Expression and prognostic significance of kallikrein-related peptidase 8 protein levels in advanced ovarian cancer by using automated quantitative analysis

Upregulation of KLK8 Predicts Poor Prognosis in Pancreatic Cancer

Pancreatic ductal adenocarcinoma (PDAC) is a growing cause of cancer-related mortality worldwide. Kallikrein-related peptidase 8 (KLK8) has potential clinical values in many cancers. However, the clinicopathological significances of KLK8 in PDAC remain unknown. We explored the relationship of KLK8 to clinicopathological features of PDAC based on public databases. KLK8 expression was examined in human PDAC tissues. Cell proliferation and apoptosis were evaluated in KLK8-overexpressed human pancreatic cancer cell lines Mia-paca-2 and Panc-1. The related signaling pathways of KLK8 involved in pancreatic cancer progression were analyzed by gene set enrichment analysis (GSEA) and further verified in in vitro studies. We found that KLK8 was up-regulated in tumor tissues in the TCGA-PAAD cohort, and was an independent prognostic factor for both overall survival and disease-free survival of PDAC. KLK8 mRNA and protein expressions were increased in PDAC tissues compared with para-cancerous pancreas. KLK8 overexpression exerted pro-proliferation and anti-apoptotic functions in Mia-paca-2 and Panc-1 cells. GSEA analysis showed that KLK8 was positively associated with PI3K-Akt-mTOR and Notch pathways. KLK8-induced pro-proliferation and anti-apoptotic effects in Mia-paca-2 and Panc-1 cells were attenuated by inhibitors for PI3K, Akt, and mTOR, but not by inhibitor for Notch. Furthermore, overexpression of KLK8 in Mia-paca-2 and Panc-1 cells significantly increased epidermal growth factor (EGF) levels in the culture media. EGF receptor (EGFR) inhibitor could block KLK8-induced activation of PI3K/Akt/mTOR pathway and attenuate pro-proliferation and anti-apoptotic of KLK8 in Mia-paca-2 and Panc-1 cells. In conclusion, KLK8 overexpression exerts pro-proliferation and anti-apoptotic functions in pancreatic cancer cells via EGF signaling-dependent activation of PI3K/Akt/mTOR pathway. Upregulated KLK8 in PDAC predicts poor prognosis and may be a potential therapeutic target for PDAC.

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.

Kallikrein-related peptidases represent attractive therapeutic targets for ovarian cancer

INTRODUCTION

Aberrant levels of kallikrein-related peptidases (KLK1-15) have been linked to cancer cell proliferation, invasion and metastasis. In ovarian cancer, the KLK proteolytic network has a crucial role in the tissue and tumor microenvironment. Publically available ovarian cancer genome and expression data from multiple patient cohorts show an upregulation of most KLKs. Areas covered: Here, we review the expression levels of all 15 members of this family in normal and ovarian cancer tissues, categorizing them into highly and moderately or weakly expressed KLKs, and their association with patient prognosis and survival. We summarize their tumor-biological functions determined in cell-based assays and xenograft models, further highlighting their suitability as cancer biomarkers and attractive candidates for drug development. Finally, we discuss some different pharmaceutical approaches, including peptide-based and small molecule inhibitors, cyclic peptides, depsipeptides, engineered natural inhibitors, antibodies, RNA/DNA-based aptamers, prodrugs, miRNA and siRNA. Expert opinion: In light of the results from clinical and tumor-biological studies, together with the available pharmaceutical tools, we suggest KLK4, KLK5, KLK6 and possibly KLK7 as preferred targets for inhibition in 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.

Clinical relevance of kallikrein-related peptidase 6 (KLK6) and 8 (KLK8) mRNA expression in advanced serous ovarian cancer

Most members of the kallikrein-related peptidase family have been demonstrated to be dysregulated in ovarian cancer and modulate tumor growth, migration, invasion, and resistance to chemotherapy. In the present study, we assessed the mRNA expression levels of KLK6 and KLK8 by quantitative PCR in 100 patients with advanced serous ovarian cancer FIGO stage III/IV. A pronounced correlation between KLK6 and KLK8 mRNA expression (rs = 0.636, p < 0.001) was observed, indicating coordinate expression of both peptidases. No significant associations of clinical parameters with KLK6, KLK8, and a combined score KLK6+KLK8 were found. In univariate Cox regression analysis, elevated mRNA levels of KLK6 were significantly linked with shortened overall survival (OS) (hazard ratio [HR] = 2.07, p = 0.007). While KLK8 values were not associated with patients' outcome, high KLK6+KLK8 values were significantly associated with shorter progression-free survival (HR = 1.82, p = 0.047) and showed a trend towards significance in the case of OS (HR = 1.82, p = 0.053). Strikingly, in multivariable analysis, elevated KLK6 mRNA values, apart from residual tumor mass, remained an independent predictive marker for poor OS (HR = 2.33, p = 0.005). As KLK6 mRNA and protein levels correlate, KLK6 may represent an attractive therapeutic target for potent and specific inhibitors of its enzymatic activity.

