Quantitative analysis of hippostasin/KLK11 gene expression in cancerous and noncancerous prostatic tissues

Prognostic impact of kallikrein-related peptidase transcript levels in prostate cancer

We aimed to study mRNA levels and prognostic impact of all 15 human kallikrein-related peptidases (KLKs) and their targets, proteinase-activated receptors (PARs), in surgically treated prostate cancer (PCa). Seventy-nine patients with localized grade group 2-4 PCas represented aggressive cases, based on metastatic progression during median follow-up of 11 years. Eighty-six patients with similar baseline characteristics, but no metastasis during follow-up, were assigned as controls. Transcript counts were detected with nCounter technology. KLK12 protein expression was investigated with immunohistochemistry. The effects of KLK12 and KLK15 were studied in LNCaP cells using RNA interference. KLK3, -2, -4, -11, -15, -10 and -12 mRNA, in decreasing order, were expressed over limit of detection (LOD). The expression of KLK2, -3, -4 and -15 was decreased and KLK12 increased in aggressive cancers, compared to controls (P < .05). Low KLK2, -3 and -15 expression was associated with short metastasis-free survival (P < .05) in Kaplan-Meier analysis. PAR1 and -2 were expressed over LOD, and PAR1 expression was higher, and PAR2 lower, in aggressive cases than controls. Together, KLKs and PARs improved classification of metastatic and lethal disease over grade, pathological stage and prostate-specific antigen combined, in random forest analyses. Strong KLK12 immunohistochemical staining was associated with short metastasis-free and PCa-specific survival in Kaplan-Meier analysis (P < .05). Knock-down of KLK15 reduced colony formation of LNCaP cells grown on Matrigel basement membrane preparation. These results support the involvement of several KLKs in PCa progression, highlighting, that they may serve as prognostic PCa biomarkers.

KLK11 acts as a tumor-inhibitor in laryngeal squamous cell carcinoma through the inactivation of Akt/Wnt/β-catenin signaling

Kallikrein-associated peptidase 11 (KLK11) has emerged as a key tumor-associated protein that is implicated in a wide spectrum of tumor types. However, the detailed involvement of KLK11 in laryngeal squamous cell carcinoma (LSCC) has not been well studied. The aims of our work were to evaluate whether KLK11 plays a role in LSCC. We found that both the mRNA and protein expression of KLK11 were significantly lower in LSCC tissues than in normal tissues. Low expression of KLK11 was also observed in LSCC cell lines, and the up-regulation of KLK11 caused a significant inhibitory effect on the proliferation, colony formation and invasion of LSCC cells. On the contrary, the knockdown of KLK11 markedly accelerated the proliferative and invasive abilities of LSCC cells. Molecular mechanism research revealed that KLK11 overexpression decreased the phosphorylation of glycogen synthase kinase-3β (GSK-3β) and down-regulated the expression of active β-catenin, leading to the inactivation of Wnt/β-catenin signaling in LSCC cells. Furthermore, GSK-3β inhibition markedly abrogated the KLK11-mediated suppressive effect on Wnt/β-catenin signaling. Notably, the reactivation of Wnt/β-catenin partially reversed KLK11-mediated tumor-inhibition effect in LSCC. In addition, the xenograft tumor assay demonstrated that the up-regulation of KLK11 retarded tumor formation and the growth of LSCC cells in vivo. Taken together, the findings of our work demonstrate that KLK11 exerts a tumor-inhibition role in LSCC by down-regulating Wnt/β-catenin signaling. Our work highlights a pivotal role of KLK11 in LSCC progression and suggests it as an attractive anticancer target for LSCC treatment.

Biochemical characterization of human tissue kallikrein 15 and examination of its potential role in cancer

OBJECTIVE

Human tissue kallikrein 15 (KLK15) is the last cloned member of the KLK-related gene family. Despite being implicated in multiple cancers, its pathophysiological role remains unknown. We aimed to biochemically characterize KLK15 and preliminarily study its role in cancer.

DESIGN & METHODS

Recombinant KLK15 protein was produced, purified to homogeneity and quantified by mass spectrometry (parallel reaction monitoring analysis). We profiled the enzymatic activity of KLK15 using fluorogenic peptide substrates, and performed kinetic analysis to discover the cleavage sites. As KLK15 has mainly been associated with prostate cancer, we used a degradomic approach and subsequent KEGG pathway analysis to identify a number of putative protein substrates in the KLK15-treated prostate cancer cell line PC3.

