Identification of mK1, a true tissue (glandular) kallikrein of mouse submandibular gland: tissue distribution and a comparison of kinin-releasing activity with other submandibular kallikreins

Reversible Conversion among Subtypes of Salivary Gland Duct Cells as Identified by Production of a Variety of Bioactive Polypeptides

Four major kallikreins (mK1, mK22, mK9, and mK13) were identified in the mouse submandibular gland (SMG). mK1, a true tissue kallikrein, was used as a protein marker to identify different types of SMG granular convoluted tubule (GCT) cells along with epidermal growth factor (EGF), nerve growth factor (NGF), and renin. Kallikrein mK1 was localized in a very small number (~5%) of GCT cells, which were scattered throughout the GCT, indicating that the majority of GCT cells are mK1-negative. Among mK1-positive cells, particularly strong signals were observed in a small number of narrow cells, recognized as slender granular cells (SG cells, Type IV), in the GCT. After postnatal development of the SMG, GCT cells are no longer uniform based on the bioactive substances (mK1, EGF, NGF, and renin) that they produce and secrete. GCT cells were classified into four subtypes, Types I–IV, and it became clear that these subtypes are complicatedly and reversibly converted by the endocrine hormones 5α-dihydrotestosterone (DHT) and triiodothyronine (T₃). Duct segments with similar morphology or hormone dependency were recognized in the sublingual and parotid glands. The presence of duct cells with such characteristics is therefore a common feature of the three major salivary glands of rodents.

Interference of kallikrein 1b26 (klk1b26) translation by microRNA specifically expressed in female mouse submandibular glands: an additional mechanism for sexual dimorphism of klk1b26 protein in the glands

Background

Mouse kallikrein 1b26 (klk1b26) protein is more abundant in male submandibular glands (SMGs) than in female ones. This sexual dimorphism has been thought to be due to increased mRNA synthesis stimulated by androgen. However, the klk1b26 protein level in female SMG is far less than that expected from the mRNA level, suggesting an additional mechanism for down-regulation of klk1b26 expression in female SMGs.

Methods

We examined the effects of small non-coding RNAs in mouse SMGs on in vitro translation of klk1b26 using a reticulocyte lysate system and reverse transcription (RT)-PCR for klk1b26 mRNA. Statistical analyses were performed with a computer package (Microsoft Excel).

Results

The microRNA (miRNA) preparation from female SMGs, but not male SMGs, interfered with the in vitro translation of the klk1b26 protein and inhibited the RT-PCR for klk1b26 mRNA with forward primers targeting its 5'-terminal region (between the 15th and 40th nucleotide from the 5'-terminal). The miRNA preparation from castrated mouse SMGs showed the inhibitory effect on the klk1b26 translation, but that from a 5α-dihydrotestosterone-treated female mouse SMGs did not. Synthetic miRNAs (miR-325 and miR-1497a), which have partial complementarity with klk1b26 mRNA at its 5'-terminal region (15th to 40th nucleotide position from the 5'-terminal), also interfered with the in vitro klk1b26 translation. When the female miRNA preparation was incubated with a 30-nucleotide-long single-strand oligoDNA (named [15th-44th]ssDNA, whose sequence corresponded to the 15th to 44th position from the 5'-terminal of klk1b26 mRNA) prior to the addition into the in vitro translation system, the inhibitory effect of the miRNA preparation on klk1b26 translation disappeared, while [15th-44th]ssDNA itself had no effect on the translation. Preincubation of the miRNA preparation with another single-strand DNA ([169th-198th]ssDNA, whose sequence corresponded with 169th to 198th position of klk1b26 mRNA) did not show the inhibitory effect.

Conclusions

The small non-coding RNA, most probably miRNA, specifically expressed in female mouse SMGs interfered with klk1b26 protein synthesis in the in vitro translation system. Therefore sexual dimorphism observed in klk1b26 expression in mouse SMGs is due at least in part to the female-specific small non-coding RNA in SMGs.

Induction of Sca-1 via activation of STAT3 system in the duct cells of the mouse submandibular gland by ligation of the main excretory duct

To examine the very initial step that takes place immediately after tissue injury and is linked to tissue regeneration, we employed the submandibular gland (SMG), which was injured by ligation of its main excretory duct (MED). Ligation of the MED of the SMG in mice induced the expression of Sca-1, a protein marker of hematopoietic stem cells. In the normal gland, a low level of Sca-1 was expressed, which was localized predominantly in the excretory duct cells. At 1 day after ligation, Sca-1 expression increased prominently in almost all of cells in the duct system, but not in the acinar cells. The level of Sca-1 mRNA had begun to increase at 6 h after ligation and continuously rose thereafter until it reached a plateau, which occurred ∼12 h after ligation. STAT3 phosphorylated at its tyrosine-705 (p-STAT3) in the ligated gland increased immediately after ligation, and it was localized in the nuclei of all duct cells. The results of an EMSA revealed the specific binding of a nuclear extract to the sequence of the γ-interferon activation site (GAS) present in the Sca-1 promoter and confirmed that such binding increased after ligation. Thus the present study suggests that STAT3, having been phosphorylated following MED ligation, was transferred to the nucleus, where it bound to the GAS element in the promoter of Sca-1 gene, resulting in promotion of Sca-1 gene expression. Actual prevention of STAT3 phosphorylation reduced the ligation-induced Sca-1 elevation.

