The expanded human kallikrein (KLK) gene family: genomic organisation, tissue-specific expression and potential functions

KLK7 expression in human tumors: a tissue microarray study on 13,447 tumors

BACKGROUND

Kallikrein-related peptidase 7 (KLK7) is a chymotrypsin-like serine protease which is essential for the desquamation of corneocytes and thus plays a pivotal role in maintaining skin homeostasis. In cancer, KLK7 overexpression was suggested to represent a route for metastasis through cleavage of cell junction and extracellular matrix proteins of cancer cells.

METHODS

To comprehensively determine KLK7 protein expression in normal and neoplastic tissues, a tissue microarray containing 13,447 samples from 147 different tumor types and subtypes as well as 608 samples of 76 different normal tissue types was analyzed by immunohistochemistry.

RESULTS

KLK7 positivity was found in 64 of 147 tumor categories, including 17 tumor categories with at least one strongly positive case. The highest rate of KLK7 positivity was found in squamous cell carcinomas from various sites of origin (positive in 18.1%-63.8%), ovarian and endometrium cancers (4.8%-56.2%), salivary gland tumors (4.8%-13.7%), bilio-pancreatic adenocarcinomas (20.0%-40.4%), and adenocarcinomas of the upper gastrointestinal tract (3.3%-12.5%). KLK7 positivity was linked to nodal metastasis (p = 0.0005), blood vessel infiltration (p = 0.0037), and lymph vessel infiltration (p < 0.0001) in colorectal adenocarcinoma, nodal metastasis in hepatocellular carcinoma (p = 0.0382), advanced pathological tumor stage in papillary thyroid cancer (p = 0.0132), and low grade of malignancy in a cohort of 719 squamous cell carcinomas from 11 different sites of origin (p < 0.0001).

CONCLUSIONS

These data provide a comprehensive overview on KLK7 expression in normal and neoplastic human tissues. The prognostic relevance of KLK7 expression and the possible role of KLK7 as a drug target need to be further investigated.

Loss of KLK4::KLKP1 pseudogene expression by RNA chromogenic in-situ hybridization is associated with PTEN loss and increased risk of biochemical recurrence in a cohort of middle eastern men with prostate cancer

BACKGROUND

KLK4::KLKP1 fusion is a recently described pseudogene that is enriched in prostate cancer (PCa). This new biomarker has not been characterized in the Middle Eastern population.

OBJECTIVE

To establish the incidence and prognostic value of KLK4::KLKP1 fusion in a cohort of Middle Eastern men with PCa and explore the relationship of this marker to other relevant biomarkers (PTEN, ERG, SPINK1).

DESIGN, SETTING, AND PARTICIPANTS

We interrogated a cohort of 340 Middle Eastern men with localized PCa treated by radical prostatectomy between 2005 and 2015. KLK4::KLKP1 fusion status was assessed by RNA Chromogenic in situ hybridization (CISH) and correlated to pathological and clinical parameters.

OUTCOME MEASUREMENTS AND STATISTICAL ANALYSIS

RNA-CISH expression of KLK4::KLKP1 was correlated with prognostic factors, ERG, PTEN, and SPINK1 expression, and biochemical recurrence (BCR) following prostatectomy.

RESULTS AND LIMITATIONS

51.7% of patient samples showed positive KLK4::KLKP1 expression; more commonly in cores of PCa (38%) versus non-cancer (20.6%) (p < 0.0001) and in lower Gleason Grade Group tumors (1-3) vs (4-5). KLK4::KLKP1 expression positively correlated with ERG positivity and inversely associated with PTEN loss. No significant association was found with SPINK1 expression, seminal vesicle invasion, positive surgical margin, pathological stage, or patient age (< 50 or ≥ 50). The association between PTEN loss and BCR increased when combined with KLK4::KLKP1 negativity (HR 2.31, CI 1.03-5.20, p = 0.042).

CONCLUSIONS

KLK4::KLKP1 expression is more common in this cohort of Middle Eastern men than has been reported in North American men. It is associated with ERG positivity and inversely correlated with PTEN loss. In isolation, KLK4::KLKP1 expression was not significantly associated with clinical outcome or pathological parameters. However, its expression is associated with certain molecular subtypes (ERG-positive, PTEN-intact) and as we demonstrate may help further stratify the risk of recurrence within these groups.

Three Months of Strength Training Changes the Gene Expression of Inflammation-Related Genes in PBMC of Older Women: A Randomized Controlled Trial

Here, we investigate changes in inflammation-related gene-expression in peripheral mononuclear blood cells (PBMC) by strength training. A total of 14 women aged ≥65 years were randomized into 3 months of either 3×/week intensive strength training (IST: 3×10 rep at 80% 1RM), strength endurance training (SET: 2×30 reps at 40% 1RM) or control (CON: 3×30 sec stretching). Differentially expressed genes (fold change ≤0.67 or ≥1.5) were identified by targeted RNA-sequencing of 407 inflammation-related genes. A total of 98 genes (n = 61 pro-inflammatory) were significantly affected. IST and SET altered 14 genes in a similar direction and 19 genes in the opposite direction. Compared to CON, IST changed the expression of 6 genes in the same direction, and 17 genes in the SET. Likewise, 18 and 13 genes were oppositely expressed for, respectively, IST and SET compared to CON. Changes in gene expression affected 33 canonical pathways related to chronic inflammation. None of the altered pathways overlapped between IST and SET. Liver X Receptor/Retinoid X Receptor Activation (LXR/RXR) and Triggering Receptor Expressed On Myeloid Cells 1 (TREM1) pathways were enriched oppositely in both training groups. We conclude that three months IST and SET can induce changes in CLIP-related gene expression in PBMC, but by affecting different genes and related pathways.

KLK4T2 Is a Hormonally Regulated Transcript from the KLK4 Locus

The human kallikrein-related peptidase 4 (KLK4) and the transcribed pseudogene KLKP1 are reported to be highly expressed in the prostate. When trying to clone transcripts of KLKP1, we partly failed. Instead, we identified an androgen-regulated transcript, KLK4T2, which appeared to be a splice variant of KLK4 that also contained exons of KLKP1. Expression analysis of KLK4, KLK4T2, and KLKP1 transcripts in prostate cancer cell lines showed high levels of KLKP1 transcripts in the nucleus and in unfractionated cell extract, whereas it was almost completely absent in the cytoplasmatic fraction. This was in contrast to KLK4 and KLK4T2, which displayed high to moderate levels in the cytoplasm. In patient cohorts we found significantly higher expression of both KLK4T2 and KLK4 in benign prostatic hyperplasia compared to both primary prostate cancer and bone metastasis. Analysis of tissue panels demonstrated the highest expression of KLK4T2 in the prostate, but in contrast to the classical KLK4, relatively high levels were also found in placenta. So far, the function of KLK4T2 is still to be explored, but the structure of the translation product indicated that it generates a 17.4 kDa intracellular protein with possible regulatory function.

