scholarly journals Measles Virus Enters Breast and Colon Cancer Cell Lines through a PVRL4-Mediated Macropinocytosis Pathway

2017 ◽  
Vol 91 (10) ◽  
Author(s):  
Sebastien Delpeut ◽  
Gary Sisson ◽  
Karen M. Black ◽  
Christopher D. Richardson
Keyword(s):  
Breast Cancer ◽  
Life Cycle ◽  
Cancer Cells ◽  
Cell Lines ◽  
Cancer Cell ◽  
Measles Virus ◽  
Breast Cancer Cells ◽  
Cancer Cell Lines ◽  
Endocytic Pathway ◽  
Insight Into

ABSTRACT Measles virus (MeV) is a member of the family Paramixoviridae that causes a highly contagious respiratory disease but has emerged as a promising oncolytic platform. Previous studies of MeV entry focused on the identification of cellular receptors. However, the endocytic and trafficking pathways utilized during MeV entry remain poorly described. The contribution of each endocytic pathway has been examined in cells that express the MeV receptors SLAM (signaling lymphocyte-activating molecule) and PVRL4 (poliovirus receptor-like 4) (nectin-4). Recombinant MeVs expressing either firefly luciferase or green fluorescent protein together with a variety of inhibitors were used. The results showed that MeV uptake was dynamin independent in the Vero.hPVRL4, Vero.hSLAM, and PVRL4-positive MCF7 breast cancer cell lines. However, MeV infection was blocked by 5-(N-ethyl-N-propyl)amiloride (EIPA), the hallmark inhibitor of macropinocytosis, as well as inhibitors of actin polymerization. By using phalloidin staining, MeV entry was shown to induce actin rearrangements and the formation of membrane ruffles accompanied by transient elevated fluid uptake. Small interfering RNA (siRNA) knockdown of p21-activated kinase 1 (PAK1) demonstrated that MeV enters both Vero.hPVRL4 and Vero.hSLAM cells in a PAK1-independent manner using a macropinocytosis-like pathway. In contrast, MeV entry into MCF7 human breast cancer cells relied upon Rac1 and its effector PAK1 through a PVRL4-mediated macropinocytosis pathway. MeV entry into DLD-1 colon and HTB-20 breast cancer cells also appeared to use the same pathway. Overall, these findings provide new insight into the life cycle of MeV, which could lead to therapies that block virus entry or methods that improve the uptake of MeV by cancer cells during oncolytic therapy. IMPORTANCE In the past decades, measles virus (MeV) has emerged as a promising oncolytic platform. Previous studies concerning MeV entry focused mainly on the identification of putative receptors for MeV. Nectin-4 (PVRL4) was recently identified as the epithelial cell receptor for MeV. However, the specific endocytic and trafficking pathways utilized during MeV infections are poorly documented. In this study, we demonstrated that MeV enters host cells via a dynamin-independent and actin-dependent endocytic pathway. Moreover, we show that MeV gains entry into MCF7, DLD-1, and HTB-20 cancer cells through a PVRL4-mediated macropinocytosis pathway and identified the typical cellular GTPase and kinase involved. Our findings provide new insight into the life cycle of MeV, which may lead to the development of therapies that block the entry of the virus into the host cell or alternatively promote the uptake of oncolytic MeV into cancer cells.

scholarly journals Antiplatelet Therapy Combined with Anastrozole Induces Features of Partial EMT in Breast Cancer Cells and Fails to Mitigate Breast-Cancer Induced Hypercoagulation

2021 ◽  
Vol 22 (8) ◽  
pp. 4153
Author(s):  
Kutlwano R. Xulu ◽  
Tanya N. Augustine
Keyword(s):  
Breast Cancer ◽  
Cancer Cells ◽  
Cancer Patients ◽  
Antiplatelet Therapy ◽  
Cell Lines ◽  
Cancer Cell ◽  
Breast Cancer Cell ◽  
Breast Cancer Cells ◽  
Cancer Cell Lines ◽  
Breast Cancer Cell Lines

