The impact on utilities of differences in body weight among Canadian patients with type 2 diabetes

OBJECTIVE

The objective of this study was to estimate utility values for hypothetical health states that describe differences in weight and quality of life associated with type 2 diabetes mellitus (DM) from Canadians with type 2 DM. The impact on utility values was examined separately for participants with a body mass index (BMI) of 18 to less than 25 kg/m(2) ('healthy'), 25 to less than 30 ('overweight'), and 30 or more ('obese').

METHODS

The health state descriptions were modified from a published diabetes utility study. Health states included a base-case type 2 DM health state (at participants' current weight), and six health states where the weight and attendant quality of life impact varied (base case ±3%, ±5%, and ±7% weight). Utilities were elicited using the time trade-off technique. Linear regression modeling was used to estimate the utility increment or decrement associated with a one unit difference in BMI.

RESULTS

Among 96 participants, the mean age was 55 years and 51% were men. The mean BMI was 32 kg/m(2) and 84% wanted to lose weight. The mean (SD) utility for the base-case state was 0.911 (0.013). Mean utilities (utility decrements) were 0.907 (-0.004), 0.865 (-0.046) and 0.806 (-0.105) for the health states describing an increased weight of 3%, 5% and 7%, respectively; and 0.923 (+0.012), 0.940 (+0.029) and 0.949 (+0.038) for the health states describing a decreased weight of 3%, 5% and 7%, respectively. For every increase of 1 kg/m(2) BMI there was an associated decrease in utility of 0.0472 (95% CI: 0.0375, 0.0569) and for every decrease of 1 kg/m(2) BMI there was an associated increase in utility of 0.0171 (95% CI: 0.0103, 0.0238).

CONCLUSIONS

The preferences of Canadian patients with type 2 DM for diabetes-related health states varied according to the weight, and quality of life impact, associated with that health state. Increased weight had a greater effect on utilities than decreased weight.

Cost-effectiveness of cetuximab for the first-line treatment of squamous cell carcinoma of the head and neck (SCCHN) in Canada

e17000

Background: Squamous cell carcinoma of the head and neck (SCCHN) is a disfiguring and potentially fatal condition. Cetuximab is a new therapeutic option which has been shown to improve locoregional control (LRC) and reduce mortality in the treatment of locally and regionally advanced disease. Objectives: To estimate the incremental cost-utility of cetuximab plus radiotherapy (CxRT) versus cisplatin plus radiotherapy (CsRT) among platinum eligible patients and versus RT alone in platinum ineligible patients in Canada. Methods: A lifetime transition model was developed with four health states: 1) acute treatment phase; 2) LRC; 3) disease progression and 4) death. Adverse events were accounted for in the first two states. Efficacy of treatment (LRC and overall survival) was obtained from the literature. Based on network meta-analyses, CsRT and CxRT were assumed to have equal efficacy. Resource use was obtained from published literature and clinical expert opinion. The perspective adopted was that of a provincial ministry of health or cancer agency. Utilities were obtained from a previous study of United Kingdom oncology nurses. Costs (2008 CDN$) and outcomes were discounted at 5% annually. Incremental cost-effectiveness ratios (ICERs) were reported with one-way and probabilistic sensitivity analyses performed to assess robustness of results. A priori sub-group analyses were carried out by baseline Karnofsky Performance Scores (KPS). Results: Among all patients (KPS 60–100), the ICERs comparing CxRT to RT were $19,740/QALY (95% CI: $11,122 to $695,295) among platinum ineligible patients and for CxRT vs. CsRT, $99,147/QALY (95% CI: $75,998 to $148,951) among platinum eligible patients. ICERs decreased with increasing KPS scores. At a willingness to pay of $50,000 among platinum-ineligible patients and $100,000 among platinum-eligible patients, the likelihood that CxRT is cost-effective is 90% and 45% respectively. Sensitivity analyses indicated that time horizon and assumptions about CsRT effectiveness had the largest impact on results. Conclusion: Cetuximab is an economically attractive option for SCCHN patients.

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Mammalian inositol polyphosphate 5-phosphatase II can compensate for the absence of all three yeast Sac1-like-domain-containing 5-phosphatases

Phosphatidylinositol 4,5-bisphosphate [PtdIns(4,5)P(2)] plays a complex role in generating intracellular signalling molecules, and also in regulating actin-binding proteins, vesicular trafficking and vacuolar fusion. Four inositol polyphosphate 5-phosphatases (hereafter called 5-phosphatases) have been identified in Saccharomyces cerevisiae: Inp51p, Inp52p, Inp53p and Inp54p. Each enzyme contains a 5-phosphatase domain which hydrolyses PtdIns(4,5)P(2), forming PtdIns4P, while Inp52p and Inp53p also express a polyphosphoinositide phosphatase domain within the Sac1-like domain. Disruption of any two yeast 5-phosphatases containing a Sac1-like domain results in abnormalities in actin polymerization, plasma membrane, vacuolar morphology and bud-site selection. Triple null mutant 5-phosphatase strains are non-viable. To investigate the role of PtdIns(4,5)P(2) in mediating the phenotype of double and triple 5-phosphatase null mutant yeast, we determined whether a mammalian PtdIns(4,5)P(2) 5-phosphatase, 5-phosphatase II, which lacks polyphosphoinositide phosphatase activity, could correct the phenotype of triple 5-phosphatase null mutant yeast and restore cellular PtdIns(4,5)P(2) levels to near basal values. Mammalian 5-phosphatase II expressed under an inducible promoter corrected the growth, cell wall, vacuolar and actin polymerization defects of the triple 5-phosphatase null mutant yeast strains. Cellular PtdIns(4,5)P(2) levels in various 5-phosphatase double null mutant strains demonstrated significant accumulation (4.5-, 3- and 2-fold for Deltainp51Deltainp53, Deltainp51Deltainp52 and Deltainp52Deltainp53 double null mutants respectively), which was corrected significantly following 5-phosphatase II expression. Collectively, these studies demonstrate the functional and cellular consequences of PtdIns(4,5)P(2) accumulation and the evolutionary conservation of function between mammalian and yeast PtdIns(4,5)P(2) 5-phosphatases.

