Tumorigenic transformation of mammalian cells induced by a normal human gene homologous to the oncogene of Harvey murine sarcoma virus

KRAS mutations detection methodology: from RFLP to CRISPR/Cas based methods

In personalized cancer medicine, the identification of KRAS mutations is essential for making treatment decisions and improving patient outcomes. This work presents a comprehensive review of the current approaches for detection of KRAS mutations in different cancers. We highlight the value of fast and reliable KRAS mutations discovery and the effectiveness of molecular testing for selecting individuals who might benefit from targeted therapy. We provide an overview of various methods and tools available for detecting KRAS mutations, such as digital droplet PCR, next-generation sequencing (NGS), and polymerase chain reaction (PCR). We also address the difficulties and limitations in the identification of KRAS mutations, namely tumor heterogeneity and the emergence of resistance mechanisms. This article aims to guide clinicians in KRAS mutation identification.

Oncogenic KRAS, Mucin 4, and Activin A-Mediated Fibroblast Activation Cooperate for PanIN Initiation

Over 90% of patients with pancreatic ductal adenocarcinoma (PDAC) have oncogenic KRAS mutations. Nevertheless, mutated KRAS alone is insufficient to initiate pancreatic intraepithelial neoplasia (PanIN), the precursor of PDAC. The identities of the other factors/events required to drive PanIN formation remain elusive. Here, optic-clear 3D histology is used to analyze entire pancreases of 2-week-old Pdx1-Cre; LSL-KrasG12D/+ (KC) mice to detect the earliest emergence of PanIN and observed that the occurrence is independent of physical location. Instead, it is found that the earliest PanINs overexpress Muc4 and associate with αSMA+ fibroblasts in both transgenic mice and human specimens. Mechanistically, KrasG12D/+ pancreatic cells upregulate Muc4 through genetic alterations to increase proliferation and fibroblast recruitments via Activin A secretion and consequently enhance cell transformation for PanIN formation. Inhibition of Activin A signaling using Follistatin (FST) diminishes early PanIN-associated fibroblast recruitment, effectively curtailing PanIN initiation and growth in KC mice. These findings emphasize the vital role of interactions between oncogenic KrasG12D/+ -driven genetic alterations and induced microenvironmental changes in PanIN initiation, suggesting potential avenues for early PDAC diagnostic and management approaches.

DNA Polymerase Theta Plays a Critical Role in Pancreatic Cancer Development and Metastasis

Pancreatic ductal adenocarcinoma (PDAC), due to its genomic heterogeneity and lack of effective treatment, despite decades of intensive research, will become the second leading cause of cancer-related deaths by 2030. Step-wise acquisition of mutations, due to genomic instability, is considered to drive the development of PDAC; the KRAS mutation occurs in 95 to 100% of human PDAC, and is already detectable in early premalignant lesions designated as pancreatic intraepithelial neoplasia (PanIN). This mutation is possibly the key event leading to genomic instability and PDAC development. Our study aimed to investigate the role of the error-prone DNA double-strand breaks (DSBs) repair pathway, alt-EJ, in the presence of the KRAS G12D mutation in pancreatic cancer development. Our findings show that oncogenic KRAS contributes to increasing the expression of Polθ, Lig3, and Mre11, key components of alt-EJ in both mouse and human PDAC models. We further confirm increased catalytic activity of alt-EJ in a mouse and human model of PDAC bearing the KRAS G12D mutation. Subsequently, we focused on estimating the impact of alt-EJ inactivation by polymerase theta (Polθ) deletion on pancreatic cancer development, and survival in genetically engineered mouse models (GEMMs) and cancer patients. Here, we show that even though Polθ deficiency does not fully prevent the development of pancreatic cancer, it significantly delays the onset of PanIN formation, prolongs the overall survival of experimental mice, and correlates with the overall survival of pancreatic cancer patients in the TCGA database. Our study clearly demonstrates the role of alt-EJ in the development of PDAC, and alt-EJ may be an attractive therapeutic target for pancreatic cancer patients.

Mutational landscape of K-Ras substitutions at 12th position-a systematic molecular dynamics approach

K-Ras is a small GTPase and acts as a molecular switch by recruiting GEFs and GAPs, and alternates between the inert GDP-bound and the dynamic GTP-bound forms. The amino acid at position 12 of K-Ras is a hot spot for oncogenic mutations (G12A, G12C, G12D, G12R, G12S, and G12V), disturbing the active fold of the protein, leading to cancer development. This study aimed to investigate the potential conformational changes induced by these oncogenic mutations at the 12^th position, impairing GAP-mediated GTP hydrolysis. Comprehensive computational tools (iStable, FoldX, SNPeffect, DynaMut, and CUPSAT) were used to evaluate the effect of these six mutations on the stability of wild type K-Ras protein. The docking of GTP with K-Ras was carried out using AutoDock4.2, followed by molecular dynamics simulations. Furthermore, on comparison of binding energies between the wild type K-Ras and the six mutants, we have demonstrated that the G12A and G12V mutants exhibited the strongest binding efficiency compared to the other four mutants. Trajectory analyses of these mutations revealed that G12A encountered the least deviation, fluctuation, intermolecular H-bonds, and compactness compared to the wildtype, which was supported by the lower Gibbs free energy value. Our study investigates the molecular dynamics simulations of the mutant K-Ras forms at the 12^th position, which expects to provide insights about the molecular mechanisms involved in cancer development, and may serve as a platform for targeted therapies against cancer. Communicated by Ramaswamy H. Sarma.

Prevention of tumor risk associated with the reprogramming of human pluripotent stem cells

Human pluripotent embryonic stem cells have two special features: self-renewal and pluripotency. It is important to understand the properties of pluripotent stem cells and reprogrammed stem cells. One of the major problems is the risk of reprogrammed stem cells developing into tumors. To understand the process of differentiation through which stem cells develop into cancer cells, investigators have attempted to identify the key factors that generate tumors in humans. The most effective method for the prevention of tumorigenesis is the exclusion of cancer cells during cell reprogramming. The risk of cancer formation is dependent on mutations of oncogenes and tumor suppressor genes during the conversion of stem cells to cancer cells and on the environmental effects of pluripotent stem cells. Dissecting the processes of epigenetic regulation and chromatin regulation may be helpful for achieving correct cell reprogramming without inducing tumor formation and for developing new drugs for cancer treatment. This review focuses on the risk of tumor formation by human pluripotent stem cells, and on the possible treatment options if it occurs. Potential new techniques that target epigenetic processes and chromatin regulation provide opportunities for human cancer modeling and clinical applications of regenerative medicine.

Sensitivity Pattern of Normal and Ha-Ras Transformed Nih3T3 Fibroblasts to Antineoplastic Drugs

Ha-ras-transformed NIH3T3 fibroblasts were compared with the parental cell line to investigate the influence of the Ha-ras oncogene on cellular chemosensitivity to antineoplastic drugs. Four NIH3T3 cell clones independently transformed by the Ha-ras oncogene, activated by mutation or overexpression, were analyzed: 3 clones were obtained by transfection of NIH3T3 cells with a mutation-activated Ha-ras gene and 1 clone by transfection of a large copy number of the normal Ha-ras protooncogene. Chemosensitivity of the transformed clones and of the parental cell line was analyzed when cells were in the same condition of proliferative activity and cell cycle phase distribution. No significant differences in chemosensitivity were observed between transformed and untrans-formed cell lines to doxorubicin, VP-16, cis-platinum or mitomycin C. Therefore, data suggest that activated Ha-ras oncogenes have no role in sensitivity to these antineoplastic agents.

