MMP-7 is involved in the aging of primary human mammary epithelial cells (HMEC)

Human MSC-Derived Exosomes Reduce Cellular Senescence in Renal Epithelial Cells

Cellular senescence of renal tubular cells is associated with chronic diseases and age-related kidney disorders. Therapies to antagonize senescence are, therefore, explored as novel approaches in nephropathy. Exosomes derived from human mesenchymal stroma-/stem-like cells (MSC) entail the transfer of multiple bioactive molecules, exhibiting profound regenerative potential in various tissues, including therapeutic effects in kidney diseases. Here, we first demonstrate that exosomes promote proliferation and reduce senescence in aged MSC cultures. For potential therapeutic perspectives in organ rejuvenation, we used MSC-derived exosomes to antagonize senescence in murine kidney primary tubular epithelial cells (PTEC). Exosome treatment efficiently reduced senescence while diminishing the transcription of senescence markers and senescence-associated secretory phenotype (SASP) factors. Concomitantly, we observed less DNA damage foci and more proliferating cells. These data provide new information regarding the therapeutic property of MSC exosomes in the development of renal senescence, suggesting a contribution to a new chapter of regenerative vehicles in senotherapy.

Reversible Growth-Arrest of a Spontaneously-Derived Human MSC-Like Cell Line

Life cycle limitation hampers the production of high amounts of primary human mesenchymal stroma-/stem-like cells (MSC) and limits cell source reproducibility for clinical applications. The characterization of permanently growing MSC544 revealed some differentiation capacity and the simultaneous presence of known MSC markers CD73, CD90, and CD105 even after continuous long-term culture for more than one year and 32 passages. The expression of CD13, CD29, CD44, and CD166 were identified as further surface proteins, all of which were also simultaneously detectable in various other types of primary MSC populations derived from the umbilical cord, bone marrow, and placenta suggesting MSC-like properties in the cell line. Proliferating steady state MSC544 exhibited immune-modulatory activity similar to a subpopulation of long-term growth-inhibited MSC544 after 189d of continuous culture in confluency. This confluent connective cell layer with fibroblast-like morphology can spontaneously contract and the generated space is subsequently occupied by new cells with regained proliferative capacity. Accordingly, the confluent and senescence-associated beta-galactosidase-positive MSC544 culture with about 95% G0/G1 growth-arrest resumed re-entry into the proliferative cell cycle within 3d after sub-confluent culture. The MSC544 cells remained viable during confluency and throughout this transition which was accompanied by marked changes in the release of proteins. Thus, expression of proliferation-associated genes was down-modulated in confluent MSC544 and re-expressed following sub-confluent conditions whilst telomerase (hTERT) transcripts remained detectable at similar levels in both, confluent growth-arrested and proliferating MSC544. Together with the capability of connective cell layer formation for potential therapeutic approaches, MSC544 provide a long term reproducible human cell source with constant properties.

Potential Role of MSC/Cancer Cell Fusion and EMT for Breast Cancer Stem Cell Formation

Solid tumors comprise of maturated cancer cells and self-renewing cancer stem-like cells (CSCs), which are associated with various other nontumorigenic cell populations in the tumor microenvironment. In addition to immune cells, endothelial cells, fibroblasts, and further cell types, mesenchymal stroma/stem-like cells (MSC) represent an important cell population recruited to tumor sites and predominantly interacting with the different cancer cells. Breast cancer models were among the first to reveal distinct properties of CSCs, however, the cellular process(es) through which these cells are generated, maintained, and expanded within neoplastic tissues remains incompletely understood. Here, we discuss several possible scenarios that are not mutually exclusive but may even act synergistically: fusion of cancer cells with MSC to yield hybrid cells and/or the induction of epithelial-mesenchymal transition (EMT) in breast cancer cells by MSC, which can relay signals for retrodifferentiation and eventually, the generation of breast CSCs (BCSCs). In either case, the consequences may be promotion of self-renewal capacity, tumor cell plasticity and heterogeneity, an increase in the cancer cells’ invasive and metastatic potential, and the acquisition of resistance mechanisms towards chemo- or radiotherapy. While specific signaling mechanisms involved in each of these properties remain to be elucidated, the present review article focusses on a potential involvement of cancer cell fusion and EMT in the development of breast cancer stem cells.

