Structured habitats and the evolution of anticompetitor toxins in bacteria

We demonstrate that in liquid cultures, defined in this study as a mass habitat, the outcome of competition between Escherichia coli that produce an antibacterial toxin (colicin) and sensitive E. coli is frequency dependent; the colicinogenic bacteria are at an advantage only when fairly common (frequencies in excess of 2 X 10(-2)). However, we also show that in a soft agar matrix, a structured habitat, the colicinogenic bacteria have an advantage even when initially rare (frequencies as low as 10(-6)). These contrasting outcomes are attributed to the colicinogenic bacteria's lower intrinsic growth rate relative to the sensitive bacteria and the different manner in which bacteria and resources are partitioned in the two types of habitats. Bacteria in a liquid culture exist as randomly distributed individuals and the killing of sensitive bacteria by the colicin augments the amount of resource available to the colicinogenic bacteria to an extent identical to that experienced by the surviving sensitive bacteria. On the other hand, the bacteria in a soft agar matrix exist as single-clone colonies. As the colicinogenic colonies release colicin, they kill neighboring sensitive bacteria and form an inhibition zone around themselves. By this action, they increase the concentration of resources around themselves and overcome their growth rate disadvantage. We suggest that structured habitats are more favorable for the evolution of colicinogenic bacteria.

Prisoner's dilemma in an RNA virus

The evolution of competitive interactions among viruses was studied in the RNA phage phi6 at high and low multiplicities of infection (that is, at high and low ratios of infecting phage to host cells). At high multiplicities, many phage infect and reproduce in the same host cell, whereas at low multiplicities the viruses reproduce mainly as clones. An unexpected result of this study was that phage grown at high rates of co-infection increased in fitness initially, but then evolved lowered fitness. Here we show that the fitness of the high-multiplicity phage relative to their ancestors generates a pay-off matrix conforming to the prisoner's dilemma strategy of game theory. In this strategy, defection (selfishness) evolves, despite the greater fitness pay-off that would result if all players were to cooperate. Viral cooperation and defection can be defined as, respectively, the manufacturing and sequestering of diffusible (shared) intracellular products. Because the low-multiplicity phage did not evolve lowered fitness, we attribute the evolution of selfishness to the lack of clonal structure and the mixing of unrelated genotypes at high multiplicity.

Fitness of RNA virus decreased by Muller's ratchet

Why sex exists remains an unsolved problem in biology. If mutations are on the average deleterious, a high mutation rate can account for the evolution of sex. One form of this mutational hypothesis is Muller's ratchet. If the mutation rate is high, mutation-free individuals become rare and they can be lost by genetic drift in small populations. In asexual populations, as Muller noted, the loss is irreversible and the load of deleterious mutations increases in a ratchet-like manner with the successive loss of the least-mutated individuals. Sex can be advantageous because it increases the fitness of sexual populations by re-creating mutation-free individuals from mutated individuals and stops (or slows) Muller's ratchet. Although Muller's ratchet is an appealing hypothesis, it has been investigated and documented experimentally in only one group of organisms--ciliated protozoa. I initiated a study to examine the role of Muller's ratchet on the evolution of sex in RNA viruses and report here a significant decrease in fitness due to Muller's ratchet in 20 lineages of the RNA bacteriophage phi 6. These results show that deleterious mutations are generated at a sufficiently high rate to advance Muller's ratchet in an RNA virus and that beneficial, backward and compensatory mutations cannot stop the ratchet in the observed range of fitness decrease.

Adipose tissue is required for the antidiabetic, but not for the hypolipidemic, effect of thiazolidinediones

