B7-H3 Expression in Breast Cancer and Brain Metastasis

Brain metastasis is a significant challenge for some breast cancer patients, marked by its aggressive nature, limited treatment options, and poor clinical outcomes. Immunotherapies have emerged as a promising avenue for brain metastasis treatment. B7-H3 (CD276) is an immune checkpoint molecule involved in T cell suppression, which is associated with poor survival in cancer patients. Given the increasing number of clinical trials using B7-H3 targeting CAR T cell therapies, we examined B7-H3 expression across breast cancer subtypes and in breast cancer brain metastases to assess its potential as an interventional target. B7-H3 expression was investigated using immunohistochemistry on tissue microarrays of three clinical cohorts: (i) unselected primary breast cancers (n = 347); (ii) brain metastatic breast cancers (n = 61) and breast cancer brain metastases (n = 80, including a subset of 53 patient-matched breast and brain metastasis cases); and (iii) mixed brain metastases from a range of primary tumours (n = 137). In primary breast cancers, B7-H3 expression significantly correlated with higher tumour grades and aggressive breast cancer subtypes, as well as poorer 5-year survival outcomes. Subcellular localisation of B7-H3 impacted breast cancer-specific survival, with cytoplasmic staining also correlating with a poorer outcome. Its expression was frequently detected in brain metastases from breast cancers, with up to 90% expressing B7-H3. However, not all brain metastases showed high levels of expression, with those from colorectal and renal tumours showing a low frequency of B7-H3 expression (0/14 and 2/16, respectively). The prevalence of B7-H3 expression in breast cancers and breast cancer brain metastases indicates potential opportunities for B7-H3 targeted therapies in breast cancer management.

Tumor heterogeneity in VHL drives metastasis in clear cell renal cell carcinoma

Loss of function of the von Hippel-Lindau (VHL) tumor suppressor gene is a hallmark of clear cell renal cell carcinoma (ccRCC). The importance of heterogeneity in the loss of this tumor suppressor has been under reported. To study the impact of intratumoral VHL heterogeneity observed in human ccRCC, we engineered VHL gene deletion in four RCC models, including a new primary tumor cell line derived from an aggressive metastatic case. The VHL gene-deleted (VHL-KO) cells underwent epithelial-to-mesenchymal transition (EMT) and exhibited increased motility but diminished proliferation and tumorigenicity compared to the parental VHL-expressing (VHL+) cells. Renal tumors with either VHL+ or VHL-KO cells alone exhibit minimal metastatic potential. Combined tumors displayed rampant lung metastases, highlighting a novel cooperative metastatic mechanism. The poorly proliferative VHL-KO cells stimulated the proliferation, EMT, and motility of neighboring VHL+ cells. Periostin (POSTN), a soluble protein overexpressed and secreted by VHL non-expressing (VHL-) cells, promoted metastasis by enhancing the motility of VHL-WT cells and facilitating tumor cell vascular escape. Genetic deletion or antibody blockade of POSTN dramatically suppressed lung metastases in our preclinical models. This work supports a new strategy to halt the progression of ccRCC by disrupting the critical metastatic crosstalk between heterogeneous cell populations within a tumor.

Landscape of Epidermal Growth Factor Receptor Heterodimers in Brain Metastases

Simple Summary

HER2+ breast cancer patients are treated with agents that tag HER2+ tumour cells for elimination by the immune system, down-modulate HER2 activity and/or block the formation of HER2 dimers, including the neuregulin-1 receptor, HER2-HER3. HER2-targeted therapies prolong survival by lowering the risk of relapse, but do not prevent brain metastases. The reasons for this are not fully understood. We quantified HER2-HER3 dimers in 203 brain metastases, and 34 primary breast tumour samples. Dimer frequency was relatively high in brain metastases from breast, ovarian, lung and kidney cancers, and in brain metastases compared to patient-matched breast tumours; but did not reliably correlate with HER2/HER3 expression or activation. In in vitro experiments, pertuzumab failed to suppress HER2-HER3 dimers in HER2+ breast cancer cells provided with a saturating concentration of neuregulin-1. These findings may provide insights about the differences in intracranial versus extracranial efficacy of HER2-targeted therapies.

Abstract

HER2+ breast cancer patients have an elevated risk of developing brain metastases (BM), despite adjuvant HER2-targeted therapy. The mechanisms underpinning this reduced intracranial efficacy are unclear. We optimised the in situ proximity ligation assay (PLA) for detection of the high-affinity neuregulin-1 receptor, HER2-HER3 (a key target of pertuzumab), in archival tissue samples and developed a pipeline for high throughput extraction of PLA data from fluorescent microscope image files. Applying this to a large BM sample cohort (n = 159) showed that BM from breast, ovarian, lung and kidney cancers have higher HER2-HER3 levels than other primary tumour types (melanoma, colorectal and prostate cancers). HER2 status, and tumour cell membrane expression of pHER2(Y^1221/1222) and pHER3(Y¹²²²) were positively, but not exclusively, associated with HER2-HER3 frequency. In an independent cohort (n = 78), BM had significantly higher HER2-HER3 levels than matching primary tumours (p = 0.0002). For patients who had two craniotomy procedures, HER2-HER3 dimer levels were lower in the consecutive lesion (n = 7; p = 0.006). We also investigated the effects of trastuzumab and pertuzumab on five different heterodimers in vitro: HER2-EGFR, HER2-HER4, HER2-HER3, HER3-HER4, HER3-EGFR. Treatment significantly altered the absolute frequencies of individual complexes in SKBr3 and/or MDA-MB-361 cells, but in the presence of neuregulin-1, the overall distribution was not markedly altered, with HER2-HER3 and HER2-HER4 remaining predominant. Together, these findings suggest that markers of HER2 and HER3 expression are not always indicative of dimerization, and that pertuzumab may be less effective at reducing HER2-HER3 dimerization in the context of excess neuregulin.

Brazilin Removes Toxic Alpha-Synuclein and Seeding Competent Assemblies from Parkinson Brain by Altering Conformational Equilibrium

Alpha-synuclein (α-syn) fibrils, a major constituent of the neurotoxic Lewy Bodies in Parkinson's disease, form via nucleation dependent polymerization and can replicate by a seeding mechanism. Brazilin, a small molecule derived from red cedarwood trees in Brazil, has been shown to inhibit the fibrillogenesis of amyloid-beta (Aβ) and α-syn as well as remodel mature fibrils and reduce cytotoxicity. Here we test the effects of Brazilin on both seeded and unseeded α-syn fibril formation and show that the natural polyphenol inhibits fibrillogenesis of α-syn by a unique mechanism that alters conformational equilibria in two separate points of the assembly mechanism: Brazilin preserves the natively unfolded state of α-syn by specifically binding to the compact conformation of the α-syn monomer. Brazilin also eliminates seeding competence of α-syn assemblies from Parkinson's disease patient brain tissue, and reduces toxicity of pre-formed assemblies in primary neurons by inducing the formation of large fibril clusters. Molecular docking of Brazilin shows the molecule to interact both with unfolded α-syn monomers and with the cross-β sheet structure of α-syn fibrils. Our findings suggest that Brazilin has substantial potential as a neuroprotective and therapeutic agent for Parkinson's disease.

Novel highly specific anti-periostin antibodies uncover the functional importance of the fascilin 1-1 domain and highlight preferential expression of periostin in aggressive breast cancer

Periostin (POSTN), a secreted homodimeric protein that binds integrins αvβ3, αvβ5, and α6β4, was originally found to be expressed in fetal tissues and in the adult upon injury particularly bone fractures due to its role in remodelling and repair. Recently it was found to be over-expressed in human breast cancer and a variety of other tumour types including head and neck squamous cell carcinoma, where its overexpression correlates with increased tumour invasion. Progress in studying its functional role in tumour pathogenesis has been hampered by the paucity of antibodies for its specific and sensitive detection. It has proven very difficult to obtain monoclonal antibodies (mAbs) against this highly conserved protein but we report here that combining infection of mice with lactate dehydrogenase elevating virus (LDV), a B cell activating arterivirus, with conjugation of human POSTN to ovalbumin as an immunogenic carrier, enabled us to develop six mAbs recognizing both human and mouse POSTN and inhibiting its binding to αvβ3 integrin. Two of the mAbs, MPB4B1 and MPC5B4, were tested and found to inhibit POSTN-induced migration of human endothelial colony forming cells. All six mAbs recognized amino acids 136-51 (APSNEAWDNLDSDIRR) within the POSTN fascilin (FAS) 1-1 domain revealing the functional importance of this motif; this was further highlighted by the ability of aa 136-151 peptide to inhibit integrin-mediated cell migration. Immunohistochemistry using MPC5B4, indicated that breast tumour cell POSTN expression was a strong prognostic indicator, along with tumour size, lymph node, and human epidermal growth factor receptor 2 (HER2) status.