Lung cancer deficient in the tumor suppressor GATA4 is sensitive to TGFBR1 inhibition

Lung cancer is the leading cause of cancer-related deaths worldwide. Tumor suppressor genes remain to be systemically identified for lung cancer. Through the genome-wide screening of tumor-suppressive transcription factors, we demonstrate here that GATA4 functions as an essential tumor suppressor in lung cancer in vitro and in vivo. Ectopic GATA4 expression results in lung cancer cell senescence. Mechanistically, GATA4 upregulates multiple miRNAs targeting TGFB2 mRNA and causes ensuing WNT7B downregulation and eventually triggers cell senescence. Decreased GATA4 level in clinical specimens negatively correlates with WNT7B or TGF-β2 level and is significantly associated with poor prognosis. TGFBR1 inhibitors show synergy with existing therapeutics in treating GATA4-deficient lung cancers in genetically engineered mouse model as well as patient-derived xenograft (PDX) mouse models. Collectively, our work demonstrates that GATA4 functions as a tumor suppressor in lung cancer and targeting the TGF-β signaling provides a potential way for the treatment of GATA4-deficient lung cancer.

The tumor suppressor GATA4 is frequently epigenetically silenced in lung cancer. In this study, Gao et al. demonstrate that GATA4 regulates the expression of TGFBR2 and that TGFRB1 inhibitors can synergise with chemotherapeutics to inhibit the growth of GATA4-deficient tumors in mice.

RAC1B: A Rho GTPase with Versatile Functions in Malignant Transformation and Tumor Progression

RAC1B is an alternatively spliced isoform of the monomeric GTPase RAC1. It differs from RAC1 by a 19 amino acid in frame insertion, termed exon 3b, resulting in an accelerated GDP/GTP-exchange and an impaired GTP-hydrolysis. Although RAC1B has been ascribed several protumorigenic functions such as cell cycle progression and apoptosis resistance, its role in malignant transformation, and other functions driving tumor progression like epithelial-mesenchymal transition, migration/invasion and metastasis are less clear. Insertion of exon 3b endows RAC1B with specific biochemical properties that, when compared to RAC1, encompass both loss-of-functions and gain-of-functions with respect to the type of upstream activators, downstream targets, and binding partners. In its extreme, this may result in RAC1B and RAC1 acting in an antagonistic fashion in regulating a specific cellular response with RAC1B behaving as an endogenous inhibitor of RAC1. In this review, we strive to provide the reader with a comprehensive overview, rather than critical discussions, on various aspects of RAC1B biology in eukaryotic cells.

Reduced Breast Tumor Growth after Immunization with a Tumor-Restricted MUC1 Glycopeptide Conjugated to Tetanus Toxoid

Preventive vaccination against tumor-associated endogenous antigens is considered to be an attractive strategy for the induction of a curative immune response concomitant with a long-lasting immunologic memory. The mucin MUC1 is a promising tumor antigen, as its tumor-associated form differs from the glycoprotein form expressed on healthy cells. Due to aberrant glycosylation in tumor cells, the specific peptide epitopes in its backbone are accessible and can be bound by antibodies induced by vaccination. Breast cancer patients develop per se only low levels of T cells and antibodies recognizing tumor-associated MUC1, and clinical trials with tumor-associated MUC1 yielded unsatisfactory therapeutic effects, indicating an urgent need to improve humoral immunity against this tumor entity. Herein, we demonstrate that preventive vaccination against tumor-associated human MUC1 results in a specific humoral immune response, a slowdown of tumor progression and an increase in survival of breast tumor-bearing mice. For preventive vaccination, we used a synthetic vaccine containing a tumor-associated glycopeptide structure of human MUC1 coupled to Tetanus Toxoid. The glycopeptide consists of a 22mer huMUC1 peptide with two immune dominant regions (PDTR and GSTA), glycosylated with the sialylated carbohydrate ST_N on serine-17. PyMT (polyomavirus middle T-antigen) and human MUC1 double-transgenic mice expressing human tumor-associated MUC1 on breast tumor tissue served as a preclinical breast cancer model.