There is uncertainty about the site(s) of action of the antidiabetic thiazolidinediones (TZDs). These drugs are agonist ligands of the transcription factor PPAR gamma, which is abundant in adipose tissue but is normally present at very low levels in liver and muscle. We have studied the effects of TZDs in A-ZIP/F-1 mice, which lack white adipose tissue. The A-ZIP/F-1 phenotype strikingly resembles that of humans with severe lipoatrophic diabetes, including the lack of fat, marked insulin resistance and hyperglycemia, hyperlipidemia, and fatty liver. Rosiglitazone or troglitazone treatment did not reduce glucose or insulin levels, suggesting that white adipose tissue is required for the antidiabetic effects of TZDs. However, TZD treatment was effective in lowering circulating triglycerides and increasing whole body fatty acid oxidation in the A-ZIP/F-1 mice, indicating that this effect occurs via targets other than white adipose tissue. A-ZIP/F-1 mice have markedly increased liver PPAR gamma mRNA levels, which may be a general property of fatty livers. Rosiglitazone treatment increased the triglyceride content of the steatotic livers of A-ZIP/F-1 and ob/ob mice, but not the "lean" livers of fat-transplanted A-ZIP/F-1 mice. In light of this evidence that rosiglitazone acts differently in steatotic livers, the effects of rosiglitazone, particularly on hepatic triglyceride levels, should be examined in humans with hepatic steatosis.

Evolution by small steps and rugged landscapes in the RNA virus phi6

Fisher's geometric model of adaptive evolution argues that adaptive evolution should generally result from the substitution of many mutations of small effect because advantageous mutations of small effect should be more common than those of large effect. However, evidence for both evolution by small steps and for Fisher's model has been mixed. Here we report supporting results from a new experimental test of the model. We subjected the bacteriophage phi6 to intensified genetic drift in small populations and caused viral fitness to decline through the accumulation of a deleterious mutation. We then propagated the mutated virus at a range of larger population sizes and allowed fitness to recover by natural selection. Although fitness declined in one large step, it was usually recovered in smaller steps. More importantly, step size during recovery was smaller with decreasing size of the recovery population. These results confirm Fisher's main prediction that advantageous mutations of small effect should be more common. We also show that the advantageous mutations of small effect are compensatory mutations whose advantage is conditional (epistatic) on the presence of the deleterious mutation, in which case the adaptive landscape of phi6 is likely to be very rugged.

Evolvability of an RNA virus is determined by its mutational neighbourhood

The ubiquity of mechanisms that generate genetic variation has spurred arguments that evolvability, the ability to generate adaptive variation, has itself evolved in response to natural selection. The high mutation rate of RNA viruses is postulated to be an adaptation for evolvability, but the paradox is that whereas some RNA viruses evolve at high rates, others are highly stable. Here we show that evolvability in the RNA bacteriophage phi6 is also determined by the accessibility of advantageous genotypes within the mutational neighbourhood (the set of mutants one or a few mutational steps away). We found that two phi6 populations that were derived from a single ancestral phage repeatedly evolved at different rates and toward different fitness maxima. Fitness measurements of individual phages showed that the fitness distribution of mutants differed between the two populations. Whereas population A, which evolved toward a higher maximum, had a distribution that contained many advantageous mutants, population B, which evolved toward a lower maximum, had a distribution that contained only deleterious mutants. We interpret these distributions to measure the fitness effects of genotypes that are mutationally available to the two populations. Thus, the evolvability of phi6 is constrained by the distribution of its mutational neighbours, despite the fact that this phage has the characteristic high mutation rate of RNA viruses.

Transposable elements as mutator genes in evolution

Strains of the bacterium Escherichia coli harbouring genes that increase mutation rates are known to have an evolutionary advantage in chemostat competition over otherwise isogeneic strains with lower mutation rates. This advantage is frequency-dependent, the mutator strain being favoured only above a starting ratio of approximately 5 x 10(-5), and it results from the fact that the necessary beneficial mutations cannot be generated in a mutator population below a certain size. Here we consider the possibility that the mutagenic properties of transposable elements confer an advantage in the same manner as mutator genes. A previous report has shown that the transposon Tn5 increases the fitness of E. coli in chemostats, although the reason for this effect has not been established. Our results show that the transposon Tn10 also confers an advantage in chemostats. In addition, we find that (1) this advantage, like that associated with mutator genes, is frequency-dependent, (2) whenever the Tn10 strains win, a segment of Tn10, probably its IS10 sequences, has undergone transposition to a new site, (3) the new insertions converge into a site contained within a 3.2 kilobase (kb) PvuII fragment of the genome, and (4) no transpositions are detected when the Tn10 population loses. We conclude that Tn10 confers an advantage by increasing the mutation rate of the host bacterium.