Thromboembolic complications are a leading cause of morbidity and mortality in cancer patients. Cancer patients often present with an increased risk for thrombosis including hypercoagulation, so the application of antiplatelet strategies to oncology warrants further investigation. This study investigated the effects of anastrozole and antiplatelet therapy (aspirin/clopidogrel cocktail or atopaxar) treatment on the tumour responses of luminal phenotype breast cancer cells and induced hypercoagulation. Ethical clearance was obtained (M150263). Blood was co-cultured with breast cancer cell lines (MCF7 and T47D) pre-treated with anastrozole and/or antiplatelet drugs for 24 h. Hypercoagulation was indicated by thrombin production and platelet activation (morphological and molecular). Gene expression associated with the epithelial-to-mesenchymal transition (EMT) was assessed in breast cancer cells, and secreted cytokines associated with tumour progression were evaluated. Data were analysed with the PAST3 software. Our findings showed that antiplatelet therapies (aspirin/clopidogrel cocktail and atopaxar) combined with anastrozole failed to prevent hypercoagulation and induced evidence of a partial EMT. Differences in tumour responses that modulate tumour aggression were noted between breast cancer cell lines, and this may be an important consideration in the clinical management of subphenotypes of luminal phenotype breast cancer. Further investigation is needed before this treatment modality (combined hormone and antiplatelet therapy) can be considered for managing tumour associated-thromboembolic disorder.

scholarly journals Super Magnetic Niosomal Nanocarrier as a New Approach for Treatment of Breast Cancer: A Case Study on SK-BR-3 and MDA-MB-231 Cell Lines

2021 ◽  
Vol 22 (15) ◽  
pp. 7948
Author(s):  
Elham Jamshidifar ◽  
Faten Eshrati Yeganeh ◽  
Mona Shayan ◽  
Mohammad Tavakkoli Yaraki ◽  
Mahsa Bourbour ◽  
...  
Keyword(s):  
Breast Cancer ◽  
Cancer Cells ◽  
Cell Lines ◽  
Cancer Cell ◽  
Cellular Uptake ◽  
Targeted Delivery ◽  
Breast Cancer Cells ◽  
Cancer Cell Lines ◽  
Breast Cancer Cell Lines ◽  
Silica Layer

In the present study, a magnetic niosomal nanocarrier for co-delivery of curcumin and letrozole into breast cancer cells has been designed. The magnetic NiCoFe2O4 core was coated by a thin layer of silica, followed by a niosomal structure, allowing us to load letrozole and curcumin into the silica layer and niosomal layer, respectively, and investigate their synergic effects on breast cancer cells. Furthermore, the nanocarriers demonstrated a pH-dependent release due to the niosomal structure at their outer layer, which is a promising behavior for cancer treatment. Additionally, cellular assays revealed that the nanocarriers had low cellular uptake in the case of non-tumorigenic cells (i.e., MCF-10A) and related high viability but high cellular uptake in cancer cell lines (i.e., MDA-MB-231 and SK-BR-3) and related low viability, which is evidenced in their high cytotoxicity against different breast cancer cell lines. The cytotoxicity of the letrozole/curcumin co-loaded nanocarrier is higher than that of the aqueous solutions of both drugs, indicating their enhanced cellular uptake in their encapsulated states. In particular, NiCoFe2O4@L-Silica-L@C-Niosome showed the highest cytotoxicity effects on MDA-MB-231 and SK-BR-3 breast cancer cells. The observed cytotoxicity was due to regulation of the expression levels of the studied genes in breast cancer cells, where downregulation was observed for the Bcl-2, MMP 2, MMP 9, cyclin D, and cyclin E genes while upregulation of the expression of the Bax, caspase-3, and caspase-9 genes was observed. The flow cytometry results also revealed that NiCoFe2O4@L-Silica-L@C-Niosome enhanced the apoptosis rate in both MDA-MB-231 and SK-BR-3 cells compared to the control samples. The findings of our research show the potential of designing magnetic niosomal formulations for simultaneous targeted delivery of both hydrophobic and hydrophilic drugs into cancer cells in order to enhance their synergic chemotherapeutic effects. These results could open new avenues into the future of nanomedicine and the development of theranostic agents.

