Emerging Proteins in CRPC: Functional Roles and Clinical Implications

Prostate cancer (PCa) is the most common cancer in men in the western world, but the lack of specific and sensitive markers often leads to overtreatment of prostate cancer which eventually develops into castration-resistant prostate cancer (CRPC). Novel protein markers for diagnosis and management of CRPC will be promising. In this review, we systematically summarize and discuss the expression pattern of emerging proteins in tissue, cell lines, and serum when castration-sensitive prostate cancer (CSPC) progresses to CRPC; focus on the proteins involved in CRPC growth, invasion, metastasis, metabolism, and immune microenvironment; summarize the current understanding of the regulatory mechanisms of emerging proteins in CSPC progressed to CRPC at the molecular level; and finally summarize the clinical applications of emerging proteins as diagnostic marker, prognostic marker, predictive marker, and therapeutic marker.

Kallikrein-related peptidases 6 and 10 are elevated in cerebrospinal fluid of patients with Alzheimer's disease and associated with CSF-TAU and FDG-PET

Background

Alterations in the expression of human kallikrein-related peptidases (KLKs) have been described in patients with Alzheimer’s disease (AD). We elucidated the suitability of KLK6, KLK8 and KLK10 to distinguish AD from NC and explored associations with established AD biomarkers.

Methods

KLK levels in cerebrospinal fluid (CSF), as determined by ELISA, were compared between 32 AD patients stratified to A/T/(N) system with evidence for amyloid pathology and of 23 normal controls with normal AD biomarkers. Associations between KLK levels and clinical severity, CSF and positron emission tomography (PET) based AD biomarkers were tested for.

Results

Levels of KLK6 and KLK10 were significantly increased in AD. KLK6 differed significantly between AD A+/T+/N+ and AD A+/T−/N+ or NC with an AUC of 0.922. CSF pTau and tTau levels were significantly associated with KLK6 in AD.

Conclusions

KLK6 deserves further investigations as a potential biomarker of Tau pathology in AD.

Electronic supplementary material

The online version of this article (10.1186/s40035-019-0168-6) contains supplementary material, which is available to authorized users.

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.

Structural basis for the Zn2+ inhibition of the zymogen-like kallikrein-related peptidase 10

Although kallikrein-related peptidase 10 (KLK10) is expressed in a variety of human tissues and body fluids, knowledge of its physiological functions is fragmentary. Similarly, the pathophysiology of KLK10 in cancer is not well understood. In some cancer types, a role as tumor suppressor has been suggested, while in others elevated expression is associated with poor patient prognosis. Active human KLK10 exhibits a unique, three residue longer N-terminus with respect to other serine proteases and an extended 99-loop nearly as long as in tissue kallikrein KLK1. Crystal structures of recombinant ligand-free KLK10 and a Zn²⁺ bound form explain to some extent the mixed trypsin- and chymotrypsin-like substrate specificity. Zn²⁺-inhibition of KLK10 appears to be based on a unique mechanism, which involves direct binding and blocking of the catalytic triad. Since the disordered N-terminus and several loops adopt a zymogen-like conformation, the active protease conformation is very likely induced by interaction with the substrate, in particular at the S1 subsite and at the unusual Ser193 as part of the oxyanion hole. The KLK10 structures indicate that the N-terminus, the nearby 75-, 148-, and the 99-loops are connected in an allosteric network, which is present in other trypsin-like serine proteases with several variations.

A new enzyme-linked immunosorbent assay (ELISA) for human free and bound kallikrein 9

Background

Kallikrein 9 (KLK9) is a member of the human kallikrein-related peptidases family, whose physiological role and implications in disease processes remain unclear. The active form of the enzyme is predicted to have chymotryptic activity. In the present study, we produced for the first time the active recombinant protein and monoclonal antibodies, and developed novel immunoassays for the quantification of free and bound KLK9 in biological samples.

Methods

The coding sequence of mature KLK9 isoform (mat-KLK9) was expressed in an Expi293F mammalian system and the synthesized polypeptide was purified through a two-step protocol. The purified protein was used as an immunogen for production of monoclonal antibodies in mice. Hybridomas were further expanded and antibodies were purified. Newly-produced monoclonal antibodies were screened for reaction with the KLK9 recombinant protein by a state-of-the-art immunocapture/parallel reaction monitoring mass spectrometry-based methodology.

Results

Anti-KLK9 antibodies were combined in pairs, resulting in the development of a highly sensitive (limit of detection: 15 pg/mL) and specific (no cross-reactivity with other KLKs) sandwich-type ELISA. Highest KLK9 protein levels were found in tonsil and sweat and lower levels in the heart, kidney and liver. Hybrid immunoassays using an anti-KLK9 antibody for antigen capture and various anti-serine protease inhibitor polyclonal antibodies, revealed the presence of an a1-antichymotrypsin-bound KLK9 isoform in biological samples.

Conclusions

The ELISAs for free and bound forms of KLK9 may be highly useful for the detection of KLK9 in a broad range of biological samples, thus enabling the clarification of KLK9 function and use as a potential disease biomarker.

Electronic supplementary material

The online version of this article (doi:10.1186/s12014-017-9140-6) contains supplementary material, which is available to authorized users.

NES1/KLK10 gene represses proliferation, enhances apoptosis and down-regulates glucose metabolism of PC3 prostate cancer cells

The normal epithelial cell-specific-1 (NES1) gene, also named as KLK10, is recognised as a novel putative tumour suppressor in breast cancer, but few studies have focused on the function of KLK10 in human prostate cancer. Our study confirms that the expression of KLK10 in prostate cancer tissue and cell lines (PC3, DU145, and LNCaP clone FGC) is low. Given that the androgen-independent growth characteristic of the PC3 cell line is more similar to clinical castration-resistant prostate cancer, we studied the role of KLK10 in PC3. In vitro and in vivo assays showed that over-expressing KLK10 in PC3 could decelerate tumour proliferation, which was accompanied with an increase in apoptosis and suppression of glucose metabolism. The related proteins, such as Bcl-2 and HK-2, were down-regulated subsequently. Furthermore, by up-regulating Bcl-2 or HK-2 respectively in the PC3-KLK10 cell line, we observed a subsequent increase of cell proliferation and a synchronous up-regulation of HK-2 and Bcl-2. Besides, KLK10 expression was also increased by Bcl-2 and HK-2, which suggests that there is a negative feedback loop between KLK10 and Bcl-2/HK-2. Thus, our results demonstrated that KLK10 may function as a tumour suppressor by repressing proliferation, enhancing apoptosis and decreasing glucose metabolism in PC3 cells.

Upregulated KLK10 inhibits esophageal cancer proliferation and enhances cisplatin sensitivity in vitro

The kallikrein-related peptidase 10 (KLK10) gene has tumor-suppressive function in various types of human cancer. However, previous studies showed that KLK10 also acts as an oncogene and is upregulated in gastrointestinal tumors. The role of KLK10 in human esophageal cancer (EC) remains unclear. In the present study, the expression of KLK10 in human esophageal and non-esophageal cancer tissues was investigated by immunohistochemistry. Quantitative RT-PCR and western blot analysis were utilized to detect KLK10 mRNA and protein expression in human esophageal cancer cell lines (TE-1 and Eca-109). Small interference RNA was utilized to specifically knockdown KLK10 expression in Eca-109 and TE-1 cells. Cell proliferation, cell cycle analysis as well as CDDP-dependent apoptosis were determined using a CCK-8 assay and flow cytometry. The results showed that, KLK10 was positive in 67 out of 83 (80.72%) human EC and positive in 3 out of 11 (27.27%) normal tissues (P=0.001). The present study indicated that KLK10 potentially plays a crucial role in Eca-109 cell growth. Additionally, the downregulation of KLK10 induced S-phase arrest and promoted cisplatin-induced apoptosis. The resutls of the present study suggested that KLK10 is a promising novel marker for the diagnostic and therapeutic target of esophageal cancer.

