The hallmarks of cancer

AP-1 in mouse development and tumorigenesis

Genetically modified mice have provided important insights into the biological functions of the dimeric transcription factor complex AP-1. Extensive analyses of mice and cells with genetically modified Fos or Jun proteins provide novel insights into the physiological functions of AP-1 proteins. Using knock-out strategies it was found that some components, such as c-Fos, FosB and JunD are dispensable, whereas others, like c-Jun, JunB and Fra-1 are essential in embryonic development and/or in the adult organism. Besides the specific roles of AP-1 proteins in developmental processes, we are beginning to obtain a better molecular understanding of the cell-context dependent function of AP-1 in cell proliferation and apoptosis, in bone biology as well as in multistep tumorigenesis.

Bcl-2 expression in F-MuLV-induced erythroleukemias: a role for the anti-apoptotic action of Bcl-2 during tumor progression

Erythroleukemias induced by various strains of Friend virus are multistage malignancies that result from the accumulation of genetic mutations, including the activation of proto-oncogenes and the inactivation of tumor suppressor genes. In this study, we demonstrate that Bcl-2 expression is activated in the majority of F-MuLV-induced erythroleukemia cell lines. In contrast, Bcl-2 was not expressed in any of the FV-P-induced erythroleukemia cell lines and protein levels were low or negligible in FV-A-induced erythroleukemia cell lines examined. In vivo, Bcl-2 expression levels gradually increased in F-MuLV-induced erythroleukemic cells prior to adaptation to culture. High expression of Bcl-2 in F-MuLV-induced erythroleukemic cells was shown to proceed the emergence of p53 mutation suggesting that Bcl-2 expression may delay p53 mutation in the leukemic cells. This is further supported by the demonstration that the majority of F-MuLV-induced erythroleukemia cell lines established from primary tumors induced in p53 mutant mice express low to negligible levels of Bcl-2. We have shown that the high levels of Bcl-2 expression in FV-P-induced erythroleukemic cells inhibited apoptosis induced by etoposide, low serum and p53 expression. Similarly, ectopic Bcl-2 expression within these cells also provided protection from apoptosis induced by etoposide and growth in low serum. These results suggest that the anti-apoptotic action of Bcl-2 may confer a selective in vivo and in vitro growth advantage to F-MuLV-induced erythroleukemic cells, which is not shared by FV-P/FV-A-induced erythroleukemic cells. The observed induction of Bcl-2 expression in vivo constitutes a novel but late oncogenic event associated with the progression of F-MuLV-induced erythroleukemias.

Oncogenic ras activates the ARF-p53 pathway to suppress epithelial cell transformation

Chemically induced skin carcinomas in mice are a paradigm for epithelial neoplasia, where oncogenic ras mutations precede p53 and INK4a/ARF mutations during the progression toward malignancy. To explore the biological basis for these genetic interactions, we studied cellular responses to oncogenic ras in primary murine keratinocytes. In wild-type keratinocytes, ras induced a cell-cycle arrest that displayed some features of terminal differentiation and was accompanied by increased expression of the p19(ARF), p16(INK4a), and p53 tumor suppressors. In ARF-null keratinocytes, ras was unable to promote cell-cycle arrest, induce differentiation markers, or properly activate p53. Although oncogenic ras produced a substantial increase in both nucleolar and nucleoplasmic p19(ARF), Mdm2 did not relocalize to the nucleolus or to nuclear bodies but remained distributed throughout the nucleoplasm. This result suggests that p19(ARF) can activate p53 without overtly affecting Mdm2 subcellular localization. Nevertheless, like p53-null keratinocytes, ARF-null keratinocytes were transformed by oncogenic ras and rapidly formed carcinomas in vivo. Thus, oncogenic ras can activate the ARF-p53 program to suppress epithelial cell transformation. Disruption of this program may be important during skin carcinogenesis and the development of other carcinomas.

Hypothesis: chemical carcinogenesis mediated by a transiently active carcinogen receptor

Biologically active small-molecular-weight compounds are actively transported into the cell nucleus by a specific receptor. This has been widely demonstrated for retinoids, polycyclic hydrocarbons (such as steroids), and dioxin. Thus, it is reasonable to assume that genotoxically active polycyclic hydrocarbons, and possibly all genotoxically active small-molecular-weight substances, exert their transformational effect in the cell nucleus via a specific receptor. I propose that the receptor is activated only at the end of the G(1) phase of the cell cycle and that the carcinogen receptor complex interferes directly with DNA synthesis, leading to mutations. This hypothesis may account for various characteristics of malignant growth, such as the organ specificity of carcinogens and the relationship between cell proliferation and malignant transformation. If so, it could form the basis for establishing a radioreceptor assay for carcinogens.

Three mutations in v-Rel render it resistant to cleavage by cell-death protease caspase-3

The retroviral oncoprotein v-Rel is a transcriptional activator in the Rel/NF-kappa B family. v-Rel causes rapidly fatal lymphomas in young chickens, and transforms and immortalizes chicken lymphoid cells in vitro. Several mutations that have enhanced the oncogenicity of v-Rel have been selected during in vitro and in vivo passage of v-Rel-containing retroviruses. In this report, we show that the C-terminal deletion and two point mutations (Asp-->Gly at residue 91 and Asp-->Asn at residue 437) in v-Rel make it resistant to cleavage by the cell-death protease caspase-3. In contrast, c-Rel, which has Asp residues at these sites, can be cleaved by caspase-3 in vitro as well as in vivo in cells induced to undergo apoptosis. We have characterized activities of v-Rel mutants with recreated single caspase-3 cleavage sites, two cleavage sites, or an introduced artificial cleavage site. All of these mutant v-Rel proteins are sensitive to caspase-3 cleavage in vitro, and show wild-type activity in terms of nuclear localization in chicken fibroblasts and DNA binding in vitro. Moreover, all caspase-3-sensitive v-Rel mutants transform chicken spleen cells in vitro and induce fatal lymphoid tumors in vivo to approximately the same extent as wild-type v-Rel. As with v-Rel mutants, caspase-3-resistant c-Rel mutants behave similarly to caspase-3-sensitive wild-type c-Rel in terms of DNA binding, transcriptional activation, in vitro transformation, and tumorigenicity. Mammalian c-Rel proteins can also be cleaved by caspase-3 in vitro, and a c-Rel mutant from a human pre-T lymphoma cell line is less sensitive than wild-type human c-Rel to cleavage by caspase-3. Taken together, these results demonstrate that specific mutations render oncogenic forms of Rel proteins resistant to cleavage by a cell-death caspase; however, the biological relevance of this resistance remains unclear. Nevertheless, to our knowledge, this is the first demonstration of mutations in caspase-3 recognition sites occurring during the evolution of an oncogenic protein.