Immunocytochemical study of granular duct cells with a hormonally enhanced granular cell phenotype in the mouse parotid gland

In the parotid glands (PGs) of intact male mice (12 weeks of age, ICR strain), immunofluorescence labels for a true tissue kallikrein, mK1, and for nerve growth factor (NGF) were recognized through the subluminal edges of the striated duct (SD) segments and interlobular duct segments. Because of their small size, secretory granules were not detectable by light microscopy in any of the duct cells. Full-fledged granular cells, containing large secretory granules that were visible by light microscopy, were induced in the SD segments of male mice after the injection of 5alpha-dehydrotestosterone (DHT) and triiodothyronine (T(3)), given either alone or in combination every other day for 2 weeks. A stronger effect was detected in the mice that were concomitantly injected with DHT and T(3), and more abundant, fully developed granular cells appeared in the SD segments of these mice. These full-fledged granular cells were immunoreactive for mK1, NGF, and epidermal growth factor, but not for renin. The present results indicate that some of the SD cells with small granules in the mouse PG can develop a granular cell phenotype, producing more kinds of growth factors, as a result of the actions of androgen and thyroid hormone.

Hypophysectomy and hormonal therapy modulate mK1-immunoreactive duct cells in the mice sublingual glands

The immunocytochemical localization of a true tissue kallikrein, mK1, in mouse sublingual glands (SLGs) was examined following hypophysectomy and hormonal replacement therapy. In the glands of intact mice (14 weeks of age), mK1 was detected in the striated ducts (SDs). Full-fledged granular cells were scattered in the SDs of male mice (but not in those of female mice), showing a cellular mosaic distribution of mK1 with some being positive and others being negative. mK1 was also detected in transitional-type granular cells, though the secretory granules were too small and scarce to be visible by a light microscopy. Hypophysectomy in male mice resulted in the atrophy and loss of secretory granules in many SD cells. Granulation recovered after the repeated injection of 5alpha-dihydrotestosterone (DHT), 3,5,3'-triiodo-L: thyronine (T3), and dexamethasone (Dex), given either alone or in combination to the hypophysectomized mice. The concomitant injection of DHT and T3, with or without Dex, resulted in the reappearance of the full-fledged granular cells, only some of which were mK1-positive. Electron microscopy revealed mK1 to be present exclusively in the secretory granules of these mK1-positive cells, and no ultrastructural differences were observed between mK1-positive and mK1-negative full-fledged granular cells. These results show that the differentiation of the granular cell phenotype in the mouse SLG duct system requires the concomitant action of androgen and thyroid hormone and retards mK1 synthesis.

Estrogen-dependent expression of the tissue kallikrein gene (Klk1) in the mouse uterus and its implications for endometrial tissue growth

Tissue kallikrein mK1 is a serine protease involved in the generation of bioactive kinins for normal cardiac and arterial function in the mouse. In the present study, the tissue kallikrein gene Klk1, which codes for mK1, was shown to be one of the most prevalent of the Klk gene species in the uteri of adult mice, and its mRNA level was significantly higher at estrus than at diestrus. Klk1 mRNA expression was enhanced in the uteri of ovariectomized mice receiving estradiol-17beta treatment. Both endometrial epithelial and stromal cells isolated from the mice exhibited Klk1 expression at detectable levels when cultured in the presence of estradiol-17beta. mK1 was characterized using the recombinant active enzyme. mK1 had trypsin-like activity with a strong preference for Arg over Lys in the P1 position, and its activity was inhibited by typical serine protease inhibitors. Casein, gelatin, fibronectin, collagen type IV, and high-molecular-weight kininogen were degraded by mK1. The single-chain tissue-type plasminogen activator was converted to the two-chain form by mK1. In addition, mK1 degraded insulin-like growth factor binding protein-3. The present data suggest that mK1 may be implicated in the growth of uterine endometrial tissues during the proliferative phase.

Substrate specificity of human kallikrein 6: salt and glycosaminoglycan activation effects

Human kallikrein 6 (hK6) is abundantly expressed in the central nervous system and is implicated in demyelinating disease. This study provided biochemical data about the substrate specificity and activation of hK6 by glycosaminoglycans and by kosmotropic salts, which followed the Hofmeister series. The screening of fluorescence resonance energy transfer (FRET) peptide families derived from Abz-KLRSSKQ-EDDnp resulted in the finding that Abz-AFRFSQ-EDDnp (where Abz is ortho-aminobenzoic acid and EDDnp is N-[2,4-dinitrophenyl]ethylenediamine)) is the best synthetic substrate described so far for hK6 (kcat/Km 38,667 s(-1) mm(-1)). It is noteworthy that the AFRFS sequence was found as a motif in the amino-terminal domain of seven human ionotropic glutamate receptor subunits. We also examined the hK6 hydrolytic activity on FRET peptides derived from human myelin basic protein, precursor of the Abeta amyloid peptide, reactive center loop of alpha1-antichymotrypsin, plasminogen, and maturation and inactivation cleavage sites of hK6, which were described earlier as natural substrates for hK6. The best substrates were derived from myelin basic protein. The hK6 maturation cleavage site was poorly hydrolyzed, and no evidence was found to support a two-step self-activation process reported previously. Finally, we assayed FRET peptides derived from sequences that span the cleavage sites for activation of protease-activated receptors (PAR) 1-4, and only the substrate with the PAR 2 sequence was hydrolyzed. These results further supported the hypothesis that hK6 expressed in the central nervous system is involved in normal myelin turnover/demyelination processes, but it is unlikely to self-activate. This report also suggested the possible modulation of ionotropic glutamate receptors and activation of PAR 2 by hK6.

