Human kallikrein 6 activity is regulated via an autoproteolytic mechanism of activation/inactivation

Anti-angiogenic activity of a novel angiostatin-like plasminogen fragment produced by a bacterial metalloproteinase

Tumor growth depends on angiogenesis, a process by which new blood vessel are formed from pre-existing normal blood vessels. Proteolytic fragments of plasminogen, containing varying numbers of plasminogen kringle domains, collectively known as angiostatin, are a naturally occurring inhibitor of angiogenesis and inhibit tumor growth. We have developed an "affinity-capture reactor" that enables a single-step method for the production/purification of an angiostatin-like plasminogen fragment from human plasma using an immobilized bacterial metalloproteinase. The resulting fragment, named BL-angiostatin, contains one or two glycosyl chains and the N-terminal PAN module, which are not present in canonical angiostatins tested for cancer treatment. BL-angiostatin inhibited angiogenesis in vitro at 20 nM and the growth of both allograft and human xenograft tumors as well as lung metastasis of primary tumors mice at 0.3-10 mg kg-1. Derivatives of BL angiostatin lacking the PAN module or the terminal sialic acids in the glycosyl chains showed reduced anti-angiogenic activity in vivo, suggesting a role for these functions in activity, possibly via conferring a pharmacokinetic advantage to BL angiostatin compared to recombinant angiostatin lacking both features. These results highlight the potential of BL-angiostatin for therapeutic applications.

A novel approach to enhance the performance of kallikrein 6 enzyme using Pichia pastoris GS115 as a host

Background and purpose

Enzyme engineering is the process of raising enzyme efficiency and activity by altering amino acid sequences. Kallikrein 6 (KLK6) enzyme is a secreted serine protease involved in a variety of physiological and pathological activities. The increased expression of KLK6 plays a key role in various diseases. Instability and spontaneous activation and deactivation are major challenges in the study of this enzyme. This study aimed to create a stable pro-KLK6 enzyme by enzyme engineering, designing a specific cleavage site for enterokinase, and using Pichia pastoris GS115 as a host cell. Then, recombinant pro-KLK6 was used to introduce a novel inhibitor for it.

Experimental approach

An engineered pro-KLK6 gene was cloned into the pPICZα A expression vector. Then, it was expressed in P. pastoris GS115 and purified by Ni-NTA chromatography. An inactive engineered pro-KLK6 gene was cleaved by enterokinase and converted to an active KLK6. The KLK6 enzyme activity and its kinetic parameters were measured using N-benzoyl-L-arginine ethyl ester (BAEE) substrates.

Findings/Results

The secretory form of the pro-KLK6 was expressed at about 11 mg/L in P. pastoris (GS115). Before activation with enterokinase, pro-KLK6 was inactive and did not activate spontaneously. The kinetic parameters, including Km and Vmax, were estimated at 113.59 μM and 0.432 μM/s, respectively.

Conclusion and implications

A stable pro-KLK6 enzyme was produced using P. pastoris (GS115) as the host cell and a specific cleavage site for enterokinase. Additionally, this study assessed the kinetic parameters of the KLK6 enzyme using the BAEE substrate for the first time.

Reconstructing the epidermal proteolytic cascades in health and disease

The epidermis is the outer stratified epithelium of the skin, forming the physical barrier that is indispensable for homeostasis. Epidermal proteolysis, mainly but not exclusively executed by kallikrein-related peptidases (KLKs), is tightly regulated to ensure maintenance of physiological skin renewal and an intact skin barrier. Perturbation of epidermal proteolytic networks is implicated in a wide array of rare and common skin pathologies of diverse genetic backgrounds. Recent studies of monogenic human skin diseases and newly developed animal models have revealed new mechanisms of regulation of proteolytic pathways in epidermal physiology and in disease states. These new data have challenged some accepted views, for example the role of matriptase in epidermal desquamation, which turned out to be restricted to mouse skin. The significance of PAR2 signaling in skin inflammation should also be reconsidered in the face of recent findings. Cumulatively, recent studies necessitate a sophisticated redefinition of the proteolytic and signaling pathways that operate in human skin. We elaborate how epidermal proteolysis is finely regulated at multiple levels, and in a spatial manner that was not taken into consideration so far, in which specific proteases are confined to distinct epidermal sublayers. Of interest, transglutaminases have emerged as regulators of epidermal proteolysis and desquamation by spatially fixing endogenous protease inhibitors, constituting regulatory factors that were not recognized before. Furthermore, new evidence suggests a link between proteolysis and lipid metabolism. By synthesis of established notions and recent discoveries, we provide an up-to-date critical parathesis of current knowledge and the extended complexity of proteolysis regulation and signaling pathways in skin. This article is protected by copyright. All rights reserved.

Deficiency of the serine peptidase Kallikrein 6 does not affect the levels and the pathological accumulation of a-synuclein in mouse brain

Several lines of evidence indicate that the propagation of misfolded α-synuclein (α-syn) plays a central role in the progression and manifestation of Parkinson's disease. Pathogenic α-syn species can be present in the extracellular space. Thus, the identification and modulation of the key enzymes implicated in extracellular α-syn turnover becomes vital. Kallikrein peptidase 6 has been identified as one of the major α-syn degrading enzymes and has been implicated in the clearance of extracellular α-syn. However, the physiological role of this enzyme in regulating α-syn, in vivo, still remains elusive. Here, by utilizing Klk6 knock-out (Klk6^-/- ) mice as our experimental model, we provide insight into the physiologic relevance of endogenous KLK6 expression on α-syn processing. Behavioral phenotyping showed that Klk6^-/- mice display no gross behavioral abnormalities. Further in vivo characterization of this mouse model, in the context of α-syn accumulation, showed that KLK6 deletion had no impact on the protein levels of intracellular or extracellular α-syn. Upon in vivo administration of α-syn pre-formed fibrils (PFF), α-syn pathologic accumulations were evident both in the brains of Klk6^-/- mice and wt mice without significant differences. Intrastriatal delivery of active KLK6, did not affect secreted α-syn levels observed in the A53T α-syn over-expressing mice. These findings suggest that in the in vivo setting of PFF pathology induction, KLK6 alone is not able to modulate pathology transmission. Our study raises implications for the use of recombinant α-syn fibrils in α-syn turnover studies.

Granzymes in cardiovascular injury and disease

Chronic inflammation and impaired wound healing play important roles in the pathophysiology of cardiovascular diseases. Moreover, the aberrant secretion of proteases plays a critical role in pathological tissue remodeling in chronic inflammatory conditions. Human Granzymes (Granule secreted enzymes - Gzms) comprise a family of five (GzmA, B, H, K, M) cell-secreted serine proteases. Although each unique in function and substrate specificities, Gzms were originally thought to share redundant, intracellular roles in cytotoxic lymphocyte-induced cell death. However, an abundance of evidence has challenged this dogma. It is now recognized, that individual Gzms exhibit unique substrate repertoires and functions both intracellularly and extracellularly. In the extracellular milieu, Gzms contribute to inflammation, vascular dysfunction and permeability, reduced cell adhesion, release of matrix-sequestered growth factors, receptor activation, and extracellular matrix cleavage. Despite these recent findings, the non-cytotoxic functions of Gzms in the context of cardiovascular disease pathogenesis remain poorly understood. Minimally detected in tissues and bodily fluids of normal individuals, GzmB is elevated in patients with acute coronary syndromes, coronary artery disease, and myocardial infarction. Pre-clinical animal models have exemplified the importance of GzmB in atherosclerosis, aortic aneurysm, and cardiac fibrosis as animals deficient in GzmB exhibit reduced tissue remodeling, improved disease phenotypes and increased survival. Although a role for GzmB in cardiovascular disease is described, further work to elucidate the mechanisms that underpin the remaining human Gzms activity in cardiovascular disease is necessary. The present review provides a summary of the pre-clinical and clinical evidence, as well as emerging areas of research pertaining to Gzms in tissue remodeling and cardiovascular disease.