Gene-specific DNA methylation association with serum levels of C-reactive protein in African Americans

A more thorough understanding of the differences in DNA methylation (DNAm) profiles in populations may hold promise for identifying molecular mechanisms through which genetic and environmental factors jointly contribute to human diseases. Inflammation is a key molecular mechanism underlying several chronic diseases including cardiovascular disease, and it affects DNAm profile on both global and locus-specific levels. To understand the impact of inflammation on the DNAm of the human genome, we investigated DNAm profiles of peripheral blood leukocytes from 966 African American participants in the Genetic Epidemiology Network of Arteriopathy (GENOA) study. By testing the association of DNAm sites on CpG islands of over 14,000 genes with C-reactive protein (CRP), an inflammatory biomarker of cardiovascular disease, we identified 257 DNAm sites in 240 genes significantly associated with serum levels of CRP adjusted for age, sex, body mass index and smoking status, and corrected for multiple testing. Of the significantly associated DNAm sites, 80.5% were hypomethylated with higher CRP levels. The most significant Gene Ontology terms enriched in the genes associated with the CRP levels were immune system process, immune response, defense response, response to stimulus, and response to stress, which are all linked to the functions of leukocytes. While the CRP-associated DNAm may be cell-type specific, understanding the DNAm association with CRP in peripheral blood leukocytes of multi-ethnic populations can assist in unveiling the molecular mechanism of how the process of inflammation affects the risks of developing common disease through epigenetic modifications.

Clinical significance of kallikrein-related peptidase (KLK10) mRNA expression in colorectal cancer

OBJECTIVES

Colorectal cancer (CRC) is one of the three most common cancers in both genders. Even though several biomarkers are in use in diagnosis and prognosis of the disease, they are marred by limited specificity and sensitivity. The human kallikrein-related peptidase 10 (KLK10) gene is a member of the human tissue kallikrein family. Because prostate specific antigen (PSA), the best biomarker for detecting and monitoring prostate cancer, is a member of this family, many other members, including KLK10, have been widely examined as novel biomarkers for different cancer types. In previous studies, KLK10 has been proposed as a diagnostic biomarker for ovarian carcinoma, while its methylation on exon 3 has been proposed as a prognostic marker for early-stage breast cancer patients. The purpose of this study was to analyse KLK10 mRNA expression and examine its prognostic value and potential clinical application as a novel molecular tissue biomarker in CRC.

DESIGN AND METHODS

The study group consisted of 190 colorectal samples. Total RNA was extracted from pulverised tissues and cDNA was prepared by reverse transcription. KLK10 was amplified by real-time PCR. B2M was used as a reference gene and HT-29 cells as positive control.

RESULTS

KLK10 expression was significantly higher in cancer tissues (P<0.001). Tumours of advanced TNM and Dukes' stage showed high KLK10 expression status (P=0.036; P=0.025). Patients with high KLK10 expression had a shorter disease-free and overall survival rates (P=0.014; P=0.020).

CONCLUSION

Our results suggest that KLK10 may serve as a new marker of unfavourable prognosis of colorectal cancer.

Kallikrein-related peptidase 10 expression in salivary gland tissues and tumours

OBJECTIVES

Kallikrein-related peptidase 10 (KLK10) has been implicated in the development of several types of cancer. The purpose of this study was to analyze the expression of KLK10 in 3 types of salivary gland tumour and normal salivary glands.

MATERIALS AND METHODS

A standard immunoperoxidase staining technique was used to assess the immunoexpression profile of KLK10 in normal salivary glands and 3 types of salivary gland tumour: pleomorphic adenoma, adenoid cystic carcinoma and mucoepidermoid carcinoma.

RESULTS

Pleomorphic adenomas showed significantly lower KLK10 levels than control tissues. Neither of the malignant tumours (adenoid cystic carcinoma and mucoepidermoid carcinoma) showed a significant alteration in the immunoreactive scores of KLK10 in comparison with the normal salivary gland tissues. KLK10 immunoreactive scores were comparable in adenoid cystic carcinoma and mucoepidermoid carcinoma. Pleomorphic adenoma had significantly lower levels of KLK10 than mucoepidermoid carcinoma.

CONCLUSIONS

The finding of lower KLK10 levels in pleomorphic adenoma suggests aberrant expression in a tumour that develops primarily from myoepithelial cells. A kallikrein cascade may play a role in the development and/or outcome of some salivary gland tumours.

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.

Diagnostic value of serum kallikrein-related peptidases 6 and 10 versus CA125 in ovarian cancer

OBJECTIVES

To assess the diagnostic value of serum KLK6 and KLK10 in patients with ovarian tumor in comparison to serum CA125.

METHODS

Based on clinical and sonographic findings, 90 patients were consecutively recruited at the Gynecological Oncology Unit, Ain Shams University Maternity Hospital. Preoperative serum KLK6 and/or KLK10 were determined by enzyme-linked immunosorbent assay technique. The patients' final diagnoses were those of the histopathological reports.

RESULTS

There were 27 malignant versus 63 benign cases. Serum markers' diagnostic specificity and sensitivity were 80.3/72.7, 56.8/64.0, and 39.53/58.3 for CA125, KLK6, and KLK10, respectively. Combination of CA125 with either of the other 2 markers revealed diagnostic enhancement with KLK10 (85.37/73.00) but not with KLK6 (42.86/86.36).

CONCLUSIONS

In ovarian cancer, serum KLK6 and KLK10 may have much lower overall sensitivities than serum CA125. However, whereas serum KLK6 may improve the sensitivity of CA125, serum KLK10 may have the highest specificity among the 3 markers.

Expression analysis and clinical evaluation of kallikrein-related peptidase 10 (KLK10) in colorectal cancer

Kallikrein-related peptidases (KLKs) represent a serine protease family having 15 members. KLK10 is a secreted protease with a trypsin-like activity. The function of KLK10 is poorly understood, although it has been suggested that KLK10 may function as a tumor suppressor gene. In human cancer, KLK10 gene shows organ-specific up- or down-regulation. Since KLKs are promising tumor biomarkers, the examination of KLK10 mRNA expression and its association with colorectal cancer (CRC) progression was studied using semi-quantitative PCR. One hundred and nineteen primary CRC specimens were examined for which follow-up information was available for a median period of 29 months (range, 1-104 months). KLK10 expression was found to be significantly associated with TNM stage (p=0.028). Cox proportional hazard regression model using univariate analysis revealed for the first time that high status KLK10 expression is a significant factor for disease-free survival (DFS; p=0.002) and overall survival (OS; p=0.026) of patients. Kaplan-Meier survival curves demonstrated that KLK10 expression of low status is significantly associated with longer DFS (p=0.001) as well as OS (p=0.021), suggesting that KLK10 gene expression may be used as a marker of unfavorable prognosis for CRC. As the epigenetics of cancer are unraveled, KLK10 may represent not only a novel biomarker, but also a promising future therapeutic target for the disease.

Nipple Aspirate Fluid Proteome of Healthy Females and Patients with Breast Cancer

Background: The ductal/alveolar system of the female breast constantly secretes and reabsorbs fluid in nonpregnant/nonlactating women. This fluid, referred to as nipple aspirate fluid (NAF), can be obtained by a noninvasive procedure and it is part of the microenvironment where more than 95% of breast cancers arise.

Methods: Using an Orbitrap® mass analyzer coupled to a linear ion trap, we performed an in-depth proteomic analysis of NAF samples obtained from 3 healthy individuals and 3 patients with breast cancer. Multiple fractionation methods such as size-exclusion and anion-exchange chromatography were applied for protein separation before mass spectrometric analysis.

