Cathepsin B, a cysteine protease implicated in metastatic progression, is also expressed during regression of the rat prostate and mammary glands

Cleavage of Histone 3 by Cathepsin D in the involuting mammary gland

The post-lactational regression of mammary gland is a complex multi-step process designed to conserve the biological function of the gland for next pregnancy. This developmental stage is a biological intrigue with great relevance to breast cancer research, and thus has been the subject of intensive scrutiny. Multipronged studies (microarray, proteomics profiling, animal knock-out models) have provided a repertoire of genes critical to involution. However, the caveat of these approaches remains in their failure to reveal post-translational modification(s), an emerging and critical aspect of gene regulation in developmental processes and mammary gland remodeling. The massive surge in the lysosomal enzymes concurrent with the onset of involution has been known for decades, and considered essential for “clearance” purposes. However, functional significance of these enzymes in diverse biological processes distinct from their proteolytic activity is just emerging. Studies from our laboratory had indicated specific post-translational modifications of the aspartyl endopeptidase Cathepsin D (CatD) at distinct stages mammary gland development. This study addresses the biological significance of these modifications in the involution process, and reveals that post-translational modifications drive CatD into the nucleus to cleave Histone 3. The cleavage of Histone 3 has been associated with cellular differentiation and could be critical instigator of involution process. From functional perspective, deregulated expression and increased secretion of CatD are associated with aggressive and metastatic phenotype of breast cancer. Thus unraveling CatD’s physiological functions in mammary gland development will bridge the present gap in understanding its pro-tumorigenic/metastatic functions, and assist in the generation of tailored therapeutic approaches.

Cathepsin B is secreted apically from Xenopus 2F3 cells and cleaves the epithelial sodium channel (ENaC) to increase its activity

The epithelial sodium channel (ENaC) plays an important role in regulating sodium balance, extracellular volume, and blood pressure. Evidence suggests the α and γ subunits of ENaC are cleaved during assembly before they are inserted into the apical membranes of epithelial cells, and maximal activity of ENaC depends on cleavage of the extracellular loops of α and γ subunits. Here, we report that Xenopus 2F3 cells apically express the cysteine protease cathepsin B, as indicated by two-dimensional gel electrophoresis and mass spectrometry analysis. Recombinant GST ENaC α, β, and γ subunit fusion proteins were expressed in Escherichia coli and then purified and recovered from bacterial inclusion bodies. In vitro cleavage studies revealed the full-length ENaC α subunit fusion protein was cleaved by active cathepsin B but not the full-length β or γ subunit fusion proteins. Both single channel patch clamp studies and short circuit current experiments show ENaC activity decreases with the application of a cathepsin B inhibitor directly onto the apical side of 2F3 cells. We suggest a role for the proteolytic cleavage of ENaC by cathepsin B, and we suggest two possible mechanisms by which cathepsin B could regulate ENaC. Cathepsin B may cleave ENaC extracellularly after being secreted or intracellularly, while ENaC is present in the Golgi or in recycling endosomes.

The role of cathepsins in involution and breast cancer

Cysteine cathepsins are proteolytic enzymes that reside in endolysosomal vesicles. Some are expressed constitutively while others are transcriptionally regulated. However, the expression and subcellular localization of cathepsins changes during cancer progression and cathepsins have been shown to be causally involved in various aspects of tumorigenesis including metastasis. The use of mouse models of breast cancer genetically ablated for cathepsin B has shown that both the growth of the primary tumor and the extend of lung metastasis is reduced by the loss of cathepsin B. The role of cathepsins in involution of the mammary gland has received little attention although it is clear that cathepsins are involved in tissue remodeling in the second phase of involution. We discuss here the roles of cathepsins and their endogenous inhibitors in breast tumorigenesis and post-lactational involution.

Participation of cathepsin B in emodin-induced apoptosis in HK-2 Cells

Emodin (1,3,8-trihydroxy-6-methyl-anthraquinone) and rhein (4,5-dihydroxyanthraquinone-2-carboxyl acid) are two main active compounds in total rhubarb anthraquinones (TRAs), which showed nephrotoxicity in Sprague Dawley (S.D.) rats in our previous study. However, it is unknown yet whether emodin and rhein have cytotoxic effects on kidney. To address this issue, HK-2 cells, a human proximal tubular epithelial cell line, were treated with different concentrations of emodin or rhein, and cell viability and morphological changes were investigated. The ratio of hypodiploid cells and the activity of caspase 3 protease were also detected. Results showed that addition of emodin but not rhein at concentrations above 40microM for 24h reduced cell viability and induced apoptosis in HK-2 cells. Additionally, emodin at apoptosis-inducing concentrations caused expression of cathepsin B (CB) protein and activation of CB protease. Addition of CB inhibitor, CA-074, significantly attenuated the ratio of hypodiploid and apoptotic cells, partially blocked caspase 3 activation and inhibited reduction of cell viability induced by emodin. These data indicate that emodin possesses cytotoxic effects on HK-2 cells partially through induction of CB protein and activation of CB protease.

ECM degrading proteases and tissue remodelling in the mammary gland

Matrix degradation and tissue remodelling directed by matrix-degrading proteases are activated in physiological situations such as wound healing and involution of the prostate, ovaries and uterus. Recently, other activities, in addition to the cleavage of matrix proteins, have been attributed to matrix proteases including the release of growth factors from the extracellular matrix and roles in the maturation of adipocytes. This review describes extracellular proteases, including MMPs, plasminogen and cathepsins involved in the tissue remodelling processes that occur in the breast during pubertal mammary development and the mammary cycle of pregnancy, lactation and weaning. It particularly focuses on development and weaning, termed mammary gland involution, when the majority of remodelling occurs. It also brings together recent findings on the exciting new functions of matrix-degrading proteases.

Cell death independent of caspases: a review

Patterns of cell death have been divided into apoptosis, which is actively executed by specific proteases, the caspases, and accidental necrosis. However, there is now accumulating evidence indicating that cell death can occur in a programmed fashion but in complete absence and independent of caspase activation. Alternative models of programmed cell death (PCD) have therefore been proposed, including autophagy, paraptosis, mitotic catastrophe, and the descriptive model of apoptosis-like and necrosis-like PCD. Caspase-independent cell death pathways are important safeguard mechanisms to protect the organism against unwanted and potential harmful cells when caspase-mediated routes fail but can also be triggered in response to cytotoxic agents or other death stimuli. As in apoptosis, the mitochondrion can play a key role but also other organelles such as lysosomes and the endoplasmic reticulum have an important function in the release and activation of death factors such as cathepsins, calpains, and other proteases. Here we review the various models of PCD and their death pathways at molecular and organelle level and discuss the relevance of the growing knowledge of caspase-independent cell death pathways for cancer.