The Role of Kallikrein 7 in Tumorigenesis

Kallikrein 7 (KLK7) is a secreted serine protease with chymotrypsic protease activity. Abnormally high expression of KLK7 is closely related to the occurrence and development of various types of cancer. Therefore, KLK7 has been identified as a potential target for cancer drug development design in recent years. KLK7 mediates various biological and pathological processes in tumorigenesis, including cell proliferation, migration, invasion, angiogenesis, and cell metabolism, by hydrolyzing a series of substrates such as membrane proteins, extracellular matrix proteins, and cytokines. This review mainly introduces the downstream cell signaling pathways involved in the activation of KLK7 and its substrate-related proteins. This review will not only help us to better understand the mechanisms of KLK7 in regulating biological and pathological processes of cancer cells, but also lay a solid foundation for the design of inhibitors targeting KLK7.

The prognostic and diagnostic potential of kallikrein-related peptidases in ovarian cancer

Introduction: Ovarian cancer is one of the deadliest malignancies among women worldwide. The lack of early diagnostic markers fuels an unfavorable prognosis as most patients are at an advanced stage when the disease is diagnosed for the first time. The role of the kallikrein-related peptidase (KLK) family in ovarian cancer progression and prognosis has been thoroughly investigated in various studies. Most of these peptidases are upregulated in ovarian cancer tissue compared to normal ovarian tissue and their expression is linked to overall and progression-free survival (OS/PFS). In this review, we address the clinical relevance of KLKs in ovarian cancer and their diagnostic potential.Areas covered: This review covers the expression and regulation of KLKs in ovarian cancer with focus on the prognostic and diagnostic potential, especially in liquid biopsies.Expert opinion: In ovarian cancer, several kallikrein-related peptidases are markedly expressed in a tissue-specific manner. Tumor-derived protease secretion results in elevated levels in serum and ascites. KLKs may thus serve as potential biomarkers alone or in combination with other serum tumor markers, such as Cancer Antigen 125 (CA125), for early detection and assessment of the prognosis of ovarian cancer patients.

Serine Protease Inhibitors to Treat Lung Inflammatory Diseases

Lung is a vital organ that ensures breathing function. It provides the essential interface of air filtering providing oxygen to the whole body and eliminating carbon dioxide in the blood; because of its exposure to the external environment, it is fall prey to many exogenous elements, such as pathogens, especially viral infections or environmental toxins and chemicals. These exogenous actors in addition to intrinsic disorders lead to important inflammatory responses that compromise lung tissue and normal functioning. Serine proteases regulating inflammation responses are versatile enzymes, usually involved in pro-inflammatory cytokines or other molecular mediator's production and activation of immune cells. In this chapter, an overview on major serine proteases in airway inflammation as therapeutic targets and their clinically relevant inhibitors is provided. Recent updates on serine protease inhibitors in the context of the COVID-19 pandemic are summarized.

Kallikrein 13 serves as a priming protease during infection by the human coronavirus HKU1

Unlike SARS-CoV-2, the human coronavirus HKU1 normally causes relatively mild respiratory tract infections; however, it shares with SARS-CoV-2 the mechanism of using its surface spike (S) protein to enter target cells. Because the host receptor for HCoV-HKU1 is unknown, efforts to study the virus in cell culture systems have proved difficult. Milewska et al. found that knockout of the protease kallikrein 13 (KLK13) in human airway epithelial cells blocked their infection by HCoV-HKU1, that overexpression of KLK13 in nonpermissive cells enabled their infection by the virus, and that KLK13 cleaved the viral S protein. Together, these findings suggest that KLK13 is a priming enzyme for viral entry and may help to establish cell lines that can facilitate further investigation of the mechanism of viral pathogenesis.

Human coronavirus HKU1 (HCoV-HKU1) is associated with respiratory disease and is prevalent worldwide, but an in vitro model for viral replication is lacking. An interaction between the coronaviral spike (S) protein and its receptor is the primary determinant of tissue and host specificity; however, viral entry is a complex process requiring the concerted action of multiple cellular elements. Here, we found that the protease kallikrein 13 (KLK13) was required for the infection of human respiratory epithelial cells and was sufficient to mediate the entry of HCoV-HKU1 into nonpermissive RD cells. We also demonstrated the cleavage of the HCoV-HKU1 S protein by KLK13 in the S1/S2 region, suggesting that KLK13 is the priming enzyme for this virus. Together, these data suggest that protease distribution and specificity determine the tissue and cell specificity of the virus and may also regulate interspecies transmission.

Identification of six novel alternative transcripts of the human kallikrein-related peptidase 15 (KLK15), using 3'RACE and high-throughput sequencing

The kallikrein-related peptidase 15 (KLK15) gene is a member of the largest cluster of serine proteases in the human genome. Exhibiting trypsin-like activity, KLK15 is most likely involved in the activation of prostate-specific antigen (PSA; also known as KLK3), an established biomarker for the diagnosis and screening of prostate cancer. High mRNA expression levels of KLK15 have already been reported in ovarian and prostate cancer, in contrast with breast cancer, where KLK15 has been proposed as a biomarker of favorable prognosis. In this study, we exploited the next-generation sequencing (NGS) technology along with 3' rapid amplification of cDNA ends (3' RACE) to discover alternative KLK15 splice variants. Extensive computational analysis of the obtained NGS data revealed the existence of novel splice junctions, thus supporting the existence of novel KLK15 transcripts. Six novel KLK15 splice variants were identified and verified by Sanger sequencing. Two of them (KLK15 v.11 and v.12) contain an open reading frame and are hence predicted to encode two novel KLK15 protein isoforms. Expression analysis of each KLK15 splice variant in sixteen cDNA pools from malignant cell lines and in normal cell lines (HEK293, HaCaT, and BJ cells) revealed very different expression profiles of particular KLK15 transcripts. Moreover, the new KLK15 splice variants were shown to be expressed in breast, ovarian, prostate, urinary bladder, colon, and renal tissue specimens. Due to the prominent clinical value of KLK15 mRNA expression, the novel KLK15 transcripts appear as candidate cancer biomarkers for diagnostic and/or prognostic purposes and, therefore, merit further investigation.

Prognostic value of kallikrein-related peptidase 12 (KLK12) mRNA expression in triple-negative breast cancer patients

BACKGROUND

The serine protease KLK12 belongs to the human fifteen-member family of kallikrein-related peptidases. Differential expression accompanied by either increased or decreased enzymatic activity has been linked to several diseases including cancer. Triple-negative breast cancer (TNBC) represents a very aggressive subgroup of breast cancer with high tumor recurrence rates and poor patient prognosis. Here, we quantified the KLK12 mRNA expression levels in tumor tissue of TNBC patients and analyzed their prognostic value.

METHODS

In the present study, KLK12 mRNA expression in tumor tissue of TNBC patients (n = 116) was determined by quantitative real-time PCR assay. The association of KLK12 mRNA levels with clinical parameters, and patients' outcome was analyzed using Chi-square tests, Cox regression models and Kaplan-Meier survival analysis.

RESULTS

Positive, but low KLK12 mRNA levels were detected in about half of the cases (54 out of 116; 47%), the other samples were negative for KLK12 mRNA expression. No significant association was observed between KLK12 mRNA levels and clinicopathological variables (age, lymph node status, tumor size, and histological grade). In univariate Cox analyses, positive KLK12 mRNA expression was significantly associated with shortened disease-free survival (DFS; hazard ratio [HR] = 2.12, 95% CI = 1.19-3.78, p = 0.010) as well as overall survival (OS; HR = 1.91, 95% CI = 1.04-3.50, p = 0.037). In multivariable Cox analysis, including all clinical parameters plus KLK12 mRNA, the latter - together with age - remained an independent unfavorable predictive marker for DFS (HR = 2.33, 95% CI = 1.28-4.24, p = 0.006) and showed a trend towards significance in case of OS (HR = 1.80, 95% CI = 0.96-3.38, p = 0.066).