Results: We identified more than 800 unique proteins in total, generating the most extensive NAF proteome thus far. Using gene ontology, we classified the identified proteins by their subcellular localization and found that more than 50% were extracellular or plasma membrane proteins. By searching against the Plasma Proteome Database, we confirmed that 40% of the proteins were also found in the plasma. Unigene database searching for transcripts of the proteins not found in the plasma revealed that the vast majority were expressed in the mammary gland.

Conclusions: Our extensive proteome database for NAF may be helpful in the identification of novel cancer biomarkers.

The Tissue Kallikrein Family of Serine Proteases: Functional Roles in Human Disease and Potential as Clinical Biomarkers

Prostate specific antigen (PSA) or human kallikrein 3 (hK3) has long been an effective biomarker for prostate cancer. Now, other members of the tissue kallikrein (KLK) gene family are fast becoming of clinical interest due to their potential as prognostic biomarkers. particularly for hormone dependent cancers. The tissue kallikreins are serine proteases that are encoded by highly conserved multi-gene family clusters in rodents and humans. The rat and mouse loci contain 10 and 25 functional genes, respectively, while the human locus at 19q 13.4 contains 15 genes. The structural organization and size of these genes are similar across species; all genes have 5 coding exons that encode a prepro-enzyme. Although the physiological activators of these zymogens have not been described, in vitro biochemical studies show that some kallikreins can auto-activate and others can activate each other, suggesting that the kallikreins may participate in an enzymatic cascade similar to that of the coagulation cascade. These genes are expressed, to varying degrees, in a wide range of tissues suggesting a functional involvement in a diverse range of physiological and pathophysiological processes. These include roles in normal skin desquamation and psoriatic lesions, tooth development, neural plasticity, and Alzheimer's disease (AD). Of particular interest is the expression of many kallikreins in prostate, ovarian, and breast cancers where they are emerging as useful prognostic indicators of disease progression.

Prostatic trypsin-like kallikrein-related peptidases (KLKs) and other prostate-expressed tryptic proteinases as regulators of signalling via proteinase-activated receptors (PARs)

The prostate is a site of high expression of serine proteinases including members of the kallikrein-related peptidase (KLK) family, as well as other secreted and membrane-anchored serine proteinases. It has been known for some time that members of this enzyme family elicit cellular responses by acting directly on cells. More recently, it has been recognised that for serine proteinases with specificity for cleavage after arginine and lysine residues (trypsin-like or tryptic enzymes) these cellular responses are often mediated by cleavage of members of the proteinase-activated receptor (PAR) family--a four member sub-family of G protein-coupled receptors. Here, we review the expression of PARs in prostate, the ability of prostatic trypsin-like KLKs and other prostate-expressed tryptic enzymes to cleave PARs, as well as the prostate cancer-associated consequences of PAR activation. In addition, we explore the dysregulation of trypsin-like serine proteinase activity through the loss of normal inhibitory mechanisms and potential interactions between these dysregulated enzymes leading to aberrant PAR activation, intracellular signalling and cancer-promoting cellular changes.

Human kallikrein-related peptidase 12: antibody generation and immunohistochemical localization in prostatic tissues

BACKGROUND

Human tissue kallikrein-related peptidases (genes, KLKs; proteins, KLKs) are a subgroup of serine proteases present in a variety of tissues and biological fluids. A number of human tissue KLKs are established or candidate serologic biomarkers for prostate cancer. Human kallikrein-related peptidase 12 (KLK12, KLK12), recently identified in our laboratory, is a novel member of the KLK gene family. Here, we report generation of antibodies against the full-length recombinant KLK12 (classical form) and the immunohistological localization of this KLK in normal and malignant prostate tissues.

METHODS

The mature form of KLK12 cDNA was amplified using PCR and cloned into a plasmid vector for protein production in E. coli. Following identification by mass spectroscopy, recombinant KLK12 was purified and used as immunogen in rabbits. Anti- KLK12 antibody was used for immunostaining of paraffin-embedded sections of human prostate tissue. Immunoexpression of KLK12 in benign and malignant prostate tissue was evaluated using a prostate cancer tissue array.

RESULTS

Anti-KLK12 antibody showed a predominantly apical and membranous staining of the luminal cells of the normal prostate in contrast with the predominantly diffuse cytoplasmic staining observed in both prostatic intra-epithelial neoplasia and adenocarcinomas. This was occasionally associated with an intense granular supranuclear staining. More than 95% of the prostate cancers on the tissue microarray were KLK12 positive.

CONCLUSION

Higher levels of KLK12 in malignant prostatic glands, and the shift in subcellular localization of KLK12 in prostate cancer observed in this study point to the potential role of this kallikrein during prostate carcinogenesis.

Human kallikrein 10 ELISA development and validation in breast cancer sera

BACKGROUND

Human kallikrein 10 (hK10) is a putative secreted serine protease belonging to the same gene family as prostate specific antigen (hK3; PSA). There is significant interest in measuring hK10 which may act as a tumor suppressor in some cancers. We have developed an ELISA for hK10 and determined its analytical and clinical performance in normal and breast cancer sera.

METHODS

The assay used a previously described pair of monoclonal anti-hK10 antibodies and recombinant hK10 protein. Serum hK10 was detected quantitatively in a 2-step sandwich ELISA with colorimetric detection. The assay was analytically validated and used to determine serum levels of hK10 in a set of breast cancer, benign breast disease and normal samples.

RESULTS

The assay covered a linear range of 0.2 to 15 ng/mL and had a detection limit of 0.08 ng/mL. The within-run and between-run imprecision was <9%. The average spike and dilution linearity recoveries were 96 and 103% respectively. Mean hK10 concentration in normal female sera was 0.79+/-0.26 ng/mL. Concentrations were not age related and were not significantly different from benign fibrocystic disease or breast cancer. However, in a subset of breast cancer patients with both early and late stage disease, serum hK10 levels were elevated, at >1.55 ng/mL, above all normal female and benign disease samples.

CONCLUSIONS

We report in detail the analytical performance of a colorimetric hK10 ELISA validated in human serum and report for the first time the hK10 serum concentration in benign and breast cancer samples.

PSA and other tissue kallikreins for prostate cancer detection

Prostate cancer is the most common neoplasia of middle-aged men. Prostate specific antigen (PSA) is the first FDA-approved tumour marker for early detection of cancer and it is now in widespread clinical use. The discovery of different PSA molecular forms in serum (free PSA, PSA complexed with various protease inhibitors) in the early 1990s renewed clinical research to enhance the specificity of PSA. Also, the use of a homologous prostate-localised antigen, human glandular kallikrein 2 (KLK2) may further reduce the number of unnecessary prostate biopsies. More recently, promising data is emerging regarding molecular forms of free PSA (proPSA, BPSA, 'intact' PSA) and other members of the expanded human kallikrein family. These new findings may add substantial clinical information for early detection of prostate cancer.

Distribution of 15 Human Kallikreins in Tissues and Biological Fluids

Background: Kallikreins (KLKs) are a group of 15 secreted serine proteases. Some KLKs are established or candidate cancer biomarkers, but for most the physiological function is unknown. We characterized the protein and mRNA abundance patterns of all 15 KLKs in multiple panels of human tissues and biological fluids.

Methods: We used sensitive and specific sandwich-type ELISAs for each KLK. Reverse transcription PCR was used for transcript amplification. Multiple panels of human tissue extracts (adult and fetal) were tested, along with various biological fluids.