Tailored Tumor Immunogenicity Reveals Regulation of CD4 and CD8 T Cell Responses against Cancer

CD4 and CD8 T cells play a pivotal role in controlling tumor growth. However, the interplay of both cell types and their role in tumor suppression still remain elusive. In this study, we investigated the regulation of CD4 and CD8 T cell responses to different classes of tumor-specific antigens in liver cancer mouse models. Tumors were induced in p19Arf-deficient mice by hydrodynamic injection of transposon plasmids encoding NrasG12V and pre-defined tumor antigens. This allowed for assessing the regulation of tumor-specific CD4 and CD8 T cell responses. We showed that MHC class I tumor immunogenicity was essential to trigger tumor-directed CD4 T cells. Tumor-specific CD8 T cell responses arose independently of CD4 T cells, but they required Th1-polarized CD4 T cells for efficient tumor suppression. Our results further indicate that the immune system is incapable of eliciting sufficient numbers of T cells directed against antigens derived from immunoedited tumors, which consequently leads to a lack of T-cell-mediated tumor suppression in untreated hosts.

Low doses and non-targeted effects in environmental radiation protection; where are we now and where should we go?

The field of low dose radiobiology has advanced considerably in the last 30 years from small indications in the 1980's that all was not simple, to a paradigm shift which occurred during the 1990's, which severely dented the dose-driven models and DNA centric theories which had dominated until then. However while the science has evolved, the application of that science in environmental health protection has not. A reason for this appears to be the uncertainties regarding the shape of the low dose response curve, which lead regulators to adopt a precautionary approach to radiation protection. Radiation protection models assume a linear relationship between dose (i.e. energy deposition) and effect (in this case probability of an adverse DNA interaction leading to a mutation). This model does not consider non-targeted effects (NTE) such as bystander effects or delayed effects, which occur in progeny cells or offspring not directly receiving energy deposition from the dose. There is huge controversy concerning the role of NTE with some saying they reflect "biology" and that repair and homeostatic mechanisms sort out the apparent damage while others consider them to be a class of damage which increases the size of the target. One thing which has recently become apparent is that NTE may be very critical for modelling long-term effects at the level of the population rather than the individual. The issue is that NTE resulting from an acute high dose such as occurred after the A-bomb or Chernobyl occur in parallel with chronic effects induced by the continuing residual effects due to radiation dose decay. This means that if ambient radiation doses are measured for example 25 years after the Chernobyl accident, they only represent a portion of the dose effect because the contribution of NTE is not included.

Oncogenic KRAS and BRAF Drive Metabolic Reprogramming in Colorectal Cancer

Metabolic reprogramming, in which altered utilization of glucose and glutamine supports rapid growth, is a hallmark of most cancers. Mutations in the oncogenes KRAS and BRAF drive metabolic reprogramming through enhanced glucose uptake, but the broader impact of these mutations on pathways of carbon metabolism is unknown. Global shotgun proteomic analysis of isogenic DLD-1 and RKO colon cancer cell lines expressing mutant and wild type KRAS or BRAF, respectively, failed to identify significant differences (at least 2-fold) in metabolic protein abundance. However, a multiplexed parallel reaction monitoring (PRM) strategy targeting 73 metabolic proteins identified significant protein abundance increases of 1.25-twofold in glycolysis, the nonoxidative pentose phosphate pathway, glutamine metabolism, and the phosphoserine biosynthetic pathway in cells with KRAS G13D mutations or BRAF V600E mutations. These alterations corresponded to mutant KRAS and BRAF-dependent increases in glucose uptake and lactate production. Metabolic reprogramming and glucose conversion to lactate in RKO cells were proportional to levels of BRAF V600E protein. In DLD-1 cells, these effects were independent of the ratio of KRAS G13D to KRAS wild type protein. A study of 8 KRAS wild type and 8 KRAS mutant human colon tumors confirmed the association of increased expression of glycolytic and glutamine metabolic proteins with KRAS mutant status. Metabolic reprogramming is driven largely by modest (<2-fold) alterations in protein expression, which are not readily detected by the global profiling methods most commonly employed in proteomic studies. The results indicate the superiority of more precise, multiplexed, pathway-targeted analyses to study functional proteome systems. Data are available through MassIVE Accession MSV000079486 at ftp://MSV000079486@massive.ucsd.edu.

Combined HSP90 and kinase inhibitor therapy: Insights from The Cancer Genome Atlas

The merging of knowledge from genomics, cellular signal transduction and molecular evolution is producing new paradigms of cancer analysis. Protein kinases have long been understood to initiate and promote malignant cell growth and targeting kinases to fight cancer has been a major strategy within the pharmaceutical industry for over two decades. Despite the initial success of kinase inhibitors (KIs), the ability of cancer to evolve resistance and reprogram oncogenic signaling networks has reduced the efficacy of kinase targeting. The molecular chaperone HSP90 physically supports global kinase function while also acting as an evolutionary capacitor. The Cancer Genome Atlas (TCGA) has compiled a trove of data indicating that a large percentage of tumors overexpress or possess mutant kinases that depend on the HSP90 molecular chaperone complex. Moreover, the overexpression or mutation of parallel activators of kinase activity (PAKA) increases the number of components that promote malignancy and indirectly associate with HSP90. Therefore, targeting HSP90 is predicted to complement kinase inhibitors by inhibiting oncogenic reprogramming and cancer evolution. Based on this hypothesis, consideration should be given by both the research and clinical communities towards combining kinase inhibitors and HSP90 inhibitors (H90Ins) in combating cancer. The purpose of this perspective is to reflect on the current understanding of HSP90 and kinase biology as well as promote the exploration of potential synergistic molecular therapy combinations through the utilization of The Cancer Genome Atlas.

MicroRNA-Based Therapeutic Strategies for Targeting Mutant and Wild Type RAS in Cancer

MicroRNAs (miRs) have been causally implicated in the progression and development of a wide variety of cancers. miRs modulate the activity of key cell signaling networks by regulating the translation of pathway component proteins. Thus, the pharmacological targeting of miRs that regulate cancer cell signaling networks, either by promoting (using miR-supplementation) or by suppressing (using antisense oligonucleotide-based strategies) miR activity is an area of intense research. The RAS-extracellular signal regulated kinase (ERK) pathway represents a major miR-regulated signaling network that endows cells with some of the classical hallmarks of cancer, and is often inappropriately activated in malignancies by somatic genetic alteration through point mutation or alteration of gene copy number. In addition, recent progress indicates that many tumors may be deficient in GTPase activating proteins (GAPs) due to the collaborative action of oncogenic miRs. Recent studies also suggest that in tumors harboring a mutant RAS allele there is a critical role for wild type RAS proteins in determining overall RAS-ERK pathway activity. Together, these two advances comprise a new opportunity for therapeutic intervention. In this review, we evaluate miR-based therapeutic strategies for modulating RAS-ERK signaling in cancers; in particular for more direct modulation of RAS-GTP levels, with the potential to complement current strategies to yield more durable treatment responses. To this end, we discuss the potential for miR-based therapies focused on three prominent miRs including the pan-RAS regulator let-7 and the GAP regulator comprised of miR-206 and miR-21 (miR-206/21).