Kallikreins: Essential epidermal messengers for regulation of the skin microenvironment during homeostasis, repair and disease

As the outermost layer of the skin, the epidermis is playing a major role in organism homeostasis providing the first barrier against external aggressions. Although considered as an extracellular matrix (ECM)-poor subtissue, the epidermal microenvironment is a key regulator of skin homeostasis and functionality. Among the proteins essential for upholding the epidermal microenvironment are the members of the kallikrein (KLK) family composed of 15 secreted serine proteases. Most of the members of these epithelial-specific proteins are present in skin and regulate skin desquamation and inflammation. However, although epidermal products, the consequences of KLK activities are not confined to the epidermis but widespread in the skin. In this review starting with the location and proteolytic activation cascade of KLKs, we present KLKs involvement in skin homeostasis, regeneration and pathology. KLKs have a large variety of substrates including ECM proteins, and evidence suggests that they are involved in the different steps of skin wound healing as discussed here. KLKs are also used as prognosis/diagnosis markers for many cancer types and we are focusing later on KLKs in cutaneous cancers, although their pathogenicity remains to be fully elucidated. Dysregulation of the KLK cascade is directly responsible for skin diseases with heavy inflammatory aspects, highlighting their involvement in skin immune homeostasis. Future studies will be needed to support the therapeutic potential of adjusting KLK activities for treatment of inflammatory skin diseases and wound healing pathologies.

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Regulation of the microenvironment even in an extracellular matrix-poor tissue can heavily impact organ function.

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Extracellular activities of kallikreins maintain skin homeostasis by regulating desquamation and inflammation.

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The activation of skin epidermal-specific kallikrein family of proteases is regulated by an intricate proteolytic cascade.

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Kallikreins are emerging as players during skin wound healing.

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Dysregulated kallikrein expression and activity occur in cancers and inflammatory skin diseases.

Kallikrein 6 protease advances colon tumorigenesis via induction of the high mobility group A2 protein

Kallikrein-related peptidase 6 (KLK6) overexpression is commonly observed in primary tumors of colorectal cancer (CRC) patients and has been associated with tumor aggressiveness, metastasis, and poor prognosis. We previously established a unique contribution of KLK6 in colon cancer metastasis via a specific network of microRNAs and mRNAs. Here we evaluated the cellular functions of KLK6 protease in Caco-2 colon adenocarcinoma cell line after introduction of the enzymatically active or inactive form of the enzyme. We found that proteolytically active KLK6 increased Caco-2 cells invasiveness in vitro and decreased the animal survival in the orthotopic colon cancer model. The active KLK6 induced phosphorylation of SMAD 2/3 proteins leading to the altered expression of the epithelial-mesenchymal transition (EMT) markers. KLK6 overexpression also induced the RNA-binding protein LIN28B and high-mobility group AT-hook 2 (HMGA2) transcription factor, two essential regulators of cell invasion and metastasis. In the CRC patients, KLK6 protein levels were elevated in the non-cancerous distant and adjacent tissues, compared to their paired tumor tissues (p < 0.0001 and p = 0.0157, respectively). Patients with mutant K-RAS tumors had significantly higher level of KLK6 protein in the luminal surface of non-cancerous distant tissue, compared to the corresponding tissues of the patients with K-RAS wild type tumors (p ≤ 0.05). Furthermore, KLK6 and HMGA2 immunohistochemistry (IHC) scores in patients' tumors and paired adjacent tissues positively correlated (Spearman correlation P < 0.01 and p = 0.03, respectively). These findings demonstrate the critical function of the KLK6 enzyme in colon cancer progression and its contribution to the signaling network in colon cancer.

Biochemical pathways mediated by KLK6 protease in breast cancer

Kallikrein-related peptidase 6 (KLK6) is a serine protease normally expressed in mammary tissue and aberrantly regulated in breast cancer. At physiological levels, KLK6 functions as a suppressor of breast cancer, while its aberrant overexpression (> 50-fold higher than normal) is characteristic of a subset of breast cancers and has been linked to accelerated growth of primary breast tumors in severe combined immunodeficiency mice (Pampalakis et al. Cancer Res 2009, 69, 3779). Here, we investigated the molecular mechanisms underlying the concentration-dependent functions of KLK6 by comparing MDA-MB-231 stable transfectants expressing increasing levels of KLK6 in in vitro and in vivo tumorigenicity assays (soft agar, xenograft growth, tail vein metastasis). Quantitative proteomics was applied to identify proteins that are altered upon re-expression of KLK6 in MDA-MB-231 at normal or constitutive levels. Overexpression of KLK6 is associated with increased metastatic ability of breast cancer cells into lungs, increased expression of certain S100 proteins (S100A4, S100A11) and keratins (KRT), and downregulation of the apoptosis-related proteases CASP7 and CASP8, and RABs. On the other hand, KLK6 re-expression at physiological levels leads to inhibition of lung metastases associated with suppression of S100 proteins (S100A4, S100A10, S100A13, S100A16) and induced CASP7 and CASP8 expression. As this is the first report that KLK6 expression is associated with S100 proteins, caspases, RABs, and KRTs, we validated this finding in clinical datasets. By integrating proteomics and microarray data from breast cancer patients, we generated two composite scores, KLK6 + S100B-S100A7 and KLK6 + S100B-S100A14-S100A16, to predict long-term survival of breast cancer patients. We present previously unknown pathways implicating KLK6 in breast cancer. The findings promise to aid our understanding of the functional roles of KLK6 in breast cancer and may yield new biomarkers for the cancer types in which KLK6 is known to be aberrantly upregulated.

How is alpha-synuclein cleared from the cell?

The levels and conformers of alpha-synuclein are critical in the pathogenesis of Parkinson's Disease and related synucleinopathies. Homeostatic mechanisms in protein degradation and secretion have been identified as regulators of alpha-synuclein at different stages of its intracellular trafficking and transcellular propagation. Here we review pathways involved in the removal of various forms of alpha-synuclein from both the intracellular and extracellular environment. Proteasomes and lysosomes are likely to play complementary roles in the removal of intracellular alpha-synuclein species, in a manner that depends on alpha-synuclein post-translational modifications. Extracellular alpha-synuclein is cleared by extracellular proteolytic enzymes, or taken up by neighboring cells, especially microglia and astrocytes, and degraded within lysosomes. Exosomes, on the other hand, represent a vehicle for egress of excess burden of the intracellular protein, potentially contributing to the transfer of alpha-synuclein between cells. Dysfunction in any one of these clearance mechanisms, or a combination thereof, may be involved in the initiation or progression of Parkinson's disease, whereas targeting these pathways may offer an opportunity for therapeutic intervention. This article is part of the Special Issue "Synuclein".

