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Biomedical subjects

S Kvist

Publications and source records attributed to S Kvist.

At least 19 recordsLinked to original sources
PubMed2001

Reduced medication and normalization of vascular structure, but continued hypertension in renovascular patients after revascularization.

OBJECTIVE: The effect of invasive treatment of renal artery stenosis on the use of antihypertensive medication, blood pressure, and morphology and function of resistance arteries was investigated in 14 renovascular hypertensive patients before and after treatment compared to normotensive controls. METHODS: Use of antihypertensive medication was calculated as defined daily doses (DDD). Resistance arteries were taken from gluteal subcutaneous biopsies and analyzed in a myograph. RESULTS: Prior to invasive treatment, blood pressure of the patients was elevated compared to normotensive controls. Six months after technically successful invasive treatment, patients were still hypertensive compared to time-matched controls. The use of antihypertensive medication was reduced from 4.4+/-0.7 DDD before invasive treatment to 3.0+/-0.6 DDD 6 months after treatment. Vascular structure of resistance arteries, expressed as media/lumen ratio (media thickness to diameter), was greater in patients before invasive treatment (10.7+/-1.0%) compared to normotensive controls (7.9+/-0.8%). Media/lumen ratio of resistance arteries was reduced to that of the controls 6 months after invasive treatment despite the remaining hypertension. The functional studies showed no difference in response to acetylcholine, adenosine, noradrenaline or angiotensin II between patients and controls before or after treatment. CONCLUSIONS: This study shows that hypertension and increased media/lumen ratio of resistance arteries prevail in renovascular hypertensive patients despite antihypertensive medication and that invasive treatment is of benefit as regards use of antihypertensive medication. The study provides the novel information that the remaining hypertension is not due to uncorrected media/lumen ratio of the resistance arteries.

Acetylcholine↗
PubMed1996

Selection and binding of peptides to human transporters associated with antigen processing and rat cim-a and -b.

Cytotoxic T lymphocytes recognize antigenic peptides presented by MHC class I molecules. The peptides are generated in the cytosol by proteasomes, and probably also other proteases, and are then translocated into the endoplasmic reticulum (ER) lumen. The transporters associated with Ag processing (TAP) are key molecules for transporting peptides from the cytosol to the lumen of the ER. Using semipermeabilized cells, TAP-dependent peptide translocation was demonstrated, and the selectivity of peptide translocation was based on the carboxyl-terminal amino acid of peptides. We have examined peptide binding proteins in the ER membrane and the selection of peptides for binding to TAP by using a panel of peptides of different sequences and carboxyl-termini as well as peptides containing D amino acids. Peptides bound to TAP molecules in the absence of ATP. The presence of ATP induced binding of peptides to two additional membrane proteins (58 and 43 kDa). The selection of peptides by TAP molecules was based on peptide sequence and the carboxyl-terminal amino acid. Peptides containing D amino acid did not bind to TAP molecules. Rat cim-a and -b selected peptides differently, and selection was not only dependent on the carboxyl-terminal residue of the peptide, but included an influence of the peptide sequence. The different off-rates after peptide binding to TAP, indicated a dual binding step of peptide to TAP. ATP regulated the off-rate of peptides at a high affinity binding step. Our results demonstrate that the binding of peptides to TAP molecules is specific and most likely involves a multiple step pathway.

ATP-Binding Cassette Transporters↗
PubMed1996

Proteasomes generate in vitro a natural peptide of influenza-A nucleoprotein functional in HLA-B27 antigen assembly.

We have studied the degradation of a set of long peptides (9-30 amino acids) from the nucleoprotein of influenza A. In common for all these peptides is the core sequence NH2-Ser-Arg-Tyr-Trp-Ala-Ile-Arg-Thr-Arg-COOH, NP383-391, known as an antigenic peptide specific for the HLA-B27 class I antigen. We show that this peptide is generated by enriched cytosolic proteasomes of two sizes, 20S and 12S. The 12S proteasome is the precursor, the preproteasome, to the 20S mature proteasome as shown by pulse-chase experiment and is most likely responsible for the proteolytic activity in the 12S region. Cleavage at the N-terminus is distinct and restricted to residue 383, independent of the N-terminal extension of the peptide. The C-terminus is generated via cleavage at three sites. Intermediate and final peptide products were identified by mass spectrometry. Finally, we show that the NP383-391 peptide generated by proteasomes in vitro is functional inasmuch as it possesses the ability to stimulate assembly of in vitro translated HLA-B27 antigens.