RESULTS

We discovered trypsin-like activity in KLK15, finding that it cleaves preferentially after arginine (R). The enzymatic activity of KLK15 was regulated by different factors such as pH, cations and serine protease inhibitors. Notably, we revealed that KLK15 most likely interacts with the extracellular matrix (ECM) receptor group.

CONCLUSION

To our knowledge, this is the first study that experimentally verifies the trypsin-like activity of KLK15. We show here for the first time that KLK15 may be able to cleave many ECM components, similar to several members of the KLK family. Thus the protease could potentially be linked to tumorigenesis by promoting metastasis via this mechanism.

Clinical utility of kallikrein-related peptidases (KLK) in urogenital malignancies

Kallikrein-related peptidases (KLK), which represent a major tissue-associated proteolytic system, stand for a rich source of biomarkers that may allow molecular classification, early diagnosis and prognosis of human malignancies as well as prediction of response or failure to cancer-directed drugs. International research points to an important role of certain KLKs in female and male urogenital tract malignancies, in addition to cancers of the lung, brain, skin, head and neck, and the gastrointestinal tract. Regarding the female/male urogenital tract, remarkably, all of the KLKs are expressed in the normal prostate, testis, and kidney whereas the uterus, the ovary, and the urinary bladder are expressing a limited number of KLKs only. Most of the information regarding KLK expression in tumour-affected organs is available for ovarian cancer; all of the 12 KLKs tested so far were found to be elevated in the malignant state, depicting them as valuable biomarkers to distinguish between the normal and the cancerous phenotype. In contrast, for kidney cancer, a series of KLKs was found to be downregulated, while other KLKs were not expressed. Evidently, depending on the type of cancer or cancer stage, individual KLKs may show characteristics of a Janus-faced behaviour, by either expanding or inhibiting cancer progression and metastasis.

KLK11 mRNA expression predicts poor disease-free and overall survival in colorectal adenocarcinoma patients

BACKGROUND

Dysregulated expression of several KLK family members has been observed in colorectal adenocarcinoma. In the present study, the prognostic value of KLK11 mRNA expression as a molecular tissue biomarker in colorectal adenocarcinoma was examined.

MATERIALS & METHODS

Using quantitative real-time PCR, KLK11 mRNA expression was studied in 120 cancerous and 41 paired noncancerous colorectal specimens obtained from 120 patients with primary colorectal adenocarcinoma.

RESULTS

A significant upregulation of KLK11 transcripts in colorectal tumors was observed. KLK11 mRNA expression was associated with the depth of tumor invasion and the histological grade. Furthermore, KLK11 mRNA expression predicted poor disease-free and overall survival, independently of patient gender, age, tumor size, location, histological subtype, grade, venous invasion, lymphatic invasion, TNM stage, radiotherapy and chemotherapy treatment.

CONCLUSION

KLK11 mRNA expression could be considered as a new molecular prognostic biomarker in colorectal adenocarcinoma, with additional prognostic value in patients with highly invasive tumors and/or positive lymph nodes.

Prognostic significance of human tissue kallikrein-related peptidases 11 and 15 in gastric cancer

Human tissue kallikrein-related peptidases (KLK) are a group of 15 serine proteases which have been investigated as potential cancer biomarkers. This study determined the prognostic significance of KLK 11 and 15 expression levels in gastric carcinoma specimens. Expression of KLK11 and KLK15 was assessed by immunohistochemistry staining on a tissue microarray constructed from 113 gastrectomy specimens from patients with gastric carcinoma. To minimize inter-observer variability, expression levels were quantified using an automated algorithm. Epithelial and stromal staining were assessed separately. Both KLK11 and KLK15 were expressed in gastric carcinoma. There was no significant correlation between either KLK11 or KLK15 expression and the presence of lymph node metastases or Lauren classification (intestinal vs. diffuse). Higher levels of KLK11 expression in gastric carcinoma were associated with significantly worse overall survival (p = 0.008), and a multivariate analysis showed that it had prognostic value independent of tumor stage and differentiation (p = 0.004). Variations in KLK15 expression were not significantly associated with prognosis. KLK11 shows promise as a potential independent prognostic marker for gastric carcinoma.