Local delivery of human tissue kallikrein gene accelerates spontaneous angiogenesis in mouse model of hindlimb ischemia

BACKGROUND

Human tissue kallikrein (HK) releases kinins from kininogen. We investigated whether adenovirus-mediated HK gene delivery is angiogenic in the context of ischemia.

METHODS AND RESULTS

Hindlimb ischemia, caused by femoral artery excision, increased muscular capillary density (P:<0.001) and induced the expression of kinin B(1) receptor gene (P:<0.05). Pharmacological blockade of B(1) receptors blunted ischemia-induced angiogenesis (P:<0.01), whereas kinin B(2) receptor antagonism was ineffective. Intramuscular delivery of adenovirus containing the HK gene (Ad. CMV-cHK) enhanced the increase in capillary density caused by ischemia (969+/-32 versus 541+/-18 capillaries/mm(2) for control, P:<0.001), accelerated blood flow recovery (P:<0.01), and preserved energetic charge of ischemic muscle (P:<0.01). Chronic blockade of kinin B(1) or B(2) receptors prevented HK-induced angiogenesis.

CONCLUSIONS

HK gene delivery enhances the native angiogenic response to ischemia. Angiogenesis gene therapy with HK might be applicable to peripheral occlusive vascular disease.

Kin selection and parasite evolution: higher and lower virulence with hard and soft selection

Conventional models predict that low genetic relatedness among parasites that coinfect the same host leads to the evolution of high parasite virulence. Such models assume adaptive responses to hard selection only. We show that if soft selection is allowed to operate, low relatedness leads instead to the evolution of low virulence. With both hard and soft selection, low relatedness increases the conflict among coinfecting parasites. Although parasites can only respond to hard selection by evolving higher virulence and overexploiting their host, they can respond to soft selection by evolving other adaptations, such as interference, that prevent overexploitation. Because interference can entail a cost, the host may actually be underexploited, and virulence will decrease as a result of soft selection. Our analysis also shows that responses to soft selection can have a much stronger effect than responses to hard selection. After hard selection has raised virulence to a level that is an evolutionarily stable strategy, the population, as expected, cannot be invaded by more virulent phenotypes that respond only to hard selection. The population remains susceptible to invasion by a less virulent phenotype that responds to soft selection, however. Thus, hard and soft selection are not just alternatives. Rather, soft selection is expected to prevail and often thwart the evolution of virulence in parasites. We review evidence from several parasite systems and find support for soft selection. Most of the examples involve interference mechanisms that indirectly prevent the evolution of higher virulence. We recognize that hard selection for virulence is more difficult to document, but we take our results to suggest that a kin selection model with soft selection may have general applicability.

Transcription factor nuclear factor kappaB regulates the inducible expression of the human B1 receptor gene in inflammation

Expression of the bradykinin B1 receptor gene is up-regulated in vascular smooth muscle cells (VSMCs) in response to a variety of inflammatory stimuli. We isolated the 5'-flanking region of the human bradykinin B1 receptor gene and examined its promoter activity by transient transfection analysis. This region (-2582 to +34) showed promoter activity inducible by lipopolysaccharide (LPS), tumor necrosis factor alpha (TNF-alpha), and interleukin-1beta (IL-1beta) in VSMCs. Further deletion analysis revealed that constructs containing 111 base pairs of 5'-flanking sequence were sufficient for transcriptional induction. Mutagenesis of a nuclear factor kappaB (NF-kappaB)-like site at -64 to -55 abolished most of the LPS, TNF-alpha, and IL-1beta inducibility, whereas a mutation of a cyclic AMP response element at -50 to -43 markedly reduced the basal promoter activity, and a mutation of the activator protein 1 (AP-1) site at -78 to -72 had minimal effects. Nuclear extracts from LPS, TNF-alpha, and IL-1beta-treated VSMCs, IL-1beta-treated human hepatoma HepG2, and human lung fibroblast IMR-90 cells showed strong inducible binding activity to the NF-kappaB-like site by gel shift assays. These results demonstrated that NF-kappaB-like nuclear factor was involved in the inducible expression of the human bradykinin B1 receptor gene during inflammatory processes.