Apoptosis, autophagy, and more

Cell death has been subdivided into the categories apoptosis (Type I), autophagic cell death (Type II), and necrosis (Type III). The boundary between Type I and II has never been completely clear and perhaps does not exist due to intrinsic factors among different cell types and the crosstalk among organelles within each type. Apoptosis can begin with autophagy, autophagy can end with apoptosis, and blockage of caspase activity can cause a cell to default to Type II cell death from Type I. Furthermore, autophagy is a normal physiological process active in both homeostasis (organelle turnover) and atrophy. "Autophagic cell death" may be interpreted as the process of autophagy that, unlike other situations, does not terminate before the cell collapses. Since switching among the alternative pathways to death is relatively common, interpretations based on knockouts or inhibitors, and therapies directed at controlling apoptosis must include these considerations.

Cathepsin L plays an active role in involution of the mouse mammary gland

Involution of the mammary gland after weaning occurs in two stages. The first stage is reversible, whereas the second stage is characterized by the irreversible collapse of the alveolar structure. A differential display analysis using cDNAs from tissues obtained at various times after forced weaning of pups identified cathepsin L as up-regulated during early involution. Levels of cathepsin L mRNA were dramatically increased within 24 hr after weaning. Cathepsin L protein detected by immunoblot was also increased during involution, reaching near maximal levels by 36 hr after weaning. In situ immunohistochemistry detected pronounced cathepsin L protein in the cytoplasm and cell periphery. Mice treated with a specific inhibitor of cathepsin L exhibited substantially reduced numbers of apoptotic cells at times up to 72 hr after weaning when compared with untreated animals. The cathepsin L inhibitor did not alter levels of cathepsin L detected in immunoblots or influence molecular weight of the cathepsin L species detected. These data suggest that cathepsin L plays a regulatory role early in the process of mammary gland involution.

Trafficking of lysosomal cathepsin B-green fluorescent protein to the surface of thyroid epithelial cells involves the endosomal/lysosomal compartment

Cathepsin B, a lysosomal cysteine proteinase, is involved in limited proteolysis of thyroglobulin with thyroxine liberation at the apical surface of thyroid epithelial cells. To analyze the trafficking of lysosomal enzymes to extracellular locations of thyroid epithelial cells, we have expressed a chimeric protein consisting of rat cathepsin B and green fluorescent protein. Heterologous expression in CHO cells validated the integrity of the structural motifs of the chimeric protein for targeting to endocytic compartments. Homologous expression, colocalization and transport experiments with rat thyroid epithelial cell lines FRT or FRTL-5 demonstrated the correct sorting of the chimeric protein into the lumen of the endoplasmic reticulum, and its subsequent transport via the Golgi apparatus and the trans-Golgi network to endosomes and lysosomes. In addition, the chimeras were secreted as active enzymes from FRTL-5 cells in a thyroid-stimulating-hormone-dependent manner. Immunoprecipitation experiments after pulse-chase radiolabeling showed that secreted chimeras lacked the propeptide of cathepsin B. Thus, the results suggest that cathepsin B is first transported to endosomes/lysosomes from where its matured form is retrieved before being secreted, supporting the view that endosome/lysosome-derived cathepsin B contributes to the potential of extracellular proteolysis in the thyroid.

Induction of invasive phenotype by Casodex in hormone-sensitive prostate cancer cells

The cellular mechanisms of anti-androgen-induced tumor regression have not been investigated in great detail. We have compared the induction of cell death in the androgen-dependent, non-invasive LNCaP prostate cancer cell line by Casodex and TNF-alpha. Both agents induce a dose and time-dependent decrease in cell viability in vitro. However, Casodex does not induce classical DNA fragmentation to oligonucleosomes typically induced by TNF-alpha, but rather induces cleavage to form intermediate 60 kb DNA fragments. RT-PCR based analysis demonstrates that in LNCaP cells Casodex coordinately alters the expression of steady-state level of mRNAs of several matrix metalloproteases and their cognate inhibitors (most notably MMP2 and TIMP1). Zymography and reverse zymography confirm that the ratio of metalloprotease(s) to inhibitor(s) is altered in favor of activation of the proteases. In a small percentage of the treated LNCaP cells, the activation of the extracellular matrix (ECM)-proteases by Casodex also induces an invasive phenotype. The acquisition of an invasive phenotype is not seen when LNCaP cells are treated with TNF-alpha, and is not seen when the LNCaP cells are treated with both compounds simultaneously, suggesting that the phenomenon may be specific to particular classes of compounds. These observations have significant implications in the treatment of prostate cancer, since the appearance of a more aggressive phenotype following treatment is clearly undesirable.

Determination of the mRNA sequence of cathepsin Y, a cysteine endopeptidase from rat spleen, 1 and confirmation of its ubiquitous expression

A cysteine endopeptidase from rat spleen was purified, characterized and its gene cloned. This enzyme was originally recognized by its action of producing kinin-potentiating peptide from a plasma protein. We named it cathepsin Y due to its localization, acidic pH optimum and the presence of the same set of active site amino acids as in other thiol cathepsins. Here we show the total sequence of the mRNA obtained by means of TaKaRa 5' Full RACE Core Set and complete the previously reported sequence. This completion of the mRNA sequence resulted in the omission of the strangely attached C-terminal peptide from cathepsin Y.

Gene expression profiling of androgen deficiency predicts a pathway of prostate apoptosis that involves genes related to oxidative stress

Androgens are critical for prostate development, growth, and functions. In general, they support proliferation and prevent cell death of prostatic epithelial cells. Here, we studied changes of gene expression after castration and testosterone replacement therapy in the rat ventral prostate using cDNA microarrays analysis. We could identify 230 genes that were regulated in either experimental condition. Using hierarchical clustering analysis, different groups of genes could be detected according to their expression pattern. This enabled us to distinguish the putative androgen-responsive genes from the secondary-responsive ones. Among genes that altered during castration and testosterone replacement, a set of oxidative stress-related genes, including thioredoxin, peroxiredoxin 5, superoxide dismutase 2, glutathione peroxidase 1, selenoprotein 15 kDa, microsomal glutathione-S-transferase, glutathione reductase, and epoxide hydrolase, were changed by castration. We hypothesize that modulation of redox status can be a factor of relevance in androgen withdrawal-induced prostate apoptosis. In selective cases, quantitative RT-PCR was used to confirm changes in gene expression. Immunohistochemistry was performed to detect thioredoxin and ezrin. Both of these were detected in the prostate and seem to be regulated in a similar manner as shown by gene expression analysis. In conclusion, gene expression profiling provides a unique opportunity for understanding the molecular mechanisms of androgen actions in prostate gland.