The α2δ1 subunit of the voltage-gated calcium channel as a potential candidate for breast cancer tumor initial cells biomarker

2021 ◽  
pp. 1-11
Author(s):  
Meng Li ◽  
Wenmin Zhang ◽  
Xiaodan Yang ◽  
Guo An ◽  
Wei Zhao
Keyword(s):  
Breast Cancer ◽  
Cancer Cells ◽  
Cell Lines ◽  
Cancer Cell ◽  
Breast Cancer Cell ◽  
Breast Cancer Cells ◽  
Cancer Cell Lines ◽  
Breast Cancer Cell Lines ◽  
Self Renewal

BACKGROUND: The voltage-gated calcium channel subunit alpha 2 delta 1 (α2δ1) is a functional tumor initial cells (TICs) marker for some solid cancer cells. This study aimed to investigate whether α2δ1 can be used as a potential TIC marker for breast cancer cells. METHODS: α2δ1+ and α2δ1- cells were identified and sorted from the breast cancer cell lines MDA-MB-231, MDA-MB-435s and ZR-75-1 by Immunofluorescence (IF) and Fluorescent-activated cell sorting (FACS) analyses. Spheroid formation in vitro and tumorigenesis in NOD/SCID mice were assessed to determine the self-renewal and serial transplantation abilities of these cells. Using a lentivirus infection system for α2δ1 in breast cancer cell lines, we determined the mRNA levels of stemnessassociated genes by quality real-time PCR (qRT-PCR). Boyden chamber and wounding assays were further performed to detect the migration of α2δ1 overexpression cells. Bioinformatics explored the relationship of molecular classification of breast cancer and drug resistance. RESULTS: α2δ1 presents on the cytomembrane of breast cancer cells, with a positive rate of 1.5–3%. The α2δ1+ cells in breast cancer cell lines have a stronger self-renewal ability and tumor initiating properties in vitro and in vivo. Overexpressing α2δ1 successfully enhanced the sphere-forming efficiency, and upregulated the expression of stemness-associated genes, and increased cell migration. However, seldom significant was available between estrogen receptor +/- (ER+/-), progesterone receptor (PR+/-), and Her2+/-. CONCLUSIONS: Breast cancer cells positive for the α2δ1 charactered tumor initiation, and α2δ1 is a potential TIC marker for breast cancer that further promotes the migration.

Solanum nigrum Anticancer Effect Through Epigenetic Modulations in Breast Cancer Cell Lines

2020 ◽  
Vol 16 (2) ◽  
pp. 121-126
Author(s):  
Atefeh Shirkavand ◽  
Zahra N. Boroujeni ◽  
Seyed A. Aleyasin
Keyword(s):  
Breast Cancer ◽  
Cancer Cells ◽  
Cell Lines ◽  
Cancer Cell ◽  
Breast Cancer Cell ◽  
Breast Cancer Cells ◽  
Methylation Status ◽  
Cancer Cell Lines ◽  
Solanum Nigrum ◽  
Breast Cancer Cell Lines