Human tissue kallikrein induces hypotension in transgenic mice

We investigated the role of the kallikrein-kinin system in blood pressure control by developing transgenic mice overexpressing human tissue kallikrein. Two lines of transgenic mice carrying the human tissue kallikrein gene under the control of the mouse metallothionein metal-responsive promoter were established. Human tissue kallikrein was identified in pancreas, salivary gland, kidney, liver, and spleen of the transgenic mice by a specific radioimmunoassay for human tissue kallikrein. The immunoreactive human tissue kallikrein reached high levels in the circulation. The linear displacement curves for the transgenic product were parallel with the human tissue kallikrein standard curve, indicating their immunologic identity. The expression of human tissue kallikrein transcript in the transgenic mice was further confirmed by Northern blot analysis and by reverse transcription-polymerase chain reaction followed by Southern blot. Both lines of transgenic mice had significantly lowered blood pressure (86.4 +/- 13.5 mm Hg [mean +/- SD], n = 8 and 78.9 +/- 12.4 mm Hg, n = 8) compared with control mice (100.9 +/- 5.0 mm Hg, n = 8). Induction with zinc did not lower the blood pressure further despite elevated expression of the transgene. Administration of aprotinin, a potent tissue kallikrein inhibitor, restored the blood pressure of the transgenic mice but had no significant effect on control littermates. Our findings raise the possibility of tissue kallikrein being a powerful modulator of blood pressure and provide a new animal model for the study of blood pressure regulation.

Direct gene delivery of human tissue kallikrein reduces blood pressure in spontaneously hypertensive rats

Hypertension is a multigene and multifactorial disorder affecting approximately 25% of the population. To demonstrate potential therapeutic effects of human tissue kallikrein in hypertension, spontaneously hypertensive rats were subjected to somatic gene therapy. Two human tissue kallikrein DNA constructs, one under the promoter control of the metallothionein metal response element and the other under the control of the Rous sarcoma virus 3'-LTR, were generated. We delivered naked DNA constructs into spontaneously hypertensive rats via intravenous injection. The expression of human tissue kallikrein in rats was identified in the heart, lung, and kidney by reverse transcription polymerase chain reaction followed by Southern blot analysis and an ELISA specific for human tissue kallikrein. A single injection of both human kallikrein plasmid DNA constructs caused a sustained reduction of blood pressure which began 1 wk after injection and continued for 6 wk. A maximal effect of blood pressure reduction of 46 mmHg in rats was observed 2-3 wk after injection with kallikrein DNA as compared to rats with vector DNA (n = 6, P < 0.05). The hypotensive effect caused by somatic gene delivery of human tissue kallikrein in hypertensive rats is reversed by subcutaneous injection of aprotinin, a potent tissue kallikrein inhibitor. No antibodies to either human tissue kallikrein or kallikrein DNA were detected in rat sera after injection of the human kallikrein gene. These results show that direct gene delivery of human tissue kallikrein causes a sustained reduction in systolic blood pressure in genetically hypertensive rats and indicate that the feasibility of kallikrein gene therapy for treating human hypertension should be studied.

Sex and the evolution of intrahost competition in RNA virus phi6

Sex allows beneficial mutations that occur in separate lineages to be fixed in the same genome. For this reason, the Fisher-Muller model predicts that adaptation to the environment is more rapid in a large sexual population than in an equally large asexual population. Sexual reproduction occurs in populations of the RNA virus phi6 when multiple bacteriophages coinfect the same host cell. Here, we tested the model's predictions by determining whether sex favors more rapid adaptation of phi6 to a bacterial host, Pseudomonas phaseolicola. Replicate populations of phi6 were allowed to evolve in either the presence or absence of sex for 250 generations. All experimental populations showed a significant increase in fitness relative to the ancestor, but sex did not increase the rate of adaptation. Rather, we found that the sexual and asexual treatments also differ because intense intrahost competition between viruses occurs during coinfection. Results showed that the derived sexual viruses were selectively favored only when coinfection is common, indicating that within-host competition detracts from the ability of viruses to exploit the host. Thus, sex was not advantageous because the cost created by intrahost competition was too strong. Our findings indicate that high levels of coinfection exceed an optimum where sex may be beneficial to populations of phi6, and suggest that genetic conflicts can evolve in RNA viruses.

