Human kallikrein 10: Genomic structure, hormonal regulation and clinical applications

Human Kallikrein 10 gene (KLK10; also known as the normal epithelial cell-specific 1, NES1) is a newly identified gene that encodes for a secreted serine protease (named as hK10). Its DNA sequence has extensive homology with all other members of the human tissue kallikrein gene family. In this study, we investigated the genomic structure, hormonal regulation and clinical applications of KLK10. We first cloned the entire KLK10 gene sequence from a genomic DNA library and established its genomic organization. Our results showed that KLK10 gene had the same intron-exon organization as all other members of the human tissue kallikrein gene family. By using fluorescence in-situ hybridization, KLK10 was localized to 19q13.4, a region which harbors all other kallikrein genes. Therefore, KLK10 was categorized as a new member of the human kallikrein gene family. We then produced recombinant hK10 in yeast and used it as immunogen to raise hK10-specific antibodies. A highly sensitive and specific immunoassay was developed for hK10, based on these antibodies. With this immunoassay, hK10 was detected in many tissue extracts and biological fluids, including serum. hK10 expression was up-regulated by estrogens, androgens, progestins, dexamethasone, and aldosterone both at the transcription and translation level, as demonstrated by using breast cancer cell lines. Functional characterization of the KLK10 promoter showed that its activity was constitutive and not modulated by steroid hormones. These data indicate that the KLK10 promoter is unlikely to harbor steroid hormone receptor response elements. Furthermore, we found that KLK10 expression was dramatically down-regulated in testicular germ cell tumors. In contrast, its expression was up-regulated in ovarian cancer, which led to elevation of serum hK10. High levels of hK10 in ovarian tumor tissues and patient serum were associated with poor prognosis. Importantly, serum hK10, in combination of CA125, can improve the diagnostic sensitivity and specificity for ovarian cancer. Taken together, in this investigation, we demonstrated that hK10, a new member of the human tissue kallikrein family, was under hormonal regulation, aberrantly expressed in testicular and ovarian cancer, and a new potential biomarker for ovarian cancer.