Amino Acid Sequence↗
PubMed1995

Time course of action of amlodipine and felodipine in the rat is most rapid in small arteries.

The time course of action of amlodipine was compared to that of felodipine in rat mesenteric resistance arteries and aorta. Both amlodipine and felodipine caused a concentration-dependent relaxation of K(+)-depolarized resistance arteries: with amlodipine 3 x 10(-8) M and felodipine 10(-9) M, complete relaxation was reached after 40 min and 10 min, respectively. Furthermore, in resistance arteries, the time course of action of both drugs was shortest in vessels with the smallest diameter. In aorta, both drugs caused a marked relaxation of K(+)-induced tone, without reaching a maximal effect within 2 h. Recovery of K(+)-induced tone after both drugs was complete in resistance arteries, but not aorta, within 2 h. In resistance arteries exposed to K+ depolarization or noradrenaline, both drugs displayed the characteristics of 1,4-dihydropyridine Ca2+ channel antagonists. The results show that amlodipine was slower to have an effect than felodipine, but that both drugs acted fastest in the smallest arteries.

Amlodipine↗
PubMed1993

Early events in the assembly of MHC class I antigens.

The MHC class I heavy chain and beta 2-microglobulin are cell surface proteins, and are synthesized on membrane bound ribosomes. They are co-translationally inserted into the endoplasmic reticulum (ER) membrane and assemble with antigenic peptides in the lumen of this compartment. These peptides are believed to be generated in the cytosol, and must be protected from degradation prior to translocation across the ER membrane. Putative peptide transporters (TAP1 and 2) belonging to the ABC transporter family of proteins, have been suggested to function in this process, and have been shown to be essential for MHC class I antigen assembly. The finding that peptides were translocated across the ER membrane in microsomes prepared from cells lacking the TAP genes has challenged this view. In this review we discuss the different events leading to correct assembly of MHC class I antigens. We suggest the TAP molecules to be part of a complex, which function to select peptides, protect them from degradation, and facilitate their translocation by targeting them to the ER membrane.

Animals↗
PubMed1991

ATP is required for in vitro assembly of MHC class I antigens but not for transfer of peptides across the ER membrane.

We have translated the HLA-B27 heavy chain in vitro and studied its assembly with beta 2-microglobulin and peptide in microsomes from human cells. The assembly process requires ATP. However, the translocation of peptide across the endoplasmic reticulum (ER) membrane does not require ATP, and binding of biotinylated peptide to BiP, an ER luminal protein, occurs after ATP depletion. Proteinase K treatment of the microsomes does not block peptide translocation. Thus, ATP is required in the lumen of the ER for efficient assembly to occur. Microsomes prepared from Raji and T1 cells show similar levels of assembly, whereas assembly in T2 microsomes is 10-fold lower. This difference remains after peptide stimulation of assembly. The inefficient assembly in T2 microsomes is not due to impaired peptide translocation across the ER membrane, as no difference was found compared with microsomes from T1 cells. Instead, the defect seems to reside in the lumen of the ER.

Adenosine Triphosphate↗
PubMed1991

Studies of the renin-angiotensin system in the wall of rat femoral resistance vessels.

The responses to angiotensinogen, angiotensinogen-(1-14) (tetradecapeptide, TDP), angiotensin I, and angiotensin II and the effect of the renin inhibitor, CH-66, the angiotensin-converting enzyme (ACE) inhibitor, perindopril, and the receptor antagonist, saralasin, were investigated in isolated femoral resistance arteries of the rat. The response to angiotensinogen in the presence of kallikrein was also investigated. Angiotensin I and TDP elicited a contraction which was not reduced by CH-66 but was inhibited by perindopril and saralasin. The response to angiotensinogen was small and not blocked by saralasin but the response to angiotensinogen that was mixed with renin for a few seconds was saralasin-sensitive and perindopril and CH-66 showed a tendency to block this response. The response to angiotensinogen was enhanced in the presence of kallikrein. These results suggest (1) the presence of a partial renin-angiotensin system (RAS) in this preparation, (2) that TDP is not converted via renin while both angiotensin I and TDP are converted through ACE in this preparation and (3) that the responses to angiotensinogen and TDP are different.