Identification of clinical target areas in the brainstem of prion-infected mice

AIMS

While prion infection ultimately involves the entire brain, it has long been thought that the abrupt clinical onset and rapid neurological decline in laboratory rodents relates to involvement of specific critical neuroanatomical target areas. The severity and type of clinical signs, together with the rapid progression, suggest the brainstem as a candidate location for such critical areas. In this study we aimed to correlate prion pathology with clinical phenotype in order to identify clinical target areas.

METHOD

We conducted a comprehensive survey of brainstem pathology in mice infected with two distinct prion strains, which produce different patterns of pathology, in mice overexpressing prion protein (with accelerated clinical onset) and in mice in which neuronal expression was reduced by gene targeting (which greatly delays clinical onset).

RESULTS

We identified specific brainstem areas that are affected by prion pathology during the progression of the disease. In the early phase of disease the locus coeruleus, the nucleus of the solitary tract, and the pre-Bötzinger complex were affected by prion protein deposition. This was followed by involvement of the motor and autonomic centres of the brainstem.

CONCLUSIONS

Neurodegeneration in the locus coeruleus, the nucleus of the solitary tract and the pre-Bötzinger complex predominated and corresponded to the manifestation of the clinical phenotype. Because of their fundamental role in controlling autonomic function and the overlap with clinical signs in sporadic Creutzfeldt-Jakob disease, we suggest that these nuclei represent key clinical target areas in prion diseases.

Tumour suppressors and cellular senescence

Cellular senescence is a stable cell cycle arrest that normal cells undergo in response to a variety of intrinsic and extrinsic stimuli, including progressive telomere shortening, changes in telomeric structure or other forms of genotoxic as well nongenotoxic stress. Senescence is thought to have originated as a remodelling program that is active in embryonic development and acts as a key tumour suppressor mechanism during the reproductive stage in early adult life, by leading to the removal of potentially cancerous cells. However, in later adult life, it promotes organismal aging by compromising tissue repair and regeneration due to the accumulation of senescent cells, depletion of stem/progenitor cells and secretion of an array of inflammatory cytokines, chemokines and matrix metalloproteases. Whilst suppressing tumour formation in the senescent cells, these inflammatory cytokines, chemokines and metalloproteases can promote tumour progression and metastasis in the neighbouring cells. Herein, we review the molecular pathways that underlie cellular senescence and how it contributes towards tumour suppression.

Cellular senescence and aging: the role of B-MYB

Cellular senescence is a stable cell cycle arrest, caused by insults, such as: telomere erosion, oncogene activation, irradiation, DNA damage, oxidative stress, and viral infection. Extrinsic stimuli such as cell culture stress can also trigger this growth arrest. Senescence is thought to have evolved as an example of antagonistic pleiotropy, as it acts as a tumor suppressor mechanism during the reproductive age, but can promote organismal aging by disrupting tissue renewal, repair, and regeneration later in life. The mechanisms underlying the senescence growth arrest are broadly considered to involve p16(INK4A) -pRB and p53-p21(CIP1/WAF1/SDI1) tumor suppressor pathways; but it is not known what makes the senescence arrest stable and what the critical downstream targets are, as they are likely to be key to the establishment and maintenance of the senescent state. MYB-related protein B (B-MYB/MYBL2), a member of the myeloblastosis family of transcription factors, has recently emerged as a potential candidate for regulating entry into senescence. Here, we review the evidence which indicates that loss of B-MYB expression has an important role in causing senescence growth arrest. We discuss how B-MYB acts, as the gatekeeper, to coordinate transit through the cell cycle, in conjunction with the multivulval class B (MuvB) complex and FOXM1 transcription factors. We also evaluate the evidence connecting B-MYB to the mTOR nutrient signaling pathway and suggest that inhibition of this pathway leading to an extension of healthspan may involve activation of B-MYB.

Regulation of p53 and Rb links the alternative NF-κB pathway to EZH2 expression and cell senescence

There are two major pathways leading to induction of NF-κB subunits. The classical (or canonical) pathway typically leads to the induction of RelA or c-Rel containing complexes, and involves the degradation of IκBα in a manner dependent on IκB kinase (IKK) β and the IKK regulatory subunit NEMO. The alternative (or non-canonical) pathway, involves the inducible processing of p100 to p52, leading to the induction of NF-κB2(p52)/RelB containing complexes, and is dependent on IKKα and NF-κB inducing kinase (NIK). Here we demonstrate that in primary human fibroblasts, the alternative NF-κB pathway subunits NF-κB2 and RelB have multiple, but distinct, effects on the expression of key regulators of the cell cycle, reactive oxygen species (ROS) generation and protein stability. Specifically, following siRNA knockdown, quantitative PCR, western blot analyses and chromatin immunoprecipitation (ChIP) show that NF-κB2 regulates the expression of CDK4 and CDK6, while RelB, through the regulation of genes such as PSMA5 and ANAPC1, regulates the stability of p21WAF1 and the tumour suppressor p53. These combine to regulate the activity of the retinoblastoma protein, Rb, leading to induction of polycomb protein EZH2 expression. Moreover, our ChIP analysis demonstrates that EZH2 is also a direct NF-κB target gene. Microarray analysis revealed that in fibroblasts, EZH2 antagonizes a subset of p53 target genes previously associated with the senescent cell phenotype, including DEK and RacGAP1. We show that this pathway provides the major route of crosstalk between the alternative NF-κB pathway and p53, a consequence of which is to suppress cell senescence. Importantly, we find that activation of NF-κB also induces EZH2 expression in CD40L stimulated cells from Chronic Lymphocytic Leukemia patients. We therefore propose that this pathway provides a mechanism through which microenvironment induced NF-κB can inhibit tumor suppressor function and promote tumorigenesis.

Although the classical NF-κB pathway is frequently associated with the induction of cellular senescence and the senescence associated secretory phenotype (SASP), the role of the alternative NF-κB pathway, which is frequently activated in hematological malignancies as well as some solid tumors, has not been defined. We therefore investigated the role of the alternative NF-κB pathway in this process. Here we report that NF-κB2 and RelB, the effectors of the alternative NF-κB pathway, suppress senescence through inhibition of p53 activity. Using primary human fibroblasts, we demonstrate that this is accomplished through NF-κB2/RelB dependent control of a previously unknown pathway, incorporating regulation of CDK4 and 6 expression as well as regulators of p21WAF1 and p53 protein stability. Loss of NF-κB2/RelB results in suppression of retinoblastoma (Rb) tumour suppressor phosphorylation, which in turn leads to inhibition of EZH2 expression and de-repression of p53 activity. Interestingly, we find that CD40 ligand stimulation of cells from Chronic Lymphocytic Leukemia patients, which strongly induces the alternative NF-κB pathway, also induces EZH2 expression. We propose that the alternative NF-κB pathway can promote tumorigenesis through suppression of p53 dependent senescence, a process that may have relevance to cancer cells retaining wild type p53.

