Procathepsin D in breast cancer: what do we know? Effects of ribozymes and other inhibitors

Assessment of Antioxidant Effect of Beta-Glucan on the Whole Blood Oxidative DNA Damage with the Comet Assay in Colorectal Cancer

OBJECTIVE

The present study aims to evaluate the antioxidant effect of beta glucan on oxidative DNA damage by comet assay.

METHODS

A total of 19 adult females and males diagnosed with stage 3-4 colorectal cancer and a control group of 20 age-matched healthy subjects were enrolled in the study. Blood samples of the participants were analyzed using Comet Assay for the parameters of DNA damage.

RESULTS

Significantly increased DNA damage was observed in patients versus control group as indicated by greater values of tail moment, tail percent DNA and tail length. Following incubation with β-glucan, a substantial reduction was found in the aforementioned parameters of DNA damage. Comet assay revealed significant levels of endogenous DNA damage in patients as shown by remarkable increases in the tail moment, the percentage of DNA in the tail and the tail length values, in comparison with the control group. Following treatment of fresh whole blood with β-glucan incubation, DNA damages were significantly reduced but lower values were observed after β-glucan incubation in the patient group versus control group.

CONCLUSION

β-Glucan was found to reduce DNA damage substantially in colorectal cancer patients and show antimutagenic effects. Our results suggested that dietary β-glucan intake might be important in the genesis of colorectal cancer tumors.

Co-Expression of Androgen Receptor and Cathepsin D Defines a Triple-Negative Breast Cancer Subgroup with Poorer Overall Survival

Background: In the triple-negative breast cancer (TNBC) group, the luminal androgen receptor subtype is characterized by expression of androgen receptor (AR) and lack of estrogen receptor and cytokeratin 5/6 expression. Cathepsin D (Cath-D) is overproduced and hypersecreted by breast cancer (BC) cells and is a poor prognostic marker. We recently showed that in TNBC, Cath-D is a potential target for antibody-based therapy. This study evaluated the frequency of AR/Cath-D co-expression and its prognostic value in a large series of patients with non-metastatic TNBC. Methods: AR and Cath-D expression was evaluated by immunohistochemistry in 147 non-metastatic TNBC. The threshold for AR positivity (AR+) was set at ≥1% of stained cells, and the threshold for Cath-D positivity (Cath-D+) was moderate/strong staining intensity. Lymphocyte density, macrophage infiltration, PD-L1 and programmed cell death (PD-1) expression were assessed. Results: Scarff-Bloom-Richardson grade 1–2 and lymph node invasion were more frequent, while macrophage infiltration was less frequent in AR+/Cath-D+ tumors (62.7%). In multivariate analyses, higher tumor size, no adjuvant chemotherapy and AR/Cath-D co-expression were independent prognostic factors of worse overall survival. Conclusions: AR/Cath-D co-expression independently predicted overall survival. Patients with TNBC in which AR and Cath-D are co-expressed could be eligible for combinatory therapy with androgen antagonists and anti-Cath-D human antibodies.

Cathepsin D in the Tumor Microenvironment of Breast and Ovarian Cancers

Cancer remains a major and leading health problem worldwide. Lack of early diagnosis, chemoresistance, and recurrence of cancer means vast research and development are required in this area. The complexity of the tumor microenvironment in the biological milieu poses greater challenges in having safer, selective, and targeted therapies. Existing strategies such as chemotherapy, radiotherapy, and antiangiogenic therapies moderately improve progression-free survival; however, they come with side effects that reduce quality of life. Thus, targeting potential candidates in the microenvironment, such as extracellular cathepsin D (CathD) which has been known to play major pro-tumorigenic roles in breast and ovarian cancers, could be a breakthrough in cancer treatment, specially using novel treatment modalities such as immunotherapy and nanotechnology-based therapy. This chapter discusses CathD as a pro-cancerous, more specifically a proangiogenic factor, that acts bi-functionally in the tumor microenvironment, and possible ways of targeting the protein therapeutically.