Background: DNA methylation plays an important role in the regulation of gene expression in mammalian cells and often occurs at CpG islands in the genome. It is more reversible than genetic variations and has therefore attracted much attention for the treatment of many diseases, especially cancer. In the present study, we investigated the effect of Solanum nigrum Extract (SNE) on the methylation status of the VIM and CXCR4 genes in breast cancer cell lines. Methods: The Trypan blue assay was used to study the effect of SNE at various concentrations of 0, 0.1, 1.5, 2.5, 3.5 and 5 mg/ml for 48 h on the survival of three human breast cancer cell lines MCF7, MDA-MB-468, MDA-MB-231. Methylation status of VIM and CXCR4 genes in breast cancer cell lines was assessed by Methylation-Specific PCR (MSP) method. Also, methylation changes of VIM and CXCR4 genes in breast cancer cell lines after treatment with 0.1 mg/ml of SNE for 6 days were analyzed by MSP method. To confirm the effect of SNE on methylation of VIM and CXCR4 genes, Real-Time PCR was performed. Results: The Trypan blue assay results indicated that treatment with SNE reduced cell viability in a dose-dependent manner in breast cancer cells. Our results showed that treatment of breast cancer cells with 0.1 mg/ml of SNE hypermethylated the VIM, CXCR4 genes and significantly reduced the expression levels of their mRNA (P<0.05). Conclusion: Our findings reveal for the first time the impact of SNE on the methylation of breast cancer cells.

scholarly journals Studying the Genomic Role of Cathepsin-D in ER+ Breast Cancer

2021 ◽  
Vol 5 (Supplement_1) ◽  
pp. A817-A818
Author(s):  
Elham Dianati ◽  
Emmanuelle Liaudet-coopman ◽  
Sylvie Mader
Keyword(s):  
Breast Cancer ◽  
Cancer Cells ◽  
Cell Lines ◽  
Cancer Cell ◽  
Breast Cancer Cell ◽  
Cathepsin D ◽  
Breast Cancer Cells ◽  
Cancer Cell Lines ◽  
Proximity Ligation Assay ◽  
Breast Cancer Cell Lines

Abstract Estrogen receptor alpha (ERα), a transcription factor implicated in induction of cell growth in breast cancer, is a therapeutic target that is expressed in &gt;70% of breast tumors. The transcriptional activity of ERα is controlled by ligands and increased through its interaction with co-activators such as the p160/SRC and p300/CBP families. In an attempt to identify the ligand-specific protein complexes involved in transcriptional regulation by ERα, BioID and TurboID screens were performed in two ER+ breast cancer cell lines, T-47D and ZR-75-1. Surprisingly, Cathepsin-D (Cath-D), a lysosomal aspartyl endoproteinase that is an ER target gene, was identified in these screens. Cath-D expression is associated with a poor prognosis and increased metastasis rate in breast cancer irrespective of its catalytic activities {Glondu, 2001 #119}[i]. Cath-D is localized in part to the nucleus where it interacts with TRPS1, a repressor of GATA-mediated transcription and modulator of ERα signaling {Bach, 2015 #117}[ii]. Co-silencing Cath-D and TRPS1 suppressed cell proliferation and inhibited growth under soft agar, suggesting that they cooperate to drive tumorigenesis {Bach, 2015 #117}[ii]. We hypothesized that Cath-D plays genomic as well as non-genomic roles in breast tumor aggressiveness and may alter ERα-mediated transcription. The nuclear localization of Cath-D was confirmed by immunofluorescence using different commercialized antibodies and observed in western blots of chromatin-bound fractions in three different ERα+ breast cancer cell lines, T-47D, ZR-75 and MCF-7. Specificity of the antibodies was confirmed using siRNA-mediated suppression of Cath-D. Moreover, Cath-D was also identified in proximity to TurboID-ERα by LC-MS after chromatin fractionation. The proximity of ERα and Cath-D both in the cytoplasm and nucleus was confirmed by proximity Ligation Assay (PLA) in three ER+ cell lines. Co-immunoprecipitation assays indicated physical interaction of Cath-D with ERα in T-47D cell extracts. Further, Cath-D was detected by ChIP-qPCR on estrogen response elements (EREs) of two ERα target genes, TFF1 and GREB1 in T-47D and ZR-75 cells. These results suggest that Cath-D can interact with ERα on DNA and play genomic roles in ER+ breast cancer cells. [i] Glondu, M., et al. (2001). “A mutated cathepsin-D devoid of its catalytic activity stimulates the growth of cancer cells.” Oncogene20(47): 6920-6929. [ii] Bach, A. S., et al. (2015). “Nuclear cathepsin D enhances TRPS1 transcriptional repressor function to regulate cell cycle progression and transformation in human breast cancer cells.” Oncotarget6(29): 28084-28103.

