Visualization of tissue kallikrein in human breast carcinoma by two-dimensional western blotting and immunohistochemistry

Human tissue kallikreins: the cancer biomarker family

Human tissue kallikreins (KLKs) are attracting increased attention due to their role as biomarkers for the screening, diagnosis, prognosis, and monitoring of various cancers including those of the prostate, ovarian, breast, testicular, and lung. Human tissue kallikrein genes represent the largest contiguous group of proteases within the human genome. Originally thought to consist of three genes, the identification of the human kallikrein locus has expanded this number to fifteen. These genes, and their encoded proteins, share a high degree of homology and are expressed in different tissues. Prostate-specific antigen (PSA), the most commonly known kallikrein, is a useful biomarker for prostate cancer. Several other kallikreins, including kallikreins 2 (KLK2) and 11 (KLK11) are emerging as complementary prostate cancer biomarkers. Along with these kallikreins, several others have been implicated in the other cancers. For example, KLK5, 6, 7, 10, 11, and 14 are emerging biomarkers for ovarian cancer. The identification of kallikrein substrates and the development of proteolytic cascade models implicate kallikrein proteins in cancer progression. This review describes the current status of kallikreins as cancer biomarkers.

Upregulation of tissue kallikrein, kinin B1 receptor, and kinin B2 receptor in mast and giant cells infiltrating oesophageal squamous cell carcinoma

BACKGROUND

The mitogenic kinin peptides formed by the serine protease, tissue kallikrein (TK1), stimulate the proliferation of tumour cells and, by increasing vascular permeability, enhance metastasis. Oesophageal mucosal epithelial cells are derived from the epithelial cell germ layer, which expresses the kallikrein-kinin cascade.

AIM

To determine the cellular distribution of active TK1, prokallikrein, and the kinin B(1) and B(2) receptors in oesophageal carcinoma by immunocytochemistry and in situ hybridisation (ISH).

METHODS

Fifty oesophageal specimens (33 biopsies and 17 resections) and 10 control specimens adjacent to tumour or normal oesophageal biopsies were studied. Specific antibodies were used to determine the cellular localisation of TK1, prokallikrein, and the kinin B(1) and B(2) receptors in normal and oesophageal specimens by standard immunohistochemical techniques. The intensity of immunolabelling was quantified by image analysis. Antisense probes for TK1 and the kinin B(1) and B(2) receptors were also used to localise mRNA.

RESULTS

TK1 (active and prokallikrein) was expressed in the mucosa of normal and tumour oesophageal epithelium. In general, expression was highest in activated mast cells, followed by giant tumour cells. Immunolabelling results were confirmed by ISH experiments.

CONCLUSIONS

This is the first demonstration that TK1 and kinin B(1) and B(2) receptors are expressed in oesophageal carcinoma. Because TK1 released from tumour cells enzymatically generates mitogenic kinins from its endogenous substrate, kininogen, it is possible that third generation kinin receptor antagonists, which have been shown to be cytotoxic to cancer cells, may be useful therapeutic agents in this disease.

The emerging roles of human tissue kallikreins in cancer

Human tissue kallikreins (hKs), which are encoded by the largest contiguous cluster of protease genes in the human genome, are secreted serine proteases with diverse expression patterns and physiological roles. Although primarily known for their clinical applicability as cancer biomarkers, recent evidence implicates hKs in many cancer-related processes, including cell-growth regulation, angiogenesis, invasion and metastasis. They have been shown to promote or inhibit neoplastic progression, acting individually and/or in cascades with other hKs and proteases, and might represent attractive targets for therapeutic intervention.

Human Tissue Kallikreins: Physiologic Roles and Applications in Cancer

Tissue kallikreins are members of the S1 family (clan SA) of trypsin-like serine proteases and are present in at least six mammalian orders. In humans, tissue kallikreins (hK) are encoded by 15 structurally similar, steroid hormone–regulated genes (KLK) that colocalize to chromosome 19q13.4, representing the largest cluster of contiguous protease genes in the entire genome. hKs are widely expressed in diverse tissues and implicated in a range of normal physiologic functions from the regulation of blood pressure and electrolyte balance to tissue remodeling, prohormone processing, neural plasticity, and skin desquamation. Several lines of evidence suggest that hKs may be involved in cascade reactions and that cross-talk may exist with proteases of other catalytic classes. The proteolytic activity of hKs is regulated in several ways including zymogen activation, endogenous inhibitors, such as serpins, and via internal (auto)cleavage leading to inactivation. Dysregulated hK expression is associated with multiple diseases, primarily cancer. As a consequence, many kallikreins, in addition to hK3/PSA, have been identified as promising diagnostic and/or prognostic biomarkers for several cancer types, including ovarian, breast, and prostate. Recent data also suggest that hKs may be causally involved in carcinogenesis, particularly in tumor metastasis and invasion, and, thus, may represent attractive drug targets to consider for therapeutic intervention.