Immunotherapy of triple-negative breast cancer with cathepsin D-targeting antibodies

BACKGROUND

Triple-negative breast cancer (TNBC) treatment is currently restricted to chemotherapy. Hence, tumor-specific molecular targets and/or alternative therapeutic strategies for TNBC are urgently needed. Immunotherapy is emerging as an exciting treatment option for TNBC patients. The aspartic protease cathepsin D (cath-D), a marker of poor prognosis in breast cancer (BC), is overproduced and hypersecreted by human BC cells. This study explores whether cath-D is a tumor cell-associated extracellular biomarker and a potent target for antibody-based therapy in TNBC.

METHODS

Cath-D prognostic value and localization was evaluated by transcriptomics, proteomics and immunohistochemistry in TNBC. First-in-class anti-cath-D human scFv fragments binding to both human and mouse cath-D were generated using phage display and cloned in the human IgG1 λ format (F1 and E2). Anti-cath-D antibody biodistribution, antitumor efficacy and in vivo underlying mechanisms were investigated in TNBC MDA-MB-231 tumor xenografts in nude mice. Antitumor effect was further assessed in TNBC patient-derived xenografts (PDXs).

RESULTS

High CTSD mRNA levels correlated with shorter recurrence-free survival in TNBC, and extracellular cath-D was detected in the tumor microenvironment, but not in matched normal breast stroma. Anti-cath-D F1 and E2 antibodies accumulated in TNBC MDA-MB-231 tumor xenografts, inhibited tumor growth and improved mice survival without apparent toxicity. The Fc function of F1, the best antibody candidate, was essential for maximal tumor inhibition in the MDA-MB-231 model. Mechanistically, F1 antitumor response was triggered through natural killer cell activation via IL-15 upregulation, associated with granzyme B and perforin production, and the release of antitumor IFNγ cytokine. The F1 antibody also prevented the tumor recruitment of immunosuppressive tumor-associated macrophages M2 and myeloid-derived suppressor cells, a specific effect associated with a less immunosuppressive tumor microenvironment highlighted by TGFβ decrease. Finally, the antibody F1 inhibited tumor growth of two TNBC PDXs, isolated from patients resistant or not to neo-adjuvant chemotherapy.

CONCLUSION

Cath-D is a tumor-specific extracellular target in TNBC suitable for antibody-based therapy. Immunomodulatory antibody-based strategy against cath-D is a promising immunotherapy to treat patients with TNBC.

Cathepsin D deficiency delays central nervous system myelination by inhibiting proteolipid protein trafficking from late endosome/lysosome to plasma membrane

This study aimed to investigate the role of cathepsin D (CathD) in central nervous system (CNS) myelination and its possible mechanism. By using CathD knockout mice in conjunction with immunohistochemistry, immunocytochemistry and western blot assays, the myelination of the CNS and the development of oligodendrocyte lineage cells in vivo and in vitro were observed. Endocytosis assays, real-time-lapse experiments and total internal reflection fluorescence microscopy were used to demonstrate the location and movement of proteolipid protein in oligodendrocyte lineage cells. In addition, the relevant molecular mechanism was explored by immunoprecipitation. The increase in Fluoromyelin Green staining and proteolipid protein expression was not significant in the corpus callosum of CathD-/- mice at the age of P11, P14 and P24. Proteolipid protein expression was weak at each time point and was mostly accumulated around the nucleus. The number of oligodendrocyte lineage cells (olig2+) and mature oligodendrocytes (CC1+) significantly decreased between P14 and P24. In the oligodendrocyte precursor cell culture of CathD-/- mice, the morphology of myelin basic protein-positive mature oligodendrocytes was simple while oligodendrocyte precursor cells showed delayed differentiation into mature oligodendrocytes. Moreover, more proteolipid protein gathered in late endosomes/lysosomes (LEs/Ls) and fewer reached the plasma membrane. Immunohistochemistry and immunoelectron microscopy analysis showed that CathD, proteolipid protein and VAMP7 could bind with each other, whereas VAMP7 and proteolipid protein colocalized with CathD in late endosome/lysosome. The findings of this paper suggest that CathD may have an important role in the myelination of CNS, presumably by altering the trafficking of proteolipid protein.

Clinical Significance of Cathepsin D Concentration in Tumor Cytosol of Primary Breast Cancer

Background

Cathepsin D is the proteolytic enzyme most frequently implicated as a prognostic factor in primary breast cancer. In the present study we evaluated by means of an immunoradiometric assay the tumor content of this protease in primary breast cancer, its relationship with tumor-related clinical and pathological parameters, and its prognostic significance in a large series of breast cancer patients.

