The glandular kallikreins are a distinct group of serine proteases with a molecular weight of 25,000-40,000 and an ability to release vasoactive peptides from kininogen in vitro, although the kininogenase activity of different kallikreins is highly variable. The true physiologic role of specific kallikreins is often unrelated to the kininogenase activity. In the mouse a major site of kallikrein synthesis is the male submaxillary gland. Glandular kallikreins are also synthesized in the pancreas and kidney. The several kallikreins found in this tissue include epidermal growth factor binding protein (EGF-BP) and the gamma subunit of nerve growth factor (NGFG; 162040) which are responsible for the processing of EGF (131530) and NGF (162030), respectively. Although EGF-BP and NGFG exhibit strict substrate specificity, they share extensive amino acid sequence homology and immunologic crossreactivity. Mason et al. (1983)concluded that the glandular kallikrein gene family comprises 25-30 highly homologous genes that encode specific proteases involved in the processing of biologically active peptides.
Expression regulated by
Luteal cells, Stromal cells
The human tissue kallikrein 13 gene (KLK13), encoding for hK13 protein, was recently cloned and characterized. Petraki CD, et al 2003 describe the immunohistochemical (IHC) localization of hK13 in normal human tissues and compare it with the expression of two other kallikreins, hK6 and hK10. They performed the streptavidin-biotin IHC method on 204 paraffin blocks from archival, current, and autopsy material prepared from almost every normal human tissue, using a polyclonal and a monoclonal hK13 antibody. The staining was cytoplasmic and both antibodies yielded similar results. The hK13 protein was revealed in a variety of tissues, mainly in glandular epithelia. Other epithelia that expressed hK13 included the urothelium, the spermatic epithelium, and the epithelium of the choroid plexus. hK13 was intensely immunoexpressed by some endocrine organs, such as the adenohypophysis, the thyroid gland, the parathyroid glands, the adrenal medulla, the Leydig cells of the testis, and the cells of the endocrine pancreas. Immunoreactivity was also observed in the primordial follicles, the corpus luteum, and sparse luteinized cells in the stroma of the ovary, the trophoblastic cells of the placenta, the Hassall's corpuscles of the thymus, and chondrocytes. Nerves and ganglia of the peripheral nervous system, and both neurons and glial cells in the central nervous system, were positive. In short, hK13 was expressed by many glandular epithelia, some endocrine organs, and some specialized epithelia and cells. Comparison of these data with hK6 and hK10 expression suggests that the three kallikreins have a similar IHC pattern in normal human tissues.
Human kallikrein 13 (hK13; encoded by the KLK13 gene) is a secreted serine protease expressed in endocrine tissues, including the prostate, testis, breast, and ovary. Scorilas A, et al have previously reported steroid hormone regulation of the KLK13 gene and its clinical value as a marker of favorable prognosis in breast cancer at the mRNA level. Using a newly developed enzyme-linked immunosorbent assay (ELISA), hK13 levels were quantified in 131 ovarian tumor extracts and correlated with various clinicopathological variables and outcome (progression-free survival [PFS], overall survival [OS]), over a median follow-up period of 42 months. RESULTS: hK13 concentration in ovarian tumor cytosols ranged from 0 to 18.4 ng/mg of total protein. An optimal cutoff value of 0.13 ng/mg (67(th) percentile) was selected, based on the ability of hK13 values to predict the PFS of the study population, to categorize tumors as hK13-positive or negative. Women with hK13-positive tumors most often had early stage (stage I/II) disease, no residual tumor after surgery and optimal debulking success (P <.05). Univariate and multivariate Cox regression analyses revealed that patients with hK13-positive tumors had a significantly longer PFS and OS than hK13-negative patients (P <.05). Kaplan-Meier survival curves further confirmed a reduced risk of relapse and death in women with hK13-positive tumors (P =.007 and P =.002, respectively). CONCLUSION: These results indicate that hK13 is an independent marker of favorable prognosis in ovarian cancer.