The effects of cell compressibility, motility and contact inhibition on the growth of tumor cell clusters using the Cellular Potts Model

There are numerous biological examples where genes associated with migratory ability of cells also confer the cells with an increased fitness even though these genes may not have any known effect on the cell mitosis rates. Here, we provide insight into these observations by analyzing the effects of cell migration, compression, and contact inhibition on the growth of tumor cell clusters using the Cellular Potts Model (CPM) in a monolayer geometry. This is a follow-up of a previous study (Thalhauser et al. 2010) in which a Moran-type model was used to study the interaction of cell proliferation, migratory potential and death on the emergence of invasive phenotypes. Here, we extend the study to include the effects of cell size and shape. In particular, we investigate the interplay between cell motility and compressibility within the CPM and find that the CPM predicts that increased cell motility leads to smaller cells. This is an artifact in the CPM. An analysis of the CPM reveals an explicit inverse-relationship between the cell stiffness and motility parameters. We use this relationship to compensate for motility-induced changes in cell size in the CPM so that in the corrected CPM, cell size is independent of the cell motility. We find that subject to comparable levels of compression, clusters of motile cells grow faster than clusters of less motile cells, in qualitative agreement with biological observations and our previous study. Increasing compression tends to reduce growth rates. Contact inhibition penalizes clumped cells by halting their growth and gives motile cells an even greater advantage. Finally, our model predicts cell size distributions that are consistent with those observed in clusters of neuroblastoma cells cultured in low and high density conditions.

Cadherin-11 mediates contact inhibition of locomotion during Xenopus neural crest cell migration

Collective cell migration is an essential feature both in embryonic development and cancer progression. The molecular mechanisms of these coordinated directional cell movements still need to be elucidated. The migration of cranial neural crest (CNC) cells during embryogenesis is an excellent model for collective cell migration in vivo. These highly motile and multipotent cells migrate directionally on defined routes throughout the embryo. Interestingly, local cell-cell interactions seem to be the key force for directionality. CNC cells can change their migration direction by a repulsive cell response called contact inhibition of locomotion (CIL). Cell protrusions collapse upon homotypic cell-cell contact and internal repolarization leads to formation of new protrusions toward cell-free regions. Wnt/PCP signaling was shown to mediate activation of small RhoGTPase RhoA and inhibition of cell protrusions at the contact side. However, the mechanism how a cell recognizes the contact is poorly understood. Here, we demonstrate that Xenopus cadherin-11 (Xcad-11) mediated cell-cell adhesion is necessary in CIL for directional and collective migration of CNC cells. Reduction of Xcad-11 adhesive function resulted in higher invasiveness of CNC due to loss of CIL. Additionally, transplantation analyses revealed that CNC migratory behaviour in vivo is non-directional and incomplete when Xcad-11 adhesive function is impaired. Blocking Wnt/PCP signaling led to similar results underlining the importance of Xcad-11 in the mechanism of CIL and directional migration of CNC.

Establishment of mouse intestinal myofibroblast cell lines

AIM

To establish novel intestinal myofibroblast (IMF) cell lines from mouse colonic mucosa and investigate their biological characters.

METHODS

Primary IMFs were isolated from mucosal tissues of mouse colon that was denuded of epithelial cells and smooth muscle layer. For immortalization, primary IMFs were transfected with simian virus 40 large T antigen (designated as LmcMF). We also isolated some primary IMFs that spontaneously became immortalized without transfection (designated as SmcMF). To check immortality and normality of these cells, we examined their proliferative ability and contact inhibition. Moreover, the expression levels of proteins characterizing IMFs [including α-smooth muscle actin (α-SMA), vimentin, desmin, and type I collagen] and proteins associated with the immune response [such as toll-like receptor 4 (TLR-4), CD14, MD2, IκBα, and p-p38] were determined by Western blotting. The localization of several myofibroblast protein markers was also detected by immunofluorescence staining.