Cysteine peptidases of mammals: their biological roles and potential effects in the oral cavity and other tissues in health and disease

Cysteine peptidases (CPs) are phylogenetically ubiquitous enzymes that can be classified into clans of evolutionarily independent proteins based on the structural organization of the active site. In mammals, two of the major clans represented in the genome are: the CA clan, whose members share a structure and evolutionary history with papain; and the CD clan, which includes the legumains and caspases. This review focuses on the properties of these enzymes, with an emphasis on their potential roles in the oral cavity. The human genome encodes at least (but possibly no more than) 11 distinct enzymes, called cathepsins, that are members of the papain family C1A. Ten of these are present in rodents, which also carry additional genes encoding other cathepsins and cathepsin-like proteins. Human cathepsins are best known from the ubiquitously expressed lysosomal cathepsins B, H, and L, and dipeptidyl peptidase I (DPP I), which until recently were considered to mediate primarily "housekeeping" functions in the cell. However, mutations in DPP I have now been shown to underlie Papillon-Lefevre syndrome and pre-pubertal periodontitis. Other cathepsins are involved in tissue-specific functions such as bone remodeling, but relatively little is known about the functions of several recently discovered enzymes. Collectively, CPs participate in multiple host systems that are active in health and in disease. They are involved in tissue remodeling and turnover of the extracellular matrix, immune system function, and modulation and alteration of cell function. Intracellularly, CPs function in diverse processes including normal protein turnover, antigen and proprotein processing, and apoptosis. Extracellularly, they can contribute directly to the degradation of foreign proteins and the extracellular matrix. However, CPs can also participate in proteolytic cascades that amplify the degradative capacity, potentially leading to pathological damage, and facilitating the penetration of tissues by cancer cells. We know relatively little regarding the role of human CPs in the oral cavity in health or disease. Most studies to date have focused on the potential use of the lysosomal enzymes as markers for periodontal disease activity. Human saliva contains high levels of cystatins, which are potent CP inhibitors. Although these proteins are presumed to serve a protective function, their in vivo targets are unknown, and it remains to be discovered whether they serve to control any human CP activity.

Comparison of differentially expressed genes in the salivary glands of male ticks, Amblyomma americanum and Dermacentor andersoni

Genes expressed differentially in the salivary glands of unfed and fed male ticks, Amblyomma americanum (L.), were identified, cloned and sequenced, and some were compared with those expressed in the salivary glands of Dermacentor andersoni. Total protein and RNA increased sixfold in the salivary glands of fed male A. americanum, while in fed male D. andersoni salivary glands, RNA increased approximately 3.5 times. Feeding D. andersoni in the presence of females increased total RNA by 25% over those fed in the absence of females. Complementary DNAs were synthesized from RNA obtained from unfed and fed ticks and amplified using RNA arbitrarily primed polymerase chain reaction (RAP-PCR) with three different primers in separate reactions. Differential display showed clear banding differences between the fed and the unfed ticks in A. americanum and D. andersoni. Sixty-one cDNA fragments that appeared to be from differentially expressed genes in A. americanum were isolated, cloned and sequenced. Hybridization reactions with labeled cDNA probes confirmed the differential expression of many of the genes in unfed and fed ticks' salivary glands; however, many of the bands contained more than one fragment and some of the fragments isolated from apparently differential bands were not specific. Sequences for 28 of the cDNA fragments (150-600 nucleotides in length) demonstrated similarity to genes in the databases, but nine of these were similar to sequences of unknown function. Some of the gene fragments identified may be important to tick feeding or tick salivary gland physiology, including a histamine-binding protein, an organic ion transporter, an apoptosis inhibitor, a cathepsin-B-like cysteine protease, proteins involved in gene regulation and several proteins involved in protein synthesis. Cross-hybridization of identified cDNAs from A. americanum with cDNA probes synthesized from D. andersoni total RNA did not show significant similarity between the two species.

Molecular characterization of three gut genes from Glossina morsitans morsitans: cathepsin B, zinc-metalloprotease and zinc-carboxypeptidase

Insect gut enzymes are involved in digestion of dietary proteins. Additionally, these enzymes have been implicated in the process of pathogen establishment in several insects including the tsetse fly (Diptera:Glossinidae), which is the vector for African trypanosomes. Both the male and female tsetse can transmit trypanosomes and are strict blood feeders during all stages of their development. Here, we describe the molecular characterization of three gut genes: cathepsin B (GmCatB), zinc-metalloprotease (GmZmp) and zinc-carboxypeptidase (GmZcp). The cDNA for GmCatB encodes a protein for 340 amino acids with a predicted molecular mass of 38.2 kDa, while the 854 bp GmZmp cDNA encodes a protein of 254 amino acids with a molecular mass of 29 kDa. The GmZcp cDNA is 1319 bp in length and has a 354 amino acids open reading frame for coding a 40 kDa protein. All three cDNAs have signal peptide sequences associated with their N-terminal domains and structure analysis indicates that GmCatB and GmZmp are expressed as zymogens with pro-domains proteolytically removed for activity. The activation domain associated with the carboxypeptidase sequences is lacking in GmZcp. While GmCatB transcription is constitutive, teneral flies express very low levels of transcripts for GmZmp and GmZcp prior to the first bloodmeal. Transcription of all genes is induced and remains high throughout the digestion cycle within a few hours following the first bloodmeal ingestion. Both GmCatB and GmZcp are parasite responsive, with the expression of both genes being higher in trypanosome infected flies.

Cathepsins B, H, and L activities in urine of patients with transitional cell carcinoma of the bladder

OBJECTIVES

Cathepsin B, H, and L (CB, CH, CL) are lysosomal proteolytic enzymes that belong to the group of cysteine proteinases. The imbalance between proteinases and their inhibitors is believed to correlate with tumor progression and shortened patient survival. In transitional cell carcinoma (TCC) only limited data have been published.

METHODS

Using spectrofluorometric assays, catalytic activities of CB, CH, and CL in urine were measured to evaluate the potential diagnostic and prognostic value for patients with TCC of the bladder. Second morning urine was collected and used for measurements. CB, CH, and CL activities were determined for groups of patients with superficial disease (Ta-1, n = 43) and muscle-invasive tumors (T2, n = 18; or greater than T2, n = 9), as well as for different tumor grades (G1, n = 12; G2, n = 26; and G3, n = 31). For comparison, 14 urine samples from patients with bladder inflammation and 43 samples from a control group were also included.