Ras history: The saga continues

Although the roots of Ras sprouted from the rich history of retrovirus research, it was the discovery of mutationally activated RAS genes in human cancer in 1982 that stimulated an intensive research effort to understand Ras protein structure, biochemistry and biology. While the ultimate goal has been developing anti-Ras drugs for cancer treatment, discoveries from Ras have laid the foundation for three broad areas of science. First, they focused studies on the origins of cancer to the molecular level, with the subsequent discovery of genes mutated in cancer that now number in the thousands. Second, elucidation of the biochemical mechanisms by which Ras facilitates signal transduction established many of our fundamental concepts of how a normal cell orchestrates responses to extracellular cues. Third, Ras proteins are also founding members of a large superfamily of small GTPases that regulate all key cellular processes and established the versatile role of small GTP-binding proteins in biology. We highlight some of the key findings of the last 28 years.

Triple-negative breast cancer: investigating potential molecular therapeutic target

INTRODUCTION

Triple-negative breast cancer (TNBC) makes up about 10 - 20% of all breast cancers and the lack of hormone receptors and human epidermal growth factor receptor-2/Neu expression is responsible for poor prognosis, no targeted therapies and trouble in the clinical management. Tumor heterogeneity, also within the same tumor, is a major cause for this difficulty. Based on the introduction of new biological drugs against different kinds of tumor, many efforts have been made for classification of genetic alterations present in TNBC, leading to the identification of several oncogenes and tumor suppressor genes involved in breast cancer carcinogenesis.

AREAS COVERED

In this review we investigated the molecular alteration present in TNBC which could lead to the creation of new targeted therapies in the future, with the aim to counteract this disease in the most effective way.

EXPERT OPINION

In this context some hormone receptors like G-protein-coupled receptor 30 and androgen receptors may be a fascinating area to investigate; also, angiogenesis, represented not only by the classical VEGF/VEGFR relationship, but also by other molecules, like semaphorins, fibroblast growth factor and heparin-binding-EGF-like, is a mechanism in which new developments are expected. In this perspective, one technique that may show promise is the gene therapy; in particular the gene transfer could correct abnormal genetic function in cancer cells.

Putting the pieces together: How is the mitochondrial pathway of apoptosis regulated in cancer and chemotherapy?

In order to solve a jigsaw puzzle, one must first have the complete picture to logically connect the pieces. However, in cancer biology, we are still gaining an understanding of all the signaling pathways that promote tumorigenesis and how these pathways can be pharmacologically manipulated by conventional and targeted therapies. Despite not having complete knowledge of the mechanisms that cause cancer, the signaling networks responsible for cancer are becoming clearer, and this information is serving as a solid foundation for the development of rationally designed therapies. One goal of chemotherapy is to induce cancer cell death through the mitochondrial pathway of apoptosis. Within this review, we present the pathways that govern the cellular decision to undergo apoptosis as three distinct, yet connected puzzle pieces: (1) How do oncogene and tumor suppressor pathways regulate apoptosis upstream of mitochondria? (2) How does the B-cell lymphoma 2 (BCL-2) family influence tumorigenesis and chemotherapeutic responses? (3) How is post-mitochondrial outer membrane permeabilization (MOMP) regulation of cell death relevant in cancer? When these pieces are united, it is possible to appreciate how cancer signaling directly impacts upon the fundamental cellular mechanisms of apoptosis and potentially reveals novel pharmacological targets within these pathways that may enhance chemotherapeutic success.

Nras in melanoma: targeting the undruggable target

RAS belongs to the guanosine 5'-triphosphate (GTP)-binding proteins' family, and oncogenic mutations in codons 12, 13, or 61 of RAS family occur in approximately one third of all human cancers with N-RAS mutations found in about 15-20% of melanomas. The importance of RAS signaling as a potential target in cancer is emphasized not only by the prevalence of RAS mutations, but also by the high number of RAS activators and effectors identified in mammalian cells that places the RAS proteins at the crossroads of several, important signaling networks. Ras proteins are crucial crossroads of signaling pathways that link the activation of cell surface receptors with a wide variety of cellular processes leading to the control of proliferation, apoptosis and differentiation. Furthermore, oncogenic ras proteins interfere with metabolism of tumor cells, microenvironment's remodeling, evasion of the immune response, and finally contributes to the metastatic process. After 40 years of basic, translational and clinical research, much is now known about the molecular mechanisms by which these monomeric guanosine triphosphatase-binding proteins promote cellular malignancy, and it is clear that they regulate signaling pathways involved in the control of cell proliferation, survival, and invasiveness. In this review we summarize the biological role of RAS in cancer by focusing our attention on the biological rational and strategies to target RAS in melanoma.

Anti-EGFR MoAb treatment in colorectal cancer: limitations, controversies, and contradictories

Anti-epidermal growth-factor receptor (EGFR) monoclonal antibody (MoAb) treatment for chemotherapy refractory or metastatic colorectal cancer has obtained great achievement. However, not every colorectal patient responds to such molecular-targeted agent well. Biomarkers associated with anti-EGFR resistance are not limited to KRAS mutation up to now. It was recently reported that cross-talking molecular effectors interacted with EGFR-related pathway were also negative predictor for anti-EGFR treatment. However, the limited data, controversial results, and contradictories between in vitro and clinical studies restrict the clinical application of these new biomarkers. Although the current theory of tumor microenvironment supported the application of multi-target treatment, the results from the clinical studies were less than expected. Moreover, WHO or RECIST guideline for response assessment in anti-EGFR MoAb treatment was also queried by recent AIO KRK-0306 trial. This review focuses on these controversies, contradictories, and limitations, in order to uncover the unmet needs in current status of anti-EGFR MoAb treatment in colorectal cancer.

Ras and rheb signaling in survival and cell death

One of the most obvious hallmarks of cancer is uncontrolled proliferation of cells partly due to independence of growth factor supply. A major component of mitogenic signaling is Ras, a small GTPase. It was the first identified human protooncogene and is known since more than three decades to promote cellular proliferation and growth. Ras was shown to support growth factor-independent survival during development and to protect from chemical or mechanical lesion-induced neuronal degeneration in postmitotic neurons. In contrast, for specific patho-physiological cases and cellular systems it has been shown that Ras may also promote cell death. Proteins from the Ras association family (Rassf, especially Rassf1 and Rassf5) are tumor suppressors that are activated by Ras-GTP, triggering apoptosis via e.g., activation of mammalian sterile 20-like (MST1) kinase. In contrast to Ras, their expression is suppressed in many types of tumours, which makes Rassf proteins an exciting model for understanding the divergent effects of Ras activity. It seems likely that the outcome of Ras signaling depends on the balance between the activation of its various downstream effectors, thus determining cellular fate towards either proliferation or apoptosis. Ras homologue enriched in brain (Rheb) is a protein from the Ras superfamily that is also known to promote proliferation, growth, and regeneration through the mammalian target of rapamycin (mTor) pathway. However, recent evidences indicate that the Rheb-mTor pathway may switch its function from a pro-growth into a cell death pathway, depending on the cellular situation. In contrast to Ras signaling, for Rheb, the cellular context is likely to modulate the whole Rheb-mTor pathway towards cellular death or survival, respectively.