Kallikrein-related peptidases targeted therapies in prostate cancer: perspectives and challenges

INTRODUCTION

Despite the emergence of several new effective treatments for metastatic castration-resistant prostate cancer patients, disease progression inevitably occurs, leading scientific community to carefully look for novel therapeutic targets of prostate cancer. Kallikrein (KLK)-related peptidases have been demonstrated to facilitate prostate tumorigenesis and disease progression through the development of an oncogenic microenvironment for prostate cells.

AREAS COVERED

This review first summarizes the large amount of preclinical data showing the involvement of KLKs in prostate cancer pathobiology. In the second part, the authors assess the current status and future directions for KLK-targeted therapy and briefly describe the advances and challenges implicated in the design of effective manufactured drugs. The authors then focus on the preclinical data and on Phase I/II studies of the most promising KLK-targeted agents in prostate cancer. The drugs discussed here are divided on the basis of their mechanism of action: KLK-engineered inhibitors; KLK-activated pro-drugs; KLK-targeted microRNAs and small interfering RNAs(-/)small hairpin RNAs; KLK vaccines and antibodies.

EXPERT OPINION

Targeting KLK expression and/or activity could be a promising direction in prostate cancer treatment. Future human clinical trials will help us to evaluate the real benefits, toxicities and the consequent optimal use of KLK-targeted drugs, as mono-therapy or in combination regimens.

Emerging PSA-based tests to improve screening

This article updates advances in prostate cancer screening based on prostate-specific antigen, its derivatives, and human kallikrein markers. Many men are diagnosed with indolent disease not requiring treatment. Although there is evidence of a survival benefit from screening, the numbers needed to screen and treat remain high. There is risk of exposing men to the side effects of treatment for nonthreatening disease. A screening test is needed with sufficiently good performance characteristics to detect disease at an early stage so treatment may be offered with curative intent, while reducing the number of negative or unnecessary biopsies.

Identification of HOXB8 and KLK11 expression levels as potential biomarkers to predict the effects of FOLFOX4 chemotherapy

AIM

To measure global gene expression in primary advanced colorectal cancer patients who have undergone fluorouracil, leucovorin and oxaliplatin (FOLFOX4) chemotherapy and screen valuable biomarkers to predict the effects of chemotherapy.

MATERIALS & METHODS

Samples from primary advanced colorectal cancer patients were collected. The effects of chemotherapy were evaluated, and patients were divided into an experimental group and a control group. Cancerous tissue gene expression profiles were detected by chip technology. Valuable biomarkers were screened by bioinformatic analysis. Immunohistochemical analysis was performed to characterize the pattern of HOXB8 and KLK11 expression. HOXB8 and KLK11 signal probe values were analyzed using receiver operating characteristic analysis.

RESULTS

There were differentially expressed genes in the two groups. HOXB8 and KLK11 proteins were observed in the nucleus and on the outside of the cancer cells, respectively. Their prediction accuracies were 79.9 and 76.7%, respectively.

CONCLUSION

HOXB8 and KLK11 may be classified as valuable biomarkers, as they can predict the effects of FOLFOX4 chemotherapy in primary advanced colorectal cancer patients.

Differential alternative splicing of human transglutaminase 4 in benign prostate hyperplasia and prostate cancer

Transglutaminase 4 is a member of enzyme family that catalyzes calcium-dependent posttranslational modification of proteins. Although transglutaminase 4 has been shown to have prostate-restricted expression pattern, little is known about the biological function of transglutaminase 4 in human. To gain insight into its role in prostate, we analyzed the expression status of human transglutaminase 4 in benign prostate hyperplasia (BPH) and prostate cancer (PCa). Unexpectedly, RT-PCR and nucleotide sequence analysis showed four alternative splicing variants of transglutaminase 4: transglutaminase 4-L, -M (-M1 and -M2) and -S. The difference between transglutaminase 4-M1 and -M2 is attributed to splicing sites, but not nucleotide size. The deduced amino acid sequences showed that transglutaminase 4-L, -M1 and -M2 have correct open reading frames, whereas transglutaminase 4-S has a truncated reading frame. RT-PCR analysis of clinical samples revealed that transglutaminase 4-M and -S were detected in all tested prostate tissue (80 BPH and 48 PCa). Interestingly, transglutaminase 4-L was found in 56% of BPH (45 out of 80) and only in 15% of PCa (7 out of 48). However, transglutaminase 4-L expression did not correlate with serum prostate-specific antigen (PSA) level, prostate volumes or PSA densities. These results will provide a clue to future investigation aiming at delineating physiological and pathological roles of human transglutaminase 4.