The yeast inositol polyphosphate 5-phosphatases inp52p and inp53p translocate to actin patches following hyperosmotic stress: mechanism for regulating phosphatidylinositol 4,5-bisphosphate at plasma membrane invaginations

The Saccharomyces cerevisiae inositol polyphosphate 5-phosphatases (Inp51p, Inp52p, and Inp53p) each contain an N-terminal Sac1 domain, followed by a 5-phosphatase domain and a C-terminal proline-rich domain. Disruption of any two of these 5-phosphatases results in abnormal vacuolar and plasma membrane morphology. We have cloned and characterized the Sac1-containing 5-phosphatases Inp52p and Inp53p. Purified recombinant Inp52p lacking the Sac1 domain hydrolyzed phosphatidylinositol 4,5-bisphosphate [PtdIns(4,5)P(2)] and PtdIns(3, 5)P(2). Inp52p and Inp53p were expressed in yeast as N-terminal fusion proteins with green fluorescent protein (GFP). In resting cells recombinant GFP-tagged 5-phosphatases were expressed diffusely throughout the cell but were excluded from the nucleus. Following hyperosmotic stress the GFP-tagged 5-phosphatases rapidly and transiently associated with actin patches, independent of actin, in both the mother and daughter cells of budding yeast as demonstrated by colocalization with rhodamine phalloidin. Both the Sac1 domain and proline-rich domains were able to independently mediate translocation of Inp52p to actin patches, following hyperosmotic stress, while the Inp53p proline-rich domain alone was sufficient for stress-mediated localization. Overexpression of Inp52p or Inp53p, but not catalytically inactive Inp52p, which lacked PtdIns(4,5)P(2) 5-phosphatase activity, resulted in a dramatic reduction in the repolarization time of actin patches following hyperosmotic stress. We propose that the osmotic-stress-induced translocation of Inp52p and Inp53p results in the localized regulation of PtdIns(3,5)P(2) and PtdIns(4,5)P(2) at actin patches and associated plasma membrane invaginations. This may provide a mechanism for regulating actin polymerization and cell growth as an acute adaptive response to hyperosmotic stress.

The cellular response to unfolded proteins: intercompartmental signaling

Both prokaryotic and eukaryotic cells respond to the accumulation of unfolded proteins by increasing the transcription of genes encoding molecular chaperones and other stress-responsive proteins. Different sets of genes are activated when particular cellular compartments are burdened with unfolded proteins. Cells thus maintain mechanisms to monitor changes in the concentration of unfolded proteins not only in the cytosol, but also in membrane-bound extracytoplasmic compartments. During the past year, work in yeast has identified a transmembrane receptor that appears to play a pivotal role in the regulation of protein folding. This receptor monitors the concentration of available chaperone molecules in the endoplasmic reticulum and transmits a signal to the cytosol to activate the transcription of nuclear genes encoding chaperones that are localized in the endoplasmic reticulum. Work using Escherichia coli suggests that prokaryotes also contain an intercompartmental 'unfolded protein' signaling pathway, in this case from the periplasmic space or outer membrane to the cytoplasm.

Genetic instability in human ovarian cancer cell lines

We have analyzed the stability of microsatellites in cell lines derived from human ovarian cancers and found that 5 out of 10 of the ovarian tumor cell lines are genetically unstable at the majority of the loci analyzed. In clones and subclones derived serially from one of these cell lines (2774; serous cystadenocarcinoma), a very high proportion of microsatellites distributed in many different regions of the genome change their size in a mercurial fashion. We conclude that genomic instability in ovarian tumors is a dynamic and ongoing process whose high frequency may have been previously underestimated by PCR-based allelotyping of bulk tumor tissue. We have identified the source of the genetic instability in one ovarian tumor as a point mutation (R524P) in the human mismatch-repair gene MSH2 (Salmonella MutS homologue), which has recently been shown to be involved in hereditary nonpolyposis colorectal cancer. Patient 2774 was a 38-year-old heterozygote, and her normal tissue carried both mutant and wild-type alleles of the human MSH2 gene. However the wild-type allele was lost at some point early during tumorigenesis so that DNA isolated either from the patient's ovarian tumor or from the 2774 cell line carries only the mutant allele of the human MSH2 gene. The genetic instability observed in the tumor and cell line DNA, together with the germ-line mutation in a mismatch-repair gene, suggest that the MSH2 gene is involved in the onset and/or progression in a subset of ovarian cancer.

Low density lipoprotein receptor-related protein is necessary for the internalization of both tissue-type plasminogen activator-inhibitor complexes and free tissue-type plasminogen activator

Tissue-type plasminogen activator (t-PA) is used as a thrombolytic agent in treatment of myocardial infarction. However, large doses of this agent must be administered in treatment to maintain a thrombolytic state because t-PA is cleared rapidly from circulation. We designed specific ligands to distinguish between two major mechanisms by which t-PA is taken into cells and degraded. One of these mechanisms involves internalization of complexes between t-PA and its cognate inhibitor plasminogen activator inhibitor type-1 (PAI-1); the other mechanism is independent of PAI-1. Using specific inhibitors for low density lipoprotein receptor-related protein/alpha 2-macroglobulin receptor (LRP), we show that the degradation by hepatocytes of both free t-PA and t-PA.PAI-1 complexes involve the receptor LRP. We demonstrate that fibroblasts degrade both free t-PA (PAI-1-independent) and t-PA complexed with its specific inhibitor PAI-1 (PAI-1-dependent), whereas genetically altered fibroblasts that do not express LRP neither internalize nor degrade these ligands. We also show that a PAI-1-independent, t-PA ligand can inhibit the degradation of both free t-PA and t-PA.PAI-1 complexes. We propose LRP is the receptor for both PAI-1-independent and PAI-1-dependent t-PA ligands.

