Methylation of cystatin M promoter is associated with unfavorable prognosis in operable breast cancer

The methylation status of cystatin M (CST6) gene in breast tumors was investigated and its prognostic significance as a novel breast cancer biomarker was evaluated. Using methylation-specific PCR (MSP), CST6 promoter methylation was examined in 134 formalin fixed paraffin-embedded tissues (FFPEs): 10 pairs of breast tumors and their surrounding normal tissues, 10 breast fibroadenomas, 11 normal breast tissues and 93 breast tumors. Methylation of CST6 promoter was observed in 2/21 (9.5%) noncancerous breast tissues, 1/10 (10%) benign breast tumors (fibroadenomas) and 52 (55.9%) operable breast cancer tumor samples. CST6 was rarely methylated in the normal tissue surrounding the tumor (10%). During the follow-up period, 24 (25.8%) patients relapsed and 19 (20.4%) died. CST6 methylation was detected in 19 (79.2%) of patients who relapsed and in 15 (78.9%) of patients who died. Disease-free-interval (DFI) and overall survival (OS) were significantly associated with CST6 promoter methylation (p=0.004 and p=0.001 respectively). Multivariate analysis revealed that CST6 methylation is an independent prognostic factor for DFI (HR=3.484; 95% CI: 1.155-10.511; p=0.027). and OS (HR=9.190; 95% CI: 1.989-42.454; p=0.004). CST6 promoter methylation status in tumor cells seems to provide important prognostic information in operable breast cancer and merits to be further evaluated and validated in a larger cohort of patients.

Functional roles of human kallikrein-related peptidases

Kallikrein-related peptidases constitute a single family of 15 (chymo)trypsin-like proteases (KLK1-15) with pleiotropic physiological roles. Aberrant regulation of KLKs has been associated with diverse diseases such as hypertension, renal dysfunction, skin disorders, inflammation, neurodegeneration, and cancer. Recent studies suggested that coordinated activation and regulation of KLK activity are achieved via a complex network of interactions referred to as the "KLK activome." However, it remains to be validated whether these hypothetical KLK activation cascade pathways are operative in vivo. In addition, KLKs have emerged as versatile signaling molecules. In summary, KLKs represent attractive biomarkers for clinical applications and potential therapeutic targets for common human pathologies.

Down-regulation of dicer expression in ovarian cancer tissues

OBJECTIVES

Although numerous recent studies have focused on analyses of microRNA expression profiles in cancer cells, the expression patterns of the enzymes responsible for the generation of miRNAs remains largely unexplored. The purpose of this study was to investigate whether Dicer mRNA expression is altered during progression of ovarian cancer.

DESIGN AND METHODS

Total RNA was extracted from ovarian tissue specimens (normal, benign and malignant tumors). The expression of Dicer was analyzed by semi-quantitative RT-PCR.

RESULTS

We analyzed a total of 34 ovarian tissue samples and found that Dicer mRNA expression is down-regulated in the majority of ovarian tumors when compared to normal tissues.

CONCLUSIONS

Our results suggest that the levels of Dicer mRNA should be evaluated as a potential new candidate biomarker for ovarian cancer.

Emerging roles of microRNAs as molecular switches in the integrated circuit of the cancer cell

Transformation of normal cells into malignant tumors requires the acquisition of six hallmark traits, e.g., self-sufficiency in growth signals, insensitivity to antigrowth signals and self-renewal, evasion of apoptosis, limitless replication potential, angiogenesis, invasion, and metastasis, which are common to all cancers (Hanahan and Weinberg 2000). These new cellular traits evolve from defects in major regulatory microcircuits that are fundamental for normal homeostasis. The discovery of microRNAs (miRNAs) as a new class of small non-protein-coding RNAs that control gene expression post-transcriptionally by binding to various mRNA targets suggests that these tiny RNA molecules likely act as molecular switches in the extensive regulatory web that involves thousands of transcripts. Most importantly, accumulating evidence suggests that numerous microRNAs are aberrantly expressed in human cancers. In this review, we discuss the emergent roles of microRNAs as switches that function to turn on/off known cellular microcircuits. We outline recent compelling evidence that deregulated microRNA-mediated control of cellular microcircuits cooperates with other well-established regulatory mechanisms to confer the hallmark traits of the cancer cell. Furthermore, these exciting insights into aberrant microRNA control in cancer-associated circuits may be exploited for cancer therapies that will target deregulated miRNA switches.