Molecular cloning, tissue-specific expression, and cellular localization of human prostasin mRNA

We have purified a novel human serine proteinase, designated as prostasin, from seminal fluid (Yu et al., 1994). In the present study, we have cloned and characterized the full-length cDNA encoding prostasin and identified its tissue-specific expression and cellular localization. A cDNA fragment was obtained by polymerase chain reaction using degenerate oligonucleotide primers derived from the NH2-terminal and internal amino acid sequences. A full-length cDNA sequence encoding prostasin was obtained by amplification of the 5'- and 3'-ends of the cDNA. It contains a 1,032-base coding region, a 572-base 3'-noncoding region and a 138-base 5'-noncoding sequence. Prostasin cDNA encodes a protein of 343 amino acids, which consists of a 32-amino acid signal peptide and a 311-amino acid proprostasin. Proprostasin is then cleaved between Arg12 and Ile13 to generate a 12-amino acid light chain and a 299-amino acid heavy chain, which are associated through a disulfide bond. The deduced amino acid sequence of the heavy chain has 34-42% identity to human acrosin, plasma kallikrein, and hepsin. A potential N-glycosylation site at Asn127 and the catalytic triad of His53, Asp102, and Ser206 have been identified. The deduced prostasin has a unique 19-amino acid hydrophobic portion at the COOH terminus, which makes it suitable to anchor in the cell membrane. Carboxyl-terminal sequencing of purified prostasin indicates that the hydrophobic portion is removed and that there is a cleavage between Arg290 and Pro291 during secretion. Southern blot analysis, following a reverse transcription polymerase chain reaction, indicates that prostasin mRNA is expressed in prostate, liver, salivary gland, kidney, lung, pancreas, colon, bronchus, renal proximal tubular cells, and prostate carcinoma LNCaP cells. Cellular localization of prostasin mRNA was identified within epithelial cells of the human prostate gland by in situ hybridization histochemistry.

Asymmetries generated by transcription-coupled repair in enterobacterial genes

Although certain replication errors occur at different frequencies on each of the complementary strands of DNA, it remains unclear whether this bias is prevalent enough during chromosome replication to affect sequence evolution. Here, nucleotide substitutions in enteric bacteria were examined, and no difference in mutation rates was detected between the leading and lagging strands, but in comparing the coding and noncoding strands, and excess of C-->T changes was observed on the coding strand. This asymmetry is best explained by transcription-coupled repair on the noncoding strand. Although the vast majority of mutations are thought to arise from spontaneous errors during replication, this result implicates DNA damage as a substantial source of mutations in the wild.

Kallistatin, a novel human tissue kallikrein inhibitor: levels in body fluids, blood cells, and tissues in health and disease

Kallistatin, a human serine proteinase inhibitor, is a newly identified tissue kallikrein inhibitor. It binds strongly to tissue kallikrein but weakly to other serine proteinases such as chymotrypsin and elastase. The tissue distribution and changes in kallistatin levels in human diseases were characterized by using specific monoclonal and polyclonal antibodies against kallistatin. Kallistatin antigen levels in blood cells, fluids, and tissues measured with a specific enzyme-linked immunosorbent assay showed displacement curves that were parallel with those in purified kallistatin, indicating their immunologic identity. Expression of kallistatin mRNA in platelets, neutrophils, lymphocytes, monocytes, endothelial cells, hepatocytes, and colon and prostate carcinoma cells was identified by reverse transcription-polymerase chain reaction followed by Southern blot analysis. Plasma kallistatin concentration was 22.1 +/- 3.5 micrograms/ml in 30 normal subjects and 21.1 +/- 3.8 micrograms/ml in 5 patients with C1 inhibitor deficiency. A significantly reduced kallistatin level (7.2 +/- 2.5 micrograms/ml, p < 0.001) was seen in plasma samples from 9 patients with liver disease and 10 patients with sepsis (7.7 +/- 3.5 micrograms/ml, p < 0 .001). Further, kallistatin levels in 10 women taking oral contraceptives (19.8 +/- 3.8 micrograms/ml) and 21 pregnant women (14.9 +/- 3.3 microg/ml) were significantly lower than those seen in healthy individuals. These data suggest that kallistatin is found in plasma, is produced mostly in the liver, and can be consumed during sepsis. Its consumption in sepsis may indicate a protective role to prevent blood pressure lowering.