Capacity of simian virus 40 T antigen to induce self-tolerance but not immunological privilege in the anterior chamber of the eye

Transgenic mice bearing the simian virus 40 (SV40) large T oncogene developed progressively growing intraocular tumors and displayed characteristics of immunological tolerance to SV40 T antigen. Transgenic mice failed to mount CTL responses to SV40 T antigen-bearing tumor cell lines derived from the transgenic intraocular tumors. Spleen cells from transgenic hosts were able to prevent the in vivo and in vitro generation of CTL responses by lymphocytes from normal syngeneic FVB/N mice. Adoptive transfer of spleen cells from tolerant transgenic donors temporarily inhibited the immunological rejection of SV40 T antigen-positive tumor cells transplanted to normal syngeneic FVB/N recipients. Thus, introduction of SV40 transforming sequences into the mouse germline induced tolerance to SV40 T antigen. However, in normal FVB/N mice, SV40 T antigen-bearing tumor cells failed to experience immune privilege in the anterior chamber and did not elicit systemic down-regulation of delayed-type hypersensitivity responses that characteristically occur when antigens are introduced into the anterior chamber. The results indicate that within the anterior chamber of the eye, SV40 T antigen-bearing cells are perceived by the host's immune system much differently than are other categories of antigen. Thus, SV40 T antigen effectively induces self-immunological tolerance when its gene is introduced into the host's germline but fails to experience immunological privilege in the anterior chamber of the eye in normal hosts.

A transmembrane protein with a cdc2+/CDC28-related kinase activity is required for signaling from the ER to the nucleus

In eukaryotic cells, the accumulation of unfolded proteins in the endoplasmic reticulum (ER) triggers a signaling pathway from the ER to the nucleus. Several yeast mutants defective in this pathway map to the ERN1 gene, which protects cells from lethal consequences of stress by signaling for increased expression of BiP and other ER proteins. ERN1 encodes a 1115 amino acid transmembrane protein (Ern1p) whose glycosylated N-terminal portion is located inside microsomes and whose cytoplasmic C-terminal portion carries an essential protein kinase activity. We postulate that Ern1p is the proximal sensor of events in the ER and that binding of ligand causes transduction of information across the ER membrane, leading to activation of a specific set of transcription factors.

Proline isomerases function during heat shock

The cyclophilins (CYPs) and FK506 binding proteins (FKBPs) are two families of distinct proline isomerases that are targets for a number of clinically important immunosuppressive drugs. Members of both families catalyze cis/trans isomerization of peptidyl-prolyl bonds, which can be a rate-limiting step during protein folding in vitro and in vivo. We demonstrate in Saccharomyces cerevisiae that heat shock causes a 2- to 3-fold increase in the level of mRNA encoded by the major cytoplasmic CYP gene, CYP1. The cloned CYP1 promoter confers heat-inducible expression upon a reporter gene, and transcriptional induction is mediated through sequences similar to the consensus heat shock response element. Disruption of CYP1 decreases survival of cells following exposure to high temperatures, indicating that CYP1 plays a role in the stress response. A second CYP gene, CYP2, encodes a cyclophilin that is located within the secretory pathway. Its expression is also stimulated by heat shock, and cells containing a disrupted CYP2 allele are more sensitive than wild-type cells to heat. By contrast, expression of the FKB1 gene, which encodes a cytoplasmic member of the yeast FKBP family, is neither heat responsive nor necessary for survival after exposure to heat stress.

The promoter region of the yeast KAR2 (BiP) gene contains a regulatory domain that responds to the presence of unfolded proteins in the endoplasmic reticulum

The endoplasmic reticulum (ER) of eukaryotic cells contains an abundant 78,000-Da protein (BiP) that is involved in the translocation, folding, and assembly of secretory and transmembrane proteins. In the yeast Saccharomyces cerevisiae, as in mammalian cells, BiP mRNA is synthesized at a high basal rate and is further induced by the presence of increased amounts of unfolded proteins in the ER. However, unlike mammalian BiP, yeast BiP is also induced severalfold by heat shock, albeit in a transient fashion. To identify the regulatory sequences that respond to these stimuli in the yeast KAR2 gene that encodes BiP, we have cloned a 1.3-kb segment of DNA from the region upstream of the sequences coding for BiP and fused it to a reporter gene, the Escherichia coli beta-galactosidase gene. Analysis of a series of progressive 5' truncations as well as internal deletions of the upstream sequence showed that the information required for accurate transcriptional regulation of the KAR2 gene in S. cerevisiae is contained within a approximately 230-bp XhoI-DraI fragment (nucleotides -245 to -9) and that this fragment contains at least two cis-acting elements, one (heat shock element [HSE]) responding to heat shock and the other (unfolded protein response element [UPR]) responding to the presence of unfolded proteins in the ER. The HSE and UPR elements are functionally independent of each other but work additively for maximum induction of the yeast KAR2 gene. Lying between these two elements is a GC-rich region that is similar in sequence to the consensus element for binding of the mammalian transcription factor Sp1 and that is involved in the basal expression of the KAR2 gene. Finally, we provide evidence suggesting that yeast cells monitor the concentration of free BiP in the ER and adjust the level of transcription of the KAR2 gene accordingly; this effect is mediated via the UPR element in the KAR2 promoter.

Tyrosine 67 in the epidermal growth factor-like domain of tissue-type plasminogen activator is important for clearance by a specific hepatic receptor

Human tissue-type plasminogen activator (t-PA) is cleared rapidly from the circulation by hepatic receptors, one of which recognizes a site in the epidermal growth factor-like domain of the molecule. To define this site more precisely, we have used oligonucleotide-mediated mutagenesis to introduce amino acid substitutions at specific positions located in turns that connect antiparallel beta-sheets in the epidermal growth factor-like domain. Mutated t-PA proteins with amino acid substitutions of the tyrosine residue at position 67 showed markedly lower rates of endocytosis and degradation by cultured cells of the rat hepatoma (H4) line that express a specific receptor for t-PA, and their half-life in the circulation of rats was extended significantly because of a reduction in the rate of the rapid alpha-phase of clearance. The enzymatic properties and fibrinolytic activity of these mutants in vitro were not significantly different from those of wild-type t-PA. We conclude that tyrosine 67 comprises a key determinant in the clearance of t-PA by a specific hepatic receptor.

Protein folding in the cell

In the cell, as in vitro, the final conformation of a protein is determined by its amino-acid sequence. But whereas some isolated proteins can be denatured and refolded in vitro in the absence of other macromolecular cellular components, folding and assembly of polypeptides in vivo involves other proteins, many of which belong to families that have been highly conserved during evolution.