Three down and counting: the transformation of human mammary cells from normal to malignant in three steps

An array of genetic mutations associated with human breast cancers has been identified. However, which specific combination of mutations permit normal cells to form breast cancer remains unknown. Elenbaas et al. recently described an experimental system for studying the genetic requirements for the development of breast cancer.

It takes a tissue to make a tumor: epigenetics, cancer and the microenvironment

How do normal tissues limit the development of cancer? This review discusses the evidence that normal cells effectively restrict malignant behavior, and that such tissue forces must be subjugated to establish a tumor. The action of ionizing radiation will be specifically discussed regarding the disruption of the microenvironment that promotes the transition from preneoplastic to neoplastic growth. Unlike the highly unpredictable nature of genetic mutations, the response of normal cells to radiation damage follows an epigenetic program similar to wound healing and other damage responses. Our hypothesis is that the persistent disruption of the microenvironment in irradiated tissue compromises its ability to suppress carcinogenesis.

Multi-modal combination gene therapy for malignant glioma using replication-defective HSV vectors

Herpes simplex virus (HSV) may be modified to produce a non-pathogenic vector that is capable of delivering multiple transgenes simultaneously to cells, both safely and efficiently. We have exploited this property to develop viruses that target glioblastoma, a malignancy that is currently associated with a poor prognosis. Using rationally selected combinations of therapeutic transgenes coupled with gamma-knife radiotherapy, the ablation of experimental tumours in animal models has been demonstrated. Combination gene therapy using replication-defective HSV vectors represents a promising and exciting approach to tackling malignancy in the CNS.

Novel expression of cyclin-dependent kinase inhibitors in human B-cell precursors

Eukaryotic cell division is regulated by cyclins, cyclin-dependent kinases (CDK), and cyclin-dependent kinase inhibitors (CKI). Genes encoding these proteins are mutated or deleted in many types of cancer. For example, 20%-30% of B-lineage acute lymphoblastic leukemias (ALL) have deletions in the CKI known as INK4a. The contribution of INK4a deletions to the progression of B-lineage ALL is uncertain, partially due to a paucity of data on expression in normal B-cell precursors. We therefore conducted a comparative analysis of normal and leukemic human B-cell development for the expression of cyclins, CDK, and CKI. Specific stages of human B-cell development from normal bone marrow were purified by fluorescence-activated cell sorting. The sorted populations and B-lineage ALL cell lines (BLIN-1, 2, 3, 4) were examined for expression of cyclins, CDK, and CKI by reverse transcriptase polymerase chain reaction (RT-PCR) and Western blotting.RT-PCR analysis showed that cyclin D2, cyclin D3, CDK4, and CDK6 were ubiquitously expressed in normal B-cell development and in the BLIN ALL cell lines. The p19(INK4d) CKI was the most commonly expressed member of the INK4 family, whereas p16(INK4a) was more weakly and variably expressed. Expression of the p57(KIP2) CKI varied as a function of the stage of B-cell development. Analysis of normal B-cell precursors by Western blotting indicated that CDK4, CDK6, p19(INK4d), and p57(KIP2) were expressed, whereas p16(INK4a) was not detected. Cyclin D/CDK expression in normal and leukemic human B-cell precursors is similar to expression of these proteins in human and murine mature B cells. In contrast, the ubiquitous expression of p19(INK4d) has not been previously described in human or murine B-lineage cells. Our results suggest that loss of INK4a may only minimally contribute to tumor cell progression in B-lineage ALL, since expression of INK4d could provide a compensatory function as a cyclin-dependent kinase inhibitor.

Tissue inhibitor of metalloproteinase-1 alters the tumorigenicity of Burkitt's lymphoma via divergent effects on tumor growth and angiogenesis

Epstein-Barr virus (EBV)-positive Burkitt's lymphoma cells and EBV-infected B cells elicit humoral factors that inhibit tumor-induced angiogenesis, resulting in tumor necrosis and regression. Of the chemokine factors identified in association with this growth behavior, none have induced complete tumor regression. We have previously identified tissue inhibitors of metalloproteinase (TIMP)-1 in various B cell lymphoma cell lines. Here we show that induction of TIMP-1 expression in an EBV-negative Burkitt's lymphoma cell line results in a biphasic, in vivo tumor growth pattern in the nude mouse that is essentially identical to EBV-positive Burkitt's lymphoma cell lines. The initial effect of TIMP-1 is to enhance tumor growth, consistent with the reported anti-apoptotic effect of TIMP-1 on B cell growth. Tumor necrosis and regression then follow the initial period of rapid, increased tumor growth. Only microscopic foci of residual, proliferating tumor cells are observed on biopsy of the tumor site. This latter effect is mediated by TIMP-1 inhibition of an angiogenic response within the developing tumor mass, as demonstrated by immunostaining and microvessel counts. These findings suggest that TIMP-1 is an important mediator of the in vivo growth properties of EBV-positive Burkitt's lymphoma.