Synthesis and Bio-evaluation of 2-Alkyl Substituted Fluorinated Genistein Analogues Against Breast Cancer

2021 ◽  
Vol 17 ◽  
Author(s):  
Yingl Zhu ◽  
Fan Zheng ◽  
Can Xiao ◽  
Xiaohe Liu ◽  
Xu Yao ◽  
...  
Keyword(s):  
Breast Cancer ◽  
Molecular Docking ◽  
Cancer Cells ◽  
Cell Lines ◽  
Cancer Cell ◽  
Breast Cancer Cell ◽  
Breast Cancer Cells ◽  
Cancer Cell Lines ◽  
Breast Cancer Cell Lines ◽  
Inhibitory Effects

Background: Breast cancer is the leading cause of cancer death in women. The current methods of chemotherapy for breast cancer generally have strong adverse reactions and drug resistance. Therefore, the discovery of novel anti-breast cancer lead compounds is urgently needed. Objective: Design and synthesize a series of 2-alkyl substituted fluorinated genistein analogues and evaluate their anti-breast cancer activity. Methods: Target compounds were obtained in a multistep reaction synthesis. The anti-tumor activity of compounds I-1~I-35 were evaluated with MCF-7, MDA-MB-231, MDA-MB-435, and MCF-10A cell lines in vitro, with tamoxifen as the positive control. Molecular docking was used to study the interaction between the synthesized compounds and PI3K-gamma. Results: A series of 2-alkyl substituted fluorinated genistein analogues were designed, synthesized and screened for their bioactivity. Most of the compounds displayed better selectivity toward breast cancer cell lines as compared with tamoxifen. Among these analogues, I-2, I-3, I-4, I-9, I-15 and I-17 have the strongest selective inhibition of breast cancer cells. Compounds I-10, I-13, I-15, I-17 and I-33 were found to have significant inhibitory effects on breast cancer cells. Molecular docking studies have shown that these compounds may act as PI3Kγ inhibitors and may further exhibit anti-breast cancer effects. Conclusion: Most of the newly synthesized compounds could highly selectively inhibit breast cancer cell lines. The experimental results indicate that the synthesized analogs may also have obvious selective inhibitory effects on other malignant proliferation cancer cells.

Apigenin Inhibits Growth of Breast Cancer Cells: The Role of ERα and HER2/neu

Acta Naturae ◽  
2015 ◽  
Vol 7 (3) ◽  
pp. 133-139 ◽  
Author(s):  
A. M. Scherbakov ◽  
O. E. Andreeva
Keyword(s):  
Breast Cancer ◽  
Cancer Cells ◽  
Cell Lines ◽  
Cancer Cell ◽  
Breast Cancer Cells ◽  
Cancer Cell Lines ◽  
Luciferase Reporter ◽  
Her2 Positive ◽  
Cytotoxic Effects ◽  
High Doses

Phytoestrogens are a group of plant-derived compounds with an estrogen-like activity. In mammalians, phytoestrogens bind to the estrogen receptor (ER) and participate in the regulation of cell growth and gene transcription. There are several reports of the cytotoxic effects of phytoestrogens in different cancer cell lines. The aim of this study was to measure the phytoestrogen activity against breast cancer cells with different levels of ER expression and to elucidate the molecular pathways regulated by the leader compound. Methods used in the study include immunoblotting, transfection with a luciferase reporter vector, and a MTT test. We demonstrated the absence of a significant difference between ER+ and ER- breast cancer cell lines in their response to cytotoxic stimuli: treatment with high doses of phytoestrogens (apigenin, genistein, quercetin, naringenin) had the same efficiency in ER-positive and ER-negative cells. Incubation of breast cancer cells with apigenin revealed the highest cytotoxicity of this compound; on the contrary, naringenin treatment resulted in a low cytotoxic activity. It was shown that high doses of apigenin (50 М) do not display estrogen-like activity and can suppress ER activation by 17-estradiol. Cultivation of HER2-positive breast cancer SKBR3 cells in the presence of apigenin resulted in a decrease in HER2/neu expression, accompanied by cleavage of an apoptosis substrate PARP. Therefore, the cytotoxic effects of phytoestrogens are not associated with the steroid receptors of breast cancer cells. Apigenin was found to be the most effective phytoestrogen that strongly inhibits the growth of breast cancer cells, including HER2-positive ones.