KRAS mutation testing in metastatic colorectal cancer

The KRAS oncogene is mutated in approximately 35%-45% of colorectal cancers, and KRAS mutational status testing has been highlighted in recent years. The most frequent mutations in this gene, point substitutions in codons 12 and 13, were validated as negative predictors of response to anti-epidermal growth factor receptor antibodies. Therefore, determining the KRAS mutational status of tumor samples has become an essential tool for managing patients with colorectal cancers. Currently, a variety of detection methods have been established to analyze the mutation status in the key regions of the KRAS gene; however, several challenges remain related to standardized and uniform testing, including the selection of tumor samples, tumor sample processing and optimal testing methods. Moreover, new testing strategies, in combination with the mutation analysis of BRAF, PIK3CA and loss of PTEN proposed by many researchers and pathologists, should be promoted. In addition, we recommend that microsatellite instability, a prognostic factor, be added to the abovementioned concomitant analysis. This review provides an overview of KRAS biology and the recent advances in KRAS mutation testing. This review also addresses other aspects of status testing for determining the appropriate treatment and offers insight into the potential drawbacks of mutational testing.

H-ras localizes to cell nuclei and varies with the cell cycle

H-Ras functions as a signal switch molecule in numerous signaling pathways in the cytoplasm, requiring H-Ras localization to the inner surface of the cytoplasmic membrane, and H-Ras is considered to be a cytoplasmic protein. Immunoblot studies of cells transformed by overexpression of c-H-ras indicated that H-Ras protein was present in both cytoplasmic and nuclear extracts, suggesting a possible correlation of nuclear H-Ras and cellular transformation. Unexpectedly, additional studies revealed that H-Ras protein was also present in the nuclei of nontransformed and primary mouse cells, which do not overexpress H-Ras. Mouse fibroblast NIH 3T3 cells, L cells, and a primary fibroblast line all had H-Ras present in both cytoplasmic and nuclear extracts. Nuclear extracts of cells synchronized by growth without serum displayed an increasing amount of H-Ras and cyclin D1 as cells grew after serum addition. Treatment with farnesyltransferase inhibitor caused loss of H-Ras from the nucleus. Immunofluorescence in situ studies of nuclei from synchronized cultures showed that H-Ras protein appeared in and disappeared from the nuclei as the cells moved through the growth cycle. This cycling occurred in both nontransformed and ras-transformed cells. Flow cytometry measurements on parallel cultures revealed that the time point at which the greatest percentage of cells were in S phase, for each line, corresponded to appearance of a noticeably stronger in situ signal for H-Ras. H-Ras may participate in nuclear signaling pathways associated with replication in addition to its cytoplasmic signaling functions.

Molecular assessment of c-H-ras p21 expression in Helicobacter pylori-mediated gastric carcinogenesis

Helicobacter pylori (H. pylori) infection plays a significant role in causing gastric cancer; the exact molecular mechanisms of gastric carcinogenesis have not yet been fully determined. Therefore, this study was planned to examine the role of c-H-ras p21 expression in H. pylori infection at different stages of disease progression from precursor lesions to gastric carcinoma. This study was carried out in 200 patients, consisting of normal gastric mucosa (n = 20), mucosa with chronic gastritis (n = 63), intestinal metaplasia (n = 20), dysplasia (n = 11), and gastric adenocarcinoma (n = 86), in which the H. pylori status have been analysed. The expression of c-H-ras p21 was studied at mRNA as well as protein level using RT-PCR and western blotting, respectively. The localization of c-H-ras p21 was also studied semiquantitatively by immunohistochemistry. The RT-PCR and western blotting results of c-H-ras p21 mRNA and protein expressions were significantly increased in chronic gastritis, intestinal metaplasia, dysplasia, and gastric adenocarcinoma patients, respectively. Immunohistochemical study also showed the increased expression of c-H-ras p21 in the similar way. Overexpression of c-H-ras p21 might be due to H-ras mutation at codon 12 of ras gene family in H. pylori infection. The rate of expression of ras p21 was higher in the H. pylori-infected precursor lesions, chronic gastritis 49/56 (87.5%), intestinal metaplasia 16/17 (94%), and dysplasia 9/11(82%) whereas in the case of H. pylori negative cases these groups, show 12.5, 5.9, and 18.2%, respectively. The data suggested that H. pylori infection may increase the expression of c-H-ras p21 early in the process of gastric carcinogenesis.

The role of centrosomal Nlp in the control of mitotic progression and tumourigenesis

The human centrosomal ninein-like protein (Nlp) is a new member of the γ-tubulin complexes binding proteins (GTBPs) that is essential for proper execution of various mitotic events. The primary function of Nlp is to promote microtubule nucleation that contributes to centrosome maturation, spindle formation and chromosome segregation. Its subcellular localisation and protein stability are regulated by several crucial mitotic kinases, such as Plk1, Nek2, Cdc2 and Aurora B. Several lines of evidence have linked Nlp to human cancer. Deregulation of Nlp in cell models results in aberrant spindle, chromosomal missegregation and multinulei, and induces chromosomal instability and renders cells tumourigenic. Overexpression of Nlp induces anchorage-independent growth and immortalised primary cell transformation. In addition, we first demonstrate that the expression of Nlp is elevated primarily due to NLP gene amplification in human breast cancer and lung carcinoma. Consistently, transgenic mice overexpressing Nlp display spontaneous tumours in breast, ovary and testicle, and show rapid onset of radiation-induced lymphoma, indicating that Nlp is involved in tumourigenesis. This review summarises our current knowledge of physiological roles of Nlp, with an emphasis on its potentials in tumourigenesis.

Death pathways triggered by activated Ras in cancer cells

Ras GTPases are best known for their ability to serve as molecular switches regulating cell growth, differentiation and survival. Gene mutations that result in expression of constitutively active forms of Ras have been linked to oncogenesis in animal models and humans. However, over the past two decades, evidence has gradually accumulated to support a paradoxical role for Ras proteins in the initiation of cell death pathways. In this review we survey the literature pointing to the ability of activated Ras to promote cell death under conditions where cancer cells encounter apoptotic stimuli or Ras is ectopically expressed. In some of these cases Ras acts through known effectors and well defined apoptotic death pathways. However, in other cases it appears that Ras operates by triggering novel non-apoptotic death mechanisms that are just beginning to be characterized. Understanding these mechanisms and the factors that go into changing the nature of Ras signaling from pro-survival to pro-death could set the stage for development of novel therapeutic approaches aimed at manipulating pro-death Ras signaling pathways in cancer.

KRAS and BRAF: drug targets and predictive biomarkers

Three decades have passed since RAS was first identified as the transformative factor in the Harvey and Kirsten strains of the mouse sarcoma virus. RAS and several of its downstream effectors, including BRAF, have since been shown to be commonly mutated in broad range of human cancers and biological studies have confirmed that RAS pathway activation promotes tumour initiation, progression and metastatic spread in many contexts. With the identification of RAS mutation as a strong predictor of clinical resistance to EGFR-targeted therapies, RAS mutational testing has been incorporated into the routine clinical care of patients with colorectal and lung cancers. This article reviews the current understanding of RAS signalling as it relates to cancer biology, current efforts to develop inhibitors of RAS and its key downstream effectors and the technical challenges of RAS mutational testing in the clinical setting.