RESULTS

Compared with the control group, patients with superficial Stage Ta-T1 disease and muscle-invasive Stage T2 or greater disease, as well as patients with G3 tumors, revealed significantly higher urinary CL activity. CB and CH did not show any tumor-related activity increase. CB was significantly lower in patients with nonrecurrent tumors.

CONCLUSIONS

These results suggest that elevated levels of CL in urine might be indicative of a cellular proteolytic imbalance in TCC of the bladder and may have a prognostic and/or diagnostic value.

Expression of cathepsins B and S in the progression of prostate carcinoma

Cathepsins B and S (CatB, CatS) are lysosomal cysteine proteases which, among other functions, appear to play a role in cancer progression in different tumor models due to their matrix-degrading properties. To investigate their possible involvement in the development of prostate carcinoma, we immunohistochemically analyzed CatB and CatS in 38 primary human prostatic adenocarcinomas, as well as concomitant high-grade prostatic intra-epithelial neoplasia, nodular hyperplasia and normal tissue. CatB expression was observed in 28 (74%) and CatS in 32 (84%) carcinomas, being concomitant in 24 cases (63%). High-grade intra-epithelial neoplasia expressed CatB in 20/23 cases (87%), and a similar result was obtained for CatS, with expression of both coinciding in 18 cases (78%). In non-neoplastic tissue, strong expression of both proteases was observed in macrophages, inflamed glands and transitional metaplasia, whereas atrophic glands and basal cells of normal glands displayed intense CatB positivity. We conclude that CatB and CatS are often expressed together in neoplastic prostatic cells from pre-invasive to invasive and clinically detectable stages, suggesting a putative role in local invasion, though other functions cannot be ruled out.

Puromycin aminonucleoside induces glomerular epithelial cell apoptosis

Glomerular epithelial cell (GEC) injury has been considered to play an important role in puromycin aminonucleoside (PAN)-induced nephrosis. We studied the effect of PAN on rat as well as human GEC apoptosis. Morphogic evaluation of GEC apoptosis and necrosis was carried out by staining with H-33342 and propidium iodide. GEC apoptosis was further confirmed by DNA fragmentation assay (by both agarose gel electrophoresis and end-labeling). To determine the dose- and time-response effect of PAN, GECs were treated with variable concentrations of PAN (10 to 500 microg/ml) for variable time periods (6 to 48 h). To determine the role of gene synthesis, we studied the effect of actinomycin D (a transcriptional inhibitor) on PAN-induced GEC apoptosis. To determine the role of free radicals, we evaluated the effect of superoxide dismutase (SOD), dimethylthiourea (DMTU), and catalase on PAN-induced GEC apoptosis. PAN induced GEC apoptosis in a dose- and time-dependent manner. PAN at a high concentration (PAN, 100 microg/ml) also induced a moderate degree of GEC necrosis. In DNA fragmentation assays PAN-treated GECs showed the classic ladder pattern. PAN-induced GEC apoptosis was partly attenuated with free radical scavengers, such as SOD, DMTU, and catalase. In addition, actinomycin D attenuated PAN-induced GEC apoptosis. PAN induces GEC apoptosis, which may be mediated through the generation of reactive oxygen species.

Expression of cathepsins B and S in the progression of prostate carcinoma

Cathepsins B and S (CatB, CatS) are lysosomal cysteine proteases which, among other functions, appear to play a role in cancer progression in different tumor models due to their matrix-degrading properties. To investigate their possible involvement in the development of prostate carcinoma, we immunohistochemically analyzed CatB and CatS in 38 primary human prostatic adenocarcinomas, as well as concomitant high-grade prostatic intra-epithelial neoplasia, nodular hyperplasia and normal tissue. CatB expression was observed in 28 (74%) and CatS in 32 (84%) carcinomas, being concomitant in 24 cases (63%). High-grade intra-epithelial neoplasia expressed CatB in 20/23 cases (87%), and a similar result was obtained for CatS, with expression of both coinciding in 18 cases (78%). In non-neoplastic tissue, strong expression of both proteases was observed in macrophages, inflamed glands and transitional metaplasia, whereas atrophic glands and basal cells of normal glands displayed intense CatB positivity. We conclude that CatB and CatS are often expressed together in neoplastic prostatic cells from pre-invasive to invasive and clinically detectable stages, suggesting a putative role in local invasion, though other functions cannot be ruled out.

Comparative localization of cathepsin B protein and activity in colorectal cancer

Cathepsin B is a lysosomal cysteine proteinase that may participate in cancer progression. We compared localization of its protein and activity during progression of human colorectal cancer. In adenomas and carcinomas, protein expression and, particularly, activity were elevated compared with those in normal colorectal mucosa. In normal mucosa, cathepsin B protein expression was moderate in stroma and variable in epithelium, whereas activity was mainly present in distinct areas of stroma directly underneath the surface of the colon and in epithelium at the surface of the colon. Stroma in adenomas and carcinomas contained moderate to high protein levels but little activity except for areas of angiogenesis, inflammation, and necrosis, in which activity was high. In adenomas and the majority of well-differentiated carcinomas and moderately differentiated carcinomas, cathepsin B protein and activity were found in granular form in the epithelium, close to the basement membrane. Protein and activity levels were low and diffusely distributed in cancer cells in the remainder of the well-differentiated and moderately differentiated carcinomas and in all poorly differentiated carcinomas. Invasive fronts in most cancers contained moderate protein levels but high activity. We conclude that (a) activity localization is essential to understand the role of cathepsin B in cancer progression, and (b) cathepsin B activity in human colon is associated with invasion of cancer cells, endothelial cells, and inflammatory cells, and in cell death, both apoptotic and necrotic.

Noncaspase proteases in apoptosis

Biochemical and genetic analysis of apoptosis has determined that intracellular proteases are key effectors of cell death pathways. In particular, early studies have pointed to the primacy of caspase proteases as mediators of execution. More recently, however, evidence has accumulated that noncaspases, including cathepsins, calpains, granzymes, and the proteasome complex, also have roles in mediating and promoting cell death. An important goal is to understand the importance of distinct noncaspases in various forms of apoptosis, and to determine whether pathways mediated by noncaspase proteases intersect with those mediated by caspases. In this review the roles of noncaspase proteases in the biochemistry of apoptosis will be discussed.

