Molecular cloning and expression of a variant form of hippostasin/KLK11 in prostate

Surface loops of trypsin-like serine proteases as determinants of function

Trypsin and chymotrypsin-like serine proteases from family S1 (clan PA) constitute the largest protease group in humans and more generally in vertebrates. The prototypes chymotrypsin, trypsin and elastase represent simple digestive proteases in the gut, where they cleave nearly any protein. Multidomain trypsin-like proteases are key players in the tightly controlled blood coagulation and complement systems, as well as related proteases that are secreted from diverse immune cells. Some serine proteases are expressed in nearly all tissues and fluids of the human body, such as the human kallikreins and kallikrein-related peptidases with specialization for often unique substrates and accurate timing of activity. HtrA and membrane-anchored serine proteases fulfill important physiological tasks with emerging roles in cancer. The high diversity of all family members, which share the tandem β-barrel architecture of the chymotrypsin-fold in the catalytic domain, is conferred by the large differences of eight surface loops, surrounding the active site. The length of these loops alters with insertions and deletions, resulting in remarkably different three-dimensional arrangements. In addition, metal binding sites for Na+, Ca2+ and Zn2+ serve as regulatory elements, as do N-glycosylation sites. Depending on the individual tasks of the protease, the surface loops determine substrate specificity, control the turnover and allow regulation of activation, activity and degradation by other proteins, which are often serine proteases themselves. Most intriguingly, in some serine proteases, the surface loops interact as allosteric network, partially tuned by protein co-factors. Knowledge of these subtle and complicated molecular motions may allow nowadays for new and specific pharmaceutical or medical approaches.

Knockdown of KLK11 inhibits cell proliferation and increases oxaliplatin sensitivity in human colorectal cancer

It has been reported that kallikrein 11 (KLK11) is crucially involved in the development and progression of various types of cancer. However, the molecular mechanisms that underlie the involvement of KLK11 in aberrant colorectal cancer (CRC) cell growth remain largely unclear. The aim of the present study was to investigate the role of KLK11 and the effects of KLK11 on oxaliplatin (L-OHP) chemosensitivity by knocking down KLK11 in LOVO and HCT-8 cells. Loss-of-function assays revealed KLK11 inhibition significantly inhibited growth and induced apoptosis of CRC cells in vitro. Notably, further experiments found that knockdown of KLK11 expression increased the L-OHP chemosensitivity of CRC cells. KLK11 inhibition of increased L-OHP-induced apoptosis may be associated with activation of caspase-3 cleavage and the apoptosis signaling pathway. The present results indicated that KLK11 may be an potential target of interest for future research into therapies for CRC.

Emerging PSA-based tests to improve screening

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

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

AIM

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

MATERIALS & METHODS

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

RESULTS

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

CONCLUSION

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

Diagnostic and prognostic significance of human kallikrein 11 (KLK11) mRNA expression levels in patients with laryngeal cancer

OBJECTIVES

Human kallikrein 11 gene (KLK11) encodes a secreted serine protease. In view of its diagnostic and prognostic strength in many malignancies, we investigated the mRNA expression levels of KLK11 in laryngeal tissues in order to unveil its clinical usefulness in laryngeal cancer.

DESIGN AND METHODS

KLK11 expression was quantified in 163 tissue samples from 105 laryngeal cancer patients with the development of a highly sensitive real-time PCR methodology, using SYBR Green® chemistry.

RESULTS

KLK11 expression in laryngeal cancer specimens of primary or recurrent nature was significantly inferior compared with their non-malignant counterparts (P<0.001 and P=0.026, respectively), a finding of immense diagnostic value as illustrated in the ROC curve analyses (P<0.001). Survival analysis showed that patients harboring KLK11-positive tumors had a significantly decreased risk of death (HR=0.26, P=0.042).

CONCLUSIONS

Our data recommend KLK11 mRNA expression as a novel and independent biomarker in laryngeal cancer for diagnostic and prognostic purposes.