Tissue kallikrein mK13 is a candidate processing enzyme for the precursor of interleukin-1beta in the submandibular gland of mice

By using Western blot analysis, high levels of 17.5- and 20-kDa interleukin-1beta (IL-1beta) proteins were detected in the submandibular gland (SMG) of mice. Despite this fact, the amount of pro-IL-1beta protein, a precursor of IL-1beta, with a molecular size of 35 kDa in this tissue was below the detectable level, although strong expression of pro-IL-1beta mRNA was observed. A large amount of 17.5-kDa IL-1beta also appeared in the saliva of mice injected with lipopolysaccharide, suggesting that this IL-1beta is a secretory form produced by the SMG. The protein for IL-1beta-converting enzyme, a processing enzyme for pro-IL-1beta, was expressed only at a low level in the SMG as compared with its level in various epithelial tissues or lipopolysaccharide-stimulated macrophages. On the other hand, mK1, mK9, mK13, and mK22, members of the kallikrein family, were detected strongly in the SMG but not in other tissues. By incubation with mK13, but not with mK1, mK9, or mK22, the 35-kDa pro-IL-1beta was cleaved into two major products with molecular masses of 17.5 and 22 kDa, and production was inhibited by phenylmethylsulfonyl fluoride, a serine protease inhibitor, but not by IL-1beta-converting enzyme inhibitors. A peptide segment corresponding to amino acid residues 107-121 of mouse pro-IL-1beta (107WDDDDNLLVCDVPIR) was cleaved by incubation with mK13, generating two peptides, 107WDDDDNL and 114LVCDVPIR. Therefore, kallikrein mK13 would appear to hydrolyze pro-IL-1beta between its Leu113 and Leu114 residues. The results of immunohistochemistry and an autonomic therapy experiment showed that IL-1beta and kallikrein mK13 were co-localized in the secretory granules of granular convoluted tubular cells. Our present results thus suggest kallikrein mK13 is a plausible candidate for the processing enzyme for pro-IL-1beta in the SMG of mice.

Acute phase protein induction by experimental inflammation in the salivary gland

BACKGROUND

The submandibular gland (SMG) is a major salivary gland, which plays an important role in maintenance the oral health. In this study, we intended to explore the role of the SMG's defense system of the animals in which experimental inflammation is induced.

METHODS

The levels of mRNAs for inflammation cytokines and acute phase proteins were detected by reverse transcriptase-polymerase chain reaction (RT-PCR).

RESULTS

The mRNAs for acute phase proteins were found to be increased in the SMG and extraorbital and intraorbital lacrimal gland (ELG and ILG) of rats at 24 h after subcutaneous injection of turpentine oil. The induction of mRNA for these inflammatory proteins by turpentine oil was preceded by a transient increase in the level of mRNAs for IL-1beta, IL-6 and TNF-alpha at 6 h after subcutaneous injection of the oil. Such cytokine induction was similarly seen by lipopolysaccharide (LPS) injection, and involvement of Toll-like receptor 4 (TLR4) was strongly suggested from experiment using C3H/HeJ mice, a TLR4-deficient mutant strain.

CONCLUSION

The up-regulation of acute phase proteins and inflammation cytokines in the SMG, ELG and ILG by experimental inflammation suggests the existence of a strict defense system via the innate immune system in the SMG and other exocrine gland.

Additive and/or synergistic action (downregulation) of androgens and thyroid hormones on the cellular distribution and localization of a true tissue kallikrein, mK1, in the mouse submandibular gland

We investigated the effects of 5alpha-dihydrotestosterone (DHT), 3,5,3'-triiodo-l-thyronine (T(3)), and dexamethasone (Dex) on the expression of mK1 in the granular convoluted tubule (GCT) cells of the submandibular gland (SMG) of hypophysectomized (Hypox) male mice by indirect enzyme-labeled antibody and immunogold antibody methods for light and electron microscopy. Hypox resulted in considerable atrophy of the GCT cells, which were always immunoreactive for mK1, and the cells were characterized by apical small dense secretory granules labeled with gold particles suggesting the presence of mK1, small Golgi apparatus, sparse rough endoplasmic reticulum (RER), and developed basal infoldings. Each of the hormones, DHT, T(3), and Dex, enhanced the GCT phenotype to various degrees in Hypox male mice. Both DHT alone and T(3) alone moderately inhibited mK1 synthesis by increasing the number of mK1-immunonegative GCT cells in Hypox males, but Dex alone had no inhibitory effect on mK1 synthesis. A significant trophic effect on GCT cells was induced by combined injection of DHT and T(3) or of all three hormones, and was reflected in the appearance of abundant large secretory granules, well-developed Golgi apparatus and RER, and reduced basal infoldings. Only a few such GCT cells were immunopositive for mK1, and the pattern of immunopositive and immunonegative cells very closely resembled the mosaic pattern seen in normal male GCTs. These findings suggested that the sexual dimorphism of mK1 expression and the morphological appearance of GCT cells can be induced by treatment with two hormones, DHT and T(3), but not by either of them alone. T(3) appears to have a permissive effect on committed GCT cells that results in downregulation of mK1 expression in these cells.