A potent, proteolysis-resistant inhibitor of kallikrein-related peptidase 6 (KLK6) for cancer therapy, developed by combinatorial engineering

Human tissue kallikrein (KLK) proteases are hormone-like signaling molecules with important functions in cancer pathophysiology. KLK-related peptidase 6 (KLK6), specifically, is highly up-regulated in several types of cancer, where its increased activity promotes cancer invasion and metastasis. This characteristic suggests KLK6 as an attractive target for therapeutic interventions. However, inhibitors that specifically target KLK6 have not yet been reported, possibly because KLK6 shares a high sequence homology and structural similarity with other serine proteases and resists inhibition by many polypeptide inhibitors. Here, we present an innovative combinatorial approach to engineering KLK6 inhibitors via flow cytometry-based screening of a yeast-displayed mutant library of the human amyloid precursor protein Kunitz protease inhibitor domain (APPI), an inhibitor of other serine proteases, such as anionic and cationic trypsins. On the basis of this screening, we generated APPI_{M17L,I18F,S19F,F34V} (APPI-4M), an APPI variant with a KLK6 inhibition constant (K_i ) of 160 pm and a turnover time of 10 days. To the best of our knowledge, APPI-4M is the most potent KLK6 inhibitor reported to date, displaying 146-fold improved affinity and 13-fold improved proteolytic stability compared with WT APPI (APPI_WT). We further demonstrate that APPI-4M acts as a functional inhibitor in a cell-based model of KLK6-dependent breast cancer invasion. Finally, the crystal structures of the APPI_WT/KLK6 and APPI-4M/KLK6 complexes revealed the structural and mechanistic bases for the improved KLK6 binding and proteolytic resistance of APPI-4M. We anticipate that APPI-4M will have substantial translational potential as both imaging agent and therapeutic.

Kallikrein-related peptidase 6 can cleave human-muscle-type 6-phosphofructo-1-kinase into highly active shorter fragments

PURPOSE

Cancer cells consume more glucose than normal human cells and convert most glucose into lactate. It has been proposed that deregulated glycolysis is triggered by the posttranslational modification of 85 kDa muscle-type 6-phosphofructo-1-kinase (PFK-M) which is cleaved by a specific protease to form shorter, highly active, feedback-inhibition-resistant PFK-M fragments.

PRINCIPAL RESULTS

To find the protease involved in PFK-M modification, analyses of the protease target sites on the human PFK-M enzyme yielding 45-47 kDa fragments were performed in silico. The results suggested that an enzyme in the kallikrein (KLK) family may be involved. Kallikreins can be self-activated in the cytosol and are often overexpressed in cancer cells. After incubating the internally quenched FRET peptide with a sequence characteristic of the target site, along with the active KLK6, the cleavage of the peptide was observed. The ability of KLK6 to cleave native PFK-M and form highly active citrate-resistant 45 kDa fragments was further confirmed by enzymatic tests and SDS-PAGE. A role of KLK6 in the posttranslational modification of native PFK-M was ultimately confirmed in vivo. A yeast strain that encoded native human PFK-M as the only PFK1 enzyme was additionally transformed with proKLK6 or KLK6 genes under the control of an inducible promoter. The transformants growth rate was found to increase after the induction of proKLK6 gene expression as compared to the strain with the native PFK-M enzyme.

CONCLUSION

KLK6 may be the key protease involved in the modification of PFK-M and trigger deregulated glycolytic flux in cancer cells.

Regulation of kallikrein-related peptidases in the skin – from physiology to diseases to therapeutic options

Kallikrein-related peptidases (KLKs) constitute a family of 15 highly conserved serine proteases, which show a tissue-specific expression profile. This made them valuable tumour expression markers. It became evident that KLKs are involved in many physiological processes like semen liquefaction and skin desquamation. More recently, we have learnt that they are involved in many pathophysiological conditions and diseases making them promising target of therapeutic intervention. Therefore, regulation of KLKs raised the interest of numerous reports. Herein, we summarise the current knowledge on KLKs regulation with an emphasis on skin-relevant KLKs regulation processes. Regulation of KLKs takes place on the level of transcription, on protease activation and on protease inactivation. A variety of protease inhibitors has been described to interact with KLKs including the irreversible serine protease inhibitors (SERPINs) and the reversible serine protease inhibitors of Kazal-type (SPINKs). In an attempt to integrate current knowledge, we propose that KLK regulation has credentials as targets for therapeutic intervention.

Methodology and Applications of Disease Biomarker Identification in Human Serum

Biomarkers are biomolecules that serve as indicators of biological and pathological processes, or physiological and pharmacological responses to a drug treatment. Because of the high abundance of albumin and heterogeneity of plasma lipoproteins and glycoproteins, biomarkers are difficult to identify in human serum. Due to the clinical significance the identification of disease biomarkers in serum holds great promise for personalized medicine, especially for disease diagnosis and prognosis. This review summarizes some common and emerging proteomics techniques utilized in the separation of serum samples and identification of disease signatures. The practical application of each protein separation or identification technique is analyzed using specific examples. Biomarkers of cancers of prostate, breast, ovary, and lung in human serum have been reviewed, as well as those of heart disease, arthritis, asthma, and cystic fibrosis. Despite the advancement of technology few biomarkers have been approved by the Food and Drug Administration for disease diagnosis and prognosis due to the complexity of structure and function of protein biomarkers and lack of high sensitivity, specificity, and reproducibility for those putative biomarkers. The combination of different types of technologies and statistical analysis may provide more effective methods to identify and validate new disease biomarkers in blood.

KLK6 proteolysis is implicated in the turnover and uptake of extracellular alpha-synuclein species

KLK6 is a serine protease highly expressed in the nervous system. In synucleinopathies, including Parkinson disease, the levels of KLK6 inversely correlate with α-synuclein in CSF. Recently, we suggested that recombinant KLK6 mediates the degradation of extracellular α-synuclein directly and via a proteolytic cascade that involves unidentified metalloproteinase(s). Here, we show that recombinant and naturally secreted KLK6 can readily cleave α-synuclein fibrils that have the potential for cell-to-cell propagation in “a prion-like mechanism”. Importantly, KLK6-deficient primary cortical neurons have increased ability for α-synuclein fibril uptake. We also demonstrate that KLK6 activates proMMP2, which in turn can cleave α-synuclein. The repertoire of proteases activated by KLK6 in a neuronal environment was analyzed by degradomic profiling, which also identified ADAMTS19 and showed that KLK6 has a limited number of substrates indicating specific biological functions such as the regulation of α-synuclein turnover. We generated adenoviral vectors for KLK6 delivery and demonstrated that the levels of extracellular α-synuclein can be reduced by neuronally secreted KLK6. Our findings open the possibility to exploit KLK6 as a novel therapeutic target for Parkinson disease and other synucleinopathies.

Biochemical and functional characterization of the human tissue kallikrein 9

Human tissue kallikrein 9 (KLK9) is a member of the kallikrein-related family of proteases. Despite its known expression profile, much less is known about the functional roles of this protease and its implications in normal physiology and disease. We present here the first data on the biochemical characterization of KLK9, investigate parameters that affect its enzymatic activity (such as inhibitors) and provide preliminary insights into its putative substrates. We show that mature KLK9 is a glycosylated chymotrypsin-like enzyme with strong preference for tyrosine over phenylalanine at the P1 cleavage position. The enzyme activity is enhanced by Mg2+ and Ca2+, but is reversibly attenuated by Zn2+. KLK9 is inhibited in vitro by many naturally occurring or synthetic protease inhibitors. Using a combination of degradomic and substrate specificity assays, we identified candidate KLK9 substrates in two different epithelial cell lines [the non-tumorigenic human keratinocyte cells (HaCaT) and the tumorigenic tongue squamous carcinoma cells (SCC9)]. Two potential KLK9 substrates [KLK10 and midkine (MDK)] were subjected to further validation. Taken together, our data delineate some functional and biochemical properties of KLK9 for future elucidation of the role of this enzyme in health and disease.

“Activography”: a novel, versatile and easily adaptable method for monitoring enzymatic activities in situ

We developed activography to map enzymatic activities on tissue sections using activity-based probes.