Friend or foe: emerging role of nuclear factor kappa-light-chain-enhancer of activated B cells in cell senescence

The nuclear factor kappa-light-chain-enhancer of activated B cells (NF-κB) proteins are a family of ubiquitously expressed transcription factors that regulate the response to cellular stress. They mediate innate and adaptive immunity through the initiation of an inflammatory response to pro-inflammatory signals. The role of persistent inflammation in aiding tumor development has led to the NF-κB family of transcription factors being strongly implicated in promoting cancer. However, recent studies have now revealed that NF-κB can also function as a tumor suppressor through the induction of cellular senescence. Cellular senescence is a stable cell cycle arrest that normal cells undergo in response to a variety of intrinsic and extrinsic stimuli including: progressive telomere shortening, changes in telomeric structure, or other forms of genotoxic stress. Senescence can compromise tissue repair and regeneration, contributing to tissue and organismal aging via the accumulation of senescent cells, depletion of stem/progenitor cells and secretion of an array of inflammatory cytokines, chemokines, and matrix metalloproteinases. Senescence can also lead to the removal of potentially cancerous cells, thereby acting as a potent tumor suppressor mechanism. Herein, we review the evidence indicating a role for NF-κB in tumor suppression via cellular senescence and suggest that depending upon the subunit expressed, the biological context, and the type and intensity of the signal, NF-κB can indeed promote senescence growth arrest.

Deciphering the role of nuclear factor-κB in cellular senescence

Cellular senescence is a program of irreversible cell cycle arrest that cells undergo in response to a variety of intrinsic and extrinsic stimuli including progressive shortening of telomeres, changes in telomeric structure or other forms of genotoxic and non-genotoxic stress. The role of nuclear factor-κB in cellular senescence is controversial, as it has been associated with both proliferation and tumour progression, and also with growth arrest and ageing. This research perspective focuses on the evidence for a functional relationship between NF-κB and senescence, and how disruption of the NF-κB pathway can lead to its bypass.

An RNA interference screen for identifying downstream effectors of the p53 and pRB tumour suppressor pathways involved in senescence

Background

Cellular senescence is an irreversible cell cycle arrest that normal cells undergo in response to progressive shortening of telomeres, changes in telomeric structure, oncogene activation or oxidative stress and acts as an important tumour suppressor mechanism.

Results

To identify the downstream effectors of the p53-p21 and p16-pRB tumour suppressor pathways crucial for mediating entry into senescence, we have carried out a loss-of-function RNA interference screen in conditionally immortalised human fibroblasts that can be induced to rapidly undergo senescence, whereas in primary cultures senescence is stochastic and occurs asynchronously. These cells are immortal but undergo a rapid irreversible arrest upon activation of the p53-p21 and p16-pRB pathways that can be readily bypassed upon their inactivation. The primary screen identified 112 known genes including p53 and another 29 shRNAmirs targetting as yet unidentified loci. Comparison of these known targets with genes known to be up-regulated upon senescence in these cells, by micro-array expression profiling, identified 4 common genes TMEM9B, ATXN10, LAYN and LTBP2/3. Direct silencing of these common genes, using lentiviral shRNAmirs, bypassed senescence in the conditionally immortalised cells.

Conclusion

The senescence bypass screen identified TMEM9B, ATXN10, LAYN and LTBP2/3 as novel downstream effectors of the p53-p21 and p16-pRB tumour suppressor pathways. Although none of them has previously been linked to cellular senescence, TMEM9B has been suggested to be an upstream activator of NF-κB signalling which has been found to have a causal role in promoting senescence. Future studies will focus on determining on how many of the other primary hits also have a casual role in senescence and what is the mechanism of action.

Proteome profiling of immortalization-to-senescence transition of human breast epithelial cells identified MAP2K3 as a senescence-promoting protein which is downregulated in human breast cancer

PURPOSE

immortalization is one of the first changes in cells undergoing carcinogenic transformation. Proteome profiling of the immortalization-senescence transition is expected to provide insights into the molecular mechanisms of early tumorigenesis.

EXPERIMENTAL DESIGN

2-DE and MALDI-MS were used to identify proteins in primary human breast epithelial cells, relevant to the immortalization-senescence transition. Cell and molecular biology and immunohistochemistry were used to validate involvement of mitogen-activated protein kinase kinase 3 (MAP2K3) in the immortalization-senescence transition.

RESULTS

we identified 71 proteins whose expression changed upon induction of senescence. The identified proteins include regulators of cell growth, death, cell assembly and organization. Analysis of the network formed by the identified proteins suggested that the immortalization-to-senescence transition could affect regulators of the cell cycle, protein synthesis, transport, post-translational modifications, DNA recombination and repair, and lipid and amino acid metabolism. We observed that MAP2K3 was downregulated in immortal human breast epithelial cells and that upregulation of MAP2K3 expression promoted cell senescence. Decreased expression of MAP2K3 was observed in human breast infiltrating ductal carcinomas, as compared to non-cancerous human breast tissues.

CONCLUSION AND CLINICAL RELEVANCE

we described a proteome profile of the immortalization-to-senescence transition for human breast epithelial cells, and identified MAP2K3 as a protein that promotes senescence in these cells.

Dissecting the transcriptional networks underlying breast cancer: NR4A1 reduces the migration of normal and breast cancer cell lines

Introduction

Breast cancer currently accounts for more than one-quarter of all female cancers and, despite the great progress in treatment observed in the past few years, the need for identification of new gene targets that can be used for diagnosis, prognosis and therapy is evident. A previous study identified the transcription factor NR4A1 as a gene upregulated in primary breast cancer compared with normal tissue by microarray analysis and sequencing technologies. The purpose of the study was to identify the role of NR4A1 in normal mammary epithelial and breast cancer cell biology.

Methods

NR4A1 expression in breast tumours was assessed by semiquantitative and real-time PCR using RNA from normal and tumour samples or breast cancer cell lines. Immunohistochemistry on tissue microarrays was performed to check NR4A1 protein expression in breast tumours. MCF-10A and 226L normal mammary epithelial cells as well as the tumour lines PMC42, ZR-75-1 and MDA-MB-231 were transduced with full-length NR4A1, and the ability of NR4A1-overexpressing cells to migrate was tested using scratch wound or transwell migration assays. Proliferation was measured using the MTT and BrdU assays, while apoptosis was determined by the Annexin V assay. The ability of the cells to adhere to extracellular matrix was tested by adhesion assays and integrin cell surface expression was measured by flow cytometry. Activation of the FAK as well as ERK1/2 and PI3K pathways was checked by western blotting.

Results

Breast tissue microarray analysis showed NR4A1 expression in primary tumours, which was reduced in higher grade and metastatic tumours. Ectopic expression of NR4A1 in MCF-10A, 226L, PMC42 and ZR-75-1 cells led to reduced ability of the cells to migrate, while no differences were observed in their proliferation and apoptotic index. NR4A1 expression altered the ability of the MCF-10A cells to adhere to the extracellular matrix and affected cell surface expression of integrins.

Conclusions

NR4A1 acts as an antimigratory factor in two normal mammary epithelial and two breast cancer cell lines tested. It is therefore possible that NR4A1 acts as an antimigratory factor in breast tumours, and further studies should be conducted to understand the mechanisms involved.

Preparation of monoclonal antibodies against the spindle checkpoint kinase Bub1

The Bub1 kinase is a critical component of the spindle checkpoint involved in monitoring the separation of sister chromatids at mitosis. The viral oncoprotein Simian virus 40 large T antigen (LT) can bind and perturb the spindle checkpoint function of Bub1. We have developed three highly specific monoclonal antibodies against the Bub1 protein and have demonstrated that they can all detect Bub1 via Western blotting and immunofluorescence, in addition to their ability to immunoprecipitate Bub1.

Surveillance mechanism linking Bub1 loss to the p53 pathway

Bub1 is a kinase believed to function primarily in the mitotic spindle checkpoint. Mutation or aberrant Bub1 expression is associated with chromosomal instability, aneuploidy, and human cancer. We now find that targeting Bub1 by RNAi or simian virus 40 (SV40) large T antigen in normal human diploid fibroblasts results in premature senescence. Interestingly, cells undergoing replicative senescence were also low in Bub1 expression, although ectopic Bub1 expression in presenescent cells was insufficient to extend lifespan. Premature senescence caused by lower Bub1 levels depends on p53. Senescence induction was blocked by dominant negative p53 expression or depletion of p21(CIP1), a p53 target. Importantly, cells with lower Bub1 levels and inactivated p53 became highly aneuploid. Taken together, our data highlight a role for p53 in monitoring Bub1 function, which may be part of a more general spindle checkpoint surveillance mechanism. Our data support the hypothesis that Bub1 compromise triggers p53-dependent senescence, which limits the production of aneuploid and potentially cancerous cells.