Autoimmunity against a tissue kallikrein in IQI/Jic Mice: a model for Sjogren's syndrome

We have recently characterized IQI/Jic mice as a model for Sjogren's syndrome (SS), a chronic autoimmune disease in humans. In SS, local lymphocytic infiltrations into salivary and lacrimal glands frequently develop to the involvement of systemic exocrine and nonexocrine organs, and the mechanism for progression of this disease remains obscure. Herein, we report identification of an autoantigen shared by various target organs in IQI/Jic mice. Polypeptides identified based on immunorecognition by autoantibodies in sera from IQI/Jic mice affected with autoimmune disease (>12 weeks of age) were tissue kallikrein (Klk)-1 and -13 and were cross-reactive to the autoantibodies. Interestingly, Klk-13, but not Klk-1, caused a proliferative response of splenic T cells from IQI/Jic mice from the age of 4 weeks onward. In addition, remarkably enhanced expression of Klk-13 was observed in the salivary glands of the mice in accordance with the development of inflammatory lesions. These results indicate that Klk-13 acts as an autoantigen and may increase T cells responsive to organs commonly expressing Klk-13, playing a pivotal role in the etiology of progression of disease in IQI/Jic mice. Our findings provide insights into the contributions of autoantigens shared by multiple organs in the progress of SS from an organ-specific to a systemic disorder.

Differences in substrate and inhibitor sequence specificity of human, mouse and rat tissue kallikreins

The kininogenase activities of mouse (mK1), rat (rK1) and human (hK1) tissue kallikreins were assayed with the bradykinin-containing synthetic peptides Abz-MTEMARRPPGFSPFRSVTVQNH2 (where Abz stands for o-aminobenzoyl) and Abz-MTSVIRRPPGFSPFRAPRV-NH2, which correspond to fragments Met374-Gln393 and Met375-Val393 of mouse and rat LMWKs (low-molecular-mass kininogens) with the addition of Abz. Bradykinin was released from these peptides by the mK1- and rK1-mediated hydrolysis of Arg-Arg and Arg-Ser (or Arg-Ala) peptide bonds. However, owing to preferential hydrolysis of Phe-Arg compared with the Arg-Ala bond in the peptide derived from rat LMWK, hK1 released bradykinin only from the mouse LMWK fragment and preferentially released des-[Arg9]bradykinin from the rat LMWK fragment (Abz-MTSVIRRPPGFSPFRAPRV-NH2). The formation of these hydrolysis products was examined in more detail by determining the kinetic parameters for the hydrolysis of synthetic, internally quenched fluorescent peptides containing six N- or C-terminal amino acids of bradykinin added to the five downstream or upstream residues of mouse and rat kininogens respectively. One of these peptides, Abz-GFSPFRAPRVQ-EDDnp (where EDDnp stands for ethylenediamine 2,4-dinitrophenyl), was preferentially hydrolysed at the Phe-Arg bond, confirming the potential des-[Arg9]bradykinin-releasing activity of hK1 on rat kininogen. The proline residue that is two residues upstream of bradykinin in rat kininogen is, in part, responsible for this pattern of hydrolysis, since the peptide Abz-GFSPFRASRVQ-EDDnp was preferentially cleaved at the Arg-Ala bond by hK1. Since this peptidase accepts the arginine or phenylalanine residue at its S1 subsite, this preference seems to be determined by the prime site of the substrates. These findings also suggested that the effects observed in rats overexpressing hK1 should consider the activation of B1 receptors by des-[Arg9]bradykinin. For further comparison, two short internally quenched fluorescent peptides that bind to hK1 with affinity in the nM range and some inhibitors described previously for hK1 were also assayed with mK1 and rK1.