RESULTS

The cell growth assay results show that both LmcMF and SmcMF cells proliferated logarithmically at least up to passage 20. In addition, the contact inhibition assays show that LmcMF and SmcMF stopped growing after the cells reached confluence. These data suggest that these 2 types of cells were immortalized without losing contact inhibition of growth. Moreover, both LmcMF and SmcMF, like primary IMFs, showed spindle-shaped appearance. The expression levels of key myofibroblast protein markers, including α-SMA, vimentin, and desmin, were also examined by the Western blotting and immunofluorescence analyses. Our results show that these cells were positive for α-SMA and vimentin, but not desmin, as well as that both LmcMF and SmcMF expressed type I collagen at a lower level than primary IMFs. Finally, we investigated the expression level of lipopolysaccharide (LPS) receptor-related proteins, as well as the response of the cells to LPS treatment. We found that the TLR4, CD14, and MD-2 proteins were present in LmcMF and SmcMF, as well as in primary IMFs, and that all these cells responded to LPS.

CONCLUSION

We established 2 novel IMF cell lines from mouse colonic mucosa, namely, LmcMF and SmcMF, both of which were able to respond to LPS.

LRIG1 regulates cadherin-dependent contact inhibition directing epithelial homeostasis and pre-invasive squamous cell carcinoma development

Epidermal growth factor receptor (EGFR) pathway activation is a frequent event in human carcinomas. Mutations in EGFR itself are, however, rare, and the mechanisms regulating EGFR activation remain elusive. Leucine-rich immunoglobulin repeats-1 (LRIG1), an inhibitor of EGFR activity, is one of four genes identified that predict patient survival across solid tumour types including breast, lung, melanoma, glioma, and bladder. We show that deletion of Lrig1 is sufficient to promote murine airway hyperplasia through loss of contact inhibition and that re-expression of LRIG1 in human lung cancer cells inhibits tumourigenesis. LRIG1 regulation of contact inhibition occurs via ternary complex formation with EGFR and E-cadherin with downstream modulation of EGFR activity. We find that LRIG1 LOH is frequent across cancers and its loss is an early event in the development of human squamous carcinomas. Our findings imply that the early stages of squamous carcinoma development are driven by a change in amplitude of EGFR signalling governed by the loss of contact inhibition.

Cancer resistance in the blind mole rat is mediated by concerted necrotic cell death mechanism

Blind mole rats Spalax (BMR) are small subterranean rodents common in the Middle East. BMR is distinguished by its adaptations to life underground, remarkable longevity (with a maximum documented lifespan of 21 y), and resistance to cancer. Spontaneous tumors have never been observed in spalacids. To understand the mechanisms responsible for this resistance, we examined the growth of BMR fibroblasts in vitro of the species Spalax judaei and Spalax golani. BMR cells proliferated actively for 7-20 population doublings, after which the cells began secreting IFN-β, and the cultures underwent massive necrotic cell death within 3 d. The necrotic cell death phenomenon was independent of culture conditions or telomere shortening. Interestingly, this cell behavior was distinct from that observed in another long-lived and cancer-resistant African mole rat, Heterocephalus glaber, the naked mole rat in which cells display hypersensitivity to contact inhibition. Sequestration of p53 and Rb proteins using SV40 large T antigen completely rescued necrotic cell death. Our results suggest that cancer resistance of BMR is conferred by massive necrotic response to overproliferation mediated by p53 and Rb pathways, and triggered by the release of IFN-β. Thus, we have identified a unique mechanism that contributes to cancer resistance of this subterranean mammal extremely adapted to life underground.

Involvement of the transcription factor FoxM1 in contact inhibition

Contact inhibition is a crucial mechanism regulating proliferation in vitro and in vivo. Although it is generally accepted that contact inhibition plays a pivotal role in maintaining tissue homeostasis, the molecular mechanisms of contact inhibition are still not fully understood. FoxM1 is known as a proliferation-associated transcription factor and is upregulated in many cancer types. Vice versa, anti-proliferative signals, such as TGF-β and differentiation signals decrease FoxM1 expression. Here we investigated the role of FoxM1 in contact inhibition in fibroblasts. We show that protein expression of FoxM1 is severely and rapidly downregulated upon contact inhibition, probably by inhibition of ERK activity, which then leads to decreased expression of cyclin A and polo-like kinase 1. Vice versa, ectopic expression of FoxM1 prevents the decrease in cyclin A and polo-like kinase 1 and causes a two-fold increase in saturation density indicating loss of contact inhibition. Hence, we show that downregulation of FoxM1 is required for contact inhibition by regulating expression of cyclin A and polo-like kinase 1.

