1513

CTSK

cathepsin K;CTSK;cathepsin K

cathepsin O|cathepsin O1|cathepsin O2|cathepsin X

1q21

protein-coding

Bone metastasis is a hallmark of advanced prostate and breast cancers, yet the critical factors behind attraction of tumors to the skeleton have not been validated. Here, we investigated the involvement of cathepsin K in the progression of prostate tumors in the bone, which occurs both by direct degradation of bone matrix collagen I and by cleavage of other factors in the bone microenvironment. Our results demonstrated that bone marrow-derived cathepsin K is capable of processing and thereby modulating SPARC, a protein implicated in bone metastasis and inflammation. The coincident up-regulation of SPARC and cathepsin K occurred both in vivo in experimental prostate bone tumors, and in vitro in co-cultures of bone marrow stromal cells with PC3 prostate carcinoma cells. PC3-bone marrow stromal cell interaction increased secretion and processing of SPARC, as did co-cultures of bone marrow stromal cells with two other cancer cell lines. In addition, bone marrow stromal cells that were either deficient in cathepsin K or treated with cathepsin K inhibitors had significantly reduced secretion and cleavage of SPARC. Increases in secretion of pro-inflammatory cytokines (ie, interleukin-6, -8) coincident with overexpression of cathepsin K suggest possible mechanisms by which this enzyme contributes to tumor progression in the bone. This is the first study implicating bone marrow cathepsin K in regulation of biological activity of SPARC in bone metastasis.

BACKGROUND: Coronins are a family of highly evolutionary conserved proteins reportedly involved in the regulation of actin cytoskeletal dynamics, although only coronin 3 has been shown to be related to cancer cell migration. In glioblastoma cells, the knockdown of coronin 3 inhibits cell proliferation and invasion. Coronin 3 is also associated with the aggression and metastasis of hepatocellular carcinoma. In this paper, we analyze the migration, invasion and metastasis abilities of gastric cancer cells after up- or down-regulation of coronin 3, and explore the mechanism of coronin 3 in the process of gastric cancer metastasis. RESULTS: The expression of coronin 3 was higher in the highly metastatic sub-cell line MKN28-M, which we established in our laboratory. We also demonstrated that the expression of coronin 3 was remarkably higher in lymph lode metastases than in primary gastric cancer tissues, and over-expression of coronin 3 was correlated with the increased clinical stage and lymph lode metastasis. Recombinant lentiviral vectors encoding shRNAs were designed to down-regulate coronin 3 expression in gastric cancer cell lines. Stable knockdown of coronin 3 by this lentiviral vector could efficiently inhibit the migration and invasion of MKN45 gastric cancer cells. In contrast, up-regulation of coronin 3 significantly enhanced migration and invasion of MKN28-NM cells. In addition, knockdown of coronin 3 significantly reduced liver metastasis in mice after tail vein injection of gastric cancer cells. The Human tumor metastasis PCR Array was used to screen the metastasis-associated genes identified by the down-regulation of coronin 3, and the results suggested that, following the knockdown of coronin 3, the tumor cell migration and invasion were inhibited by the reduced expression of MMP-9 and cathepsin K. CONCLUSION: Coronin 3 is highly expressed in gastric cancer metastases and can promote the metastatic behaviors of gastric cancer cells, including their migration and invasion.

Cathepsin X, a recently discovered lysosomal cysteine protease, shares common structural features and activity properties with cysteine protease cathepsin B. Based on its widespread mRNA distribution in primary tumors and tumor cell lines, a redundant function in tumor progression has been proposed. In this study, we have shown that these two related proteases exhibit different profiles with respect to their protein distribution in cells and tissues and to their possible roles in malignancy. Protein level of cathepsin X did not differ significantly between matched pairs of lung tumor and adjacent lung tissue obtained from patients with lung cancer whereas that of cathepsin B was 9.6-fold higher in tumor compared to adjacent lung tissue. Immunohistochemical analysis of lung tumor cathepsin X revealed very faint staining in tumor cells but positive staining in infiltrated histiocytes, alveolar macrophages, bronchial epithelial cells, and alveolar type II cells. Cathepsin X stained positive also in CD68+ cells in germinal centers of secondary follicles in lymph nodes, corresponding to tingible body macrophages. Two cell lines with proven invasive behavior, MCF-10A neoT and MDA-MB 231, showed positive staining for cathepsin B, but negative for cathepsin X. We showed that the invasive potential of MCF-10A neoT cells can be impaired by specific inhibitor of cathepsin B but not by that of cathepsin X. Cathepsin X was found in large amounts in the pro-monocytic U-937 cell line, in monocytes and in dendritic cells, generated from monocytes in vitro. Our results show that cathepsin X is not involved in degradation of extracellular matrix, a proteolytic event leading to tumor cell invasion and metastasis. Its expression, restricted to immune cells suggests a role in phagocytosis and the regulation of immune response.