Direct comparison of the sensitivity of enzyme histochemical and immunohistochemical methods: cathepsin B expression in human colorectal mucosa

Immunohistochemical localization of the proteinase cathepsin B has been compared directly with localization of cathepsin B activity with a catalytic (enzyme) histochemical method. The 2 approaches demonstrate principally different aspects of an enzyme. The immunohistochemical method localizes the enzyme protein whether it is active or not whereas the catalytic method visualizes the functionally active enzyme only. Sensitivity of both approaches to localize low amounts of enzyme protein or activity has never been compared. In the present study, we show that cathepsin B protein has a wider distribution pattern than cathepsin B activity in human colorectal mucosa, which means that inactive cathepsin B protein is present. With respect to sensitivity of the methods, it is shown that cathepsin B protein could only be demonstrated properly when strong signal amplification was applied by using Nanogold with silver enhancement, whereas activity could be demonstrated with a simple and direct fluorogenic histochemical assay. It is concluded that catalytic histochemical methods are relatively simple methods for the localization of activity of enzymes in tissues and cells and that their sensitivity is high in comparison with immunohistochemical methods.

Embigin, a developmentally expressed member of the immunoglobulin super family, is also expressed during regression of prostate and mammary gland

Cell adhesion molecules (CAMs) are intimately involved in a variety of cellular processes, including development, cell growth, apoptosis, and differentiation. Interaction of CAMs with components of the extracellular matrix (ECM) growth factors, and other CAMs provides an intricate regulatory mechanism for a diverse range of cellular responses. Embigin is a developmentally expressed protein that is a member of the immunoglobulin superfamily (IgSF) class of CAMs. We have identified embigin as a gene expressed during tissue regression in rat prostate and lactating mammary gland following hormonal ablation. In the absence of the appropriate hormone, the secretory epithelial cells of these two tissues undergo successive waves of apoptotic cell death co-incident with extensive reorganization of the surviving tissue. Using Northern analysis, in situ hybridization analysis, RT-PCR, and Western analysis we have characterized the expression of embigin mRNA and protein in both regressing prostate and mammary gland. During development of the prostate gland, increased expression of embigin is correlated with the appearance of highly organized lumenal and ductal structures. Embigin is also expressed in a variety of adult tissues including heart, liver, lung, and brain Zoo-blot analysis with the rat embigin cDNA indicates that embigin homologs exist in species as diverse as Homo sapiens and Drosophila melanogaster, suggesting that it has been highly conserved during evolution. Embigin protein is expressed at readily detectable levels in a variety of prostate and mammary cancer cell lines, and in some cell lines the expression of embigin appears to be down-regulated in the presence of ECM. Our data have led us to propose a model in which embigin functions as a regulator of cell/ECM interactions during development and in the homeostasis of normal adult tissues.

Genes upregulated during castration-induced rat prostatic apoptosis: cloning and characterization of new cDNAs

OBJECTIVE

To isolate new cDNAs corresponding to genes whose expression is increased during castration-induced rat prostate apoptosis.

MATERIALS AND METHODS

Differential display of mRNAs from 3-day castrated and normal rat ventral prostates was used to identify differentially expressed clones. Northern blots were hybridized to confirm the positive regulation of the candidates and to follow the change in their expression in the involuting rat prostate, and in thymocytes of dexamethazone-treated rats.

RESULTS

Five cDNAs were cloned: one encoding ribosomal protein L7, one coding for the insulin-like growth factor binding protein-3 (IGFBP-3), and three whose products are unknown. After castration, all five genes had expression kinetics that closely paralleled the proportion of prostatic epithelial cells undergoing apoptosis. The gene encoding L7 and two of the unknown genes were also upregulated in glucocorticoid-induced programmed death in thymocytes. In addition to the IGFBP-3 gene, those coding for proteins IGFBP-4, -5 and -6 were also overexpressed in the involuting prostate of androgen-deprived rats.

CONCLUSION

Five new genes were identified that are up-regulated during castration-induced rat prostate apoptosis, three of which are potentially involved in the common intracellular pathway leading to programmed cell death.

Cell surface complex of cathepsin B/annexin II tetramer in malignant progression

The cysteine protease cathepsin B is upregulated in a variety of tumors, particularly at the invasive edges. Cathepsin B can degrade extracellular matrix proteins, such as collagen IV and laminin, and can activate the precursor form of urokinase plasminogen activator (uPA), perhaps thereby initiating an extracellular proteolytic cascade. Recently, we demonstrated that procathepsin B interacts with the annexin II heterotetramer (AIIt) on the surface of tumor cells. AIIt had previously been shown to interact with the serine proteases: plasminogen/plasmin and tissue-type plasminogen activator (tPA). The AIIt binding site for cathepsin B differs from that for either plasminogen/plasmin or tPA. AIIt also interacts with extracellular matrix proteins, e.g., collagen I and tenascin-C, forming a structural link between the tumor cell surface and the extracellular matrix. Interestingly, cathepsin B, plasminogen/plasmin, t-PA and tenascin-C have all been linked to tumor development. We speculate that colocalization through AIIt of proteases and their substrates on the tumor cell surface may facilitate: (1) activation of precursor forms of proteases and initiation of proteolytic cascades; and (2) selective degradation of extracellular matrix proteins. The recruitment of proteases to specific regions on the cell surface, regions where potential substrates are also bound, could well function as a 'proteolytic center' to enhance tumor cell detachment, invasion and motility.

The roles of caspase-3 and bcl-2 in chemically-induced apoptosis but not necrosis of renal epithelial cells

The kidney is a target for toxicants including cisplatin and S-(1,2-dichlorovinyl)-L-cysteine (DCVC), a metabolite of the environmental contaminant, trichloroethylene. Necrosis is well characterized in kidney cells, but pathways leading to apoptosis are less clear. Cysteine conjugates are useful toxicants because they induce either necrosis or apoptosis depending on chemical structure or antioxidant status. Herein, we show that in the renal epithelial cell line LLC-PK1, activation of caspase-3 (CPP32/Yama/apopain) is crucial for apoptosis, but not necrosis. Apoptosis was blocked by zVAD.fmk, and partially by a cathepsin inhibitor. Caspase-3 activity and cleavage of poly(ADP-ribose) polymerase (PARP) was detected only during apoptosis. S-(1,1,2,2-Tetrafluoroethyl)-L-cysteine (TFEC), a metabolite of tetrafluoroethylene, kills cells only by necrosis, and did not activate caspases under any conditions. Apoptosis and activation of caspase-3 by cisplatin, but not DCVC, was prevented by bcl-2. Thus, caspase-3 activation by bcl-2-dependent and -independent mechanisms is a terminal event in chemical-apoptosis of renal epithelial cells.