CONCLUSIONS

Positive KLK12 expression is remarkably associated with shortened DFS and OS, suggesting that KLK12 plays a tumor-supporting role in TNBC.

A Versatile and Robust Serine Protease Inhibitor Scaffold from Actinia tenebrosa

Serine proteases play pivotal roles in normal physiology and a spectrum of patho-physiological processes. Accordingly, there is considerable interest in the discovery and design of potent serine protease inhibitors for therapeutic applications. This led to concerted efforts to discover versatile and robust molecular scaffolds for inhibitor design. This investigation is a bioprospecting study that aims to isolate and identify protease inhibitors from the cnidarian Actinia tenebrosa. The study isolated two Kunitz-type protease inhibitors with very similar sequences but quite divergent inhibitory potencies when assayed against bovine trypsin, chymostrypsin, and a selection of human sequence-related peptidases. Homology modeling and molecular dynamics simulations of these inhibitors in complex with their targets were carried out and, collectively, these methodologies enabled the definition of a versatile scaffold for inhibitor design. Thermal denaturation studies showed that the inhibitors were remarkably robust. To gain a fine-grained map of the residues responsible for this stability, we conducted in silico alanine scanning and quantified individual residue contributions to the inhibitor's stability. Sequences of these inhibitors were then used to search for Kunitz homologs in an A. tenebrosa transcriptome library, resulting in the discovery of a further 14 related sequences. Consensus analysis of these variants identified a rich molecular diversity of Kunitz domains and expanded the palette of potential residue substitutions for rational inhibitor design using this domain.

Knockdown of KLK12 inhibits viability and induces apoptosis in human colorectal cancer HT-29 cell line

Kallikrein-related peptidase 12 (KLK12) is overexpressed in cancer tissues including gastric, breast and prostate cancer. However, the role of KLK12 in colorectal cancer is not fully understood. In the present study, the level of KLK12 was determined by performing reverse transcription-polymerase chain reaction (RT-qPCR) in colorectal cancer tissues and cell lines. Lipofectamine^® 2000 was used to transfect HT-29 cells to overexpress and knockdown KLK12. Cell viability, migration, invasion and apoptosis were detected by MTT, wound healing, Transwell and flow cytometry assays, respectively. The mRNA and protein expression levels of EMT-associated proteins, apoptosis-associated proteins, phosphorylated adenosine monophosphate-activated protein kinase (p-AMPK) and phosphorylated mammalian target of rapamycin (p-mTOR) were determined by RT-qPCR and western blot analysis. It was identified that the KLK12 mRNA levels were increased significantly in colorectal cancer tissues and cell lines. KLK12 small interfering RNA inhibited cell viability, migration and invasion. Furthermore, epithelial-mesenchymal transition (EMT)-associated proteins were altered by siKLK12. Cell apoptosis was induced by KLK12 downregulation, which was demonstrated by the changes in apoptosis-associated proteins; however, KLK12 overexpression produced the opposite effect. SiKLK12 enhanced the expression of p-AMPK and suppressed the expression of p-mTOR, while KLK12 overexpression had the opposite effect. Promotion of KLK12 overexpression-induced cell viability was reversed by 5-aminoimidazole-4-carboxamide ribonucleotide, an activator of the AMPK signaling pathway, and rapamycin, a specific inhibitor of the mTOR signaling pathway. Taken together, the results of the present study indicated that KLK12 was overexpressed in colorectal cancer and may regulate cell behavior, potentially via the AMPK and mTOR pathways.

Pseudogene Associated Recurrent Gene Fusion in Prostate Cancer

We present the functional characterization of a pseudogene associated recurrent gene fusion in prostate cancer. The fusion gene KLK4-KLKP1 is formed by the fusion of the protein coding gene KLK4 with the noncoding pseudogene KLKP1. Screening of a cohort of 659 patients (380 Caucasian American; 250 African American, and 29 patients from other races) revealed that the KLK4-KLKP1 is expressed in about 32% of prostate cancer patients. Correlative analysis with other ETS gene fusions and SPINK1 revealed a concomitant expression pattern of KLK4-KLKP1 with ERG and a mutually exclusive expression pattern with SPINK1, ETV1, ETV4, and ETV5. Development of an antibody specific to KLK4-KLKP1 fusion protein confirmed the expression of the full-length KLK4-KLKP1 protein in prostate tissues. The in vitro and in vivo functional assays to study the oncogenic properties of KLK4-KLKP1 confirmed its role in cell proliferation, cell invasion, intravasation, and tumor formation. Presence of strong ERG and AR binding sites located at the fusion junction in KLK4-KLKP1 suggests that the fusion gene is regulated by ERG and AR. Correlative analysis of clinical data showed an association of KLK4-KLKP1 with lower preoperative PSA values and in young men (<50 years) with prostate cancer. Screening of patient urine samples showed that KLK4-KLKP1 can be detected noninvasively in urine. Taken together, we present KLK4-KLKP1 as a class of pseudogene associated fusion transcript in cancer with potential applications as a biomarker for routine screening of prostate cancer.

Glycosylation products in prostate diseases

Although prostate cancer is notable for its high incidence and mortality in men worldwide, its identification remains a challenge. Biomarkers have been useful tools for the specific detection of prostate cancer. Unfortunately, benign prostate diseases cause similar alterations in screening assays thus reducing the potential for early and specific diagnosis. Changes in glycan and glycoprotein expression have often been associated with the onset and progression of cancer. Abnormal glycans and glycoproteins have been reported as new biomarkers of prostate metabolism that can distinguish benign prostate disease and cancer in non-aggressive and aggressive stages. Carbohydrate-binding proteins known as lectins have been valuable tools to detect these changes, investigate potential biomarkers and improve our understanding aberrant glycosylation in cancer. Here we review progress in elucidating prostate disease and discuss the roles of glycans in the differential detection of benign and cancerous prostate disease. We also summarize the lectin-based tools for detecting glycosylation changes.

Gene expression profiling identifies potential molecular markers of papillary thyroid carcinoma

BACKGROUND

Thyroid cancer is the most common endocrine malignancy worldwide, with the predominant form papillary thyroid carcinoma (PTC) representing approximately 80% of cases.

OBJECTIVE

This study was addressed to identify potential genes and pathways involved in the pathogenesis of PTC and potential novel biomarkers for this disease.

METHODS

Gene expression profiling was carried out by DNA microarray technology. Validation of microarray data by qRT-PCR, western blot, and enzyme linked immunosorbent assay was also performed in a selected set of genes and gene products, with the potential to be used as diagnostic or prognostic biomarkers, such as those associated with cell adhesion, extracellular matrix (ECM) remodeling and immune/inflammatory response.