Prognostic value and biological role of the kallikrein-related peptidases in human malignancies

Cancer is a substantial health problem for the populations of the Western world. The discovery of new molecular biomarkers for diagnosis, prognosis and monitoring patients' response to therapy can aid in combating this complicated disease. The human kallikrein-related peptidases (human tissue kallikreins [KLKs]) are encoded by a continuous multigene family, located on chromosomal region 19q13.3-4. KLK3 (prostate-specific antigen) is the most efficient cancer biomarker ever employed. KLK genes are expressed abnormally in various malignancies, where they affect cancer-cell growth and metastasis. Their deregulated expression pattern, often associated with various clinicopathological characteristics of cancer patients, can be exploited, solely or within multiparametric panels, as a prognostic biomarker. Recent data illustrate that discernible molecular modulations of KLKs, occurring as a result of cancer cells' treatment with antitumor agents, may serve as new potential biomarkers, possibly predicting patients' treatment response. It is believed that KLKs might be employed in future clinical practice as novel and effective tumor markers.

Expression analysis and study of the KLK15 mRNA splice variants in prostate cancer and benign prostatic hyperplasia

Prostate cancer is the most commonly diagnosed malignancy in male populations in the Western world. The KLK15 gene, the newest member of the kallikrein family, is expressed in the prostate gland. The purpose of this study is the expression analysis and the clinical evaluation of the KLK15 mRNA spliced variants in prostate cancer (CaP) and benign prostatic hyperplasia (BPH) patients. Total RNA was isolated from 104 CaP and BPH tissue specimens. After testing the quality of the RNA, cDNA was produced by reverse transcription, and PCR was performed for the amplification of the KLK15 mRNA transcripts. GAPDH and HPRT genes were used as endogenous controls Our data revealed that mRNA spliced variants of KLK15 were differentially expressed in prostate tissue specimens. Analysis of data showed a statistically significant (P < 0.001) increase in the frequency of overexpression of KLK15 transcripts encoding for both the active isoform and for the isoform 3 in CaP compared to BPH samples. Furthermore, KLK15 transcripts were found to be highly expressed in more aggressive tumors (P = 0.017). These results suggest that KLK15 expression analysis could be employed as a valuable tool for the discrimination between BPH and CaP tissue specimens and as an unfavorable prognostic marker for prostate cancer.

Androgen regulated genes in human prostate xenografts in mice: relation to BPH and prostate cancer

Benign prostatic hyperplasia (BPH) and prostate carcinoma (CaP) are linked to aging and the presence of androgens, suggesting that androgen regulated genes play a major role in these common diseases. Androgen regulation of prostate growth and development depends on the presence of intact epithelial-stromal interactions. Further, the prostatic stroma is implicated in BPH. This suggests that epithelial cell lines are inadequate to identify androgen regulated genes that could contribute to BPH and CaP and which could serve as potential clinical biomarkers. In this study, we used a human prostate xenograft model to define a profile of genes regulated in vivo by androgens, with an emphasis on identifying candidate biomarkers. Benign transition zone (TZ) human prostate tissue from radical prostatectomies was grafted to the sub-renal capsule site of intact or castrated male immunodeficient mice, followed by the removal or addition of androgens, respectively. Microarray analysis of RNA from these tissues was used to identify genes that were; 1) highly expressed in prostate, 2) had significant expression changes in response to androgens, and, 3) encode extracellular proteins. A total of 95 genes meeting these criteria were selected for analysis and validation of expression in patient prostate tissues using quantitative real-time PCR. Expression levels of these genes were measured in pooled RNAs from human prostate tissues with varying severity of BPH pathologic changes and CaP of varying Gleason score. A number of androgen regulated genes were identified. Additionally, a subset of these genes were over-expressed in RNA from clinical BPH tissues, and the levels of many were found to correlate with disease status. Our results demonstrate the feasibility, and some of the problems, of using a mouse xenograft model to characterize the androgen regulated expression profiles of intact human prostate tissues.