Complementing mutant alleles define three loci involved in mannosylation of Man5-GlcNAc2-P-P-dolichol in Chinese hamster ovary cells

Dolichol-linked oligosaccharides consisting of two N-acetylglucosamine, nine mannose, and three glucose residues (Glc3Man9GlcNAc2) are transferred to proteins that contain the consensus sequence Asn-X-Ser/Thr. This transfer occurs upon protein import into the lumen of the endoplasmic reticulum. An intermediate in the biosynthesis of the Glc3Man9GlcNAc2 lipid-linked oligosaccharide contains two GlcNAc and five mannose residues. This intermediate serves as a substrate for further mannosylation and glucosylation before transfer to protein. The addition of the sixth mannose residue to this intermediate requires the enzyme mannosyltransferase VI and the mannose donor, mannose-P-dolichol. Several different CHO cell line mutants that fail to efficiently catalyze this transfer have been described. In this report, we examine seven independent mutant cell lines with various biochemical phenotypes and demonstrate that all can be assigned to one of three genetic complementation groups. One mutation affects mannose-P-dolichol biosynthesis (Lec15), three affect dolichol phosphate biosynthesis (Lec9), and three appear to affect the functional orientation of enzyme substrates (PIR).

The functional efficiency of a mammalian signal peptide is directly related to its hydrophobicity

We have previously shown that the signal sequence of the Saccharomyces cerevisiae vacuolar protein carboxypeptidase Y (CPY) does not function in mammalian cells unless a glycine residue in the central core is replaced by leucine. Additional mutants were constructed to investigate the features of this hydrophobic core (h) region that are important for signal sequence function in mammalian cells. We find that the degree of hydrophobicity of the h region of any particular mutant signal is directly related to the efficiency with which it directs the translocation of CPY. A minimal h region in a functional signal appears to consist of five hydrophobic residues interrupted by 1 glycine. Analysis of potential secondary structures suggests that a functional mutant signal is more likely than the nonfunctional CPY signal to adopt either a beta strand or an alpha-helical conformation.

Transport and assembly processes in the endoplasmic reticulum

Until recently, the endoplasmic reticulum (ER) of eukaryotic cells was regarded as an open corridor for the unregulated movement of newly-synthesized exocytotic proteins from their site of membrane translocation to the vesicles that ferry them from the transitional elements of the ER to the Golgi apparatus. Moreover, it was widely assumed that the folding and assembly of newly translocated polypeptides into their tertiary and quaternary structure is a spontaneous process that does not involve the intervention of other cellular proteins. In this article we review evidence that the ER is a highly discriminatory organelle that grants passage only to proteins that have attained an essentially native conformation, and summarize current knowledge about resident ER proteins that appear to facilitate and/or monitor protein folding and assembly in this organelle.

S. cerevisiae encodes an essential protein homologous in sequence and function to mammalian BiP

The endoplasmic reticulum (ER) of mammalian cells contains a 78 kd protein (BiP) that is believed to assist in the folding of secretory and transmembrane proteins. We have used a cDNA encoding mouse BiP to isolate the homologous gene from S. cerevisiae, which encodes a sequence of 682 amino acids, 431 of which are identical to mouse BiP. Like its mammalian counterpart, yeast BiP is encoded by an HSP70-like gene whose transcription is stimulated by the presence of unfolded polypeptides in the ER. The gene encoding yeast BiP is essential for cell growth and, unexpectedly, is identical to the recently cloned KAR2 gene. Expression of mammalian BiP in S. cerevisiae can complement a mutant allele of KAR2 that is temperature sensitive for growth and nonconditionally defective for karyogamy. These results suggest that deficiencies in BiP may cause generalized failure of protein folding in the ER, leading to pleiotropic effects on cellular metabolism.

Isolation of Chinese hamster ovary cell lines temperature conditional for the cell-surface expression of integral membrane glycoproteins

A procedure is described to select mutants of Chinese hamster ovary cells that are conditionally defective for the cell-surface expression of integral membrane glycoproteins, including the hemagglutinin (HA) of influenza virus. Using a combination of cell sorting and biochemical screening, seven cell lines were obtained that express more cell-surface HA at 32 degrees C than at 39 degrees C. The production of infectious vesicular stomatitis virus, whose growth requires insertion of an integral membrane protein into the plasma membrane, was also temperature conditional in the majority of these mutant cell lines. Five of the lines synthesized apparently normally core-glycosylated HA at the elevated temperature but the protein was neither displayed on the cell surface nor accumulated intracellularly. In these cell lines, little or no terminally glycosylated HA molecules were observed after synthesis at 39 degrees C. By contrast, the core glycosylation of HA and several other integral membrane proteins was abnormal in the remaining two cell lines at both permissive and restrictive temperatures, due to a lesion in a cellular gene(s) that affects the formation of and/or the addition of mannose-rich oligosaccharide chains to newly synthesized polypeptides. Although HA was transported to the plasma membrane at both 32 and 39 degrees C, it did not accumulate on the cell surface at the higher temperature, apparently because of an increased rate of degradation.

Addition of truncated oligosaccharides to influenza virus hemagglutinin results in its temperature-conditional cell-surface expression

In the preceding paper (Hearing, J., E. Hunter, L. Rodgers, M.-J. Gething, and J. Sambrook. 1989. J. Cell Biol. 108:339-353) we described the isolation and initial characterization of seven Chinese hamster ovary cell lines that are temperature conditional for the cell-surface expression of influenza virus hemagglutinin (HA) and other integral membrane glycoproteins. Two of these cell lines appeared to be defective for the synthesis and/or addition of mannose-rich oligosaccharide chains to nascent glycoproteins. In this paper we show that at both 32 and 39 degrees C in two mutant cell lines accumulate a truncated version, Man5GlcNAc2, of the normal lipid-linked precursor oligosaccharide, Glc3Man9GlcNAc2. This is possibly due to a defect in the synthesis of dolichol phosphate because in vitro assays indicate that the mutant cells are not deficient in mannosylphosphoryldolichol synthase at either temperature. A mixture of truncated and complete oligosaccharide chains was transferred to newly synthesized glycoproteins at both the permissive and restrictive temperatures. Both mutant cell lines exhibited altered sensitivity to cytotoxic plant lectins when grown at 32 degrees C, indicating that cellular glycoproteins bearing abnormal oligosaccharide chains were transported to the cell surface at the permissive temperature. Although glycosylation was defective at both 32 and 39 degrees C, the cell lines were temperature conditional for growth, suggesting that cellular glycoproteins were adversely affected by the glycosylation defect at the elevated temperature. The temperature-conditional expression of HA on the cell surface was shown to be due to impairment at 39 degrees C of the folding, trimerization, and stability of HA molecules containing truncated oligosaccharide chains.