Putative functions of tissue kallikrein-related peptidases in vaginal fluid

Cervical-vaginal fluid (CVF) is a complex biological fluid that hydrates the mucosa of the lower female reproductive system. In-depth proteomic and biochemical studies on CVF have revealed that it contains large amounts of endogenous proteases and protease inhibitors, including an abundance of several members of the tissue kallikrein-related peptidase (KLK) family. Despite their ubiquitous presence in human tissues and fluids, KLK expression levels vary considerably, with maximum expression observed in reproduction-related tissues and fluids. The roles of KLKs in the lower female reproductive system are not fully understood. The activation of KLKs in CVF is dependent on pH and various modes of KLK regulation in the vagina exist. KLKs have been postulated to have roles in physiological functions related to antimicrobial processes, vaginal and cervical epithelial desquamation, sperm transport, and the processing of fetal membranes as observed in preterm premature rupture of membranes. Increased understanding of the functional roles of KLKs in the lower female reproductive system could lead to new diagnostic and therapeutic modalities for conditions such as vaginal infections and vaginal atrophy.

KLK6-regulated miRNA networks activate oncogenic pathways in breast cancer subtypes

KLK6 is expressed in normal mammary tissues and is aberrantly regulated in breast cancer. At physiological levels of expression, i.e. those found in normal mammary tissues, KLK6 acts as a tumor suppressor in human breast cancer. However, aberrant overexpression of KLK6 (i.e. 50-100-fold higher than normal), a characteristic of a subset of human breast cancers is associated with increased tumorigenicity (Pampalakis et al. Cancer Res 69:3779-3787, 2009). Here, we stably transfected KLK6-non-expressing MDA-MB-231 breast cancer cells with the full-length KLK6 cDNA to overexpress KLK6 at levels comparable to those observed in patients, and investigated potential oncogenic miRNA networks regulated by these abnormally high KLK6 expression levels and increased activity of this serine protease. A number of miRNAs that are upregulated (e.g. miR-146a) or downregulated (e.g. miR-34a) via KLK6-induced alterations in the miRNA biogenesis machinery were identified. Integrated experimental and bioinformatics analyses identified convergent miRNA networks targeting the cell cycle, MYC, MAPK, and other signaling pathways. In large clinical datasets, significant correlations between KLK6 and downstream MAPK and MYC targets at both the RNA and protein levels was confirmed, as well as negative correlation with GATA3. It was also demonstrated that KLK6 overexpression and likely its proteolytic activity is associated with alterations in downstream miRNAs and their targets, and these differ with the molecular subtypes of breast cancer. The data partly explains the different characteristics of breast cancer subtypes. Importantly, we introduce a combined KLK6-CDKN1B+MYC+CDKN1C score for prediction of long-term patient survival outcomes, with higher scores indicating poor survival.

A brain-targeted, modified neurosin (kallikrein-6) reduces α-synuclein accumulation in a mouse model of multiple system atrophy

Background

Multiple system atrophy (MSA) is a progressive, neurodegenerative disease characterized by parkinsonism, resistance to dopamine therapy, ataxia, autonomic dysfunction, and pathological accumulation of α-synuclein (α-syn) in oligodendrocytes. Neurosin (kallikrein-6) is a serine protease capable of cleaving α-syn in the CNS, and we have previously shown that lentiviral (LV) vector delivery of neurosin into the brain of a mouse model of dementia with Lewy body/ Parkinson’s disease reduces the accumulation of α-syn and improves neuronal synaptic integrity.

Results

In this study, we investigated the ability of a modified, systemically delivered neurosin to reduce the levels of α-syn in oligodendrocytes and reduce the cell-to-cell spread of α-syn to glial cells in a mouse model of MSA (MBP-α-syn). We engineered a viral vector that expresses a neurosin genetically modified for increased half-life (R80Q mutation) that also contains a brain-targeting sequence (apoB) for delivery into the CNS. Peripheral administration of the LV-neurosin-apoB to the MBP-α-syn tg model resulted in accumulation of neurosin-apoB in the CNS, reduced accumulation of α-syn in oligodendrocytes and astrocytes, improved myelin sheath formation in the corpus callosum and behavioral improvements.

Conclusion

Thus, the modified, brain-targeted neurosin may warrant further investigation as potential therapy for MSA.

Electronic supplementary material

The online version of this article (doi:10.1186/s13024-015-0043-6) contains supplementary material, which is available to authorized users.

The kallikrein-related peptidase family: Dysregulation and functions during cancer progression

Cancer is the second leading cause of death with 14 million new cases and 8.2 million cancer-related deaths worldwide in 2012. Despite the progress made in cancer therapies, neoplastic diseases are still a major therapeutic challenge notably because of intra- and inter-malignant tumour heterogeneity and adaptation/escape of malignant cells to/from treatment. New targeted therapies need to be developed to improve our medical arsenal and counter-act cancer progression. Human kallikrein-related peptidases (KLKs) are secreted serine peptidases which are aberrantly expressed in many cancers and have great potential in developing targeted therapies. The potential of KLKs as cancer biomarkers is well established since the demonstration of the association between KLK3/PSA (prostate specific antigen) levels and prostate cancer progression. In addition, a constantly increasing number of in vitro and in vivo studies demonstrate the functional involvement of KLKs in cancer-related processes. These peptidases are now considered key players in the regulation of cancer cell growth, migration, invasion, chemo-resistance, and importantly, in mediating interactions between cancer cells and other cell populations found in the tumour microenvironment to facilitate cancer progression. These functional roles of KLKs in a cancer context further highlight their potential in designing new anti-cancer approaches. In this review, we comprehensively review the biochemical features of KLKs, their functional roles in carcinogenesis, followed by the latest developments and the successful utility of KLK-based therapeutics in counteracting cancer progression.

Development and immunochemical evaluation of a novel chicken IgY antibody specific for KLK6

Background

Human kallikrein-related peptidase 6 (KLK6) has been implicated in various types of cancer and in neurodegenerative and demyelinating diseases including multiple sclerosis. Further, anti-KLK6 antibodies attenuated disease manifestations in the mouse model of multiple sclerosis. Availability of specific antibodies against KLK6 is fundamental to the development of improved diagnostic and/or immunotherapeutic applications. Here, we exploited the enhanced immunogenicity of mammalian proteins in avian species to generate a polyclonal antibody against KLK6.

Results

Chicken were immunized with recombinant KLK6 and antibodies Y (IgYs) were purified from egg yolk with a simple procedure and evaluated for KLK6 detection by ELISA and Western blot using recombinant proteins and human cell lysates and supernatants. The anti-KLK6 Y polyclonal exhibited high affinity for KLK6 with a detection limit of 30 fmol. On the other hand, the widely used rabbit polyclonal antibody that was raised against the same recombinant KLK6 had a detection limit of 300 fmol. Moreover, the IgYs did not display any crossreactivity with recombinant KLKs or endogenous KLKs and other cellular proteins.

Conclusions

Based on its high specificity and sensitivity the developed anti-KLK6 IgY is expected to aid the development of improved diagnostic tools for the detection of KLK6 in biological and clinical samples.

Kallikrein-related peptidase 6 (KLK6)gene expression in intracranial tumors

Kallikrein-related peptidases (KLKs) are emerging novel new biomarkers for prognosis, diagnosis and therapeutic intervention of cancer. Kallikrein-related peptidase 6 (KLK6) has the highest expression in normal brain among other tissues. Although its expression has been extensively studied in many types of cancer and in neurodegenerative diseases, very little is known for its expression in intracranial tumors. In the present study, 73 intracranial tumor samples were examined for KLK6 messenger ribunucleic acid (mRNA) gene expression using quantitative real-time polymerase chain reaction. Statistical analysis revealed the significant association of KLK6 expression with clinical and pathological parameters. Follow-up information was available for a median time of 20 months (range 1-59 months). KLK6 is expressed more frequently in tumors of high malignancy like the glioblastomas (70.6 %) and less in tumors of low malignancy like the meningiomas (12.5 %). KLK6 positive expression is associated with tumor grade (p < 0.001), malignancy status (p < 0.001), and tumor histologic type (p = 0.001). Cox proportional hazard regression model using univariate analysis revealed for the first time that positive KLK6 expression is a significant factor for disease-free survival (DFS; p = 0.041) of patients suffering from intracranial tumors. Kaplan-Meier survival curves demonstrated that negative KLK6 expression is significantly associated with longer DFS (p = 0.032). KLK6 gene expression may have clinical utility as a marker of unfavorable prognosis for intracranial tumors, and consequently, it could be used as target for therapeutic intervention.