Pathology of lymphoma progression

Reflecting the stepwise process of oncogenesis, lymphomas may cumulatively develop a more aggressive phenotype during the course of disease, a process referred to as lymphoma progression. Although morphological, clinical and biological aspects of lymphoma progression do not always overlap, changes in lymphoma morphology frequently indicate alterations in the clinical and biological behaviour of the disease. Indolent and aggressive lymphomas in disease progression can either be clonally related or represent clonally unrelated neoplasms. We propose to use the term 'lymphoma progression' in a biological sense denoting only clonal development of and within a lymphoma entity. The term 'composite lymphoma' should be used as a merely descriptive morphological designation for different lymphoma entities in one individual irrespective of clonal relationship. Many types of aggressive B-cell non-Hodgkin's lymphomas and Hodgkin's lymphomas are reported to secondarily develop in lymphoma progression. Genetic changes associated with lymphoma progression frequently abrogate the differentiating effects of alterations occurring in indolent lymphomas, leading to increased cell proliferation. Within different lymphoma entities, high-risk disease variants mimicking lymphoma progression exist.

Repair of double-strand breaks by homologous recombination in mismatch repair-defective mammalian cells

Chromosomal double-strand breaks (DSBs) stimulate homologous recombination by several orders of magnitude in mammalian cells, including murine embryonic stem (ES) cells, but the efficiency of recombination decreases as the heterology between the repair substrates increases (B. Elliott, C. Richardson, J. Winderbaum, J. A. Nickoloff, and M. Jasin, Mol. Cell. Biol. 18:93-101, 1998). We have now examined homologous recombination in mismatch repair (MMR)-defective ES cells to investigate both the frequency of recombination and the outcome of events. Using cells with a targeted mutation in the msh2 gene, we found that the barrier to recombination between diverged substrates is relaxed for both gene targeting and intrachromosomal recombination. Thus, substrates with 1.5% divergence are 10-fold more likely to undergo DSB-promoted recombination in Msh2(-/-) cells than in wild-type cells. Although mutant cells can repair DSBs efficiently, examination of gene conversion tracts in recombinants demonstrates that they cannot efficiently correct mismatched heteroduplex DNA (hDNA) that is formed adjacent to the DSB. As a result, >20-fold more of the recombinants derived from mutant cells have uncorrected tracts compared with recombinants from wild-type cells. The results indicate that gene conversion repair of DSBs in mammalian cells frequently involves mismatch correction of hDNA rather than double-strand gap formation. In cells with MMR defects, therefore, aberrant recombinational repair may be an additional mechanism that contributes to genomic instability and possibly tumorigenesis.

Molecular and cellular biology of pre-malignancy in the gastrointestinal tract

Important pathogenic alterations within established cancers are acquired during the pre-malignant stage. These genetic alterations can be grouped into specific neoplastic pathways that differ within and between anatomical sites. By understanding the mechanisms that determine the initiation and progression of each pathway, it will be possible to develop novel approaches to the diagnosis, prevention and treatment of cancer. This chapter outlines the principles underlying the molecular characterization of pre-malignant lesions, taking colorectal neoplasia as the main model.

Proteases in invasion: matrix metalloproteinases

The role of proteases in general, and the matrix metalloproteinases in particular, in tumor invasion and metastasis is well established. However, the classic view that these enzymes simply provide a mechanism for the breakdown of connective tissue barriers has been challenged. This overview summarizes recent evidence to support the changing view of the role of matrix metalloproteinases in cancer progression. First we briefly review the central role of cell invasion in cancer progression and also the matrix metalloproteinase family members. We then focus on the emerging roles for these enzymes in cancer progression, including the role of matrix metalloproteinases in cell proliferation and release of growth factors, cell migration and in modification of the extracellular matrix to reveal cryptic sites that alter cell behaviour.

Comparative genome-scale analysis of gene expression profiles in T cell lymphoma cells during malignant progression using a complementary DNA microarray

Using a cDNA microarray, we compared the expression of approximately 8000 genes between two unique, clonally related T cell lines derived from different stages of a progressive T cell lymphoma involving skin. A total of 180 genes was found to be differentially expressed at the RNA level by a factor of fivefold or greater. Compared with the cells from the earlier, clinically indolent stage of the lymphoma, 56 genes were up-regulated, whereas 124 genes were down-regulated in the cells from the advanced, clinically aggressive stage lymphoma. The functions of approximately 65% of these genes are currently unknown. The 22 genes with a known function that were up-regulated in the advanced lymphoma cells included several genes involved in promotion of cell proliferation and survival as well as drug resistance. The 42 functionally characterized genes that were down-regulated in the advanced lymphoma cells included negative regulators of cell activation and cell cycle, and mediators of cell adhesion, apoptosis, and genome integrity. The differential expression identified by the cDNA microarray analysis was confirmed for selected genes by reverse transcription-polymerase chain reaction and Northern blotting. The identified differences in gene expression may be related to the differences in behavior between the early and advanced stages of the T cell lymphoma and point to directions for further investigations into mechanisms of lymphoma progression.

Tumors are unique organs defined by abnormal signaling and context

Many cancer investigations have focussed on the eradication of the cancer cell itself and in doing so, overlook the inherent complexity and heterogeneity of solid tumors. Here, we argue that, in many cases, it is the altered communication within the tumor, rather than mutations per se, that is the defining characteristic of cancer. As a result, tumorigenesis can be indirectly initiated by environmental or inherited factors that affect the stromal cells. We propose that anticancer research might be more effective if aimed at eradicating the cause of abnormality rather than just treating the end result.

Mutational and functional analyses reveal that ST7 is a highly conserved tumor-suppressor gene on human chromosome 7q31

Loss of heterozygosity (LOH) of markers on human chromosome 7q31 is frequently encountered in a variety of human neoplasias, indicating the presence of a tumor-suppressor gene (TSG). By a combination of microcell-fusion and deletion-mapping studies, we previously established that this TSG resides within a critical region flanked by the genetic markers D7S522 and D7S677. Using a positional cloning strategy and aided by the availability of near-complete sequence of this genomic interval, we have identified a TSG within 7q31, named ST7 (for suppression of tumorigenicity 7; this same gene was recently reported in another context and called RAY1). ST7 is ubiquitously expressed in human tissues. Analysis of a series of cell lines derived from breast tumors and primary colon carcinomas revealed the presence of mutations in ST7. Introduction of the ST7 cDNA into the prostate-cancer-derived cell line PC3 had no effect on the in vitro proliferation of the cells, but abrogated their in vivo tumorigenicity. Our data indicate that ST7 is a TSG within chromosome 7q31 and may have an important role in the development of some types of human cancer.