The single-chain form of tissue-type plasminogen activator has catalytic activity: studies with a mutant enzyme that lacks the cleavage site

Tissue-type plasminogen activator (t-PA), the serine protease responsible for catalyzing the production of plasmin from plasminogen at the site of blood clots, is synthesized as a single-chain polypeptide precursor. Proteolytic cleavage at the C-terminal side of Arg275 generates a two-chain form of the enzyme whose subunits are held together by a single disulfide bond. We have measured the activities of both forms of the wild-type enzyme, as well as that of a mutant enzyme (Arg275----Gly), created by oligonucleotide-directed mutagenesis, that cannot be cleaved into a two-chain form. Both types of single-chain t-PAs are enzymatically active and exhibit identical Vmax and Km values when assayed with synthetic peptide substrates, indicating that the single amino acid change had no effect on the amidolytic activity of the enzyme. However, cleavage of wild-type t-PA into the two-chain form results in increased activity both on a peptide substrate and on the natural substrates Lys- and Glu-plasminogen in the absence or presence of stimulation by soluble fibrin. The enhanced activity is due to a 3-5-fold increase in the Vmax of the cleaved enzyme, rather than to any change in the Km values for the various substrates. During incubation with plasminogen, the single-chain form of wild-type t-PA is converted to the two-chain form by plasmin generated during the reaction. This conversion, from the less active form of the enzyme, results in a reaction that displays biphasic kinetics.(ABSTRACT TRUNCATED AT 250 WORDS)

Identification of immunoglobulin heavy chain binding protein as glucose-regulated protein 78 on the basis of amino acid sequence, immunological cross-reactivity, and functional activity

Immunoglobulin heavy chain binding protein (BiP) associates transiently with various proteins destined for the secretory pathway. To investigate the relationship between BiP and the 78K (K = 10(3) Mr) glucose-regulated protein (GRP78), we have determined a partial amino acid sequence of purified mouse BiP and isolated and sequenced a full-length cDNA clone encoding mouse GRP78. The 26 amino-terminal residues of the mature BiP protein are identical to a sequence of amino acids located near the start of the open reading frame encoding GRP78. A polyclonal antiserum raised against mouse GRP78 protein expressed in bacteria from the cloned GRP78 cDNA could immunoprecipitate complexes consisting of BiP and unfolded forms of immunoglobulin heavy chains. Furthermore, a monoclonal antibody raised against mouse BiP immunoprecipitated mouse GRP78 expressed in monkey CV-1 cells from an SV40-GRP78 recombinant vector. Finally, like the endogenous BiP of simian cells, mouse GRP78 associated with malfolded, non-glycosylated forms of influenza hemagglutinin (HA) when GRP78 and HA were co-expressed from SV40 vectors in CV-1 cells. These studies confirm that BiP is identical to GRP78. Comparison of the nucleic acid and deduced amino acid sequence of mouse GRP78 with those of other rodent and human GRP78s revealed an extremely high degree of sequence identity. BiP/GRP78 is closely related (approximately 60% identity) to the cytoplasmic 70K heat-shock proteins. Surprisingly, the carboxy-terminal 29 amino acids of BiP/GRP78, which are not conserved in HSP70 proteins, are almost identical in sequence to the steroidogenesis activator peptide found in the cytoplasm of rat Leydig tumor cells. Possible relationships between these polypeptides are discussed.

Addition of carbohydrate side chains at novel sites on influenza virus hemagglutinin can modulate the folding, transport, and activity of the molecule

We have constructed and expressed a series of mutant influenza virus hemagglutinins, each containing a new consensus site for glycosylation in addition to the seven sites found on the wild-type protein. Oligosaccharide side chains were added with high efficiency at four of the five novel sites, located on areas of the protein's surface that are not normally shielded by carbohydrate. Investigations of the structure, intracellular transport, and biological activities of the mutant hemagglutinin molecules indicated that (a) supernumerary carbohydrate side chains can be used to shield or disrupt functional epitopes on the surface of hemagglutinin, and (b) the presence of an additional oligosaccharide may cause temperature-dependent defects in the transport of the glycoprotein. We discuss the addition of supernumerary oligosaccharides as a general tool for shielding chosen areas of the surface of proteins that enter or traverse the secretory pathway.

Variants of human tissue-type plasminogen activator that lack specific structural domains of the heavy chain

The heavy chain of tissue plasminogen activator (t-PA) consists of four domains [finger, epidermal-growth-factor (EGF)-like, kringle 1 and kringle 2] that are homologous to similar domains present in other proteins. To assess the contribution of each of the domains to the biological properties of the enzyme, site-directed mutagenesis was used to generate a set of mutants lacking sequences corresponding to the axons encoding the individual structural domains. The mutant proteins were assayed for their ability to hydrolyze artificial and natural substrates in the presence and absence of fibrin, to bind to lysine-Sepharose and to be inhibited by plasminogen activator inhibitor-1. All the deletion mutants exhibit levels of basal enzymatic activity very similar to that of wild-type t-PA assayed in the absence of fibrin. A mutant protein lacking the finger domain has a 2-fold higher affinity for plasminogen than wild-type t-PA, while the mutant that lacks both finger and EGF-like domains is less active at low concentrations of plasminogen. Mutants lacking both kringles neither bind to lysine-Sepharose nor are stimulated by fibrin. However, mutants containing only one kringle (either kringle 1 or kringle 2) behave indistinguishably from one another and from the wild-type protein. We conclude that kringle 1 and kringle 2 are equivalent in their ability to mediate stimulation of catalytic activity by fibrin.