RESULTS

In this study we found that upregulation of extracellular activities, such as proteoglycans, ECM-receptor interaction, and cell adhesion molecules, were the most prominent feature of PTC. Significantly over-expressed genes included SDC1 (syndecan 1), SDC4 (syndecan 4), KLK7 (kallikrein-related peptidase 7), KLK10 (kallikrein-related peptidase 10), SLPI (secretory leukocyte peptidase inhibitor), GDF15 (growth/differentiation factor-15), ALOX5 (arachidonate 5-lipoxygenase), SFRP2 (secreted Frizzled-related protein 2), among others. Further, elevated KLK10 levels were detected in patients with PTC. Many of these genes belong to KEGG pathway "Proteoglycans in cancer".

CONCLUSIONS

Using DNA microarray analysis allowed the identification of genes and pathways with known important roles in malignant transformation, and also the discovery of novel genes that may be potential biomarkers for PTC.

Characterization of kallikrein-related peptidase 4 (KLK4) mRNA expression in tumor tissue of advanced high-grade serous ovarian cancer patients

Overexpression of several members of the kallikrein-related peptidase (KLK) family, including KLK4, has been reported in ovarian cancer tissue, consistent with the fact that elevated levels of KLK protein are often also found in serum and in effusion fluids of ovarian cancer patients. In the present study, we quantitatively analyzed KLK4 tumor tissue mRNA expression levels in a homogeneous cohort including 138 patients of advanced high-grade serous ovarian cancer (FIGO stage III/IV). Age as well as ascites fluid volume were found to be significantly associated with KLK4 mRNA expression levels. In univariate Cox regression analysis, the clinical factors residual tumor mass and ascites fluid volume represented univariate predictors for both overall survival (OS) and progression-free survival (PFS). Furthermore, elevated KLK4 mRNA expression levels were significantly linked with reduced OS (p = 0.001), but not with PFS. The results concerning the association of KLK4 mRNA expression with OS were validated in a publicly available Affymetrix-based mRNA data set from The Cancer Genome Atlas (n = 252) applying the Kaplan-Meier Plotter tool (p = 0.047). In multivariable analyses, elevated KLK4 mRNA values turned out as an additional, independent predictive marker for shortened OS (p = 0.006), whereas residual tumor mass, but not ascites fluid volume, remained an independent indicator for both OS and PFS (p < 0.001 and p = 0.002, respectively). The results of the present study, obtained in a well-defined, homogenous cohort of patients afflicted with advanced high-grade serous ovarian cancer, are in line with previous reports describing high KLK4 levels as an unfavorable marker in ovarian cancer patients.

Identifying Candidate Biomarkers for Pleomorphic Adenoma: A Case-Control Study

Pleomorphic adenoma (PA) is the most common benign salivary gland tumor. Kallikrein-related peptidases have been identified as biomarkers in many human tumors and may influence tumor behavior. We investigated KLK1-15 messenger ribonucleic acid and proteins in PA specimens to determine a KLK expression profile for this tumor. Fresh frozen PA tissue specimens (n = 26) and matched controls were subjected to quantitative real-time reverse transcription polymerase chain reaction to detect KLK1-15 mRNA. Expression of KLK1, KLK12, KLK13, and KLK8 proteins were then evaluated via immunostaining techniques. Statistical analyses were performed with the level of significance set at P < .05. We observed downregulation of KLK1, KLK12, and KLK13 mRNA expression, and immunostaining studies revealed downregulation of the corresponding proteins. Histologic evidence of capsular perforation was associated with increased KLK1 protein expression. Tumor size was not associated with capsular invasion and/or perforation. This study is the first to detail a KLK expression profile for PA at both the transcriptional level and the protein level. Future work is required to develop clinical applications of these findings.

Kallikrein-related peptidases and associated microRNAs as promising prognostic biomarkers in gastrointestinal malignancies

Gastrointestinal (GI) malignancies represent a wide spectrum of diseases of the GI tract and its accessory digestive organs, including esophageal (EC), gastric (GC), hepatocellular, pancreatic (PC) and colorectal cancers (CRC). Malignancies of the GI system are responsible for nearly 30% of cancer-related morbidity and approximately 40% of cancer-related mortality, worldwide. For this reason, the discovery of novel prognostic biomarkers that can efficiently provide a better prognosis, risk assessment and prediction of treatment response is an imperative need. Human kallikrein-related peptidases (KLKs) are a subgroup of trypsin and chymotrypsin-like serine peptidases that have emerged as promising prognosticators for many human types of cancer, being aberrantly expressed in cancerous tissues. The aberrant expression of KLKs in human malignancies is often regulated by KLK/microRNAs (miRNAs) interactions, as many miRNAs have been found to target KLKs and therefore alter their expression levels. The biomarker utility of KLKs has been elucidated not only in endocrine-related human malignancies, including those of the prostate and breast, but also in GI malignancies. The main purpose of this review is to summarize the existing information regarding the prognostic significance of KLKs in major types of GI malignancies and highlight the regulatory role of miRNAs on the expression levels of KLKs in these types of cancer.

Human kallikrein-related peptidase 12 (KLK12) splice variants discriminate benign from cancerous breast tumors

OBJECTIVES

As kallikrein-related peptidase 12 (KLK12) has been implicated in the cancer progression and alternative splicing plays significant role in this disease, the aim of this study was to examine the expression profile and the clinical impact of the KLK12 splice variants in breast cancer.

DESIGN AND METHODS

Total RNA was isolated and reverse transcripted from 141 tissues. Afterwards, quantitative real-time PCR were conducted, followed by the performance of the comparative CT (2-ΔΔCT) method for relative quantification, whilst their correlation with the clinicopathological features of breast malignancies were assessed by statistical analysis.

RESULTS

Both KLK12sv1/2 and KLK12sv3 showed higher expression in non-cancerous than in cancerous samples. KLKsv1/2 (P = 0.001) upregulated and KLK12sv3 (P < 0.001) downregulated in the malignant compared to the benign tumors and their discriminative ability was verified by ROC curve analysis. Moreover, KLK12sv3 was associated with grade (P = 0.012) and hormonal receptor status (P = 0.001). Furthermore, Kaplan-Meier and Cox regression analyses showed that patients with positive KLK12sv1/2 and KLK12sv3 levels presented a significantly longer disease-free survival (P = 0.014 and P = 0.013, respectively) and overall survival (P = 0.062 and P = 0.004, respectively).

CONCLUSIONS

Our results demonstrate the discriminative value of KLK12sv1/2 and KLK12sv3 between benign and malignant breast tumors as well as their potential favorable prognostic significance in breast adenocarcinoma.

Serine protease inhibitors to treat inflammation: a patent review (2011-2016)

INTRODUCTION

Inflammation is a physiological part of the complex biological response of tissues to counteract various harmful signals. This process involves diverse actors such as immune cells, blood vessels, and nerves as sources of mediators for inflammation control. Among them serine proteases are key elements in both physiological and pathological inflammation.

AREAS COVERED

Serine protease inhibitors to treat inflammatory diseases are being actively investigated by various industrial and academic institutions. The present review covers patent literature on serine protease inhibitors for the therapy of inflammatory diseases patented between 2011 and 2016.