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

AIM

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

METHODS

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

RESULTS

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

CONCLUSION

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

Over-expression of human kallikrein 11 is associated with poor prognosis in patients with low rectal carcinoma

AIM

The goal of this study was to analyze the expression of human kallikrein 11 (hK11) in low rectal carcinoma (LRC) tissues, as well as its association with the clinicopathologic features of LRC patients and its prognostic significance.

METHODS

Between January 1998 and January 2003, 126 patients with LRC were randomized to receive laparoscopic-assisted abdominoperineal resection (APR). Their hK11 expression levels were examined by immunostaining on paraffin-embedded tumor specimens. Then the association of hK11 expression with clinicopathologic characteristics and patients' prognosis was analyzed.

RESULTS

The positive degree of immunohistochemical staining in cancerous tissues (1.86 +/- 0.02) was higher than that in the control group (1.18 +/- 0.11, P = 0.008). Strong positive hK11 staining associated significantly with various clinicopathologic features, such as Dukes Staging (P < 0.001), histological differentiation grade (P = 0.003), CEA level (P = 0.01), lymph node metastasis (P < 0.001), and invasion depth (P = 0.002). Patients with weak hK11 positive expression showed better survival rates of 5-year follow-up than those with strong positive expression (80.85% for weak positive expression and 58.23% in strong positive expression, respectively; P < 0.01 for analyses). Using Cox regression analysis of the 126 patients, strong positive expression of hK11, Dukes Staging, lymph node metastasis, and invasion depth seemed to be independent prognostic indicators (P < 0.01, P = 0.02, P < 0.01 and P < 0.01, respectively).

CONCLUSION

hK11 may be another prognostic biomarker of LRC. Knowledge of hK11 expression in LRC tissues could contribute to the prediction of prognosis of LRC patients.

The Tissue Kallikrein Family of Serine Proteases: Functional Roles in Human Disease and Potential as Clinical Biomarkers

Prostate specific antigen (PSA) or human kallikrein 3 (hK3) has long been an effective biomarker for prostate cancer. Now, other members of the tissue kallikrein (KLK) gene family are fast becoming of clinical interest due to their potential as prognostic biomarkers. particularly for hormone dependent cancers. The tissue kallikreins are serine proteases that are encoded by highly conserved multi-gene family clusters in rodents and humans. The rat and mouse loci contain 10 and 25 functional genes, respectively, while the human locus at 19q 13.4 contains 15 genes. The structural organization and size of these genes are similar across species; all genes have 5 coding exons that encode a prepro-enzyme. Although the physiological activators of these zymogens have not been described, in vitro biochemical studies show that some kallikreins can auto-activate and others can activate each other, suggesting that the kallikreins may participate in an enzymatic cascade similar to that of the coagulation cascade. These genes are expressed, to varying degrees, in a wide range of tissues suggesting a functional involvement in a diverse range of physiological and pathophysiological processes. These include roles in normal skin desquamation and psoriatic lesions, tooth development, neural plasticity, and Alzheimer's disease (AD). Of particular interest is the expression of many kallikreins in prostate, ovarian, and breast cancers where they are emerging as useful prognostic indicators of disease progression.

Specificity Profiling of Seven Human Tissue Kallikreins Reveals Individual Subsite Preferences

Human tissue kallikreins (hKs) form a family of 15 closely related (chymo)trypsin-like serine proteinases. These tissue kallikreins are expressed in a wide range of tissues including the central nervous system, the salivary gland, and endocrine-regulated tissues, such as prostate, breast, or testis, and may have diverse physiological functions. For several tissue kallikreins, a clear correlation has been established between expression and different types of cancer. For example, the prostate-specific antigen (PSA or hK3) serves as tumor marker and is used to monitor therapy response. Using a novel strategy, we have cloned, expressed in Escherichia coli or in insect cells, refolded, activated, and purified the seven human tissue kallikreins hK3/PSA, hK4, hK5, hK6, hK7, hK10, and hK11. Moreover, we have determined their extended substrate specificity for the nonprime side using a positional scanning combinatorial library of tetrapeptide substrates. hK3/PSA and hK7 exhibited a chymotrypsin-like specificity preferring large hydrophobic or polar residues at the P1 position. In contrast, hK4, hK5, and less stringent hK6 displayed a trypsin-like specificity with strong preference for P1-Arg, whereas hK10 and hK11 showed an ambivalent specificity, accepting both basic and large aliphatic P1 residues. The extended substrate specificity profiles are in good agreement with known substrate cleavage sites but also in accord with experimentally solved (hK4, hK6, and hK7) or modeled structures. The specificity profiles may lead to a better understanding of human tissue kallikrein functions and assist in identifying their physiological protein substrates as well as in designing more selective inhibitors.