The presence of malfolded proteins in the endoplasmic reticulum signals the induction of glucose-regulated proteins

Two glucose-regulated proteins, GRP78 and GRP94, are major constituents of the endoplasmic reticulum (ER) of mammalian cells. These proteins are synthesized constitutively in detectable amounts under normal growth conditions; they can also be induced under a variety of conditions of stress including glucose starvation and treatment with drugs that inhibit cellular glycosylation, with calcium ionophores or with amino-acid analogues. Unlike the closely-related heat shock protein (HSP) family, the GRPs are not induced significantly by high temperature. Recently, GRP78 has been identified as the immunoglobulin heavy chain binding protein (BiP) (ref. 5 and Y.K. et al., in preparation) which binds transiently to a variety of nascent, wild-type secretory and transmembrane proteins and permanently to malfolded proteins that accumulate within the ER. We have tested the hypothesis that the presence of malfolded proteins may be the primary signal for induction of GRPs by expressing wild-type and mutant forms of influenza virus haemagglutinin (HA) in simian cells. Only malfolded HAs, whose transport from the ER is blocked, induced the synthesis of GRPs 78 and 94. Additional evidence is presented that malfolding per se, rather than abnormal glycosylation, is the proximal inducer of this family of stress proteins.

Translocation in yeast and mammalian cells: not all signal sequences are functionally equivalent

In Saccharomyces cerevisiae, nascent carboxypeptidase Y (CPY) is directed into the endoplasmic reticulum by an NH2-terminal signal peptide that is removed before the glycosylated protein is transported to the vacuole. In this paper, we show that this signal peptide does not function in mammalian cells: CPY expressed in COS-1 cells is not glycosylated, does not associate with membranes, and retains its signal peptide. In a mammalian cell-free protein-synthesizing system, CPY is not translocated into microsomes. However, if the CPY signal is either mutated to increase its hydrophobicity or replaced with that of influenza virus hemagglutinin, the resulting precursors are efficiently translocated both in vivo and in vitro. The implications of these results for models of signal sequence function are discussed.

Posttranslational translocation of influenza virus hemagglutinin across microsomal membranes

The biosynthesis of influenza virus hemagglutinin (HA) and its translocation across microsomal membranes were studied in a mammalian cell-free system. All forms of HA could be cotranslationally translocated with high efficiency. However, only truncated forms of HA were translocated after protein synthesis has been terminated. The efficiency of this posttranslational translocation was dependent on the extent of the truncation. Posttranslational translocation was ribosome dependent and occurred only in the presence of a functional N-terminal signal sequence. The molecular mechanism of protein targeting and translocation across the membrane of the endoplasmic reticulum is discussed.

On the role of the transmembrane anchor sequence of influenza hemagglutinin in target cell recognition by class I MHC-restricted, hemagglutinin-specific cytolytic T lymphocytes

We have examined the requirement for the transmembrane hydrophobic anchor sequence of the influenza hemagglutinin (HA) in the formation of the antigenic moiety on the surface of target cells recognized by class I MHC-restricted murine CTL. For this analysis we have used a line of CV-1 monkey epithelial cells that express the transfected murine H-2Kd gene product as target cells and have used recombinant SV40-based late replacement vectors to achieve expression of genes encoding wild-type and mutant forms of HA. We have found that the majority of Kd-restricted HA-specific CTL clones recognize target cells that express a secreted HA molecule that lacks the transmembrane and cytoplasmic domains of the parent glycoprotein. Several Kd-restricted CTL clones that recognize subtype-specific and crossreactive epitopes on HA fail to recognize the anchor-negative, secreted HA or chimeric HA molecules containing the transmembrane and cytoplasmic domains of unrelated glycoproteins. These CTL clones appear to be directed to antigenic epitopes located within the transmembrane domain of HA, as defined by their capacity to recognize target cells sensitized with a synthetic 23-amino-acid peptide corresponding to sequences within this domain. The implications of these results for class I MHC-restricted CTL recognition are discussed.

Antigen presentation pathways to class I and class II MHC-restricted T lymphocytes

Our observations on the cellular immune response to type-A influenza suggest the existence of two distinct pathways of protein antigen presentation to T lymphocytes. One of these pathways is involved with presentation of antigens introduced into the presenting cell from without. This exogenous presentation pathway is the well-recognized route of presentation of soluble and particulate antigens to T lymphocytes. This pathway probably involves uptake of antigen into endocytic vesicles, alteration of antigen within an intracellular compartment, and subsequent display of antigen on the presenting cell surface (Unanue 1984). The second pathway is one which we have tentatively designated as an endogenous presentation pathway. The constraints on this pathway have yet to be fully defined. At a minimum, this pathway appears to involve the presentation of antigens which are synthesized de novo in the presenting cell utilizing the cell's biosynthetic machinery. This pathway may also handle preformed antigens located within the cytosolic compartment of the presenting cell. Perhaps the most striking feature of these two antigen presentation pathways is the close association between the MHC restriction of an antigen-specific T lymphocyte and the pathway of antigen presentation to that T lymphocyte. Our data suggest that this association holds both at the effector level and at the level of induction of T lymphocytes. Thus, presentation of a given antigen by the endogenous pathway preferentially triggers a response from class I MHC-restricted T lymphocytes directed to that antigen. The molecular basis for this link of class I MHC-restriction to the endogenous pathway and MHC class II restriction to the exogenous pathway is unknown. It seems likely that interactions between MHC molecules and antigen within the presenting cell may be critical for the demarcation of these pathways. Thus, for example, antigen presented by the endogenous route may only be able to associate intracellularly with newly synthesized or recycling class I MHC molecules. An understanding of the molecular basis of this phenomenon will require detailed information on the expression, intracellular trafficking, and transport of class I and class II MHC molecules in the antigen-presenting cell. An unresolved issue, at least in the case of viral antigens, is the nature and form of the antigenic moieties presented by the exogenous and endogenous pathways. In the case of viral antigen presentation to class II MHC-restricted T lymphocytes, there is strong, albeit indirect, evidence for processing of antigen and recognition of fragments of viral polypeptides (Lamb et al. 1982, Hackett et al. 1983).(ABSTRACT TRUNCATED AT 400 WORDS)

Expression of human tissue-type plasminogen activator from lytic viral vectors and in established cell lines