Mitogenic signalling by B2 bradykinin receptor in epithelial breast cells

The kinin peptides are released during inflammation and are amongst the most potent known mediators of vasodilatation, pain, and oedema. A role in the modulation or induction of healthy breast tissue growth has been postulated for tissue kallikrein present in human milk. Moreover, tissue kallikrein was found in malignant human breast tissue and bradykinin (BK) stimulates the proliferation of immortalised breast cancer cells. Aim of the present article was to investigate whether BK also exerts mitogenic activity in normal breast epithelial cells and partially characterise the signalling machinery involved. Results show that BK increased up to 2-fold the 24 h proliferation of breast epithelial cells in primary culture, and that the BK B2 receptor (not B1) inhibitor alone fully blocked the BK response. Intracellular effects of B2 stimulation were the following: (a) the increase of free intracellular Ca(2+) concentration by a mechanism dependent upon the phospholipase C (PLC) activity; (b) the cytosol-to-membrane translocation of conventional (PKC)-alpha and -beta isozymes, novel PKC-delta, -epsilon, and -eta isozymes; (c) the phosphorylation of the extracellular-regulated kinase 1 and 2 (ERK1/2); and (d) the stimulation of the expression of c-Fos protein. EGF, a well known stimulator of cell proliferation, regulated the proliferative response in human epithelial breast cells to the same extent of BK. The effects of BK on proliferation, ERK1/2 phosphorylation, and c-Fos expression were abolished by GF109203X, which inhibits PKC-delta isozyme. Conversely, Gö6976, an inhibitor of PKC-alpha and -beta isozymes, and the 18-h treatment of cells with PMA, that led to the complete down-regulation of PKC-alpha, -beta, -epsilon, and -eta, but not of PKC-delta, did not have any effect, thereby indicating that the PKC-delta mediates the mitogenic signalling of BK. Phosphoinositide 3-kinase (PI3K), tyrosine kinase of the epidermal growth factor receptor (EGFR), and mitogen activated protein kinase kinases (MEK) inhibitors were also tested. The results suggest that EGFR, PI3K, and ERK are required for the proliferative effects of BK. In addition, the BK induced cytosol-to-membrane translocation of PKC-delta was blocked by PI3K inhibition, suggesting that PI3K is upstream to PKC-delta. In conclusion, BK has mitogenic actions in cultured human epithelial breast cells; the activation of PKC-delta through B2 receptor acts in concert with ERK and PI3K pathways to induce cell proliferation.

The release and vascular action of bradykinin in the isolated perfused bovine udder

It has been postulated that the mammary kinin system may play a role in modulating mammary blood flow. Until the present study, the local release of bradykinin (BK) or other kinin system constituents into the mammary vasculature had not been reported and there were also conflicting findings on the action of BK on udder vasculature. Udders were removed from healthy lactating cows at slaughter. Pairs of ipsilateral quarters were perfused with Tyrode solution through the external pudendalis artery and drained via the cranial superficial epigastric vein. Mammary secretion was collected through teat cannulae. The perfusion pressure was linearly related to perfusate flux between 60 and 210 ml min(-1) and the flow rate was adjusted (110-150 ml min(-1)) to give a basal pressure of 85 mmHg. PO2, PCO2 and pH in the venous effluent perfusate stabilised at 157 +/- 10 mmHg, 50.1 +/- 2.4 mmHg and 7.1 +/- 0.03, respectively. The venous effluent contained immunoreactive BK and BK precursor, tissue kallikrein activity, and bradykinin-destroying enzyme. The concentration of BK stabilised at 378 +/- 48 pg (ml perfusate)(-1), that of trypsin-activated BK precursor was 679 +/- 59 pg BK equivalents ml(-1) and that of tissue kallikrein, measured as cleavage of D-Val.Leu.Arg-p-nitroanilide (D-Val.Leu.Arg-pNA), was 5.5 +/- 1.7 nmol p-NA h(-1) ml(-1). Arterial infusion of phenylephrine (0.49-490 microM) produced increases in perfusion pressure (vasoconstriction). Acetylcholine (ACh) (0.55-55 microM) and BK (0.1-10 microM) produced only vasodilatation. BK (EC50 = 1.00+/-0.04 microM) was a more potent vasodilator than ACh (EC50 = 9.57+/-0.49 microM). The basal BK concentration was 250 times below the threshold for vasoactivity. The udder produced a milk-like secretion, which was dependent on perfusate flow and contained a concentration of BK which remained unchanged from 60 to 180 min of perfusion (231 +/- 31 pg ml(-1)) unlike that in the venous effluent which doubled between 60 and 120 min. Thus, in addition to its secretion into milk, BK, together with its precursor and tissue kallikrein, is continuously released into the vasculature of the isolated, perfused, lactating bovine udder.