Results: Quantitative protein expression data on 7 sets of adult and 3 sets of fetal tissues were collected for all 15 KLKs. KLKs were also quantified in the following biological fluids: seminal plasma, breast milk, follicular fluid, breast cyst fluid, breast cancer cytosol, amniotic fluid, ovarian cancer ascites, cerebrospinal fluid, cervicovaginal fluid, and urine. The data were used to generate heat maps of KLK concentrations in tissues and fluids and categorize KLK abundance as highly restricted (KLK2 and KLK3 in prostate), restricted (KLK5 in skin, salivary gland, breast, and esophagus; KLK6 in brain and central nervous system; KLK7 in esophagus, heart, liver, and skin; KLK8 in breast, esophagus, skin, and tonsil; KLK13 in esophagus and tonsil), or wide (KLKs 1, 4, 9, 10, 11, 12, 14, and 15).

Conclusions: Quantitative KLK concentrations in tissues and fluids aid in the elucidation of KLK function, and coexpression patterns provide clues for KLK participation in proteolytic cascades.

Proteomics analysis of conditioned media from three breast cancer cell lines: a mine for biomarkers and therapeutic targets

A "bottom-up" proteomics approach and a two-dimensional (strong cation exchange followed by reversed-phase) LC-MS/MS strategy on a linear ion trap (LTQ) were utilized to identify and compare expressions of extracellular and membrane-bound proteins in the conditioned media of three breast cell lines (MCF-10A, BT474, and MDA-MB-468). Proteomics analysis of the media identified in excess of 600, 500, and 700 proteins in MCF-10A, BT474, and MDA-MB-468, respectively. We successfully identified the internal control proteins, kallikreins 5, 6, and 10 (ranging in concentration from 2 to 50 microg/liter) in MDA-MB-468 conditioned medium as validated by ELISA and confidently identified Her-2/neu in BT474 cells. Subcellular localization was determined based on Genome Ontology terms for all the 1,139 proteins of which 34% were classified as extracellular and membrane-bound. Proteomics analysis of MDA-MB-468 cell lysate demonstrated that only 5% of all identified proteins were extracellular. This confirmed our hypothesis that examining the CM of cell lines, as opposed to the cell lysates, leads to a significant enrichment in secreted proteins. Tissue specificity, functional classifications, and spectral counting were performed. Elafin, a protease inhibitor, identified in the conditioned media of BT474 and MDA-MB-468 and the three kallikreins (KLK5, KLK6, and KLK10) were validated using an immunoassay on various serum and biological samples. Some of the secreted proteins identified have established roles in breast cancer development (cell growth, differentiation, and metastasis) and/or are linked to early onset breast cancer. Our approach to mining for low abundance molecules could identify proteins in various stages of breast cancer development. Many of the identified proteins are potentially useful to investigate as circulating serum breast cancer biomarkers.

Primary tumor levels of human tissue kallikreins affect surgical success and survival in ovarian cancer patients

PURPOSE

Proteolytic factors of the human tissue kallikrein (hK) family and the plasminogen activation system play a key role in tumor progression in various malignancies. We determined antigen levels of urokinase-type plasminogen activator (uPA), its inhibitor PAI-1, and hK5-8, hK10, hK11, and hK13 by ELISA in primary tumor tissue extracts of 142 International Federation of Gynecology and Obstetrics (FIGO) I to IV ovarian cancer patients (median follow-up 41 months).

RESULTS

After radical surgery, absence of macroscopically visible residual tumor (RT) was achieved in 72 patients; all patients received postoperative platinum-containing chemotherapy. Significant univariate predictors of poor progression-free survival (PFS) were RT (>0), FIGO stages (III/IV versus I/II/III), ascites volume >500 mL, nodal status, and the difference between PAI-1 and uPA (fractionally ranked). In multivariate analysis, significant independent factors for poor PFS were RT [hazard ratio (HR), 4.53] and low hK11 fractional rank (HR, 0.30). Univariate predictors of poor overall survival were RT, FIGO stages, nodal status, ascites volume, nuclear grade, and low hK10 and hK13. In multivariate analysis, significant independent factors for poor overall survival were RT (HR, 7.49), ascites (HR, 1.97), and low hK10 (HR, 0.196). We constructed a multivariate scoring model estimating RT probability, based on ascites [odds ratio (OR), 13.1], nuclear grade (OR, 2.92), hK6 (OR, 8.54), and hK13 (OR, 0.14), with good in-sample predictive performance (area under receiver operating characteristic, 0.833).

CONCLUSIONS

In view of risks and benefits of radical surgery, such a score could support preoperative risk stratification and identify candidates for alternative therapeutic strategies. These results highlight the distinct roles of the hKs for different disease end points in ovarian cancer and their potential to support individualized therapy decisions.

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.

Development of an immunofluorometric assay for human kallikrein 15 (KLK15) and identification of KLK15 in tissues and biological fluids

BACKGROUND

Human kallikrein 15 (KLK15) may have some utility as a prostate, ovarian, and breast cancer biomarker, based on previous studies, which examined mRNA levels of KLK15. The aim of this study was to develop analytical technology for human kallikrein 15, including recombinant protein, specific antibodies, and a sensitive and specific ELISA immunoassay. The assay was then used to examine levels of KLK15 in tissues and biological fluids.

METHODS

We produced human, recombinant pro-KLK15 in HEK 293 cells. Recombinant KLK15 was purified with various chromatographic steps and used to immunize rabbits and mice for production of KLK15 polyclonal antibodies. We used these antibodies to develop a highly sensitive and specific KLK15 immunoassay and to study KLK15 expression in various tissues and biological fluids.

RESULTS

Large amounts of pure, recombinant KLK15 have been produced and characterized. KLK15 mouse and rabbit polyclonal antibodies have been employed for development of a KLK15 immunoassay. This assay has a lower detection limit of 0.05 microg/L, and no cross-reactivity with any of the other fourteen kallikreins. Using this assay, KLK15 was detected in prostate, colon, and thyroid tissues, as well as in breast milk and seminal plasma.

CONCLUSIONS

The KLK15 reagents developed here will allow for analysis of KLK15 protein expression levels in tissues and biological fluids, both normal and cancerous. This will expand upon previously characterized tissue KLK15 mRNA expression studies which suggested that KLK15 might be useful as a biomarker for breast, ovarian, and prostate cancer. KLK15 is another serine protease that is produced in prostate and other tissues and is secreted in seminal plasma and other fluids. Its physiological function needs to be further elucidated.

The role of kallikrein-related peptidases in prostate cancer: potential involvement in an epithelial to mesenchymal transition

Several members of the kallikrein-related peptidase family of serine proteases have proteolytic activities that may affect cancer progression; however, the in vivo significance of these activities remains uncertain. We have demonstrated that expression of PSA or KLK4, but not KLK2, in PC-3 prostate cancer cells changed the cellular morphology from epithelial to spindle-shaped, markedly reduced E-cadherin expression, increased vimentin expression and increased cellular migration. These changes are indicative of an epithelial to mesenchymal transition (EMT), a process important in embryonic development and cancer progression. The potential novel role of kallikrein-related peptidases in this process is the focus of this brief review.

Human kallikrein 10, a predictive marker for breast cancer

Our laboratory is involved in identifying genes that can be used as early diagnostic or prognostic markers in breast cancer. We previously identified a gene (NES1) that is expressed in normal but not in transformed mammary epithelial cells (MECs). NES1 is located on chromosome 19q13.4 within the kallikrein locus and thus was designated as human kallikrein 10 (hK10), although we have been unable to detect any protease activity. Importantly, hK10 expression is decreased in a majority of breast cancer cell lines. Transfection of hK10 into hK10-negative breast cancer cells reduces the tumorigenicity. Using methylation-specific PCR and subsequent sequencing, we demonstrate a strong correlation between hypermethylation of hK10 and loss of mRNA expression. Further analysis showed that essentially 100% of normal breast specimens had hK10 expression, whereas 46% of ductal carcinoma in situ (DCIS) and the majority of infiltrating ductal carcinoma (IDC) samples lacked the hK10 mRNA. Importantly, hK10-negative DCIS diagnosed at the time of biopsy were subsequently diagnosed as IDC at the time of definitive surgery. It has been shown that hK10 protein expression is regulated by steroids. In addition to breast cancers, hK10 is downregulated in cervical cancer, prostate cancer and acute lymphocytic leukemia, whereas it is upregulated in ovarian cancers. These results point to the paradoxical role of hK10 in human cancers and underscore the importance of further studies of this kallikrein.