A novel gene overexpressed in the prostate of castrated rats: hormonal regulation, relationship to apoptosis and to acquired prostatic cell androgen independence

We have identified a novel complementary DNA (cDNA) corresponding to a gene overexpressed in the rat ventral prostate after castration. This cDNA displays 89.4% identity with 453 bp of a mouse EST and 81.5% identity with 157 bp of a human EST and was named PARM-1 for prostatic androgen-repressed message-1. The complete cDNA is 1187 bp long and codes for a protein of 298 amino acids that contains four potential glycosylation sites and three half cystinyl residues. The PARM-1 gene was found to be expressed at quite low levels in most rat tissues including those of the urogenital tract. The kinetic of induction of PARM-1 gene in the prostate was highly correlated to the development of apoptosis in the whole organ. Supplementation of castrated animals with androgens reversed both the process of apoptosis and the overexpression of PARM-1 gene. Supplementation with estrogens did not result in an increase in the PARM-1 messenger RNA levels when compared with the castration alone. However, the treatment resulted in a more rapid return to intact levels in the castrated plus estrogen group. When apoptosis of testis and prostate was induced in vivo by hypophysectomy, it was found that PARM-1 was only overexpressed in the prostate. Therefore, PARM-1 seems to be regulated by androgens only in the prostate. Using in situ hybridization and immunohistological techniques, we have shown that PARM-1 gene product is found exclusively in the epithelial cells of involuting prostate. Analysis by flow cytometry of MAT LyLu epithelial cells transiently expressing PARM-1 protein did not allow us to demonstrate a direct effect of PARM-1 gene overexpression on the programmed death of the transfected cells. Treatment of MAT LyLu cells by transforming growth factor-beta induced apoptosis but had no effect on PARM-1 production. However PARM-1 protein has been detected by Western blotting in various cell lines such as MAT LyLu, MAT Lu, and PIF, which are androgen independent. This would suggest that PARM-1 gene product would be a marker for acquired androgen-independence of these tumor cells.

Defined characteristics of cathepsin B-like proteins from nematodes: inferred functional diversity and phylogenetic relationships

Numerous cathepsin B-like protein sequences (CBLs) have been reported from nematodes. However, the relationships among these proteins remain unclear. Here, expression of several CBL transcripts in the gut of the parasitic nematode Haemonchus contortus was demonstrated. To assess potential functional diversity, multiple nematode CBL sequences were compared with known functional domains of cathepsin B. These domains included the occluding loop, S2' and S2 subsites, and the pro region. Four groups of CBLs were defined based on variable characteristics in the occluding loop region, which incorporates a portion of the S2' subsite. Further diversity was observed in amino acids expected to contribute to the S2 subsite. In addition, short signature sequences near the cysteinyl active site region characterized known CBLs of parasites from the orders Strongylida and Rhabditida. The criteria established were used to identify two predicted CBLs from parasitic (Ascaris suum) and free-living (Caenorhabditis elegans) nematodes as potential orthologues, and provided a basis to evaluate orthologue status of other CBLs. Variability in the domains analyzed suggests substantial functional diversity in enzymatic properties of nematode CBLs. Results suggest that the selective amplification and evolution of distinct CBL lineages has contributed to differences in CBLs among species and groups of nematodes. Nutrient digestion is one potential factor promoting CBL diversification in these organisms.

Expression of p190A during apoptosis in the regressing rat ventral prostate

After hormonal ablation, 90% of the secretory epithelial cells of the prostate undergo apoptosis, and the remaining cells are reorganized as the tissue is remodeled. Using differential display RT-PCR of total RNA extracted from the rat ventral prostate before and 4 days after castration, we have cloned and sequenced a number of complementary DNAs whose cognate messenger RNAs (mRNAs) may be either up- or down-regulated during prostatic regression. One sequence of particular interest, 25.2, is up-regulated after castration and is homologous to p190, a protein associated with cytoskeletal reorganization. RT-PCR has confirmed that the steady state level of p190A mRNA is increased in the rat ventral prostate after castration, and Western blot analysis indicates that the protein levels for p190A also increase. The steady state level of p190B mRNA, the second isoform of p190, does not appear to change significantly after hormone ablation. Immunohistochemical analysis demonstrates that p190A is up-regulated primarily in the columnar epithelial cells that actively undergo cell death after hormone ablation. As Rho-GAP signaling had been shown to be influenced by p190 levels, leading to the disassembly of focal adhesion contacts and the loss of cytoskeletal architecture, we also measured the changes in Rho-GAP during prostate regression. Rho-GAP levels do not change significantly, suggesting that changes in stoichiometry of the interaction between p190A and Rho-GAP may be a prerequisite for the initiation of cytoplasmic condensation. These intracellular events coupled with the proteolytic degradation of the extracellular matrix appear to be integral to the apoptotic process in glandular epithelia.

Regulation of Apoptosis in the Prostate Gland by Androgenic Steroids

The prostate gland requires androgenic steroids for its appropriate embryological formation and postpubertal growth and, once at adult size, remains dependent on a continuous supply of androgens for its vitality and function. A reduction of the levels of circulating androgens will rapidly induce apoptosis of the cells of the prostate, leading to extensive glandular regression. Studies of rodent models of prostate response to castration have shown that there are some remarkable changes in the gene activity of prostate epithelial cells leading up to apoptosis. There is now evidence for a critical cell signaling pathway, regulated by c-fos expression, necessary for castration-induced apoptosis, as well as evidence that this signaling initiates an abrupt and transient alteration in the synthesis of fas antigen, p53, bax and bcl-2 proteins in the androgen receptor-expressing prostate epithelial cells, the cellular compartment that appears to be the most affected by castration. However, more recent studies suggest that these castration-induced effects on the prostate epithelial cells might be, at least in part, an indirect response to a critical reduction in blood flow to the prostate gland that precedes the onset of epithelial cell apoptosis. The castration effects on blood flow to the prostate gland seem to be related to vascular degeneration associated with apoptosis of a subset of prostate endothelial cells.

Non-specific effects of methyl ketone peptide inhibitors of caspases

Caspases are a family of cysteine proteases which play a crucial role in apoptosis and inflammation. The involvement of caspases in these processes can be demonstrated by their irreversible inhibition with fluoromethyl ketone and chloromethyl ketone derivatives of peptides resembling the cleavage site of known caspase substrates. These inhibitors irreversibly alkylate the cysteine residue in the active site of caspases. In this study we show that a biotinylated fluoromethyl ketone peptide inhibitor of caspases (z-VAD.fmk) also efficiently affinity-labeled cathepsin B and cathepsin H. In addition, the caspase inhibitors z-VAD.fmk, z-DEVD.fmk and Ac-YVAD.cmk also efficiently inhibited cathepsin B activity in vitro and in tissue culture cells at concentrations that are generally used to demonstrate the involvement of caspases.