In Vitro Fusion of Normal and Neoplastic Breast Epithelial Cells with Human Mesenchymal Stroma/Stem Cells Partially Involves Tumor Necrosis Factor Receptor Signaling

Formation of hybrid cells by "accidental cell fusion" of normal and neoplastic breast epithelial cells with local tissue-associated mesenchymal stroma/stem-like cells (MSC) in an inflammatory microenvironment can generate new cancer cell populations whereby molecular signaling mechanisms of this process remain unclear. Fusions of lentiviral enhanced green fluorescent protein-labeled MSC with mcherry-labeled breast epithelial cells were quantified and effects of tumor necrosis factor alpha (TNF-α) and receptor downstream signaling were investigated. Cocultures of MSC with normal human mammary epithelial cells, with neoplastic MCF10A, or with MDA-MB-231 or MCF7 breast cancer cells demonstrated hybrid cell formation between 0.1% and about 2% of the populations within 72 hours, whereby the fusion process occurred in less than 5 minutes. Addition of the pro-inflammatory cytokine TNF-α significantly enhanced MCF10A-MSC cell fusion. Small-interfering RNA (siRNA) knockdown experiments revealed an involvement of tumor necrosis factor (TNF) receptor-1 and -2 in this process. This was also substantiated by siRNA knockdown of tumor necrosis factor receptor type 1-associated death domain which abolished TNF-α-stimulated fusion. While TNF receptor signaling can be relayed via the Mitogen-activated protein kinase 8 (MAPK8), NF-κB or cell death pathways, examination of further downstream signaling exhibited little if any effects of MAPK8 or RelA (p65) on TNF-α-mediated cell fusion, respectively. These data suggested that cell fusion between MSC and MCF10A breast epithelial cells can be stimulated by TNF-α involving TNF receptor-activated cell death pathways or additional NF-κB signaling. Stem Cells 2018;36:977-989.

Epithelial cell senescence: an adaptive response to pre-carcinogenic stresses?

Senescence is a cell state occurring in vitro and in vivo after successive replication cycles and/or upon exposition to various stressors. It is characterized by a strong cell cycle arrest associated with several molecular, metabolic and morphologic changes. The accumulation of senescent cells in tissues and organs with time plays a role in organismal aging and in several age-associated disorders and pathologies. Moreover, several therapeutic interventions are able to prematurely induce senescence. It is, therefore, tremendously important to characterize in-depth, the mechanisms by which senescence is induced, as well as the precise properties of senescent cells. For historical reasons, senescence is often studied with fibroblast models. Other cell types, however, much more relevant regarding the structure and function of vital organs and/or regarding pathologies, are regrettably often neglected. In this article, we will clarify what is known on senescence of epithelial cells and highlight what distinguishes it from, and what makes it like, replicative senescence of fibroblasts taken as a standard.

TGF-β-Dependent Growth Arrest and Cell Migration in Benign and Malignant Breast Epithelial Cells Are Antagonistically Controlled by Rac1 and Rac1b

Despite improvements in diagnosis and treatment, breast cancer is still the most common cancer type among non-smoking females. TGF-β can inhibit breast cancer development by inducing cell cycle arrest in both, cancer cells and, as part of a senescence program in normal human mammary epithelial cells (HMEC). Moreover, TGF-β also drives cell migration and invasion, in part through the small GTPases Rac1 and Rac1b. Depletion of Rac1b or Rac1 and Rac1b in MDA-MB-231 or MDA-MB-435s breast cancer cells by RNA interference enhanced or suppressed, respectively, TGF-β1-induced migration/invasion. Rac1b depletion in MDA-MB-231 cells also increased TGF-β-induced p21^WAF1 expression and ERK1/2 phosphorylation. Senescent HMEC (P15/P16), when compared to their non-senescent counterparts (P11/P12), presented with dramatically increased migratory activity. These effects were paralleled by elevated expression of genes associated with TGF-β signaling and metastasis, downregulated Rac1b, and upregulated Rac1. Our data suggest that acquisition of a motile phenotype in HMEC resulted from enhanced autocrine TGF-β signaling, invasion/metastasis-associated gene expression, and a shift in the ratio of antimigratory Rac1b to promigratory Rac1. We conclude that although enhanced TGF-β signaling is considered antioncogenic in HMEC by suppressing oncogene-induced transformation, this occurs at the expense of a higher migration and invasion potential.