scholarly journals A systematic flux analysis approach to identify metabolic vulnerabilities in human breast cancer cell lines

2019 ◽  
Vol 7 (1) ◽  
Author(s):  
Sheree D. Martin ◽  
Sean L. McGee
Keyword(s):  
Breast Cancer ◽  
Cancer Cells ◽  
Cell Lines ◽  
Cancer Cell ◽  
Breast Cancer Cell ◽  
Breast Cancer Cells ◽  
Cancer Cell Lines ◽  
Breast Cancer Cell Lines ◽  
Flux Analysis ◽  
Human Breast

Abstract Background Increased flux through both glycolytic and oxidative metabolic pathways is a hallmark of breast cancer cells and is critical for their growth and survival. As such, targeting this metabolic reprograming has received much attention as a potential treatment approach. However, the heterogeneity of breast cancer cell metabolism, even within classifications, suggests a necessity for an individualised approach to treatment in breast cancer patients. Methods The metabolic phenotypes of a diverse panel of human breast cancer cell lines representing the major breast cancer classifications were assessed using real-time metabolic flux analysis. Flux linked to ATP production, pathway reserve capacities and specific macromolecule oxidation rates were quantified. Suspected metabolic vulnerabilities were targeted with specific pathway inhibitors, and relative cell viability was assessed using the crystal violet assay. Measures of AMPK and mTORC1 activity were analysed through immunoblotting. Results Breast cancer cells displayed heterogeneous energy requirements and utilisation of non-oxidative and oxidative energy-producing pathways. Quantification of basal glycolytic and oxidative reserve capacities identified cell lines that were highly dependent on individual pathways, while assessment of substrate oxidation relative to total oxidative capacity revealed cell lines that were highly dependent on individual macromolecules. Based on these findings, mild mitochondrial inhibition in ESH-172 cells, including with the anti-diabetic drug metformin, and mild glycolytic inhibition in Hs578T cells reduced relative viability, which did not occur in non-transformed MCF10a cells. The effects on viability were associated with AMPK activation and inhibition of mTORC1 signalling. Hs578T were also found to be highly dependent on glutamine oxidation and inhibition of this process also impacted viability. Conclusions Together, these data highlight that systematic flux analysis in breast cancer cells can identify targetable metabolic vulnerabilities, despite heterogeneity in metabolic profiles between individual cancer cell lines.

scholarly journals WD-3 inhibits the proliferation of breast cancer cells by regulating the glycolytic pathway

2020 ◽  
Author(s):  
Xiaodan Zhu ◽  
Lu Zhao ◽  
Jianliang You ◽  
Yiqun Ni ◽  
Zhipeng Wei ◽  
...  
Keyword(s):  
Breast Cancer ◽  
Cancer Cells ◽  
Cell Lines ◽  
Cancer Cell ◽  
Breast Cancer Cell ◽  
Breast Cancer Cells ◽  
Cancer Cell Lines ◽  
Breast Cancer Cell Lines ◽  
Hexokinase 2 ◽  
Mcf 7