EXPERT OPINION

Serine proteases regulating inflammation are versatile enzymes, usually involved in proinflammatory cytokine production and activation of immune cells. Their dysregulation during inflammation can have devastating consequences, promoting various diseases including skin and lung inflammation, neuroinflammation, and inflammatory arthritis. Several serine proteases were selected for their contribution to inflammatory diseases and significant efforts that are spread to develop inhibitors. Strategies developed for inhibitor identification consist on either peptide-based inhibitor derived from endogenous protein inhibitors or small-organic molecules. It is also worth noting that among the recent patents on serine protease inhibitors related to inflammation a significant number are related to retinal vascular dysfunction and skin diseases.

Mass spectrometry based proteomics analyses in kallikrein-related peptidase research: implications for cancer research and therapy

INTRODUCTION

Kallikrein-related peptidases (KLKs) are a family of serine peptidases that are deregulated in numerous pathological conditions, with a multitude of KLK-mediated functional roles implicated in the progression of cancer. Advances in multidimensional mass spectrometry (MS)-based proteomics have facilitated the quantitative measurement of deregulated KLK expression in cancer, identifying certain KLKs, as well as their substrates, as potential cancer biomarkers. Areas covered: In this review, we discuss how these approaches have been utilized for KLK biomarker discovery and unbiased substrate determination in complex protein pools that mimic the in vivo extracellular microenvironment. Expert commentary: Although a limited number of studies have been performed, the quantity of information generated has greatly improved our understanding of the functional roles of KLKs in cancer progression. In addition, these data suggest additional means through which deregulated KLK expression may be targeted in cancer treatment, highlighting the potential therapeutic value of these state-of-the-art MS-based studies.

Mass spectrometry-based determination of Kallikrein-related peptidase 7 (KLK7) cleavage preferences and subsite dependency

The cleavage preferences of Kallikrein-related peptidase 7 (KLK7) have previously been delineated using synthetic peptide libraries of fixed length, or single protein chains and have suggested that KLK7 exerts a chymotryptic-like cleavage preference. Due to the short length of the peptides utilised, only a limited number of subsites have however been assessed. To determine the subsite preferences of KLK7 in a global setting, we used a mass spectrometry (MS)-based in-depth proteomics approach that utilises human proteome-derived peptide libraries of varying length, termed Proteomic Identification of protease Cleavage Sites (PICS). Consistent with previous findings, KLK7 was found to exert chymotryptic-like cleavage preferences. KLK7 subsite preferences were also characterised in the P2-P2′ region, demonstrating a preference for hydrophobic residues in the non-prime and hydrophilic residues in the prime subsites. Interestingly, single catalytic triad mutant KLK7 (mKLK7; S195A) also showed residual catalytic activity (k_cat/K_M = 7.93 × 10² s⁻¹M⁻¹). Catalytic inactivity of KLK7 was however achieved by additional mutation in this region (D102N). In addition to characterising the cleavage preferences of KLK7, our data thereby also suggests that the use of double catalytic triad mutants should be employed as more appropriate negative controls in future investigations of KLK7, especially when highly sensitive MS-based approaches are employed.

Kallikrein-related peptidase 4 contributes to the tumor metastasis of oral squamous cell carcinoma

Oral squamous cell carcinoma (OSCC) is a disfiguring malignancy and significantly impacts the quality of patient's life. Kallikrein-related peptidase 4 (KLK4), which is closely related to cancers, is highly expressed in OSCC. To explore the biological function of KLK4 in OSCC, a KLK4-specific shRNA was used to silence its endogenous expression, and then the migration and invasion of OSCC cells were explored. Results of our study showed that silencing KLK4 inhibited the migration and invasion of OSCC cells. The protein levels of epithelial mesenchymal transition-associated markers and proteases were also altered by KLK4 silencing. Further study showed that the phosphatidylinositol 3-kinase (PI3 K)/protein kinase B (AKT) signaling pathway was involved in the function of KLK4. Treatment with a PI3 K/AKT activator reversed the migration-inhibitory effect of KLK4 shRNA. Our study suggests that KLK4 may contribute to the metastasis of OSCC through the PI3 K/AKT signaling pathway.

Proteinases, Their Extracellular Targets, and Inflammatory Signaling

Given that over 2% of the human genome codes for proteolytic enzymes and their inhibitors, it is not surprising that proteinases serve many physiologic-pathophysiological roles. In this context, we provide an overview of proteolytic mechanisms regulating inflammation, with a focus on cell signaling stimulated by the generation of inflammatory peptides; activation of the proteinase-activated receptor (PAR) family of G protein-coupled receptors (GPCR), with a mechanism in common with adhesion-triggered GPCRs (ADGRs); and by proteolytic ion channel regulation. These mechanisms are considered in the much wider context that proteolytic mechanisms serve, including the processing of growth factors and their receptors, the regulation of matrix-integrin signaling, and the generation and release of membrane-tethered receptor ligands. These signaling mechanisms are relevant for inflammatory, neurodegenerative, and cardiovascular diseases as well as for cancer. We propose that the inflammation-triggering proteinases and their proteolytically generated substrates represent attractive therapeutic targets and we discuss appropriate targeting strategies.

Evolving Role of Serum Biomarkers in the Management of Ovarian Cancer

The availability of an ideal serum tumor marker would be of great clinical benefit for both the diagnosis and management of patients with epithelial ovarian cancer. Serum cancer antigen 125 assay significantly increases the diagnostic reliability of ultrasound in discriminating a malignant from a benign ovarian mass, especially in postmenopausal women, and it is the only well validated tumor marker for monitoring disease course. Several other tumor-associated antigens have been assessed, including glycoprotein antigens other than cancer antigen 125, soluble cytokeratin fragments, kallikreins, cytokines and cytokine receptors, vascular endothelial growth factor, D-dimer, and lisophosphatidic acid. This article assesses the potential diagnostic and prognostic role of these novel biomarkers, both alone and in combination with cancer antigen 125. The future for serum tumor marker research is represented by the emerging technology of proteomics, which may allow scientific advances comparable to those achieved with the introduction of monoclonal antibody technology.

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.

Proteomic and other analyses to determine the functional consequences of deregulated kallikrein-related peptidase (KLK) expression in prostate and ovarian cancer

Rapidly developing proteomic tools are improving detection of deregulated kallikrein-related peptidase (KLK) expression, at the protein level, in prostate and ovarian cancer, as well as facilitating the determination of functional consequences downstream. MS-driven proteomics uniquely allows for the detection, identification, and quantification of thousands of proteins in a complex protein pool, and this has served to identify certain KLKs as biomarkers for these diseases. In this review, we describe applications of this technology in KLK biomarker discovery and elucidate MS-based techniques that have been used for unbiased, global screening of KLK substrates within complex protein pools. Although MS-based KLK degradomic studies are limited to date, they helped to discover an array of novel KLK substrates. Substrates identified by MS-based degradomics are reported with improved confidence over those determined by incubating a purified or recombinant substrate and protease of interest, in vitro. We propose that these novel proteomic approaches represent the way forward for KLK research, in order to correlate proteolysis of biological substrates with tissue-related consequences, toward clinical targeting of KLK expression and function for cancer diagnosis, prognosis, and therapies.