Epigenetic remodeling regulates transcriptional changes between ovarian cancer and benign precursors

Regulation of lineage-restricted transcription factors has been shown to influence malignant transformation in several types of cancer. Whether similar mechanisms are involved in ovarian cancer pathogenesis is unknown. PAX8 is a nuclear transcription factor that controls the embryologic development of the Müllerian system, including the fallopian tubes. Recent studies have shown that fallopian tube secretory epithelial cells (FTSECs) give rise to the most common form of ovarian cancer, high-grade serous ovarian carcinomas (HGSOCs). We designed the present study in order to understand whether changes in gene expression between FTSECs and HGSOCs relate to alterations in PAX8 binding to chromatin. Using whole transcriptome shotgun sequencing (RNA-Seq) after PAX8 knockdown and ChIP-Seq, we show that FTSECs and HGSOCs are distinguished by marked reprogramming of the PAX8 cistrome. Genes that are significantly altered between FTSECs and HGSOCs are enriched near PAX8 binding sites. These sites are also near TEAD binding sites, and these transcriptional changes may be related to PAX8 interactions with the TEAD/YAP1 signaling pathway. These data suggest that transcriptional changes after transformation in ovarian cancer are closely related to epigenetic remodeling in lineage-specific transcription factors.

Development of Monoclonal Antibodies and Characterization of an ELISA Platform Against Kallikrein-Related Peptidase 6 as a Tumor Biomarker

Kallikrein-related peptidase 6 (KLK6) is a serine protease, and one of fifteen kallikrein members located on chromosome 19. KLK6 is associated with the regulation of axonal growth following spinal injury, tumor cell metastasis, and alpha synuclein aggregate pathologies like Parkinson's, making KLK6 a potentially important biomarker. We generated a KLK6 expression vector for large-scale expression in Escherichia coli. After affinity chromatography purification and SDS-PAGE confirmation, mice were immunized with the purified protein for development of monoclonal B cell populations. Our immunizations generated five hybridomas (1D8, 2E3, 3B7, 5G8, and 5H12) against KLK6. Isotyping analysis revealed that clone 2E3 was IgG2b, while the other four clones were IgG1. Further studies found that clone 5G8 could be used to visualize specific KLK6 bands by Western blot analysis from ovarian cancer patient serum and plasma, and also in mouse liver lysates. Finally, we established a sandwich ELISA pair and determined their sensitivity for KLK6 to be 10 ng/mL. These findings establish an essential tool for the detection and analysis of KLK6.

Involvement of Kallikrein-Related Peptidases in Normal and Pathologic Processes

Human kallikrein-related peptidases (KLKs) are a subgroup of serine proteases that participate in proteolytic pathways and control protein levels in normal physiology as well as in several pathological conditions. Their complex network of stimulatory and inhibitory interactions may induce inflammatory and immune responses and contribute to the neoplastic phenotype through the regulation of several cellular processes, such as proliferation, survival, migration, and invasion. This family of proteases, which includes one of the most useful cancer biomarkers, kallikrein-related peptidase 3 or PSA, also has a protective effect against cancer promoting apoptosis or counteracting angiogenesis and cell proliferation. Therefore, they represent attractive therapeutic targets and may have important applications in clinical oncology. Despite being intensively studied, many gaps in our knowledge on several molecular aspects of KLK functions still exist. This review aims to summarize recent data on their involvement in different processes related to health and disease, in particular those directly or indirectly linked to the neoplastic process.

The kallikrein-related peptidase family: Dysregulation and functions during cancer progression

Cancer is the second leading cause of death with 14 million new cases and 8.2 million cancer-related deaths worldwide in 2012. Despite the progress made in cancer therapies, neoplastic diseases are still a major therapeutic challenge notably because of intra- and inter-malignant tumour heterogeneity and adaptation/escape of malignant cells to/from treatment. New targeted therapies need to be developed to improve our medical arsenal and counter-act cancer progression. Human kallikrein-related peptidases (KLKs) are secreted serine peptidases which are aberrantly expressed in many cancers and have great potential in developing targeted therapies. The potential of KLKs as cancer biomarkers is well established since the demonstration of the association between KLK3/PSA (prostate specific antigen) levels and prostate cancer progression. In addition, a constantly increasing number of in vitro and in vivo studies demonstrate the functional involvement of KLKs in cancer-related processes. These peptidases are now considered key players in the regulation of cancer cell growth, migration, invasion, chemo-resistance, and importantly, in mediating interactions between cancer cells and other cell populations found in the tumour microenvironment to facilitate cancer progression. These functional roles of KLKs in a cancer context further highlight their potential in designing new anti-cancer approaches. In this review, we comprehensively review the biochemical features of KLKs, their functional roles in carcinogenesis, followed by the latest developments and the successful utility of KLK-based therapeutics in counteracting cancer progression.