Reduced cardiac hypertrophy and altered blood pressure control in transgenic rats with the human tissue kallikrein gene

To evaluate the cardiovascular actions of kinins, we established a transgenic rat line harboring the human tissue kallikrein gene, TGR(hKLK1). Under the control of the zinc-inducible metallothionein promoter, the transgene was expressed in most tissues including the heart, kidney, lung, and brain, and human kallikrein was detected in the urine of transgenic animals. Transgenic rats had a lower 24-h mean arterial pressure in comparison with control rats, which was further decreased when their diet was supplemented with zinc. The day/night rhythm of blood pressure was significantly diminished in TGR(hKLK1) animals, whereas the circadian rhythms of heart rate and locomotor activity were unaffected. Induction of cardiac hypertrophy by isoproterenol treatment revealed a marked protective effect of the kallikrein transgene because the cardiac weight of TGR(hKLK1) increased significantly less, and the expression of atrial natriuretic peptide and collagen III as markers for hypertrophy and fibrosis, respectively, were less enhanced. The specific kinin-B2 receptor antagonist, icatibant, abolished this cardioprotective effect. In conclusion, the kallikrein-kinin system is an important determinant in the regulation of blood pressure and its circadian rhythmicity. It also exerts antihypertrophic and antifibrotic actions in the heart.

Adrenomedullin gene delivery attenuates hypertension, cardiac remodeling, and renal injury in deoxycorticosterone acetate-salt hypertensive rats

Adrenomedullin (AM) is a potent vasodilator and natriuretic peptide that plays an important role in cardiorenal function. In this study, we explored the potential protective role of AM in volume-dependent hypertension by somatic gene delivery. Adenovirus containing the human AM cDNA under the control of the cytomegalovirus promoter/enhancer was administered into deoxycorticosterone acetate (DOCA)-salt hypertensive rats via tail vein injection. A single injection of the human AM gene resulted in a prolonged reduction of blood pressure with a maximal reduction of 41 mm Hg 9 days after gene delivery. Human AM gene delivery enhanced renal function, as indicated by a 3-fold increase in renal blood flow and a 2-fold increase in glomerular filtration rate (n=5, P<0.05). Histological examination of the kidney revealed a significant reduction in glomerular sclerosis, tubular injury, luminol protein cast accumulation, and interstitial fibrosis as well as urinary protein. Human AM gene delivery caused significant decreases in left ventricular weight and cardiomyocyte diameter, which were accompanied by reduced interstitial fibrosis and extracellular matrix formation within the heart. Expression of human AM mRNA was detected in the kidney, adrenal gland, heart, aorta, lung, and liver; immunoreactive human AM levels were measured in urine and plasma. Significant increases in urinary and cardiac cAMP levels were observed in DOCA-salt rats receiving the human AM gene, indicating activation of the AM receptor. These findings showed that AM gene delivery attenuates hypertension, protects against cardiac remodeling and renal damage in volume-overload hypertension, and may have significance in therapeutic applications in cardiovascular and renal diseases.

Prostasin is a glycosylphosphatidylinositol-anchored active serine protease

A recombinant human prostasin serine protease was expressed in several human cell lines. Subcellular fractionation showed that this serine protease is synthesized as a membrane-bound protein while a free-form prostasin is secreted into the culture medium. Prostasin was identified in nuclear and membrane fractions. Membrane-bound prostasin can be released by phosphatidylinositol-specific phospholipase C treatment, or labeled by [(3)H]ethanolamine, indicating a glycosylphosphatidylinositol anchorage. A prostasin-binding protein was identified in mouse and human seminal vesicle fluid. Both the secreted and the membrane-bound prostasin were able to form a covalently linked 82-kDa complex when incubated with seminal vesicle fluid. The complex formation between prostasin and the prostasin-binding protein was inhibited by a prostasin antibody, heparin, and serine protease inhibitors. Prostasin's serine protease activity was inhibited when bound to the prostasin-binding protein in mouse seminal vesicle fluid. This study indicates that prostasin is an active serine protease in its membrane-bound form.