Atractyloside-induced release of cathepsin B, a protease with caspase-processing activity

Recent data show that a strong relation exists in certain cells between mitochondria and caspase activation in apoptosis. We further investigated this relation and tested whether treatment with the permeability transition (PT)-inducing agent atractyloside of Percoll-purified mitochondria released a caspase-processing activity. Following detection of procaspase-11 processing, we further purified this caspase-processing protease and identified it as cathepsin B. The purified cathepsin B, however, was found to be derived from lysosomes which were present as minor contaminants in the mitochondrial preparation. Besides procaspase-11, caspase-1 is also readily processed by cathepsin B. Procaspase-2, -6, -7, -14 are weak substrates and procaspase-3 is a very poor substrate, while procaspase-12 is no substrate at all for cathepsin B. In addition, cathepsin B induces nuclear apoptosis in digitonin-permeabilized cells as well as in isolated nuclei. All newly described activities of cathepsin B, namely processing of caspase zymogens and induction of nuclear apoptosis, are inhibited by the synthetic peptide caspase inhibitors z-VAD.fmk, z-DEVD.fmk and to a lesser extent by Ac-YVAD.cmk.

Participation of cathepsins B and D in apoptosis of PC12 cells following serum deprivation

Cathepsin D, a lysosomal aspartic proteinase, has been shown to induce apoptosis of HeLa cells when overexpressed. To further understand regulatory mechanisms of cathepsin D-induced cell death, we examined whether lysosomal cysteine and aspartic proteinases are involved in apoptosis of PC12 cells following serum deprivation. In serum deprived culture, PC12 cells overexpressing cathepsin D died more rapidly than wild-type cells. When the active forms of cathepsins B and D were examined during the apoptotic process of wild-type cells, the amount of cathepsin B was drastically reduced 24 hr after the onset of culture, whereas that of cathepsin D considerably increased. The viability of PC12 cells overexpressing cathepsin B was significantly higher in serum-deprived culture than wild-type cells. In this situation, the amount of the cathepsin B protein did not decrease. The results suggest that there exists an apoptotic pathway regulated by lysosomal cathepsins B and D.

Cystatin A expression reduces bile salt-induced apoptosis in a rat hepatoma cell line

We have previously demonstrated abrogation of bile salt-induced apoptosis by cathepsin B inhibitors. However, caspases have been strongly implicated in apoptosis, and the mechanistic interface between caspase and cathepsin B activation is unclear. Thus our aims were to determine the mechanistic relationship between caspases and cathepsin B in bile salt-induced apoptosis in a rat hepatoma cell line. Expression of cystatin A was used to inhibit cathepsin B, whereas Z-Val-Ala-Asp-fluoromethyl ketone (Z-VAD-FMK) was used to inhibit caspases. Cystatin A expression prevented cathepsin B activation and apoptosis during treatment with glycochenodeoxycholate (GCDC), a toxic bile salt. Caspase N-acetyl-Asp-Glu-Val-Asp-7-amino-4-methylcoumarin (DEVD-AMC) hydrolytic activity increased in both wild-type and cystatin A-transfected cells treated with GCDC, demonstrating caspase activation despite inhibition of cathepsin B. In contrast, Z-VAD-FMK blocked both DEVD-AMC hydrolytic activity and cathepsin B activity during GCDC treatment. Our data demonstrate that 1) bile salt-induced apoptosis can be inhibited by the cystatin A transgene and 2) caspase and cathepsin B activation are linked mechanistically with cathepsin B downstream of caspases.

Extracellular matrix modulates mesangial cell apoptosis and mRNA expression of cathepsin-B and tissue transglutaminase

Mesangial matrix is a dynamic structure which modulates mesangial cell function. Since accumulation of matrix precedes the development of focal glomerulosclerosis, we studied the effect of different matrices on mesangial cell (MC) apoptosis. Suspended mesangial cells became apoptotic in a time dependent manner. Collagen type III did not modulate MC apoptosis when compared to cells grown on plastic. MCs grown on Matrigel, collagen type I and IV showed an increased number of apoptotic cells when compared to MCs grown on plastic. DNA end-labeling further confirmed these observations. MCs grown on Matrigel showed enhanced (P < 0.05) mRNA expression for tissue transglutaminase (TTG) and cathepsin-B. Mesangial cells grown on Matrigel also showed enhanced expression of superoxide dismutase (SOD). We conclude that mesangial cells require attachment to the matrix for their survival and alteration of the quality of matrix modulates mesangial cell apoptosis.

Morphine induces splenocyte apoptosis and enhanced mRNA expression of cathepsin-B

Morphine has been demonstrated to modulate immune function. We studied whether morphine modulates apoptosis of splenocytes. Splenocytes were isolated from control and morphine treated rats. Splenocytes isolated from morphine treated rats showed increased percentage (P < 0.001) of apoptosis when compared to splenocytes isolated from untreated rats (control, 4.7 +/- 1.0% apoptotic splenocytes/field vs. morphine, 47.8 +/- 3.4% apoptotic splenocytes/field). These results were further confirmed by gel electrophoresis as well as by end-labeling DNA of splenocytes isolated from control and morphine treated rats. Splenocytes from morphine treated rats showed a classical ladder pattern with integer multiples of 180 base pairs. Splenocytes from morphine treated rats also showed increased mRNA expression of cathepsin-B, a gene associated with active cell death. These results suggest that morphine may also be modulating immune function by enhancing apoptosis of splenocytes.

Examination of the potential structure of human salivary cystatins based on computer modelling

The cystatin family of proteins exists in both excreted and intracellular forms, and appears to be involved in protective and regulatory roles, inhibiting a variety of bacterial, viral and intracellular proteases. The amino acid sequences of several human forms of cystatin are known, but currently only the structure of chicken cystatin (approx. 40% homologous to the human forms) has been experimentally determined. The objective of this study was to use the X-ray coordinates of chicken cystatin to construct computer models of the structures of three human salivary forms (SN, S and SA). These structures were energy-minimized and subjected to dynamic simulations. The resultant structures were compared to determine conformational differences. Global root mean square deviations between equivalent atoms ranged from 1.4 A to 3.9 A. The closest structural similarity to chicken cystatin involved cystatin SN, which also showed the highest (68%) functional sequence homology. Local secondary structure was examined in more detail. In comparisons of alpha-carbon position the third beta-strand (77% functional sequence conservation) and its preceding loop (60% conserved) showed the highest structural conservation in S, while beta-strand 4 showed the highest structural conservation in SN and SA. Throughout their structures, SN and SA were more structurally similar to chicken cystatin than to salivary cystatin S. There are two regions of conserved, negatively charged residues in the salivary cystatins, which appear to be spaced so that they are capable of interaction with hydroxypatite. It is concluded that not only does structural modelling by analogy provide detailed models of salivary cystatins that can be tested by future experimentation, but also that examination of the models has revealed potential sites of interaction with hydroxyapatite.