Gene expression and amplification in breast carcinoma cells with intrinsic and acquired doxorubicin resistance

The multidrug resistance (MDR) phenotype is a major cause of cancer treatment failure. Here the expressions of 4224 genes were analysed for association with intrinsic or acquired doxorubicin (DOX) resistance. A cluster of overexpressed genes related to DOX resistance was observed. Included in this cluster was ABCB1 the P-glycoprotein transporter protein gene and MMP1 (Matrix Metalloproteinase 1), indicative of the invasive nature of resistant cells, and the oxytocin receptor (OXTR), a potential new therapeutic target. Overexpression of genes associated with xenobiotic transformation, cell transformation, cell signalling and lymphocyte activation was also associated with DOX resistance as was estrogen receptor negativity. In all carcinoma cells, compared with HBL100 a putatively normal breast epithelial cell line, a cluster of overexpressed genes was identified which included several keratins, in particular keratins 8 and 18 which are regulated through the ras signalling pathway. Analysis of genomic amplifications and deletions revealed specific genetic alterations common to both intrinsic and acquired DOX resistance including ABCB1, PGY3 (ABCB4) and BAK. The findings shown here indicate new possibilities for the diagnosis of DOX resistance using gene expression, and potential novel therapeutic targets for pharmacological intervention.

Mouse models for sporadic cancer

Much of the advancement in mouse models for cancer during the past 2 decades can be attributed to our increasing capacity to specifically modify the mouse germ line. The first generations of oncomice and tumor-suppressor gene knockouts are now being succeeded by regulatable or conditional mouse tumor models, which can be utilized more effectively to establish correlations between distinct genetic lesions and specific tumor characteristics and to design and improve therapeutic intervention strategies. In this review we try to give the reader a flavor of how the latest reagents can be utilized.

Molecular cloning and characterization of endosialin, a C-type lectin-like cell surface receptor of tumor endothelium

Endosialin, the antigen identified with monoclonal antibody FB5, is a highly restricted 165-kDa cell surface glycoprotein expressed by tumor blood vessel endothelium in a broad range of human cancers but not detected in blood vessels or other cell types in many normal tissues. Functional analysis of endosialin has been hampered by a lack of information about its molecular structure. In this study, we describe the purification and partial amino acid sequencing of endosialin, leading to the cloning of a full-length cDNA with an open reading frame of 2274 base pairs. The endosialin cDNA encodes a type I membrane protein of 757 amino acids with a predicted molecular mass of 80.9 kDa. The sequence matches with an expressed sequence tag of unknown function in public data bases, named TEM1, which was independently linked to tumor endothelium by serial analysis of gene expression profiling. Bioinformatic evaluation classifies endosialin as a C-type lectin-like protein, composed of a signal leader peptide, five globular extracellular domains (including a C-type lectin domain, one domain with similarity to the Sushi/ccp/scr pattern, and three EGF repeats), followed by a mucin-like region, a transmembrane segment, and a short cytoplasmic tail. Carbohydrate analysis shows that the endosialin core protein carries abundantly sialylated, O-linked oligosaccharides and is sensitive to O-sialoglycoprotein endopeptidase, placing it in the group of sialomucin-like molecules. The N-terminal 360 amino acids of endosialin show homology to thrombomodulin, a receptor involved in regulating blood coagulation, and to complement receptor C1qRp. This structural kinship may indicate a function for endosialin as a tumor endothelial receptor for as yet unknown ligands, a notion now amenable to molecular investigation.

Human kallikrein gene 5 (KLK5) expression is an indicator of poor prognosis in ovarian cancer

Kallikrein gene 5 (KLK5, also known as KLK-L2), located on chromosome 19q13.4, is one of the newly identified members of the kallikrein gene family, which is a subgroup of the serine protease enzyme family. In normal human tissues, KLK5 is highly expressed in skin, mammary gland and testis. Preliminary RT-PCR analysis has indicated that KLK5 is expressed in a subset of ovarian tumours. We have thus hypothesized that KLK5 may be a new prognostic indicator in ovarian cancer. We have examined the mRNA expression of KLK5 in 142 malignant ovarian tissues. Tumours were pulverized, total RNA was extracted, and cDNA was prepared by reverse transcription. KLK5 was amplified by PCR using gene specific primers, and the identity of the PCR product was verified by sequencing. Ovarian tissues were then classified as KLK5 positive or negative, based on ethidium bromide staining of the PCR product on agarose gels. KLK5 was found to be highly expressed in 58/142 (41%) of ovarian cancer samples while its level of expression was very low in normal ovarian tissues. We found a strong positive relation between KLK5 expression and tumour grade (P = 0.006) and disease stage (P = 0.027). Univariate survival analysis revealed that patients with ovarian tumours positive for KLK5 expression had an increased risk for relapse and death (P = 0.018 and 0.022, respectively). In multivariate analysis, KLK5 expression showed independent prognostic value only in the subset of tumours with lower grade disease (grades I and II). We conclude that KLK5 expression is associated with more aggressive forms of epithelial ovarian carcinoma and has indepdent prognostic value in low grade tumours.