Roles of the P1, P2, and P3 residues in determining inhibitory specificity of kallistatin toward human tissue kallikrein

Kallistatin is a serpin with a unique P1 Phe, which confers an excellent inhibitory specificity toward tissue kallikrein. In this study, we investigated the P3-P2-P1 residues (residues 386-388) of human kallistatin in determining inhibitory specificity toward human tissue kallikrein by site-directed mutagenesis and molecular modeling. Human kallistatin mutants with 19 different amino acid substitutions at each P1, P2, or P3 residue were created and purified to compare their kallikrein binding activity. Complex formation assay showed that P1 Arg, P1 Phe (wild type), P1 Lys, P1 Tyr, P1 Met, and P1 Leu display significant binding activity with tissue kallikrein among the P1 variants. Kinetic analysis showed the inhibitory activities of the P1 mutants toward tissue kallikrein in the order of P1 Arg > P1 Phe > P1 Lys >/= P1 Tyr > P1 Leu >/= P1 Met. P1 Phe displays a better selectivity for human tissue kallikrein than P1 Arg, since P1 Arg also inhibits several other serine proteinases. Heparin distinguishes the inhibitory specificity of kallistatin toward kallikrein versus chymotrypsin. For the P2 and P3 variants, the mutants with hydrophobic and bulky amino acids at P2 and basic amino acids at P3 display better binding activity with tissue kallikrein. The inhibitory activities of these mutants toward tissue kallikrein are in the order of P2 Phe (wild type) > P2 Leu > P2 Trp > P2 Met and P3 Arg > P3 Lys (wild type). Molecular modeling of the reactive center loop of kallistatin bound to the reactive crevice of tissue kallikrein indicated that the P2 residue required a long and bulky hydrophobic side chain to reach and fill the hydrophobic S2 cleft generated by Tyr(99) and Trp(219) of tissue kallikrein. Basic amino acids at P3 could stabilize complex formation by forming electrostatic interaction with Asp(98J) and hydrogen bond with Gln(174) of tissue kallikrein. Our results indicate that tissue kallikrein is a specific target proteinase for kallistatin.

The diagnostic and prognostic utility of prostate-specific antigen for diseases of the breast

Although prostate-specific antigen (PSA) is the most valuable tumor marker for the diagnosis and management of prostate carcinoma, it is widely accepted that PSA is not prostate specific. Numerous studies have shown that PSA is present in some female hormonally regulated tissues, principally the breast and its secretions. In this review, we summarize the findings of PSA in the breast, and focus on its potential for clinical applications in breast disease. PSA is produced by the majority of breast tumors and is a favorable indicator of prognosis in breast cancer. Low levels of PSA are released into the female circulation, and while the level of serum PSA is elevated in both benign and malignant breast disease, the molecular form of circulating PSA differs between women with and without breast cancer. These findings indicate that PSA may have potential diagnostic utility in breast cancer. PSA may also have a clinical application in benign breast disease, as both the level and molecular form of PSA differ between Type I and II breast cysts. High levels of PSA have been reported in nipple aspirate fluid (NAF) and recent studies have shown that the concentration of PSA in NAF is inversely related to breast cancer risk, indicating that NAF PSA may represent a clinical tool for breast cancer risk assessment. Thus, PSA represents a marker with numerous potential clinical applications as a diagnostic and/or prognostic tool in breast disease.

