronic active hepatitis patient (age 9) and in one of two hepatocellular carcinoma patients (age 11). Molecular cloning in two cases with chronic active hepatitis showed that the HBV genome structure was preserved in five of six HBV DNA inserts. Our findings confirm that HBV DNA integration can occur at early stages of chronic HBV infection. In Japanese children, the process of integration seems to be common regardless of HBeAg/anti-HBe status.(ABSTRACT TRUNCATED AT 250 WORDS)

Cell cycle regulation of glucocorticoid receptor function

Glucocorticoid receptor (GR) nuclear translocation, transactivation and phosphorylation were examined during the cell cycle in mouse L cell fibroblasts. Glucocorticoid-dependent transactivation of the mouse mammary tumor virus promoter was observed in G0 and S phase synchronized L cells, but not in G2 synchronized cells. G2 effects were selective on the glucocorticoid hormone signal transduction pathway, since glucocorticoid but not heavy metal induction of the endogenous Metallothionein-1 gene was also impaired in G2 synchronized cells. GRs that translocate to the nucleus of G2 synchronized cells in response to dexamethasone treatment were not efficiently retained there and redistributed to the cytoplasmic compartment. In contrast, GRs bound by the glucocorticoid antagonist RU486 were efficiently retained within nuclei of G2 synchronized cells. Inefficient nuclear retention was observed for both dexamethasone- and RU486-bound GRs in L cells that actively progress through G2 following release from an S phase arrest. Finally, site-specific alterations in GR phosphorylation were observed in G2 synchronized cells suggesting that cell cycle regulation of specific protein kinases and phosphatases could influence nuclear retention, recycling and transactivation activity of the GR.

[Factors in recurrence after curative resection of rectal cancer]

Data on 409 Patients who had a curative resection for rectal cancer at the National Taiwan University Hospital between 1977 and 1989 were analysed to determine the independent effect on recurrence. In our series, the total operative mortality rate was 1.7% and the resectability rate was 88.1%. For these cases who received curative resection, the overall 5-year survival rate was 62.6%. The 5-year survival rate varied according to the Dukes' stage: stage A, 96.4%; stage B, 73.3% and stage C, 39.6%. The total recurrence rate after curative resection was 35.9%, including local recurrence 18.3%, systemic recurrence 12.0%, and combined recurrence 5.6%. According to Dukes' staging system, the recurrence rate for stage A, B and C were 0%, 22.4% and 63.8%, respectively. We used Cox's regression model to analyse the patients characteristics and pathological variables on recurrence and to assess the independent influence of each when all other factors were held constant. The pathological stage of the cancer had the strongest association. Other variables found to have an independent yet significant importance, were CEA level and tumor size. The identification of the patient group, at a high risk of recurrence, might promote a more judicious selection for surgical procedure and trials of adjuvant therapy.

Production and characterisation of a monoclonal antibody (Cx-99) against cervical carcinoma

An IgG1 monoclonal antibody (MAb Cx-99) has been established which recognises a surface antigen on epithelial cells, but not on fibroblastic or hematopoietic cells. Immunohistochemical studies showed that this antigen was present in all 37 squamous cell carcinomas (SCC) including 33 cervical SCC, and 30 of the 32 adenocarcinomas examined; most of the 33 cervical SCC were stained extensively. It was also detected in the culture medium of cervical cancer cell lines. In the normal cervix, this antigen was restricted to the undifferentiated basal cells. This observation suggests that the widespread expression of the antigen was triggered by oncogenesis. The MAb Cx-99 recognised an epitope on an asialyted glycoprotein which has an apparent molecular weight of 37 kilodaltons (kD) (and 2 minor proteins at 18 and 27 kD) and an isoelectric point (pI) of 5.3. It may have potential for studies on differentiation and oncogenesis and for diagnostic applications.

Tumorigenicity of interleukin-2 (IL-2)-cDNA-transfected L1210 lymphoma and its in vivo variants is modulated by changes in IL-2 expression; potential therapeutic implications

To study parameters that affect the tumorigenicity of L1210 lymphoma we have analyzed the structure of MHC class I antigens of this tumor. In addition this tumor was transfected with interleukin-2 (IL-2) cDNA in order to determine the effects of high concentrations of IL-2 within the tumor environment. The nucleotide sequence of the class I Kd, Dd and Ld mRNAs from this tumor showed that the encoded amino acid sequence of the corresponding antigens is normal, thus suggesting that the tumorigenicity of L1210 lymphoma is not due to defective antigen presentation to tumor-specific cytotoxic T cells. In contrast, induction of IL-2 expression by cDNA transfection led to loss of tumorigenicity of the IL-2-secreting tumor cells. However, a fraction of long-term-surviving mice developed progressively growing variant tumors that showed substantial decrease or loss of IL-2 expression. These results suggest that IL-2 secretion by tumors is suicidal but, because of tumor heterogeneity, IL-2-loss-variant tumors may arise that are able to escape the immune defenses of the host. The observed consistent loss of IL-2 expression in variant tumors implies that specific targeting of large quantities of IL-2 to tumor cells may be a valuable approach to immunotherapy of cancer. In addition we find that under specific gamma ray irradiation IL-2-secreting tumor cells lose their ability to multiply yet continue to secrete IL-2 at levels equivalent to those secreted by unirradiated cells. Such IL-2-secreting irradiated tumor cells were found to be superior immunogens in comparison to the irradiated parental tumor cells, suggesting their use as tumor vaccines.

Glycolytic enzymes and a GLUT-1 glucose transporter in the outer segments of rod and cone photoreceptor cells

The presence of glycolytic enzymes and a GLUT-1-type glucose transporter in rod and cone outer segments was determined by enzyme activity assays, glucose uptake measurements, Western blotting, and immunofluorescence microscopy. Enzyme activities of six glycolytic enzymes including hexokinase, phosphofructokinase, aldolase, glyceraldehyde-3-phosphate dehydrogenase, phosphoglycerate kinase, pyruvate kinase, and lactate dehydrogenase, were found to be present in purified rod outer segment (ROS) preparations. Immunofluorescence microscopy of bovine and chicken retina sections labeled with monoclonal antibodies against glyceraldehyde-3-phosphate dehydrogenase, phosphoglycerate kinase, and lactate dehydrogenase have confirmed that these enzymes are present in rod and cone outer segments and not simply contaminants from the inner segments or other cells. Rod outer segments were also found to contain glucose transport activity as detected by 3-O-[14C]methylglucose uptake and exchange. The glucose transporter had a Km of 6.3 mM and a Vmax of 0.15 nmol of 3-O-methylglucose/s/mg of ROS membrane protein for net uptake and a Km of 29 mM and a Vmax of 1.06 nmol of 3-O-methylglucose/s/mg of ROS membrane protein for equilibrium exchange. These Km values for net uptake and equilibrium exchange are similar to values obtained for human red blood cells and are characteristic of GLUT-1-type glucose transporter. The transport was inhibited by both cytochalasin B and phloretin. Western blot analysis and immunofluorescence microscopy using type-specific glucose transporter antibodies indicated that both rod and cone outer segment plasma membranes have a GLUT-1 glucose transporter of Mr 45K as found in red blood cells and brain microsomal membranes. Solid-phase radioimmune competitive inhibition studies indicated that rod outer segment plasma membranes contained 15% the number of glucose transporters found in human red blood cell membranes and had an estimated density of 400 glucose transporter per micron2 of plasma membrane. These studies support the view that outer segments can generate energy in the form of ATP and GTP by anaerobic glycolysis to supply at least some of the energy requirements for phototransduction and other metabolic processes.