Method

The study comprised 1033 women with histologically established invasive breast cancer. Cathepsin D was measured in cytosol samples by means of an immunoradiometric assay to determine the total amount of cathepsin D (52 kDa, 48 kDa and 34 kDa). Evaluation of relapse-free survival and cause-specific survival was performed in the group of 1003 patients without evidence of metastasis at the time of initial diagnosis. The median follow-up of the patients who were free of recurrence was 54 months.

Results

Cathepsin D levels showed a wide range among the studied tumors (n=1033; median (range) 41 (0.9–2504) pmol/mg protein). Statistical analysis showed that the median cathepsin D levels were considerably higher in large tumors (T2–4) than in smaller ones (T1) (p=0.017), as well as in node-positive than in node-negative tumors (p=0.004). Cathepsin D levels were also higher in ductal tumors than in the other histological types (p=0.001), as well as in moderately or poorly differentiated tumors (p<0.001). Likewise, the median value of the protease was significantly higher in ER or PgR-positive tumors than in hormone receptor-negative ones (p=0.011 and p=0.004, respectively), as well as in aneuploid tumors than in diploid tumors (p=0.029). Multivariate analysis demonstrated that elevated cathepsin D levels (>59 pmol/mg protein) were notably associated with a shorter cause-specific survival in the whole group of patients with breast cancer, as well as in the subgroup of node-positive patients (p<0.05).

Conclusions

This study suggests that elevated intratumoral cathepsin D levels may identify a subset of node-positive breast cancer patients showing a high probability of earlier death.

Hybrid 2D/3D-quantitative structure-activity relationship and modeling studies perspectives of pepstatin A analogs as cathepsin D inhibitors

AIM

Cathepsin D, one of the attractive targets in the treatment of breast cancer, has been implicated in HIV neuropathogenesis with potential proteolytic effects on chemokines. Methodology/result: Diverse modeling tools were used to reveal the key structural features affecting the inhibitory activities of 78 pepstatin A analogs. Analyses were performed to investigate the stability, rationality and fluctuation of the analogs. Results showed a clear correlation between the experimental and predicted activities of the analogs as well as the variation in their activities relative to structural modifications.

CONCLUSION

The insight gained from this study offers theoretical references for understanding the mechanism of action of cathepsin D and will aid in the design of more potent and clinically-relevant drugs. Graphical abstract [Formula: see text].

Molecular Dynamics Simulations of Ligand-Induced Flap Conformational Changes in Cathepsin-D-A Comparative Study

The flap region in aspartic proteases is a unique structural feature to this class of enzymes, and found to have a profound impact on protein overall structure, function, and dynamics. Understanding the structure and dynamic behavior of the flap regions is crucial in the design of selective inhibitors against aspartic proteases. Cathepsin-D, an aspartic protease enzyme, has been implicated in a long list of degenerative diseases as well as breast cancer progression. Presented herein, for the first time, is a comprehensive description of the conformational flap dynamics of cathepsin-D using a comparative 50 ns "multiple" molecular dynamics simulations. Diverse collective metrics were proposed to accurately define flap dynamics. These are distance d1 between the flap tips residues (Gly79 and Met301); dihedral angle ϕ; in addition to TriCα angles Gly79-Asp33-Asp223, θ1 , and Gly79-Asp223-Met301, θ2 . The maximum distance attained throughout the simulation was 17.42 and 11.47 Å for apo and bound cathepsin-D, respectively, while the minimum distance observed was 8.75 and 6.32 Å for apo and bound cathepsin-D, respectively. The movement of the flap as well as the twist of the active pocket can properly be explained by measuring the angle, θ1 , between Gly79-Asp33-Met301 and correlating it with the distance Cα of the flap tip residues. The asymmetrical opening of the binding cavity was best described by the large shift of -6.26° to +20.94° in the dihedral angle, ϕ, corresponding to the full opening of the flap at a range of 31-33 ns. A wide-range of post-dynamic analyses was also applied in this report to supplement our findings. We believe that this report would augment current efforts in designing potent structure-based inhibitors against cathepsin-D in the treatment of breast cancer and other degenerative diseases. J. Cell. Biochem. 117: 2643-2657, 2016. © 2016 Wiley Periodicals, Inc.

