Prostate Cancer-Associated Kallikrein-Related Peptidase 4 Activates Matrix Metalloproteinase-1 and Thrombospondin-1.

Prostate cancer metastasis to bone is terminal; thus, novel therapies are required to prevent end-stage disease. Kallikrein-related peptidase 4 (KLK4) is a serine protease that is overproduced in localized prostate cancer and is abundant in prostate cancer bone metastases. In vitro, KLK4 induces tumor-promoting phenotypes; however, the underlying proteolytic mechanism is undefined. The protein topography and migration analysis platform (PROTOMAP) was used for high-depth identification of KLK4 substrates secreted by prostate cancer bone metastasis-derived PC-3 cells to delineate the mechanism of KLK4 action in advanced prostate cancer. Thirty-six putative novel substrates were determined from the PROTOMAP analysis. In addition, KLK4 cleaved the established substrate, urokinase-type plasminogen activator, thus validating the approach. KLK4 activated matrix metalloproteinase-1 (MMP1), a protease that promotes prostate tumor growth and metastasis. MMP1 was produced in the tumor compartment of prostate cancer bone metastases, highlighting its accessibility to KLK4 at this site. KLK4 further liberated an N-terminal product, with purported angiogenic activity, from thrombospondin-1 (TSP1) and cleaved TSP1 in an osteoblast-derived matrix. This is the most comprehensive analysis of the proteolytic action of KLK4 in an advanced prostate cancer model to date, highlighting KLK4 as a potential multifunctional regulator of prostate cancer progression.

In vitro evidence that KLK14 regulates the components of the HGF/Met axis, pro-HGF and HGF-activator inhibitor 1A and 1B.

Kallikrein-related peptidase (KLK) 14 is a serine protease linked to several pathologies including prostate cancer. We show that KLK14 has biphasic effects in vitro on activating and inhibiting components of the prostate cancer associated hepatocyte growth factor (HGF)/Met system. At 5-10 nm, KLK14 converts pro-HGF to the two-chain heterodimer required for Met activation, while higher concentrations degrade the HGF α-chain. HGF activator-inhibitor (HAI)-1A and HAI-1B, which inhibit pro-HGF activators, are degraded by KLK14 when protease:inhibitor stoichiometry is 1:1 or the protease is in excess. When inhibitors are in excess, KLK14 generates HAI-1A and HAI-1B fragments known to inhibit pro-HGF activating serine proteases. These in vitro data suggest that increased KLK14 activity could contribute at multiple levels to HGF/Met-mediated processes in prostate and other cancers.

EphB4 localises to the nucleus of prostate cancer cells.

The EphB4 receptor tyrosine kinase is over-expressed in a variety of different epithelial cancers including prostate where it has been shown to be involved in survival, migration and angiogenesis. We report here that EphB4 also resides in the nucleus of prostate cancer cell lines. We used in silico methods to identify a bipartite nuclear localisation signal (NLS) in the extracellular domain and a monopartite NLS sequence in the intracellular kinase domain of EphB4. To determine whether both putative NLS sequences were functional, fragments of the EphB4 sequence containing each NLS were cloned to create EphB4NLS-GFP fusion proteins. Localisation of both NLS-GFP proteins to the nuclei of transfected cells was observed, demonstrating that EphB4 contains two functional NLS sequences. Mutation of the key amino residues in both NLS sequences resulted in diminished nuclear accumulation. As nuclear translocation is often dependent on importins we confirmed that EphB4 and importin-α can interact. To assess if nuclear EphB4 could be implicated in gene regulatory functions potential EphB4-binding genomic loci were identified using chromatin immunoprecipitation and Lef1 was confirmed as a potential target of EphB4-mediated gene regulation. These novel findings add further complexity to the biology of this important cancer-associated receptor.

Reactivation of embryonic nodal signaling is associated with tumor progression and promotes the growth of prostate cancer cells.