Angiotensin I↗
PubMed1991

The endoplasmic reticulum retention signal of the E3/19K protein of adenovirus-2 is microtubule binding.

The signal for retention in the endoplasmic reticulum of the E3/19K protein of adenovirus type 2 is located within the carboxyl-terminal cytoplasmic extension. A synthetic peptide corresponding to this sequence showed affinity for beta-tubulin, could promote tubulin polymerization in vitro, and bound to taxol-polymerized microtubules. When compared with the microtubule binding sequences from two microtubule-associated proteins (MAPs; MAP2 and tau), we found similarities suggesting that the cytoplasmic tail might bind to tubulin/microtubules in a MAPs-like fashion. A synthetic peptide corresponding to the cytoplasmic tail of an E3/19K deletion mutant not retained in the endoplasmic reticulum was also tested. It had the same net charge but did not promote tubulin polymerization in vitro nor did it show measurable affinity for tubulin or microtubules. This indicates that binding to microtubules is important for retention of the E3/19K protein in the endoplasmic reticulum.

Adenovirus E3 Proteins↗
PubMed1991

Translocation of peptides through microsomal membranes is a rapid process and promotes assembly of HLA-B27 heavy chain and beta 2-microglobulin translated in vitro.

We have translated major histocompatibility complex (MHC) class I heavy chains and human beta 2-microglobulin in vitro in the presence of microsomal membranes and a peptide from the nucleoprotein of influenza A. This peptide stimulates assembly of HLA-B27 heavy chain and beta 2-microglobulin about fivefold. By modifying this peptide to contain biotin at its amino terminus, we could precipitate HLA-B27 heavy chains with immobilized streptavidin, thereby directly demonstrating class I heavy chain-peptide association under close to physiological conditions. The biotin-modified peptide stimulates assembly to the same extent as the unmodified peptide. Both peptides bind to the same site on the HLA-B27 molecule. Immediately after synthesis of the HLA-B27 heavy chain has been completed, it assembles with beta 2-microglobulin and peptide. These interactions occur in the lumen of the microsomes (endoplasmic reticulum), demonstrating that the peptide must cross the microsomal membrane in order to promote assembly. The transfer of peptide across the microsomal membrane is a rapid process, as peptide binding to heavy chain-beta 2-microglobulin complexes is observed in less than 1 min after addition of peptide. By using microsomes deficient of beta 2-microglobulin (from Daudi cells), we find a strict requirement of beta 2-microglobulin for detection of peptide interaction with the MHC class I heavy chain. Furthermore, we show that heavy chain interaction with beta 2-microglobulin is likely to precede peptide binding. Biotin-modified peptides are likely to become a valuable tool in studying MHC antigen interaction and assembly.

Amino Acid Sequence↗
PubMed1990

A nucleoprotein peptide of influenza A virus stimulates assembly of HLA-B27 class I heavy chains and beta 2-microglobulin translated in vitro.

Most cytotoxic T lymphocytes (CTL) recognize epitopes of foreign viral proteins in association with class I major histocompatibility complex (MHC) molecules. Viral proteins synthesized in the cytoplasm require intracellular fragmentation and exposure to the class I antigens for the development of CTL responses. Although indirect evidence for binding of peptides to class I antigens has accumulated, direct binding has only been shown recently. The formation of complexes between peptide and class I antigen may occur in the endoplasmic reticulum (ER) and peptides have been shown to induce assembly of the class I complex. We have translated the messenger RNAs encoding HLA-B27 (subtype 2705) and beta 2-microglobulin in a rabbit reticulocyte lysate supplemented with human microsomal membranes (to mimic ER membranes), in the absence and presence of a peptide derived from the nucleoprotein (residues 384-394) of influenza A virus. This peptide induces CTL activity against target cells expressing the HLA-B27 antigen. Here we report direct evidence that the nucleoprotein peptide promotes assembly of the HLA-B27 heavy chain and beta 2-microglobulin, and that this can occur in the ER immediately after synthesis of the two proteins.

Cell Compartmentation↗
PubMed1990

The endoplasmic reticulum retention signal of the E3/19K protein of adenovirus type 2 consists of three separate amino acid segments at the carboxy terminus.