Breast Carcinoma: From Initial Tumor Cell Detachment to Settlement at Secondary Sites

Metastasis represents a multistep cascade of cancer cell alterations accompanied by structural and functional changes within the tumor microenvironment which may involve the induction of a retrodifferentiation program. Major steps in metastatic developments include (A) cell detachment from the primary tumor site involving epithelial-mesenchymal transition (EMT), (B) migration and invasion into surrounding tissue, (C) transendothelial intravasation into the vasculature of blood and/or lymphatic vessels as circulating tumor cells (CTCs), (D) dissemination to distant organs, and (E) extravasation of CTCs to secondary sites as disseminated tumor cells (DTCs). This article highlights some aspects of the metastatic cascade with a focus on breast cancer cells. Metastatic steps critically depend on the capability of cancer cells to adapt to distant tissues and the corresponding new microenvironment. As a consequence, increasing plasticity and developmental changes paralleled by acquisition of new cancer cell functionalities challenge a successful therapeutic approach.

Cancer stem cell niche models and contribution by mesenchymal stroma/stem cells

Background

The initiation and progression of malignant tumors is driven by distinct subsets of tumor-initiating or cancer stem-like cells (CSCs) which develop therapy/apoptosis resistance and self-renewal capacity. In order to be able to eradicate these CSCs with novel classes of anti-cancer therapeutics, a better understanding of their biology and clinically-relevant traits is mandatory.

Main body

Several requirements and functions of a CSC niche physiology are combined with current concepts for CSC generation such as development in a hierarchical tumor model, by stochastic processes, or via a retrodifferentiation program. Moreover, progressive adaptation of endothelial cells and recruited immune and stromal cells to the tumor site substantially contribute to generate a tumor growth-permissive environment resembling a CSC niche. Particular emphasis is put on the pivotal role of multipotent mesenchymal stroma/stem cells (MSCs) in supporting CSC development by various kinds of interaction and cell fusion to form hybrid tumor cells.

Conclusion

A better knowledge of CSC niche physiology may increase the chances that cancer stemness-depleting interventions ultimately result in arrest of tumor growth and metastasis.

A Synthetic Glycopeptide Vaccine for the Induction of a Monoclonal Antibody that Differentiates between Normal and Tumor Mammary Cells and Enables the Diagnosis of Human Pancreatic Cancer

In studies within the realm of cancer immunotherapy, the synthesis of exactly specified tumor-associated glycopeptide antigens is shown to be a key strategy for obtaining a highly selective biological reagent, that is, a monoclonal antibody that completely differentiates between tumor and normal epithelial cells and specifically marks the tumor cells in pancreas tumors. Mucin MUC1, which is overexpressed in many prevalent cancers, was identified as a promising target for this strategy. Tumor-associated MUC1 differs significantly from that expressed by normal cells, in particular by altered glycosylation. Structurally defined tumor-associated MUC1 cannot be isolated from tumor cells. We synthesized MUC1-glycopeptide vaccines and analyzed their structure-activity relationships in immunizations; a monoclonal antibody that specifically distinguishes between human normal and tumor epithelial cells was thus generated.

Human mesenchymal stroma/stem cells exchange membrane proteins and alter functionality during interaction with different tumor cell lines

To analyze effects of cellular interaction between human mesenchymal stroma/stem cells (MSC) and different cancer cells, direct co-cultures were performed and revealed significant growth stimulation of the tumor populations and a variety of protein exchanges. More than 90% of MCF-7 and primary human HBCEC699 breast cancer cells as well as NIH:OVCAR-3 ovarian adenocarcinoma cells acquired CD90 proteins during MSC co-culture, respectively. Furthermore, SK-OV-3 ovarian cancer cells progressively elevated CD105 and CD90 proteins in co-culture with MSC. Primary small cell hypercalcemic ovarian carcinoma cells (SCCOHT-1) demonstrated undetectable levels of CD73 and CD105; however, both proteins were significantly increased in the presence of MSC. This co-culture-mediated protein induction was also observed at transcriptional levels and changed functionality of SCCOHT-1 cells by an acquired capability to metabolize 5'cAMP. Moreover, exchange between tumor cells and MSC worked bidirectional, as undetectable expression of epithelial cell adhesion molecule (EpCAM) in MSC significantly increased after co-culture with SK-OV-3 or NIH:OVCAR-3 cells. In addition, a small population of chimeric/hybrid cells appeared in each MSC/tumor cell co-culture by spontaneous cell fusion. Immune fluorescence demonstrated nanotube structures and exosomes between MSC and tumor cells, whereas cytochalasin-D partially abolished the intercellular protein transfer. More detailed functional analysis of FACS-separated MSC and NIH:OVCAR-3 cells after co-culture revealed the acquisition of epithelial cell-specific properties by MSC, including increased gene expression for cytokeratins and epithelial-like differentiation factors. Vice versa, a variety of transcriptional regulatory genes were down-modulated in NIH:OVCAR-3 cells after co-culture with MSC. Together, these mutual cellular interactions contributed to functional alterations in MSC and tumor cells.