The C. elegans E2F- and DP-related proteins are required for embryonic asymmetry and negatively regulate Ras/MAPK signaling

Early C. elegans embryos exhibit protein asymmetries that allow rapid diversification of cells. Establishing these asymmetries requires the novel protein MEX-5. We show that mutations in the efl-1 and dpl-1 genes cause defects in protein localization resembling defects caused by mutations in mex-5. efl-1 and dpl-1 encode homologs of vertebrate E2F and DP proteins that regulate transcription as a heterodimer. efl-1 and dpl-1 mutants have elevated levels of activated Map kinase in oocytes. Their mutant phenotype and that of mex-5 mutants can be suppressed by reducing Ras/Map kinase signaling. We propose this signaling pathway has a role in embryonic asymmetry and that EFL-1/DPL-1 control the level of Map kinase activation.

A low-molecular-weight fraction of human seminal plasma activates adenylyl cyclase and induces caspase 3-independent apoptosis in prostatic epithelial cells by decreasing mitochondrial potential and Bcl-2/Bax ratio

The majority of elderly men are affected by benign and malign diseases of the prostate that are governed by endocrine factors and local stromal/epithelial and luminal/epithelial interactions. Prostate epithelial cells secrete numerous factors into the seminal plasma (SMP) that are thought to be responsible for nutrition, accurate pH, and ionic environment of sperm. Our hypothesis assumes that prostatic factors responsible for optimal fertility might have retrograde influences on epithelial cell growth, differentiation, and function. SMP was analyzed for proteins and other biologically active substances by size exclusion high-performance liquid chromatography. Each fraction was investigated for its effect on cell growth and death. A low molecular mass fraction (2-4 kDa) was responsible for inducing apoptosis in proliferating prostate epithelial cells. Signal transduction was mediated by the production of cAMP; no significant changes in tyrosine phosphorylation of membrane receptors were observed. Mechanisms of apoptosis, i.e., caspase- and mitochondria-dependent pathways, were investigated in prostate epithelial cells by caspase activity assays, annexin/propidium iodide staining, changes in mitochondrial potential, p53, Par-4, Bax, and Bcl-2 protein levels. SMP induced p53- and Bcl-2-dependent apoptosis without activation of caspase-3. Obviously, SMP contains protective factors that help eliminate degenerated cells and control epithelial renewal. Age-related changes in the composition of SMP or the susceptibility of epithelial cells might, therefore, contribute to proliferative prostatic diseases

Ski/Sno and TGF-beta signaling

Transforming growth factor-beta is a potent inhibitor of epithelial cell proliferation. Proteins involved in TGF-beta signaling are bona fide tumor suppressors and many tumor cells acquire the ability to escape TGF-beta growth inhibition through the loss of key signaling transducers in the pathway or through the activation of oncogenes. Recent studies indicate that there is a specific connection between the TGF-beta signaling pathway and the Ski/SnoN family of oncoproteins. We summarize evidence that Ski and SnoN directly associate with Smad proteins and block the ability of the Smads to activate expression of many if not all TGF-beta-responsive genes. This appears to cause abrogation of TGF-beta growth inhibition in epithelial cells.

Molecular, metabolic, and genetic control: An introduction

The living cell is a miniature, self-reproducing, biochemical machine. Like all machines, it has a power supply, a set of working components that carry out its necessary tasks, and control systems that ensure the proper coordination of these tasks. In this Special Issue, we focus on the molecular regulatory systems that control cell metabolism, gene expression, environmental responses, development, and reproduction. As for the control systems in human-engineered machines, these regulatory networks can be described by nonlinear dynamical equations, for example, ordinary differential equations, reaction-diffusion equations, stochastic differential equations, or cellular automata. The articles collected here illustrate (i) a range of theoretical problems presented by modern concepts of cellular regulation, (ii) some strategies for converting molecular mechanisms into dynamical systems, (iii) some useful mathematical tools for analyzing and simulating these systems, and (iv) the sort of results that derive from serious interplay between theory and experiment. (c) 2001 American Institute of Physics.

Degradation of cellular and viral Fos proteins

c-Fos proto-oncoprotein is a short-lived transcription factor with oncogenic potential. We have shown that it is massively degraded by the proteasome in vivo under various experimental conditions. Other proteolytic systems including lysosomes and calpains, might, however, also marginally operate on it. Although there is evidence that c-Fos can be ubiquitinylated in vitro, the unambiguous demonstration that ubiquitinylation is necessary for its addressing to the proteasome in vivo is still lacking. c-Jun, one of the main dimerization partners of c-Fos within the AP-1 transcription complex, is also an unstable protein. Its degradation is clearly proteasome- and ubiquitin-dependent in vivo. Interestingly, several lines of evidence indicate that the addressing of c-Fos and c-Jun to the proteasome is, at least in part, governed by different mechanisms. c-Fos has been transduced by two murine osteosarcomatogenic retroviruses under mutated forms which are more stable and more oncogenic. The stabilization is not simply accounted for by simple deletion of c-Fos main destabilizer but, rather, by a complex balance between opposing destabilizing and stabilizing mutations. Though mutations in viral Fos proteins confer full resistance to proteasomal degradation, stabilization is limited because mutations also entail sensitivity to an unidentified proteolytic system. This observation is consistent with the idea that Fos-expressing viruses have evolved to ensure control protein levels to avoid high protein accumulation-linked apoptosis. In conclusion, the unveiling of the complex mechanism network responsible for the degradation of AP-1 family members is still at its beginning and a number of issues regarding the regulation of this process and the addressing to the proteasome are still unresolved.

Predictive molecular markers in non-small cell lung cancer

Recent biotechnologic knowledge has enabled the discovery of a cornucopia of genetic abnormalities commonly involved not only in cancer but also in other diseases ranging from the plague to arteriosclerosis. The wealth of possibilities uncovered by this knowledge inspires the hope that today's dream of a unified concept of common treatment for multiple diseases could become a future reality. This review arbitrarily categorizes recent findings into five major areas. First, cisplatin resistance associated with the nucleotide excision repair pathway can help clinical oncologists to choose between cisplatin and noncisplatin combinations. Second, the relevant role of nuclear factor-kappa B as a predictor of chemosensitivity can lead to the development of new drugs abrogating nuclear factor-kappa B expression. Third, the presence of tubulin mutations, which are directly involved in resistance to microtubule-interactive drugs, can guide chemotherapy based on taxane or nontaxane combinations. In addition, certain chromosomal deletions affect genes involved in deoxyribonucleotide synthesis, like ribonucleotide reductase, that intervene in gemcitabine metabolism; this raises interest in investigating deletion at chromosome 11p15.5 as a potential mechanism of gemcitabine resistance. Finally, an overwhelming number of publications have analyzed genes involved in cell cycle regulation and development as predictive markers of survival; however, where these pieces fit into the puzzle of cancer management is still unclear.