Upregulation and secretion of kallikrein-related peptidase 6 (KLK6) in gastric cancer

KLK6 encoding kallikrein-related peptidase 6, a trypsin-like serine protease, has been shown to be upregulated in several cancers, although the tumorigenic role of KLK6 has not been elucidated. In this study, KLK6 was identified as a highly upregulated gene in gastric cancer; therefore, the possibility that KLK6 might be a suitable candidate tumor marker was examined. RT-PCR and immunohistochemical analysis showed overexpression of KLK6 in gastric cancer tissues compared to nontumor regions. Sera from gastric cancer patients had a 1.7-fold increase in KLK6 (373.1 μg/L, P = 0.048) compared to healthy individuals (214.2 μg/L), although there was no significant difference among patients with various tumor stages. Cellular invasiveness decreased by 45% in cells transfected with KLK6-specific small interfering RNA. Exogenous overexpression of KLK6 led to decreased activity of the E-cadherin promoter. This study shows that KLK6 is significantly upregulated and secreted in gastric cancer tissues and sera, suggesting that KLK6 might be used as a potential biomarker and therapeutic target for gastric cancer.

Kallikreins 5, 6 and 10 differentially alter pathophysiology and overall survival in an ovarian cancer xenograft model

Human tissue kallikreins (KLKs) are members of a multigene family of serine proteases aberrantly expressed in many cancer types. In ovarian cancer, 12 KLKs are upregulated, and of those KLK5, 6 and 10 have been the focus of investigations into new diagnostic and prognostic biomarkers. However, little is known about the contributions of KLK5, 6 and 10 to ovarian cancer pathophysiology.

In this study, a panel of 13 human ovarian cancer cell lines was screened by ELISA for secretion of KLK5, 6, 8, 10, 13, and 14. The ES-2 cell line, devoid of these kallikreins, was transfected with expression vectors of KLK5, 6 and 10 individually or in pairs. Co-expression of KLK5, 6 and 10 was correlated with lessened aggressivity of ovarian cancer cell lines as defined by reduced colony formation in soft agar and tumorigenicity in nude mice. ES-2 clones overexpressing KLK5, 10/5, 10/6, 5/6 made significantly fewer colonies in soft agar. When compared to control mice, survival of mice injected with ES-2 clones overexpressing KLK10, 10/5, 10/6, 5/6 was significantly longer, while KLK6 was shorter. All groups displaying a survival advantage also differed quantitatively and qualitatively in their presentation of ascites, with both a reduced incidence of ascites and an absence of cellular aggregates within those ascites. The survival advantage conferred by KLK10 overexpression could be recapitulated with the exogenous administration of a recombinant KLK10. In conclusion, these findings indicate that KLK5, 6 and 10 may modulate the progression of ovarian cancer, and interact together to alter tumour pathophysiology. Furthermore, results support the putative role of KLK10 as a tumour suppressor and suggest it may hold therapeutic potential in ovarian cancer.

The physiology and pathobiology of human kallikrein-related peptidase 6 (KLK6)

The human kallikrein-related peptidase 6 (KLK6) gene belongs to the 15-member kallikrein (KLK) gene family mapping to chromosome 19q13.3-13.4. Encoding for an enzyme with trypsin-like properties, KLK6 can degrade components of the extracellular matrix. The successful utilisation of another KLK member (KLK3/PSA) for prostate cancer diagnosis has led many to evaluate KLK6 as a potential biomarker for other cancer and diseased states. The observed dysregulated expression in cancers, neurodegenerative diseases and skin conditions has led to the discovery that KLK6 participates in other cellular pathways including inflammation, receptor activation and regulation of apoptosis. Moreover, the improvements in high-throughput genomics have not only enabled the identification of sequence polymorphisms, but of transcript variants, whose functional significances have yet to be realised. This comprehensive review will summarise the current findings of KLK6 pathophysiology and discuss its potential as a viable biomarker.

Impact of expression differences of kallikrein-related peptidases and of uPA and PAI-1 between primary tumor and omentum metastasis in advanced ovarian cancer

BACKGROUND

Primary tumor levels of serine proteases of the kallikrein-related peptidases (KLK) family as well as urokinase-type plasminogen activator (uPA) and its inhibitor PAI-1 impact disease course in ovarian cancer. The changes in levels of these factors from primary tumor to omentum metastasis ('level differentials') could thus be associated with metastastic processes.

PATIENTS AND METHODS

Protein levels of seven tissue KLK (KLK5-8, 10, 11, 13), uPA, and PAI-1 were determined in extracts of primary tumor tissue and corresponding omentum metastasis of 54 ovarian cancer patients.

RESULTS

Higher level differentials of KLK5-8, 10-11, and uPA were associated with residual tumor >10 mm. Residual tumor and larger level differentials of KLK5-7, 10, and uPA were associated with disease progression in the whole cohort. Remarkably, level differentials of KLK5-8 and 10-11 strongly impacted disease progression even in patients with residual tumor mass ≤10 mm; hence, the observed impact of level differentials in KLK5-7 and 10 on disease progression was not simply attributable to their association with surgical success.

CONCLUSION

Since they impact both surgical outcome and survival in advanced ovarian cancer, measurement of level differentials could support clinical decisions on surgical and systemic therapy or help in patient selection for novel targeted therapies.

Kallikrein-related peptidases: bridges between immune functions and extracellular matrix degradation

Kallikrein-related peptidases (KLKs) constitute a family of 15 highly conserved serine proteases encoded by the largest uninterrupted cluster of protease-encoding genes within the human genome. Recent studies, mostly relying on in vitro proteolysis of recombinant proteins, have suggested that KLK activities are regulated by proteolytic activation cascades that can operate in a tissue-specific manner, such as the semen liquefaction and skin desquamation cascades. The validity of KLK activation cascades in vivo largely remains to be demonstrated. Here, we focus on recent investigations showing that KLKs represent interesting players in the broader field of immunology based on their ability to bridge their inherent ability to degrade the extracellular matrix with major functions of the immune system. More specifically, KLKs assist in the infiltration of immune cells through the skin and the blood brain barrier, whereas they catalyze the generation of antimicrobial peptides by proteolytic activation and further processing of protein precursors. In an attempt to integrate current knowledge, we propose KLK-mediated pathways that are putatively involved in inflammation associated with skin wounding and central nervous system disorders, including multiple sclerosis. Finally, we present evidence of KLK participation in autoimmune diseases and allergies.