Mesenchymal stem cells directly interact with breast cancer cells and promote tumor cell growth in vitro and in vivo

Cellular interactions were investigated between human mesenchymal stem cells (MSC) and human breast cancer cells. Co-culture of the two cell populations was associated with an MSC-mediated growth stimulation of MDA-MB-231 breast cancer cells. A continuous expansion of tumor cell colonies was progressively surrounded by MSC(GFP) displaying elongated cell bodies. Moreover, some MSC(GFP) and MDA-MB-231(cherry) cells spontaneously generated hybrid/chimeric cell populations, demonstrating a dual (green fluorescent protein+cherry) fluorescence. During a co-culture of 5-6 days, MSC also induced expression of the GPI-anchored CD90 molecule in breast cancer cells, which could not be observed in a transwell assay, suggesting the requirement of direct cellular interactions. Indeed, MSC-mediated CD90 induction in the breast cancer cells could be partially blocked by a gap junction inhibitor and by inhibition of the notch signaling pathway, respectively. Similar findings were observed in vivo by which a subcutaneous injection of a co-culture of primary MSC with MDA-MB-231(GFP) cells into NOD/scid mice exhibited an about 10-fold increased tumor size and enhanced metastatic capacity as compared with the MDA-MB-231(GFP) mono-culture. Flow cytometric evaluation of the co-culture tumors revealed more than 90% of breast cancer cells with about 3% of CD90-positive cells, also suggesting an MSC-mediated in vivo induction of CD90 in MDA-MB-231 cells. Furthermore, immunohistochemical analysis demonstrated an elevated neovascularization and viability in the MSC/MDA-MB-231(GFP)-derived tumors. Together, these data suggested an MSC-mediated growth stimulation of breast cancer cells in vitro and in vivo by which the altered MSC morphology and the appearance of hybrid/chimeric cells and breast cancer-expressing CD90(+) cells indicate mutual cellular alterations.

Mesenchymal stem cells as all-round supporters in a normal and neoplastic microenvironment

Mesenchymal stem cells (MSC) represent a heterogeneous population exhibiting stem cell-like properties which are distributed almost ubiquitously among perivascular niches of various human tissues and organs. Organismal requirements such as tissue damage determine interdisciplinary functions of resident MSC including self-renewal, migration and differentiation, whereby MSC support local tissue repair, angiogenesis and concomitant immunomodulation. However, growth of tumor cells and invasion also causes local tissue damage and injury which subsequently activates repair mechanisms and consequently, attracts MSC. Thereby, MSC exhibit a tissue-specific functional biodiversity which is mediated by direct cell-to-cell communication via adhesion molecule signaling and by a tightly regulated exchange of a multifactorial panel of cytokines, exosomes, and micro RNAs. Such interactions determine either tumor-promoting or tumor-inhibitory support by MSC. Moreover, fusion with necrotic/apoptotic tumor cell bodies contributes to re-program MSC into an aberrant phenotype also suggesting that tumor tissue in general represents different types of neoplastic cell populations including tumor-associated stem cell-like cells. The present work summarizes some functional characteristics and biodiversity of MSC and highlights certain controversial interactions with normal and tumorigenic cell populations, including associated modulations within the MSC microenvironment.

LEF-1 regulates proliferation and MMP-7 transcription in breast cancer cells

Matrix metalloproteinase-7 (MMP-7) is a small secreted proteolytic enzyme with broad substrate specificity. Its expression is associated with tumor invasion, metastasis, and survival in a variety of cancers including breast cancer. Using bioinformatics analysis, a conserved LEF-1 binding site became obvious that is mapped at the promoter region of the genomic MMP-7 locus. Consequently, electrophoretic mobility shift assay demonstrated in vitro binding of LEF-1 to the predicted MMP-7 promoter binding site. Here, we demonstrate that lymphoid enhancer binding factor-1 (LEF-1) is associated with regulation of the proliferation-associated cyclin D1 and a gene encoding MMP-7 in breast cancer cells. Thus, a decrease of LEF-1 expression using LEF-1 siRNA resulted in down-regulation of cyclin D and MMP-7 expression, respectively. Moreover, cell cycle analysis of LEF-1 siRNA-transfected human breast cancer cells revealed a significant arrest in G2/M phase. Taken together, our results indicate a pivotal role of LEF-1 in the regulation of proliferation and MMP-7 transcription in breast cancer cells.

