Human kallikrein 6 (zyme/protease M/neurosin): a new serum biomarker of ovarian carcinoma
Introduction
Until recently, the human kallikrein gene family was thought to consist of only genes: pancreatic/renal kallikrein (KLK1, encoding for hK1 protein), human glandular kallikrein 2 (KLK2, encoding for hK2 protein) and human kallikrein 3 (KLK3, encoding for hK3 protein or prostate-specific antigen [PSA]). The latter two kallikreins, PSA and hK2, are relatively prostatic-specific and they have already found important applications as biomarkers for the diagnosis and monitoring of prostate cancer 1, 2, 3, 4, 5, 6.
New members of the human kallikrein gene family have recently been discovered (1). This gene family now contains at least 14 genes that are all encoding for serine proteases, show significant homology at both the DNA and amino acid level and they are all localized at the chromosomal locus 19q13.3-q13.4, in tandem, without any intervention from other nonkallikrein genes. This area of investigation has recently been reviewed (1).
The KLK6 gene (encoding for human kallikrein 6, hK6) has been cloned independently by three groups of investigators and was previously given the names zyme (7), protease M (8), and neurosin (9). Recently, uniform nomenclature for all newly discovered and the traditional kallikrein genes has been established (10). The KLK6 gene encodes for a trypsin-like serine protease of 244 amino acids in length, of which 16 amino acids constitute the signal peptide and 5 amino acids, the activation peptide. The mature enzyme consists of 223 amino acids. It has been previously predicted that hK6 is a secreted protein 7, 8, 9, 11. This was recently verified by finding hK6 protein in various biologic fluids, including cerebrospinal fluid, nipple aspirate fluid, breast cyst fluid, male and female serum, seminal plasma, amniotic fluid, and breast cancer cytosols (12). Little et al. (7) have demonstrated that this enzyme has amyloidogenic potential in the brain and may play a role in the development and progression of Alzheimer’s disease. Others have cloned the same gene by the method of differential display, and found that it is down-regulated in aggressive forms of breast cancer (8). The same gene was cloned by Yamashiro et al. from the human colon adenocarcinoma cell line COLO 201 (9). The availability of a highly sensitive hK6 immunoassay made possible the measurement of hK6 in various biologic fluids (12). We here hypothesize that hK6 concentration in serum may be altered during various disease processes, and especially, in cancer. In this paper, we report measurement of hK6 protein in a large number of serum samples obtained from patients with diverse malignancies. Although, in most cancer cases, hK6 concentration was not elevated, we found that hK6 concentration in serum is significantly increased in a large proportion of patients with ovarian cancer. These data suggest that hK6 may constitute a new biomarker for diagnosis and monitoring of ovarian carcinoma.
Section snippets
Immunofluorometric assay for hK6
The details of this immunofluorometric assay have been recently described (12). The assay utilizes two hK6-specific polyclonal antibodies, one raised in mouse and the other raised in rabbit. This is a noncompetitive immunofluorometric procedure that incorporates the principles of time-resolved fluorometry for detection. The assay measures hK6 in the range of 0.5 to 200 μg/L with precision < 10%. Serum samples were analyzed without sample pretreatment.
Clinical samples
For this investigation, we used leftover
Results
A total of 378 serum samples were analyzed with the previously described immunofluorometric assay for hK6 (13). These samples were from either normal individuals (male and female) or from patients with various malignancies. The obtained data are shown in Table 1. While in none of the normal controls and in only two samples from patients with nonovarian malignancies the hK6 concentration was above 15 μg/L (an arbitrary cutoff), the majority of patients with ovarian carcinoma (∼66%) had highly
Discussion
Ovarian cancer is a serious disease that causes more deaths than any other cancer of the female reproductive system (13). Since survival could be dramatically improved if the disease is diagnosed early (14), there is great interest in the identification of biomarkers that could aid in the early detection and facilitate grading and/or staging (15). Unfortunately, the current serologic markers for ovarian carcinoma, including CA125 16, 17, 18, 19, inhibin 20, 21, 22, 23, OVX1 (24), as well as
Acknowledgements
We would like to thank Diagnostic Systems Laboratories for financial support and J. Ahlan for technical assistance.
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2012, Pathology Research and PracticeCitation Excerpt :This study identified that KLK6 was up-regulated in CRC but not in premalignant dysplastic lesions, such as tubular- or tubulovillous adenomas, or in non-tumorous colonic tissue. As is the case with other KLKs, the identification of elevated KLK6 secretion in the serum of patients with CRC may prove to be a useful screening or diagnostic tool for CRC [4–6,21,26,32]. In conclusion, our study showed that KLK6 IHC in patients with CRC is a simple method for contributing to disease outcome prediction.