Immunohistochemical Distributions of the Tissue Kallikrein-Kinin System in Ischemic and Non-Ischemic Mouse Heart

Kinins have been shown to play a cardioprotective role during myocardial ischemia. However, the localization of each of the components of the kallikrein-kinin system in the heart has not been determined in a cell type-specific manner. Recently, mK1 has been identified as the major tissue kallikrein with the strongest bradykinin-forming activity among the products of the mouse tissue kallikrein gene superfamily. In the study presented here, we investigated the localizations of mK1, kininogen and bradykinin B2 receptors (B2Rs) in ischemic and non-ischemic left ventricles by immunohistochemistry. Kininogen, which contains bradykinin as a surface epitope, was detected by an anti-bradykinin antibody. Changes in the amounts of mK1 and B2R were evaluated by Western blot analysis. Myocardial ischemia was induced by ligation of the left anterior descending coronary artery for 60 min followed by reperfusion for 24 h. mK1 and B2Rs were most abundantly expressed in the vascular endothelium and, to a lesser extent, in fibroblasts. No immunohistochemical signal of these molecules was detected in myocytes. Kininogen was localized in the vascular endothelium and the smooth muscle layer. Myocardial ischemia, although it had no effect on the localization of these molecules, increased the amounts of mK1 and B2R. We have obtained immunohistochemical evidence that all components of the tissue kallikrein-kinin system are present in the mouse heart. The coronary artery is the major site of kallikrein-kinin activity both in ischemic and non-ischemic hearts.

Specificity of S'1 and S'2 subsites of human tissue kallikrein using the reactive-centre loop of kallistatin: the importance of P'1 and P'2 positions in design of inhibitors

We have demonstrated that the S'(1) and S'(2) subsites of human tissue kallikrein (hK1) play determinant roles in the recognition and hydrolysis of substrates. The presence of serine at position P'(1) and arginine at P'(2) resulted in the best substrate, Abz-Ala-Ile-Lys-Phe-Phe-Ser-Arg-Gln-EDDnp, which was derived from the kallistatin reactive-centre loop sequence and quencher groups o-aminobenzoic acid (Abz) and N-(2,4-dinitrophenyl)ethylenediamine (EDDnp). Serine and arginine are also the residues at positions P'(1) and P'(2) in human kininogen, from which hK1 releases Lys-bradykinin. Several peptide analogues of Abz-Ala-Ile-Lys-Phe-Phe-Ser-Arg-Gln-EDDnp, in which the Ser and Arg residues were substituted with various other amino acids, were synthesized and tested as substrates. Most of them were hydrolysed slowly, although they showed significant binding to hK1, as demonstrated by their competitive inhibition constants (K(i)). Using this information, six peptides were designed, synthesized and assayed as inhibitors of hK1. Abz-Lys-Phe-Phe-Pro-Arg-Gln-EDDnp, Abz-Lys-Phe-Arg-Pro-Arg-Gln-EDDnp and acetyl-Lys-Phe-Phe-Pro-Leu-Glu-NH(2) inhibited hK1 in the range 20-30 nM (letters in italics denote the D-form of the amino acid). The peptide acetyl-Lys-Phe-Phe-Pro-Leu-Glu-NH(2) was a weak inhibitor for other serine proteases, as indicated by the higher K (i) values compared with hK1, but this peptide was a potent inhibitor of human plasma kallikrein, which has a K (i) value of 8 nM. This result was surprising, since this enzyme is known to be a restricted arginyl-hydrolase. In conclusion, acetyl-Lys-Phe-Phe-Pro-Leu-Glu-NH(2) can be used as a leader compound to design specific inhibitors for hK1, plasma kallikrein, or for both at same time, if the inhibition of kinin release is the main goal.

Crystal structure and biochemical characterization of human kallikrein 6 reveals that a trypsin-like kallikrein is expressed in the central nervous system

The human kallikreins are a large multigene family of closely related serine-type proteases. In this regard, they are similar to the multigene kallikrein families characterized in mice and rats. There is a much more extensive body of knowledge regarding the function of mouse and rat kallikreins in comparison with the human kallikreins. Human kallikrein 6 has been proposed as the homologue to rat myelencephalon-specific protease, an arginine-specific degradative-type protease abundantly expressed in the central nervous system and implicated in demyelinating disease. We present the x-ray crystal structure of mature, active recombinant human kallikrein 6 at 1.75-A resolution. This high resolution model provides the first three-dimensional view of one of the human kallikreins and one of only a few structures of serine proteases predominantly expressed in the central nervous system. Enzymatic data are presented that support the identification of human kallikrein 6 as the functional homologue of rat myelencephalon-specific protease and are corroborated by a molecular phylogenetic analysis. Furthermore, the x-ray data provide support for the characterization of human kallikrein 6 as a degradative protease with structural features more similar to trypsin than the regulatory kallikreins.

Design of inhibitors for human tissue kallikrein using non-natural aromatic and basic amino acids

We explored the unique substrate specificity of the primary S, subsite of human urinary kallikrein (hK1), which accepts both Phe or Arg synthesizing and assaying peptides derived from Phenylacetyl-Phe-Ser-Arg-EDDnp, a previously described inhibitor with analgesic and anti-inflammatory activities [Emim et al., Br. J. Pharmacol. 130 (2000), 1099-1107]. Phe was substituted by amino acids containing larger aliphatic or aromatic side chains as well as by non-natural basic amino acids, which were designed to combine a large hydrophobic and/or aromatic group with a positively-charged group at their side chains. In general, all peptides with basic amino acids represented better inhibitors than those with hydrophobic amino acids. Furthermore, the S1 subsite specificity proved to be much more selective than the mere distinction between Phe and Arg, for minor differences in the side chains of the non-natural amino acids resulted in major differences in the Ki values. Finally, we present a series of peptides that were assayed as competitive inhibitors for human tissue kallikrein that may lead to the development of novel peptides, which are both more potent and selective.