Retrovirus-mediated conditional immortalization and analysis of established cell lines of osteoclast precursor cells

Osteoclast precursor cells (OPCs) have previously been established from bone marrow cells of SV40 temperature-sensitive T antigen-expressing transgenic mice. Here, we use retrovirus-mediated gene transfer to conditionally immortalize OPCs by expressing temperature-sensitive large T antigen (tsLT) from wild type bone marrow cells. The immortalized OPCs proliferated at the permissive temperature of 33.5 degrees C, but stopped growing at the non-permissive temperature of 39 degrees C. In the presence of receptor activator of NFkappaB ligand (RANKL), the OPCs differentiated into tartrate-resistant acid phosphatase (TRAP)-positive cells and formed multinucleate osteoclasts at 33.5 degrees C. From these OPCs, we cloned two types of cell lines. Both differentiated into TRAP-positive cells, but one formed multinucleate osteoclasts while the other remained unfused in the presence of RANKL. These results indicate that the established cell lines are useful for analyzing mechanisms of differentiation, particularly multinucleate osteoclast formation. Retrovirus-mediated conditional immortalization should be a useful method to immortalize OPCs from primary bone marrow cells.

Glucose induces increases in levels of the transcriptional repressor Id2 via the hexosamine pathway

Changes in glucose levels are known to directly alter gene expression. A number of previous studies have found that these effects are in part mediated by modulating the levels and the activity of transcription factors. We have investigated an alternative mechanism by which glucose might regulate gene expression by modulating levels of a transcriptional repressor. We have focused on Id2, which is a protein that indirectly regulates gene expression by sequestering certain transcription factors and preventing them from forming functional dimers. Id2 targets include the class A basic helix-loop-helix transcription factors and the sterol regulatory element-binding protein (SREBP)-1. We demonstrate that increases in glucose levels cause a rapid increase in levels of Id2 in J774.2 macrophages, and a number of lines of evidence indicate that this is via the hexosamine pathway because 1) the effect of glucose requires glutamine; 2) the effect of glucose is mimicked by low levels of glucosamine; 3) the effect of glucose is inhibited by azaserine, an inhibitor of glutamine:fructose-6-phosphate amidotransferase (GFAT); and 4) adenoviral mediated overexpression of GFAT increases levels of Id2. We go on to show that increases in Id2 can have functional effects on metabolic genes, because Id2 blocked the SREBP-1-induced induction of hormone-sensitive lipase (HSL) promoter activity, whereas Id2 alone does not modulate activity of the HSL promoter. In summary, these studies define a new mechanism by which glucose uses the hexosamine pathway to regulate gene expression by increasing levels of a transcriptional repressor.

Establishment of the epithelial-specific transcriptome of normal and malignant human breast cells based on MPSS and array expression data

INTRODUCTION

Diverse microarray and sequencing technologies have been widely used to characterise the molecular changes in malignant epithelial cells in breast cancers. Such gene expression studies to identify markers and targets in tumour cells are, however, compromised by the cellular heterogeneity of solid breast tumours and by the lack of appropriate counterparts representing normal breast epithelial cells.

METHODS

Malignant neoplastic epithelial cells from primary breast cancers and luminal and myoepithelial cells isolated from normal human breast tissue were isolated by immunomagnetic separation methods. Pools of RNA from highly enriched preparations of these cell types were subjected to expression profiling using massively parallel signature sequencing (MPSS) and four different genome wide microarray platforms. Functional related transcripts of the differential tumour epithelial transcriptome were used for gene set enrichment analysis to identify enrichment of luminal and myoepithelial type genes. Clinical pathological validation of a small number of genes was performed on tissue microarrays.

RESULTS

MPSS identified 6,553 differentially expressed genes between the pool of normal luminal cells and that of primary tumours substantially enriched for epithelial cells, of which 98% were represented and 60% were confirmed by microarray profiling. Significant expression level changes between these two samples detected only by microarray technology were shown by 4,149 transcripts, resulting in a combined differential tumour epithelial transcriptome of 8,051 genes. Microarray gene signatures identified a comprehensive list of 907 and 955 transcripts whose expression differed between luminal epithelial cells and myoepithelial cells, respectively. Functional annotation and gene set enrichment analysis highlighted a group of genes related to skeletal development that were associated with the myoepithelial/basal cells and upregulated in the tumour sample. One of the most highly overexpressed genes in this category, that encoding periostin, was analysed immunohistochemically on breast cancer tissue microarrays and its expression in neoplastic cells correlated with poor outcome in a cohort of poor prognosis estrogen receptor-positive tumours.

CONCLUSION

Using highly enriched cell populations in combination with multiplatform gene expression profiling studies, a comprehensive analysis of molecular changes between the normal and malignant breast tissue was established. This study provides a basis for the identification of novel and potentially important targets for diagnosis, prognosis and therapy in breast cancer.

Functional genetic screen for genes involved in senescence: role of Tid1, a homologue of the Drosophila tumor suppressor l(2)tid, in senescence and cell survival

We performed a genetic suppressor element screen to identify genes whose inhibition bypasses cellular senescence. A normalized library of fragmented cDNAs was used to select for elements that promote immortalization of rat embryo fibroblasts. Fragments isolated by the screen include those with homology to genes that function in intracellular signaling, cellular adhesion and contact, protein degradation, and apoptosis. They include mouse Tid1, a homologue of the Drosophila tumor suppressor gene l(2)tid, recently implicated in modulation of apoptosis as well as gamma interferon and NF-kappaB signaling. We show that GSE-Tid1 enhances immortalization by human papillomavirus E7 and simian virus 40 T antigen and cooperates with activated ras for transformation. Expression of Tid1 is upregulated upon cellular senescence in rat and mouse embryo fibroblasts and premature senescence of REF52 cells triggered by activated ras. In accordance with this, spontaneous immortalization of rat embryo fibroblasts is suppressed upon ectopic expression of Tid1. Modulation of endogenous Tid1 activity by GSE-Tid1 or Tid1-specific RNA interference alleviates the suppression of tumor necrosis factor alpha-induced NF-kappaB activity by Tid1. We also show that NF-kappaB sequence-specific binding is strongly downregulated upon senescence in rat embryo fibroblasts. We therefore propose that Tid1 contributes to senescence by acting as a repressor of NF-kappaB signaling.

Transcriptional networks and cellular senescence in human mammary fibroblasts

Senescence, the molecular program that limits the finite proliferative potential of a cell, acts as an important barrier to protect the body from cancer. Techniques for measuring transcriptome changes and for modulating their expression suggest that it may be possible to dissect the transcriptional networks underlying complex cellular processes. HMF3A cells are conditionally immortalized human mammary fibroblasts that can be induced to undergo coordinated senescence. Here, we used these cells in conjunction with microarrays, RNA interference, and in silico promoter analysis to promote the dissection of the transcriptional networks responsible for regulating cellular senescence. We first identified changes in the transcriptome when HMF3A cells undergo senescence and then compared them with those observed upon replicative senescence in primary human mammary fibroblasts. In addition to DUSP1 and known p53 and E2F targets, a number of genes such as PHLDA1, NR4A3, and a novel splice variant of STAC were implicated in senescence. Their role in senescence was then analyzed by RNA silencing followed by microarray analysis. In silico promoter analysis of all differential genes predicted that nuclear factor-kappaB and C/EBP transcription factors are activated upon senescence, and we confirmed this by electrophoretic mobility shift assay. The results suggest a putative signaling network for cellular senescence.

Loss of c-abl facilitates anchorage-independent growth of p53- and RB- deficient primary mouse embryonic fibroblasts

The c-abl tyrosine kinase is the proto-oncogene of the v-abl oncogene of the Abelson murine leukemia virus. Although mutational variants of c-Abl can exhibit gain of function and can produce a transformed phenotype, the function of c-Abl in transformation remained unclear. Here, we report that the loss of c-abl facilitates transformation. c-abl-knockout mouse embryonic fibroblasts (MEFs) immortalized by SV40 T antigen acquired anchorage-independent growth, and by constructing mutational variants of T antigen we showed that binding of large T antigen to p53 and RB was necessary to induce anchorage-independent growth. Although c-abl/p53 double-knockout MEFs did not undergo anchorage-independent growth, those expressing human papilloma virus 16 E7, which mainly inactivates RB, did. Our results show that the loss of c-abl facilitates anchorage-independent growth in the context of p53 and RB deficiency, and suggest that loss of function of c-abl facilitates some types of transformation.