Kinin receptors are expressed in human astrocytic tumour cells

Tissue kallikrein (TK) is known to be present in several tumours in which increased KLK1 (TK) gene expression has been demonstrated. By degrading components of the extracellular matrix, TK may facilitate tumour proliferation and invasion. The vasodilatory effect of the bioactive kinin peptides causes an increase in vascular permeability, thereby enhancing metastasis. Since kinins act by receptor-linked signal transduction mechanisms, the aim of this study was to elucidate the localization and expression of kinin B1 and B2 receptors in surgical samples of human astrocytic tumours. Tumour tissue collected was processed for light, confocal and electron microscopy (EM) and RNA extraction. The mean high intensity of immunolabeling in tumour cells was quantified in pixels per square micrometer using the Analysis 2.1 Prosystem (Soft-Imaging Software, Germany, 1996). The ultrastructural localization of B1 and B2 kinin receptors was performed on ultrathin sections of the resin-embedded tissue, using immunogold-labeled probes. In the human brain, immunoreactive B2 occurs in cortical neurones but not in glial cells, and immunolabeling for B1 receptors is absent in cortical areas. In the present study, in all of the tumours studied so far, immunolabeling for B2 (28.42 pixels/microm2, n = 12) and B1 (14.07 pixels/ microm2, n = 10) was observed on the astrocytic cells. Immunoreactive kinin receptors were also present in endothelial cells of the stromal blood vessels. At EM, the average number of immunogold particles was 14 for B2 receptors and eight for B1 receptors. The immunoreactive B2 receptors were located closer to the periphery of the tumour cells while B1 immunolabeling was observed throughout the cell.

Pathophysiology of the kallikrein-kinin system in mammalian nervous tissue

The nervous system and peripheral tissues in mammals contain a large number of biologically active peptides and proteases that function as neurotransmitters or neuromodulators in the nervous system, as hormones or cellular mediators in peripheral tissue, and play a role in human neurological diseases. The existence and possible functional relevance of bradykinin and kallidin (the peptides), kallikreins (the proteolytic enzymes), and kininases (the peptidases) in neurophysiology and neuropathological states are discussed in this review. Tissue kallikrein, the major cellular kinin-generating enzyme, has been localised in various areas of the mammalian brain. Functionally, it may assist also in the normal turnover of brain proteins and the processing of peptide-hormones, neurotransmitters, and some of the nerve growth factors that are essential for normal neuronal function and synaptic transmission. A specific class of kininases, peptidases responsible for the rapid degradation of kinins, is considered to be identical to enkephalinase A. Additionally, kinins are known to mediate inflammation, a cardinal feature of which is pain, and the clearest evidence for a primary neuronal role exists so far in the activation by kinins of peripherally located nociceptive receptors on C-fibre terminals that transmit and modulate pain perception. Kinins are also important in vascular homeostasis, the release of excitatory amino acid neurotransmitters, and the modulation of cerebral cellular immunity. The two kinin receptors, B2 and B1, that modulate the cellular actions of kinins have been demonstrated in animal neural tissue, neural cells in culture, and various areas of the human brain. Their localisation in glial tissue and neural centres, important in the regulation of cardiovascular homeostasis and nociception, suggests that the kinin system may play a functional role in the nervous system.

Crystal structure of recombinant human tissue kallikrein at 2.0 A resolution

Human tissue kallikrein, a trypsin-like serine protease involved in blood pressure regulation and inflammation processes, was expressed in a deglycosylated form at high levels in Pichia pastoris, purified, and crystallized. The crystal structure at 2.0 A resolution is described and compared with that of porcine kallikrein and of other trypsin-like proteases. The active and S1 sites (nomenclature of Schechter I, Berger A, 1967, Biochem Biophys Res Commun 27:157-162) are similar to those of porcine kallikrein. Compared to trypsin, the S1 site is enlarged owing to the insertion of an additional residue, cis-Pro 219. The replacement Tyr 228 --> Ala further enlarges the S1 pocket. However, the replacement of Gly 226 in trypsin with Ser in human tissue kallikrein restricts accessibility of substrates and inhibitors to Asp 189 at the base of the S1 pocket; there is a hydrogen bond between O delta1Asp189 and O gammaSer226. These changes in the architecture of the S1 site perturb the binding of inhibitors or substrates from the modes determined or inferred for trypsin. The crystal structure gives insight into the structural differences responsible for changes in specificity in human tissue kallikrein compared with other trypsin-like proteases, and into the structural basis for the unusual specificity of human tissue kallikrein in cleaving both an Arg-Ser and a Met-Lys peptide bond in its natural protein substrate, kininogen. A Zn+2-dependent, small-molecule competitive inhibitor of kallikrein (Ki = 3.3 microM) has been identified and the bound structure modeled to guide drug design.