Activation and enzymatic characterization of recombinant human kallikrein 8

Human kallikrein 8 (hK8), whose gene was originally cloned as the human ortholog of a mouse brain protease, is known to be associated with diseases such as ovarian cancer and Alzheimer's disease. Recombinant human pro-kallikrein 8 was activated with lysyl endopeptidase-conjugated beads. Amino-terminal sequencing of the activated enzyme demonstrated the cleavage of a 9-aa propeptide from the pro-enzyme. The substrate specificity of activated hK8 was characterized using synthetic fluorescent substrates. hK8 showed trypsin-like specificity, as predicted from sequence analysis and enzymatic characterization of the mouse ortholog. All synthetic substrates tested containing either arginine or lysine at P1 position were cleaved by hK8. The highest kcat/Km value of 20x10(3)M-1 s-1 was observed with Boc-Val-Pro-Arg-7-amido-4-methylcoumarin. The activity of hK8 was inhibited by antipain, chymostatin, and leupeptin. The concentration for 50% inhibition by the best inhibitor, antipain, was 0.46 microM. The effect of different metal ions on the enzyme activity was analyzed. Whereas Na+ had no effect on hK8 activity, Ni2+ and Zn2+ decreased the activity and Ca2+, Mg2+, and K+ had a stimulatory effect. Ca2+ was the best activator, with an optimal concentration of approximately 10 microM.

Coordinated steroid hormone-dependent and independent expression of multiple kallikreins in breast cancer cell lines

The regulation of gene expression by steroid hormones plays an important role in the normal development and function of many organs, as well in the pathogenesis of endocrine-related cancers. Previous experiments have shown that many kallikrein genes are under steroid hormone regulation in breast cancer cell lines. We here examine the coordinated expression of multiple kallikrein genes in several breast cancer cell lines after steroid hormone stimulation. Breast cancer cell lines were treated with various steroid hormones and kallikrein (KLK/hK) expression of hK3 (prostate-specific antigen, PSA), hK5, hK6, hK7, hK8, hK10, hK11, hK13, and hK14 was analyzed at the RNA level via RT-PCR and at the protein level by immunofluorometric ELISA assays. We identified several distinct hK hormone-dependent and hormone-independent expression patterns. Hormone-specific modulation of expression was seen for several kallikreins in BT-474, MCF-7, and T-47D cell lines. hK6 was specifically up-regulated upon estradiol treatment in all three cell lines whereas PSA expression was induced by dihydrotestosterone (DHT) and norgestrel stimulation in BT-474 and T-47D. hK10, hK11, hK13, and hK14 were specifically up-regulated by DHT in T-47D and by estradiol in BT-474 cells. Bioinformatic analysis of upstream proximal promoter sequences for these hKs did not identify any recognizable hormone-response elements (HREs), suggesting that the coordinated activation of these four hKs represents a unique expression "cassette", utilizing a common hormone-dependent mechanism. We conclude that groups of human hKs are coordinately expressed in a steroid hormone-dependent manner. Our data supports clinical observations linking expression of multiple hKs with breast cancer prognosis.

Effect of Testosterone Administration on Serum and Urine Kallikrein Concentrations in Female-to-Male Transsexuals

Background: Concentrations of human tissue kallikreins (hKs), a group of 15 secreted serine proteases found in many tissues, are modulated by steroid hormones in cancer cell lines. To gain insight into in vivo kallikrein regulation we measured kallikrein concentrations in serum and urinary tissue in female-to-male transsexuals before and after testosterone administration.

Methods: We collected blood and urine samples before treatment and after 4 and 12 months from 28 female-to-male transsexuals who received 250 mg of testosterone esters intramuscularly every 2 weeks. We used ELISA assays to measure multiple kallikreins in serum and urine.

Results: After testosterone administration, serum testosterone concentrations increased by ∼15-fold. Serum kallikrein concentrations increased dramatically for hK3 (prostate-specific antigen) and increased moderately for hK2, hK5, hK6, hK7, hK8, hK10, and hK11. In urine, we noted major increases for hK3 and hK2 only. For all other kallikrein concentrations, we observed no considerable changes.

Conclusions: We conclude that, in serum and urine of female-to-male transsexuals after testosterone administration, hK3 (prostate-specific antigen) and to a lesser extent hK2 concentrations increase dramatically, but concentration of other kallikreins increase either moderately in serum (hK5, hK6, hK7, hK8, hK10, and hK11) or not at all in either serum (hK4, hK13, hK14) or urine (hK4, hK5, hK6, hK7, hK8, hK10, hK11, hK13, hK14).

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.

Serum and Urine Tissue Kallikrein Concentrations in Male-to-Female Transsexuals Treated with Antiandrogens and Estrogens

Background: The expression of human tissue kallikrein genes is regulated by steroid hormones, but most studies have been conducted with cancer cell lines. Our purpose was to examine serum and urinary tissue kallikrein concentration changes in male-to-female transsexuals before and after treatment with antiandrogens and estrogens.

Methods: Thirty-five male-to-female transsexuals receiving cyproterone acetate and estrogens (orally or transdermally) were included in this study. Serum and urine samples were collected before initiation of therapy and 4 and 12 months post therapy. ELISAs were used to measure multiple kallikreins in serum and urine.

Results: After antiandrogen and estrogen therapy, serum testosterone concentrations decreased dramatically, as did serum and urinary concentrations of human glandular kallikrein (hK2) and prostate-specific antigen (PSA; hK3). Statistically significant but relatively small changes in serum and urinary concentrations of many other kallikreins were also seen. Kallikreins in serum and urine were correlated before and after treatment.

Conclusions: The concentrations of hK2 and hK3, but not of any other kallikreins, decrease dramatically after combined antiandrogen and estrogen treatment in male-to-female transsexuals. The smaller responses of the other kallikreins presumably reflect their expression in multiple tissues.

Overexpression of kallikrein 10 (hK10) in uterine serous papillary carcinomas

OBJECTIVE

Kallikrein 10 is a secreted serine protease recently implicated in the growth and invasion of several human tumors. The goal of this study was to investigate the expression and secretion levels in vitro and in vivo of kallikrein 10 in uterine serous papillary carcinoma, a highly aggressive variant of endometrial tumor.

STUDY DESIGN

Human kallikrein 10 gene expression levels were evaluated in 11 snap-frozen uterine serous papillary carcinoma biopsies and 6 normal endometrial cell biopsies by real-time polymerase chain reaction. Secretion of kallikrein 10 protein by 10 primary tumor cultures including 3 uterine serous papillary carcinomas, 2 endometrioid carcinomas, and 5 ovarian serous papillary tumors was measured using a sensitive ELISA. Finally, kallikrein 10 concentration in 75 serum and plasma samples from 22 healthy women, 20 women with benign diseases, 21 women with endometrioid carcinomas, and 12 uterine serous papillary carcinoma patients was studied.

