Characterisation of human kallikrein 6/protease M expression in ovarian cancer

Gene Signature Associated with Nervous System in an Experimental Radiation- and Estrogen-Induced Breast Cancer Model

Breast cancer is frequently the most diagnosed female cancer in the world. The experimental studies on cancer seldom focus on the relationship between the central nervous system and cancer. Despite extensive research into the treatment of breast cancer, chemotherapy resistance is an important issue limiting the efficacy of treatment. Novel biomarkers to predict prognosis or sensitivity to chemotherapy are urgently needed. This study examined nervous-system-related genes. The profiling of differentially expressed genes indicated that high-LET radiation, such as that emitted by radon progeny, in the presence of estrogen, induced a cascade of events indicative of tumorigenicity in human breast epithelial cells. Bioinformatic tools allowed us to analyze the genes involved in breast cancer and associated with the nervous system. The results indicated that the gene expression of the Ephrin A1 gene (EFNA1), the roundabout guidance receptor 1 (ROBO1), and the kallikrein-related peptidase 6 (KLK6) was greater in T2 and A5 than in the A3 cell line; the LIM domain kinase 2 gene (LIMK2) was greater in T2 than A3 and A5; the kallikrein-related peptidase 7 (KLK7), the neuroligin 4 X-linked gene (NLGN4X), and myelin basic protein (MBP) were greater than A3 only in T2; and the neural precursor cell expressed, developmentally down-regulated 9 gene (NEDD9) was greater in A5 than in the A3 and E cell lines. Concerning the correlation, it was found a positive correlation between ESR1 and EFNA1 in BRCA-LumA patients; with ROBO1 in BRCA-Basal patients, but this correlation was negative with the kallikrein-related peptidase 6 (KLK6) in BRCA-LumA and -LumB, as well as with LIMK2 and ROBO1 in all BRCA. It was also positive with neuroligin 4 X-linked (NLGN4X) in BRCA-Her2 and BRCA-LumB, and with MBP in BRCA-LumA and -LumB, but negative with KLK7 in all BRCA and BRCA-LumA and NEDD9 in BRCA-Her2. The differential gene expression levels between the tumor and adjacent tissue indicated that the ROBO1, KLK6, LIMK2, KLK7, NLGN4X, MBP, and NEDD9 gene expression levels were higher in normal tissues than in tumors; however, EFNA1 was higher in the tumor than the normal ones. EFNA1, LIMK2, ROBO1, KLK6, KLK7, and MBP gene expression had a negative ER status, whereas NEDD9 and NLGN4X were not significant concerning ER status. In conclusion, important markers have been analyzed concerning genes related to the nervous system, opening up a new avenue of studies in breast cancer therapy.

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.

The impact of ultraviolet- and infrared-based laser microdissection technology on phosphoprotein detection in the laser microdissection-reverse phase protein array workflow

Reversible protein phosphorylation represents a key mechanism by which signals are transduced in eukaryotic cells. Dysregulated phosphorylation is also a hallmark of carcinogenesis and represents key drug targets in the precision medicine space. Thus, methods that preserve phosphoprotein integrity in the context of clinical tissue analyses are crucially important in cancer research. Here we investigated the impact of UV laser microdissection (UV LMD) and IR laser capture microdissection (IR LCM) on phosphoprotein abundance of key cancer signaling protein targets assessed by reverse-phase protein microarray (RPPA). Tumor epithelial cells from consecutive thin sections obtained from four high-grade serous ovarian cancers were harvested using either UV LMD or IR LCM methods. Phosphoprotein abundances for ten phosphoproteins that represent important drug targets were assessed by RPPA and revealed no significant differences in phosphoprotein integrity from those obtained using higher-energy UV versus the lower-energy IR laser methods.

MiR-203a-3p regulates the biological behaviors of ovarian cancer cells through mediating the Akt/GSK-3β/Snail signaling pathway by targeting ATM

OBJECTIVE

To investigate whether miR-203a-3p can regulate the biological behaviors of ovarian cancer cells by targeting ATM to affect the Akt/GSK-3β/Snail signaling pathway.

METHODS

The expression levels of miR-203a-3p and ATM were detected by qRT-PCR, immunohistochemical staining and Western blotting in ovarian cancer tissues and adjacent normal tissues obtained from 152 subjects. A dual-luciferase reporter gene assay was performed to verify the relationship between miR-203a-3p and ATM. Human ovarian cancer cell lines (A2780 and SKOV3) were used to generate the Blank, miR-NC, miR-203a-3p mimic, Control siRNA, ATM siRNA, and miR-203a-3p inhibitor + ATM siRNA groups. The biological behaviors of ovarian cancer cells were evaluated by CCK-8, wound healing, and Transwell invasion assays, annexin V-FITC/PI staining and flow cytometry. The levels of Akt/GSK-3β/Snail pathway-related proteins were assessed by Western blotting.