Functional proteomics of kallikrein-related peptidases in ovarian cancer ascites fluid

Kallikrein-related peptidases (KLKs) are secreted serine proteinases with trypsin or chymotrypsin-like activity. Several family members, such as KLKs 6 and 10, are potential ovarian cancer biomarkers. Recently, using a newly developed assay for active KLK6, we found that only a very small proportion of immunoreactive KLK6 in tumor-derived clinical samples (malignant ascites fluid), in cerebrospinal fluid, and in cancer cell line supernatants is enzymatically active. We therefore hypothesized that a proportion of other immunoreactive KLKs in such samples could be present, but might be partly complexed to endogenous serine proteinase inhibitors. Using a combination of immunological isolation of the enzymes, activity-based probe analysis and proteomics, we identified active KLK10 in ovarian cancer ascites and we provide preliminary data that the activity of other KLKs present in these samples can be decreased by known proteinase inhibitors (e.g., alpha2-macroglobulin, alpha1-antitrypsin). Our data suggest that the enzymatic activity of ovarian cancer-released KLKs that are detected by regular immunoassays is low in vivo and very likely regulated by proteinase inhibitors.

Functional intersection of the kallikrein-related peptidases (KLKs) and thrombostasis axis

A large body of emerging evidence indicates a functional interaction between the kallikrein-related peptidases (KLKs) and proteases of the thrombostasis axis. These interactions appear relevant for both normal health as well as pathologies associated with inflammation, tissue injury, and remodeling. Regulatory interactions between the KLKs and thrombostasis proteases could impact several serious human diseases, including neurodegeneration and cancer. The emerging network of specific interactions between these two protease families appears to be complex, and much work remains to elucidate it. Complete understanding how this functional network resolves over time, given specific initial conditions, and how it might be controllably manipulated, will probably contribute to the emergence of novel diagnostics and therapeutic agents for major diseases.

Natural and synthetic inhibitors of kallikrein-related peptidases (KLKs)

Including the true tissue kallikrein KLK1, kallikrein-related peptidases (KLKs) represent a family of fifteen mammalian serine proteases. While the physiological roles of several KLKs have been at least partially elucidated, their activation and regulation remain largely unclear. This obscurity may be related to the fact that a given KLK fulfills many different tasks in diverse fetal and adult tissues, and consequently, the timescale of some of their physiological actions varies significantly. To date, a variety of endogenous inhibitors that target distinct KLKs have been identified. Among them are the attenuating Zn(2+) ions, active site-directed proteinaceous inhibitors, such as serpins and the Kazal-type inhibitors, or the huge, unspecific compartment forming α(2)-macroglobulin. Failure of these inhibitory systems can lead to certain pathophysiological conditions. One of the most prominent examples is the Netherton syndrome, which is caused by dysfunctional domains of the Kazal-type inhibitor LEKTI-1 which fail to appropriately regulate KLKs in the skin. Small synthetic inhibitory compounds and natural polypeptidic exogenous inhibitors have been widely employed to characterize the activity and substrate specificity of KLKs and to further investigate their structures and biophysical properties. Overall, this knowledge leads not only to a better understanding of the physiological tasks of KLKs, but is also a strong fundament for the synthesis of small compound drugs and engineered biomolecules for pharmaceutical approaches. In several types of cancer, KLKs have been found to be overexpressed, which makes them clinically relevant biomarkers for prognosis and monitoring. Thus, down regulation of excessive KLK activity in cancer and in skin diseases by small inhibitor compounds may represent attractive therapeutical approaches.

Extracellular neurosin degrades α-synuclein in cultured cells

Neurosin, also called kallikrein 6, is a trypsin-like serine protease predominantly expressed in the central nervous system. Neurosin may degrade alpha-synuclein, a major component of the Lewy bodies commonly observed in dopaminergic neurons of patients with sporadic Parkinson's disease. In the present study, we investigated the localization and proteolytic activity of human neurosin using cultured cells to elucidate the physiological role of this enzyme at the cellular level. Heterologous expression of pre-pro-neurosin was localized to the endoplasmic reticulum and secreted. The proteolytic activity of neurosin was analyzed by zymography and fluorescent substrate, and showed that extracellular neurosin had protease activity but intracellular neurosin did not. We also coexpressed alpha-synuclein with neurosin and demonstrated that alpha-synuclein was not cleaved within cells, but extracellular alpha-synuclein was degraded by secreted neurosin. These findings suggest that neurosin targets the extracellular alpha-synuclein.

Plasmatic level of neurosin predicts outcome of mild cognitive impairment

Background

Mild Cognitive Impairment (MCI) is a disorder considered to be a transitional stage from health to dementia. Diagnosis of dementias at these early stages is always troublesome because the pathophysiologic events leading to dementia precede clinical symptoms. Thus, the development of biomarkers that can be used to support the diagnosis of dementias at early stages is rapidly becoming a high priority. We have recently reported the value of measuring plasmatic levels of neurosin in the diagnosis of Alzheimer's disease (AD). The aim of this study is to determine whether measuring plasmatic concentration of neurosin is a valuable test to predict progression of MCI.

Methods

Plasmatic neurosin concentrations were measured in 68 MCI patients and 70 controls subjects. Blood samples were obtained at the beginning of the study. Sixty six patients diagnosed with MCI were observed for 18 months. In 36 patients a second blood sample was obtained at the endpoint.

Results

The mean value of plasmatic neurosin concentration differs significantly between MCI patients who converted to Dementia with vascular component, those who converted to AD, or those who remained at MCI stage. The relative risk of developing Dementia with vascular component when neurosin levels are higher than 5.25 ng/ml is 13 while the relative risk of developing mild AD when neurosin levels are lower than 5.25 ng/ml is 2. Increases in the levels of neurosin indicate progression to Dementia with vascular component.

Conclusion

The measurement of plasmatic neurosin level in patients diagnosed with MCI may predict conversion from MCI to Dementia with vascular component. A single measurement is also valuable to estimate the risk of developing AD and Dementia with vascular component. Finally, repeated measurement of plasmatic neurosin might be a useful test to predict outcome in patients with MCI.

Identification and analysis of mammalian KLK6 orthologue genes for prediction of physiological substrates

Human kallikrein-related peptidase 6 (KLK6) is a novel serine protease that is aberrantly expressed in human cancers and represents a serum biomarker for the molecular diagnosis and monitoring of ovarian cancer. Here, we report the cloning and analysis of human kallikrein-related peptidase 6 gene (KLK6) orthologues in model organisms and farm animals. The corresponding full-length cDNAs were assembled from partial sequences retrieved from EST and genomic databases. Alignment of inferred protein sequences indicated a high degree of conservation of the encoded enzyme. We found that, similarly to (HUMAN)KLK6, monkey, cattle, mouse and rat orthologue genes encode for multiple transcript variants. This strengthens our previously published data showing that (HUMAN)KLK6 transcription is coordinately regulated by alternative promoters. Analysis of the KLK6 upstream genomic region led to the identification of multiple conserved regulatory regions with motifs for nuclear receptor transcription factors. Interestingly, we found that specific CpG dinucleotides in the proximal promoter, that were shown to regulate (HUMAN)KLK6 gene expression via DNA methylation, are conserved in orthologue genes, indicating epigenetic regulation of the KLK6 gene. Construction of a protein-protein interaction network indicated that KLK6 likely acts on the TGF-b1 signal transduction pathway to regulate certain cytoskeletal proteins, such as vimentin and keratin 8, thus, KLK6 may control cell shape that, in turn, regulates cell migration and motility.

New insights into the functional mechanisms and clinical applications of the kallikrein-related peptidase family

The Kallikrein-related peptidase (KLK) family consists of fifteen conserved serine proteases that form the largest contiguous cluster of proteases in the human genome. While primarily recognized for their clinical utilities as potential disease biomarkers, new compelling evidence suggests that this family plays a significant role in various physiological processes, including skin desquamation, semen liquefaction, neural plasticity, and body fluid homeostasis. KLK activation is believed to be mediated through highly organized proteolytic cascades, regulated through a series of feedback loops, inhibitors, auto-degradation and internal cleavages. Gene expression is mainly hormone-dependent, even though transcriptional epigenetic regulation has also been reported. These regulatory mechanisms are integrated with various signaling pathways to mediate multiple functions. Dysregulation of these pathways has been implicated in a large number of neoplastic and non-neoplastic pathological conditions. This review highlights our current knowledge of structural/phylogenetic features, functional role and regulatory/signaling mechanisms of this important family of enzymes.