RESULTS

Kallikrein 10 gene expression levels were significantly higher in uterine serous papillary carcinoma when compared with normal endometrial cell biopsies (mean copy number by real time polymerase chain reaction = 743 versus 1.4; uterine serous papillary carcinoma versus endometrioid carcinoma: P < .02). In vitro kallikrein 10 secretion was detected in all primary uterine serous papillary carcinoma cell lines tested (mean = 2.7 microg/L), and the secretion levels were not significantly different to those found in primary ovarian serous papillary tumor cultures (mean 4.2 microg/L). In contrast, no kallikrein 10 secretion was detectable in primary endometrioid carcinomas. Kallikrein 10 serum and plasma concentrations (microg/L; mean +/- SEM) among normal healthy females (0.6 +/- 0.04), patients with benign diseases (0.6 +/- 0.06), and patients with endometrioid carcinomas (0.7 +/- 0.06) were not significantly different. In contrast, serum and plasma kallikrein 10 values in uterine serous papillary carcinoma patients (1.2 +/- 0.1) were significantly higher than those in the non-cancer group (P = .002), benign group (P = .002), and endometrioid carcinoma patients (P = .005).

CONCLUSION

Kallikrein 10 is highly expressed in uterine serous papillary carcinoma, and it is released in the plasma and serum of uterine serous papillary carcinoma patients. Kallikrein 10 may represent a novel biomarker for uterine serous papillary carcinoma.

Expression of the human kallikrein genes 10 (KLK10) and 11 (KLK11) in cancerous and non-cancerous lung tissues

Only one transcript for KLK10 was identified by RT-PCR in lung tissue, whereas KLK11 expressed at least four alternative transcripts. Quantitative analysis of KLK10 and KLK11 expression levels was assessed by real-time PCR, in a cohort of 47 patients with non-small-cell lung cancer (NSCLC). Expression levels of these genes were widely distributed in the population studied. Multivariate analysis revealed a correlation between KLK10 over-expression and the squamous cell carcinoma histotype (p=0.034). There was no correlation between gene expression and patient survival. Overall, both genes behaved similarly (p<0.001). These results suggest a co-regulation of KLK10 and KLK11 expression in lung and a lack of KLK10 suppressor role in NSCLC. Finally, our findings indicate that these genes are likely involved in normal physiology processes in bronchus.

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.

Quantification of Human Tissue Kallikreins in the Stratum Corneum: Dependence on Age and Gender

Human tissue kallikreins are a family of 15 trypsin or chymotrypsin-like secreted serine proteases (hK1-hK15). hK5, hK6, hK7, hK8, and hK13 have been identified in the stratum corneum (SC), stratum granulosum, and skin appendages. It has been reported that hK5 and hK7 degrade desmosomes/corneodesmosomes, suggesting that kallikreins are responsible for desquamation. We report the quantification of hK5, hK6, hK7, hK8, hK10, hK11, hK13, and hK14 in the SC by ELISA and their variation among age groups. The total SC trypsin and chymotrypsin-like activities were also measured. The amount of hK7, hK8, and hK11 (ng per mg dry weight) were high, and varied from 6 to 14, hK5 (2.0-4.0) was present at intermediate levels, and hK10 (0.65-1.0), hK14 (0.1-0.3), hK6 (0.1-0.3), and hK13 (0.02-0.1) were present at lower levels. hK6 and hK14 were significantly lower in females between 20 and 59 y. hK5, hK7, hK10, hK11, and hK14 were not significantly different across the age groups. hK8 was lowest at extremes of age (highest at 30-39 y), hK6 was lower at >30 y, and hK13 was lower at >20 y. Overall trypsin-like activity did not differ across age groups but was higher in subjects <11 y. Overall chymotrypsin-like activity was not related to age. In conclusion, we found multiple kallikreins in the SC and suggest that these enzymes may be responsible for desquamation through an enzymatic cascade pathway.

Downregulation of human kallikrein 10 (KLK10/NES1) by CpG island hypermethylation in breast, ovarian and prostate cancers

OBJECTIVE

The human kallikrein 10 (KLK10)/normal epithelial cell-specific-1 (NES1) gene is highly expressed in normal mammary, ovary and prostate cells, but its expression is dramatically decreased in cancer cell lines. Recently, it has been shown that CpG island hypermethylation of the KLK10 gene is responsible for the tumor-specific loss of KLK10 gene expression in certain breast cancer cell lines.

METHOD

We examined the role of CpG island hypermethylation in the tumor-specific loss of KLK10 expression in breast, ovarian and prostate cancers. We treated cells with the demethylating agent 5-aza-2'-deoxycytidine (dC) and monitored changes in KLK10 mRNA by RT-PCR and secreted hK10 protein expression by ELISA. The following cell lines were used: MDA-MB-231, MDA-MB-468, MCF-7, ZR-75-1, T-47D and BT-474 (breast); BG-1, MDAH-2774, HTB-75, HTB-161, PA-1 and ES-2 (ovary), and LNCaP and PC-3 (prostate).

RESULTS

Upregulation of KLK10 mRNA levels, which was accompanied by an increase in secreted hK10 protein concentration, was observed for a subset of breast, ovarian, and prostate tumor cell lines after 5-aza-2'-dC. Genomic sequencing of sodium-bisulfite-treated DNA demonstrated that CpG sites within the KLK10 gene exon 3 were highly methylated. Hypermethylation of exon 3 CpG regions was also detected in primary ovarian cancers.

CONCLUSION

These data suggest that CpG island hypermethylation plays an important role in the downregulation of kallikrein 10 mRNA and protein expression, but it cannot explain the pattern of expression of this gene in all cell lines or tissue tested.

Multiple tissue kallikrein mRNA and protein expression in normal skin and skin diseases

BACKGROUND

Human tissue kallikreins are a gene family (KLK1-KLK15) encoding for 15 secretory serine proteases (hK1-hK15). Two tissue kallikrein proteins, hK5 and hK7, were previously found in the stratum corneum (SC), stratum granulosum (SG) and appendages. hK8 was also shown to be secreted via lamellar granules and numerous KLK mRNAs were previously identified. KLKs are believed to be responsible for desquamation of corneocytes and sebum, sweat and hair maturation.

OBJECTIVES

To demonstrate immunohistochemically the expression of hK6, hK8 and hK13 in normal skin tissue and to show an increased cell number expressing kallikrein mRNAs and proteins in psoriasis vulgaris (PV) and atopic dermatitis (AD).

METHODS

Samples of normal, PV and AD skin were obtained. hK6-, hK8- and hK13-specific antibodies were produced and used for immunohistochemical analysis. Multiple KLK mRNAs were synthesized and used for in situ hybridization study.

RESULTS

Three other hKs, namely hK6, hK8 and hK13, were immunohistochemically identified as new skin serine proteases in the whole SC, SG, sebaceous glands, eccrine sweat glands, hair follicles and nerves. We also demonstrated an increased number of cells expressing KLK mRNAs and hKs in PV and AD. In PV, KLK mRNAs/hKs were predominantly expressed in the upper epidermis. In AD, hK distribution was rather diffuse and expanded into the lower epidermis.

CONCLUSIONS

The colocalization of various hKs seems to be essential for the regulation of serine protease activity in skin and for steady desquamation and skin barrier function. Moreover, the increased number of cells expressing multiple KLK mRNA and hK in PV and AD could be a clue to elucidate their pathogenesis.

Human kallikrein 4: quantitative study in tissues and evidence for its secretion into biological fluids

BACKGROUND

Human kallikrein 4 (hK4) is a proteolytic enzyme belonging to the tissue kallikrein family of serine proteases. Previous tissue expression studies have demonstrated highest KLK4 mRNA expression in prostatic tissue, but there has been only limited evidence for the presence of hK4 protein in prostate and other tissues and in corresponding biological secretions.

METHODS

To investigate the concentrations of hK4 in tissues and biological fluids, we developed a new hK4-specific sandwich-type immunoassay using a monoclonal antibody as the capture reagent.