The expression and function of cystatin C and cathepsin B and cathepsin L during mouse embryo implantation and placentation

The implantation of the mouse embryo requires the controlled invasion of the uterine stroma by the embryonic trophoblast. This event is dependent, in part, on the secretion of matrix metalloproteinases and serine proteinases for the extracellular degradation of the uterine matrix. Proteinase activity is controlled by stromal decidualization and specific proteinase inhibitors. This work adds to our understanding of implantation and placentation by reporting the expression and function of another class of proteinases/inhibitors closely related to invasive cell behavior. We focused on the cysteine proteinases, cathepsins B and L, and their inhibitor cystatin C. Northern blots showed that trophoblast expressed cathepsin B throughout the invasive period (days 5.5-10.5). Both cathepsin B message and cathepsin L protein were localized to the mature, invasive trophoblast giant cells. Substrate gel electrophoresis showed an increase in giant cell cathepsin activity with enzyme profiles changing at the end of the invasive period. Northern and western blotting showed that cystatin C, the main inhibitor of cathepsins, was a major product of the decidualizing stroma. Message levels first increased in peripheral decidualizing cells, with the protein localizing close to the embryo during implantation (days 5.5-8.5). With the regression of the decidua beginning on day 9.5, a coordinated upregulation of both cathepsin B and cystatin C was observed implying a role for controlled cathepsin expression during apoptosis. E-64, a synthetic inhibitor of cathepsins B and L, was injected into pregnant females at the stage of blastocyst attachment (days 4.5-5.5). High doses resulted in the complete failure of implantation while lower doses resulted in stunted embryos and a reduced decidual reaction. These results suggested that cathepsins B and L are necessary for normal embryo development and uterine decidualization, and that decidua contributes to their control by a coordinated expression of cystatin C within the implantation site.

A comparison of cathepsin B processing and distribution during neuronal death in rats following global ischemia or decapitation necrosis

The objective of this study was to examine the possible role of the cysteine protease cathepsin B (E.C. 3.4.22.1) in the delayed neuronal death in rats subjected to the two-vessel occlusion model of global ischemia. Immunohistochemistry of the hippocampus showed an alteration in the distribution of cathepsin B in CA1 neurons from a lysosomal pattern to a more intense label redistributed into the cytoplasm. This change was not detected until the neurons had become morphologically altered with obvious shrinkage of the cytoplasmic region. Western blotting and enzyme activity measurements of subcellular fractions, including lysosomes and a cell soluble fraction, demonstrated that there was an overall decrease in cathepsin B activity at this time but an increase in the proenzyme form, particularly in the soluble fraction. This was found to be completely different from the marked loss of all forms of cathepsin B in necrotic neurons following decapitation.

Leishmania major: comparison of the cathepsin L- and B-like cysteine protease genes with those of other trypanosomatids

Cysteine proteases play important roles in the pathogenesis of several parasitic infections and have been proposed as targets for the structure-based strategy of drug design. As a first step toward applying this strategy to design inhibitors as antiparasitic agents for leishmaniasis, we have isolated and sequenced the full-length clones of two cysteine protease genes from Leishmania major. One of the genes is structurally similar to the cathepsin L-like family and the other is similar to the cathepsin B-like family of cysteine proteases. The L. major cathepsin L-like sequence has a proregion that shares high sequence similarity with other cathepsin L sequences but not cathepsin B sequences and has a proline/threonine-rich C-terminal extension. The cathepsin L-like gene occurs in multiple copies, whereas there may be only one copy of the cathepsin B-like gene. Northern blot analyses show that both genes are expressed in the promastigote and amastigote stages, and pulse field gel electrophoresis revealed that the cathepsin L- and B-like genes are each found on two nonhomologous chromosomes. The L. major L-like amino acid sequence is 75% identical to the L. mexicana sequence, 74% identical to the L. pifanoi sequence, 47% identical with the Trypanosoma cruzi sequence, 47% identical with the T. congolense sequence, and 45% identical with the T. brucei sequence. L. major is one of two trypanosomatid species for which a cathepsin B-like gene has been identified and sequenced; its amino acid sequence is 82% identical to the one from L. mexicana. Tree inference based on distance and parsimony methods of kinetoplastid cathepsin L proteins yielded independent support for phylogenetic hypotheses inferred from analyses of ribosomal RNA genes. Because the cathepsin L locus has a high level of phylogenetic signal with respect to trypanosomatid taxa, this locus has great potential utility for investigating the evolutionary history of trypanosomatids and related organisms.

Comparative effects of 1,25(OH)2D3 and EB1089 on cell cycle kinetics and apoptosis in MCF-7 breast cancer cells

1,25-dihydroxyvitamin D3 [1,25(OH)2D3], the active metabolite of vitamin D2 inhibits breast cancer cell growth both in vivo and in vitro. In addition to its anti-proliferative effects, 1,25(OH)2D3 induces morphological and biochemical markers of apoptosis in MCF-7 cells. In the studies reported here, we compared the effects of 1,25(OH)2D3 and EB1089, a low calcemic vitamin D analog, on cell cycle kinetics and apoptosis in MCF-7 cells. Both vitamin D compounds reduced viable MCF-7 cell number in a time and dose dependent manner, with EB1089 approximately 50 fold more potent than 1,25(OH)2D3. Flow cytometric analysis indicated that both agents induced cell cycle arrest in G, G1 which was associated with accumulation of the hypophosphorylated form of the retinoblastoma (Rb) protein. MCF-7 cells treated with either 1,25(OH)2D3 or EB1089 for 48 h exhibited characteristics of apoptosis, including cytoplasmic condensation, pyknotic nuclei, condensed chromatin and DNA fragmentation. Cells treated with either agent exhibited up regulation of proteins associated with mammary gland regression (clusterin and cathepsin B) and down regulation of the anti-apoptotic protein bcl-2. These studies demonstrate that, despite its lower calcemic activity in vivo, the vitamin D analog EB1089 induces effects that are indistinguishable from those of 1,25(OH)2D3 on cell number, cell cycle and indices of apoptosis in MCF-7 cells in vitro. In addition, since both agents rapidly down regulate estrogen receptor, disruption of estrogen dependent signalling may play a role in the induction of apoptosis by vitamin D compounds in MCF-7 cells.