RESULTS

Ovarian cancer tissues showed lower miR-203a-3p levels and higher ATM levels than adjacent normal tissues, both of which were associated with the FIGO stage, grade and prognosis of ovarian cancer. As confirmed by a dual-luciferase reporter gene assay, miR-203a-3p could target ATM. Furthermore, the miR-203a-3p mimic had multiple effects, including the inhibition of the proliferation, invasion and migration of A2780 and SKOV3 cells, the promotion of cell apoptosis, the arrest of the cell cycle at the G1 phase, and the blockage of the Akt/GSK-3β/Snail signaling pathway. ATM siRNA had similar effects on the biological behaviors of ovarian cancer cells, and these effects could be reversed by a miR-203a-3p inhibitor.

CONCLUSION

miR-203a-3p was capable of hindering proliferation, migration, and invasion and facilitating the apoptosis of ovarian cancer cells through its modulation of the Akt/GSK-3β/Snail signaling pathway by targeting ATM, and therefore it could serve as a potential therapeutic option for ovarian cancer.

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.

Study of kallikrein-related peptidase 6 (KLK6) and its complex with α1-antitrypsin in biological fluids

BACKGROUND

Human kallikrein-related peptidase 6 (KLK6) is a member of the kallikrein family of serine proteases. KLK6 is synthesized as a preproenzyme, mainly in tissues of the central nervous system (CNS), and secreted as an inactive precursor. Serum KLK6 is a biomarker of unfavorable prognosis for ovarian cancer, but its sensitivity for early detection is relatively low. Differential glycosylation of KLK6 has been identified in ascites fluid obtained from ovarian cancer patients, suggesting the presence of unique KLK6 isoforms in biological samples.

METHODS

In the present study, we applied a two-step enrichment approach for KLK6 in ovarian cancer ascites, followed by mice immunization and production of monoclonal antibodies. Immunoaffinity techniques coupled to mass spectrometric methods were employed for hybridoma screening and target antigen identification.

RESULTS

We found that the main target of the newly-generated monoclonal antibodies target was the serine protease inhibitor α1-antitrypsin (A1AT). Additional experiments confirmed that A1AT is the main inhibitor of KLK6 in biological fluids. One new antibody (24ED138) was chosen to build a hybrid assay for the accurate quantification of the A1AT-KLK6 complex in biological samples. The aforementioned assay was evaluated with serum samples collected from patients with ovarian cancer (n=24) and normal donors (n=16) and showed slight improvement in sensitivity (~12%) compared to the standard in-house KLK6 assay.

CONCLUSIONS

We conclude that KLK6 is present in biological fluids either as free form, or bound to A1AT, and the bound form performs better than total KLK6 as a biomarker of ovarian carcinoma.

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.

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

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

Deletion at 6q24.2-26 predicts longer survival of high-grade serous epithelial ovarian cancer patients

Standard treatments for advanced high-grade serous ovarian carcinomas (HGSOCs) show significant side-effects and provide only short-term survival benefits due to disease recurrence. Thus, identification of novel prognostic and predictive biomarkers is urgently needed. We have used 42 paraffin-embedded HGSOCs, to evaluate the utility of DNA copy number alterations, as potential predictors of clinical outcome. Copy number-based unsupervised clustering stratified HGSOCs into two clusters of different immunohistopathological features and survival outcome (HR = 0.15, 95%CI = 0.03-0.81; Padj = 0.03). We found that loss at 6q24.2-26 was significantly associated with the cluster of longer survival independently from other confounding factors (HR = 0.06, 95%CI = 0.01-0.43, Padj = 0.005). The prognostic value of this deletion was validated in two independent series, one consisting of 36 HGSOCs analyzed by fluorescent in situ hybridization (P = 0.04) and another comprised of 411 HGSOCs from the Cancer Genome Atlas study (TCGA) (HR = 0.67, 95%CI = 0.48-0.93, Padj = 0.019). In addition, we confirmed the association of low expression of the genes from the region with longer survival in 799 HGSOCs (HR = 0.74, 95%CI = 0.61-0.90, log-rank P = 0.002) and 675 high-FIGO stage HGSOCs (HR = 0.76, 95%CI = 0.61-0.96, log-rank P = 0.02) available from the online tool KM-plotter. Finally, by integrating copy number, RNAseq and survival data of 296 HGSOCs from TCGA we propose a few candidate genes that can potentially explain the association. Altogether our findings indicate that the 6q24.2-26 deletion is an independent marker of favorable outcome in HGSOCs with potential clinical value as it can be analyzed by FISH on tumor sections and guide the selection of patients towards more conservative therapeutic strategies in order to reduce side-effects and improve quality of life.