Lowering Endogenous Cathepsin D Abundance Results in Reactive Oxygen Species Accumulation and Cell Senescence

Cathepsin D is reportedly to be closely associated with tumor development, migration, and invasion, but its pathological mechanism is not fully elucidated. We aimed to evaluate phenotypic changes and molecular events in response to cathepsin D knockdown. Lowering endogenous cathepsin D abundance (CR) induced senescence in HeLa cells, leading to reduced rate of cell proliferation and impaired tumorigenesis in a mouse model. Quantitative proteomics revealed that compared with control cells (EV), the abundances of several typical lysosomal proteases were decreased in the lysosomal fraction in CR cells. We further showed that cathepsin D knockdown caused increased permeability of lysosomal membrane and reactive oxygen species accumulation in CR cells, and the scavenging of reactive oxygen species by antioxidant was able to rescue cell senescence. Despite the increased reactive oxygen species, the proteomic data suggested a global reduction of redox-related proteins in CR cells. Subsequent analysis indicated that the transcriptional activity of nuclear factor erythroid-related factor 2 (Nrf2), which regulates the expression of groups of antioxidant enzymes, was down-regulated by cathepsin D knockdown. Importantly, Nrf2 overexpression significantly reduced cell senescence. Although transient oxidative stress promoted the accumulation of Nrf2 in the nucleus, we showed that the Nrf2 protein exited nucleus if oxidative stress persisted. In addition, when cathepsin D was transiently knocked down, the cathepsin-related events followed a sequential order, including lysosomal leakage during the early stage, followed by oxidative stress augmentation, and ultimately Nrf2 down-regulation and senescence. Our results suggest the roles of cathepsin D in cancer cells in maintaining lysosomal integrity, redox balance, and Nrf2 activity, thus promoting tumorigenesis. The MS Data are available via ProteomeXchange with identifier PXD002844.

Yeast as a tool to explore cathepsin D function

Cathepsin D has garnered increased attention in recent years, mainly since it has been associated with several human pathologies. In particular, cathepsin D is often overexpressed and hypersecreted in cancer cells, implying it may constitute a therapeutic target. However, cathepsin D can have both anti- and pro-survival functions depending on its proteolytic activity, cellular context and stress stimulus. Therefore, a more detailed understanding of cathepsin D regulation and how to modulate its apoptotic functions is clearly needed. In this review, we provide an overview of the role of cathepsin D in physiological and pathological scenarios. We then focus on the opposing functions of cathepsin D in apoptosis, particularly relevant in cancer research. Emphasis is given to the role of the yeast protease Pep4p, the vacuolar counterpart of cathepsin D, in life and death. Finally, we discuss how insights from yeast cathepsin D and its role in regulated cell death can unveil novel functions of mammalian cathepsin D in apoptosis and cancer.

Propeptides as modulators of functional activity of proteases

Most proteases are synthesized in the cell as precursor-containing propeptides. These structural elements can determine the folding of the cognate protein, function as an inhibitor/activator peptide, mediate enzyme sorting, and mediate the protease interaction with other molecules and supramolecular structures. The data presented in this review demonstrate modulatory activity of propeptides irrespective of the specific mechanism of action. Changes in propeptide structure, sometimes minor, can crucially alter protein function in the living organism. Modulatory activity coupled with high variation allows us to consider propeptides as specific evolutionary modules that can transform biological properties of proteases without significant changes in the highly conserved catalytic domains. As the considered properties of propeptides are not unique to proteases, propeptide-mediated evolution seems to be a universal biological mechanism.