Novel splice variants of prostate-specific antigen and applications in diagnosis of prostate cancer

OBJECTIVES

We aimed to identify novel splice variants of prostate-specific antigen/or human kallikrein 3 (PSA/KLK3), the most widely used serum biomarker for case-finding, screening and monitoring of prostate cancer.

DESIGN AND METHODS

The full-length sequences of splice variants were assembled as contigs from human ESTs that displayed homology to the cDNA sequence encoding PSA. Expression of variants in clinical samples was analyzed by semi-quantitative RT-PCR.

RESULTS

EST database mining led to the identification of seven previously unidentified splice variants encoding PSA-like proteins that are predicted to contain epitope sequences recognized by PSA-specific antibodies, therefore, expression of these isoforms may affect the amount of total PSA measured by established immunoassays. Analysis of the differential expression profile of isoform PSA-SV5 in patients with benign prostate hyperplasia and prostate cancer showed that it is specifically expressed in prostate cancers.

CONCLUSIONS

A novel splice variant of PSA was identified, PSA-SV5, that may be exploited in clinical diagnosis to distinguish prostate cancer from benign prostate hyperplasia.

Tissue kallikrein proteolytic cascade pathways in normal physiology and cancer

Human tissue kallikreins (KLKs or kallikrein-related peptidases) are a subgroup of extracellular serine proteases that act on a wide variety of physiological substrates, while they display aberrant expression patterns in certain types of cancer. Differential expression patterns lead to the exploitation of these proteins as new cancer biomarkers for hormone-dependent malignancies, in particular. The prostate-specific antigen or kallikrein-related peptidase 3 (PSA/KLK3) is an established tumor marker for the diagnosis and monitoring of prostate cancer. It is well documented that specific KLK genes are co-expressed in tissues and in various pathologies suggesting their participation in complex proteolytic cascades. Here, we review the currently established knowledge on the involvement of KLK proteolytic cascades in the regulation of physiological and pathological processes in prostate tissue and in skin. It is well established that the activity of KLKs is often regulated by auto-activation and subsequent autolytic internal cleavage leading to enzymatic inactivation, as well as by inhibitory serpins or by allosteric inhibition by zinc ions. Redistribution of zinc ions and alterations in their concentration due to physiological or pathological reasons activates specific KLKs initiating the kallikrein cascade(s). Recent studies on kallikrein substrate specificity allowed for the construction of a kallikrein interaction network involved in semen liquefaction and prostate cancer, as well as in skin pathologies, such as skin desquamation, psoriasis and cancer. Furthermore, we discuss the crosstalks between known proteolytic pathways and the kallikrein cascades, with emphasis on the activation of plasmin and its implications in prostate cancer. These findings may have clinical implications for the underlying molecular mechanism and management of cancer and other disorders in which KLK activity is elevated.

Development of an immunofluorometric assay for human kallikrein 15 (KLK15) and identification of KLK15 in tissues and biological fluids

BACKGROUND

Human kallikrein 15 (KLK15) may have some utility as a prostate, ovarian, and breast cancer biomarker, based on previous studies, which examined mRNA levels of KLK15. The aim of this study was to develop analytical technology for human kallikrein 15, including recombinant protein, specific antibodies, and a sensitive and specific ELISA immunoassay. The assay was then used to examine levels of KLK15 in tissues and biological fluids.

METHODS

We produced human, recombinant pro-KLK15 in HEK 293 cells. Recombinant KLK15 was purified with various chromatographic steps and used to immunize rabbits and mice for production of KLK15 polyclonal antibodies. We used these antibodies to develop a highly sensitive and specific KLK15 immunoassay and to study KLK15 expression in various tissues and biological fluids.

RESULTS

Large amounts of pure, recombinant KLK15 have been produced and characterized. KLK15 mouse and rabbit polyclonal antibodies have been employed for development of a KLK15 immunoassay. This assay has a lower detection limit of 0.05 microg/L, and no cross-reactivity with any of the other fourteen kallikreins. Using this assay, KLK15 was detected in prostate, colon, and thyroid tissues, as well as in breast milk and seminal plasma.

CONCLUSIONS

The KLK15 reagents developed here will allow for analysis of KLK15 protein expression levels in tissues and biological fluids, both normal and cancerous. This will expand upon previously characterized tissue KLK15 mRNA expression studies which suggested that KLK15 might be useful as a biomarker for breast, ovarian, and prostate cancer. KLK15 is another serine protease that is produced in prostate and other tissues and is secreted in seminal plasma and other fluids. Its physiological function needs to be further elucidated.