Regulation of apoptosis in prostatic disease

BACKGROUND

Recent studies suggest that aberrant regulation of apoptosis, including acquired apoptosis resistance, contributes to perturbations in cell growth that, in part, underlie the development of benign prostatic hyperplasia (BPH) and prostate cancer. Importantly, apoptosis resistance can enhance the malignant properties of prostate cancer cells, contributing to their widespread metastatic activities. Since apoptosis resistance likely contributes to benign and malignant prostate disease, the promotion of apoptosis represents a reasonable therapeutic objective.

METHODS

This brief review focuses on the role of apoptosis in prostatic disease and discusses potential intervention points for novel therapeutics.

CONCLUSIONS

Novel therapies for prostatic disease, including gene therapy and biological therapy that involve apoptosis as a mechanism of action, are being developed and tested. Ultimately, the identification of proapoptotic and antiapoptotic genes and the pathways through which they operate will serve to provide more rational approaches for further development of more efficacious therapeutic strategies for benign and malignant prostatic disease.

Hyperproliferation and defects in epithelial polarity upon conditional ablation of alpha-catenin in skin

When surface epithelium was conditionally targeted for ablation of alpha-catenin, hair follicle development was blocked and epidermal morphogenesis was dramatically affected, with defects in adherens junction formation, intercellular adhesion, and epithelial polarity. Differentiation occurred, but epidermis displayed hyperproliferation, suprabasal mitoses, and multinucleated cells. In vitro, alpha-catenin null keratinocytes were poorly contact inhibited and grew rapidly. These differences were not dependent upon intercellular adhesion and were in marked contrast to keratinocytes conditionally null for another essential intercellular adhesion protein, desmoplakin (DP). KO keratinocytes exhibited sustained activation of the Ras-MAPK cascade due to aberrations in growth factor responses. Thus, remarkably, features of precancerous lesions often attributed to defects in cell cycle regulatory genes can be generated by compromising the function of alpha-catenin.

Cellular and viral Fos proteins are degraded by different proteolytic systems

c-Fos proto-oncoprotein is a short-lived transcription factor degraded by the proteasome in vivo. Its mutated forms expressed by the mouse osteosarcomatogenic retroviruses, FBJ-MSV and FBR-MSV, are stabilized two- and threefold, respectively. To elucidate the mechanisms underlying v-Fos(FBJ) and v-Fos(FBR) protein stabilization, we conducted a genetic analysis in which the half-lives and the sensitivities to various cell-permeable protease inhibitors of a variety of cellular and viral protein mutants were measured. Our data showed that the decreased degradation of v-Fos(FBJ) and v-Fos(FBR) is not simply explained by the deletion of a c-Fos destabilizing C-terminal domain. Rather, it involves a complex balance between opposing destabilizing and stabilizing mutations which are distinct and which include virally-introduced peptide motifs in both cases. The mutations in viral Fos proteins conferred both total insensitivity to proteasomal degradation and sensitivity to another proteolytic system not naturally operating on c-Fos, explaining the limited stabilization of the two proteins. This observation is consistent with the idea that FBR-MSV and FBJ-MSV expression machineries have evolved to ensure controlled protein levels. Importantly, our data illustrate that the degradation of unstable proteins does not necessarily involve the proteasome and provide support to the notion that highly related proteins can be broken down by different proteolytic systems in living cells.

Pathways governing G1/S transition and their response to DNA damage

The ability to self-replicate is a fundamental feature of life, reflected at the cellular level by a highly regulated process initiated in G1 phase via commitment to a round of DNA replication and cell division. Here we briefly highlight recent advances in understanding the molecular pathways which govern the decision of mammalian somatic cells to enter S phase, and the so-called cell cycle checkpoints which guard the G1/S transition and S phase progression against potentially deleterious effects of genotoxic stress. Particular emphasis is put on the emerging parallel yet cooperative pathways of retinoblastoma protein (pRB)-E2F and Myc, their convergence to control the activity of the cyclin-dependent kinase 2 (Cdk2) at the G1/S boundary, as well as the two waves of checkpoint responses at G1/S: the rapid pathway(s) leading to Cdc25A degradation, and the delayed p53-p21 cascade, both silencing the Cdk2 activity upon DNA damage.

STAT3-mediated constitutive expression of SOCS-3 in cutaneous T-cell lymphoma

A characteristic feature of neoplastic transformation is the loss of external control by cytokines and extracellular matrix of cellular differentiation, migration, and mitogenesis. Because suppressors of cytokine signaling (SOCS) proteins are negative regulators of cytokine-induced signaling, it has been hypothesized that an aberrant SOCS expression plays a role in neoplastic transformation. This study reports on a constitutive SOCS-3 expression in cutaneous T-cell lymphoma (CTCL) cell lines. SOCS-3 protein is constitutively expressed in tumor cell lines (but not in nonmalignant T cells) obtained from affected skin from a patient with mycosis fungoides (MF) and from peripheral blood from a patient with Sezary syndrome (SS). In contrast, constitutive SOCS-3 expression is not found in the leukemic Jurkat T-cell line, the MOLT-4 acute lymphoblastic leukemia cell line, and the monocytic leukemic cell line U937. Expression of SOCS-3 coincides with a constitutive activation of STAT3 in CTCL tumor cells, and stable transfection of CTCL tumor cells with a dominant negative STAT3 strongly inhibits SOCS-3 expression, whereas transfection with wild-type STAT3 does not. Moreover, the reduced SOCS-3 expression in cells transfected with the dominant negative STAT3 is associated with an increased sensitivity to interferon-alpha (IFN-alpha). In conclusion, evidence is provided for a constitutive SOCS-3 expression in cancer cells obtained from patients with CTCL. Moreover, the findings indicate that the aberrant expression of SOCS-3 is mediated by a constitutive activation of STAT3 in CTCL cells and affects the IFN-alpha sensitivity of these cells. (Blood. 2001;97:1056-1062)

