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

Single-cell transcriptomics reveals cell type diversity of human prostate

Extensive studies have been performed to describe the phenotypic changes occurring during malignant transformation of the prostate. However, the cell types and associated changes that contribute to the development of prostate diseases and cancer remain elusive, largely due to the heterogeneous composition of prostatic tissues. Here, we conduct a comprehensive evaluation of four human prostate tissues by single-cell RNA sequencing (scRNA-seq) to analyze their cellular compositions. We identify 18 clusters of cell types, each with distinct gene expression profiles and unique features; of these, one cluster of epithelial cells (Ep) is found to be associated with immune function. In addition, we characterize a special cluster of fibroblasts and aberrant signaling changes associated with prostate cancer (PCa). Moreover, we provide insights into the epithelial changes that occur during the cellular senescence and aging. These results expand our understanding of the unique functional associations between the diverse prostatic cell types and the contributions of specific cell clusters to the malignant transformation of prostate tissues and PCa development.

Tissue factor pathway inhibitor 2 is a potent kallikrein-related protease 12 inhibitor

The protease activities are tightly regulated by inhibitors and dysregulation contribute to pathological processes such as cancer and inflammatory disorders. Tissue factor pathway inhibitor 2 (TFPI-2) is a serine proteases inhibitor, that mainly inhibits plasmin. This protease activated matrix metalloproteases (MMPs) and degraded extracellular matrix. Other serine proteases are implicated in these mechanisms like kallikreins (KLKs). In this study, we identified for the first time that TFPI-2 is a potent inhibitor of KLK5 and 12. Computer modeling showed that the first Kunitz domain of TFPI-2 could interact with residues of KLK12 near the catalytic triad. Furthermore, like plasmin, KLK12 was able to activate proMMP-1 and -3, with no effect on proMMP-9. Thus, the inhibition of KLK12 by TFPI-2 greatly reduced the cascade activation of these MMPs and the cleavage of cysteine-rich 61, a matrix signaling protein. Moreover, when TFPI-2 bound to extracellular matrix, its classical localisation, the KLK12 inhibition was retained. Finally, TFPI-2 was downregulated in human non-small-cell lung tumour tissue as compared with non-affected lung tissue. These data suggest that TFPI-2 is a potent inhibitor of KLK12 and could regulate matrix remodeling and cancer progression mediated by KLK12.

Beyond the biomarker role: prostate-specific antigen (PSA) in the prostate cancer microenvironment

The prostate-specific antigen (PSA) blood test is the accepted biomarker of tumor recurrence. PSA levels in serum correlate with disease progression, though its diagnostic accuracy is questionable. As a result, significant progress has been made in developing modified PSA tests such as PSA velocity, PSA density, 4Kscore, PSA glycoprofiling, Prostate Health Index, and the STHLM3 test. PSA, a serine protease, is secreted from the epithelial cells of the prostate. PSA has been suggested as a molecular target for prostate cancer therapy due to the fact that it is not only active in prostate tissue but also has a pivotal role on prostate cancer signaling pathways including proliferation, invasion, metastasis, angiogenesis, apoptosis, immune response, and tumor microenvironment regulation. Here, we summarize the current standing of PSA in prostate cancer progression as well as its utility in prostate cancer therapeutic approaches with an emphasis on the role of PSA in the tumor microenvironment.

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

BACKGROUND

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

METHODS

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

RESULTS

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

CONCLUSIONS

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

Kallikrein-related peptidases protein expression in lymphoid tissues suggests potential implications in immune response

OBJECTIVES

Kallikrein-related peptidases (KLKs) are a subgroup of 15 secreted chymotrypsin- and trypsin-like serine proteases that have been reported to possess novel functions in innate immunity and inflammation. Since the potential role of KLKs in immunity has not been studied in detail at the protein level, we examined the expression pattern of 12 members of the KLK family in immune-related tissues.

DESIGN & METHODS

Protein expression in tissue extracts was evaluated using immunoassays (ELISA). Immunohistochemistry (IHC) was performed on representative sections of tonsil and lymph nodes to determine the cellular localization of the KLK family members.

RESULTS

ELISA profiling of KLK3-KLK15 (except KLK12) revealed higher protein levels in the tonsil, compared to the lymph nodes and spleen. Relatively high protein levels in the tonsil were observed for KLK7, KLK9, KLK10 and KLK13. Expression of these KLKs was significantly lower in lymph nodes and spleen. IHC analysis in tonsil unveiled that KLK9 and KLK10 were differentially expressed in lymphoid cells. KLK9 was strongly expressed in the germinal center of lymphoid follicles where activated B-cells reside, whereas KLK10 was expressed in the follicular dendritic cells (FDCs) that are vital for maintaining the cycle of B cell maturation.

CONCLUSION

Overall, our study revealed the possible implications of KLK expression and regulation in the immune cells of lymphoid tissues.

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.