Genomic and biological characterization of exon 4 KRAS mutations in human cancer

Mutations in RAS proteins occur widely in human cancer. Prompted by the confirmation of KRAS mutation as a predictive biomarker of response to epidermal growth factor receptor (EGFR)-targeted therapies, limited clinical testing for RAS pathway mutations has recently been adopted. We performed a multiplatform genomic analysis to characterize, in a nonbiased manner, the biological, biochemical, and prognostic significance of Ras pathway alterations in colorectal tumors and other solid tumor malignancies. Mutations in exon 4 of KRAS were found to occur commonly and to predict for a more favorable clinical outcome in patients with colorectal cancer. Exon 4 KRAS mutations, all of which were identified at amino acid residues K117 and A146, were associated with lower levels of GTP-bound RAS in isogenic models. These same mutations were also often accompanied by conversion to homozygosity and increased gene copy number, in human tumors and tumor cell lines. Models harboring exon 4 KRAS mutations exhibited mitogen-activated protein/extracellular signal-regulated kinase kinase dependence and resistance to EGFR-targeted agents. Our findings suggest that RAS mutation is not a binary variable in tumors, and that the diversity in mutant alleles and variability in gene copy number may also contribute to the heterogeneity of clinical outcomes observed in cancer patients. These results also provide a rationale for broader KRAS testing beyond the most common hotspot alleles in exons 2 and 3.

Targeting the mitogen-activated protein kinase pathway: physiological feedback and drug response

Mitogen-activated protein kinase (MAPK) pathway activation is a frequent event in human cancer and is often the result of activating mutations in the BRAF and RAS oncogenes. Targeted inhibitors of BRAF and its downstream effectors are in various stages of preclinical and clinical development. These agents offer the possibility of greater efficacy and less toxicity than current therapies for tumors driven by oncogenic mutations in the MAPK pathway. Early clinical results with the BRAF-selective inhibitor PLX4032 suggest that this strategy will prove successful in a select group of patients whose tumors are driven by V600E BRAF. Relief of physiologic feedback upon pathway inhibition may, however, attenuate drug response and contribute to the development of acquired resistance. An improved understanding of the adaptive response of cancer cells to MAPK pathway inhibition may thus aid in the identification of those patients most likely to respond to targeted pathway inhibitors and provide a rational basis for tailored combination strategies.

Mitotic chromosomal instability and cancer: mouse modelling of the human disease

The stepwise progression from an early dysplastic lesion to full-blown metastatic malignancy is associated with increases in genomic instability. Mitotic chromosomal instability - the inability to faithfully segregate equal chromosome complements to two daughter cells during mitosis - is a widespread phenomenon in solid tumours that is thought to serve as the fuel for tumorigenic progression. How chromosome instability (CIN) arises in tumours and what consequences it has are still, however, hotly debated issues. Here we review the recent literature with an emphasis on models that recapitulate observations from human disease.

Targeting oncogenic BRAF in human cancer

Mitogen Activated Protein Kinase (MAPK) pathway activation is a frequent event in human cancer and is often the result of activating mutations in the BRAF and RAS oncogenes. BRAF missense mutations, the vast majority of which are V600E, occur in approximately 8% of human tumors. These kinase domain mutations, which are non-overlapping in distribution with RAS mutations, are observed most frequently in melanoma but are also common in tumors arising in the colon, thyroid, lung, and other sites. Supporting its classification as an oncogene, (V600E)BRAF stimulates ERK signaling, induces proliferation, and is capable of promoting transformation. Given the frequent occurrence of BRAF mutations in human cancer and the continued requirement for BRAF activity in the tumors in which it is mutated, efforts are underway to develop targeted inhibitors of BRAF and its downstream effectors. These agents offer the possibility of greater efficacy and less toxicity than the systemic therapies currently available for tumors driven by activating mutations of MAPK pathway components. Early clinical results with the BRAF-selective inhibitors PLX4032 and GSK2118436 suggest that this strategy will prove successful in a select group of patients whose tumors are driven by oncogenic BRAF.

Tumor suppressive effect of lysyl oxidase proenzyme

Lysyl oxidase acts as both a matrix modifying enzyme and an oncogene suppressor. It is synthesized as a 50-kDa proenzyme, secreted, and processed into an approximately 30 kDa mature, active enzyme and an 18-kDa propeptide. The tumor suppressive effect of lysyl oxidase appears to be exerted within the cell, so the subcellular localization of protein forms was investigated. Propeptide-specific antibody detected 50-kDa proenzyme in cytoplasmic and nuclear extracts of non-transformed mouse fibroblasts, but free 18-kDa propeptide was not detected in any extract. Antibody to epitope near the N-terminus of mature lysyl oxidase detected the proenzyme product in non-transformed cells, and a 30-kDa cytoplasmic protein in both non-transformed and transformed cells. RNA interference reduced the expression of lysyl oxidase mRNA and 50-kDa proenzyme in non-transformed cells, but had no effect on 30-kDa protein, indicating that although this protein displays a lysyl oxidase epitope, it is not derived from lysyl oxidase message. The absence of both free 18-kDa propeptide and mature lysyl oxidase within non-transformed cells suggests that cellular reversion after restoration of lysyl oxidase gene expression is mediated by the 50-kDa proenzyme within cells.

KIT and RAS signalling pathways in testicular germ cell tumours: new data and a review of the literature

Testicular germ cell tumours (TGCTs) are the leading cause of cancer deaths in young male Caucasians. Identifying changes in DNA copy number can pinpoint genes involved in tumour development. We defined the smallest overlapping regions of imbalance in TGCTs using array comparative genomic hybridization analysis. Novel regions, or regions which refined those previously reported, were identified. The expression profile of genes from 12p, which is invariably gained in TGCTs, and amplicons defined at 12p11.2-12.1 and 4q12, suggest KRAS and KIT involvement in TGCT and seminoma development, respectively. Amplification of these genes was not found in intratubular germ cell neoplasia adjacent to invasive disease showing these changes, suggesting their involvement in tumour progression. Activating mutations of RAS genes (KRAS or NRAS) and overexpression of KRAS were mutually exclusive events. These, correlations between the expression levels of KIT, KRAS and GRB7 (which encodes an adapter molecule known to interact with the KIT tyrosine kinase receptor) and other reported evidence reviewed here, are consistent with a role for activation of KIT and RAS signalling in TGCT development. In order to assess a role for KIT in seminomas, we modulated the level of KIT expression in TCam-2, a seminoma cell line. The likely seminomatous origin of this cell line was supported by demonstrating KIT and OCT3/4 overexpression and gain of 12p material. Reducing the expression of KIT in TCam-2 through RNA inhibition resulted in decreased cell viability. Further understanding of KIT and RAS signalling in TGCTs may lead to novel therapeutic approaches for these tumours.

The molecular scaffold kinase suppressor of Ras 1 is a modifier of RasV12-induced and replicative senescence

In primary mouse embryo fibroblasts (MEFs), oncogenic Ras induces growth arrest via Raf/MEK/extracellular signal-regulated kinase (ERK)-mediated activation of the p19ARF/p53 and INK4/Rb tumor suppressor pathways. Ablation of these same pathways causes spontaneous immortalization in MEFs, and oncogenic transformation by Ras requires ablation of one or both of these pathways. We show that Kinase Suppressor of Ras 1 (KSR1), a molecular scaffold for the Raf/MEK/ERK cascade, is necessary for RasV12-induced senescence, and its disruption enhances primary MEF immortalization. RasV12 failed to induce p53, p19ARF, p16INK4a, and p15INK4b expression in KSR1-/- MEFs and increased proliferation instead of causing growth arrest. Reintroduction of wild-type KSR1, but not a mutated KSR1 construct unable to bind activated ERK, rescued RasV12-induced senescence. On continuous culture, deletion of KSR1 accelerated the establishment of spontaneously immortalized cultures and increased the proportion of cultures escaping replicative crisis. Despite enhancing escape from both RasV12-induced and replicative senescence, however, both primary and immortalized KSR1-/- MEFs are completely resistant to RasV12-induced transformation. These data show that escape from senescence is not necessarily a precursor for oncogenic transformation. Furthermore, these data indicate that KSR1 is a member of a unique class of proteins whose deletion blocks both senescence and transformation.