Secretome and degradome profiling shows that Kallikrein-related peptidases 4, 5, 6, and 7 induce TGFβ-1 signaling in ovarian cancer cells

Kallikrein‐related peptidases, in particular KLK4, 5, 6 and 7 (4–7), often have elevated expression levels in ovarian cancer. In OV‐MZ‐6 ovarian cancer cells, combined expression of KLK4–7 reduces cell adhesion and increases cell invasion and resistance to paclitaxel. The present work investigates how KLK4–7 shape the secreted proteome (“secretome”) and proteolytic profile (“degradome”) of ovarian cancer cells. The secretome comparison consistently identified >900 proteins in three replicate analyses. Expression of KLK4–7 predominantly affected the abundance of proteins involved in cell–cell communication. Among others, this includes increased levels of transforming growth factor β‐1 (TGFβ‐1). KLK4–7 co‐transfected OV‐MZ‐6 cells share prominent features of elevated TGFβ‐1 signaling, including increased abundance of neural cell adhesion molecule L1 (L1CAM). Augmented levels of TGFβ‐1 and L1CAM upon expression of KLK4–7 were corroborated in vivo by an ovarian cancer xenograft model. The degradomic analysis showed that KLK4–7 expression mostly affected cleavage sites C‐terminal to arginine, corresponding to the preference of kallikreins 4, 5 and 6. Putative kallikrein substrates include chemokines, such as growth differentiation factor 15 (GDF 15) and macrophage migration inhibitory factor (MIF). Proteolytic maturation of TGFβ‐1 was also elevated. KLK4–7 have a pronounced, yet non‐degrading impact on the secreted proteome, with a strong association between these proteases and TGFβ‐1 signaling in tumor biology.

Expression of KLK4, 5, 6, and 7 yields subtle secretome and degradome alterations.

Pro‐ and anti‐tumorigenic proteins are affected.

TGFβ‐1 signaling is elevated.

Degradomic analysis supports cell‐contextual KLK activity.

Potential substrates of KLK4–7 have been identified.

Copy number and expression alterations of miRNAs in the ovarian cancer cell line OVCAR-3: impact on kallikrein 6 protein expression

BACKGROUND

Kallikrein-related peptidase 6 (KLK6), a member of the serine protease family of kallikrein (KLK) genes, is dysregulated in ovarian carcinomas (OCa) and its overexpression is associated with poor prognosis. Regulation of its expression is poorly understood and is likely to be influenced by multiple mechanisms. The KLK locus is subject to copy number changes and heterogeneity in serous OCas. These copy number imbalances generally correlate with KLK6 protein expression; however, this is not always the case. In this study we explored the role of miRNAs in the posttranscriptional control of KLK6 expression and the contributions of copy numbers, not only of the KLK locus, but also of the miRNAs predicted to regulate it.

METHODS AND RESULTS

By miRNA profiling of the KLK6-overexpressing OCa cell line, OVCAR-3, we identified overexpressed and underexpressed miRNAs. Publically available miRNA databases identified the human miRNA lethal 7 (hsa-let-7) family members as putative regulating miRNAs, from which hsa-let-7a was chosen for functional analysis. The transient transfection of hsa-let-7a to OVCAR-3 resulted in a decrease of KLK6 secreted protein. Moreover, such transfection was also able to weakly affect the expression of another member of the KLK gene family, KLK10 (kallikrein-related peptidase 10). Cytogenomic analysis, including array comparative genomic hybridization, fluorescence in situ hybridization, and spectral karyotyping revealed the overall net copy number losses of hsa-let-7a and other miRNAs predicted to target KLK6.

CONCLUSIONS

The hsa-let-7 family member hsa-let-7a is a modulator of KLK6 protein expression that is independent of the KLK6 copy number status.

Combined panel of serum human tissue kallikreins and CA-125 for the detection of epithelial ovarian cancer

Objective

To determine the predictive accuracy of the combined panels of serum human tissue kallikreins (hKs) and CA-125 for the detection of epithelial ovarian cancer.

Methods

Serum specimens collected from 5 Indonesian centers and 1 Vietnamese center were analyzed for CA-125, hK6, and hK10 levels. A total of 375 specimens from patients presenting with ovarian tumors, which include 156 benign cysts, 172 epithelial ovarian cancers (stage I/II, n=72; stage III/IV, n=100), 36 germ cell tumors and 11 borderline tumors, were included in the study analysis. Receiver operating characteristic analysis were performed to determine the cutoffs for age, CA-125, hK6, and hK10. Sensitivity, specificity, negative, and positive predictive values were determined for various combinations of the biomarkers.

Results

The levels of hK6 and hK10 were significantly elevated in ovarian cancer cases compared to benign cysts. Combination of 3 markers, age/CA-125/hk6 or CA-125/hk6/hk10, showed improved specificity (100%) and positive predictive value (100%) for prediction of ovarian cancer, when compared to the performance of single markers having 80-92% specificity and 74-87% positive predictive value. Four-marker combination, age/CA-125/hK6/hK10 also showed 100% specificity and 100% positive predictive value, although it demonstrated low sensitivity (11.9%) and negative predictive value (52.8%).

Conclusion

The combination of human tissue kallikreins and CA-125 showed potential for improving prediction of epithelial ovarian cancer in patients presenting with ovarian tumors.