A potential role for multiple tissue kallikrein serine proteases in epidermal desquamation

Desquamation of the stratum corneum is a serine protease-dependent process. Two members of the human tissue kallikrein (KLK) family of (chymo)tryptic-like serine proteases, KLK5 and KLK7, are implicated in desquamation by digestion of (corneo)desmosomes and inhibition by desquamation-related serine protease inhibitors (SPIs). However, the epidermal localization and specificity of additional KLKs also supports a role for these enzymes in desquamation. This study aims to delineate the probable contribution of KLK1, KLK5, KLK6, KLK13, and KLK14 to desquamation by examining their interactions, in vitro, with: 1) colocalized SPI, lympho-epithelial Kazal-type-related inhibitor (LEKTI, four recombinant fragments containing inhibitory domains 1-6 (rLEKTI(1-6)), domains 6-8 and partial domain 9 (rLEKTI(6-9')), domains 9-12 (rLEKTI(9-12)), and domains 12-15 (rLEKTI(12-15)), secretory leukocyte protease inhibitor, and elafin and 2) their ability to digest the (corneo)desmosomal cadherin, desmoglein 1. KLK1 was not inhibited by any SPI tested. KLK5, KLK6, KLK13, and KLK14 were potently inhibited by rLEKTI(1-6), rLEKTI(6-9'), and rLEKTI(9-12) with Ki values in the range of 2.3-28.4 nm, 6.1-221 nm, and 2.7-416 nm for each respective fragment. Only KLK5 was inhibited by rLEKTI(12-15) (Ki = 21.8 nm). No KLK was inhibited by secretory leukocyte protease inhibitor or elafin. Apart from KLK13, all KLKs digested the ectodomain of desmoglein 1 within cadherin repeats, Ca2+ binding sites, or in the juxtamembrane region. Our study indicates that multiple KLKs may participate in desquamation through cleavage of desmoglein 1 and regulation by LEKTI. These findings may have clinical implications for the treatment of skin disorders in which KLK activity is elevated.

Evaluation of ER, PR, MIB-1, pS2, and nuclear grade in FNA specimens of cT1 breast carcinomas: clinicopathological correlation

Objectives were to determine oestrogen (ER), progesterone receptors (PR), and antigen related to ER (pS2) and to characterize their relationship with the cellular proliferation marker MIB-1 and the nuclear grade (NG) of the cancer cells, using fine-needle aspirates (FNA), as well as the evaluation of their clinical usefulness. The expression of ER, PR, pS2, and MIB-1 was preoperatively detected by immunocytochemistry in FNAs of 70 patients with breast adenocarcinoma and clinical tumor size up to 2 cm. The NG of the tumor cells was also assessed in these samples. We analyzed whether there was any correlation between these biocytologic markers and the invasion of ipsillateral axillary lymph nodes (LN), which were histologically identified after standard surgical treatment in each case. Of the 70 patients 50, 42.85, 50, and 41.42% were positive for ER, PR, pS2, and MIB-1, respectively. Only NG alone was strongly related to the invasion of the LN (P < 0.001). All the patients with NG1 (100%) tumors presented free LN, whereas the majority of those with NG3 (72.72%) had invaded LN (P < 0.001). Patients (14.28%) with NG1 expressed MIB-1, 85.71% ER or PR, and 71.42% pS2. Among the MIB-1-positive tumors a high proportion of NG3 (65.51%) was observed. This finding underlined a relationship between MIB-1 and NG (P < 0.05), identifying an aggressive cancer type. Remarkably 93.33% of the patients with positive MIB-1 and invaded axilla had NG3, whereas 66.66% of them expressed ER or PR and 40% pS2. The findings of the present prospective, multivariate study indicate that NG of the tumor cells, obtained from the preoperative FNAs of breast cancer patients, is a strong predictive marker for the axillary status and in parallel with MIB-1 expression can with sufficient accuracy be of clinical utility. ER, PR, or pS2 on the other hand did not show any relation to the LN status and were not dependent to NG or MIB-1.

The epigenetic basis for the aberrant expression of kallikreins in human cancers

The tissue kallikrein gene family consists of 15 genes tandemly arranged on human chromosome 19q13.4. Most kallikrein genes are characterized by aberrant expression patterns in various human cancers, a feature that makes them ideal cancer biomarkers. In the present study, we investigated the effect of the epigenetic drug compound 5-aza-2'-deoxycytidine on the expression of downregulated kallikrein genes in prostate, breast, and ovarian cancer cell lines. Reactivation of multiple kallikrein genes was observed, although some of these genes do not contain CpG islands in their genomic sequence. Epigenetic regulation provides a new mechanism for the pharmacological modulation of kallikreins in human cancers with putative therapeutic implications.