In vitro and intrathecal siRNA mediated K(V)1.1 knock-down in primary sensory neurons

K(V)1.1 is a Shaker homologue K(+) channel that contributes to the juxta-paranodal membrane conductance in myelinated axons, and is blocked by fampridine (4-aminopyridine), used to treat the symptoms of multiple sclerosis. The present experiments investigate K(V)1.1 function in primary sensory neurons and A-fibres, and help define its characteristics as a drug-target using sequence specific small-interfering RNAs (siRNAs). siRNA (71nM) was used to knock-down functional expression of K(V)1.1 in sensory neurons (>25μm in apparent diameter) in culture, and was also delivered intrathecally in vivo (9.3μg). K(+) channel knock-down in sensory neurons was found to make the voltage-threshold for action potential generation significantly more negative than in control (p=0.02), led to the breakdown of accommodation and promoted spontaneous action potential firing. Exposure to dendrotoxin-K (DTX-K, 10-100nM) also selectively abolished K(+) currents at negative potentials and made voltage-threshold more negative, consistent with K(V)1.1 controlling excitability close to the nominal resting potential of the neuron cell body, near -60mV. Introduction of one working siRNA sequence into the intrathecal space in vivo was associated with a small increase in the amplitude of the depolarising after-potential in sacral spinal roots (p<0.02), suggesting a reduction in the number of working K(+) channels in internodal axon membrane. Our study provides evidence that K(V)1.1 contributes to the control of peripheral sensory nerve excitability, and suggests that its characteristics as a putative drug target can be assessed by siRNA transfection in primary sensory neurons in vitro and in vivo.

Extracellular signals in young and aging breast epithelial cells and possible connections to age-associated breast cancer development

Aging of human breast tissue is accompanied by certain structural and functional variations and several studies suggest a possible contribution of these changes to an aging-related breast cancer development. At the cellular level, aging of human mammary epithelial cells is associated with significant morphological and functional alterations such as an increased cell size and a reduced proliferation. Cellular senescence of HMEC cannot be explained by a single mechanism but represents an interaction of numerous extra- and intracellular events and the complexity of such orchestrating pathways is still hardly understood. Besides the contribution of reactive oxygen species and telomere dysfunction to aging, it is the aim of this mini-review, to compare distinct changes to extracellular signals by certain matrix metalloproteinases including MMP-7 and associated growth factor pathways mediated by HB-EGF activation in young and aging HMEC. Such changes can alter hormone receptor levels within aged HMEC, induce tissue fibrosis and promote epithelial-to-mesenchymal transition as a potential prerequisite for breast cancer development. Moreover, an accumulation of aging cells during the normal life span of the breast tissue may also substantially effect and interact with adjacent neighboring populations in the local microenvironment to provide optimized growth conditions which would also support neoplastic cells.

Characterization of human breast cancer epithelial cells (HBCEC) derived from long term cultured biopsies

Introduction

For a more individualized therapeutic approach we explored a protease-free method to culture primary cells from breast cancer biopsies.

Methods and Results

Tumor tissue from breast cancer patients after surgery was cultured ex vivo without enzymatic digestion for more than one year and revealed the continuous outgrowth of adherent and proliferating primary cell populations. Immunofluorescence staining of these human breast cancer-derived epithelial cells (HBCEC) and quantification by flow cytometry revealed nearly exclusively cytokeratin-expressing cells. Analysis of surface markers during long term tumor culture of primary HBCEC (more than 476d) demonstrated a prominent expression of CD24, CD44 and MUC1 (CD227). According to aging markers, expression of senescence-associated β-galactosidase revealed little if any positive staining in a primary tumor-derived HBCEC population after 722d in culture, whereas the majority of normal human mammary epithelial cells (HMEC) demonstrated senescent cells already after a culture period of 32d. In this context, HBCEC populations derived from a tumor culture after 152d and 308d, respectively, exhibited a significant telomerase activity, suggesting continuous proliferative capacity. Treatment with several chemotherapeutic compounds and their combinations revealed distinct cytotoxic effects among HBCEC from different breast cancer patients, indicating an individualized response of these tumor-derived primary cells.