A new structural class of serine protease inhibitors revealed by the structure of the hirustasin-kallikrein complex

BACKGROUND

Hirustasin belongs to a class of serine protease inhibitors characterized by a well conserved pattern of cysteine residues. Unlike the closely related inhibitors, antistasin/ghilanten and guamerin, which are selective for coagulation factor Xa or neutrophil elastase, hirustasin binds specifically to tissue kallikrein. The conservation of the pattern of cysteine residues and the significant sequence homology suggest that these related inhibitors possess a similar three-dimensional structure to hirustasin.

RESULTS

The crystal structure of the complex between tissue kallikrein and hirustasin was analyzed at 2.4 resolution. Hirustasin folds into a brick-like structure that is dominated by five disulfide bridges and is sparse in secondary structural elements. The cysteine residues are connected in an abab cdecde pattern that causes the polypeptide chain to fold into two similar motifs. As a hydrophobic core is absent from hirustasin the disulfide bridges maintain the tertiary structure and present the primary binding loop to the active site of the protease. The general structural topography and disulfide connectivity of hirustasin has not previously been described.

CONCLUSIONS

The crystal structure of the kallikrein-hirustasin complex reveals that hirustasin differs from other serine protease inhibitors in its conformation and its disulfide bond connectivity, making it the prototype for a new class of inhibitor. The disulfide pattern shows that the structure consists of two domains, but only the C-terminal domain interacts with the protease. The disulfide pattern of the N-terminal domain is related to the pattern found in other proteins. Kallikrein recognizes hirustasin by the formation of an antiparallel beta sheet between the protease and the inhibitor. The P1 arginine binds in a deep negatively charged pocket of the enzyme. An additional pocket at the periphery of the active site accommodates the sidechain of the P4 valine.

Recombinant hirustasin: production in yeast, crystallization, and interaction with serine proteases

A synthetic gene coding for the 55-amino acid protein hirustasin, a novel tissue kallikrein inhibitor from the leech Hirudo medicinalis, was generated by polymerase chain reaction using overlapping oligonucleotides, fused to the yeast alpha-factor leader sequence and expressed in Saccharomyces cerevisiae. Recombinant hirustasin was secreted mainly as incompletely processed fusion protein, but could be processed in vitro using a soluble variant of the yeast yscF protease. The processed hirustasin was purified to better than 97% purity. N-terminal sequence analysis and electrospray ionization mass spectrometry confirmed a correctly processed N-terminus and the expected amino acid sequence and molecular mass. The biological activity of recombinant hirustasin was identical to that of the authentic leech protein. Crystallized hirustasin alone and in complex with tissue kallikrein diffracted beyond 1.4 A and 2.4 A, respectively. In order to define the reactive site of the inhibitor, the interaction of hirustasin with kallikrein, chymotrypsin, and trypsin was investigated by monitoring complex formation in solution as well as proteolytic cleavage of the inhibitor. During incubation with high, nearly equimolar concentration of tissue kallikrein, hirustasin was cleaved mainly at the peptide bond between Arg 30 and Ile 31, the putative reactive site, to yield a modified inhibitor. In the corresponding complex with chymotrypsin, mainly uncleaved hirustasin was found and cleaved hirustasin species accumulated only slowly. Incubation with trypsin led to several proteolytic cleavages in hirustasin with the primary scissile peptide bond located between Arg 30 and Ile 31. Hirustasin appears to fall into the class of protease inhibitors displaying temporary inhibition.

Kallikrein and kallikrein-like proteinases: purification and determination by chromatographic and electrophoretic methods

Kallikreins and kallikrein-like enzymes make up a family of serine proteinases present in tissues and body fluids of mammals and in some snake venoms. This review deals with the procedures of purification, detection and determination of these enzymes by chromatographic and electrophoretic methods. The procedures are reported in tables, described and discussed with the aim of illustrating the state-of-the-art of research in the field.