RESULTS

The assay has a detection limit of 0.02 microg/L and <0.1% cross-reactivity toward any of the other 14 human kallikreins. Twelve of 40 tissue extracts prepared from various human tissues contained detectable hK4 concentrations (0.68-7143 ng/g of total protein), with healthy prostate tissue containing the highest amount of hK4. Examination of 16 malignant and 18 benign prostate tissues revealed no significant differences in hK4 protein content, and the tissues contained a wide range of values (benign, <0.02 to 801 ng/g; malignant, <0.02 to 824 ng/g). Among the biological fluids tested, seminal plasma and urine contained widely varying amounts of hK4; concentrations in 54 urine samples were <0.02 to 2.6 microg/L, whereas concentrations in 58 seminal plasma samples were 0.2-202 microg/L. Affinity purification of hK4 from seminal plasma and subsequent mass spectrometry demonstrated the secreted nature of hK4 in seminal plasma.

CONCLUSIONS

hK4 is found primarily in prostate tissue and is secreted in seminal plasma. Its value as a novel prostatic biomarker needs to be defined further.

Enzymatic profiling of human kallikrein 14 using phage-display substrate technology

The humanKLK14gene is one of the newly identified serine protease genes belonging to the human kallikrein family, which contains 15 members.KLK14, like all other members of the human kallikrein family, is predicted to encode for a secreted serine protease already found in various biological fluids. This new kallikrein is mainly expressed in prostate and endocrine tissues, but its function is still unknown. Recent studies have demonstrated thatKLK14gene expression is up-regulated in prostate and breast cancer tissues, and that higher expression levels correlate with more aggressive tumors. In this work, we used phage-display substrate technology to study the substrate specificity of hK14. A phage-displayed random pentapeptide library with exhaustive diversity was screened with purified recombinant hK14. Highly specific and sensitive substrates were selected from the library. We show that hK14 has dual activity, trypsin- and chymotrypsin-like, with a preference for cleavage after arginine residues. A SwissProt database search with selected sequences identified six potential human protein substrates for hK14. Two of them, laminin α-5 and collagen IV, which are major components of the extracellular matrix, have been demonstrated to be hydrolyzed efficiently by hK14.

Biochemical and enzymatic characterization of human kallikrein 5 (hK5), a novel serine protease potentially involved in cancer progression

Human kallikrein 5 (KLK5) is a member of the human kallikrein gene family of serine proteases. Preliminary results indicate that the protein, hK5, may be a potential serological marker for breast and ovarian cancer. Other studies implicate hK5 with skin desquamation and skin diseases. To gain further insights on hK5 physiological functions, we studied its substrate specificity, the regulation of its activity by various inhibitors, and identified candidate physiological substrates. After producing and purifying recombinant hK5 in yeast, we determined the k(cat)/K(m) ratio of the fluorogenic substrates Gly-Pro-Arg-AMC and Gly-Pro-Lys-AMC, and showed that it has trypsin-like activity with strong preference for Arg over Lys in the P1 position. The serpins alpha(2)-antiplasmin and antithrombin were able to inhibit hK5 with an inhibition constant (k(+2)/K(i)) of 1.0 x 10(-) (2)and 4.2 x 10(-4) m(-1) min(-1), respectively. No inhibition was observed with the serpins alpha(1)-antitrypsin and alpha(1)-antichymotrypsin, although alpha(2)-macroglobulin partially inhibited hK5 at high concentrations. We also demonstrated that hK5 can efficiently digest the extracellular matrix components, collagens type I, II, III, and IV, fibronectin, and laminin. Furthermore, our results suggest that hK5 can potentially release (a) angiostatin 4.5 from plasminogen, (b) "cystatin-like domain 3" from low molecular weight kininogen, and (c) fibrinopeptide B and peptide beta15-42 from the Bbeta chain of fibrinogen. hK5 could also play a role in the regulation of the binding of plasminogen activator inhibitor 1 to vitronectin. Our findings suggest that hK5 may be implicated in tumor progression, particularly in invasion and angiogenesis, and may represent a novel therapeutic target.

Human Tissue Kallikreins: Physiologic Roles and Applications in Cancer

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

Immunohistochemical localization of human kallikreins 6, 10 and 13 in benign and malignant prostatic tissues

Human kallikreins 6, 10 and 13 (hK6, hK10 and hK13) are expressed by many normal, mainly glandular tissues, including prostatic epithelium. Some kallikreins may function as tumor suppressors or are downregulated during cancer progression. The aim of this study was to evaluate the immunoexpression of these kallikreins in benign and malignant prostatic tissues and correlate their expression with prostate cancer (PC) prognosis. Included in the study were 25 cases of nonmalignant prostate and 179 cases of PC. Among them, 122 PC cases were immunostained for hK6, 94 for hK10 and 113 for hK13, respectively. The follow-up period for a subset of 68 patients who had undergone radical prostatectomy (RP) was 1-58 months (mean=13.4 +/- 1.7 and median=8.0 months). A cutoff value of 0.2 microg/l of serum PSA was established as a biochemical recurrence threshold. Follow-up information was available for 26/55 RP cases stained for hK6, 14/32 cases stained for hK10 and 25/59 cases stained for hK13. Gleason score (GS) 7 carcinomas were stratified as 7a and 7b, according to the primary grade. PC with GS 2-7a were histologically categorized as low malignant (LM) and PC with GS 7b-10 as high malignant (HM). The immunohistochemical method of streptavidin-biotin-peroxidase using monoclonal and polyclonal antibodies was performed. In the benign prostate and in prostatic intraepithelial neoplasia, a cytoplasmic immunostaining of varying intensity was evident. In PC, the immunoexpression of all kallikreins was decreased: 102/122 cases (84%) were positive for hK6, 73/94 (78%) for hK10 and 97/113 (86%) for hK13, respectively. A statistically significant difference in expression was found, in comparison to nonmalignant prostates (P=0.029, 0.009 and 0.045, respectively). Also, a positive correlation was observed between the immunoexpression of these three kallikreins. Concerning the histological grade, HM-PC expressed all three kallikreins with a slightly higher percentage than LM-PC: 79 vs 88% for hK6, 76 vs 79% for hK10 and 76 vs 92% for hK13. These differences were statistically significant only in the case of hK13 (P=0.024). Serum PSA did not correlate with kallikrein immunoexpression in PC. Furthermore, there was no significant correlation between kallikrein expression and pathological stage or recurrence, in the cases of RP. All three kallikreins are expressed in the nonmalignant and malignant prostate, with cancer tissues demonstrating slightly lower expression. Expression levels did not correlate with aggressiveness and they do not seem to have value for prostate cancer prognosis.

Development of an Immunofluorometric Assay and Quantification of Human Kallikrein 7 in Tissue Extracts and Biological Fluids

Background: Human kallikrein 7 (hK7), also known as human stratum corneum chymotryptic enzyme, is a chymotrypsin-like serine protease first identified in human skin extracts and predicted to be a secreted protease. The aim of this study was to develop a sensitive and specific immunoassay for hK7 and to examine the distribution of hK7 in tissue extracts and biological fluids.

Methods: Recombinant hK7 was produced in human embryonic kidney cells (HEK293T) and purified by a three-step column chromatographic procedure. The purified hK7 was injected into mice for antibody generation. A sandwich-type immunoassay was developed with the anti-hK7 monoclonal antibodies.

Results: The assay had imprecision (CV) &lt;10% through the dynamic range of 0.2–20 μg/L and had no detectable cross-reactivity from other members in the human kallikrein gene family. Highest concentrations were found in skin, esophagus, and kidney. hK7 was also found in amniotic fluid, ascites from ovarian cancer patients, breast milk, cerebrospinal fluid, saliva, seminal plasma, serum, sweat, synovial fluid, and urine.

Conclusions: This study describes the first ELISA-type immunoassay for hK7 protein quantification. hK7 is found many human tissues and in various biological fluids.