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

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

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

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

Advancements in the use of blood tests for cancer screening in women at high risk for endometrial and breast cancer

Several years ago, it was argued that the identification of serum biomarkers is one of the most promising approaches for the detection of early-stage malignant or even premalignant lesions. In this review, the need to establish better monitoring protocols is described for obese women who are at higher risk for the development of malignancies commonly associated with excess weight; specifically endometrial and postmenopausal breast cancer. These cancers have been chosen for this review article as our aim was to focus on female cancers that have been linked with obesity. Cancer screening is essential in detecting disease in its earliest stage in order to reduce morbidity and mortality; however, effective screening is not available for many cancer types. Even for cancers that have effective screening protocols available, there are barriers to screening in obese individuals, such as reduced mobility and embarrassment. These barriers often delay screening in these vulnerable population groups, leading to detection of the disease at a more advanced stage and ultimately leading to a poorer prognosis. As of today, biomarkers do not replace but augment imaging and other existing screening approaches. Future development of blood- or urine-based biomarkers as a way to screen individuals at high risk for certain cancers may prove to be an excellent method for overcoming the barriers that individuals at high risk are facing today. The overall purpose of this manuscript is to provide an overview of screening techniques and to identified barriers and alternate biomarker-based approaches for improvement of endometrial and breast cancer screening in obese women.

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

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

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

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

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

Differential hRad17 expression by histologic subtype of ovarian cancer

BACKGROUND

In the search for unique ovarian cancer biomarkers, ovarian specific cDNA microarray analysis identified hRad17, a cell cycle checkpoint protein, as over-expressed in ovarian cancer. The aim of this study was to validate this expression.

METHODS

Immunohistochemistry was performed on 72 serous, 19 endometrioid, 10 clear cell, and 6 mucinous ovarian cancers, 9 benign ovarian tumors, and 6 normal ovarian tissue sections using an anti-hRad17 antibody. Western blot analysis and quantitative PCR were performed using cell lysates and total RNA prepared from 17 ovarian cancer cell lines and 6 normal ovarian epithelial cell cultures (HOSE).

RESULTS

Antibody staining confirmed upregulation of hRad17 in 49.5% of ovarian cancer cases. Immunohistochemistry demonstrated that only 42% of serous and 47% of endometrioid subtypes showed overexpression compared to 80% of clear cell and 100% of mucinous cancers. Western blot confirmed overexpression of hRad17 in cancer cell lines compared to HOSE. Quantitative PCR demonstrated an upregulation of hRad17 RNA by 1.5-7 fold. hRad17 RNA expression differed by subtype.

CONCLUSIONS

hRad17 is over-expressed in ovarian cancer. This over-expression varies by subtype suggesting a role in the pathogenesis of these types. Functional studies are needed to determine the potential role of this protein in ovarian cancer.

Genomic instability and copy-number heterogeneity of chromosome 19q, including the kallikrein locus, in ovarian carcinomas

Many tissue kallikrein (KLK) genes and proteins are candidate diagnostic, prognostic and predictive biomarkers for ovarian cancer (OCa). We previously demonstrated that the KLK locus (19q13.3/4) is subject to copy-number gains and structural rearrangements in a pilot study of cell lines and ovarian cancer primary tissues, shown to overexpress KLK gene family members. To determine the overall frequency of genomic instability and copy-number changes, a retrospective study was conducted using formalin-fixed paraffin embedded (FFPE) tissues. Eighty-one chemotherapy naïve serous OCas were examined using 3-colour fluorescence in situ hybridization (FISH) to identify structural and numerical changes on 19q, including the KLK locus; in addition to immunohistochemistry (IHC) for KLK6, which has been shown to be overexpressed in OCa. The KLK locus was subject to copy-number changes in ∼83% of cases: net gain in 51%, net loss in 30% and amplified in 2%; and found to be chromosomally unstable (p < 0.001). All cases showed a wide range of immuoreactivity for KLK6 by IHC. Although no strong correlation could be found with copy-number, the latter was contributing factor to the observed KLK6 protein overexpression. Moreover, univariate and multivariate analyses showed an association between the net loss of the KLK locus and longer disease-free survival. Interestingly, FISH analyses indicated that chromosome 19q was subjected to structural rearrangement in 62% of cases and was significantly correlated to tumor grade (p < 0.001). We conclude that numerical and structural aberrations of chromosome 19q, affect genes including the KLK gene members, may contribute to ovarian carcinoma progression and aggressiveness.

Kallikreins on steroids: structure, function, and hormonal regulation of prostate-specific antigen and the extended kallikrein locus

The 15 members of the kallikrein-related serine peptidase (KLK) family have diverse tissue-specific expression profiles and putative proteolytic functions. The kallikrein family is also emerging as a rich source of disease biomarkers with KLK3, commonly known as prostate-specific antigen, being the current serum biomarker for prostate cancer. The kallikrein locus is also notable because it is extraordinarily responsive to steroids and other hormones. Indeed, at least 14 functional hormone response elements have been identified in the kallikrein locus. A more comprehensive understanding of the transcriptional regulation of kallikreins may help the field make more informed hypotheses about the physiological functions of kallikreins and their effectiveness as biomarkers. In this review, we describe the organization of the kallikrein locus and the structure of kallikrein genes and proteins. We also focus on the transcriptional regulation of kallikreins by androgens, progestins, glucocorticoids, mineralocorticoids, estrogens, and other hormones in animal models and human prostate, breast, and reproductive tract tissues. The interaction of the androgen receptor with androgen response elements in the promoter and enhancer of KLK2 and KLK3 is also summarized in detail. There is evidence that all kallikreins are regulated by multiple nuclear receptors. Yet, apart from KLK2 and KLK3, it is not clear whether all kallikreins are direct transcriptional targets. Therefore, we argue that gaining more detailed information about the mechanisms that regulate kallikrein expression should be a priority of future studies and that the kallikrein locus will continue to be an important model in the era of genome-wide analyses.