Kallikrein gene delivery attenuates myocardial infarction and apoptosis after myocardial ischemia and reperfusion

The tissue kallikrein-kinin system is present in the heart, and kinin has been shown to have cardioprotective effects. In this study, we investigated the potential role of tissue kallikrein in myocardial ischemia/reperfusion injury through adenovirus-mediated human kallikrein gene delivery. One week after gene delivery, the rats were subjected to a 30-minute coronary occlusion followed by a 2-hour reperfusion. Kallikrein gene delivery caused significant decreases in the ratio of infarct size to ischemic area at risk (from 69.6% to 44.5%, n=10 and 8, P<0.01) and in the incidence of ventricular fibrillation (from 64.3% to 16.7%, n=14 and 24, P<0.01) compared with the group injected with control adenovirus. Kallikrein gene delivery also attenuated programmed cell death in the ischemic area compared with the control area as assessed with the terminal deoxynucleotidyl transferase-mediated nick end labeling assay (n=6, P<0.01). Icatibant, a specific bradykinin B(2) receptor antagonist, abolished these kallikrein-mediated beneficial effects. The expression of human tissue kallikrein mRNA was identified in rat heart, kidney, lung, liver, and adrenal gland. After kallikrein gene delivery, cardiac kinin and cGMP levels were significantly elevated compared with the control (29.6+/-12.7 versus 6.1+/-2.1 pg/mg protein, n=7, P<0.01; 1.30+/-0.06 versus 0.86+/-0.09 pmol/mg protein, n=5, P<0.05). These results indicate that kallikrein gene delivery protects against myocardial infarction, ventricular arrhythmias, and apoptosis in ischemia/reperfusion injury via kinin-cGMP signal pathway. The successful application of this technology may have potential therapeutic value in the treatment of coronary artery diseases.

Human kallikrein gene delivery attenuates hypertension, cardiac hypertrophy, and renal injury in Dahl salt-sensitive rats

The tissue kallikrein-kinin system has been documented to be involved in the pathogenesis of hypertension and renal diseases. To investigate the protective effects of kallikrein gene delivery on salt-induced renal damage, cardiac dysfunction, and hypertension, adenovirus harboring the human tissue kallikrein gene under the control of the cytomegalovirus promoter Ad.CMV-cHK was delivered into Dahl salt-sensitive (Dahl-SS) rats fed to a high-salt (4% NaCl) diet. A single intravenous injection of Ad.CMV-cHK resulted in a significant reduction of blood pressure beginning 2 days post injection and the effect lasted for 4 weeks. The human kallikrein mRNA was detected in rat heart, kidney, lung, liver, and adrenal gland; immunoreactive human kallikrein can be measured in the liver, kidney, sera, and urine of rats receiving kallikrein gene delivery. Following Ad.CMV-cHK injection, a significant increase in urine excretion, urinary sodium output, kinin, and cGMP level was observed. Kallikrein gene delivery caused a significant reduction in the left ventricular mass and cardiomyocyte size as well as inhibition of glomerular sclerotic lesions and tubular dilatation. This study shows that adenovirus-mediated gene delivery in Dahl-SS rats fed a high-salt diet resulted in (i) prolonged reduction of blood pressure and increased urinary kinin and cGMP levels, consistent with blood pressure reductions mediated via kinin through a cGMP-dependent signal transduction pathway, (ii) inhibition of cardiac hypertrophy, and (iii) attenuation of renal injury. The ability of kallikrein gene transfer to produce a wide spectrum of beneficial effects makes it an excellent candidate in treating salt-related hypertension as well as cardiovascular and renal diseases.