Altered kallikrein 7 and 10 concentrations in cerebrospinal fluid of patients with Alzheimer's disease and frontotemporal dementia

BACKGROUND

The role of various proteases in the pathogenesis of Alzheimer's disease is well documented. Recently, many members of the human tissue kallikrein family, a group of 15 secreted serine proteases, were found to be highly expressed in the central nervous system (CNS). Some of these enzymes can be measured in cerebrospinal fluid (CSF) by using ELISA-type methodologies.

METHODS

We quantified various kallikreins in CSF of 20 patients with Alzheimer's disease (AD), 16 patients with frontotemporal dementia (FTD), and 15 controls. We then correlated the levels of various kallikreins with presence of AD or FTD. Among all kallikreins measured, detectable levels in CSF were identified for kallikreins hK6, hK7, and hK10. Other tested kallikreins (hK5, hK8, hK11, and hK13) were unmeasurable. The most notable differences between kallikrein levels in CSF and the three groups of subjects were seen between controls and FTD patients for hK6 (decrease in FTD; P = 0.017), controls and FTD patients for hK7 (decrease in FTD; P < 0.001), and controls and AD patients for hK7 (decrease in AD; P = 0.019). In addition, significant differences were seen between FTD patients or control subjects and patients with AD patients for hK10 (increase in AD; P < 0.02). Approximately half of the AD patients had CSF hK10 levels that were higher than all patients with FTD except one and all control subjects except two. Various kallikrein concentrations in CSF were correlated, the strongest correlation seen between hK6 and hK7 (r(s) = 0.58). We also observed a statistically significant association between decreasing hK7 concentration in CSF and possession of one or two ApoE4 alleles (P = 0.014).

CONCLUSIONS

We demonstrate for the first time significant alterations of hK6, hK7, and hK10 concentration in CSF of patients with AD and FTD. Notably, all three kallikreins (hK6, hK7, and hK10) are decreased in CSF of FTD patients and hK10 is increased in CSF of AD patients, in comparison to control subjects. The possible connection between these enzymes and the pathogenesis and progression of AD and FTD needs to be further investigated.

Kallikrein gene downregulation in breast cancer

Recent evidence suggests that many members of the human kallikrein gene family are differentially regulated in breast cancer and other endocrine-related malignancies. In this study, we utilised the serial analysis of gene expression (SAGE) and expressed sequence tag (EST) databases of the Cancer Genome Anatomy Project (CGAP) to perform in silico analyses of the expression pattern of the 15 human kallikrein genes in normal and cancerous breast tissues and cell lines using different analytical tools such as Virtual Northern blotting, Digital Differential Display and X-profiler. Our results indicate that at least four kallikrein genes (KLK5, 6, 8, 10) are downregulated in breast cancer. Probing eight normal and 24 breast cancer SAGE libraries with gene-specific tags for each of the above kallikreins indicated moderate-to-high expression densities in normal breast (27–319 tags per million; tpm, in two to five out of eight libraries), compared to no or low expression (0 – 34 tpm in zero to two libraries out of 24) in breast cancer. These data were verified by screening the EST databases, where all mRNA clones isolated for these genes, except for one in each, were from normal breast libraries, with no clones detected from breast cancer tissues or cell lines (with the exception of KLK8). X-profiler comparison of two pools of normal and breast cancer libraries further verified the presence of significant downregulation of expression levels of 4 of the kallikreins genes (KLK5, 6, 10, 12). We experimentally verified the downregulation of these four kallikreins (KLK5, 6, 8, 10 and 12) by RT – PCR analysis.

Steroid hormone regulation of the human kallikrein 10 (KLK10) gene in cancer cell lines and functional characterization of the KLK10 gene promoter

BACKGROUND

The human kallikrein 10 (KLK10) gene is a new member of the human tissue kallikrein gene family. It encodes for a secreted serine protease (hK10) with predicted trypsin-like enzymatic activity. KLK10 is highly expressed in the sex organs and its expression level changes in malignancy.

METHODS

To determine the role of steroid hormones in KLK10 gene expression, we investigated its modulation by 17beta-estradiol, 5alpha-dihydrotestosterone, norgestrel, dexamethasone and aldosterone, at both the transcription and translation level, in a panel of cancer cell lines. After steroid hormone stimulation, the change of KLK10 mRNA was monitored with reverse transcriptase polymerase chain reaction and hK10 protein levels in the culture supernatant were quantified with an hK10-specific immunoassay. The presence of hormone response elements in the KLK10 gene promoter was examined with the chloramphenicol acetyltransferase reporter gene system.

RESULTS

The KLK10 expression was mainly up-regulated by estrogens, androgens and progestins, and to a lesser extent by dexamethasone and aldosterone in the breast cancer cell lines BT-474, MCF-7 and T-47D, both at the mRNA and protein levels. The effect of stimulation of these steroids on KLK10 expression varied among the cell lines. Estrogens, androgens and progestins were most potent in the BT-474, T-47D and MCF-7 cells, respectively. The up-regulation effect of estrogens, androgens, and progestins on KLK10 expression can be blocked by their antagonists ICI-182, 780, RU-56,187, and mifepristone, respectively. Time course studies showed that hK10 protein started to increase 1 day after steroid hormone stimulation and this increase persisted for 7 days. These data suggest that steroid hormones up-regulate KLK10 gene expression through direct interaction between hormone-receptor complexes and their cognate hormone response elements. To search for hormone response elements, we functionally characterized the KLK10 promoter by placing it upstream of the chloramphenicol acetyltransferase reporter gene. We found that KLK10 promoter activity did not rely on the presence of functional estrogen and androgen receptors. Also, the presence of functional estrogen and androgen receptors did not increase its constitutive activity. We suggest that the hormone response elements that mediate the transcriptional regulation of KLK10 are unlikely to locate in the KLK10 promoter.

CONCLUSIONS

Estrogens, androgens and progestins modulate KLK10 expression through their own receptors but this regulation is not mediated by steroid hormone response elements in the promoter of the KLK10 gene.

Are cardiovascular and sympathoadrenal effects of human "new pressor protein" preparations attributable to human coagulation beta-FXIIa?

"New pressor protein" (NPP) derived from normal human plasma is an extra renal enzyme that shares strong sequence homology with human coagulation beta-FXIIa. Under our bioassay conditions, human NPP (10-20 microl plasma equivalent/ approximately 300 g rat iv) can raise the systolic blood pressure (SBP) by 40-50 mmHg, the diastolic blood pressure (DBP) by 15-20 mmHg, and the heart rate (HR) by 70-90 beats/min. Plasma epinephrine (of adrenal medullary origin) and norepinephrine rise by about 50- and 10-fold, respectively. Because beta-FXIIa is not normally associated with pressor properties, we endeavored to substantiate that the hypertensive effects of impure NPP preparations used in our experiments are attributable to their content of beta-FXIIa. We carried out comparisons with highly purified (>90%) commercial human beta-FXIIa and found that by gel filtration (Sephadex G-100 and G-75), NPP bioactivity appeared in the approximately 30-kDa elution zone, consistent with the molecular mass of beta-FXIIa. Retention time using fast-protein liquid chromatography anion exchange chromatography was identical. Molecular mass and comigration were confirmed by SDS-PAGE gel electrophoresis, and the recovered approximately 30-kDa protein bands yielded beta-FXIIa fragments identified by mass spectrometry. Matched doses of the NPP preparations produced dose-response curves very similar to those elicited by beta-FXIIa with respect to increments of SBP, DBP, and HR, whereas plasma catecholamine increments were generally comparable. We propose that beta-FXIIa is substantially, if not exclusively, responsible for the observed effects of our NPP preparations and that this points to a novel axis connecting the FXII coagulation cascade and the sympathoadrenal gland to other cardiovascular regulatory mechanisms.