The association with age, human tissue kallikreins 6 and 10 and hemostatic markers for survival outcome from epithelial ovarian cancer

PURPOSE

To assess known cancer biomarkers CA-125, human tissue kallikreins KLK6 and KLK10, hemostatic markers and age with 5-year survival outcome from epithelial ovarian cancer.

METHODS

Forty-one benign cyst cohorts and 83 patients diagnosed with ovarian cancer were recruited. The following assays were performed: fibrinogen, vWF antigen, D: -dimer, ATIII activity, tPA, PAI-1, uPAR, KLK6, KLK10 and CA-125. Follow-up visits of cancer patients of more than 60 months were noted. Data between those who survived past 60 months and mortality from cancer were analyzed.

RESULTS

Only 24 patients lived past 60 months, and 31 died (advanced stage n = 27). Those living past 60 months were significantly older and associated with similar pre-operative levels seen in benign cyst cohorts especially for KLK6, fibrinogen, vWF, AT levels despite upregulation of D: -dimer, CA-125 and KLK10. Ovarian cancer cohorts living past 60 months were younger than those who died within 12 months (n = 12). Mortality within 12 months was associated with older age, upregulation of KLK6, fibrinogen, D: -dimer, vWF, tPA antigen and reduced ATIII levels. Similarly, mortality within 36 months of disease showed older age with upregulation of CA-125, KLK6 D: -dimer vWF antigen and tPA antigen levels. Late stage cancer (III/IV) showed upregulated CA-125, KLK6, KLK10, D: -dimer and reduced AT compared to early stage cancer (I/II). The 5-year survival rate for early cancer was 80%, advanced 22.9% and overall 5-year survival rate was 43.6%.

CONCLUSION

Older age together with the novel biomarkers studied and their association with adverse outcome from epithelial ovarian cancer was seen especially within 12 and 36 months of disease. Those who lived past 60 months of disease showed similar pre-operative levels seen in benign cyst cohorts despite elevated D: -dimer, CA125 and KLK 10. An enlarged study is needed to confirm these findings.

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.

Three dysregulated miRNAs control kallikrein 10 expression and cell proliferation in ovarian cancer

BACKGROUND

Kallikrein-related peptidases (KLKs) are a family of serine proteases that have been shown to be dysregulated in several malignancies including ovarian cancer. The control of kallikrein genes and their physiological function in cancer is not well understood. We hypothesized that microRNAs (miRNAs) represent a novel mechanism for post-transcriptional control of KLK expression in cancer.

METHODS

We first analysed miRNA expression in ovarian cancer in silico. A total of 98 miRNAs were reported to have altered expression in ovarian cancer. Three of these miRNAs were predicted to target KLK10. We experimentally verified the predicted miR-KLK10 interaction using two independent techniques, a luciferase assay with a construct containing the KLK10 3' untranslated region (UTR), pMIR-KLK10, and measuring KLK10 protein levels after transfection with miRNA.

RESULTS

When we co-transfected cells with pMIR-KLK10 and either let-7f, miR-224, or mR-516a, we saw decreased luciferase signal, suggesting that these miRNAs can target KLK10. We then examined the effect of these three miRNAs on KLK10 protein expression and cell growth. Transfection of all miRNAs, let-7f, miR-224, and miR-516a led to a decrease in protein expression and cellular growth. This effect was shown to be dose dependent. The KLK10 protein levels were partially restored by co-transfecting let-7f and its inhibitor. In addition, there was a slight decrease in KLK10 mRNA expression after transfection with let-7f.

CONCLUSION

Our results confirm that KLKs can be targeted by more than one miRNA. Increased expression of certain miRNAs in ovarian cancer can lead to decreased KLK protein expression and subsequently have a negative effect on cell proliferation. This dose-dependent effect suggests that a 'tweaking' or 'fine-tuning' mechanism exists in which the expression of one KLK can be controlled by multiple miRNAs. These data together suggest that miRNA may be used as potential therapeutic options and further studies are required.

KLK6 and KLK13 predict tumor recurrence in epithelial ovarian carcinoma

Background:

The human kallikrein-related peptidase family consists of 15 genes. Twelve of these genes are overexpressed in ovarian cancer and may represent potential markers for diagnosis, prognosis, and/or response to treatment. The aim of this study was to determine the prognostic significance of kallikrein-related peptidase 6 (KLK6) and kallikrein-related peptidase 13 (KLK13) in epithelial ovarian cancer by quantifying gene expression levels with tumour pathology and patient survival data.

Methods:

Total RNA was isolated from 106 patients diagnosed with primary ovarian cancer, as well as 8 normal ovary controls. Samples were analysed by quantitative real-time PCR for KLK6 and KLK13 expression. Correlation between kallikrein gene expression and clinical characteristics was evaluated with the χ²-test. Survival analysis was performed using Kaplan–Meier and Cox proportional hazards regression models.