Defective interplay of activators and repressors with TFIH in xeroderma pigmentosum

Inherited mutations of the TFIIH helicase subunits xeroderma pigmentosum (XP) B or XPD yield overlapping DNA repair and transcription syndromes. The high risk of cancer in these patients is not fully explained by the repair defect. The transcription defect is subtle and has proven more difficult to evaluate. Here, XPB and XPD mutations are shown to block transcription activation by the FUSE Binding Protein (FBP), a regulator of c-myc expression, and repression by the FBP Interacting Repressor (FIR). Through TFIIH, FBP facilitates transcription until promoter escape, whereas after initiation, FIR uses TFIIH to delay promoter escape. Mutations in TFIIH that impair regulation by FBP and FIR affect proper regulation of c-myc expression and have implications in the development of malignancy.

Angiogenic potential of prostate carcinoma cells overexpressing bcl-2

BACKGROUND

Tumors commonly outgrow their blood supply, thereby creating hypoxic conditions, which induce apoptosis and increase expression of angiogenic growth factors. The bcl-2 oncogene inhibits apoptosis induced by a variety of stimuli, including hypoxia. On the basis of bcl-2's role in regulating apoptosis in response to hypoxia, we hypothesized that this oncogene might affect other responses to hypoxia, such as the expression of angiogenic growth factors.

METHODS

Three prostate carcinoma cell lines, PC3, LNCaP, and DU-145, were stably transfected with a bcl-2 complementary DNA (cDNA), and transfectants were analyzed in vitro for the expression of angiogenic factors after exposure to either normoxic (19% O(2)) or hypoxic (1% O(2)) conditions. The in vivo angiogenic potential of the transfected cells was determined by analyzing vessel density in xenografts derived from them and by measuring the ability of these xenografts to induce neovascularization when implanted in mouse corneal micropockets. Statistical tests were two-sided.

RESULTS

When exposed to hypoxic conditions, prostate carcinoma cells overexpressing bcl-2 expressed statistically significantly higher levels of vascular endothelial growth factor (VEGF), an angiogenic factor, than control-transfected cells (P = .001 for PC3, P = .04 for DU-145 after 48 hours). This effect of bcl-2 was independent of its antiapoptotic activity because increased expression of VEGF was detected in PC3 cells overexpressing bcl-2 even though PC3 cells are inherently resistant to hypoxia-induced apoptosis. In vivo, xenograft tumors derived from the bcl-2-overexpressing prostate carcinoma cell lines displayed increased angiogenic potential and grew more aggressively than tumors derived from the control cell lines (P =.03 for PC3). Treatment of bcl-2-overexpressing and control tumors with the antiangiogenic drug TNP-470 neutralized the aggressive angiogenesis in bcl-2-overexpressing tumors (P = .04 for PC3, P = .004 for DU-145) and the moderate angiogenesis in control tumors (P = .01 for PC3, P = .05 for DU-145), resulting in similar growth rates for both tumors.

CONCLUSIONS

bcl-2 may play a dual role in tumorigenesis by suppressing apoptosis and by stimulating angiogenesis.

Tissue inhibitor of metalloproteinases-2 (TIMP-2) suppresses TKR-growth factor signaling independent of metalloproteinase inhibition

The tissue inhibitors of metalloproteinases (TIMPs) block matrix metalloproteinase (MMP)-mediated increases in cell proliferation, migration, and invasion that are associated with extracellular matrix (ECM) turnover. Here we demonstrate a direct role for TIMP-2 in regulating tyrosine kinase-type growth factor receptor activation. We show that TIMP-2 suppresses the mitogenic response to tyrosine kinase-type receptor growth factors in a fashion that is independent of MMP inhibition. The TIMP-2 suppression of mitogenesis is reversed by the adenylate cyclase inhibitor SQ22536, and implicates cAMP as the second messenger in these effects. TIMP-2 neither altered the release of transforming growth factor alpha from the cell surface, nor epidermal growth factor (EGF) binding to the cognate receptor, EGFR. TIMP-2 binds to the surface of A549 cells in a specific and saturable fashion (K(d) = 147 pm), that is not competed by the synthetic MMP inhibitor BB-94 and is independent of MT-1-MMP. TIMP-2 induces a decrease in phosphorylation of EGFR and a concomitant reduction in Grb-2 association. TIMP-2 prevents SH2-protein-tyrosine phosphatase-1 (SHP-1) dissociation from immunoprecipitable EGFR complex and a selective increase in total SHP-1 activity. These studies represent a new functional paradigm for TIMP-2 in which TIMP suppresses EGF-mediated mitogenic signaling by short-circuiting EGFR activation.

Lack of replicative senescence in cultured rat oligodendrocyte precursor cells

Most mammalian somatic cells are thought to have a limited proliferative capacity because they permanently stop dividing after a finite number of divisions in culture, a state termed replicative cell senescence. Here we show that most oligodendrocyte precursor cells purified from postnatal rat optic nerve can proliferate indefinitely in serum-free culture if prevented from differentiating; various cell cycle-inhibitory proteins increase, but the cells do not stop dividing. The cells maintain high telomerase activity and p53- and Rb-dependent cell cycle checkpoint responses, and serum or genotoxic drugs induce them to acquire a senescence-like phenotype. Our findings suggest that some normal rodent precursor cells have an unlimited proliferative capacity if cultured in conditions that avoid both differentiation and the activation of checkpoint responses that arrest the cell cycle.