Quantitative Analysis of Human Kallikrein 5 (KLK5) Expression in Prostate Needle Biopsies: An Independent Cancer Biomarker

Background: Kallikrein 5 (KLK5), a recently cloned member of the kallikrein family, codes for the secreted protein KLK5. Active KLK5 protein has a trypsin activity, and the expression of KLK5 gene seems to be regulated by steroid hormones. We performed an expression analysis and clinical evaluation of the KLK5 gene, at the mRNA level, in prostate needle biopsies.

Methods: We examined KLK5 mRNA concentrations in 103 prostate tissue specimens. After testing of RNA quality, cDNA was prepared by reverse transcription. A highly sensitive quantitative real-time PCR (qRT-PCR) method for KLK5 mRNA quantification was developed using the SYBR Green chemistry. GAPDH was used as a housekeeping gene.

Results: Specimens from patients with benign prostatic hyperplasia (BPH) showed higher levels of KLK5 mRNA expression than those from patients with prostate cancer (PCa) (P = 0.024). ROC analysis demonstrated that KLK5 expression had significant discriminatory value between BPH and PCa (AUC 0.64; P = 0.016). KLK5 mRNA expression showed a statistically significant negative correlation with the total PSA serum concentration in the PCa patients (P = 0.003). Early-stage tumors showed higher KLK5 expression than late-stage ones (P = 0.014), whereas KLK5 expression was negatively correlated to Gleason score (P = 0.005).

Conclusions: KLK5 mRNA, analyzed by quantitative PCR in prostate needle biopsies, could be an independent biomarker for the differential diagnosis and prognosis in prostate cancer.

Association of TMPRSS2 and KLK11 gene expression levels with clinical progression of human prostate cancer

AIM

The aim of this study was to analyze the clinicopathological characteristics of TMPRSS2 and KLK11 gene expression levels in human prostate cancer (PCa), and to evaluate their clinical significance in the progression of PCa.

METHODS

The expression of prostate-type and brain-type isoforms of KLK11 gene, and TMPRSS2 gene was analyzed by quantitative reverse transcriptase-polymerase chain reaction (QRT-PCR) in 63 PCa tissues. The correlation of TMPRSS2 and KLK11 gene expression with the clinicopathological characteristics and with the prognosis of PCa was subsequently assessed.

RESULTS

The mean values of TMPRSS2 (3.91 +/- 0.78 in PCa vs. 0.26 +/- 0.04 in normal prostate tissues) and both isoforms of KLK11 (prostate-type: 3.63 +/- 0.42 in PCa vs. 0.49 +/- 0.07 in normal prostate tissues; brain-type: 3.11 +/- 0.30 in PCa vs. 0.46 +/- 0.05 in normal prostate tissues) were significantly higher in cancer tissues compared with their normal counterparts. We found a significant positive correlation between TMPRSS2 expression and tumor stage (P = 0.02), Gleason score (P = 0.008), and tumor grade (P = 0.016). Regarding prostate-type KLK11, we identified a significant association between lower expression and higher tumor stage (P = 0.009), Gleason score (P = 0.01), and tumor grade (P = 0.006). No such association was seen with the brain-type isoform. The survival rate of the patients with TMPRSS2-high/KLK11-low expression was lowest (P = 0.003).

CONCLUSION

The results suggest that the up-regulation of TMPRSS2 gene and the down-regulation of KLK11 gene in advanced and more aggressive tumors may open the feasibility of being used as biomarkers distinguishing the tumor aggressiveness as well as novel prognostic indicators for PCa.

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.

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.

Improved prostate cancer detection with a human kallikrein 11 and percentage free PSA-based artificial neural network

Human kallikrein 11 (hK11) was evaluated in a percentage free PSA-based artificial neural network (ANN) to reduce unnecessary prostate biopsies. Serum samples from 357 patients with (n=132) and without (n=225) prostate cancer (PCa) were analyzed and ANN models were constructed and compared to all parameters. The discriminatory power of hK11 was lower than that of PSA, but receiver operator characteristic (ROC) analyses demonstrated significantly larger areas under the curves for the ANN compared to all other parameters. ANNs with hK11 may lead to a further reduction in unnecessary prostate biopsies, especially when analyzing patients with less than 15% free PSA.

mRNA expression analysis of human kallikrein 11 (KLK11) may be useful in the discrimination of benign prostatic hyperplasia from prostate cancer after needle prostate biopsy