Results:

Expression levels of both KLK6 and KLK13 mRNA were significantly increased in invasive cancers relative to normal ovaries (P=0.002 and 0.039 respectively). High KLK6 and KLK13 expression was an indicator of poor prognosis, with patients having a shorter recurrence-free survival (P=0.002 and 0.027 respectively). High KLK6 expression was also significantly associated with lower overall survival (P=0.011). When subjected to multivariate analysis, patients with either high KLK6 or KLK13 were 3- and 2.2-fold, respectively, more likely to have a recurrence than patients with low kallikrein expression.

Conclusion:

These data show increased mRNA expression of KLK6 and KLK13 in ovarian cancer compared to normal ovarian tissues. High KLK6 or KLK13 expression in primary ovarian tumours can significantly predict prognosis in terms of recurrence-free survival and overall survival. In all, this study shows KLK6 and KLK13 as potential biomarkers and may be therapeutic targets for treatment of ovarian cancer.

Prediction of ovarian cancer prognosis and response to chemotherapy by a serum-based multiparametric biomarker panel

Currently, there are no effective biomarkers for ovarian cancer prognosis or prediction of therapeutic response. The objective of this study was to examine a panel of 10 serum biochemical parameters for their ability to predict response to chemotherapy, progression and survival of ovarian cancer patients. Sera from ovarian cancer patients were collected prior and during chemotherapy and were analysed by enzyme-linked immunosorbent assay for CA125, kallikreins 5, 6, 7, 8, 10 and 11, B7-H4, regenerating protein IV and Spondin-2. The odds ratio and hazard ratio and their 95% confidence interval (95% CI) were calculated. Time-dependent receiver-operating characteristic (ROC) curves were utilised to evaluate the prognostic performance of the biomarkers. The levels of several markers at baseline (c₀), or after the first chemotherapy cycle (rc₁), predicted chemotherapy response and overall or progression-free survival in univariate analysis. A multiparametric model (c₀ of CA125, KLK5, KLK7 and rc₁ of CA125) provided predictive accuracy with area under the ROC curve (AUC) of 0.82 (0.62 after correction for overfitting). Another marker combination (c₀ of KLK7, KLK10, B7-H4, Spondin-2) was useful in predicting short-term (1-year) survival with an AUC of 0.89 (0.74 after correction for overfitting). All markers examined, except KLK7 and regenerating protein IV, were powerful predictors of time to progression (TTP) among chemotherapy responders. Individual and panels of biomarkers from the kallikrein family (and other families) can predict response to chemotherapy, overall survival, short-term (1-year) survival, progression-free survival and TTP of ovarian cancer patients treated with chemotherapy.

Impact of cytogenetic and genomic aberrations of the kallikrein locus in ovarian cancer

The tissue kallikrein (KLK) genes are a new source for biomarkers in ovarian cancer. However, there has been no systematic analysis of copy number and structural rearrangements related to their protein expression. Chromosomal rearrangements and copy number changes of the KLK region were studied by FISH with protein levels measured by ELISA. Ovarian cancer and cell lines revealed the KLK region was subject to copy number imbalances or involved in unbalanced translocations and were associated with increased protein expression of KLKs 5, 6, 7, 8, 9, 10 and 11. In this initial study, we introduce the potential for long-range chromosomal effects and copy number as a mechanism for the previously reported aberrant expression of many KLK genes in ovarian cancers.

A multiparametric panel for ovarian cancer diagnosis, prognosis, and response to chemotherapy

PURPOSE

Our goal was to examine a panel of 11 biochemical variables, measured in cytosolic extracts of ovarian tissues (normal, benign, and malignant) by quantitative ELISAs for their ability to diagnose, prognose, and predict response to chemotherapy of ovarian cancer patients.

EXPERIMENTAL DESIGN

Eleven proteins were measured (9 kallikreins, B7-H4, and CA125) in cytosolic extracts of 259 ovarian tumor tissues, 50 tissues from benign conditions, 35 normal tissues, and 44 tissues from nonovarian tumors that metastasized to the ovary. Odds ratios and hazard ratios and their 95% confidence interval were calculated. Time-dependent receiver operating characteristic curves for censored survival data were used to evaluate the performance of the biomarkers. Resampling was used to validate the performance.

RESULTS

Most biomarkers effectively separated cancer from noncancer groups. A composite marker provided an area under the curve of 0.97 (95% confidence interval, 0.95-0.99) for discriminating normal and cancer groups. Univariately, hK5 and hK6 were positively associated with progression. After adjusting for clinical variables in multivariate analysis, both hK10 and hK11 significantly predicted time to progression. Increasing levels of hK13 were associated with chemotherapy response, and the predictive power of hK13 to chemotherapy response was improved by a panel of five biomarkers.

CONCLUSIONS

The evidence shows that a group of kallikreins and multiparametric combinations with other biomarkers and clinical variables can significantly assist with ovarian cancer classification, prognosis, and response to platinum-based chemotherapy. In particular, we developed a multiparametric strategy for predicting ovarian cancer response to chemotherapy, comprising several biomarkers and clinical features.