Cathepsin D: Autoantibody profiling as a diagnostic marker for cancers

Current diagnostic assays for many cancers are antigen-based and rely on the detection of circulating proteins that are associated with a particular cancer. These assays depend on the expression, synthesis, and release of specific proteins by cells (e.g., tumor cells) through either active secretion or shedding, or as a consequence of cell death (either necrosis or apoptosis). As such, these antigenic proteins must “escape” the primary site of disease, saturate the antigen-processing capacity of the individual’s immune components, gain access to the circulation, and reach a sufficient steady-state concentration to be detected by enzyme- or radiolabel-based immunoassays. These events usually occur after the initial establishment of disease. Thus, and despite the fact that certain specific antigenic epitopes exhibit common recognition among patients with the same tumor types, the use of these antigen-based cancer assays has not been widely accepted in clinical practice, and many individual countries differ in the use of these potential diagnostic factors. Lately, an increasing number of studies demonstrated that procathepsin D secreted from cancer cells, acts as a mitogen on cancer cells and stimulates their pro-invasive and pro-metastatic properties. In this report, we focused on the possibility to use anti-procathepsin D autoantibodies as a diagnostic and/or predictive marker for cancers.

Clinical and Biological Significance of Cathepsin D Levels in Breast Cancer Cytosol in Women Over 70 years

Objective

To study cytosolic cathepsin D behavior and possible relationship with other clinical and biological parameters in women affected by breast invasive ductal carcinomas and older than 70 years (range: 71–88).

Material and methods

cytosolic levels of cathepsin D were determined by an Immunoradiometric Assay (IRMA-CIS France). Clinical and biological factors analyzed were: size, axillary lymph node involvement, distant metastasis, histological grade, ploidy, S phase cell, cytosolic estrogen receptor, progesterone receptor and pS2, and concentrations of epidermal growth factor receptor (EGFR) in cell membranes.

Results

Cathepsin D concentrations ranged between 13 and 1228 pmol/mg prot.. Median value of 41 was considered as threshold of positivity. Cathepsin D positive tumors showed higher S-phase values (P = 0.046) and were most often histological grade III (P = 0.047). However, the most important finding was the existence of a positive correlation (r = 0.51786) and statistically significant (P < 0.05) between S-phase values and cathepsin D in the overall group of tumors, and those ER+, but not in ER−. We determined cathepsin D concentrations in 131 women with invasive ductal breast carcinomas, but aged between 50 and 70 years (median 61) and we did not find differences based on those values in women >70 years. In addition, we found no correlation between S-phase values and Cathepsin D, both overall and in relation with hormone dependence (ER).

Conclusions

Those results led us to the following conclusions: (1) cytosolic concentrations of cathepsin D in invasive infiltrating breast carcinomas in women over 70 are similar to those seen in women with the same type of tumor, but aged 50 to 70 years and are associated with increased cell proliferation measured by S phase, and histological grade III; (2) in women older than 70 years, cathepsin D concentrations are statistically significantly correlated with phase synthesis values in hormone-dependent tumors, but not in hormone-independent, fact not observed in infiltrating ductal breast carcinomas of women aged between 50 and 70. This could reflect a different mitogenic role of the aspartyl protease enzyme linked to hormone dependence as age function parameter.

New insights into procathepsin D in pathological and physiological conditions

Procathepsin D is a major glycoprotein that is secreted from numerous types of cancer cells including breast, lung and prostrate carcinomas. It affects multiple stages of tumorigenesis that include proliferation, invasion, metastasis and apoptosis. Previous studies showed that the mitogenic effect of procathepsin D on cancer cells was mediated through its propeptide or activation peptide. Recent studies have also implicated the possible use of procathepsin D/activation peptide as a marker of cancer progression. Considering the broad range of functions of procathepsin D, the present review summarizes the three major potentials of procathepsin D-cancer progression, tumor marker and wound healing.

Procathepsin D and cancer: From molecular biology to clinical applications

Procathepsin D (pCD) is overexpressed and secreted by cells of various tumor types including breast and lung carcinomas. pCD affects multiple features of tumor cells including proliferation, invasion, metastases and apoptosis. Several laboratories have previously shown that the mitogenic effect of pCD on cancer cells is mediated via its propeptide part (APpCD). However, the exact mechanism of how pCD affects cancer cells has not been identified. Recent observations have also revealed the possible use of pCD/APpcD as a marker of cancer progression. The purpose of this review is to summarize the three major potentials of pCD-tumor marker, potential drug, and screening agent.