Kallikrein 11 (KLK11,TLSP, hippostatin) is a member of the human kallikrein gene family, which includes PSA,KLK2and 12 other members, all localized on chromosome 19q13.4. The aim of this study was to investigate whetherKLK11expression could be used to discriminate prostate cancer (CaP) from benign prostatic hyperplasia (BPH) in needle prostate biopsies. We analyzed the expression of the prostate-type variant of theKLK11gene in 64 CaP and BPH tissues obtained by transrectal ultrasound-guided needle biopsy. Reverse transcription (RT), PCR and image analysis methodologies were developed and used. Of the 42 BPH tissues examined, only 10 (23.8%) were positive for prostate-typeKLK11expression, while of the 22 CaP patients, 12 (54.5%) wereKLK11-positive (p=0.025). Logistic regression and receiver operating characteristic curve analyses demonstrated thatKLK11expression has a significant discriminatory value (crude odds ratio=3.84,p=0.016; area under the curve, 0.65, 95% CI 0.51–0.80) between CaP and BPH in needle prostate biopsies.

Purification and Characterization of Human Kallikrein 11, a Candidate Prostate and Ovarian Cancer Biomarker, from Seminal Plasma

PURPOSE

Preliminary data suggest that hK11 is a novel serum biomarker for prostate and ovarian cancer. To examine the enzymatic characteristics of hK11, we purified and functionally characterized native hK11 from seminal plasma.

EXPERIMENTAL DESIGN

hK11 was purified from seminal plasma by immunoaffinity chromatography and characterized by kinetic analysis, electrophoresis, Western blots, and mass spectrometry.

RESULTS

hK11 is present in seminal plasma at concentrations ranging from 2 to 37 microg/mL. Using immunoaffinity chromatography and reverse-phase high-performance liquid chromatography, we purified hK11 to homogeneity. In seminal plasma, hK11 is present as a free enzyme of approximately 40 kDa. About 40% of hK11 is enzymatically active, whereas the rest is inactivated by internal cleavage after Arg156 (Genbank accession no. AF164623), which generates two peptides of approximately 20 kDa, connected by internal disulfide bonds. Purified hK11 possesses trypsin-like activity and cleaves synthetic peptides after arginine but not lysine residues. It does not cleave chymotrypsin substrates. Antithrombin, alpha1-antichymotrypsin, alpha2-antiplasmin, and alpha1-antitrypsin have no effect on hK11 activity and do not form complexes with hK11 in vitro. The strongest inhibitor, APMSF, completely inhibited hK11 activity at a concentration of 2.5 mmol/L. Aprotinin and an hK11-specific monoclonal antibody inhibited hK11 activity up to 40%. Plasmin is a strong candidate for cleaving hK11 at Arg156.

CONCLUSION

This is the first report on purification and characterization of native hK11. We speculate that hK11, along with other kallikreins, proteases, and inhibitors, participates in a cascade enzymatic pathway responsible for semen liquefaction after ejaculation.

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.

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.

Kallikrein-related peptidase (KLK) family mRNA variants and protein isoforms in hormone-related cancers: do they have a function?

The kallikrein-related peptidase (KLK) gene family of 15 serine proteases encodes many proteins, including prostate specific antigen (PSA or KLK3), that are well described and/or are potential biomarkers for hormone-related cancers. Variant mRNA transcripts produced by alternative splicing, polyadenylation or AUG sites, or intron retention have been found for each of the KLK genes. The predicted protein for many of these alternative transcripts is different from that of the classical kallikrein-related peptidases and would not be an active serine protease. The majority of these novel protein isoforms have not been studied in vivo. The possible function(s) of the variant transcripts/protein isoforms and potential roles that they may play in hormone-related cancers are still unknown and are the focus of this short review.