Biochemical and functional characterization of the human tissue kallikrein 9

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

Common variation in Kallikrein genes KLK5, KLK6, KLK12, and KLK13 and risk of prostate cancer and tumor aggressiveness

The human tissue Kallikrein family consists of 15 genes with the majority shown to be differentially expressed in cancers and/or indicators of cancer prognosis. We sought to elucidate the role of common genetic variation in four of the Kallikrein genes, KLK5, KLK6, KLK12, and KLK13, in prostate cancer risk and tumor aggressiveness. Genotyping of all 22 tagging single nucleotide polymorphisms (tagSNPs) in the KLK5, KLK6, KLK12, and KLK13 genes was performed in approximately 1,000 prostate cancer cases and 1,300 male controls from Australia. Data from any positive results were also accessed for 1,844 cases and 1,886 controls from a previously published prostate cancer genome-wide association study set from the United Kingdom. For one SNP in KLK12, rs3865443, there was evidence for association with prostate cancer risk of similar direction and magnitude in the replication set to that seen in the Australian cohort. We conducted genotyping of a further 309 prostate cancer cases, and combined analyses revealed an increased risk of prostate cancer for carriers of the rare homozygous genotype for rs3865443 (OR 1.28, 95% CI 1.04-1.57; P = 0.018). No other tagSNPs in the KLK5, KLK6, and KLK13 genes were consistently associated with prostate cancer risk or tumor aggressiveness. Analysis of a combined sample of 3,153 cases and 3,199 controls revealed the KLK12 tagSNP rs3865443 to be marginally statistically significantly associated with risk of prostate cancer. Considering the total number of SNPs investigated in this study, this finding should be interpreted cautiously and requires additional validation from very large datasets such as those of the Prostate Cancer Association group to investigate cancer associated alterations (PRACTICAL) Consortium.

Clinical significance of human kallikrein 12 gene expression in gastric cancer

AIM: To investigate whether the expression of kallikrein 12 (KLK12) is related to the development of gastric cancer (GC) and to determine the role of KLK12 in gastric cancer cells growth, invasion and migration.

METHODS: Between September 2007 and March 2008, 133 patients with histologically confirmed GC were recruited for the study. Expression of KLK12 was detected in samples from GC patients by quantitative real-time reverse transcription polymerase chain reaction and immunohistochemistry. The relationship between KLK12 protein expression and clinicopathological features of GC was analyzed. The difference in 5-year survival rates between the high KLK12 protein expression group and the low KLK12 expression group was compared. Additionally, the expression of KLK12 was examined in various human GC cell lines, including MKN-28, SGC-7901 and MKN-45. Small interfering RNA (siRNA) was used to inhibit KLK12 expression in MKN-45 cells. Cell clones stably transfected with KLK12 siRNA were tested for KLK12 expression by quantitative real-time reverse transcription-polymerase chain reaction and Western blotting. Furthermore, a series of functional assays were performed in this study to assess the biological features of transfected cells. Cell proliferation was assessed using the methylthiazolyltetrazoliumassay. Finally, cell migration and invasion were assessed using transwell chamber assays.

RESULTS: Of the 133 GC patients included in the study, 126 (94.7%) showed a higher expression level of KLK12 mRNA when compared to noncancerous tissue specimens. Expression of KLK12 mRNA was significantly higher in GC tissues than in normal tissue (P < 0.001). KLK12 protein expression was detected in 96 of 133 (72.2%) GC samples with moderate or strong staining primarily in the cytoplasm. In contrast, negative immunostaining for KLK12 protein was observed in the corresponding normal gastric mucosal tissue. Overexpression of KLK12 protein was significantly associated with lymph node metastasis (P = 0.001), histological type (P < 0.001) and tumor-node-metastasis stage (P = 0.005), while no significant correlation was observed between expression of KLK12 protein and sex, age, depth of invasion, tumor size or lymphatic invasion. Furthermore, patients with high KLK12 expression had a significantly poorer 5-year survival rate than those with low KLK12 expression (P = 0.002). Expression of KLK12 mRNA was significantly higher in MKN-45 GC cells compared to normal mucosal cells or two other GC cell lines (P < 0.01). Expression of KLK12 in MKN-45 cells was downregulated after transfection with siRNA. Knockdown of KLK12 markedly decreased the proliferation of MKN-45 cells when compared with parent or mock-transfected cells (P = 0.001), especially from the 3rd to the 5th day of the assay. In migration assays, fewer KLK12 siRNA cells migrated through the chambers (22.00 ± 1.81) when compared to the parent (46.47 ± 2.42) or mock-transfected cells (45.40 ± 1.99); these differences were statistically significant (P < 0.001). However, in the invasion assay, the number of KLK12 siRNA cells that invaded the chambers was 18.40 ± 1.12, closely similar to both the parent (18.67 ± 0.98) and mock-transfected cells (18.53 ± 0.92). There was no significantly difference between the three groups in the invasion assay (P = 0.054).

CONCLUSION: The KLK12 gene is markedly overexpressed in GC tissue, and its expression status may be a powerful prognostic indicator for patients with GC. KLK12 might serve as a novel diagnosis and prognosis biomarker in GC.

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

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