Cathepsin D--many functions of one aspartic protease

For years, it has been held that cathepsin D (CD) is involved in rather non-specific protein degradation in a strongly acidic milieu of lysosomes. Studies with CD knock-out mice revealed that CD is not necessary for embryonal development, but it is indispensable for postnatal tissue homeostasis. Mutation that abolishes CD enzymatic activity causes neuronal ceroid lipofuscinosis (NCL) characterized by severe neurodegeneration, developmental regression, visual loss and epilepsy in both animals and humans. In the last decade, however, an increasing number of studies demonstrated that enzymatic function of CD is not restricted solely to acidic milieu of lysosomes with important consequences in regulation of apoptosis. In addition to CD enzymatic activity, it has been shown that apoptosis is also regulated by catalytically inactive mutants of CD which suggests that CD interacts with other important molecules and influences cell signaling. Moreover, procathepsin D (pCD), secreted from cancer cells, acts as a mitogen on both cancer and stromal cells and stimulates their pro-invasive and pro-metastatic properties. Numerous studies found that pCD/CD level represents an independent prognostic factor in a variety of cancers and is therefore considered to be a potential target of anti-cancer therapy. Studies dealing with functions of cathepsin D are complicated by the fact that there are several simultaneous forms of CD in a cell-pCD, intermediate enzymatically active CD and mature heavy and light chain CD. It became evident that these forms may differently regulate the above-mentioned processes. In this article, we review the possible functions of CD and its various forms in cells and organisms during physiological and pathological conditions.

The expression of prolactin and its cathepsin D-mediated cleavage in the bovine corpus luteum vary with the estrous cycle

In the corpus luteum (CL), blood vessels develop, stabilize, and regress. This process depends on the ratio of pro- and antiangiogenic factors, which change during the ovarian cycle. The present study focuses on the possible roles of 23,000 (23K) prolactin (PRL) in the bovine CL and its antiangiogenic NH(2)-terminal fragments after extracellular cleavage by cathepsin D (Cath D). PRL RNA and protein were demonstrated in the CL tissue, in luteal endothelial cells, and in steroidogenic cells. Cath D was detected in CL tissue, cell extracts, and corresponding cell supernatants. In the intact CL, 23K PRL levels decreased gradually, whereas Cath D levels concomitantly increased between early and late luteal stages. In vitro, PRL cleavage occurred in the presence of acidified homogenates of CL tissue, cells, and corresponding cell supernatants. Similar fragments were obtained with purified Cath D, and their appearance was inhibited by pepstatin A. The aspartic protease specific substrate MOCAc-GKPILF~FRLK(Dnp)-D-R-NH(2) was cleaved by CL cell supernatants, providing further evidence for Cath D activity. The 16,000 PRL inhibited proliferation of luteal endothelial cells accompanied by an increase in cleaved caspase-3. In conclusion, 1) the bovine CL is able to produce PRL and to process it into antiangiogenic fragments by Cath D activity and 2) PRL cleavage might mediate angioregression during luteolysis.

Procathepsin D expression correlates with invasive and metastatic phenotype of MDA-MB-231 derived cell lines

Procathepsin D (pCD) is a glycoprotein secreted abundantly by cancerous cells with a documented role in tumor development. The levels of pCD in primary tumors are highly correlated with an increased incidence of metastasis. Our earlier studies have shown that pCD exerts its effect on cancer cells through its activation peptide (AP) and involves both autocrine and paracrine modes of action. In this study, we analyzed the expression and role of pCD in MDA-MB-231 and its derived cell lines 1833 and 4175 possessing discrete metastatic abilities. Our results demonstrated a direct relationship between expression and secretion of pCD to the differential invasive potential of these cells. Also, the cell lines responded to AP treatment by enhancing their invasive potential, proliferation and induction of secretion of various cytokines, suggesting that pCD plays a role in metastasis through its AP region.

Secretion of Cytokines in Breast Cancer Cells: The Molecular Mechanism of Procathepsin D Proliferative Effects