Activation profiles and regulatory cascades of the human kallikrein-related peptidases

The human kallikrein (KLK)-related peptidases are the largest family of serine peptidases, comprising 15 members (KLK1-15) and with the majority (KLK4-15) being identified only within the last decade. Members of this family are associated with important diseased states (including cancer, inflammation, and neurodegeneration) and have been utilized or proposed as clinically important biomarkers or therapeutic targets of interest. All human KLKs are synthesized as prepro-forms that are proteolytically processed to secreted pro-forms via the removal of an amino-terminal secretion signal peptide. The secreted inactive pro-KLKs are then activated extracellularly to mature peptidases by specific proteolytic release of their amino-terminal propeptide. Although a key step in the regulation of KLK function, details regarding the activation of the human pro-KLKs (i.e. the KLK "activome") are unknown, to a significant extent, but have been postulated to involve "activation cascades" with other KLKs and endopeptidases. To characterize more completely the KLK activome, we have expressed from Escherichia coli individual KLK propeptides fused to the amino terminus of a soluble carrier protein. The ability of 12 different mature KLKs to process the 15 different pro-KLK peptide sequences has been determined. Various autolytic and cross-activation relationships identified using this system have subsequently been characterized using recombinant pro-KLK proteins. The results demonstrate the potential for extensive KLK activation cascades and, when combined with available data for the tissue-specific expression of the KLK family, permit the construction of specific regulatory cascades. One such tissue-specific cascade is proposed for the central nervous system.

Tissue kallikrein proteolytic cascade pathways in normal physiology and cancer

Human tissue kallikreins (KLKs or kallikrein-related peptidases) are a subgroup of extracellular serine proteases that act on a wide variety of physiological substrates, while they display aberrant expression patterns in certain types of cancer. Differential expression patterns lead to the exploitation of these proteins as new cancer biomarkers for hormone-dependent malignancies, in particular. The prostate-specific antigen or kallikrein-related peptidase 3 (PSA/KLK3) is an established tumor marker for the diagnosis and monitoring of prostate cancer. It is well documented that specific KLK genes are co-expressed in tissues and in various pathologies suggesting their participation in complex proteolytic cascades. Here, we review the currently established knowledge on the involvement of KLK proteolytic cascades in the regulation of physiological and pathological processes in prostate tissue and in skin. It is well established that the activity of KLKs is often regulated by auto-activation and subsequent autolytic internal cleavage leading to enzymatic inactivation, as well as by inhibitory serpins or by allosteric inhibition by zinc ions. Redistribution of zinc ions and alterations in their concentration due to physiological or pathological reasons activates specific KLKs initiating the kallikrein cascade(s). Recent studies on kallikrein substrate specificity allowed for the construction of a kallikrein interaction network involved in semen liquefaction and prostate cancer, as well as in skin pathologies, such as skin desquamation, psoriasis and cancer. Furthermore, we discuss the crosstalks between known proteolytic pathways and the kallikrein cascades, with emphasis on the activation of plasmin and its implications in prostate cancer. These findings may have clinical implications for the underlying molecular mechanism and management of cancer and other disorders in which KLK activity is elevated.

Enzymatic properties of human kallikrein-related peptidase 12 (KLK12)

Human kallikrein-related peptidase 12 (KLK12) is a new member of the human tissue kallikrein family. Preliminary studies suggest that KLK12 is differentially expressed in breast cancer and may have potential use as a cancer biomarker. It has been predicted that KLK12 is a secreted serine protease. However, the enzymatic properties of this protein have not been reported so far. Here, we report the production of recombinant KLK12 and analyses of its enzymatic characteristics, including zymogen activation, substrate specificity, and regulation of its activity. KLK12 is secreted as an inactive pro-enzyme, which is able to autoactivate to gain enzymatic activity. Through screening of a panel of fluorogenic and chromogenic peptide substrates, we establish that active KLK12 possesses trypsin-like activity, cleaving peptide bonds after both arginine and lysine. Active KLK12 quickly loses its activity due to autodegradation, and its activity can also be rapidly inhibited by zinc ions and by alpha2-antiplasmin through covalent complex formation. Furthermore, we demonstrate that KLK12 is able to activate KLK11 zymogen in vitro. Our results indicate that KLK12 may participate in enzymatic cascades involving other kallikreins.

The autolytic regulation of human kallikrein-related peptidase 6

Human kallikrein-related peptidase 6 (KLK6) is a member of the kallikrein family of serine-type proteases, characterized as an arginine-specific digestive-type protease capable of degrading a wide-variety of extracellular matrix proteins. KLK6 has been proposed to be a useful biomarker for breast and ovarian cancer prognosis, is abundantly expressed in the CNS and cerebrospinal fluid, and is intimately associated with regions of active inflammatory demyelination in multiple sclerosis (MS) lesions. Inhibition of KLK6 results in delayed onset and reduced severity of symptoms associated with experimental autoimmune encephalomyelitis, suggesting a key effector role for this protease in CNS inflammatory disease. KLK6 has been shown to autolytically cleave internally, leading to inactivation and suggesting a negative feedback inhibition control mechanism. Alternatively, the ability of KLK6 to self-activate has also been reported, suggesting a positive feedback activation loop control mechanism. Activation of pro-KLK6 requires hydrolysis after a Lys residue; however, KLK6 exhibits 2 order of magnitude reduced affinity for hydrolysis after Lys versus Arg residues; therefore, the ability to autolytically activate has been called into question. In the present study the catalytic activity of KLK6 toward its pro-sequence and internal autolytic sequence is characterized. The results show that the ability of KLK6 to activate pro-KLK6 is essentially negligible when compared to the rate of the internal autolytic inactivation or to the ability of other proteases to activate pro-KLK6. The results thus show that the primary autolytic regulatory mechanism of KLK6 is negative feedback inhibition, and activation is likely achieved through the action of a separate protease.

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.

Expression and Functional Characterization of the Cancer-related Serine Protease, Human Tissue Kallikrein 14

Human tissue kallikrein 14 (KLK14) is a novel extracellular serine protease. Clinical data link KLK14 expression to several diseases, primarily cancer; however, little is known of its (patho)-physiological role. To functionally characterize KLK14, we expressed and purified recombinant KLK14 in mature and proenzyme forms and determined its expression pattern, specificity, regulation, and in vitro substrates. By using our novel immunoassay, the normal and/or diseased skin, breast, prostate, and ovary contained the highest concentration of KLK14. Serum KLK14 levels were significantly elevated in prostate cancer patients compared with healthy males. KLK14 displayed trypsin-like specificity with high selectivity for P1-Arg over Lys. KLK14 activity could be regulated as follows: 1) by autolytic cleavage leading to enzymatic inactivation; 2) by the inhibitory serpins alpha1-antitrypsin, alpha2-antiplasmin, antithrombin III, and alpha1-antichymotrypsin with second order rate constants (k(+2)/Ki) of 49.8, 23.8, 1.48, and 0.224 microM(-1) min(-1), respectively, as well as plasminogen activator inhibitor-1; and 3) by citrate and zinc ions, which exerted stimulatory and inhibitory effects on KLK14 activity, respectively. We also expanded the in vitro target repertoire of KLK14 to include collagens I-IV, fibronectin, laminin, kininogen, fibrinogen, plasminogen, vitronectin, and insulin-like growth factor-binding proteins 2 and 3. Our results indicate that KLK14 may be implicated in several facets of tumor progression, including growth, invasion, and angiogenesis, as well as in arthritic disease via deterioration of cartilage. These findings may have clinical implications for the management of cancer and other disorders in which KLK14 activity is elevated.