Reconstruction of human papillomavirus type 16-mediated early-stage neoplasia implicates E6/E7 deregulation and the loss of contact inhibition in neoplastic progression

Infection with human papillomavirus type 16 (HPV-16) can lead to low- or high-grade squamous intraepithelial lesions (LSIL or HSIL). Here we show that these in vivo disease states can be replicated in raft cultures of early-pass HPV-16 episomal cell lines, at both the level of pathology and the level of viral gene expression. A reduced responsiveness to cell-cell contact inhibition and an increase in E6/E7 activity correlated closely with phenotype. Similar deregulation is likely to underlie the appearance of LSIL or HSIL soon after infection.

AMPK regulates NADPH homeostasis to promote tumour cell survival during energy stress

Overcoming metabolic stress is a critical step for solid tumour growth. However, the underlying mechanisms of cell death and survival under metabolic stress are not well understood. A key signalling pathway involved in metabolic adaptation is the liver kinase B1 (LKB1)-AMP-activated protein kinase (AMPK) pathway. Energy stress conditions that decrease intracellular ATP levels below a certain level promote AMPK activation by LKB1. Previous studies showed that LKB1-deficient or AMPK-deficient cells are resistant to oncogenic transformation and tumorigenesis, possibly because of the function of AMPK in metabolic adaptation. However, the mechanisms by which AMPK promotes metabolic adaptation in tumour cells are not fully understood. Here we show that AMPK activation, during energy stress, prolongs cell survival by redox regulation. Under these conditions, NADPH generation by the pentose phosphate pathway is impaired, but AMPK induces alternative routes to maintain NADPH and inhibit cell death. The inhibition of the acetyl-CoA carboxylases ACC1 and ACC2 by AMPK maintains NADPH levels by decreasing NADPH consumption in fatty-acid synthesis and increasing NADPH generation by means of fatty-acid oxidation. Knockdown of either ACC1 or ACC2 compensates for AMPK activation and facilitates anchorage-independent growth and solid tumour formation in vivo, whereas the activation of ACC1 or ACC2 attenuates these processes. Thus AMPK, in addition to its function in ATP homeostasis, has a key function in NADPH maintenance, which is critical for cancer cell survival under energy stress conditions, such as glucose limitations, anchorage-independent growth and solid tumour formation in vivo.

ALK-activating homologous mutations in LTK induce cellular transformation

Leukocyte tyrosine kinase (LTK) is a receptor tyrosine kinase reported to be overexpressed in human leukemia. Though much regarding the function of LTK remains unknown, it shares a high degree of similarity with anaplastic lymphoma kinase (ALK), which is found mutated in human cancer. In order to determine if LTK has transforming potential, we created two LTK mutants, F568L and R669Q, that correspond to two well-characterized activating mutations of ALK (F1174L and R1275Q). LTK-F568L, but not wildtype LTK or LTK-R669Q, transformed hematopoietic cells to cytokine independence. LTK-F568L exhibited a stronger ability to induce loss of contact inhibition and anchorage-independent growth of epithelial cells compared to LTK-R669Q, while wildtype LTK was non-transforming in the same cells. Likewise, LTK-F568L induced greater neurite outgrowth of PC12 cells than R669Q, while wildtype LTK could not. Correlating with transforming activity, LTK-F568L displayed significantly enhanced tyrosine phosphorylation compared to wildtype LTK and LTK-R668Q and induced activation of various signaling proteins including Shc, ERK and the JAK/STAT pathway. Expression of wildtype LTK or LTK-R669Q generally led to weaker activation of signaling proteins than expression of LTK-F568L, or no activation at all. Thus, mutating LTK at residue F568, and to a lesser extent at R669, activates the receptor tyrosine kinase, inducing cell signaling that results in transforming properties. These studies suggest that aberrant activation of LTK may contribute to neoplastic cell growth.