The E3/19K protein of adenovirus type 2 is a resident of the ER. Immediately after synthesis it binds to human major histocompatibility complex class I antigens and prevents their departure from the ER compartment. The ER retention signal of the E3/19K protein is contained within the 15 amino acids that protrude on the cytoplasmic side at the carboxy terminus of the protein. To define the ER retention sequence in more detail, we have generated 10 mutants of the E3/19K protein that differ only within this segment. Analysis of the rate of intracellular transport and cell surface expression of HLA antigens associated to these mutants, show that the sequences Ser-Phe-Ile, located in the middle of the 15-residue segment and Met-Pro, at the extreme carboxy terminus, are crucial for retention. Four charged residues, Asp-Glu-Lys-Lys, are located between these two retention elements but are of little or no importance. The basic cluster of amino acids close to the membrane also has some effect on retention. Thus, the retention signal of the E3/19K protein is not a contiguous sequence of amino acids but has a complex spatial arrangement.

Adenovirus Early Proteins↗
PubMed1990

Co-expression of the human HLA-B27 class I antigen and the E3/19K protein of adenovirus-2 in insect cells using a baculovirus vector.

We have expressed the human MHC class I HLA-B27 antigen, human beta 2-microglobulin, and the E3/19K protein of adenovirus-2 in Spodoptera frugiperda insect cells (Sf9) by using the Autographa californica nuclear polyhedrosis virus. All genes were inserted under the strong polyhedrin promoter in the vector pVL941. The proteins were expressed at high levels, ranging from 1 to 8 mg protein per 3 x 10(9) cells. Both a full-length and a truncated form of HLA-B27 were expressed. The latter was terminated at the border of the membrane-spanning segment at the extracellular side of the membrane. The HLA-B27 antigens and the E3/19K protein showed considerable heterogeneity with respect to glycosylation. Only a small fraction of HLA-B27 was assembled (less than 5%) with beta 2-microglobulin. Nevertheless, we were able to find the heavy chain at the cell surface, and by co-infection with the recombinant virus for beta 2-microglobulin we observed an increase in cell surface expression. The E3/19K protein of adenovirus-2 blocks cell surface expression of HLA class I antigens in human cells and has a similar effect in insect cells. In contrast to beta 2-microglobulin it assembles efficiently to the heavy HLA-B27 chain, both the full-length and truncated forms. The E3/19K protein does not stimulate assembly of HLA-B27-beta 2-microglobulin. Due to these problems of assembly and the heterogeneity of glycosylation we predict that it will be difficult to use HLA antigens produced in insect cells for X-ray crystallographic studies.

Adenovirus E3 Proteins↗
PubMed1990

Requirements for the association of adenovirus type 2 E3/19K wild-type and mutant proteins with HLA antigens.

The E3/19K protein of human adenovirus type 2 is a resident of the endoplasmic reticulum (ER). Immediately after synthesis, it associates with major histocompatibility complex class I antigens and prevents their intracellular transport and cell surface expression. We have generated several C-terminal deletion mutants of the E3/19K protein that are preterminated at various positions on both sides of the membrane-spanning segment of the protein. One of these mutants is terminated at the luminal side of the membrane (M310), and two are terminated in the hydrophobic segment (M374 and M392), whereas mutant M621 is terminated on the cytoplasmic side of the ER membrane. The M310, M374, and M392 mutants are soluble proteins. They do not associate with HLA antigens in transfected 293 cells, and they are, to some extent, secreted into the medium. The M621 mutant protein is integrated in the ER membrane, associates immediately after its synthesis with HLA antigens, and exits from the ER. By using either an in vitro translation system supplemented with microsomes or overexpression in insect cells, we showed that M374 and E3/19K are able to associate with HLA antigens. These results indicate that the conformation of the luminal part of the E3/19K protein is not grossly altered by the mutations. Rapid transport of the M374 mutant out of the ER and partial degradation of this protein may prevent the interaction with HLA class I antigens in transfected 293 cells.

Adenovirus Early Proteins↗
PubMed1988

Cytolytic T cells recognize a chimeric MHC class I antigen expressed in influenza A infected transgenic mice.