Preoperative prediction of the axillary lymph nodes status in patients with breast cancer

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Background: We developed a preoperative score-system (S) and evaluated prospectively its predictive value for the axillary(a) status of patients (p) with breast cancer. Our aim was to select preoperatively (p) with negative axilla, who could possibly avoid the standard (a) surgery. (S) uses preoperative clinical, epidemiological and immunocytological data, obtained from the FNA-smears of (p)‘ tumors, and attempts to guide the choice of (a) treatment, as an alternative to the method of sentinel lymph node. Methods: (S) is calculated by adding the preoperative values of clinical tumor size, (p) age, nuclear grade (NG), type of the cancer cells and the immunocytochemical positiveness of the biomarkers p53, HER2 and MIB1. Values range from 1–4 for size (1–10, 11–15, 16–20, 20–30 mm), 1 to 4 for age (70 and over, 51–69, 41–50, 40 years or less), 1–3 for NG1–3, 1–2 for type of cancer cells (lobular, ductal) respectively and 0–3 for the expression (1 point for every positive biomarker) or absence (0) of p53, HER2 and MIB1 in the FNA of the primary tumors of the (p). (S) ranges from 4 to 16.We applied (S) to 224 (p), with clinically negative axilla. These (p) underwent modified radical mastectomy or lumpectomy and standard (a) dissection level I and II. The number of the infiltrated nodes was identified in each case. Results: (S) of 4 - 8 (57 patients, group 1) identify (p) with free nodes ( node positive rate 0%). (S) of 9 and 10 (67 patients, group 2) carry an average node positive rate of 65,67%, of which 31,34% involves the invasion of 1 node, 23,88% of 2–3 and 10,44% of 4 or more nodes (P < 0.001, group 1 versus group 2). (S) of 11 and more (100 patients, group 3) identify (p) with an average node positive rate of 83%, of which 55% involves the invasion of 4 or more nodes (P < 0.001, group 3 versus group 1). (S) allows the separation of (p) into two (a) management groups. Group 1 are those (p), who possibly have free lymph nodes and therefore may need no (a) surgery at all, whereas group 2 and 3 may be considered for standard (a) dissection, because they present with increased possibility infiltrated nodes. Conclusion: (S) was studied to aid the selection of (p) towards reasonable (a) treatment choices for the benefit of (p). (S) might serve as a guideline in the clinical practice to reduce the postoperative morbidity of the breast cancer (p).

No significant financial relationships to disclose.

Human tissue kallikrein 5 is a member of a proteolytic cascade pathway involved in seminal clot liquefaction and potentially in prostate cancer progression

Human tissue kallikreins (hKs) are a family of fifteen serine proteases. Several lines of evidence suggest that hKs participate in proteolytic cascade pathways. Human kallikrein 5 (hK5) has trypsin-like activity, is able to self-activate, and is co-expressed in various tissues with other hKs. In this study, we examined the ability of hK5 to activate other hKs. By using synthetic heptapeptides that encompass the activation site of each kallikrein and recombinant pro-hKs, we demonstrated that hK5 is able to activate pro-hK2 and pro-hK3. We then showed that, following their activation, hK5 can internally cleave and deactivate hK2 and hK3. Given the predominant expression of hK2 and hK3 in the prostate, we examined the pathophysiological role of hK5 in this tissue. We studied the regulation of hK5 activity by cations (Zn2+, Ca2+, Mg2+, Na2+, and K+) and citrate and showed that Zn can efficiently inhibit hK5 activity at levels well below its normal concentration in the prostate. We also show that hK5 can degrade semenogelins I and II, the major components of the seminal clot. Semenogelins can reverse the inhibition of hK5 by Zn2+, providing a novel regulatory mechanism of its serine protease activity. hK5 is also able to internally cleave insulin-like growth factor-binding proteins 1, 2, 3, 4, and 5, but not 6, suggesting that it might be involved in prostate cancer progression through growth factor regulation. Our results uncover a kallikrein proteolytic cascade pathway in the prostate that participates in seminal clot liquefaction and probably in prostate cancer progression.