Detection of noncovalent complexes in biological samples by intensity fading and high-mass detection MALDI-TOF mass spectrometry

Matrix-assisted laser desorption/ionization (MALDI) mass spectrometry has not yet contributed widely to the study of intact noncovalent biomolecular complexes, because MALDI is known to cause dissociation of the interaction partners and induce formation of nonspecific aggregates. Here, we present a new strategy to circumvent this problem. It is based on intensity fading (in the low m/z range) and high-mass detection MALDI mass spectrometry (MS), using a cryodetector (in the high m/z range), with and without chemical cross-linking of the interaction partners. The study focuses on noncovalent interactions between the human enzyme carboxypeptidase A (hCPA) and three protease inhibitors (PCI, TCI, and LCI) present in heterogeneous mixtures of other nonbinding molecules derived from a biological source, an extract from leech (Hirudo medicinalis). Another example involves an extract of the sea anemone Stichodactyla helianthus, which is used without previous fractionation to detect the specific complex between the enzyme trypsin and the endogenous SphI-1 inhibitor. The results give insight into the mechanism of intensity fading MS and demonstrate that the specificity of binding is greatly favored when the overall concentrations of the analytes (nonbinding molecules, protease inhibitor and target enzyme) present in a biological sample of interest are kept at low concentrations, in the sub-micromolar range. Higher concentrations may lead to unspecific interactions and the formation of aggregates both during the MALDI process and during reaction with the cross-linking reagents. This strategy is expected to advance the field of high-throughput affinity-based approaches, by taking advantage of a new generation of high mass detectors for MALDI-TOF instruments.

Overexpression of the human tissue kallikrein genes KLK4, 5, 6, and 7 increases the malignant phenotype of ovarian cancer cells

The human tissue kallikrein family of serine proteases (hK1-hK15 encoded by the genes KLK1-KLK15) is involved in several cancer-related processes. Accumulating evidence suggests that certain tissue kallikreins are part of an enzymatic cascade pathway that is activated in ovarian cancer and other malignant diseases. In the present study, OV-MZ-6 ovarian cancer cells were stably co-transfected with plasmids expressing hK4, hK5, hK6, and hK7. These cells displayed similar proliferative capacity as the vector-transfected control cells (which do not express any of the four tissue kallikreins), but showed significantly increased invasive behavior in an in vitro Matrigel invasion assay (p<0.01; Mann-Whitney U-test). For in vivo analysis, the cancer cells were inoculated into the peritoneum of nude mice. Simultaneous expression of hK4, hK5, hK6, and hK7 resulted in a remarkable 92% mean increase in tumor burden compared to the vector-control cell line. Five out of 14 mice in the 'tissue kallikrein overexpressing' group displayed a tumor/situs ratio greater than 0.198, while this weight limit was not exceeded at all in the vector control group consisting of 13 mice (p=0.017; chi2 test). Our results strongly support the view that tumor-associated overexpression of tissue kallikreins contributes to ovarian cancer progression.

Characterization of human kallikreins 6 and 10 in ascites fluid from ovarian cancer patients

OBJECTIVES

Human kallikreins 6 (hK6) and 10 (hK10) are secreted serine proteases. We previously found that hK6 and hK10 are highly overexpressed in epithelial ovarian tumors and demonstrated that serum levels of hK6 and hK10 are valuable biomarkers for ovarian cancer diagnosis and prognosis. Our aim is to purify and characterize these two kallikreins from ascites fluid of ovarian cancer patients.

METHODS

Protein concentrations of hK6 and hK10 in ovarian cancer ascites fluids were measured with ELISA-type immunoassays. hK6 and hK10 were purified from the ascites fluids with immunoaffinity columns, followed by reverse-phase high performance liquid chromatography. Purified hK6 and hK10 were then subjected to N-terminal sequencing. Enzymatic analyses were performed with synthetic fluorogenic peptides.

RESULTS

hK6 and hK10 were present in ovarian cancer ascites fluid at concentrations ranging from 0.2-571 and 0.7-220 microg/l, respectively. The majority of hK6 and hK10 in the ascites fluids were present in the free (uncomplexed) form. Both hK6 and hK10 purified from the ascites fluid were zymogens with a molecular mass of 30 kDa. Purified hK6 exhibited trypsin-like enzymatic activity, whereas no enzymatic activity was observed for purified hK10. The enzymatic activity of hK6 could be suppressed by a neutralizing monoclonal antibody.

CONCLUSIONS

The majority of hK6 secreted by the ovarian tumor cells into the ascites fluid are present in the uncomplexed, zymogen form, possessing weak trypsin-like enzymatic activity. All hK10 present in ovarian cancer ascites fluids are in the uncomplexed, zymogen form and have no detectable enzymatic activity.

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.

Multiple mechanisms underlie the aberrant expression of the human kallikrein 6 gene in breast cancer

Human kallikrein 6 (KLK6) was identified based on its transient upregulation in a primary breast tumor and its subsequent silencing in a metastatic tumor from the same patient. The molecular mechanism(s) underlying the deregulated expression of KLK6 during cancer progression are currently unknown. Here, we provide evidence that aberrant expression of KLK6 is regulated at the level of transcription by multiple cooperating mechanisms. KLK6 can be reactivated in non-expressing breast cancer cells by treatment with 5-aza-2'-deoxycytidine (5-aza-dC), a compound causing DNA demethylation. Trichostatin A (TSA), an inhibitor of histone deacetylases, resulted in moderate induction of KLK6 only in MDA-MB-231 cells. However, combined 5-aza-dC/TSA treatment resulted in synergistic activation of KLK6. We show that KLK6 inactivation is associated with hypermethylation of specific CpG dinucleotides located in the KLK6 proximal promoter and overexpression with complete demethylation. These results indicate a causal role of DNA methylation and chromatin structure in cancer-associated loss of KLK6 expression. In some breast cancer cell lines, KLK6 expression could be restored by the vitamin D3 analog EB1089. Our data indicate that transcriptional deregulation of KLK6 in cancer cells during breast cancer progression is complex and certainly not uniform in different tumors, involving epigenetic mechanisms as well as pathways regulated by nuclear receptors. This allows for the pharmacological modulation of KLK6 with potential therapeutic implications.

Recombinant kallikrein expression: site-specific integration for hK6 production in human cells

Kallikreins have been implicated in carcinogenesis and are promising biomarkers for the diagnosis and follow-up of various cancers. To evaluate the functions and clinical interest of kallikreins, it is important to be able to produce them as recombinant proteins. Here we summarize the various strategies used to produce kallikreins, emphasizing their advantages and limitations. We also describe an approach to achieve high-level production of kallikreins, such as hK6, with correct folding and activity, combining an expression system with targeted transgene integration and an efficient cultivation device to increase yield, the CELLine bioreactor. This novel method for recombinant kallikrein production will be useful to study their bio-pathological functions and to develop anti-bodies.

The kallikrein world: an update on the human tissue kallikreins

Human tissue kallikreins (hKs) are attracting increased attention owing to their association with various forms of cancer and other diseases. Human tissue kallikrein genes represent the largest contiguous group of proteases within the human genome. There are many areas of kallikrein research that need to be further explored, including their tissue expression patterns, their regulation, identification of specific substrates, their participation in proteolytic cascades, and their clinical applicability as cancer biomarkers and therapeutic targets. In this review, we briefly describe the current status of kallikrein research and identify future avenues that will enhance our understanding of their function and involvement in human diseases.