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

BACKGROUND

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

METHODS

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

RESULTS

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

CONCLUSION

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

Association of KLK5 overexpression with invasiveness of urinary bladder carcinoma cells

Array-based comparative genomic hybridization (array-CGH) has powerful potential for high-throughput identification of genetic aberrations in cell genomes. We identified high-level amplification of kallikrein (KLK) genes, which are mapped to 19q13.3 and belong to the serine protease family, in the course of a program to screen a panel of urinary bladder carcinoma cell lines for genomic copy number aberrations using our in-house CGH-array. Expression levels of KLK5, -6, -8 and -9 were significantly increased in three cell lines with copy number gains of these KLK genes. Knockdown of these KLK transcripts by specific small interfering RNA significantly inhibited the invasion of a bladder carcinoma cell line through Matrigel in vitro. Reverse transcription-polymerase chain reaction analysis of 42 primary bladder tumor samples showed that increased expression of KLK5 was frequently observed in invasive tumors (pT2-pT4) (14.3%, 6/42) compared with superficial tumors (pTa, pT1) (0%, 0/42; P = 0.0052), and expression levels of KLK5, -6, -8 and -9 mRNA were higher in invasive tumors than in superficial tumors (P < 0.0001, P = 0.0043, P = 0.0790 and P = 0.0037, respectively). These observations indicate that KLK5, -6, -8 and -9 may be the most likely targets of the 19q13.3 amplification, and may play a crucial role in promoting cancer-cell invasion in bladder tumor.

Transcriptional upregulation of human tissue kallikrein 6 in ovarian cancer: clinical and mechanistic aspects

The human tissue kallikrein family (KLK for protein; KLK for gene) includes 15 members. Twelve kallikreins, including KLK6, are concurrently upregulated in ovarian cancer. However, the mechanism of this phenomenon remains unclear. In this study, we measured KLK6 expression in a large series of ovarian tissue cytosols and examined possible mechanisms of KLK6 up-regulation in ovarian cancer. Using a newly developed enzyme-linked immunosorbent assay (ELISA) with two monoclonal antibodies, we quantified KLK6 expression in ovarian tissue cytosols, and confirmed the upregulation of KLK6 in ovarian cancer and its unfavourable prognostic value. We then examined KLK6 mRNA expression using reverse transcription-polymerase chain reaction and established its good concordance with KLK6 protein expression. This finding suggested that the KLK6 gene is under transcriptional regulation. We then scrutinised a few mechanisms that could explain KLK6 upregulation. The relative abundance of two KLK6 mRNA transcripts was studied; we found the same differential expression pattern in all samples, regardless of KLK6 levels. Genomic mutation screening of all exons and the 5'-flanking region of the KLK6 gene identified two linked single-nucleotide polymorphisms in the 5'-untranslated region, but neither correlated with KLK6 expression. Ovarian cell lines were separately treated with five steroid hormones. None of the treatments produced significant effects on KLK6 expression. We conclude that KLK6 is transcriptionally upregulated in ovarian cancer, but probably not through alternative mRNA transcript expression, genomic mutation, or steroid hormone induction.

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.

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

OBJECTIVES

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

METHODS

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

RESULTS

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

CONCLUSIONS

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

Screening for gynaecological cancers

BACKGROUND

The role of screening in gynaecological cancers is under evaluation. With mass screening proven effective in significantly reducing cervical cancer mortality, there is an interest in developing other screening methods to detect gynaecological malignancies early. This review covers advances in cervical cancer screening, strategies being investigated in ovarian cancer screening and the lack of justification in screening for endometrial, vulval and vaginal cancers.

METHODS

A Medline based literature search was performed for articles relating to screening for different gynaecological malignancies. Additional original papers cited in those identified by the initial search were also reviewed.

RESULTS

Advances in cervical cancer screening include liquid-based cytology and HPV testing. Results of ongoing trials are awaited before these can be fully implemented. The results of the two large, multicentre, randomised controlled trials being conducted in the United Kingdom and United States (UKCTOCS and PLCO study, respectively) to assess impact of screening on ovarian cancer mortality will shed some light on the need to implement screening for ovarian cancer in the general population. Novel markers, serum proteomic profiles and Doppler are some of the other technologies being explored. Currently, screening for endometrial cancer is not advocated as most women present with symptoms in early disease with good survival outcomes. Vulval and vaginal cancers are too rare to justify mass screening.

CONCLUSION

Methods to screen for various gynaecological malignancies need further evaluation before implementation in the general population. Results of large multicentred trials are awaited. Presently, screening for endometrial, vaginal and vulval cancers is not justified.

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

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

Clinicopathologic and biological significance of kallikrein 6 overexpression in human gastric cancer

PURPOSE

Human kallikrein genes (KLK) have been reported to be involved in human malignancies and several KLKs are promising biomarkers of prostate, ovarian, testicular, and breast cancers. Herein, we investigated the clinicopathologic and biological significance of KLK6 gene expression in human gastric cancer.