Critical role for PAR1 in kallikrein 6-mediated oligodendrogliopathy

Kallikrein 6 (KLK6) is a secreted serine protease preferentially expressed by oligodendroglia in CNS white matter. Elevated levels of KLK6 occur in actively demyelinating multiple sclerosis (MS) lesions and in cases of spinal cord injury (SCI), stroke, and glioblastoma. Taken with recent evidence establishing KLK6 as a CNS-endogenous activator of protease-activated receptors (PARs), we hypothesized that KLK6 activates a subset of PARs to regulate oligodendrocyte physiology and potentially pathophysiology. Here, primary oligodendrocyte cultures derived from wild type or PAR1-deficient mice and the murine oligodendrocyte cell line, Oli-neu, were used to demonstrate that Klk6 (rodent form) mediates loss of oligodendrocyte processes and impedes morphological differentiation of oligodendrocyte progenitor cells (OPCs) in a PAR1-dependent fashion. Comparable gliopathy was also elicited by the canonical PAR1 agonist, thrombin, as well as PAR1-activating peptides (PAR1-APs). Klk6 also exacerbated ATP-mediated oligodendrogliopathy in vitro, pointing to a potential role in augmenting excitotoxicity. In addition, Klk6 suppressed the expression of proteolipid protein (PLP) RNA in cultured oligodendrocytes by a mechanism involving PAR1-mediated Erk1/2 signaling. Microinjection of PAR1 agonists, including Klk6 or PAR1-APs, into the dorsal column white matter of PAR1(+/+) but not PAR1(-/-) mice promoted vacuolating myelopathy and a loss of immunoreactivity for myelin basic protein (MBP) and CC-1(+) oligodendrocytes. These results demonstrate a functional role for Klk6-PAR1 signaling in oligodendroglial pathophysiology and suggest that antagonists of PAR1 or its protease agonists may represent new modalities to moderate demyelination and to promote myelin regeneration in cases of CNS white matter injury or disease.

From prostate-specific antigen (PSA) to precursor PSA (proPSA) isoforms: a review of the emerging role of proPSAs in the detection and management of early prostate cancer

Despite the popularity of PSA blood testing for prostate cancer, there are a number of important limitations of this popular serum marker including the limited ability to accurately distinguish patients with and without prostate cancer and those who harbour an aggressive form of the disease. This is especially true when the total PSA is <10 ng/mL. Thus, significant efforts have been placed to find new serum markers that can help overcome these limitations. In this review article, we discuss the emerging role of the various precursor forms of PSA (proPSAs), with a special emphasis on [-2]proPSA in the detecion and management of early prostate cancer. The clinical utility of Prostate Health Index (phi) is also discussed. Despite the overall success of prostate-specific antigen (PSA) blood test, its use as a serum marker for prostate cancer has been limited due to the lack of specificity, especially in men presenting with a total PSA (tPSA) level of <10 ng/mL. PSA testing has also resulted in an increase in the number of patients being diagnosed with low-grade, potentially clinically insignificant prostate cancer. There is therefore an urgent need for new markers that can accurately detect as well as differentiate patients with aggressive vs unaggressive prostate cancer. In this review, we discuss the emerging role of precursor forms of PSA (proPSAs) and the Prostate Health Index (phi) measurement in the detection and management of early stage prostate cancer. A literature search was conducted using PubMed® to identify key studies. Studies to date suggest that [-2]proPSA, a truncated form of proPSA is the most cancer-specific form of all, being preferentially expressed in cancerous prostatic epithelium and being significantly elevated in serum of men with prostate cancer. There is evidence to suggest that %[-2]proPSA measurement ([-2]proPSA/free PSA [fPSA] × 100) improves the specificity of both tPSA and fPSA in detecting prostate cancer. phi incorporating [-2]proPSA, fPSA and tPSA measurements has also yielded promising results and appears superior to tPSA and fPSA in predicting those patients with prostate cancer. Increased phi levels also seem to preferentially detect patients harbouring more aggressive disease. Further studies in the form of large, multicentre, prospective trials with detailed health economic analyses are required to evaluate the true clinical applicability of these novel markers.

Association between Prostinogen (KLK15) genetic variants and prostate cancer risk and aggressiveness in Australia and a meta-analysis of GWAS data

BACKGROUND

Kallikrein 15 (KLK15)/Prostinogen is a plausible candidate for prostate cancer susceptibility. Elevated KLK15 expression has been reported in prostate cancer and it has been described as an unfavorable prognostic marker for the disease.

OBJECTIVES

We performed a comprehensive analysis of association of variants in the KLK15 gene with prostate cancer risk and aggressiveness by genotyping tagSNPs, as well as putative functional SNPs identified by extensive bioinformatics analysis. METHODS AND DATA SOURCES: Twelve out of 22 SNPs, selected on the basis of linkage disequilibrium pattern, were analyzed in an Australian sample of 1,011 histologically verified prostate cancer cases and 1,405 ethnically matched controls. Replication was sought from two existing genome wide association studies (GWAS): the Cancer Genetic Markers of Susceptibility (CGEMS) project and a UK GWAS study.

RESULTS

Two KLK15 SNPs, rs2659053 and rs3745522, showed evidence of association (p<0.05) but were not present on the GWAS platforms. KLK15 SNP rs2659056 was found to be associated with prostate cancer aggressiveness and showed evidence of association in a replication cohort of 5,051 patients from the UK, Australia, and the CGEMS dataset of US samples. A highly significant association with Gleason score was observed when the data was combined from these three studies with an Odds Ratio (OR) of 0.85 (95% CI = 0.77-0.93; p = 2.7×10(-4)). The rs2659056 SNP is predicted to alter binding of the RORalpha transcription factor, which has a role in the control of cell growth and differentiation and has been suggested to control the metastatic behavior of prostate cancer cells.

CONCLUSIONS

Our findings suggest a role for KLK15 genetic variation in the etiology of prostate cancer among men of European ancestry, although further studies in very large sample sets are necessary to confirm effect sizes.

Effects of the demethylating agent, 5-azacytidine, on expression of the kallikrein-kinin genes in carcinoma cells of the lung and pleura

Tissue kallikrein (KLK1) and plasma kallikrein (KLKB1) may regulate the growth and proliferation of tumours of the lung and pleura, through the generation of kinin peptides that signal through the kinin B(1) (BDKRB1) and B(2) (BDKRB2) receptors. The development and progression of cancer results from genetic mutations, as well as epigenetic changes that include methylation of DNA at CpG islands. The aim of this study was to assess whether expression of the kallikrein-kinin genes in lung cancer and mesothelioma cells is regulated by DNA methylation. Quantitative reverse transcriptase-PCR and immunocytochemistry showed differences in the basal expression of the kallikrein-kinin genes and proteins in lung carcinoma and mesothelioma cells, compared with non-malignant lung epithelial and mesothelial cells, respectively. Following treatment with the demethylating agent, 5-azacytidine (5-AZA), KLKB1 mRNA expression was consistently increased in both lung carcinoma and mesothelioma cells, whereas KLK1, BDKRB1 and BDKRB2 mRNA expression was decreased or unchanged. Increased expression of KLKB1 after 5-AZA treatment suggests it may function as a tumour suppressor gene in cancers of the lung and pleura. Studies on DNA methylation of the kallikrein-kinin genes will enhance understanding of their role in carcinogenesis and provide insights into the importance of kallikreins as tumour biomarkers.