Telomerase: biology and phase I trials

In normal somatic cells, the ends of chromosomes (the telomeres) shorten with each cell division. By contrast, in tumour cells, telomere length is maintained, generally through the reactivation of the reverse transcriptase enzyme, telomerase. At least three applications relating to telomeres and telomerase have been proposed: in cancer diagnosis and prognosis (especially through measurements of the catalytic component of telomerase, hTERT) and as a means of monitoring tumour response to therapy; as an aid to tissue engineering; and inhibition as a cancer therapeutic strategy. Mouse knockout, hTERT dominant negative, and antisense experiments suggest that telomerase inhibitors will confer anticancer activity, especially in tumours with short telomeres. Inhibitory strategies have focused on antisense molecules, inhibitors of reverse transcriptases, and small molecules able to interact with and stabilise four-stranded (G-quadruplex) structures formed by telomeres. Clinical trials involving telomerase inhibitors require careful consideration compared to those looking at conventional anticancer cytotoxic drugs.

Molecular markers of tumor initiation and progression

Of the hundreds of genes and proteins reported to be altered in human cancers, only a few are sufficiently central to warrant translation into diagnostic or therapeutic tools. Three recent developments have the potential to alter radically the discovery of molecular markers: the compendium of human genes; the advent of technologies that provide the means to identify simultaneously several known and unknown genes and proteins; and an appreciation of the critical processes involved in tumor initiation and progression.

Analysis of c-Ha-ras gene mutations in skin tumors induced in carcinogenesis-susceptible and carcinogenesis-resistant mice by different two-stage protocols or tumor promoter alone

In the present study we describe the molecular analysis of c-Ha-ras gene mutations in 47 papillomas and 17 carcinomas developed in two lines of mice, carcinogenesis-susceptible (Car-S) and carcinogenesis-resistant (Car-R), selectively bred for extreme susceptibility or resistance to chemical skin carcinogenesis initiated and promoted with different doses of 7,12-dimethylbenz[a]anthracene (DMBA) and 12-O-tetradecanoylphorbol-13-acetate (TPA). This study also presents the analysis of c-Ha-ras gene mutations in 22 papillomas and 22 carcinomas in Car-S mice initiated with DMBA and promoted with benzoyl peroxide (BzPo) and in seven papillomas and one carcinoma from a group of uniniated Car-S mice that received only BzPo treatment. The data showed that a A(182)-->T transversion in the c-Ha-ras gene was present in 100% and 81% of the skin tumors developed in Car-S and Car-R mice, respectively, after DMBA initiation and TPA promotion, suggesting that differences in genetic susceptibility can influence the frequency of c-Ha-ras mutations in the skin tumors produced. The same A(182)-->T mutation with an incidence of 68% was found in papillomas from DMBA-initiated and BzPo-promoted Car-S mice. The difference in the mutation frequency between DMBA/BzPo and DMBA/TPA papillomas suggested that the promotion step contributes to the final mutation pattern. The tumor induction experiment with BzPo alone showed that this compound can induce tumor development in 26% of Car-S mice, and the molecular analysis of the tumors showed a broad mutation spectrum, including mutations in codons 12, 13, and 61 of the c-Ha-ras gene. Mol. Carcinog. 30:111-118, 2001.

E2Fs regulate the expression of genes involved in differentiation, development, proliferation, and apoptosis

The retinoblastoma protein (pRB) and its two relatives, p107 and p130, regulate development and cell proliferation in part by inhibiting the activity of E2F-regulated promoters. We have used high-density oligonucleotide arrays to identify genes in which expression changed in response to activation of E2F1, E2F2, and E2F3. We show that the E2Fs control the expression of several genes that are involved in cell proliferation. We also show that the E2Fs regulate a number of genes involved in apoptosis, differentiation, and development. These results provide possible genetic explanations to the variety of phenotypes observed as a consequence of a deregulated pRB/E2F pathway.

Tumour metastasis: is tissue an issue?

Single tumour cells, or multicellular aggregates, escape into blood and lymphatic vessels from a primary solid tumour as it progresses. However, the ability of such cells to develop into metastatic outgrowths is very limited, as shown by the poor prognostic power of the presence of circulating tumour cells in cancer patients. An explanation for this low efficiency may be a temporary absence of a suitable microenvironment once the tumour cells escape from their original tissue compartment. On the basis of histopathological observations, experimental studies, and the generally accepted poor prognosis of histopathologically confirmed intravascular tumour location, we propose that the structural and functional organisation of intravascular tumour cells as a tissue has a key role in providing the optimum microenvironment for sustained malignant dissemination. Such a tissue may be a fixed or a mobile intravascular microsatellite, or an intravascular micrometastasis, which locally develops into an overt in-transit metastasis.

Laminin-5-mediated gene expression in human prostate carcinoma cells

Interactions between extracellular matrix (ECM) proteins and prostate carcinoma cells provide a dynamic model of prostate tumor progression. Previous work in our laboratory showed that laminin-5, an important member of a family of ECM glycoproteins expressed in the basal lamina, is lost in prostate carcinoma. Moreover, we showed that the receptor for laminin-5, the alpha6beta4 integrin, is altered in prostate tumors. However, the genes that laminin-5 potentially regulates and the significance of its loss of expression in prostate cancer are not known. We selected cDNA microarray as a comprehensive and systematic method for surveying and examining gene expression induced by laminin-5. To establish a definitive role for laminin-5 in prostate tumor progression and understand the significance of its loss of expression, we used a cDNA microarray containing 5289 human genes to detect perturbations of gene expression when DU145 prostate carcinoma cells interacted with purified laminin-5 after 0.5, 6, and 24 h. Triplicate experiments showed modulations of four, 61, and 14 genes at 0.5, 6, and 24 h, respectively. Genes associated with signal transduction, cell adhesion, the cell cycle, and cell structure were identified and validated by northern blot analysis. Protein expression was further assessed by immunohistochemistry. Mol. Carcinog. 30:119-129, 2001.