Induction of pro-renin converting enzyme mk9 by thyroid hormone in the guinea-pig liver

Kallikreins are a group of specific serine proteases and are an integral part of kallikrein-kinin system. The kallikrein-kinin system is hypotensive in nature and counteracts with the renin-angiotensin system in the maintenance of normal blood pressure. So far, four kallikrein-like enzymes, namely, mK9, mK13, mK22, and mK26, have been known to convert the inactive pro-renin into biologically active renin. Some of these enzymes are induced by the thyroid hormone. In the proposed study, we investigated the effects of thyroid hormone on the expression of genes for mk9, mk13, and mk22 enzymes. We used guinea pigs as models because these animals share many characteristics in common to humans. Male adult guinea pigs were intramuscularly injected with 2 mg/kg body weight of thyronine. Forty-eight hours following the last injection, the liver was processed for Northern blot analysis using labeled mK9, mK13, and mK22 specific RNA probes. Only mK9 was found to be transcriptionally regulated by the hormone.

Developmental and androgenic regulation of the immunocytochemical distribution of mK1, a true tissue kallikrein, in the granular convoluted tubule of the mouse submandibular gland

The action of androgens on the immunocytochemical distribution of mK1, a true tissue kallikrein, was examined in the submandibular gland (SMG) of developing and adult mice by indirect enzyme-labeled and immunogold-labeled antibody methods for light and electron microscopy, respectively. In both sexes at 3 weeks of age, essentially all of the immature granular convoluted tubule (GCT) cells were uniformly immunostained. At 4 weeks of age (the onset of puberty), morphological differences between the two sexes appeared in the GCTs, in which some cells became immunonegative. Thereafter, the immunonegative GCT cells became more abundant in the SMG of males than of females and considerable intercellular variation in staining intensity for mK1 was seen, especially in males. A few slender GCT cells with strong immunoreactivity appeared in GCT segments only in males. Castration of males resulted in an increase in the number of immunopositive GCT cells, whereas administration of dihydrotestosterone (DHT) decreased the number of immunopositive GCT cells in the SMGs of both sexes. Slender GCT cells immunoreactive for mK1 were seen in females treated with DHT for 6 days. However, there were no immunostained slender GCT cells in female SMGs after injection of DHT for 2 weeks. Immunoelectron microscopy disclosed this type of cell in male SMGs, which closely resembles immature GCT cells of prepubertal mice, with a few small secretory granules uniformly labeled with gold particles, a sparse Golgi apparatus and RER, and basal infoldings. In mature male SMGs and in SMGs of DHT-treated females and castrated males, typical GCT cells had a well-developed Golgi apparatus and a net-like RER but few to no basal infoldings, whereas in the female gland equivalent cells had moderately developed RER and some basal infoldings. These results suggest that mK1 is one of the enzymes characteristically present in immature GCT cells and that its synthesis is inhibited in part by androgens, resulting in decreased numbers of immunopositive cells.

Enzymatic properties of rat myelencephalon-specific protease

Myelencephalon-specific protease (MSP), first identified in the rat and now known to have a human homologue (human kallikrein 6), is preferentially expressed in the central nervous system (CNS), compared with nonneural tissues. MSP has been postulated to have trypsin-like activity, is upregulated in response to glutamate receptor-mediated excitotoxic injury in the CNS, and is downregulated in the brain of Alzheimer's patients. The preferential expression of this enzyme by oligodendrocytes in CNS white matter points to a role in myelin homeostasis. To further characterize the activity and substrate specificity of this newly identified enzyme, we have heterologously expressed MSP in a baculovirus/insect cell line system. We demonstrate that recombinant MSP exhibits a broad specificity for cleavage after arginine but not lysine residues, with kinetic characteristics intermediate between trypsin and pancreatic kallikrein. We show that the pro form of MSP does not self-activate but, rather, requires cleavage after lysine, indicating that mature active MSP is regulated by a distinct protease. MSP may be regulated in part by autolysis, since the active protein is readily inactivated through autolysis at specific internal arginine positions. Additionally, we show that MSP is abundantly expressed in inflammatory cells at sites of demyelination in the Theiler's murine encephalomyelitis virus (TMEV) model of multiple sclerosis (MS). In conjunction with data demonstrating the ability of MSP to degrade myelin-associated as well as several extracellular matrix proteins, these findings delineate MSP as a broad-specificity arginine-specific protease with the potential to play a key role in immune-mediated demyelination.