Activating mutations and/or expression levels of tyrosine kinase receptors GRB7, RAS, and BRAF in testicular germ cell tumors

Amplification and/or overexpression of genes encoding tyrosine kinase receptors KIT and ERBB2 have been reported in testicular germ cell tumors (TGCTs). These receptors can bind the adaptor molecule GRB7 encoded by a gene adjacent to ERBB2 at 17q12, a region also frequently gained in TGCTs. GRB7 binding may be involved in the activation of RAS signaling and KRAS2 maps to 12p, which is constitutively gained in TGCT and lies within a minimum overlapping region of amplification at 12p11.2-12.1, a region we have previously defined. RAS proteins activate BRAF, and activating mutations of genes encoding these proteins have been described in various tumors. Here we determine the relationships between expression levels and activating mutations of these genes in a series of 65 primary TGCTs and 4 TCGT cell lines. High levels of expression and activating mutations in RAS were mutually exclusive events, and activating mutations in RAS were only identified in the seminoma subtype. Mutations in BRAF were not identified. Increased ERBB2 expression was associated with differentiated nonseminoma histology excised from lymph nodes postchemotherapy. Mutation, elevated expression, and correlations between expression levels of KRAS2, GRB7, and KIT are consistent with their involvement in the development of TGCTs.

The Ras effector RASSF2 is a novel tumor-suppressor gene in human colorectal cancer

BACKGROUND & AIMS

Activation of Ras signaling is a hallmark of colorectal cancer (CRC), but the roles of negative regulators of Ras are not fully understood. Our aim was to address that question by surveying genetic and epigenetic alterations of Ras-Ras effector genes in CRC cells.

METHODS

The expression and methylation status of 6 RASSF family genes were examined using RT-PCR and bisulfite PCR in CRC cell lines and in primary CRCs and colorectal adenomas. Colony formation assays and flow cytometry were used to assess the tumor suppressor activities of RASSF1 and RASSF2. Immunofluorescence microscopy was used to determine the effect of altered RASSF2 expression on cell morphology. Mutations of K- ras , BRAF, and p53 were identified using single-strand conformation analysis and direct sequencing.

RESULTS

Aberrant methylation and histone deacetylation of RASSF2 was associated with the gene's silencing in CRC. The activities of RASSF2, which were distinct from those of RASSF1, included induction of morphologic changes and apoptosis; moreover, its ability to prevent cell transformation suggests that RASSF2 acts as a tumor suppressor in CRC. Primary CRCs that showed K- ras /BRAF mutations also frequently showed RASSF2 methylation, and inactivation of RASSF2 enhanced K- ras -induced oncogenic transformation. RASSF2 methylation was also frequently identified in colorectal adenomas.

CONCLUSIONS

RASSF2 is a novel tumor suppressor gene that regulates Ras signaling and plays a pivotal role in the early stages of colorectal tumorigenesis.

Central roles of Mg2+ and MgATP2- in the regulation of protein synthesis and cell proliferation: significance for neoplastic transformation

Growth factors are polypeptides that combine with specific membrane receptors on animal cells to stimulate proliferation, but they also stimulate glucose transport, uridine phosphorylation, intermediary metabolism, protein synthesis, and other processes of the coordinate response. There are a variety of nonspecific surface action treatments which stimulate the same set of reactions as the growth factors do, of which protein synthesis is most directly related to the onset of DNA synthesis. Mg(2+) is required for a very wide range of cellular reactions, including all phosphoryl transfers, and its deprivation inhibits all components of the coordinate response that have so far been tested. Growth factors raise the level of free Mg(2+) closer to the optimum for the initiation of protein synthesis. The resulting increase in protein synthesis accelerates progression through G1 to the onset of DNA synthesis and mitosis. None of the other 3 major cellular cations are similarly involved in growth regulation, although internal pH may play an auxiliary role. Almost 10(5) externally bound divalent cations are displaced from membranes for every attached insulin molecule, implying a conformational membrane change that releases enough Mg(2+) from the internal surface of the plasma membrane to account for the increase in free cytosolic Mg(2+). It is proposed that mTOR, the central control point for protein synthesis of the PI 3-K kinase cascade stimulated by insulin, is regulated by MgATP(2-) which varies directly with cytosolic Mg(2+). Other elements of the coordinate response to growth factors such as the increased transport of glucose and phosphorylation of uridine are also dependent upon an increase of Mg(2+). Deprivation of Mg(2+) in neoplastically transformed cultures normalizes their appearance and growth behavior and raises their abnormally low Ca(2+) concentration. Tight packing of the transformed cells at very high saturation density confers the same normalizing effects, which are retained for a few days after subculture at low density. The results suggest that the activity of Mg(2+) within the cell is a central regulator of normal cell growth, and the loss of its membrane-mediated control can account for the neoplastic phenotype.

The Propeptide Domain of Lysyl Oxidase Induces Phenotypic Reversion of Ras-transformed Cells

Lysyl oxidase is an extracellular enzyme critical for the normal biosynthesis of collagens and elastin. In addition, lysyl oxidase reverts ras-mediated transformation, and lysyl oxidase expression is down-regulated in human cancers. Since suramin inhibits growth factor signaling pathways and induces lysyl oxidase in ras-transformed NIH3T3 cells (RS485 cells), we sought to investigate the effects of suramin on the phenotype of transformed cells and the role of lysyl oxidase in mediating these effects. Suramin treatment resulted in a more normal phenotype as judged by growth rate, cell cycle parameters, and morphology. beta-aminopropionitrile, the selective inhibitor of lysyl oxidase enzyme activity, was remarkably unable to block suramin-induced reversion. By contrast, ectopic antisense lysyl oxidase demonstrated that lysyl oxidase gene expression mediated phenotypic reversion. Since lysyl oxidase is synthesized as a 50 kDa precursor and processed to a 30 kDa active enzyme and 18 kDa propeptide, the effects of these two products on the transformed phenotype of RS485 cells were then directly assessed in the absence of suramin. Here we report, for the first time, that the lysyl oxidase propeptide, and not the lysyl oxidase enzyme, inhibits ras-dependent transformation as determined by effects on cell proliferation assays, growth in soft agar, and Akt-dependent induction of NF-kappaB activity. Thus, the lysyl oxidase propeptide, which is released during extracellular proteolytic processing of pro-lysyl oxidase, functions to inhibit ras-dependent cell transformation.