Procathepsin D (pCD) is a major secreted protein in estrogen receptor-positive (ER+) breast cancer cell lines. Several independent studies have documented pronounced mitogenic effect of secreted pCD on cancer tissue-derived cell lines, including those from breast, lung, and prostate cancer. It has also been shown that the proliferative effect of pCD involves both autocrine and paracrine modes of action. Recent studies have suggested that pCD could act as a key paracrine communicator between cancer and stromal cells. We have shown earlier that the proliferative activity of pCD depends on the activation peptide sequence of pCD. The present study casts light on the mechanism by which pCD influences the proliferation of cancer cells expressing the ER. Results described in the current paper clearly show that pCD initiates secretion of cytokines interleukin-4 (IL-4), IL-8, IL-10, IL-13, macrophage inflammatory protein-1beta and (MIP-1beta) from such tumor cells. Secreted cytokines take part in the proliferation of the cancer cells, as proven by selective inhibition using antibodies. In addition, expression of cytokine receptors on tested cell lines corresponded to the effects of individual cytokines. An analogous pattern was also observed for fibroblasts, which, under physiologic conditions, are the cells in closest contact with the tumor tissue and play a role in tumor growth and invasion. Our observations were further supported by coculture experiments that are in agreement. Although very similar in response to addition of pCD, the invasive ER- cells do not secrete cytokines. Together with previous in vivo results, these data point to pCD as one of key molecules for therapeutic attack in breast cancer.

Insulin-like growth factor II mediates resveratrol stimulatory effect on cathepsin D in breast cancer cells

Cathepsin D (CD) is an enzyme that promotes breast cancer. CD is stored intracellularly; however, we demonstrated that IGF-II promotes CD secretion in estrogen receptor positive (ER+) breast cancer cells. We also showed that resveratrol (RSV) stimulates IGF-II in ER(+) breast cancer cells. Thus, we designed this study to determine whether RSV regulates CD in MCF-7, T47D (ER+) breast cancer cells as well as in Hs578t (cancer) and MCF-10A (normal) ER - cell lines. RSV (10(- 6) M) increased CD and IGF-II secretion in ER+ but not ER - cells. RSV treatment (10(- 4) M) inhibited CD in ER+ but not in ER - cells. Transfection of ER - cells with proIGF-II increased CD secretion. RSV (10(- 6) M) modulates CD secretion through IGF-II while RSV (10(- 4) M) inhibits CD in ER+ but not ER - cells. Regulation of CD by RSV represents a novel mechanism by which RSV may protect against breast cancer.

Possible role of procathepsin D in human cancer

For the past ten years, our research has been focused on elucidating the mechanism by which procathepsin D (pCD) impacts cancer development. Various studies have shown that pCD is overexpressed and secreted by numerous cancer cell lines. After secretion, it exhibits "growth hormone-like" activity on cancerous cells but the exact mechanism of this mitogenic activity is not yet understood. The activation peptide of pCD (APpCD) (which is cleaved off upon activation of the zymogen) is responsible for the mitogenic function of pCD. Various in vitro and in vivo studies support our theory that the APpCD interacts with both parent and neighborhood cancer cells and thus functions as an autocrine mitogen. We propose a model of pCD mitogenic function and also some possible approaches for treatment and prevention of certain types of cancer.

DUAL ROLE OF CATHEPSIN D: LIGAND AND PROTEASE

Cathepsin D is peptidase belonging to the family of aspartic peptidases. Its mostly described function is intracellular catabolism in lysosomal compartments, other physiological effect include hormone and antigen processing. For almost two decades, there have been an increasing number of data describing additional roles imparted by cathepsin D and its pro-enzyme, resulting in cathepsin D being a specific biomarker of some diseases. These roles in pathological conditions, namely elevated levels in certain tumor tissues, seem to be connected to another, yet not fully understood functionality. However, despite numerous studies, the mechanisms of cathepsin D and its precursor's actions are still not completely understood. From results discussed in this article it might be concluded that cathepsin D in its zymogen status has additional function, which is rather dependent on a "ligand-like" function then on proteolytic activity.

Ribozymes: recent advances in the development of RNA tools

The discovery 20 years ago that some RNA molecules, called ribozymes, are able to catalyze chemical reactions was a breakthrough in biology. Over the last two decades numerous natural RNA motifs endowed with catalytic activity have been described. They all fit within a few well-defined types that respond to a specific RNA structure. The prototype catalytic domain of each one has been engineered to generate trans-acting ribozymes that catalyze the site-specific cleavage of other RNA molecules. On the 20th anniversary of ribozyme discovery we briefly summarize the main features of the different natural catalytic RNAs. We also describe progress towards developing strategies to ensure an efficient ribozyme-based technology, dedicating special attention to the ones aimed to achieve a new generation of therapeutic agents.