Simian virus 40 large T antigen targets the spindle assembly checkpoint protein Bub1

The mitotic spindle checkpoint protein Bub1 has been found to be mutated at low frequency in certain human cancers characterized by aneuploidy. Simian virus 40 large T antigen efficiently immortalizes rodent cells and occasionally transforms them to tumorigenicity. T antigen can also cause genomic instability, inducing chromosomal aberrations and aneuploidy. Here, we report an interaction between Bub1 and T antigen. T antigen coimmunoprecipitates with endogenous Bub1 and Bub3, another component of the spindle checkpoint complex. Genetic analysis demonstrates that the interaction of T antigen with Bub1 is not required for immortalization but is closely correlated with transformation. T antigen induces an override of the spindle checkpoint dependent on Bub1 binding. This interaction with proteins of the spindle checkpoint machinery suggests another role for T antigen and provides insight into its ability to cause chromosomal aberrations, aneuploidy, and transformation.

Order of genetic events is critical determinant of aberrations in chromosome count and structure

A sequential acquisition of genetic events is critical in tumorigenesis. A key step is the attainment of infinite proliferative potential. Acquisition of this immortalization requires the activation of telomerase in addition to other activities, including inactivation of TP53 and the retinoblastoma family of tumor-suppressor proteins. However, the importance of the order in which these genetic events occur has not been established. To address this question, we used a panel of normal mammary fibroblasts and endothelial cultures that were immortalized after transduction with the catalytic subunit of telomerase (hTERT) and a temperature-sensitive mutant of the SV40 large-tumor (tsLT) oncoprotein in different orders in early- and late-passage stocks. These lines were maintained in continuous culture for up to 90 passages, equivalent to >300 population doublings (PDs) post-explantation during 3 years of continuous propagation. We karyotyped the cultures at different passages. Cultures that received hTERT first followed by tsLT maintained a near-diploid karyotype for more than 150 PDs. However, in late-passage stocks (>200 PDs), metaphase cells were mostly aneuploid. In contrast, the reverse order of gene transduction resulted in a marked early aneuploidy and chromosomal instability, already visible after 50 PDs. These results suggest that the order of genetic mutations is a critical determinant of chromosome count and structural aberration events.

cDNA microarray analysis of genes associated with ERBB2 (HER2/neu) overexpression in human mammary luminal epithelial cells

To investigate changes in gene expression associated with ERBB2, expression profiling of immortalized human mammary luminal epithelial cells and variants expressing a moderate and high level of ERBB2 has been carried out using cDNA microarrays corresponding to approximately 6000 unique genes/ESTs. A total of 61 significantly up- or downregulated (2.0-fold) genes were identified and further validated by RT-PCR analysis as well as microarray comparisons with a spontaneously ERBB2- overexpressing breast cancer cell line and ERBB2-positive primary breast tumors. The expression and clinical relevance of proteins predicted to be associated with ERBB2 overexpression in breast cancers were analysed together with their clinical relevance by antibody screening using a tissue array. Differentially regulated genes include those involved in cell-matrix interactions including proline 4-hydroxylase (P4HA2), galectin 1 (LGALS1) and galectin 3 (LGALS3), fibronectin 1 (FN1) and p-cadherin (CDH3), and cell proliferation (CRIP1, IGFBP3) and transformation (S100P, S100A4). A number of genes associated with MYC signalling were also differentially expressed, including NDRG1, USF2 and the epithelial membrane proteins 1 and 3 (EMP1, EMP3). These data represent profiles of the transcriptional changes associated with ERBB2-related pathways in the breast, and identify novel and potentially useful targets for prognosis and therapy.

Identification of novel candidates for replicative senescence by functional proteomics

To identify the underlying mechanisms that limit the mitotic potential of normal somatic cells, we have undertaken a high resolution differential proteomic analysis aimed at identifying proteins that were differentially expressed upon replicative senescence. Since replicative senescence in heterogeneous primary fibroblast cultures is asynchronous, we analysed a group of conditionally immortalized rat embryo fibroblast cell lines that have previously been shown to undergo synchronous senescence upon inactivation of SV40 tsA58 T antigen. This identified 43 spots that were differentially expressed in these cell lines. Comparison of the identity of these features with those identified in a complimentary independent differential proteomic analysis of replicative senescence, directly in primary rat embryo fibroblasts upon serial passaging, identified nine features that were in common between the two studies even though they had been conducted entirely separately. None of these proteins have previously been recognized to be involved with replicative senescence. Thus, they represent novel starting points for elucidating the underlying mechanism that regulates the finite mitotic life span of somatic cells and how it can be overcome in cancer cells.

Differential proteome analysis of replicative senescence in rat embryo fibroblasts

Normal somatic cells undergo a finite number of divisions and then cease dividing whereas cancer cells are able to proliferate indefinitely. To identify the underlying mechanisms that limit the mitotic potential, a two-dimensional differential proteome analysis of replicative senescence in serially passaged rat embryo fibroblasts was undertaken. Triplicate independent two-dimensional gels containing over 1200 spots each were run, curated, and analyzed. This revealed 49 spots whose expression was altered more than 2-fold. Of these, 42 spots yielded positive protein identification by mass spectrometry comprising a variety of cytoskeletal, heat shock, and metabolic proteins, as well as proteins involved in trafficking, differentiation, and protein synthesis, turnover, and modification. These included gelsolin, a candidate tumor suppressor for breast cancer, and alpha-glucosidase II, a member of the family of glucosidases that includes klotho; a defect in klotho expression in mice results in a syndrome that resembles human aging. Changes in expression of TUC-1, -2, -4, and -4 beta, members of the TUC family critical for neuronal differentiation, were also identified. Some of the identified changes were also shown to occur in two other models of senescence, premature senescence of REF52 cells and replicative senescence of mouse embryo fibroblasts. The majority of these candidate proteins were unrecognized previously in replicative senescence. They are now implicated in a new role.

Differential protein expression, DNA binding and interaction with SV40 large tumour antigen implicate the p63-family of proteins in replicative senescence

P53 activity plays a key role in mammalian cells when they undergo replicative senescence at their Hayflick limit. To determine whether p63 proteins, members of the family of p53-related genes, are also involved in this process, we examined their expression in serially passaged rat embryo fibroblasts. Upon senescence, two truncated DeltaNp63 proteins decreased in abundance whereas two TAp63 isoforms accumulated. 2-D gel analysis showed that the DeltaNp63 proteins underwent post-translational modifications in both proliferating and senescent cells. Direct binding of DeltaNp63 proteins to a p53 consensus motif was greater in proliferating cells than senescent cells. In contrast p63alpha isoforms bound to DNA in a p53 dependent manner and this was higher in senescent cells than proliferating cells. An interaction of p63alpha proteins with SV40 large tumour antigen was also detected and ectopic expression of DeltaNp63alpha can extend the lifespan of rat embryo fibroblasts. Taken together the results indicate that p63 proteins may play a role in replicative senescence either by competition for p53 DNA binding sites or by direct interaction with p53 protein bound to DNA.