Conclusion

The protease-free outgrowth of primary HBCEC offers a patient-specific approach to optimize an individually-designed cancer therapy. Moreover, HBCEC from long term breast tumor tissue cultures resemble tumor cell-like properties by an intact ECM formation and a stable cell surface protein expression providing a reproducible screening platform to identify new biomarkers and to test new therapeutics in individual tumor samples.

Retrodifferentiation--a mechanism for cellular regeneration?

Cellular differentiation can be characterized by the acquisition of specified properties during several steps of development whereby the original stem- or precursor-like populations can finally obtain a certain phenotype with highly specific cell functions. The continuing maturation process can be paralleled by progressively reduced proliferative capacity in various cell types functioning as postmitotic tissues. Conversely, other cell populations (e.g., distinct immune cells) may carry out their specific function upon stimulation of proliferation. While these differentiated phenotypes perform their appropriate specific duties throughout the functioning organism, nature may provide an interesting alternative within this concept of life: sometimes, differentiation steps appear to be reversible. Thus, retrograde differentiation--also termed retrodifferentiation--and accordingly rejuvenation may occur when differentiated cells lose their specific properties acquired during previous steps of maturation. Consequently, retrodifferentiation and rejuvenation could provide enormous potential for tissue repair and cell renewal; however, regulatory dysfunctions within these retrograde developments may also involve the risk of tumor promotion.

Enhanced endothelial cell senescence by lithium-induced matrix metalloproteinase-1 expression

Endothelial cell (EC) senescence and dysfunction occurring after chronic injury and inflammation are highly associated with the development and progression of cardiovascular diseases. However, the factors involved in the establishment of EC senescence remain poorly understood. We have previously shown that lithium, an inhibitor of glycogen synthase kinase (GSK)-3beta and activator of the Wnt/beta-catenin signaling pathway, induces an EC senescent-like phenotype. Herein, we show that lithium induces a rapid and pronounced up-regulation of the matrix metalloproteinase (MMP)-1, an inflammation and senescent cell marker, at the mRNA and protein levels, whereas the induction of two other senescent cell markers is either weak (interleukin-8) or delayed (plasminogen activator inhibitor-1). Lithium effect on MMP-1 expression is also specific among other MMPs and not mediated by GSK3beta inhibition. Lithium affects MMP-1 expression mainly at the transcriptional level but neither the AP1/Ets regulatory sites nor the redox sensitive (-1607/2G) site in MMP-1 promoter are involved in lithium-dependent MMP-1 regulation. However, down-regulation of p53, a target of lithium in EC, dampens both basal and lithium-induced MMP-1 expression, which further links MMP-1 up-regulation with the establishment of cell senescence. Although increased MMP-1 levels are usually associated with angiogenesis in enabled proliferative EC, the exogenous addition of activated MMP-1 on lithium- arrested EC increases the number of EC positive for the senescent-associated-beta-galactosidase marker. Conversely, down-regulation of MMP-1 expression by small interfering RNAs blunts the lithium-dependent increase in senescent-associated-beta-galactosidase positive cells. Altogether our data indicate that lithium-induced MMP-1 may participate in the reinforcement of EC senescence and reveal a novel mechanism for lithium-induced tissue remodeling.

Matrix metalloproteinase-7 and the 20S proteasome contribute to cellular senescence

A detailed understanding of aging and senescence is limited by the complex interplay of the effects of extracellular and environmental stimuli on cellular metabolic, mutational, and epigenetic phenomena. For example, STASIS (stress or aberrant signaling-induced senescence) is affected by the exposure to free radicals and conditions that cause an increased cellular production of reactive oxygen species (ROS) during normal life span. In addition, progressive telomere erosion and telomeric dysfunction contribute to a cellular feature termed replicative or cellular senescence. To focus on distinct cellular pathways that contribute to these different forms of senescence, we investigated the reversible differentiation and aging process of the human U937 leukemia cell line. This was compared to cellular senescence that occurred in normal primary human mammary epithelial cells (HMECs). These two cell systems revealed an important role of the proteolytic activity of the 20S proteasome and its activation by the nuclear protein poly(ADP-ribose) polymerase-1 (PARP-1) during "retrodifferentiation" and rejuvenation of the leukemic cells. Moreover, reduced extracellular proteolytic activity of certain matrix metalloproteinases-for example, MMP-7-is associated with accelerated aging and senescence in normal HMECs.