Human tissue kallikrein gene family: applications in cancer

Human tissue kallikrein genes, located on the long arm of chromosome 19, are a subgroup of the serine protease family of proteolytic enzymes. Initially thought to consist of three members, the human kallikrein locus has now been extended and includes 15 tandemly located genes. These genes, and their protein products, share a high degree of homology and are expressed in a wide array of tissues, mainly those that are under steroid hormone control. PSA (hK3) is one of the human kallikreins, and is the most useful tumor marker for prostate cancer screening, diagnosis, prognosis and monitoring. hK2, another prostate-specific kallikrein, has also been proposed as a complementary prostate cancer biomarker. In the past 5 years, the newly discovered kallikreins (KLK4-KLK15) have been associated with several types of cancer. For example, hK4, hK5, hK6, hK7, hK8, hK10, hK11, hK13 and hK14 are emerging biomarkers for ovarian, breast, prostate and testicular cancer. New evidence raises the possibility that some kallikreins are directly involved with cancer progression. We here review the evidence linking kallikreins and cancer and their applicability as novel biomarkers for cancer diagnosis and management.

Expression analysis and prognostic significance of human kallikrein 11 in prostate cancer

BACKGROUND

Kallikrein 11 (KLK11) is a newly discovered human kallikrein gene that is mainly expressed in the central nervous system and endocrine tissues. KLK11 has two alternative splicing isoforms, known as the brain type and prostate type. Many members of the human kallikrein gene family are differentially expressed in cancer and a few have potential as diagnostic/prognostic markers.

METHODS

In the present study, the expression of prostate type variant of KLK11 gene was analyzed by RT-PCR in 66 prostate cancer tissues. Tumors were pulverized, total RNA was extracted, and cDNA was prepared by reverse transcription. KLK11 was amplified by PCR using gene specific primers and its identity was verified by sequencing. Prostate tissues were then classified as KLK5 positive or negative based on eithidium bromide staining in agarose gels and image analysis.

RESULTS

KLK11 was found to be highly expressed in 43/66 (65%) of prostate cancer samples. We found a significant negative relationship between KLK11 expression and Gleason score (p = 0.004) and disease stage (p = 0.038). Serum total PSA concentration was found to be lower in patients with overexpression of KLK11 (p = 0.044).

CONCLUSIONS

We conclude that down-regulation of the KLK11 gene in advanced and more aggressive tumors may open the possibility of being used as a future biological marker distinguishing the tumor aggressiveness as well as a useful prognostic biomarker for prostate cancer.

Intron Retention: A Common Splicing Event within the Human Kallikrein Gene Family

Background: All human kallikrein (KLK) genes have at least one splice variant, some of which possess clinical utility in cancer diagnostics/prognostics. Given that introns &lt;100 bp in length are retained in 95% of human genes and that splice variants of KLK3 and KLK4 retain intron III, we hypothesized that other proteins in this family, with a small intron III, may also retain it.

Methods: Variant-specific reverse transcription-PCRs (RT-PCRs) for KLK1, KLK2, KLK5, and KLK15 were used to identify and clone the full coding sequence of intron III-containing splice variants. In addition, variant-specific RT-PCRs for the cloned KLK3 and KLK4 variants as well as for the “classical” forms of the six genes were used to determine their expression profiles in healthy tissues, their regulation by steroids, and their differential expression in prostate cancer.

Results: KLK1, KLK2, KLK3, KLK4, KLK5, and KLK15 showed a common type of splice variant in which intron III is retained. Expression profiling of these splice variants revealed expression profiles similar to those of the classical mRNA forms, although the pattern of hormonal regulation was different. The KLK15 splice variant was up-regulated in 8 of 12 cancerous prostate tissues. All encoded variant proteins were predicted to be truncated and catalytically inactive because of a lack of the serine residue of the catalytic triad.

Conclusions: The first six centromeric members of the KLK gene family have splice variants that retain intron III. Some variants show tissue-specific expression. The KLK15 splice variant appears to be a candidate biomarker for prostate cancer.

The emerging roles of human tissue kallikreins in cancer

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

Splice variants as cancer biomarkers

Inherited and acquired changes in pre-mRNA splicing have been documented to play a significant role in human disease development and many cancer-associated genes are regulated by alternative splicing. Loss of fidelity, variation of the splicing process, even controlled switching to specific splicing alternatives may occur during tumor progression and could play a major role in carcinogenesis. Splice variants that are found predominantly in tumors have clear diagnostic value and may provide potential drug targets. Moreover, understanding the process of aberrant splicing and the detailed characterization of the splice variants may prove crucial to our understanding of malignant transformation. This review discusses the basic mechanism of alternative splicing, alternative splicing in cancer-associated genes, tools to identify splice variants, and the development of clinical tests based on alternatively spliced biomarkers.

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.