Multiple promoters regulate tissue-specific alternative splicing of the human kallikrein gene, KLK11/hippostasin

The human kallikrein (KLK) family consists of 15 genes located on human chromosome 19q13.4. KLK11/hippostasinis a member of the kallikrein family and is expressed in various tissues. Two types of KLK11 isoforms, isoform 1 and isoform 2, have been predicted from cDNA sequences. Isoform 1 has been isolated from human hippocampus, whereas isoform 2 has been isolated from prostate. However, the regulation and characteristics of these isoforms are unknown. We identified the first three exons (1a, 1b, and 1c) by determining their transcription initiation sites. Exon 1b contained the initiation codon of isoform 2, and noncoding exons 1a and 1c contributed to isoform 1 mRNA. The dual luciferase promoter assay revealed three promoter regions, corresponding to the first exon of each isoform. Reverse transcription and PCR showed that exon 1a was expressed in the hippocampus, thalamus, and non-central nervous system (CNS) tissues, whereas exon 1b was detected only in non-CNS tissues. Exon 1c was observed in both CNS and non-CNS tissues, except for salivary glands. In vitro mutagenesis revealed that the initiation codon for isoform 2 in exon 1b was functional. Isoform 2 had additional hydrophilic amino acids at the amino terminal and was secreted from the neuroblastoma cell line Neuro2a. Isoform 1 fused with green fluorescent protein (GFP) was distributed to cellular processes, whereas isoform 2-GFP was retained in the Golgi apparatus. We suggest that not only alternative splicing but also tissue-specific use of multiple promoters regulate the expression and intracellular trafficking of KLK11/hippostasin isoforms.

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

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

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

PURPOSE

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

EXPERIMENTAL DESIGN

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

RESULTS

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

CONCLUSION

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

Expression of the human kallikrein genes 10 (KLK10) and 11 (KLK11) in cancerous and non-cancerous lung tissues

Only one transcript for KLK10 was identified by RT-PCR in lung tissue, whereas KLK11 expressed at least four alternative transcripts. Quantitative analysis of KLK10 and KLK11 expression levels was assessed by real-time PCR, in a cohort of 47 patients with non-small-cell lung cancer (NSCLC). Expression levels of these genes were widely distributed in the population studied. Multivariate analysis revealed a correlation between KLK10 over-expression and the squamous cell carcinoma histotype (p=0.034). There was no correlation between gene expression and patient survival. Overall, both genes behaved similarly (p<0.001). These results suggest a co-regulation of KLK10 and KLK11 expression in lung and a lack of KLK10 suppressor role in NSCLC. Finally, our findings indicate that these genes are likely involved in normal physiology processes in bronchus.