Functional role of kallikrein 6 in regulating immune cell survival

BACKGROUND

Kallikrein 6 (KLK6) is a newly identified member of the kallikrein family of secreted serine proteases that prior studies indicate is elevated at sites of central nervous system (CNS) inflammation and which shows regulated expression with T cell activation. Notably, KLK6 is also elevated in the serum of multiple sclerosis (MS) patients however its potential roles in immune function are unknown. Herein we specifically examine whether KLK6 alters immune cell survival and the possible mechanism by which this may occur.

METHODOLOGY/PRINCIPAL FINDINGS

Using murine whole splenocyte preparations and the human Jurkat T cell line we demonstrate that KLK6 robustly supports cell survival across a range of cell death paradigms. Recombinant KLK6 was shown to significantly reduce cell death under resting conditions and in response to camptothecin, dexamethasone, staurosporine and Fas-ligand. Moreover, KLK6-over expression in Jurkat T cells was shown to generate parallel pro-survival effects. In mixed splenocyte populations the vigorous immune cell survival promoting effects of KLK6 were shown to include both T and B lymphocytes, to occur with as little as 5 minutes of treatment, and to involve up regulation of the pro-survival protein B-cell lymphoma-extra large (Bcl-XL), and inhibition of the pro-apoptotic protein Bcl-2-interacting mediator of cell death (Bim). The ability of KLK6 to promote survival of splenic T cells was also shown to be absent in cell preparations derived from PAR1 deficient mice.

CONCLUSION/SIGNIFICANCE

KLK6 promotes lymphocyte survival by a mechanism that depends in part on activation of PAR1. These findings point to a novel molecular mechanism regulating lymphocyte survival that is likely to have relevance to a range of immunological responses that depend on apoptosis for immune clearance and maintenance of homeostasis.

Kallikrein-related peptidase 13 (KLK13) gene expressional status contributes significantly in the prognosis of primary gastric carcinomas

OBJECTIVES

Gastric cancer is a fatal human malignancy with poor prognosis. Modifications in gene expression, including those of the kallikrein-related peptidase family, have been portrayed in gastric carcinogenesis. Given KLK13 involvement in human malignancies, we aimed to uncover its prognostic strength in stomach cancer.

DESIGN AND METHODS

Quantitative analysis of KLK13 profiles was accomplished in human gastric cancer cells and in a statistically significant sample size of stomach tissue specimens with the development of the highly sensitive real-time PCR methodology.

RESULTS

Decreased KLK13 expression was demonstrated in cancerous compared with their matching non-malignant pairs (p=0.002) and in poorly differentiated gastric tumors (p=0.029). KLK13-positive patients were shown to live considerably longer (p=0.014) and with low risk of disease recurrences (p=0.043).

CONCLUSIONS

This is the first study disclosing the possible clinical utility of KLK13 as a new tumor biomarker capable of predicting a favorable outcome for gastric cancer patients.

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.

Keratinocytes synthesize enteropeptidase and multiple forms of trypsinogen during terminal differentiation

Members of the trypsin-like and chymotrypsin-like kallikrein family are important in the desquamation process. In this study, we isolated cDNA clones encoding trypsinogen 4 (brain trypsinogen) and a previously unreported isoform of trypsinogen from a human keratinocyte cDNA library. The nucleotide sequence of the new isoform only differs from those of trypsinogen 3 (mesotrypsinogen) and trypsinogen 4 in an exon encoding the N-terminal region, indicating that this isoform is an alternative splicing variant of the mesotrypsinogen gene PRSS3. Both isoforms contained the sequence DDDDK-I, a putative cleavage site for activation by enteropeptidase. Thus, after activation, mesotrypsin would be produced. Immunohistochemical and in situ hybridization studies revealed that trypsinogens were expressed and localized in the upper epidermis, especially in the granular layer. In cultured keratinocytes, enteropeptidase mRNA was expressed at the confluent stage, and its expression was strongly upregulated after air exposure. Interestingly, it was synthesized and localized only at the granular layer, suggesting that the generation of active mesotrypsin is restricted to this layer. The enteropeptidase-cleavage product was also found at the same layer. When a skin equivalent model was cultured in the medium without air exposure, the cornified layer was not formed, and many cells expressed trypsinogens and enteropeptidase. Those cells were found to be TUNEL positive. Because mesotrypsin is resistant to naturally occurring trypsin inhibitors, confined expression of the isoforms of mesotrypsinogens and enteropeptidase may indicate that mesotrypsin is involved in keratinocyte terminal differentiation.

T-SP1: a novel serine protease-like protein predominantly expressed in testis

Here, we describe a novel member in the group of membrane-anchored chymotrypsin (S1)-like serine proteases, namely testis serine protease 1 (T-SP1), as it is principally expressed in testis tissue. The human T-SP1 gene encompasses 28.7 kb on the short arm of chromosome 8 and consists of seven exons. Rapid amplification of cDNA ends (RACE) experiments revealed that due to alternative splicing three different variants (T-SP1/1, -2, -3) are detectable in testis tissue displaying pronounced heterogeneity at their 3'-end. T-SP1/1 consists of an 18 amino acid signal peptide and of a 49 amino acid propeptide. The following domain with the catalytic triad of His(108), Asp(156), and Ser(250) shares sequence identities of 42% and 40% with the blood coagulation factor XI and plasma kallikrein, respectively. Only T-SP1/1 contains a hydrophobic part at the C-terminus, which provides the basis for cell membrane anchoring. Using a newly generated polyclonal anti-T-SP1 antibody, expression of the T-SP1 protein was found in the Leydig and Sertoli cells of the testis and in the epithelial cells of the ductuli efferentes. Notably, T-SP1 protein was also detectable in prostate cancer and in some ovarian cancer tissues, indicating tumor-related synthesis of T-SP1 beyond testis tissue.

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.

Expression of tissue and plasma kallikreins and kinin B1 and B2 receptors in lung cancer

Tissue kallikrein (hK1) and plasma kallikrein (PK, hKB1) are serine proteases that produce biologically active kinin peptides from endogenous kininogen substrates. There is evidence linking the kallikreins and the mitogenic kinin peptides to carcinogenesis. The aim of this study was to investigate the expression of tissue prokallikrein (pro-hK1), plasma prekallikrein (PPK, pre-hKB1) and kinin B1 and B2 receptor proteins in different subtypes of lung cancer. Immunohistochemistry, using specific antibodies, was performed on archived normal lung sections and sections from adenocarcinomas, squamous cell carcinomas, large cell carcinomas, small cell carcinomas and carcinoid tumours of the lung. Immunoperoxidase labelling was visualised by brightfield microscopy and immunofluorescence labelling by confocal microscopy. Extensive cytoplasmic expression of pro-hK1 and PPK was observed, which was similar in small cell and non-small cell tumours. However, nuclear labelling for the kallikreins was absent or limited. The kinin B1 and B2 receptors were highly expressed in the cytoplasm of all tumour types and in the nuclei of non-small cell tumours. Further studies are required to assess the functional significance of the expression of hK1, PK and kinin receptors in lung tumours, and whether any of these proteins may be potential biomarkers for specific subtypes of lung carcinoma.