Conditional immortalization of growth factor-responsive cardiac endothelial cells from H-2K(b)-tsA58 mice

Although mouse endothelial cells (EC) may advance our understanding of endothelial function, primary EC remain difficult to isolate. We have established a murine cardiac endothelial cell line (MCEC-1) from transgenic mice harboring a temperature-sensitive simian virus 40 large TAg gene (tsA58 TAg) under H-2K(b) class I promoter control. MCEC-1 cells were characterized by their ability to form tubes, Griffonia simplicifolia isolectin B4 binding, and CD31, intercellular adhesion molecule (ICAM)-2, and endoglin expression. MCEC-1 cells proliferated rapidly under permissive conditions [33 degrees C with interferon (IFN)-gamma], where the T antigen is active and transcription is activated by the presence of IFN-gamma, whereas under nonpermissive conditions (38 degrees C without IFN-gamma) proliferation was reduced by 30-fold and the EC showed enhanced proliferation in response to growth factors. Expression of E- and P-selectin, ICAM-1, and vascular cell adhesion molecule-1 was upregulated by tumor necrosis factor-alpha and interleukin-1 beta, and MCEC-1 cells, in contrast to primary EC, were amenable to transfection by lipofection. This novel line will allow further study of the role of the endothelium in cardiovascular disease. Moreover, this technique will allow EC to be readily obtained from genetically modified mice backcrossed with H-2K(b)-tsA58 mice.

Establishment and characterization of equine autonomic ganglion cell lines to enable direct testing of candidate toxins involved in equine dysautonomia (grass sickness)

To enable direct testing of a range of potential toxins or pathogens that might be involved in grass sickness, equine thoracic sympathetic chain ganglion cell lines were established from primary cell cultures by retroviral-mediated transduction of the temperature-sensitive mutant of the establishment oncogene encoding SV40 large T antigen. Morphological and behavioral features, temperature dependence, and immunocytochemical characteristics of the cell lines were investigated. The majority of cells were noradrenergic neurons in which dopamine-beta-hydroxylase, the enzyme that catalyzes norepinephrine synthesis, and neuropeptide Y coexisted. Cells treated with plasma from grass sickness cases that had previously been shown to induce autonomic nervous system damage when injected into normal horses showed significantly decreased mitochondrial function after 1 day. After 3 days exposure most cells showed severe degeneration in contrast to those treated with normal plasma. Liver and lung cell lines were also susceptible to plasma, suggesting that the toxin is not specifically neurotoxic.

Conditional immortalization of freshly isolated human mammary fibroblasts and endothelial cells

Reports differ as to whether reconstitution of telomerase activity alone is sufficient for immortalization of different types of human somatic cells or whether additional activities encoded by other "immortalizing" genes are also required. Here we show that ectopic expression of either the catalytic subunit of human telomerase (hTERT) or a temperature-sensitive mutant (U19tsA58) of simian virus 40 large-tumor antigen alone was not sufficient for immortalization of freshly isolated normal adult human mammary fibroblasts and endothelial cells. However, a combination of both genes resulted in the efficient generation of immortal cell lines irrespective of the order in which they were introduced or whether they were introduced early or late in the normal proliferative lifespan of the cultures. The order and timing of transduction, however, did influence genomic stability. Karyotype analysis indicated that introduction of both transgenes at early passage, with hTERT first, yielded diploid cell lines. Temperature-shift experiments revealed that maintenance of the immortalized state depended on continued expression of functional U19tsA58 large-tumor antigen, with hTERT alone unable to maintain growth at nonpermissive temperatures for U19tsA58 large-tumor antigen. Such conditional diploid lines may provide a useful resource for both cell engineering and for studies on immortalization and in vitro transformation.

BAP37 and Prohibitin are specifically recognized by an SV40 T antigen antibody

We have identified two cellular proteins that are specifically immunoprecipitated by an anti-SV40 T antigen monoclonal antibody. This antibody, PAb419, recognizes an epitope contained within a region of T antigen which we have recently demonstrated is required for the initiation of immortalization by SV40 T antigen, but is not essential for maintenance of the immortal state. The two proteins were identified as BAP37 and Prohibitin. Recent results suggest Prohibitin may enhance the transcriptional inactivation of E2F by the retinoblastoma family of pocket proteins (pRb, p107, p130). BAP37 and Prohibitin are specifically recognized by PAb419 and PAb210, another anti-SV40 T antigen monoclonal antibody, which has an overlapping epitope, but not by other anti-SV40 T antigen monoclonal antibodies, demonstrating the specificity of the interaction.

Different functions are required for initiation and maintenance of immortalization of rat embryo fibroblasts by SV40 large T antigen

We have used two different, but complementary assays to characterize functions of SV40 T antigen that are necessary for its ability to immortalize rat embryo fibroblasts. In accordance with previous work, we found that several functions were required. These include activities that map to the p53 binding domain and the amino terminal 176 amino acids which contain the J domain as well as the CR1 and CR2 domain required for binding and sequestering the RB family of pocket proteins. Moreover, we found that even though activities dependent only upon the amino terminus were sufficient for immortalization they were unable to maintain it. This suggests that immortalization by these amino terminal functions requires either additional events or immortalization of a subset of cells within the heterogeneous rat embryo fibroblast population. We further found that an activity dependent upon amino acids 17 - 27 which remove a portion of the CR1 domain and the predicted alpha-1 helix of the J domain was not necessary to maintain growth but was required for direct immortalization suggesting that at least one of the functions required initially was not required to maintain the immortal state. This represents the first demonstration that some of the functions required for maintenance of the immortal state differ from those required for initiation of immortalization.

Immortalization of rat embryo fibroblasts by a 3'-untranslated region

We have exploited a cross-species expression screen to search for cellular immortalizing activities. A newt blastemal cDNA expression library was transfected into rat embryo fibroblasts and immortal cell lines were selected. This identified a 1-kb cDNA fragment which has a low representation in the cDNA library and is derived from the 3'-UTR of an alpha-glucosidase-related mRNA. Expression of this sequence in rat embryo fibroblasts has shown that it is active in promoting colony formation and immortalization. It is also able to cooperate with an immortalization-defective deletion mutant of SV40 T antigen, indicating that it can exert its growth-stimulatory activity in the pathway activated by a viral immortalizing oncogene. This is the first example of an immortalizing activity mediated by an RNA sequence, and further analysis of its mechanism should provide new insights into senescence and immortalization.

Cloning and identification of genes that associate with mammalian replicative senescence

Cellular senescence and limited proliferative capacity of normal diploid cells has a dominant phenotype over immortality of cancerous cells, suggesting its regulation by the expression of a set of genes. In order to isolate the genes that associate with senescence, we have employed a clonal system of conditional SV40 T antigen rat embryo fibroblast cell lines which undergo senescence upon T antigen inactivation. Construction of cDNA libraries from two conditional cell lines and application of differential screening and subtractive hybridization techniques have resulted in the cloning of eight senescence-induced genes (SGP-2/Apo J, alpha 1-procollagen, osteonectin, fibronectin, SM22, cytochrome C oxidase, GTP-alpha, and a novel gene) and a senescence-repressed gene (FRS-2). Three of these genes encode for extracellular matrix proteins, others are involved in the calcium-dependent signal transduction pathways, while the SGP-2/Apo J gene may have a cellular protective function. RNA analysis has shown that the senescence-associated genes are overexpressed in both normal rat embryonic fibroblasts and human osteoblasts cell cultures undergoing aging in vitro. In comparison, the expression of these genes in a rat fibroblast immortalized cell line (208F cells) was down-regulated after both its partial and its full transformation by ras oncogenes. Thus, cloning of senescence-associated genes opens up new ways to elucidate and/or to modulate aging and cancer.

Recovery of spatial learning by grafts of a conditionally immortalized hippocampal neuroepithelial cell line into the ischaemia-lesioned hippocampus

Transient global cerebral ischaemia in rats causes relatively circumscribed and specific damage to the CA1 pyramidal cells of the dorsal hippocampus, along with a cognitive deficit manifest as difficulties in the performance of a range of spatial learning and memory tasks. Our previous studies have shown that restoration of behavioural performance in ischaemic rats by neural grafts taken relatively late in fetal development occurs only after local replacement of cells homotypic to those lost through the ischaemic insult. This lesion-plus-behaviour model therefore offers a powerful means for establishing whether multipotent embryonic neuroepithelial cells will engraft the damaged CA1, develop into appropriate neuronal phenotypes and produce behavioural recovery. Here we report that, in rats subjected to 15 min of global cerebral ischaemia, intrahippocampal implants of a conditionally immortal, multipotent cell line, directly derived from the embryonic day 14 hippocampal neuroepithelium of the H-2Kb-tsA58 transgenic mouse, selectively repopulated the lesioned CA1 pyramidal layer and restored ischaemia-induced deficits in acquisition of a hidden platform location in the Morris water maze.