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

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

Human tissue kallikrein gene family: applications in cancer

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

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

BACKGROUND

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

METHODS

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

RESULTS

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

CONCLUSIONS

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

A survey of alternative transcripts of human tissue kallikrein genes

Alternative splicing is prevalent within the human tissue kallikrein gene locus. Aside from being the most important source of protein diversity in eukaryotes, this process plays a significant role in development, physiology and disease. A better understanding of alternative splicing could lead to the use of gene variants as drug targets, therapeutic agents or diagnostic markers. With the rapidly rising number of alternative kallikrein transcripts, classifying new transcripts and piecing together the significance of existing data are becoming increasingly challenging. In this review, we present a systematic analysis of all currently known kallikrein alternative transcripts. By defining a reference form for each of the 15 kallikrein genes (KLK1 to KLK15), we were able to classify alternative splicing patterns. We identified 82 different kallikrein gene transcript forms, including reference forms. Alternative splicing may lead to the synthesis of 56 different protein forms for KLK1-15. In the kallikrein locus, the majority of alternative splicing events occur within the protein-coding region, and to a lesser extent in the 5' untranslated regions (UTRs). The most common alternative splicing event is exon skipping (35%) and the least common events are cryptic exons (3%) and internal exon deletion (3%). Seventy-six percent of kallikrein splice variants that are predicted to encode truncated proteins are the result of frameshifts. Eighty-nine percent of putative proteins encoded by splice variants are predicted to be secreted. Although several reports describe the identification of kallikrein splice variants and their potential clinical utility, this is the first extensive review on this subject. Accumulating evidence suggests that alternative kallikrein forms could be involved in many pathologic conditions or could have practical applications as biomarkers. The organization and analysis of the kallikrein transcripts will facilitate future work in this area and may lead to novel clinical and diagnostic applications.

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

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

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

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

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

Molecular cloning and tissue-specific expression analysis of mouse spinesin, a type II transmembrane serine protease 5

We have previously reported novel serine proteases isolated from cDNA libraries of the human and mouse central nervous system (CNS) by PCR using degenerate oligodeoxyribonucleotide primers designed on the basis of the serine protease motifs, AAHC and DSGGP. Here we report a newly isolated serine protease from the mouse CNS. This protease is homologous (77.9% identical) to human spinesin type II transmembrane serine protease 5. Mouse spinesin (m-spinesin) is also composed of (from the N-terminus) a short cytoplasmic domain, a transmembrane domain, a stem region containing a scavenger-receptor-like domain, and a serine protease domain, as is h-spinesin. We also isolated type 1, type 2, and type 3 variant cDNAs of m-spinesin. Full-length spinesin (type 4) and type 3 contain all the domains, whereas type 1 and type 2 variants lack the cytoplasmic, transmembrane, and scavenger-receptor-like domains. Subcellular localization of the variant forms was analyzed using enhanced green fluorescent protein (EGFP) fusion proteins. EGFP-type 4 fusion protein was predominantly localized to the ER, Golgi apparatus, and plasma membrane, whereas EGFP-type 1 was localized to the cytoplasm, reflecting differential classification of m-spinesin variants into transmembrane and cytoplasmic types. We analyzed the distribution of m-spinesin variants in mouse tissues, using RT-PCR with variant-specific primer sets. Interestingly, transmembrane-type spinesin, types 3 and 4, was specifically expressed in the spinal cord, whereas cytoplasmic type, type 1, was expressed in multiple tissues, including the cerebrum and cerebellum. Therefore, m-spinesin variants may have distinct biological functions arising from organ-specific variant expression.

Human Tissue Kallikreins: Physiologic Roles and Applications in Cancer

Tissue kallikreins are members of the S1 family (clan SA) of trypsin-like serine proteases and are present in at least six mammalian orders. In humans, tissue kallikreins (hK) are encoded by 15 structurally similar, steroid hormone–regulated genes (KLK) that colocalize to chromosome 19q13.4, representing the largest cluster of contiguous protease genes in the entire genome. hKs are widely expressed in diverse tissues and implicated in a range of normal physiologic functions from the regulation of blood pressure and electrolyte balance to tissue remodeling, prohormone processing, neural plasticity, and skin desquamation. Several lines of evidence suggest that hKs may be involved in cascade reactions and that cross-talk may exist with proteases of other catalytic classes. The proteolytic activity of hKs is regulated in several ways including zymogen activation, endogenous inhibitors, such as serpins, and via internal (auto)cleavage leading to inactivation. Dysregulated hK expression is associated with multiple diseases, primarily cancer. As a consequence, many kallikreins, in addition to hK3/PSA, have been identified as promising diagnostic and/or prognostic biomarkers for several cancer types, including ovarian, breast, and prostate. Recent data also suggest that hKs may be causally involved in carcinogenesis, particularly in tumor metastasis and invasion, and, thus, may represent attractive drug targets to consider for therapeutic intervention.