Multiple mechanisms underlie the aberrant expression of the human kallikrein 6 gene in breast cancer

Human kallikrein 6 (KLK6) was identified based on its transient upregulation in a primary breast tumor and its subsequent silencing in a metastatic tumor from the same patient. The molecular mechanism(s) underlying the deregulated expression of KLK6 during cancer progression are currently unknown. Here, we provide evidence that aberrant expression of KLK6 is regulated at the level of transcription by multiple cooperating mechanisms. KLK6 can be reactivated in non-expressing breast cancer cells by treatment with 5-aza-2'-deoxycytidine (5-aza-dC), a compound causing DNA demethylation. Trichostatin A (TSA), an inhibitor of histone deacetylases, resulted in moderate induction of KLK6 only in MDA-MB-231 cells. However, combined 5-aza-dC/TSA treatment resulted in synergistic activation of KLK6. We show that KLK6 inactivation is associated with hypermethylation of specific CpG dinucleotides located in the KLK6 proximal promoter and overexpression with complete demethylation. These results indicate a causal role of DNA methylation and chromatin structure in cancer-associated loss of KLK6 expression. In some breast cancer cell lines, KLK6 expression could be restored by the vitamin D3 analog EB1089. Our data indicate that transcriptional deregulation of KLK6 in cancer cells during breast cancer progression is complex and certainly not uniform in different tumors, involving epigenetic mechanisms as well as pathways regulated by nuclear receptors. This allows for the pharmacological modulation of KLK6 with potential therapeutic implications.

A comprehensive nomenclature for serine proteases with homology to tissue kallikreins

The human kallikrein locus on chromosome 19q13.3-13.4 contains kallikrein 1--the tissue kallikrein--and 14 related serine proteases. Recent investigations into their function and evolution have indicated that the present nomenclature for these proteins is inadequate or insufficient. Here we present a new nomenclature in which proteins without proven kininogenase activity are denoted kallikrein-related peptidase. Names are also given to the unique rodent proteins that are closely related to kallikrein 1.

Downregulation of human kallikrein 10 (KLK10/NES1) by CpG island hypermethylation in breast, ovarian and prostate cancers

OBJECTIVE

The human kallikrein 10 (KLK10)/normal epithelial cell-specific-1 (NES1) gene is highly expressed in normal mammary, ovary and prostate cells, but its expression is dramatically decreased in cancer cell lines. Recently, it has been shown that CpG island hypermethylation of the KLK10 gene is responsible for the tumor-specific loss of KLK10 gene expression in certain breast cancer cell lines.

METHOD

We examined the role of CpG island hypermethylation in the tumor-specific loss of KLK10 expression in breast, ovarian and prostate cancers. We treated cells with the demethylating agent 5-aza-2'-deoxycytidine (dC) and monitored changes in KLK10 mRNA by RT-PCR and secreted hK10 protein expression by ELISA. The following cell lines were used: MDA-MB-231, MDA-MB-468, MCF-7, ZR-75-1, T-47D and BT-474 (breast); BG-1, MDAH-2774, HTB-75, HTB-161, PA-1 and ES-2 (ovary), and LNCaP and PC-3 (prostate).

RESULTS

Upregulation of KLK10 mRNA levels, which was accompanied by an increase in secreted hK10 protein concentration, was observed for a subset of breast, ovarian, and prostate tumor cell lines after 5-aza-2'-dC. Genomic sequencing of sodium-bisulfite-treated DNA demonstrated that CpG sites within the KLK10 gene exon 3 were highly methylated. Hypermethylation of exon 3 CpG regions was also detected in primary ovarian cancers.

CONCLUSION

These data suggest that CpG island hypermethylation plays an important role in the downregulation of kallikrein 10 mRNA and protein expression, but it cannot explain the pattern of expression of this gene in all cell lines or tissue tested.

Human kallikrein 4: quantitative study in tissues and evidence for its secretion into biological fluids

BACKGROUND

Human kallikrein 4 (hK4) is a proteolytic enzyme belonging to the tissue kallikrein family of serine proteases. Previous tissue expression studies have demonstrated highest KLK4 mRNA expression in prostatic tissue, but there has been only limited evidence for the presence of hK4 protein in prostate and other tissues and in corresponding biological secretions.

METHODS

To investigate the concentrations of hK4 in tissues and biological fluids, we developed a new hK4-specific sandwich-type immunoassay using a monoclonal antibody as the capture reagent.