Cathepsin K (catK) is a lysosomal cysteine protease with strong collagenolytic activity that mediates bone resorption in osteoclasts. Recently, catK expression has been reported in skin and lung fibroblasts, which suggests a role in maintaining homeostasis of the extracellular matrix outside of bone. Matrix degradation is a pivotal step in tumor invasion and metastasis. As other proteases, in particular matrix metalloproteinases and some cathepsins, but not catK, have been described to mediate melanoma invasion, we studied catK in melanoma. Immunostaining revealed strong catK expression in most primary melanomas and all cutaneous melanoma metastases. Melanocytic nevi also demonstrated catK expression, but it was less intense than in melanomas. Melanoma lines express both the pro- and the active form of catK and internalize extracellular collagen into lysosomes. Inhibition of catK greatly reduced melanoma cell invasion through Matrigel basement membrane matrix and increased detection of internalized collagen. We suggest that catK may play an important role in melanoma invasion and metastasis by mediating intracellular degradation of matrix proteins after phagocytosis. Clinical use of catK inhibitors, a class of medication currently in clinical trials for the treatment of osteoporosis, may be a promising avenue for the treatment of melanoma.

Bone metastasis is a hallmark of advanced prostate and breast cancers, yet the critical factors behind attraction of tumors to the skeleton have not been validated. Here, we investigated the involvement of cathepsin K in the progression of prostate tumors in the bone, which occurs both by direct degradation of bone matrix collagen I and by cleavage of other factors in the bone microenvironment. Our results demonstrated that bone marrow-derived cathepsin K is capable of processing and thereby modulating SPARC, a protein implicated in bone metastasis and inflammation. The coincident up-regulation of SPARC and cathepsin K occurred both in vivo in experimental prostate bone tumors, and in vitro in co-cultures of bone marrow stromal cells with PC3 prostate carcinoma cells. PC3-bone marrow stromal cell interaction increased secretion and processing of SPARC, as did co-cultures of bone marrow stromal cells with two other cancer cell lines. In addition, bone marrow stromal cells that were either deficient in cathepsin K or treated with cathepsin K inhibitors had significantly reduced secretion and cleavage of SPARC. Increases in secretion of pro-inflammatory cytokines (ie, interleukin-6, -8) coincident with overexpression of cathepsin K suggest possible mechanisms by which this enzyme contributes to tumor progression in the bone. This is the first study implicating bone marrow cathepsin K in regulation of biological activity of SPARC in bone metastasis.

Osteosarcoma is the most frequent malignant bone tumor with a poor survival rate for patients with metastasis. Previous studies have shown that beside other proteases, distinct sets of cathepsins are involved in the process of metastasis of different tumors. In this study we investigated the expression of cathepsin proteases in human osteosarcoma metastasis. First, the mRNA expression of 14 human cathepsins was studied in SAOS-2 osteosarcoma cells and the highly metastatic LM5 and LM7 sublines by reverse transcriptase (RT)-polymerase chain reaction (PCR). The expression of cathepsin D, K, and L mRNA was found upregulated and that of cathepsin F, H, and V downregulated in the highly metastatic LM5 and LM7 cells. A subgroup of the cathepsin proteases was further studied at the protein level by Western blot analysis of cell extracts. The expression of cathepsin B and H was decreased and that of cathepsin D, K, and L was increased in the highly metastatic cell lines as compared to the SAOS-2 cell line. Diagnostic relevance of cathepsin K expression in osteosarcoma was revealed upon correlation of survival and metastasis with immunohistochemical cathepsin K staining of biopsies collected from 92 patients prior to chemotherapy. Patients with metastatic high-grade osteosarcoma and low cathepsin K expression at diagnosis had a better prognosis than those with high expression. Thus, it appears that cathepsin K expression is of predictive prognostic value for patients with high-grade tumors and metastasis at diagnosis.

Bone metastasis is a hallmark of advanced prostate and breast cancers, yet the critical factors behind attraction of tumors to the skeleton have not been validated. Here, we investigated the involvement of cathepsin K in the progression of prostate tumors in the bone, which occurs both by direct degradation of bone matrix collagen I and by cleavage of other factors in the bone microenvironment. Our results demonstrated that bone marrow-derived cathepsin K is capable of processing and thereby modulating SPARC, a protein implicated in bone metastasis and inflammation. The coincident up-regulation of SPARC and cathepsin K occurred both in vivo in experimental prostate bone tumors, and in vitro in co-cultures of bone marrow stromal cells with PC3 prostate carcinoma cells. PC3-bone marrow stromal cell interaction increased secretion and processing of SPARC, as did co-cultures of bone marrow stromal cells with two other cancer cell lines. In addition, bone marrow stromal cells that were either deficient in cathepsin K or treated with cathepsin K inhibitors had significantly reduced secretion and cleavage of SPARC. Increases in secretion of pro-inflammatory cytokines (ie, interleukin-6, -8) coincident with overexpression of cathepsin K suggest possible mechanisms by which this enzyme contributes to tumor progression in the bone. This is the first study implicating bone marrow cathepsin K in regulation of biological activity of SPARC in bone metastasis.