Intracellular signaling by cathepsin X: molecular mechanisms and diagnostic and therapeutic opportunities in cancer.

Cathepsin X is a cysteine carboxypeptidase, localized predominantly in immune cells, regulating their proliferation, maturation, migration and adhesion. It has recently been confirmed as a significant promoter of malignant progression. Its role in signal transduction was first implied through the interaction with integrin receptors, either by binding with the RGD motif or by proteolytic cleavage of the C-terminal amino acids of the cytosolic part of the integrin beta chain. Several other molecules, involved in cellular signaling, have since been shown to be targets for cathepsin X, such as γ-enolase, chemokine CXCL-12, bradykinin, kallidin, huntingtin and profilin 1. In cancer, cathepsin X regulates adhesion of tumor and endothelial cells and their migration and invasion through the extracellular matrix. It also promotes tumor progression by bypassing cellular senescence and by inducing an epithelial-mesenchymal transition. The high RNA and protein levels of cathepsin X, found in tumor samples and bodily fluids of patients with various cancer types, further support its active role in tumor progression. Its prognostic value and relation to response to chemotherapy confirm cathepsin X as a new target for improving diagnosis and treating cancer patients.

Gamma-enolase: a well-known tumour marker, with a less-known role in cancer.

BACKGROUND: Gamma-enolase, known also as neuron-specific enolase (NSE), is an enzyme of the glycolytic pathway, which is expressed predominantly in neurons and cells of the neuroendocrine system. As a tumour marker it is used in diagnosis and prognosis of cancer; however, the mechanisms enrolling it in malignant progression remain elusive. As a cytoplasmic enzyme gamma-enolase is involved in increased aerobic glycolysis, the main source of energy in cancer cells, supporting cell proliferation. However, different cellular localisation at pathophysiological conditions, proposes other cellular engagements. CONCLUSIONS: The C-terminal part of the molecule, which is not related to glycolytic pathway, was shown to promote survival of neuronal cells by regulating neuronal growth factor receptor dependent signalling pathways, resulting also in extensive actin cytoskeleton remodelling. This additional function could be important also in cancer cells either to protect cells from stressful conditions and therapeutic agents or to promote tumour cell migration and invasion. Gamma-enolase might therefore have a multifunctional role in cancer progression: it supports increased tumour cell metabolic demands, protects tumour cells from stressful conditions and promotes their invasion and migration.

Prognostic and predictive value of cathepsin X in serum from colorectal cancer patients.

BACKGROUND: Cathepsin X is a cysteine protease involved in mechanisms of malignant progression. It is secreted from tumour cells as a proenzyme and may serve to predict the disease status and risk of death for cancer patients. In a previous, pilot, study on 77 colorectal patients we demonstrated the correlation of higher serum levels with shorter overall survival. METHODS: 264 patients with colorectal cancer were included in a prospectively accrued multi-centre observational cohort study with the aim of testing novel biomarkers. Blood samples were collected before preoperative large bowel endoscopy and total cathepsin X was measured in sera by ELISA. As a control group we selected at random 77 subjects who had no findings at endoscopy and reported no co-morbidity. RESULTS: The mean level of cathepsin X in cancer patients did not differ from the control levels (23.4 ng/ml ± 6.4 SD vs. 18.8 ng/ml ± 11.4 SD, p > 0.05) and there was no association with age, gender, disease stage, tumour location or CEA. In univariate analysis no association between cathepsin X levels and overall survival was demonstrated for the entire set of patients, however, cathepsin X was associated with survival in a group of patients with local resectable disease (stages I-III) (HR = 1.69, 95% CI: 1.03-2.75, p = 0.03). For this group, multivariate Cox regression analysis showed an association (HR = 3.13, 95% CI: 1.37-7.18, p = 0.003) between high cathepsin X levels and shorter overall survival for patients who did not receive chemotherapy, whereas, for patients who received chemotherapy, there was no association between cathepsin X and survival (HR = 0.51, 95% CI: 0.20-1.33, p = 0.88). CONCLUSIONS: Association of cathepsin X levels with overall survival was not confirmed for an entire set of 264 colorectal patients, but for patients in stages I-III with local resectable disease. The significant association of cathepsin X with survival in a group of patients who received no chemotherapy and the absence of this association in the group who received chemotherapy, suggest the possible predictive value for response to chemotherapy. The results have to be confirmed in a further prospective study.

Relationship of High Circulating Cystatin C to Biochemical Markers of Bone Turnover and Bone Mineral Density in Elderly Males with a Chronic Heart Failure.

BACKGROUND: The aim of the study was to investigate the association of Cystatin C (CysC) to biochemical markers of bone turnover and bone mass, and to evaluate its prognostic significance in elderly males with chronic heart failure (CHF). METHODS: A prospective cohort study was executed on sixtyeight males (mean age 68±7 years) with mild to moderate CHF, together with 19 of corresponding age- and body mass index-matched healthy individuals who underwent cardio vascular, bone mineral density (BMD), and body com position assessment. Biochemical assessment of all subjects included NT-pro-BNP, parathyroid hormone (PTH), 25-hydroxy vitamin D (25(OH)D), CysC, and biochemical markers of bone turnover including osteocalcin (OC), alkaline phosphatase (ALP), ß-CrossLaps (ß-CTx), osteoprotegerin (OPG), and receptor activator of nuclear factor κB ligand (RANKL). RESULTS: Serum CysC was significantly increased in males with CHF in comparison to healthy control ones. A significant positive association was found between CysC levels and OC in males with CHF, while OC and ß-CTx increased in increasing CysC tertiles. In multivariate regression analysis, OC and smoking were a significant determinant of CysC in males with CHF. Level of CysC was found to be positively associated with an increased fatal risk in males with CHF. CONCLUSIONS: Serum osteocalcin is an independent predictor of CysC level in elderly males with CHF. Higher CysC level showed a negative relation to survival and bone loss in males with CHF. Further research is needed to confirm the potential role of CysC in the crosstalk between heart, kidney, bone, and energy metabolism in CHF.

Cathepsin X in serum from patients with colorectal cancer: relation to prognosis.

BACKGROUND: Up-regulation of lysosomal cysteine protease cathepsin X (Cat X) is associated with disorders of the immune system and neurodegenerative diseases, while its role in the development and progression of cancer is less understood. Enhanced secretion of pro-Cat X was observed in malignant processes, and therefore, the level of total serum Cat X rather than the active enzyme may better reflect the tumour status. PATIENTS AND METHODS: Seventy-seven patients with colorectal cancer (CRC) were included in a retrospective study. Blood samples were collected prior to therapy. Using ELISA, the values of total Cat X were measured in serum. Groups of healthy persons (n=77), patients with adenomas (n=77) and patients with non-neoplastic findings (n=77) were included. RESULTS: Significant differences between the group of colorectal patients and the groups of healthy persons, adenoma patients and patients with non-malignant findings could not be shown (p=0.89). Within the group of CRC, higher levels of total Cat X significantly correlated to shorter overall survival (HR=2.08, 95% CI:1.07-4.05, p=0.028). CONCLUSIONS: Total serum Cat X could be a useful prognostic indicator for determining survival of patients with CRC. Increased serum levels of total Cat X may reflect more aggressive tumour cell phenotypes and suggest the involvement of Cat X in processes involved in later stages of tumour progression.