Role of JNK-1 regulation in the protection of contact-inhibited fibroblasts from oxidative stress

The molecular signaling events leading to protection from oxidative stress-induced apoptosis upon contact inhibition have not been fully investigated. Previous research has indicated a role for mitogen-activated protein kinases (MAPKs) in the regulation of contact inhibition, and these proteins have also been associated with cell cycle regulation and stress-induced apoptosis. The potential role of the MAPK JNK-1 in the stress-response of actively proliferating and contact-inhibited cells was investigated. Actively proliferating normal fibroblasts (BJ) and fibrosarcoma cells (HT-1080) were stressed with H2O2, and levels of activated JNK-1 and cleaved PARP were ascertained. Similarly, these results were compared with levels of activated JNK-1 and cleaved PARP detected in H2O2-stressed confluent fibrosarcoma or contact-inhibited fibroblast cells. Contact-inhibited fibroblasts were protected from apoptosis in comparison to subconfluent fibroblasts, concurrent with decreased JNK-1 activation. Increased culture density of fibrosarcoma cells was not protective against apoptosis, and these cells did not demonstrate density-dependent alterations in the JNK-1 stress response. This decreased activation of JNK-1 in stressed, contact-inhibited cells did not appear to be dependent upon increased expression of MKP-1; however, over-expression of MKP-1 was sufficient to result in a slight decrease in H2O2-stimulated PARP cleavage. Increasing the antioxidant capacity of fibroblasts through NAC-treatment not only lessened H2O2-stimulated JNK-1 activation, but also did not influence the expression of MKP-1. Taken together, these results suggest that regulation of negative regulation of JNK-1 upon contact inhibition is protective against apoptosis, and that this regulation is independent of MKP-1.

A hybrid model of mammalian cell cycle regulation

The timing of DNA synthesis, mitosis and cell division is regulated by a complex network of biochemical reactions that control the activities of a family of cyclin-dependent kinases. The temporal dynamics of this reaction network is typically modeled by nonlinear differential equations describing the rates of the component reactions. This approach provides exquisite details about molecular regulatory processes but is hampered by the need to estimate realistic values for the many kinetic constants that determine the reaction rates. It is difficult to estimate these kinetic constants from available experimental data. To avoid this problem, modelers often resort to ‘qualitative’ modeling strategies, such as Boolean switching networks, but these models describe only the coarsest features of cell cycle regulation. In this paper we describe a hybrid approach that combines the best features of continuous differential equations and discrete Boolean networks. Cyclin abundances are tracked by piecewise linear differential equations for cyclin synthesis and degradation. Cyclin synthesis is regulated by transcription factors whose activities are represented by discrete variables (0 or 1) and likewise for the activities of the ubiquitin-ligating enzyme complexes that govern cyclin degradation. The discrete variables change according to a predetermined sequence, with the times between transitions determined in part by cyclin accumulation and degradation and as well by exponentially distributed random variables. The model is evaluated in terms of flow cytometry measurements of cyclin proteins in asynchronous populations of human cell lines. The few kinetic constants in the model are easily estimated from the experimental data. Using this hybrid approach, modelers can quickly create quantitatively accurate, computational models of protein regulatory networks in cells.

The physiological behaviors of cells (growth and division, differentiation, movement, death, etc.) are controlled by complex networks of interacting genes and proteins, and a fundamental goal of computational cell biology is to develop dynamical models of these regulatory networks that are realistic, accurate and predictive. Historically, these models have divided along two basic lines: deterministic or stochastic, and continuous or discrete; with scattered efforts to develop hybrid approaches that bridge these divides. Using the cell cycle control system in eukaryotes as an example, we propose a hybrid approach that combines a continuous representation of slowly changing protein concentrations with a discrete representation of components that switch rapidly between ‘on’ and ‘off’ states, and that combines the deterministic causality of network interactions with the stochastic uncertainty of random events. The hybrid approach can be easily tailored to the available knowledge of control systems, and it provides both qualitative and quantitative results that can be compared to experimental data to test the accuracy and predictive power of the model.

[Research progress on proliferative property and capacity of human corneal endothelium]

Primary and secondary corneal endothelial decompensation leads to stromal edema, corneal opacity and loss of visual acuity. The pathogenesis of corneal endothelial decompensation is that adult corneal endothelium in vivo lacks of a robust proliferative response to injury, does not divide sufficiently to replace the lost cells. Previous studies indicate that cell-cell contact inhibition and transforming growth factor-beta2 (TGF-β2) in aqueous humor may be responsible for maintaining human endothelial cells in a non-replicative state in vivo. The results of the experimental investigation by using immunofluorescent staining of the cell cycle-associated proteins and cell proliferation marker Ki67 in corneal endothelium indicate that human corneal endothelial cells in vivo are arrested in the G1-phase and have not exited from the cell cycle. Successful outgrowth in culture of human corneal endothelial cells in vitro and the establishment of the immortalized human endothelial cell line, provide strong evidence that corneal endothelial cells retain proliferative capacity. Experiments with cell culture ex vivo demonstrate that corneal endothelial cells cultured from young donors grow more robustly than those from older donors, and cells cultured from peripheral area of corneas show greater cell density than central regions. Studies have demonstrated that in vitro human corneal endothelia undergo mitotic changes in response to stimulation of growth promoting agents, such as growth factors, EDTA and extracellular matrix. Identification of corneal endothelial stem cells and isolation and culture of human endothelial precursor cells in vitro will be beneficial for further investigation regarding the mechanism of corneal endothelial regeneration as well as corneal endothelial cells in vitro culture.