We have used two kinds of vectors to express a cDNA of human tissue plasminogen activator (t-PA) in mammalian cells. In one case, cDNAs inserted into vectors based on bovine papilloma virus were introduced into cultured murine cells and cell lines were established that efficiently and continuously secrete enzymatically active t-PA into the medium. Second, the t-PA gene was used to replace the sequences of the simian virus (SV40) genome that code for the viral coat proteins. Virus stocks were generated and used to infect a stable line of cultured simian cells. During the resulting lytic infection, expression of the t-PA gene is governed by the potent SV40 late promoter and enzymatically active t-PA accumulates rapidly in the medium. We have used these two vector systems to analyze the biosynthesis and transport of recombinant t-PA and to compare its properties with those of "natural" t-PA secreted by the Bowes line of human melanoma cells. t-PA secreted from all three sources is identical in specific activity (approximately 20,000 units/mg) despite differences in patterns of terminal glycosylation. Furthermore, non-glycosylated t-PA synthesized in the presence of tunicamycin was secreted efficiently and was indistinguishable in specific activity from glycosylated t-PAs.

Analysis of progressive deletions of the transmembrane and cytoplasmic domains of influenza hemagglutinin

Site-directed oligonucleotide mutagenesis has been used to introduce chain termination codons into the cloned DNA sequences encoding the carboxy-terminal transmembrane (27 amino acids) and cytoplasmic (10 amino acids) domains of influenza virus hemagglutinin (HA). Four mutant genes were constructed which express truncated forms of HA that lack the cytoplasmic domain and terminate at amino acids 9, 14, 17, or 27 of the wild-type hydrophobic domain. Analysis of the biosynthesis and intracellular transport of these mutants shows that the cytoplasmic tail is not needed for the efficient transport of HA to the cell surface; the stop-transfer sequences are located in the hydrophobic domain; 17 hydrophobic amino acids are sufficient to anchor HA stably in the membrane; and mutant proteins with truncated hydrophobic domains show drastic alterations in transport, membrane association, and stability.

Expression of wild-type and mutant forms of influenza hemagglutinin: the role of folding in intracellular transport

The hemagglutinin of influenza virus is synthesized as a monomeric subunit that is cotranslationally translocated across the membrane of the rough endoplasmic reticulum. We show that folding and assembly of hemagglutinin monomers into trimeric structures takes approximately 7-10 min and is completed before the protein leaves the endoplasmic reticulum. Mutants of hemagglutinin that fail to be transported from the endoplasmic reticulum are blocked at different stages of the folding pathway. Unfolded molecules of hemagglutinin are associated with a cellular protein of 77 kd that has been shown previously to bind to IgG heavy chain in the endoplasmic reticulum of certain myelomas. We discuss why assembly of native structures is required for transport of proteins through the exocytotic pathway.

Heterologous transmembrane and cytoplasmic domains direct functional chimeric influenza virus hemagglutinins into the endocytic pathway

Chimeric genes were created by fusing DNA sequences encoding the ectodomain of the influenza virus hemagglutinin (HA) to DNA coding for the transmembrane and cytoplasmic domains of either the G glycoprotein of vesicular stomatitis virus or the gC glycoprotein of Herpes simplex virus 1. CV-1 cells infected with SV40 vectors carrying the recombinant genes expressed large amounts of the chimeric proteins, HAG or HAgC on their surfaces. Although the ectodomains of HAG and HAgC differed in their immunological properties from that of HA, the chimeras displayed the biological functions characteristic of the wild-type protein. Both HAG and HAgC bound erythrocytes as efficiently as HA did and, after brief exposure to an acidic environment, induced the fusion of erythrocyte and CV-1 cell membranes. However, the behavior of HAG and HAgC at the cell surface differed from that of HA in several important respects. HAG and HAgC were observed to collect in coated pits whereas wild-type HA was excluded from those structures. In the presence of chloroquine, which inhibits the exit of receptors from endosomes, HAG and HAgC accumulated in intracellular vesicles. By contrast, chloroquine had no effect on the location of wild-type HA. HAG and HAgC labeled at the cell surface exhibited a temperature-dependent acquisition of resistance to extracellular protease at a rate similar to the rates of internalization observed for many cell surface receptors. HA acquired resistance to protease at a rate at least 20-fold slower. We conclude that HAG and HAgC are efficiently routed into the endocytic pathway and HA is not. However, like HA, HAG was degraded slowly, raising the possibility that HAG recycles to the plasma membrane.

An efficient method for introducing macromolecules into living cells

The hemagglutinin (HA) of influenza virus was used to obtain efficient and rapid bulk delivery of antibodies and horseradish peroxidase (HRP) into the cytoplasm of living tissue culture cells. By exploiting HA's efficient cell surface expression, its high affinity for erythrocytes, and its acid-dependent membrane fusion activity, a novel delivery method was developed. The approach is unique in that the mediator of both binding and fusion (the HA) is present on the surfaces of the target cells. A recently developed 3T3 cell line which permanently expresses HA, Madin-Darby canine kidney cells infected with influenza virus, and CV-1 cells infected with a simian virus 40 vector carrying the HA gene were used as recipient cells. Protein-loaded erythrocytes were bound to the HA on the cell surface and a brief drop in pH to 5.0 was used to trigger HA's fusion activity and hence delivery. About 3 to 8 erythrocytes fused per 3T3 and CV-1 cell, respectively, and 75-95% of the cells received IgG or HRP. Quantitative analysis showed that 1.8 X 10(8) molecules of HRP and 1.4 X 10(7) IgG molecules were delivered per CV-1 cell and 6.2 X 10(7) HRP molecules per 3T3 cell. Cell viability, as judged by methionine incorporation into protein and cell growth and division, was not impaired. Electron and fluorescence microscopy showed that the fused erythrocyte membranes remained as discrete domains in the cell's plasma membrane. The method is simple, reliable, and nonlytic. The ability to simultaneously and rapidly deliver impermeable substances into large numbers of cells will permit biochemical analysis of the fate and effect of a variety of delivered molecules.