The diagnostic and prognostic value of serum human kallikrein-related peptidases 11 in non-small cell lung cancer

The aim of this study was to explore the diagnostic and prognostic value of serum human kallikrein-related peptidases 11 (KLK11) level in non-small cell lung cancer (NSCLC). Serum specimens from 138 patients with NSCLC and 40 healthy controls were collected. The concentration of KLK11 was measured by enzyme-linked immunosorbent assay (ELISA). The concentration of KLK11 in NSCLC was significantly higher compared to that in the controls (P<0.01). The serum KLK11 levels decreased with stage, presence of lymph node, and distant metastases, regardless of histology, age, and sex. With a cutoff point of 1.05 ng/ml, KLK11 showed a good diagnostic performance for NSCLC. Univariate analysis revealed that NSCLC patients with serum high KLK11 had a longer overall survival (OS) and progression-free survival (PFS) than those with low KLK11 (HR of 0.36, P=0.002; HR of 0.46, P=0.009). Cox multivariate analysis indicated that KLK11 was an independent prognostic indicator of PFS and OS (HR of 0.53, P=0.042; HR of 0.48, P=0.037). Kaplan-Meier survival curves further confirmed that patients with high KLK11 have longer PFS and OS (P=0.003 and P=0.018, respectively). In conclusion, the measurement of KLK11 might be a useful diagnostic and prognostic test for NSCLC patients.

Optimizing molecular-targeted therapies in ovarian cancer: the renewed surge of interest in ovarian cancer biomarkers and cell signaling pathways

The hallmarks of ovarian cancer encompass the development of resistance, disease recurrence and poor prognosis. Ovarian cancer cells express gene signatures which pose significant challenges for cancer drug development, therapeutics, prevention and management. Despite enhancements in contemporary tumor debulking surgery, tentative combination regimens and abdominal radiation which can achieve beneficial response rates, the majority of ovarian cancer patients not only experience adverse effects, but also eventually relapse. Therefore, additional therapeutic possibilities need to be explored to minimize adverse events and prolong progression-free and overall response rates in ovarian cancer patients. Currently, a revival in cancer drug discovery is devoted to identifying diagnostic and prognostic ovarian cancer biomarkers. However, the sensitivity and reliability of such biomarkers may be complicated by mutations in the BRCA1 or BRCA2 genes, diverse genetic risk factors, unidentified initiation and progression elements, molecular tumor heterogeneity and disease staging. There is thus a dire need to expand existing ovarian cancer therapies with broad-spectrum and individualized molecular targeted approaches. The aim of this review is to profile recent developments in our understanding of the interrelationships among selected ovarian tumor biomarkers, heterogeneous expression signatures and related molecular signal transduction pathways, and their translation into more efficacious targeted treatment rationales.

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.

Alternative splicing variant of kallikrein-related peptidase 8 as an independent predictor of unfavorable prognosis in lung cancer

BACKGROUND

A relatively unexplored area for biomarker identification is alternative splice variants. We undertook this study to evaluate the usefulness of mRNA isoforms encoded by the KLK8 (kallikrein-related peptidase 8) gene as prognostic markers for lung cancer.

METHODS

Real-time reverse-transcription PCR was used to analyze the mRNAs encoded by KLK8 (particularly 2 mRNA splice variants, KLK8-T3 and KLK8-T4) in 60 non-small-cell lung cancer (NSCLC) tumors and in paired unaffected tissues. The ratios of these mRNAs to those encoded by the KLK5, KLK6, KLK7, KLK10, KLK11, KLK13, and KLK14 genes were also determined and analyzed for correlations with various clinicopathologic variables.

RESULTS

KLK8-T3 and KLK8-T4 were the most abundant of the 6 mRNA isoforms identified in lung tissues. The overall expression of the KLK8 gene and the amounts of the KLK8-T3 and KLK8-T4 mRNAs were significantly increased in lung tumor tissue (P < 0.0001). Univariate survival analysis revealed significant relationships of the relative concentrations of mRNA splice variants KLK8 (P = 0.043), KLK8-T3 (P = 0.037), and KLK8-T4 (P = 0.009) with overall survival (OS). Cox multivariate analysis indicated that the amount of KLK8-T4 mRNA was an independent prognostic factor for OS (relative risk = 3.90; P = 0.016) and that high KLK8-T4/KLK7, KLK8-T4/KLK10, and KLK8-T4/KLK11 mRNA ratios in NSCLC indicated increased risk of death. The increase was approximately 5-fold for the KLK8-T4/KLK7 and KLK8-T4/KLK10 ratios (P = 0.006, and P = 0.011, respectively) and 8-fold for the KLK8-T4/KLK11 ratio (P = 0.001).

CONCLUSIONS

The KLK8-T4 alternative splice variant, alone or in combination, may be a new independent marker of unfavorable prognosis in lung cancer.

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.