A reaction-diffusion model of the cadherin-catenin system: a possible mechanism for contact inhibition and implications for tumorigenesis

Contact inhibition is the process by which cells switch from a motile growing state to a passive and stabilized state upon touching their neighbors. When two cells touch, an adhesion link is created between them by means of transmembrane E-cadherin proteins. Simultaneously, their actin filaments stop polymerizing in the direction perpendicular to the membrane and reorganize to create an apical belt that colocalizes with the adhesion links. Here, we propose a detailed quantitative model of the role of cytoplasmic beta-catenin and alpha-catenin proteins in this process, treated as a reaction-diffusion system. Upon cell-cell contact the concentration in alpha-catenin dimers increases, inhibiting actin branching and thereby reducing cellular motility and expansion pressure. This model provides a mechanism for contact inhibition that could explain previously unrelated experimental findings on the role played by E-cadherin, beta-catenin, and alpha-catenin in the cellular phenotype and in tumorigenesis. In particular, we address the effect of a knockout of the adenomatous polyposis coli tumor suppressor gene. Potential direct tests of our model are discussed.

Gene expression profiling reveals new protective roles for vitamin C in human skin cells

The skin is a protective barrier against external insults and any lesion must be rapidly and efficiently repaired. Dermal fibroblasts are the major source of extracellular connective tissue matrix and play an important role in wound healing. Vitamin C is an important water-soluble free radical scavenger and an essential cofactor for collagen synthesis by dermal fibroblasts and, consequently, may contribute to the maintenance of healthy skin. Using microarray analysis, we investigated the effects of long-term exposure to a stable vitamin C derivative, ascorbic acid 2-phosphate (AA2P), in contact-inhibited populations of primary human dermal fibroblasts. Compared with "scorbutic" cells, cells exposed to AA2P increased the expression of genes associated with DNA replication and repair and with the G(2)/M phase of the cell cycle. Consistent with the gene expression changes, AA2P increased the mitogenic stimulation of quiescent fibroblasts by serum factors and cell motility in the context of wound healing. Furthermore, AA2P-treated fibroblasts showed faster repair of oxidatively damaged DNA bases. We propose that vitamin C may protect the skin by promoting fibroblast proliferation, migration, and replication-associated base excision repair of potentially mutagenic DNA lesions, and we discuss the putative involvement of hypoxia-inducible transcription factor-1 and collagen receptor-related signaling pathways.

Contact inhibition of locomotion in vivo controls neural crest directional migration

Contact inhibition of locomotion was discovered by Abercrombie more than 50 years ago and describes the behaviour of fibroblast cells confronting each other in vitro, where they retract their protrusions and change direction on contact. Its failure was suggested to contribute to malignant invasion. However, the molecular basis of contact inhibition of locomotion and whether it also occurs in vivo are still unknown. Here we show that neural crest cells, a highly migratory and multipotent embryonic cell population, whose behaviour has been likened to malignant invasion, demonstrate contact inhibition of locomotion both in vivo and in vitro, and that this accounts for their directional migration. When two migrating neural crest cells meet, they stop, collapse their protrusions and change direction. In contrast, when a neural crest cell meets another cell type, it fails to display contact inhibition of locomotion; instead, it invades the other tissue, in the same manner as metastatic cancer cells. We show that inhibition of non-canonical Wnt signalling abolishes both contact inhibition of locomotion and the directionality of neural crest migration. Wnt-signalling members localize at the site of cell contact, leading to activation of RhoA in this region. These results provide the first example of contact inhibition of locomotion in vivo, provide an explanation for coherent directional migration of groups of cells and establish a previously unknown role for non-canonical Wnt signalling.