Human tissue kallikrein S1 subsite recognition of non-natural basic amino acids

We explored the unique substrate specificity of the primary S(1) subsite of human urinary kallikrein (hK1), which accepts both Phe and Arg, using internally quenched fluorescent peptides Abz-F-X-S-R-Q-EDDnp and Abz-G-F-S-P-F-X-S-S-R-P-Q-EDDnp [Abz is o-aminobenzoic acid; EDDnp is N-(2,4-dinitrophenyl)ethylenediamine], which were based on the human kininogen sequence at the C-terminal region of bradykinin. Position X, which in natural sequence stands for Arg, received the following synthetic basic non-natural amino acids: 4-(aminomethyl)phenylalanine (Amf), 4-guanidine phenylalanine (Gnf), 4-(aminomethyl)-N-isopropylphenylalanine (Iaf), N(im)-(dimethyl)histidine [H(2Me)], 3-pyridylalanine (Pya), 4-piperidinylalanine (Ppa), 4-(aminomethyl)cyclohexylalanine (Ama), and 4-(aminocyclohexyl)alanine (Aca). Only Abz-F-Amf-S-R-Q-EDDnp and Abz-F-H(2Me)]-S-R-Q-EDDnp were efficiently hydrolyzed, and all others were resistant to hydrolysis. However, Abz-F-Ama-S-R-Q-EDDnp inhibited hK1 with a K(i) of 50 nM with high specificity compared to human plasma kallikrein, thrombin, plasmin, and trypsin. The Abz-G-F-S-P-F-X-S-S-R-P-Q-EDDnp series were more susceptible to hK1, although the peptides with Gnf, Pya, and Ama were resistant to it. Unexpectedly, the peptides in which X is His, Lys, H(2Me), Amf, Iaf, Ppa, and Aca were cleaved at amino or at carboxyl sites of these amino acids, indicating that the S(1)' subsite has significant preference for basic residues. Human plasma kallikrein did not hydrolyze any peptide of this series except the natural sequence where X is Arg. In conclusion, the S(1) subsite of hK1 accepts amino acids with combined basic and aromatic side chain, although for the S(1)-P(1) interaction the preference is for aliphatic and basic side chains.

Cardiovascular abnormalities with normal blood pressure in tissue kallikrein-deficient mice

Tissue kallikrein is a serine protease thought to be involved in the generation of bioactive peptide kinins in many organs like the kidneys, colon, salivary glands, pancreas, and blood vessels. Low renal synthesis and urinary excretion of tissue kallikrein have been repeatedly linked to hypertension in animals and humans, but the exact role of the protease in cardiovascular function has not been established largely because of the lack of specific inhibitors. This study demonstrates that mice lacking tissue kallikrein are unable to generate significant levels of kinins in most tissues and develop cardiovascular abnormalities early in adulthood despite normal blood pressure. The heart exhibits septum and posterior wall thinning and a tendency to dilatation resulting in reduced left ventricular mass. Cardiac function estimated in vivo and in vitro is decreased both under basal conditions and in response to beta-adrenergic stimulation. Furthermore, flow-induced vasodilatation is impaired in isolated perfused carotid arteries, which express, like the heart, low levels of the protease. These data show that tissue kallikrein is the main kinin-generating enzyme in vivo and that a functional kallikrein-kinin system is necessary for normal cardiac and arterial function in the mouse. They suggest that the kallikrein-kinin system could be involved in the development or progression of cardiovascular diseases.

Expression of kininogens in the connective tissue-type mast cells of the rat

The connective tissue-type mast cells present in the submandibular gland (SMG) and peritoneal cavity of rats were found to express kininogens (KGs), the expression of which was demonstrated by Western blotting, reverse transcription-polymerase chain reaction (RT-PCR), RT-PCR Southern blotting, and light- and electron-microscopic immunocytochemistry. In the SMG, the analysis of cDNA amplified by RT-PCR revealed that the molecular species of mRNAs expressed were high-molecular-weight (HMW)-K KG and T-I KG. Light microscopic immunocytochemistry exclusively localized the KG protein(s) in the mast cells present in the SMG. The signals in the mast cells were very strong, but no positive reaction was observed in the granular convoluted tubular cells, acinar cells or striated duct cells. As determined by using electron microscopy, extremely strong labelling with immunogold was observed in the secretory granules of the mast cells, but no labelling in their nucleus or cytoplasm. Analysis by Western blotting and RT-PCR Southern blotting indicated that both protein and mRNA of KGs were present in the mast cells separated from the peritoneal cavity, indicating de novo synthesis of KG in these cells. Preliminary experiments implied that the connective tissue-type mast cells in other rat tissues also expressed KG.

Thyroid hormone (3,5,3'-triido-L-thyronine) masking/inversion of stimulatory effect of androgen on expression of mk1, a true tissue kallikrein, in the mouse submandibular gland