Expression of p24, a novel p21Waf1/Cip1/Sdi1-related protein, correlates with measurement of the finite proliferative potential of rodent embryo fibroblasts

Normal mammalian fibroblasts undergo a limited number of divisions when cultured in vitro before entering a state of replicative senescence. The molecular basis for the determination of the finite mitotic potential is not known. Nevertheless, simian virus 40 T antigen, among other oncogenes, is able to prevent senescence in rodent embryo fibroblasts. T antigen immortalized cells are dependent upon this protein for maintaining growth once their normal mitotic life span has elapsed. Even though the mechanism that measures the finite mitotic potential of rodent fibroblasts is not known, it has been shown that it continues to function normally in the presence of this immortalizing gene. Accumulation of cyclin-dependent kinase inhibitors such as p21Waf1/Cip1/Sdi1 could potentially be a component of the mechanism that determines the finite life span. Here we show that accumulation of p21Waf1/Cip1/Sdi1 does not correlate with this biological counting mechanism, but we have identified p24, a p21Waf1/Cip1/Sdi1-related protein, whose accumulation does correlate with the measurement of the finite proliferative potential of rodent embryo fibroblasts and suggest that sequestration might be a mechanism by which its activity is regulated.

Rat embryo fibroblasts immortalized with simian virus 40 large T antigen undergo senescence upon its inactivation

Introduction of simian virus 40 T antigen into rodent fibroblasts gives rise to cells that can proliferate indefinitely but are dependent upon it for maintenance of their growth once the normal mitotic life span has elapsed. Inactivation of T antigen in these immortalized cells causes rapid and irreversible cessation of growth. To determine whether this growth arrest is associated with entry into senescence, we have undertaken a genetic and biological analysis of conditionally immortal (tsa) cell lines derived by immortalizing rat embryo fibroblasts with the thermolabile tsA58 T antigen. This analysis has identified the following parallels between the tsa cells after inactivation of T antigen and senescent rat embryo fibroblasts: (i) growth arrest is irreversible; (ii) it occurs in G1 as well as G2; (iii) the G1 block can be partially overcome by stimulation with 20% fetal calf serum, but the G2 block cannot be overcome; (iv) 20% fetal calf serum induces c-fos, but c-myc is unaltered; and (v) fibronectin and p21(Waf1/Cip1/Sdi1) are upregulated upon growth arrest. These results suggest that T-antigen-immortalized fibroblasts are committed to undergo senescence but are prevented from undergoing this process by T antigen. Inactivation of T antigen removes this block and results in senescence of the cells. Thus, these cell lines may represent a powerful system for study of the molecular basis of entry into senescence.

Immortalization of epithelial cells

The methodologies for isolating cell lines have become very powerful, particularly in terms of retaining differentiated features of the parent cells. Cell lines can be developed from primary or early passage cells as well as from transgenic animals that carry an immortalizing gene. Cell lines from epithelia have been selected for their polar orientation, tight junction formation, and expression of differentiated markers or functions. These cell lines provide useful models for studying cell biology of specific tissues, tumorigenicity, genetic abnormalities, or to help screen for effective methods of gene therapy.

Vascular smooth muscle cells of H-2Kb-tsA58 transgenic mice. Characterization of cell lines with distinct properties

BACKGROUND

The vascular wall is composed of at least two different populations of smooth muscle cells that are distinct in their structure and protein composition. According to the developmental stage of tissue taken for culture, the ratio between cells of epithelioid phenotype and spindle-shaped cells is variable. In particular, the epithelioid cells display characteristic features associated with immaturity. Because their increased appearance can be observed in endothelial denudation, the represent a dedifferentiated, proliferative smooth muscle cell type with a repair function in vascular injury.

METHODS AND RESULTS

To investigate this cellular heterogeneity, we established vascular smooth muscle cell lines from H-2Kb-tsA58 transgenic mice. Due to temperature-sensitive expression of the SV 40 large T-antigen in cells derived from this mouse strain, our smooth muscle lines were conditionally immortalized from the onset of their life in culture. Thus, we were able to clone cell lines representing the two different phenotypes described so far. Epithelioid cells derived from newborn animals are characterized by their expression of cytokeratins and the development of tight junctional complexes. Spindle-shaped cells, which could be isolated from newborn or adult animals, corresponded in phenotype and protein expression to smooth muscle cell lines established previously.

CONCLUSIONS

The special properties of vascular smooth muscle cells of the epithelioid phenotype suggest an endothelial replacement function in the course of injury to the vascular wall.

The H-2KbtsA58 transgenic mouse: a new tool for the rapid generation of novel cell lines

The ability to generate expanded populations of individual cell types able to undergo normal differentiation in vitro and in vivo is of critical importance in the investigation of the mechanisms that underly differentiation and in studies on the use of cell transplantation to repair damaged tissues. This review discusses the development of a strain of transgenic mice that allows the direct derivation of conditionally immortal cell lines from a variety of tissues, simply by dissociation of the tissue of interest and growth of cells in appropriate conditions. In these mice the tsA58 mutant of SV40 large T antigen is controlled by the interferon-inducible Class I antigen promoter. Cells can be grown for extended periods in vitro simply by growing them at 33 degrees C in the presence of interferon, while still retaining the capacity to undergo normal differentiation in vivo and in vitro. In addition, it appears that cell lines expressing mutant phenotypes can readily be generated by preparing cultures from appropriate offspring of matings between H-2KbtsA58 transgenic mice and mutant mice of interest.

Roles of hepatocyte growth factor/scatter factor and the met receptor in the early development of the metanephros

Several lines of evidence suggest that hepatocyte growth factor/scatter factor (HGF/SF), a soluble protein secreted by embryo fibroblasts and several fibroblast lines, may elicit morphogenesis in adjacent epithelial cells. We investigated the role of HGF/SF and its membrane receptor, the product of the c-met protooncogene, in the early development of the metanephric kidney. At the inception of the mouse metanephros at embryonic day 11, HGF/SF was expressed in the mesenchyme, while met was expressed in both the ureteric bud and the mesenchyme, as assessed by reverse transcription PCR, in situ hybridization, and immunohistochemistry. To further investigate the expression of met in renal mesenchyme, we isolated 13 conditionally immortal clonal cell lines from transgenic mice expressing a temperature-sensitive mutant of the SV-40 large T antigen. Five had the HGF/SF+/met+ phenotype and eight had the HGF/SF-/met+ phenotype. None had the HGF/SF+/met- nor the HGF/SF-/met- phenotypes. Thus the renal mesenchyme contains cells that express HGF/SF and met or met alone. When metanephric rudiments were grown in serum-free organ culture, anti-HGF/SF antibodies (a) inhibited the differentiation of metanephric mesenchymal cells into the epithelial precursors of the nephron; (b) increased cell death within the renal mesenchyme; and (c) perturbed branching morphogenesis of the ureteric bud. These data provide the first demonstration for coexpression of the HGF/SF and met genes in mesenchymal cells during embryonic development and also imply an autocrine and/or paracrine role for HGF/SF and met in the survival of the renal mesenchyme and in the mesenchymal-epithelial transition that occurs during nephrogenesis. They also confirm the postulated paracrine role of HGF/SF in the branching of the ureteric bud.

The biological clock that measures the mitotic life-span of mouse embryo fibroblasts continues to function in the presence of simian virus 40 large tumor antigen

Normal mammalian fibroblasts cultured in vitro undergo a limited number of divisions before entering a senescent phase in which they can be maintained for long periods but cannot be induced to divide. In rodent fibroblasts senescence can be prevented by expression of simian virus 40 large tumor antigen (T antigen). Cells expressing T antigen can proliferate indefinitely; however, such cells are absolutely dependent upon continued expression of T antigen for maintenance of growth; inactivation of T antigen results in a rapid and irreversible entry into a postmitotic state. To determine when, after the initial expression of T antigen, fibroblasts become dependent upon it for continued growth, we serially cultivated embryonic fibroblasts prepared from H-2Kb-tsA58 transgenic mice. We show that these fibroblasts become dependent upon T antigen for maintenance of proliferation only when their normal mitotic life-span has elapsed and that the biological clock that limits the mitotic potential continues to function normally, even in cells expressing this immortalizing gene. Our results suggest that random accumulation of cellular damage is unlikely to be the factor that limits fibroblast division but support the hypothesis that senescence is regulated via a genetic program.

