Expression and Function of the Kallikrein-Related Peptidase 6 in the Human Melanoma Microenvironment

Abstract

Cutaneous malignant melanoma is an aggressive disease of poor prognosis. Clinical and experimental studies have provided major insight into the pathogenesis of the disease, including the functional interaction between melanoma cells and surrounding keratinocytes, fibroblasts and immune cells. Nevertheless, patients with metastasized melanoma have a very poor prognosis and are largely refractory to clinical therapies. Hence, novel diagnostic tools to monitor melanoma development as well as therapeutic targets are urgently needed. We investigated the expression pattern of the kallikrein-related peptidase 6 (KLK6) in human melanoma tissue sections throughout tumor development. Although, KLK6 was not detectable in tumor cells, we found strong KLK6 protein expression in keratinocytes and stromal cells located adjacent to benign nevi, primary melanomas and cutaneous metastatic lesions, suggesting a paracrine function of extracellular KLK6 during neoplastic transformation and malignant progression. Accordingly, recombinant Klk6 protein significantly induced melanoma cell migration and invasion accompanied by an accelerated intracellular Ca2+-flux. We could further demonstrate that KLK6-induced intracellular Ca2+-flux and tumor cell invasion critically depends on the protease-activated receptor PAR1. Our data provide experimental evidence that specific inhibition of the KLK6-PAR1 axis may interfere with the deleterious effect of tumor-microenvironment interaction and represent a potential option for translational melanoma research.

A potent, proteolysis-resistant inhibitor of kallikrein-related peptidase 6 (KLK6) for cancer therapy, developed by combinatorial engineering

“…The 15 serine proteases in this family are involved in the tissue-specific proteolysis of numerous endogenous substrates (1-3) and are considered major regulatory proteases with key signaling properties, acting either individually or as part of other proteolytic cascades (4). KLKs can also be employed clinically as markers for the diagnosis and prognosis of cancer (5) and as targets for therapeutic intervention; KLK6, specifically, has been shown to be a key factor in driving the invasion and migration of cancer cells (6)(7)(8).…”

Expression of Kallikrein-Related Peptidase 6 in Primary Mucosal Malignant Melanoma of the Head and Neck

“…In 2011, Krenzer et al investigated the KLK6 expression pattern in cutaneous melanoma throughout malignant progression. Interestingly, KLK6 could not be detected in tumor cells but in the adjacent microenvironment of benign nevi, primary melanoma and cutaneous metastatic lesions [18]. Exclusive expression of KLK6 in adjacent keratinocytes and stromal cells but not in tumor cells strongly suggested a paracrine mode of action by extracellular KLK6 to foster malignant progression and tumor cell dissemination, which was confirmed by administration of recombinant KLK6 on melanoma cell lines in vitro.…”

“…Immunohistochemical staining revealed a strong expression of KLK6 in distinct stromal cells, including endothelial cells of blood vessels. This staining served as an internal control and has been described before in cutaneous melanoma [18]. The staining pattern for tumor cells was more heterogeneous with a predominant cytoplasmic staining (Fig.…”

“…In the past, the expression of KLK6 has been identified in the microenvironment of skin melanoma and correlated with malignant progression [18,24,28]. In HNSCC and breast cancer cells, reactivation of KLK6 was not correlated with poor clinical outcome, but associated with prominent down-regulation of Vimentin, a protein that is expressed in mesenchymal cells.…”

“…Kallikreins (KLKs) are a group of serine proteases with diverse physiological functions, and several KLKs, including KLK6 have been implicated in neoplastic transformation and malignant progression [16]. Dysregulation of KLK6 expression is a common event in several human malignancies [17] such as glioma, ovarian, breast, uterine, pancreatic, colorectal, gastric, skin [18], urinary bladder, lung and salivary gland cancers. Most tumors were characterized by a strong increase of KLK6 transcript and protein levels as compared to normal tissues [14,19].…”