Identification of a new tissue-kallikrein-binding protein

We have identified a tissue-kallikrein-binding protein in human serum and in the serum-free culture media from human lung fibroblasts (WI-38) and rodent neuroblastoma X glioma hybrid cells (NG108-15). Purified and 125I-labelled tissue kallikrein and human serum form an approximately 92,000-Mr SDS-stable complex. The relative quantity of this complex-formation is measured by densitometric scanning of autoradiograms. Complex-formation between tissue kallikrein and the serum binding protein was time-dependent and detectable after 5 min incubation at 37 degrees C, with half-maximal binding at 28 min. Binding of 125I-kallikrein to kallikrein-binding protein is temperature-dependent and can be inhibited by heparin or excess unlabelled tissue kallikrein but not by plasma kallikrein, collagenase, thrombin, urokinase, alpha 1-antitrypsin or kininogens. The kallikrein-binding protein is acid- and heat-labile, as pretreatment of sera at pH 3.0 or at 60 degrees C for 30 min diminishes complex-formation. However, the formed complexes are stable to acid or 1 M-hydroxylamine treatment and can only be partially dissociated with 10 mM-NaOH. When kallikrein was inhibited by the active-site-labelling reagents phenylmethanesulphonyl fluoride or D-Phe-D-Phe-L-Arg-CH2Cl no complex-formation was observed. An endogenous approximately 92,000-Mr kallikrein-kallikrein-binding protein complex was isolated from normal human serum by using a human tissue kallikrein-agarose affinity column. These complexes were recognized by anti-(human tissue kallikrein) antibodies, but not by anti-alpha 1-antitrypsin serum, in Western-blot analyses. The results show that the kallikrein-binding protein is distinct from alpha 1-antitrypsin and is not identifiable with any of the well-characterized plasma proteinase inhibitors such as alpha 2-macroglobulin, inter-alpha-trypsin inhibitor, C1-inactivator or antithrombin III. The functional role of this kallikrein-binding protein and its impact on kallikrein activity or metabolism in vivo remain to be investigated.

Tissue kallikrein in rat brain and pituitary: regional distribution and estrogen induction in the anterior pituitary

We have detected tissue kallikrein and kallikrein mRNA in various brain regions with a kallikrein direct RIA and with nucleic acid hybridization using a kallikrein cDNA probe. In the direct RIA, rat urinary kallikrein-like activity was found in the pituitary and pineal glands, hypothalamus, cerebral cortex, cerebellum, and brain stem. Pituitary and pineal gland kallikrein concentrations were significantly higher than those in other regions. Only in pituitary was there a significant difference in tissue kallikrein concentration according to sex, with glands from female rats showing levels 4-fold higher than those from male rats. Kallikrein mRNAs were detected in all of the regions and were about 4-fold higher in female than in male pituitary gland. Northern blot analyses show sex dimorphism of pituitary kallikrein mRNA, similar in size to submandibular gland and kidney mRNA. In castrated male rats, whole pituitary kallikrein content was reduced to 50% of the control value and increased 1.7-fold with testosterone replacement and 18-fold with 17 beta-estradiol treatment. Neither T4 nor cortisol affected whole pituitary kallikrein levels in the castrated male rat, but testosterone decreased pituitary kallikrein in normal female rats by 35%. When anterior pituitary or neurointermediate lobe extracts were separately examined, immunoreactive kallikrein was 10.2- and 1.3-fold higher respectively, in female than in male rat lobes. Estradiol benzoate (30 micrograms/kg) administration increased kallikrein levels 90- and 22-fold, respectively, in the anterior pituitary of gonadectomized male and female rats, while it increased by only 40-50% kallikrein levels in the male and female neurointermediate lobe. In dot blot analysis, kallikrein mRNA levels were increased 5-fold by 17 beta-estradiol in the whole pituitary of castrated male rats. In the cytoplasmic dot hybridization analysis, estradiol benzoate treatment increased kallikrein mRNA levels 54-fold in the anterior pituitary of ovariectomized rats. The data show that a tissue kallikrein indistinguishable thus far from a urinary kallikrein is widely distributed in brain and pituitary and that levels of enzyme and mRNA are comparable in certain central sites. Kallikrein levels in the anterior and neurointermediate pituitaries are differentially regulated by estrogen.