Protease-activated receptor dependent and independent signaling by kallikreins 1 and 6 in CNS neuron and astroglial cell lines

While protease-activated receptors (PARs) are known to mediate signaling events in CNS, contributing both to normal function and pathogenesis, the endogenous activators of CNS PARs are poorly characterized. In this study, we test the hypothesis that kallikreins (KLKs) represent an important pool of endogenous activators of CNS PARs. Specifically, KLK1 and KLK6 were examined for their ability to evoke intracellular Ca(2+) flux in a PAR-dependent fashion in NSC34 neurons and Neu7 astrocytes. Both KLKs were also examined for their ability to activate mitogen-activated protein kinases (extracellular signal-regulated kinases, C-Jun N-terminal kinases, and p38) and protein kinase B (AKT) intracellular signaling cascades. Cumulatively, these studies show that KLK6, but not KLK1, signals through PARs. KLK6 evoked intracellular Ca(2+) flux was mediated by PAR1 in neurons and both PAR1 and PAR2 in astrocytes. Importantly, both KLK1 and KLK6 altered the activation state of mitogen-activated protein kinases and AKT, suggestive of important roles for each in CNS neuron and glial differentiation, and survival. The cellular specificity of CNS-KLK activity was underscored by observations that both proteases promoted AKT activation in astrocytes, but inhibited such signaling in neurons. PAR1 and bradykinin receptor inhibitors were used to demonstrate that KLK1-mediated activation of extracellular signal-regulated kinases in neurons occurred in a non-PAR, bradykinin 2 (B2) receptor-dependent fashion, while similar signaling by KLK6 was mediated by the combined activation of PAR1 and B2. Cumulatively results indicate KLK6, but not KLK1 is an activator of CNS PARs, and that both KLKs are poised to signal in a B2 receptor-dependent fashion to regulate multiple signal transduction pathways relevant to CNS physiologic function and dysfunction.

Activation profiles of human kallikrein-related peptidases by proteases of the thrombostasis axis

The human kallikrein-related peptidases (KLKs) comprise 15 members (KLK1-15) and are the single largest family of serine proteases. The KLKs are utilized, or proposed, as clinically important biomarkers and therapeutic targets of interest in cancer and neurodegenerative disease. All KLKs appear to be secreted as inactive pro-forms (pro-KLKs) that are activated extracellularly by specific proteolytic release of their N-terminal pro-peptide. This processing is a key step in the regulation of KLK function. Much recent work has been devoted to elucidating the potential for activation cascades between members of the KLK family, with physiologically relevant KLK regulatory cascades now described in skin desquamation and semen liquefaction. Despite this expanding knowledge of KLK regulation, details regarding the potential for functional intersection of KLKs with other regulatory proteases are essentially unknown. To elucidate such interaction potential, we have characterized the ability of proteases associated with thrombostasis to hydrolyze the pro-peptide sequences of the KLK family using a previously described pro-KLK fusion protein system. A subset of positive hydrolysis results were subsequently quantified with proteolytic assays using intact recombinant pro-KLK proteins. Pro-KLK6 and 14 can be activated by both plasmin and uPA, with plasmin being the best activator of pro-KLK6 identified to date. Pro-KLK11 and 12 can be activated by a broad-spectrum of thrombostasis proteases, with thrombin exhibiting a high degree of selectivity for pro-KLK12. The results show that proteases of the thrombostasis family can efficiently activate specific pro-KLKs, demonstrating the potential for important regulatory interactions between these two major protease families.

Specific increase of human kallikrein 4 mRNA and protein levels in breast cancer stromal cells

The kallikrein family (KLK) has been implicated in cancer and may be useful as tumor markers. Here, we compared the 15 KLK genes' expression in malignant and normal breast tissues using real-time quantitative PCR. Most KLKs were expressed at lower levels in breast cancer compared to normal breast tissue. The only exception was the eightfold increase level of KLK4 in breast cancer tissues (P=0.008). KLK4 level was strongly associated with tumor grade (P=0.0015). Interestingly, based on laser cell microdissection analysis and immunochemistry, the up-regulation of kallikrein 4 occurred in the surrounding stromal cells. Our findings suggest that KLK4 may be associated with the development and progression of breast cancer and suggest its potential use in breast cancer monitoring.

A novel transcript from the KLKP1 gene is androgen regulated, down-regulated during prostate cancer progression and encodes the first non-serine protease identified from the human kallikrein gene locus

BACKGROUND

The kallikrein-related (KLK) serine protease, prostate specific antigen is the current marker for prostate cancer (PCa). Other members of the KLK family are also emerging as potential adjunct biomarkers for this disease. Our aim was to identify and characterize novel KLK-related genes with potential as PCa bio-markers.

METHODS

Low stringency DNA screening was coupled with amplification techniques to identify novel sequences. Transcripts were examined by Northern blot, RT-PCR, and in situ hybridization analysis and in silico bioinformatics approaches. Protein characterization was performed by Western blot and confocal microscopy analysis. Gene regulation studies were performed by quantitative PCR and promoter reporter assays.

RESULTS

We identified a novel kallikrein-related mRNA designated KRIP1 (kallikrein-related, expressed in prostate 1) which, together with the recently reported PsiKLK1 and KLK31P transcripts, is transcribed from KLKP1; a gene evolved from, and located within, the KLK locus. Significantly, in contrast to these other non-coding KLKP1 transcripts, the KRIP1 mRNA generates an approximately 18 kDa intracellular protein-the first non-serine protease identified from the KLK locus. KRIP1 mRNA is abundant only in normal prostate and is restricted to cells of epithelial origin in normal and diseased glands. Ligand binding of the androgen receptor increases transcription from the KLKP1 gene. Consistently, KRIP1 mRNA levels are lower in PCa samples compared to benign prostatic hyperplasia.

CONCLUSIONS

Transcription from KLKP1 is reduced as cells de-differentiate on the pathway to malignancy. KLKP1/KRIP1 has potential as a marker of both PCa progression and recent evolutionary events within the KLK locus.

Novel expression of kallikreins, kallikrein-related peptidases and kinin receptors in human pleural mesothelioma

Malignant mesothelioma is an aggressive cancer of the pleura that is causally related to exposure to asbestos fibres. The kallikrein serine proteases [tissue (hK1) and plasma (hKB1) kallikreins, and kallikrein-related peptidases (KRP/hK2-15)] and the mitogenic kinin peptides may have a role in tumourigenesis. However, it is not known whether hK1, hKB1, KRP/hK proteins or kinin receptors are expressed in pleural mesotheliomas. The expression of hK1, hKB1, KRP/hK2, 5, 6, 7, 8 and 9, and kinin B(1) and B(2) receptors was assessed in archived selected normal tissue and mesothelioma tumour sections by immunoperoxidase and immunofluorescence labelling. hK1, hKB1 and kinin B(1) and B(2) receptors were expressed in malignant cells of the epithelioid and sarcomatoid components of biphasic mesothelioma tumour cells. The percentage of cells with cytoplasmic and nuclear labelling and the intensity of labelling were similar for hK1, hKB1 and the kinin receptors. KRP/hK2, 6, 8 and 9 were also expressed in the cytoplasm and nuclei of mesothelioma cells, whereas KRP/hK5 and hK7 showed predominantly cytoplasmic localisation. This is a first report, but further studies are required to determine whether these proteins have a functional role in the pathogenesis of mesothelioma and/or may be potential biomarkers for pleural mesothelioma.