Myogenic cell lines derived from transgenic mice carrying a thermolabile T antigen: a model system for the derivation of tissue-specific and mutation-specific cell lines

Skeletal myoblasts cloned from limb muscles of H-2Kb-tsA58 transgenic mice remained proliferative through at least 80 generations under conditions permissive for expression and function of the tsA58 gene product. When switched to nonpermissive conditions or implanted into muscles of nude mdx mice they underwent differentiation but, in one clonal cell line, a small proportion appeared to become quiescent muscle precursors in vivo. H-2Kb-tsA58 X mdx/mdx F1 male mice yielded dystrophin-deficient myoblasts. By such simple genetic crosses, H-2Kb-tsA58 transgenic mice provide a valuable tool for the rapid isolation of cell lines, myogenic or otherwise, bearing mutations of interest.

A model for primitive neuroectodermal tumors in transgenic neural transplants harboring the SV40 large T antigen

Using retrovirus-mediated transfer of the SV40 virus large T antigen into neural transplants, we have observed a high incidence of primitive neuroectodermal tumors (PNET). These neoplasms developed in 8 of 14 (57%) neural grafts after latency periods of 176 to 311 days. Histopathologically, the tumors exhibited features of human PNET such as formation of neuroblastic rosettes and immunocytochemical evidence for neuronal differentiation, synaptogenesis, and focal astrocytic differentiation. All neoplasms showed a striking migratory potential. The presence of the large T gene in the tumors was demonstrated by polymerase chain reaction-mediated amplification of a specific 242 bp segment of large T and DNA sequence analysis. Large T antigen was identified in tissue sections using an immunocytochemical reaction with the monoclonal antibody Pab 108. Cell lines were established from several tumors and subjected to G418 selection. Secondary tumors induced by intracerebral transplantation of these cells retained the characteristic morphological and immunocytochemical properties of PNETs. These experiments demonstrate a considerable transforming potential of SV40 large T antigen for neural precursor cells. The long latency period suggests that neoplastic transformation initiated by the large T gene requires additional spontaneous mutations of cooperating cellular genes. Because the mechanism of transformation by large T antigen appears to involve complex formation with and inactivation of cellular tumor suppressor gene products, these cell lines may serve as an interesting tool to search for novel neural tumor suppressor genes.

The characterization of astrocyte cell lines that display properties of glial scar tissue

The glial scar has been proposed to be a major impediment to regeneration in the adult CNS. Analysis of glial scars in vivo is complicated, however, by the large number of cell types present in such lesions. We have attempted to simplify analysis of the glial scar environment by deriving a series of conditionally immortal astrocyte cell lines that display several properties expressed by glial scar tissue in vitro. The astrocyte lines, which were derived from H-2KbtsA58 transgenic mice, expressed macromolecules associated with glial scars in vivo and were significantly less effective than neonatal astrocytes at promoting neurite outgrowth from postnatal central and peripheral neurons. The astrocyte lines also inhibited migration of oligodendrocyte type-2 astrocyte progenitor cells in vitro. We propose that certain properties shown previously to be expressed by glial scars may be reconstituted in vitro by astrocytes alone.

Generation of osteoclast-inductive and osteoclastogenic cell lines from the H-2KbtsA58 transgenic mouse

The development of osteoclastic cell lines would greatly facilitate analysis of the cellular and molecular biology of bone resorption. Several cell lines have previously been reported to be capable of osteoclastic differentiation. However, such cell lines form at best only occasional excavations, suggesting that osteoclastic differentiation is either incomplete or that osteoclasts represent a very small proportion of the cells present. We have used the recently developed H-2KbtsA58 transgenic mouse, in which the interferon-inducible major mouse histocompatibility complex H-2Kb promoter drives the temperature-sensitive (ts) immortalizing gene of simian virus 40 (tsA58), to develop cell lines from bone marrow with high efficiency. Bone marrow cells were incubated with gamma interferon at 33 degrees C, then cloned, and expanded. The cell lines were characterized at 39.5 degrees C in the absence of gamma interferon. First, stromal cell lines were established that induced osteclast formation (resorption of bone slices) when cocultured with hemopoietic spleen cells. Some of the stromal cell lines so generated were able to resorb approximately 30 mm2/cm2 of bone surface. We then established cell lines of hemopoietic origin, several of which possess osteoclastic potential. When these osteoclast-precursor cell lines were cocultured with stromal cell lines, extensive bone resorption was observed. Osteoclast formation did not occur if the precursor cell lines were incubated on bone slices without stromal cells; osteoclast formation was also dependent upon the presence of 1 alpha,25-dihydroxyvitamin D3. These cell lines represent a model for osteoclast formation and a valuable resource for identification of the mechanisms and factors that regulate osteoclast differentiation and function.

Establishment of conditionally immortalized epithelial cell lines from both colon and small intestine of adult H-2Kb-tsA58 transgenic mice

Intestinal mucosal cells have proved difficult to culture in vitro. Many attempts have been made to develop long-term cultures of these cells either by direct culturing or by attempting to immortalize these cells by using a range of transforming viral genes, but with little success. The recent development of a transgenic mouse bearing a temperature-sensitive mutation of the simian virus 40 large tumor antigen gene (tsA58) has enabled us to initiate conditionally immortalized cultures of epithelial cells from both small intestinal and colonic mucosa of adult mice. Crypts were isolated from either the small intestines or colons of young adult mice and cultured at the permissive temperature (33 degrees C) in medium containing conditioned medium from a human colon carcinoma cell line, LIM1863. Crypts from both tissues yielded cultures of epithelial cells that have now been in culture for more than 12 months with regular passaging. The epithelial nature of the cells has been confirmed by staining with anti-keratin antibodies. The intestinal origin of the cells was demonstrated by the ability of the cells to synthesize low levels of both brush border peptidases and a disaccharidase. The levels of expression of these enzymes were modulated by the addition of sodium butyrate or phorbol myristate acetate to the medium, which resulted in an increase in the synthesis of the peptidases and a decrease in the synthesis of the disaccharidase. The cells proliferate continuously at the permissive temperature (33 degrees C), but proliferation ceases at the nonpermissive temperature (39.5 degrees C). To our knowledge, this is the first description of the establishment of epithelial cell lines from both small intestine and colon of the same mouse strain. The success reported here indicates that this transgenic mouse will be a useful source of tissue for the study of the mechanisms that control the proliferation and eventual differentiation and senescence of the cells of the intestinal mucosa. These mice will also be a useful source of cells for attempts to culture cells from other tissues that have proved difficult to culture in vitro.

Molecular mechanisms in the evolution of chronic myelocytic leukemia

Chronic myelocytic or Ph1-positive acute lymphoblastic leukemias have been analyzed for alterations in a variety of proto-oncogenes and anti-oncogenes implicated in the progression of chronic myeloid leukemia (CML) from its chronic phase to blast crisis. The most frequent genetic change found in disease evolution is an alteration of the p53 gene involving a point mutation, a rearrangement or a deletion. These gene changes are common in myeloid and undifferentiated variants of blast crisis but are usually undetectable in lymphoid leukemic transformants. Other molecular changes also occur in the clonal evolution of CML. The retinoblastoma-susceptibility (Rb) gene is an anti-oncogene. Structural abnormalities of Rb are frequent in all types of human acute leukemia, but are particularly common in Ph1-positive leukemia of lymphoid phenotype including both Ph1-positive ALL and lymphoid blast crisis of CML. Changes in Rb occur early in the transition to blast crisis with loss of Rb protein being the common factor. Mutations in the N-RAS gene also occur, but are rare in typical blast crisis. They are sometimes seen in Ph1-negative myeloid blast crisis. Since changes in the p53 gene are generally associated with progression of disease of a myeloid phenotype and changes in the Rb gene occur more often with a lymphoid phenotype, a particular molecular alteration may influence the character of disease evolution in CML.