Analysis of gene expression profiles of forestomach tumors in rasH2 mice initiated with N-ethyl-N-nitrosourea

To clarify the mechanisms underlying enhancement of carcinogenesis in transgenic mice carrying a human prototype c-Ha- ras gene (rasH2 mouse), animals received a single intraperitoneal injection of 120 mg/kg N-ethyl-N-nitrosourea (ENU) and at 20 weeks thereafter expression profiles in three induced forestomach squamous cell carcinomas were assessed using high-density oligonucleotide microarrays. In addition, the reverse transcriptase-polymerase chain reaction (RT-PCR) was performed to assess mRNA expression of human c-Ha- ras gene and some molecules involved in the Ras-regulated mitogen-activated protein kinase (MAPK) pathway. Compared with normal forestomach tissue from control mice, 416 and 368 genes, respectively, were found to be commonly up- and down-regulated by 2-fold or more in the three tumors. Many genes involved in tumor invasion and metastasis such as transforming growth factor beta1 and matrix metalloproteinases were up-regulated, reflecting tumor progression. RT-PCR analysis confirmed up-regulation of transgene, mouse endogenous Ha- ras, N- ras, raf, Mekk2, c- fos, junB, c- myc and cyclin D1. These results suggest that activation of the Ras-MAPK cascade following up-regulation of both human and mouse endogenous ras genes is involved in the enhanced tumorigenesis of ENU-induced forestomach squamous cell carcinomas in rasH2 mice.

Deregulated expression of interferon regulatory factor-1 in oncogene-transformed mouse fibroblasts

Interferon (IFN) regulatory factor-1 (IRF-1) is a transcription factor that has been historically associated with type I IFN activation and antioncogenic properties. We studied IRF-1 expression and DNA-binding capacity in nontransformed and transformed mouse fibroblasts. A 43-kDa nuclear IRF-1 protein was expressed biphasically during the cell cycle in primary mouse embryo fibroblasts, nontransformed NIH 3T3 cells, and ras revertants. IRF-1 expression became constitutive in ras-transformed NIH 3T3 cells and in cells transformed by oncogenes ets, fes, fos, her-2/neu, met, mos, raf, or trk, suggesting that deregulated IRF-1 expression may be associated with loss of growth control. Lysyl oxidase (LO), a ras suppressor that is downregulated in ras transformants, is an IRF-1 target gene, but it is not stimulated by abundant IRF-1 present in transformants, while another IRF-1 target gene (iNOS) is transcribed. IRF-1 from either normal or ras-transformed cells bound to IRF elements in the IFN-beta and LO promoters. IRF-1 in transformants can, therefore, bind to but not transactivate the LO promoter, and the presence of IRF-1 is not sufficient to suppress ras transformation. LO expression may effect the regulated expression of IRF-1: a ras revertant, which was generated by stable transfection of LO cDNA, regained the normal biphasic IRF-1 pattern. A mainly cytoplasmic, constitutively expressed 46-kDa protein with immunologic identity to the 43-kDa nuclear IRF-1 was also present in normal and transformed cells, but as it did not bind to the IRF elements, its function is unclear.

Methotrexate and Ras Methylation: A New Trick for an Old Drug?

Ras plays a central role in the development and progression of human cancer. Ras function depends on its ability to associate with cellular membranes. Nascent Ras is targeted to membranes by virtue of a series of posttranslational modifications of a C-terminal "CAAX" motif that include farnesylation, proteolysis, and carboxyl methylation. This pathway is an attractive target for anti-Ras drug development. Farnesyltransferase inhibitors have been developed and are in clinical trials. Their success has prompted interest in developing pharmacologically useful inhibitors of the other two enzymes in the Ras processing pathway. Ironically, it now appears that methotrexate, one of the oldest chemotherapeutic drugs, may work, in part, by inhibiting carboxyl methylation of Ras.

ras oncogene mutations in diethylnitrosamine-induced hepatic tumors in medaka (Oryzias latipes), a teleost fish

Medaka fish are an established non-mammalian research model for the study of liver carcinogenesis and exposure to environmental pollutants. Studies have emphasized the development of hepatic neoplasms in medaka following exposure to model carcinogens. To date however, little information is known regarding the mechanisms underlying initiation of hepatic tumors in this species. The aim of this study was to relate our understanding of diethylnitrosamine (DEN)-induced tumor formation to ras gene activation in hepatic neoplasms of exposed medaka. Initial studies were conducted to identify medaka ras exons 1 and 2 by reverse transcriptase polymerase chain reaction (RT-PCR). Amplification of ras exons 1 and 2 from untreated medaka liver resulted in the identification of three polymorphic ras sequence variants exhibiting a high degree of homology to other teleost and mammalian ras genes. Exposure of medaka to 159 ppm of DEN resulted in a wide range of hepatic neoplasms including: hepatocellular adenomas, hepatocellular carcinomas, cholangiomas, and mixed hepatocholangiocellular carcinomas. Individual liver tumors were examined for oncogenically activating ras mutations by probing genomic DNA with probes specific for activating point mutations or by direct cloning and sequencing of ras transcripts using RT-PCR. Using allele-specific oligonucleotide (ASO) analysis, a single point mutation was detected in codon 12 position two in 8/25 (32%) tumors examined. Mutated ras alleles were additionally detected in 12 of 39 (30%) medaka liver tumors by sequence analysis. Ten of the 12 mutations identified contained a single point mutation at codon 12 resulting in a Gly to Asp amino acid substitution. Two unique mutations were identified at codon 16 resulting in either Lys to Asn or Lys to Thr amino acid substitutions. Our results show that ras mutations are induced by DEN and are present in over 30% of the fish that developed tumors. A ras mutation incidence of 30% is similar to that reported in mammalian species exposed to DEN. While mutations at codon 12 have previously been reported, the present study is the first in vivo report of ras point mutations at codon 16.

Antisense therapeutics: from theory to clinical practice

The use of antisense (AS) oligonucleotides as therapeutic agents was proposed as far back as the 1960s/1970s when the AS strategy was initially developed. However, it has taken almost a quarter of a century for this potential to be realized. The last few years has seen a rapid increase in the number of AS molecules progressing past Phase I in clinical trials, due in part to our increased knowledge of their structure and chemistry. Here, we describe the most prominent of these modifications with respect to clinical applicability. However, the main focus of this review is clinical application, with a focus on cancer. We will discuss in detail both the status of the current AS clinical trials and the molecules that are likely to be the targets of the next group of AS molecules entering the clinic.

Oncogenic H-ras induces cyclin B1 expression in a p53-independent manner

The role of p53 in controlling the G2 checkpoint, in part by repressing cyclin B1 transcription, has been well established. However, accumulating evidence indicate that p53-independent pathways may also play an important role. Ras proteins have been shown to regulate G1/S, but also G2/M transitions. Since cyclin B1/cdc2 complex is the key regulator controlling the G2/M checkpoint, we were interested in addressing if the H-ras oncogene could regulate cyclin B1 expression in a p53-independent manner. We observed an induction of cyclin B1 promoter activity in the presence of H-ras oncogene in SW480 cells, which contain null p53 alleles. In addition, HeLa cells known to express the HPV18 E6 oncogene that inactivates p53, exhibited increased levels of cyclin B1 mRNA and protein when transfected with the H-ras oncogene. Higher expression of cyclin B1 correlated with higher levels of cyclin B1/cdc2 complex and kinase activity that interestingly, showed no inhibition at G2/M after DNA damage. These data suggest that H-ras participates in pathways that regulate cyclin B1 expression and therefore controls the G2/M checkpoint in a p53-independent manner.