RESULTS

The assay has a detection limit of 0.02 microg/L and <0.1% cross-reactivity toward any of the other 14 human kallikreins. Twelve of 40 tissue extracts prepared from various human tissues contained detectable hK4 concentrations (0.68-7143 ng/g of total protein), with healthy prostate tissue containing the highest amount of hK4. Examination of 16 malignant and 18 benign prostate tissues revealed no significant differences in hK4 protein content, and the tissues contained a wide range of values (benign, <0.02 to 801 ng/g; malignant, <0.02 to 824 ng/g). Among the biological fluids tested, seminal plasma and urine contained widely varying amounts of hK4; concentrations in 54 urine samples were <0.02 to 2.6 microg/L, whereas concentrations in 58 seminal plasma samples were 0.2-202 microg/L. Affinity purification of hK4 from seminal plasma and subsequent mass spectrometry demonstrated the secreted nature of hK4 in seminal plasma.

CONCLUSIONS

hK4 is found primarily in prostate tissue and is secreted in seminal plasma. Its value as a novel prostatic biomarker needs to be defined further.

Human kallikrein 6 degrades extracellular matrix proteins and may enhance the metastatic potential of tumour cells

Human kallikrein 6 (hK6), a trypsin-like serine protease, is a newly identified member of the kallikrein gene family. Its involvement in inflammatory CNS lesions and in demyelination has been reported. Recent work has suggested that expression of this enzyme is significantly elevated in patients with ovarian cancer. We have identified many tumour cell lines that secrete hK6, but its physiological role is unknown. Here, we try to unveil the role of this kallikrein in the metastasis and invasion of tumour cells. We demonstrate that purified human recombinant hK6 can cleave gelatin in zymography and can efficiently degrade high-molecular-weight extracellular matrix proteins such as fibronectin, laminin, vitronectin and collagen. In Boyden chamber assays, we found that tumour cells treated with a neutralizing hK6 antibody migrate less than control cells. We conclude that hK6 might play a role in the invasion and metastasis of tumour cells and may be a candidate therapeutic target.

Biochemical and enzymatic characterization of human kallikrein 5 (hK5), a novel serine protease potentially involved in cancer progression

Human kallikrein 5 (KLK5) is a member of the human kallikrein gene family of serine proteases. Preliminary results indicate that the protein, hK5, may be a potential serological marker for breast and ovarian cancer. Other studies implicate hK5 with skin desquamation and skin diseases. To gain further insights on hK5 physiological functions, we studied its substrate specificity, the regulation of its activity by various inhibitors, and identified candidate physiological substrates. After producing and purifying recombinant hK5 in yeast, we determined the k(cat)/K(m) ratio of the fluorogenic substrates Gly-Pro-Arg-AMC and Gly-Pro-Lys-AMC, and showed that it has trypsin-like activity with strong preference for Arg over Lys in the P1 position. The serpins alpha(2)-antiplasmin and antithrombin were able to inhibit hK5 with an inhibition constant (k(+2)/K(i)) of 1.0 x 10(-) (2)and 4.2 x 10(-4) m(-1) min(-1), respectively. No inhibition was observed with the serpins alpha(1)-antitrypsin and alpha(1)-antichymotrypsin, although alpha(2)-macroglobulin partially inhibited hK5 at high concentrations. We also demonstrated that hK5 can efficiently digest the extracellular matrix components, collagens type I, II, III, and IV, fibronectin, and laminin. Furthermore, our results suggest that hK5 can potentially release (a) angiostatin 4.5 from plasminogen, (b) "cystatin-like domain 3" from low molecular weight kininogen, and (c) fibrinopeptide B and peptide beta15-42 from the Bbeta chain of fibrinogen. hK5 could also play a role in the regulation of the binding of plasminogen activator inhibitor 1 to vitronectin. Our findings suggest that hK5 may be implicated in tumor progression, particularly in invasion and angiogenesis, and may represent a novel therapeutic target.

Cloning and characterization of novel isoforms of the human kallikrein 6 gene

Human kallikrein 6 (protease M/zyme/neurosin) was originally identified based on its aberrant expression in tumor cells and is considered a biomarker for ovarian cancer. Here, we describe the identification, cloning, and tissue expression of three novel transcript variants of the KLK6 gene that encode for wild-type kallikrein 6. Contrary to the classical form, transcript variants contain one untranslated exon, exploit intronic sequences, and are likely products of alternative promoters. In addition, we cloned splice variants 2 and 3 produced by splicing out exons 3 and 4, respectively. Given the potential diagnostic applications of kallikrein 6 at both the mRNA and protein levels, we developed a duplex RT-PCR, in order to differentially detect and quantitate mRNA species corresponding to splice variants. We show that in normal mammary epithelial cells and mammary tumor cell lines that overexpress the KLK6 gene, splice variants account for approximately 10-20% of all mRNA species.