SV40 T antigen and the exocytotic pathway

A chimeric gene consisting of DNA coding for the 15-amino acid signal peptide of influenza virus hemagglutinin and the C-terminal 694 amino acids of SV40 large T antigen was inserted into a bovine papilloma virus (BPV) expression vector and introduced into NIH-3T3 cells. Cell lines were obtained that express high levels (approximately 5 X 10(6) molecules/cell) of the chimeric protein (HA-T antigen). The biochemical properties and intracellular localization of HA-T antigens were compared with those of wild-type T antigen. Wild-type T antigen. Wild-type T antigen is located chiefly in the cell nucleus, although a small fraction is detected on the cell surface. By contrast, HA-T antigen is found exclusively in the endoplasmic reticulum (ER). During biosynthesis, HA-T antigen is co-translationally translocated across the membrane of the ER, the signal peptide is cleaved and a mannose-rich oligosaccharide is attached to the polypeptide (T antigen contains one potential N-linked glycosylation site at Asn154). HA-T antigen does not become terminally glycosylated or acylated and little or none reaches the cell surface. These results suggest that T antigen is incapable of being transported along the exocytotic pathway. To explain the presence of wild-type T antigen on the surface of SV40-transformed cells, an alternative route is proposed involving transport of T antigen from the nucleus to the cell surface.

Mutations in the cytoplasmic domain of the influenza virus hemagglutinin affect different stages of intracellular transport

Mutations have been introduced into the cloned DNA sequences coding for influenza virus hemagglutinin (HA), and the resulting mutant genes have been expressed in simian cells by the use of SV40-HA recombinant viral vectors. In this study we analyzed the effect of specific alterations in the cytoplasmic domain of the HA molecule on its rate of biosynthesis and transport, cellular localization, and biological activity. Several of the mutants displayed abnormalities in the pathway of transport from the endoplasmic reticulum to the cell surface. One mutant HA remained within the endoplasmic reticulum; others were delayed in reaching the Golgi apparatus after core glycosylation had been completed in the endoplasmic reticulum, but then progressed at a normal rate from the Golgi apparatus to the cell surface; another was delayed in transport from the Golgi apparatus to the plasma membrane. However, two mutants were indistinguishable from wild-type HA in their rate of movement from the endoplasmic reticulum through the Golgi apparatus to the cell surface. We conclude that changes in the cytoplasmic domain can powerfully influence the rate of intracellular transport and the efficiency with which HA reaches the cell surface. Nevertheless, absolute conservation of this region of the molecule is not required for maturation and efficient expression of a biologically active HA on the surface of infected cells.

Cytotoxic T lymphocyte recognition of the influenza hemagglutinin gene product expressed by DNA-mediated gene transfer

We have used the technique of DNA-mediated gene transfer to examine cytotoxic T lymphocyte (CTL) recognition of the product of the cloned A/JAPAN/305/57 hemagglutinin (HA) gene in murine (L929) cells. Using both heterogeneous and homogeneous (clonal) populations of type A influenza-specific CTL, we have demonstrated that the HA molecule can serve as a target antigen for both the subtype-specific and the cross-reactive subpopulations of influenza-specific CTL. Our results also raise the possibility that other virus-specified polypeptides may serve as target molecules for cross-reactive CTL.

Influenza virus hemagglutinin expression is polarized in cells infected with recombinant SV40 viruses carrying cloned hemagglutinin DNA

Primary cell cultures of African Green monkey kidney (AGMK) contain polarized epithelial cells in which influenza virus matures predominantly at the apical surfaces above tight junctions. Influenza virus glycoproteins were found to be localized at the same membrane domain from which the virus budded. When polarized primary AGMK cells were infected with recombinant SV40 viruses containing DNA coding for either an influenza virus H1 or H2 subtype hemagglutinin (HA), the HA proteins were preferentially expressed at the apical surface in a manner identical to that observed in influenza virus-infected cells. Thus, cellular mechanisms for sorting membrane glycoproteins recognize some structural feature of the HA glycoprotein itself, and other viral proteins are not necessary for this process.

Construction of influenza haemagglutinin genes that code for intracellular and secreted forms of the protein

The DNA sequences encoding the amino-terminal signal peptide or the carboxy-terminal hydrophobic anchor have been deleted from a cloned gene coding for the haemagglutinin (HA) of influenza virus. The wild-type gene has previously been shown to be expressed with high efficiency from simian virus 40 (SV40)-HA recombinant vectors into a fully glycosylated protein that is displayed on the infected cell's surface in an antigenically and biologically active form. The anchor-minus HA also is glycosylated but is secreted efficiently into the medium. By contrast, the signal-minus HA is produced only at low levels, is not glycosylated and is located intracellularly.

Cell-surface expression of influenza haemagglutinin from a cloned DNA copy of the RNA gene

By replacing either the eight early or the late genes of SV40 with a cloned copy of the influenza virus haemagglutinin gene we have constructed recombinant viruses which, in infected cells, express large quantities of haemagglutinin. This glycoprotein, over 10(8) molecules of which are produced per cell, is identical in molecular weight to authentic influenza virus haemagglutinin, accumulates at the cell surface and displays haemabsorbing activity.

Integration of viral DNA sequences in cells transformed by adenovirus 2 or SV40

We have cloned and propagated in prokaryotic vectors the viral DNA sequences that are integrated in a variety of cells transformed by adenovirus 2 or SV40. Analysis of the clones reveals that the viral DNA sequences sometimes are arranged in a simple fashion, collinear with the viral genome; in other cell lines there are complex arrangements of viral sequences in which tracts of the viral genome are inverted with respect to each other. In several cases the nucleotide sequences at the joints between cell and viral sequences have been determined: usually there is a sharp transition between cellular and viral DNAs. The viral sequences are integrated at different locations within the genomes of different cell lines; likewise there is no specific site on the viral genomes at which integration occurs. Sometimes the viral sequences are integrated within repetitive cellular DNA, and sometimes within unique sequences. In some cases there is evidence that the viral sequences along with the flanking cell DNA have been amplified after integration. The sequences that flank the viral insertion in the line of SV40-transformed rat cells known as 14B have been used as probes to isolate, from untransformed rat cells, clones that carry the region of the chromosome in which integration occurred. Analysis of the structure of these clones by restriction endonculease digestion and heteroduplex formation shows that a rearrangement of cellular sequences has occurred, presumably as a consequence of integration.