Number 3 Prescription (WD-3) is an herbal remedy used in traditional Chinese medicine that has been shown to improve the outcomes of patients with advanced colon and gastric cancers. This study aimed to investigate the effect of WD-3 on proliferation, glycolysis, and hexokinase 2 expression in breast cancer cells. Four breast cancer cell lines (MDA-MB-231, BT-549, MCF-7, and MCF-7/ADR-RES) were treated with different concentrations of WD-3 compared with blank control (phosphate-buffered saline). Each of the breast cancer cell lines was also divided into WD-3, paclitaxel, and blank control group. Cell proliferation and morphology were assessed by MTT assay, nuclear Hoechst 33258 staining, or immunofluorescence. Apoptosis was analyzed by flow cytometry. High performance liquid chromatography was used for measurement of ATP, ADP, and AMP. Hexokinase 2 expression was analyzed by Western blot and quantitative reverse transcription PCR. WD-3 inhibited proliferation and increased apoptosis in all four breast cancer cell lines, in a dose-dependent manner. ATP and EC (energy charge) were significantly decreased in WD-3-treated BT-549 and MDA-MB-231 cells. WD-3 significantly downregulated the protein and mRNA expression of hexokinase II in BT-549 cells, however, not in the other three breast cancer cell lines. Our findings indicate that WD-3 targets the glycolytic pathway in breast cancer cells to exert its antitumor activity.

Endocytosis of pro-cathepsin D into breast cancer cells is mostly independent of mannose-6-phosphate receptors

1998 ◽  
Vol 111 (17) ◽  
pp. 2539-2549 ◽  
Author(s):  
V. Laurent-Matha ◽  
M.R. Farnoud ◽  
A. Lucas ◽  
C. Rougeot ◽  
M. Garcia ◽  
...  
Keyword(s):  
Breast Cancer ◽  
Cancer Cells ◽  
Cell Lines ◽  
Cancer Cell ◽  
Cathepsin D ◽  
Breast Cancer Cells ◽  
Cancer Cell Lines ◽  
Breast Cancer Cell Lines ◽  
Mannose 6 Phosphate ◽  
Mcf 7

Cathepsin D trafficking is altered in cancer cells, leading to increased secretion of the pro-enzyme, which can be reinternalized by the same cancer cells and by stromal cells. We studied pro-cathepsin D endocytosis in two human breast cancer cell lines (MDA-MB231, MCF-7) and in human normal fibroblasts. Pro-enzyme uptake was studied indirectly through immunofluorescence analysis of anti-pro-cathepsin D monoclonal antibodies internalized in living cells. Both cancer cell lines internalized the pro-cathepsin D-antibody complex into endosomal compartments in the presence of 10 mM mannose-6-phosphate. Non-malignant fibroblasts, which do not secrete pro-cathepsin D, only internalized anti-cathepsin D antibody when purified pro-cathepsin D was added and this endocytosis was totally inhibited by mannose-6-phosphate. Cathepsin D endocytosis in cancer cells was not mediated by lectins or another receptor binding the cathepsin profragment. It was not due to fluid endocytosis, since another protein pS2 secreted by MCF-7 was not endocytosed with its antibody in the same conditions. Double-immunofluorescence and confocal microscopy analyses revealed that antibodies specific to pro-cathepsin D (M2E8) and to the mannose-6-phosphate/IGFII receptor were co-internalized independently in non-permeabilized MDA-MB231 cells and MCF-7 cells, but not in fibroblasts. Moreover, when metabolically labelled pro-cathepsin D secreted by MCF-7 or MDA-MB231 cells was incubated with homologous or heterologous non-radioactive cells, the time-dependent uptake and maturation of the pro-enzyme into fibroblasts were totally inhibited by mannose-6-phosphate, whereas they were not in the two breast cancer cell lines. The percentage of mannose-6-phosphate-independent binding of radioactively labelled pro-cathepsin D to MDA-MB231 cells at 16 degrees C was higher (7–8%) at low pro-cathepsin D concentration than at high concentration (1.5%), indicating the presence of saturable binding site(s) at the cell surface that are different from the mannose-6-phosphate receptors. We conclude that, in contrast to fibroblasts, breast cancer cells can endocytose the secreted pro-cathepsin D by a cell surface receptor that is different from the mannose-6-phosphate receptors or other lectins. The nature of this alternative receptor and its significance in the action of secreted pro-cathepsin D remain to be elucidated.

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