Lipid droplet changes in proliferating and quiescent 3T3 fibroblasts

Lipid droplets (LDs) are fat-storing organelles present in virtually all eukaryotic cells and involved in many aspects of cell biology related to lipid metabolism and cholesterol homeostasis. In this study, we investigated the presence of LDs in proliferating and quiescent (contact-inhibited) 3T3 fibroblasts to verify a correlation with cell growth. LDs were characterized by Nile red staining, positivity to adipophilin and negativity to perilipin. LDs were numerous in proliferating cells, but very few in quiescent cells. However, the fraction of quiescent cells, which resumed proliferation after scratch-wound assay, also resumed the formation of LDs. In proliferating cells, the number of LDs correlated with the DNA content, suggesting a continuous accumulation of LDs during cell growth. These findings were supported by biochemical data showing much higher rates of cholesterol esterification and triglyceride synthesis in proliferating cells. Both filipin staining and the fluorescent cholesterol analog dehydroergosterol revealed the presence of an intense traffic of free cholesterol, mediated by acidic vesicles, in proliferating cells. Nile red ratiometric measurements revealed a different lipid composition of LDs in proliferating and quiescent cells. Changes in the number and composition of LDs were also found in growing cells treated with inhibitors of cholesterol esterification (Sandoz 58-035), endosomal cholesterol efflux (U18666A) and V-ATPase (bafilomycin-A1).

Attenuation of p38 MAPK activity upon contact inhibition in fibroblasts

The molecular events, which govern growth control upon contact inhibition have not yet been clearly defined. Previous work has indicated that there is an increase in the expression of mitogen-activated protein kinase phosphatases (MKPs) upon the attainment of contact inhibition in normal fibroblasts, concurrently with a decrease in ERK activity. To investigate the potential role of p38 and JNK in the transition to a contact-inhibited state, normal human fibroblasts (BJ) were grown to subconfluent and confluent densities. The total levels and phosphorylation states of p38 and JNK were assayed, and were compared to protein levels seen in HT-1080 fibrosarcoma cells, which lack contact-inhibited growth control. Activation of JNK was not apparent in these cells, though p38 was found to be active in proliferating cells, but attenuated in contact-inhibited cultures. Such fluctuations in p38 activity were not seen in cultures of fibrosarcoma cells of increasing density. This alteration in p38 activity was also reflected by attenuated activation of the downstream transcription factor ATF-2 upon contact inhibition. Overexpression of MKP-1 in fibrosarcoma cells and fibroblasts reduced proliferation, while expression of a phosphatase-resistant p38 protein (p38(N316)) enhanced proliferation of normal fibroblasts. Taken together, these results suggest the involvement of negative regulation of p38 in contact-inhibited growth control.

Cytotoxic G-rich oligodeoxynucleotides: putative protein targets and required sequence motif

It has recently been shown that certain oligodeoxynucleotides (ODNs) designed as catalytic DNA molecules (DNAzymes) exhibit potent cytotoxicity independent of RNA-cleavage activity in a number of cell lines. These cytotoxic ODNs all featured a 5' G-rich sequence and induced cell death by a TLR9-independent mechanism. In this study, we examined the sequence and length dependence of ODNs for cytotoxicity. A G-rich sequence at the 5' terminus of the molecule was necessary for cytotoxicity and the potency of ODNs with active 5' sequences was length dependent. Cytotoxicity appeared to be generally independent of 3' sequence composition, although 3' sequences totally lacking G-nucleotides were mostly inactive. Nucleolin, elongation factor 1-alpha (eEF1A) and vimentin were identified as binding to a cytotoxic ODN (Dz13) using protein pull-down assays and LC-MS/MS. Although these proteins have previously been described to bind G-rich ODNs, the binding of eEF1A correlated with cytotoxicity, whereas binding of nucleolin and vimentin did not. Quiescent non-proliferating cells were resistant to cytotoxicity, indicating cytotoxicity may be cell cycle dependent. Although the exact mechanism of cytotoxicity remains unknown, marked potency of the longer (> or =25 nt) ODNs in particular, indicates the potential of these molecules for treatment of diseases associated with abnormal cell proliferation.