PATIENTS AND METHODS

Using real-time reverse transcription-PCR, we analyzed the KLK6 expression status with respect to various clinicopathologic variables in 66 patients with gastric cancer. In addition, we established a KLK6 stably suppressed gastric cancer cell line (MKN28) using small interfering RNA-mediated gene silencing, and investigated its effects on the cell proliferation rate, cell cycle, and invasiveness.

RESULTS

The KLK6 gene expression in cancerous tissue (0.37 +/- 0.53) was significantly (P < 0.000001) higher than that in noncancerous tissue (0.026 +/- 0.060). Elevated KLK6 expression was significantly associated with lymphatic invasion (P = 0.03). Furthermore, patients with a high KLK6 expression had a significantly poorer survival rate than those with a low KLK6 expression (P = 0.03). Therefore, we showed that KLK6 gene silencing with KLK6 small interfering RNA effectively suppressed the cell proliferation rate (P = 0.002), cell population in the S phase (P < 0.01), and invasiveness (P < 0.01) in comparison to mock-transfected cells.

CONCLUSIONS

The KLK6 gene is markedly overexpressed in gastric cancer tissue and its expression status may be a powerful prognostic indicator for patients with gastric cancer. Our findings also suggest that KLK6 may possibly be a novel target for gastric cancer therapy by gene-silencing procedures.

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.

Kallikreins as Markers of Disseminated Tumour Cells in Ovarian Cancer – A Pilot Study

BACKGROUND

Kallikreins are a family of secreted serine proteases, encoded by 15 genes which all localize in tandem on chromosome 19q13.4. Several members of this family have been previously associated with ovarian cancer. Kallikreins 6 (KLK6) and 10 (KLK10) are elevated in tumour cells, serum and ascites fluid of ovarian cancer patients and correlate with disease prognosis. Other kallikreins that have been related to ovarian cancer include KLK4, 5, 7, 8, 9, 11, 13, 14 and 15. We hypothesized that KLK6 and KLK10 can be utilized to monitor dissemination of ovarian cancer cells in blood and ascites fluid of ovarian cancer patients.

METHODS

RNA was isolated by immunomagnetic separation of cancer cells and was amplified by RT-PCR.

RESULTS

Screening for disseminated cancer cells in blood from 24 ovarian cancer patients, with RT-PCR for KLK6 mRNA, resulted in 75% positivity; however, this was not different from the positivity of normal controls. By utilizing KLK10 as a marker, the positivity of patients was 40% versus 20% of controls. Screening of ascites fluid of ovarian cancer patients revealed 90% positivity for KLK6 and KLK10 mRNA compared with 33% for other cancer types. Significant correlations were identified among mRNA of KLK4, 5, 6, 7, 8, 9, 10, 11, 13, 14 and 15 in cancer cells isolated from ascites fluid.

CONCLUSION

Kallikrein expression by ovarian cancer cells is not specific enough for detecting disseminated disease. Kallikrein expression may have some value for differentiating ovarian cancer from other types of cancer or from non-malignant diseases that lead to ascites accumulation.

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.

Ovarian cancer, the coagulation pathway, and inflammation

Epithelial ovarian cancer (EOC) represents the most frequent cause of death in the United States from a cancer involving the female genital tract. Contributing to the overall poor outcome in EOC patients, are the metastases to the peritoneum and stroma that are common in this cancer. In one study, cDNA microarray analysis was performed on fresh tissue to profile gene expression in patients with EOC. This study showed a number of genes with significantly altered expression in the pelvic peritoneum and stroma, and in the vicinity of EOC implants. These genes included those encoding coagulation factors and regulatory proteins in the coagulation cascade and genes encoding proteins associated with inflammatory responses. In addition to promoting the formation of blood clots, coagulation factors exhibit many other biologic functions as well as tumorigenic functions, the later including tumor cell proliferation, angiogenesis, invasion, and metastasis. Coagulation pathway proteins involved in tumorigenesis consist of factor II (thrombin), thrombin receptor (protease-activated receptors), factor III (tissue factor), factor VII, factor X and factor I (fibrinogen), and fibrin and factor XIII. In a recent study we conducted, we found that factor XII, factor XI, and several coagulation regulatory proteins, including heparin cofactor-II and epithelial protein C receptor (EPCR), were also upregulated in the peritoneum of EOC. In this review, we summarize evidence in support of a role for these factors in promoting tumor cell progression and the formation of ascites. We also discuss the different roles of coagulation factor pathways in the tumor and peritumoral microenvironments as they relate to angiogenesis, proliferation, invasion, and metastasis. Since inflammatory responses are another characteristic of the peritoneum in EOC, we also discuss the linkage between the coagulation cascade and the cytokines/chemokines involved in inflammation. Interleukin-8, which is considered an important chemokine associated with tumor progression, appears to be a linkage point for coagulation and inflammation in malignancy. Lastly, we review findings regarding the inflammatory process yielded by certain clinical trials of agents that target members of the coagulation cascade in the treatment of cancer. Current data suggest that disrupting certain elements of the coagulation and inflammation processes in the tumor microenvironment could be a new biologic approach to cancer therapeutics.

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.