Ras-MAP kinase signaling pathways and control of cell proliferation: relevance to cancer therapy

The mitogen-activated protein (MAP) kinase pathways represent several families of signal transduction cascades that mediate information provided by extracellular stimuli. MAP kinase pathways regulate a wide range of physiological responses, including cell proliferation, apoptosis, cell differentiation, and tissue development. Constitutive activation of MAP kinase proteins in experimental models has been shown to cause cell transformation and is implicated in tumorigenesis. Of clinical importance, MAP kinase pathways are regulated by Ras G-proteins, which are found to be mutated and constitutively active in approximately 30% of all human cancers. Thus, a major goal in the treatment of cancer is the development of specific compounds that target Ras and critical downstream signaling proteins responsible for uncontrolled cell growth. A variety of biochemical, molecular, and structural approaches have been used to develop drug compounds that target signaling proteins important for MAP kinase pathway activation. These compounds have been useful tools for identifying the mechanisms of MAP kinase pathway signaling and hold promise for clinical use. This review will present an overview of the major proteins involved in Ras and MAP kinase signaling pathways and their function in regulating cell cycle events and proliferation. In addition, some of the relevant compounds that have been developed to inhibit the activities of these proteins and MAP kinase signaling are discussed.

Enhancement of anchorage-independent growth of human pancreatic carcinoma MIA PaCa-2 cells by signaling from protein kinase C to mitogen-activated protein kinase

We found that 12-O-tetradecanoylphorbol-13-acetate (TPA) promoted anchorage-independent growth but did not affect anchorage-dependent growth of MIA PaCa-2 human pancreatic carcinoma cells. TPA markedly activated mitogen-activated protein kinase (MAPK)/extracellular signal-regulated kinase in an anchorage-independent manner. Two protein kinase C (PKC) isoforms, conventional PKC (cPKC) and novel PKC (nPKC), but not apical PKC, translocated from the cytosolic to the particulate fraction upon TPA treatment. To identify the PKC isoforms involved in the regulation of anchorage-independent growth, four PKC isoforms (alpha, delta, epsilon, and zeta) were forced to be expressed in MIA PaCa-2 cells with an adenovirus vector. Overexpression of nPKCdelta or nPKC epsilon activated MAPK and promoted anchorage-independent growth. Overexpression of cPKCalpha alone did not influence anchorage-independent growth but lowered the concentration of TPA that was required to enhance such growth. Expression of constitutively active MAPK kinase-1 (MEK1) also promoted anchorage-independent growth. Furthermore, PKC inhibitors or an MEK inhibitor completely suppressed both TPA-induced activation of MAPK and promotion of anchorage-independent growth, but a cPKC-selective inhibitor partially suppressed TPA-induced promotion of the growth. Based on these results, we suggest that MAPK activation, mediated by certain isoforms of PKC, plays a part in oncogenic growth of MIA PaCa-2 cells. In summary, our data indicated that specific inhibitors of the cPKC and nPKC signaling pathway might be selective anti-oncogenic growth agents for some types of human pancreatic cancer.

Expression and alteration of ras and p53 proteins in patients with lung carcinoma accompanied by idiopathic pulmonary fibrosis

BACKGROUND

The ras oncogene and the p53 tumor suppressor gene play important roles in the carcinogenic process of lung carcinoma. The authors evaluated whether alterations of the ras and p53 proteins may contribute to the development of lung carcinoma in patients with idiopathic pulmonary fibrosis (IPF) and whether such alterations may explain the high incidence of lung carcinoma among patients with IPF.

METHODS

Lung tissues were obtained from 35 patients who had IPF without complications of lung carcinoma and from 36 patients who had IPF with complications of lung carcinoma. Altered expression of ras and p53 proteins was evaluated by immunohistochemistry, and mutations of both genes were evaluated by polymerase chain reaction-single strand conformation polymorphism and sequencing analyses.

RESULTS

The frequency of expression of ras protein in type II alveolar pneumocytes was significantly greater in lung tissues from patients with IPF who had lung carcinoma compared with lung tissues from patients with IPF who did not have lung carcinoma (75% vs. 40%, respectively; P < 0.01). K-ras point mutation in codon 12 (GGT to GTT transversion) was detected in lung tissue with interstitial pneumonia, in which ras protein was overexpressed in type II alveolar pneumocytes obtained from 2 of 41 patients with IPF complicated by lung carcinoma, causing amino acid substitution (Gly to Val) in both patients. A p53 mutation was detected in three of six lung tissue samples from patients who had IPF lung with positive p53 immunoreactivity, and multiple mutations were detected in two samples.

CONCLUSIONS

Expression of ras protein in type II alveolar pneumocytes and mutation in the codon 12 of K-ras gene in lung tissue may contribute to the induction of lung carcinoma in patients with IPF. Furthermore, the presence of multiple mutations in the p53 gene may explain the high incidence lung carcinoma in patients with IPF.

The rasH2 transgenic mouse: nature of the model and mechanistic studies on tumorigenesis

The rasH2 mouse is a hemizygous transgenic mouse carrying the c-Ha-ras oncogene and that gene's promotor/enhancer within the genetic background of a BALB/cByJ x C57BL/6J F1 mouse. Approximately 3 copies of the transgene are integrated in a tandem array into chromosome number 15. The transgene is transmitted stably without point mutation in hot spots and is expressed in all tissues over 20 backcross generations. The homozygous c-Ha-ras genotype is lethal. Hemizygotes are selected by polymerase chain reaction (PCR) analysis of tail tips after birth. Spontaneous tumors in hemizygous transgenic mice are rare until 6 months of age. The observed rasH2 tumor spectrum, including lung adenoma/adenocarcinoma, forestomach and skin papillomas, Harderian gland adenoma, liver proliferative lesions, splenic hemangioma/sarcoma, and lymphoma is consistent with the BALB/c and C57BL/6 background. In the rasH2 mouse, point mutations of the transgene induced by genotoxins are reported frequently but not in all tumors. Elevated levels of transgene expression were detected in all genotoxin-induced tumors in the rasH2. Increased transgene expression was independent of the mutation rate in transgenic and endogenous ras genes. These observations suggest that the overexpression of transgenic c-Ha-ras is responsible for accelerated tumor development.

Wildtype Kras2 can inhibit lung carcinogenesis in mice

Although the ras genes have long been established as proto-oncogenes, the dominant role of activated ras in cell transformation has been questioned. Previous studies have shown frequent loss of the wildtype Kras2 allele in both mouse and human lung adenocarcinomas. To address the possible tumor suppressor role of wildtype Kras2 in lung tumorigenesis, we have carried out a lung tumor bioassay in heterozygous Kras2-deficient mice. Mice with a heterozygous Kras2 deficiency were highly susceptible to the chemical induction of lung tumors when compared to wildtype mice. Activating Kras2 mutations were detected in all chemically induced lung tumors obtained from both wildtype and heterozygous Kras2-deficient mice. Furthermore, wildtype Kras2 inhibited colony formation and tumor development by transformed NIH/3T3 cells and a mouse lung tumor cell line containing an activated Kras2 allele. Allelic loss of wildtype Kras2 was found in 67% to 100% of chemically induced mouse lung adenocarcinomas that harbor a mutant Kras2 allele. Finally, an inverse correlation between the level of wildtype Kras2 expression and extracellular signal-regulated kinase (ERK) activity was observed in these cells. These data strongly suggest that wildtype Kras2 has tumor suppressor activity and is frequently lost during lung tumor progression.