Characterization of telomerase-immortalized, non-neoplastic, human Barrett's cell line (BAR-T)

Barrett's esophagus, a metaplasia predisposed to malignant transformation, has been studied in vitro using esophageal adenocarcinoma cell lines. However, findings in such transformed cells may not be applicable to the non-neoplastic cells of benign Barrett's esophagus. Therefore, we have developed and characterized a Barrett's cell line derived from a patient without malignancy or dysplasia. Human Barrett's epithelial cells were immortalized with the insertion of hTERT (human telomerase reverse transcriptase) using a Cre-lox recombination system. We then examined properties of this continuous cell line, such as in vitro tumorigenicity, growth patterns, histological differentiation characteristics, karyotype, and checkpoint arrest mechanisms (e.g., p16, p21, and p53). Non-neoplastic Barrett's epithelial cells infected with hTERT (BAR-T cells) have been sustained in culture beyond 200 population doublings. BAR-T cells maintain a diploid chromosome number and exhibit non-neoplastic properties, such as contact inhibition and anchorage-dependent growth. BAR-T cells express differentiation Barrett's epithelial markers, such as villin and cytokeratins 4, 8 and 18, and stain positive for Alcian blue, indicating the presence of mucin-producing cells. Expression of checkpoint arrest proteins p21 and p53 are intact, while p16 expression is lost. Thus, we have created a human Barrett's cell line that is not malignantly transformed, and yet can be maintained indefinitely in culture. BAR-T cells are diploid, have histological differentiation markers characteristic of benign Barrett's epithelium, and also maintain appropriate expression of p21 and p53. This cell line should be a useful model for the study of the early events in carcinogenesis in Barrett's esophagus.

Insulin-like growth factor II receptor-mediated intracellular retention of cathepsin B is essential for transformation of endothelial cells by Kaposi's sarcoma-associated herpesvirus

Kaposi's sarcoma-associated herpesvirus (KSHV) is the pathological agent of Kaposi's sarcoma (KS), a tumor characterized by aberrant proliferation of endothelial-cell-derived spindle cells. Since in many cancers tumorigenesis is associated with an increase in the activity of the cathepsin family, we studied the role of cathepsins in KS using an in vitro model of KSHV-mediated endothelial cell transformation. Small-molecule inhibitors and small interfering RNA (siRNA) targeting CTSB, but not other cathepsins, inhibited KSHV-induced postconfluent proliferation and the formation of spindle cells and foci of dermal microvascular endothelial cells. Interestingly, neither CTSB mRNA nor CTSB protein levels were induced in endothelial cells latently infected with KSHV. Secretion of CTSB was strongly diminished upon KSHV infection. Increased targeting of CTSB to endosomes was caused by the induction by KSHV of the expression of insulin-like growth factor-II receptor (IGF-IIR), a mannose-6-phosphate receptor (M6PR) that binds to cathepsins. Inhibition of IGF-IIR/M6PR expression by siRNA released CTSB for secretion. In contrast to the increased cathepsin secretion observed in most other tumors, viral inhibition of CTSB secretion via induction of an M6PR is crucial for the transformation of endothelial cells.

A simple cell motility assay demonstrates differential motility of human periodontal ligament fibroblasts, gingival fibroblasts, and pre-osteoblasts

During periodontal regeneration, multiple cell types can invade the wound site, thereby leading to repair. Cell motility requires interactions mediated by integrin receptors for the extracellular matrix (ECM), which might be useful in guiding specific cell populations into the periodontal defect. Our data demonstrate that fibroblasts exhibit differential motility when grown on ECM proteins. Specifically, gingival fibroblasts are twice as motile as periodontal ligament fibroblasts, whereas osteoblasts are essentially non-motile. Collagens promote the greatest motility of gingival fibroblasts in the following order: collagen III>collagen V>collagen I. Differences in motility do not correlate with cell proliferation or integrin expression. Osteoblasts display greater attachment to collagens than does either fibroblast population, but lower motility. Gingival fibroblast motility on collagen I is generally mediated by alpha2 integrins, whereas motility on collagen III involves alpha1 integrins. Other integrins (alpha10 or alpha11) may also contribute to gingival fibroblast motility. Thus, ECM proteins do indeed differentially promote the cell motility of periodontal cells. Because of their greater motility, gingival fibroblasts have more of a potential to invade periodontal wound sites and to contribute to regeneration. This finding may explain the formation of disorganized connective tissue masses rather than the occurrence of the true regeneration of the periodontium.