We studied hormonal regulation of the expression of mkl, a true tissue kallikrein, in the submandibular gland (SMG) of ICR, C3H/ HeN, and F1 (mice from male C3H/HeN x female ICR and in the ones from male ICR x female C3H/HeN). In these mouse strains, mk1 was low in content in males, abundant in females, and increased remarkably by castration of males. In the case of ICR and both F1 mice, injection of 5alpha-dihydrotestosterone (DHT) reduced the mkl level of castrated and female mice. However, the mkl content in female C3H/ HeN mice (or castrated C3H/HeN) was further increased by DHT. To investigate the real action of DHT on mk1 expression, we examined the effects of adrenoectomy/glucocorticoid (dexamethasone, Dex) administration; DHT administration into castrated and adrenoectomized mice; ovariectomy/female hormone (17beta-estradiol, progesterone) administration; and hypophysectomy/combinatory administration of DHT, Dex, and thyroid hormone (3,5,3'-triiodo-L-thyronine, T3) on the mk1 expression in the SMG of ICR mice. Adrenoectomy or ovariectomy did not change the characteristic pattern of mk1 expression in male and female ICR mice. In hypophysectomized (Hypox) ICR male mice, the mk1 content was increased to the same level as in normal ICR females, and DHT administration into the Hypox mice further increased the mk1 level. However, combinatory administration of DHT + T3 or of DHT + T3 + Dex into the Hypox mice lowered the mkl content to the level of normal ICR males, whereas T3 single administration had no effect. Dex single administration into the Hypox mice increased the mkl level to an even higher than that observed with DHT administration. The mk1 level in Hypox mice was not significantly changed by coadministration of Dex with T3. From these results, we conclude that 1) mk1 expression is fundamentally stimulated by androgen (DHT) as are other mk isozymes, such as mk9, mk13, mk22, and mk26 in the mouse SMG, 2) the effect (stimulatory) of DHT on mk1 expression becomes, however, inverted (inhibitory) in the presence of T3. Although the serum T3 level of C3H/HeN female (0.52 ng/ml) was not significantly different from that of C3H/HeN males or ICR mice, coadministration of T3 into C3H/HeN females with a fixed amount of DHT (20 mg/kg body weight) dose dependently repressed the DHT-induced increase in mkl expression, suggesting the lower sensitivity of C3H/HeN females to T3.

An unusual sexually dimorphic mosaic distribution of a subset of kallikreins in the granular convoluted tubule of the mouse submandibular gland detected by an antibody with restricted immunoreactivity

The granular convoluted tubule of the mouse submandibular gland contains a wide variety of biologically active proteins, including several kallikreins. The tubule is under multihormonal regulation, and is sexually dimorphic, being larger in males than in females. Correspondingly, levels of its various protein secretory products are more abundant in males than in females. However, isoelectric focussing studies show that the true tissue kallikrein, mK1, is more abundant in the female than in the male submandibular gland. In this study, an antiserum was prepared with restricted immunoreactivity for mouse mK1, and possibly other kallikrein family members of low abundance in the mouse submandibular gland, and used for the immunocytochemical staining of the granular convoluted tubule cells in the submandibular gland of adult male and female mice, by indirect enzyme-labeled and immunogold-labeled antibody methods for light and electron microscopy, respectively. The distribution of immunoreactive tubule cells showed an unusual sexual dimorphism. In males only a few scattered slender tubule cells were strongly stained, while the more typical large tubule cells were only occasionally weakly positive, and many of them were not stained. By contrast, in females slender tubule cells were not seen, and about two thirds of the more typical tubule cells showed moderate to strong immunostaining. Immunoelectron microscopy revealed that immunostaining was confined to the secretion granules in granular convoluted tubule cells in both sexes. The slender tubule cells of males had many strongly stained small apical secretion granules and occasional basal infoldings; in the weakly positive larger more typical tubule cells not all secretion granules were positive, and there was intergranular variation in the intensity of staining of positive granules. In females, although more tubule cells were stained, intergranular variations in staining intensity were also noted. In both sexes, many tubule cells did not contain any secretion granules that showed immunogold labeling for kallikreins. These findings establish that, in contrast to the situation for the majority of granular convoluted tubules proteins, mK1 and possibly other minor kallikrein family members are more abundant in the granular convoluted tubules of female mice, and that there is considerable variation in the content of these kallikreins not only between different tubule cells, but also in individual secretion granules in any given tubule cell in either sex.

Prorenin processing and restricted endoproteolysis by mouse tissue kallikrein family enzymes (mK1, mK9, mK13, and mK22)

Four members of the tissue kallikrein family, mK1, mK9, mK13, and mK22, all of which exhibit extensive homology in amino acid sequence among themselves, were obtained from the submandibular gland of ICR mice and examined for their ability to cleave prorenin. Tissue kallikrein mK13 was confirmed to be a prorenin-converting enzyme; and mK9, which was earlier shown to be an EGF-binding protein, was found to cleave mouse Ren 2 prorenin specifically and convert it to mature renin with an activity of approximately 1/10 of that of mK13. With the same substrate, mK22 (beta-NGF endopeptidase) gave two products, renin and arginyl-renin; whereas mK1 (true tissue kallikrein) did not process it at all. The endoproteolytic activity of tissue kallikreins was examined with various peptide-MCA substrates. The substrates contained three key structures; X(Y)-Arg-Arg, X(Y)-Lys-Arg and X-Lys-Lys motifs (where X and Y are hydrophilic and hydrophobic amino acids, respectively). We found that mK1, mK9 and mK13 preferentially cleaved the former two types of substrate, except Y-Arg-Arg-MCA. The substrate X-Lys-Lys-MCA was hardly cleaved by these three tissue kallikreins but was preferentially cleaved by mK22. The four tissue kallikreins seem to have the ability to process precursor proteins containing a pair of basic amino acid residues; the specificities of three of the enzymes (mK1, mK9 and mK13) were similar to each other but were different from that of mK22.