BACKGROUND: Nodal is a member of the transforming growth factor ß (TGFß) superfamily that directs embryonic patterning and promotes the plasticity and tumorigenicity of tumor cells, but its role in the prostate is unknown. The goal of this study was to characterize the expression and function of Nodal in prostate cancer and determine whether, like other TGFß ligands, it modulates androgen receptor (AR) activity. METHODS: Nodal expression was investigated using immunohistochemistry of tissue microarrays and Western blots of prostate cell lines. The functional role of Nodal was examined using Matrigel and soft agar growth assays. Cross-talk between Nodal and AR signaling was assessed with luciferase reporter assays and expression of endogenous androgen regulated genes. RESULTS: Significantly increased Nodal expression was observed in cancer compared with benign prostate specimens. Nodal was only expressed by DU145 and PC3 cells. All cell lines expressed Nodal's co-receptor, Cripto-1, but lacked Lefty, a critical negative regulator of Nodal signaling. Recombinant human Nodal triggered downstream Smad2 phosphorylation in DU145 and LNCaP cells, and stable transfection of pre-pro-Nodal enhanced the growth of LNCaP cells in Matrigel and soft agar. Finally, Nodal attenuated AR signaling, reducing the activity of a PSA promoter construct in luciferase assays and down-regulating the endogenous expression of androgen regulated genes. CONCLUSIONS: An aberrant Nodal signaling pathway is re-expressed and functionally active in prostate cancer cells.

Kallikrein-related peptidase 4 induces cancer-associated fibroblast features in prostate-derived stromal cells.

The reciprocal communication between cancer cells and their microenvironment is critical in cancer progression. Although involvement of cancer-associated fibroblasts (CAF) in cancer progression is long established, the molecular mechanisms leading to differentiation of CAFs from normal fibroblasts are poorly understood. Here, we report that kallikrein-related peptidase-4 (KLK4) promotes CAF differentiation. KLK4 is highly expressed in prostate epithelial cells of premalignant (prostatic intraepithelial neoplasia) and malignant lesions compared to normal prostate epithelia, especially at the peristromal interface. KLK4 induced CAF-like features in the prostate-derived WPMY1 normal stromal cell line, including increased expression of alpha-smooth muscle actin, ESR1 and SFRP1. KLK4 activated protease-activated receptor-1 in WPMY1 cells increasing expression of several factors (FGF1, TAGLN, LOX, IL8, VEGFA) involved in prostate cancer progression. In addition, KLK4 induced WPMY1 cell proliferation and secretome changes, which in turn stimulated HUVEC cell proliferation that could be blocked by a VEGFA antibody. Importantly, the genes dysregulated by KLK4 treatment of WPMY1 cells were also differentially expressed between patient-derived CAFs compared to matched nonmalignant fibroblasts and were further increased by KLK4 treatment. Taken together, we propose that epithelial-derived KLK4 promotes tumour progression by actively promoting CAF differentiation in the prostate stromal microenvironment.

Long terminal repeats act as androgen-responsive enhancers for the PSA-kallikrein locus.

The androgen receptor (AR) signaling pathway is a common therapeutic target for prostate cancer, because it is critical for the survival of both hormone-responsive and castrate-resistant tumor cells. Most of the detailed understanding that we have of AR transcriptional activation has been gained by studying classical target genes. For more than two decades, Kallikrein 3 (KLK3) (prostate-specific antigen) has been used as a prototypical AR target gene, because it is highly androgen responsive in prostate cancer cells. Three regions upstream of the KLK3 gene, including the distal enhancer, are known to contain consensus androgen-responsive elements required for AR-mediated transcriptional activation. Here, we show that KLK3 is one of a specific cluster of androgen-regulated genes at the centromeric end of the kallikrein locus with enhancers that evolved from the long terminal repeat (LTR) (LTR40a) of an endogenous retrovirus. Ligand-dependent recruitment of the AR to individual LTR-derived enhancers results in concurrent up-regulation of endogenous KLK2, KLK3, and KLKP1 expression in LNCaP prostate cancer cells. At the molecular level, a kallikrein-specific duplication within the LTR is required for maximal androgen responsiveness. Therefore, KLK3 represents a subset of target genes regulated by repetitive elements but is not typical of the whole spectrum of androgen-responsive transcripts. These data provide a novel and more detailed understanding of AR transcriptional activation and emphasize the importance of repetitive elements as functional regulatory units.

Substrate-guided design of a potent and selective kallikrein-related peptidase inhibitor for kallikrein 4.

Human kallikrein-related peptidase 4 (KLK4/prostase), a trypsin-like serine protease, is a potential target for prostate cancer treatment because of its proteolytic ability to activate many tumorigenic and metastatic pathways including the protease activated receptors (PARs). Currently there are no KLK4-specific small-molecule inhibitors available for therapeutic development. Here we re-engineer the naturally occurring sunflower trypsin inhibitor to selectively block the proteolytic activity of KLK4 and prevent stimulation of PAR activity in a cell-based system. The re-engineered inhibitor was designed using a combination of molecular modeling and sparse matrix substrate screening.