A chimeric H-2Kd/Kk gene, called pC31, contains the extracellular alpha 1 domain of Kd origin whereas the rest of the molecule is of Kk origin. Disruption of the syngeneic alpha 1-alpha 2 structure results in a total abrogation of the function of the C31 protein as a restriction element for H-2Kd and Kk restricted T cells during virus infection. In an attempt to obtain information on the functional polymorphism of MHC class I antigens as restriction elements, we have introduced the pC31 gene into the germ line of C3H/He mice (H-2k). The pC31 gene was transcribed in all tissues examined and the expression pattern paralleled the endogenous H-2Kk gene. However, the mRNA for the transgene was approximately 10-times more abundant, which was reflected in an elevated expression of the C31 protein in transgenic splenocytes. Most of the C31 antigen was found intracellularly. The C31 antigen could condition transgenic cytotoxic T lymphocytes in a specific manner during influenza A virus infection and functioned as the restricting element during T cell lysis of the infected cells. These results suggest that entire exons may be exchanged between MHC class I genes and that this exchange can generate novel and functional restriction elements.

Animals↗
PubMed1987

The E3/19K protein of adenovirus type 2 binds to the domains of histocompatibility antigens required for CTL recognition.

The E3/19K protein of human adenovirus type 2 binds to HLA class I antigens and blocks their terminal glycosylation and cell surface expression. The nature of this interaction is non-covalent and involves neither disulfide bridges between the two molecules nor their carbohydrates. The murine H-2 Kd antigen associates with the E3/19K protein in a similar fashion to human HLA antigens whereas the allelic product H-2 Kk does not. Hybrid genes between the Kd and Kk alleles were constructed and their products were expressed in embryonic kidney cells together with the E3/19K protein. This allowed us to identify the alpha 1 and alpha 2 domains as the essential structures of the histocompatibility antigens for binding the viral protein. Interestingly, these domains are also crucial for T cell recognition. The implications for the evolution of adenoviruses and their ability to cause persistent infections are discussed.

Adenovirus Early Proteins↗
PubMed1987

"E3/19K" protein of adenovirus type 2 inhibits lysis of cytolytic T lymphocytes by blocking cell-surface expression of histocompatibility class I antigens.

The E3 19,000-dalton protein termed "E3/19K" of adenovirus type 2 binds to human class I histocompatibility antigens (HLA antigens). Human 293.12 cultured cells that express a cloned gene for the E3/19K protein show reduced levels of HLA antigens on the cell surface compared to parental 293 cells. We have transfected these cell lines with plasmid DNA containing the murine histocompatibility H-2Kd allele to demonstrate that this antigen binds also to the E3/19K protein. The resulting association prevents the H-2Kd antigen from being terminally glycosylated and inhibits its cell-surface expression. Two murine cytolytic T-lymphocyte clones specific for HLA antigens and restricted by the H-2Kd antigen lyse the human 293Kd cells. In the presence of the E3/19K protein, a dramatically reduced cell surface density of both HLA and H-2Kd antigens was shown. This decreased amount of cell-surface HLA/H-2Kd antigens correlated with a reduction in susceptibility to lysis of the target cells. In particular, the cell-surface level of the H-2Kd antigen, which is the restricting element, was crucial for efficient lysis. Thus, the E3/19K protein of adenovirus type 2 indirectly reduces the cellular immune recognition in the in vitro system. This might be the mechanism involved in latent and persistent infections caused by adenoviruses in vivo.

Adenovirus E3 Proteins↗
PubMed1986

Different structural constraints for recognition of mouse H-2Kd and -Kk antigens by alloimmune cytolytic T lymphocytes.

We have constructed a new series of hybrid genes among the H-2Kd,-Kk, and -Kb. The site of recombination occurs in the third exon, encoding the alpha 2 domain, and divides this domain into two parts, alpha 2A and alpha 2B. The novel genes differ only in the COOH-terminal half of the alpha 2 domain, i.e., the alpha 2B region. This region, comprising residues 142-182, contains a limited number of amino acid differences between the three alleles. The hybrid genes have been introduced into 1T 22-6 cells (H-2q), and cell surface expression of hybrid antigens was verified. Cells expressing different types of hybrid antigens have been examined for their susceptibility to lysis by cytotoxic T lymphocytes directed either against the H-2Kd antigen or the H-2Kk antigen. Our results show that the alpha 1 and alpha 2A domains of the H-2Kk antigen can constitute target molecules for alloimmune anti-Kk T cells, whereas the alpha 2B region, when exchanged for Kd or Kb sequences, plays only a limited role. In contrast, the alpha 1 and alpha 2A domains of Kd are not sufficient to be recognized by alloimmune anti-Kd T cells. In this instance, the alpha 2B domain seems to play an essential role. This region has undergone several amino acid substitutions involving charged residues.

Amino Acid Sequence↗