Susceptibility to apoptosis is differentially regulated by c-myc and mutated Ha-ras oncogenes and is associated with endonuclease availability

Andrew David Hamilton Wyllie. 24 January 1944—26 May 2022

Andrew Wyllie graduated from the University of Aberdeen, becoming an academic pathologist in Aberdeen, Edinburgh and Cambridge. He was the co-discoverer of apoptotic cell death, having observed single cells dying following carcinogen exposure. Together with Alastair Currie and John Kerr, he realized the profound importance of this novel mode of cell death that showed a distinctive series of morphological changes, which he first described as a new cell death process. Wyllie and Currie introduced the term ‘apoptosis’ for this cell death process in a seminal paper in 1972. Another landmark discovery was of chromatin fragmentation in apoptosis, due to activation of an endogenous endonuclease that caused internucleosomal DNA cleavage (‘chromatin laddering’), which was the first biochemical mechanism of apoptosis described. He further characterized chromatin fragmentation in the 1980s, followed by investigations of cell surface changes to produce ‘eat-me’ signals to trigger rapid phagocytosis of the apoptotic cells and bodies, intracellular calcium ion signalling, caspase activation and other mechanisms of apoptosis. His cancer research helped identify the location of APC and generated his demonstration that apoptosis was regulated by oncogenes MYC and RAS and by tumour suppressor genes, such as TP53 . He showed how apoptosis occurred in response to DNA damage and was a key process influencing both carcinogenesis and tumour growth. Andrew made a major scientific observation that changed the understanding of how cells die in health and disease, although it took time for the scientific establishment to understand its fundamental importance. Andrew Wyllie is widely known as the ‘Father of Apoptosis’.

Wild-type K-ras has a tumour suppressor effect on carcinogen-induced murine colorectal adenoma formation

K-ras mutations are found in ~40% of human colorectal adenomas and carcinomas and contribute to colorectal tumour formation at an early stage. Wild-type K-ras has been reported to be deleted in some tumours, but the consequences of changes in wild-type K-ras copy number for experimental colorectal carcinogenesis have not been investigated. To characterize the effects of K-ras copy number changes on formation of carcinogen-induced colorectal neoplasms in mice, wild-type (K-ras(+/+) ) and heterozygous K-ras exon 1 knockout (K-ras(+/-) ) mice were given 10 weekly treatments of 1, 2-dimethylhydrazine (DMH) to induce colorectal tumours. Colorectal expression levels of K-ras 4A and 4B transcripts in K-ras(+/-) mice were ~50% decreased compared with K-ras(+/+) mice. One year after DMH treatment, survival of K-ras(+/-) mice decreased from 88 to 82% compared with wild-type mice. Colorectal adenomas significantly increased from 0.52 ± 0.15 in K-ras(+/+) mice to 0.87 ± 0.14 in K-ras(+/-) mice (mean ± SEM per mouse, P < 0.01); total tumour volume increased 2.13-fold (P < 0.05). Comparing K-ras(+/+) with K-ras(+/-) murine adenomas, Ki-67-positive proliferating tumour cells significantly increased from 7.77 ± 0.64% to 9.15 ± 0.92% and cleaved caspase-3-positive apoptotic tumour cells decreased from 1.40 ± 0.37% to 0.80 ± 0.22% (mean ± SEM, P < 0.05 for both). No K-ras or B-raf mutations were detected in the adenomas. Immunohistochemical studies showed no significant changes in extracellular signal regulating kinase/mitogen-activated protein kinase (Erk/MapK) or PI3K/Akt pathway activation in the adenomas. In conclusion, the data collectively show that a 50% reduction in K-ras gene dosage and RNA expression promoted experimental colorectal tumourigenesis, consistent with wild-type K-ras having a tumour suppressor effect on carcinogen-induced murine colorectal adenoma formation.

A microarray method for identifying tumor antigens by screening a tumor cDNA expression library against cancer sera

The immune system responds to tumor cells. The challenge has been how to effectively use these responses to treat or protect against cancer. Toward the goal of developing a cancer vaccine, we are pursuing methodologies for the discovery and testing of useful antigens. We present an array-based approach for discovering these B cell antigens by directly screening for specific host-sera reactivity to lysates from tumor-derived cDNA expression libraries. Several cancer-specific antigens were identified, and these are currently being validated as potential candidates.

Activation of K-RAS by co-mutation of codons 19 and 20 is transforming

The K-RAS oncogene is widely mutated in human cancers. Activating mutations in K-RAS give rise to constitutive signalling through the MAPK/ERK and PI3K/AKT pathways promoting increased cell division, reduced apoptosis and transformation. The majority of activating mutations in K-RAS are located in codons 12 and 13. In a human colorectal cancer we identified a novel K-RAS co-mutation that altered codons 19 and 20 resulting in transitions at both codons (L19F/T20A) in the same allele. Using focus forming transformation assays in vitro , we showed that co-mutation of L19F/T20A in K-RAS demonstrated intermediate transforming ability that was greater than that of individual L19F and T20A mutants, but less than that of G12D and G12V K-RAS mutants. This demonstrated the synergistic effects of co-mutation of codons 19 and 20 and illustrated that co-mutation of these codons is functionally significant.

Mutant K-ras promotes carcinogen-induced murine colorectal tumourigenesis, but does not alter tumour chromosome stability

K-ras (KRAS) mutations are observed in around 40% of human colorectal adenomas and carcinomas. Previously, we developed and characterized a strain of transgenic mice with inducible intestinal epithelial expression of K-ras{Val12} via a Cre/LoxP system. To evaluate the influence of mutant K-ras on carcinogen-induced colorectal tumourigenesis, we induced neoplastic alterations in the large intestines of wild-type and K-ras{Val12} mice using the colon-selective carcinogen 1,2-dimethylhydrazine (DMH), which has been widely used to induce colorectal tumours that are histopathologically similar to those observed in humans. K-ras{Val12} expression significantly promoted DMH-induced colorectal tumourigenesis: the average lifespan of the mice decreased from 38.52 ± 1.97 weeks for 40 control mice to 32.42 ± 2.17 weeks for 26 K-ras{Val12} mice (mean ± SEM, p < 0.05) and the abundance of large intestinal tumours increased from 2.27 ± 0.15 per control mouse to 3.85 ± 0.20 in K-ras{Val12} mice (mean ± SEM, p < 0.01). Adenomas from DMH-treated K-ras{Val12} mice showed significantly higher proportions of Ki-67-positive proliferating cells (10.9 ± 0.69%) compared with those from DMH-treated wild-type mice (7.77 ± 0.47%) (mean ± SEM, p < 0.01) and a mild increase in apoptotic nuclei staining for cleaved caspase-3 (1.94 ± 0.21% compared with 1.15 ± 0.14%, mean ± SEM, p < 0.01). In the adenomas from DMH-treated K-ras{Val12} mice, K-ras{Val12} transgene recombination and expression were confirmed, with immunohistochemical evidence of strong Erk/MapK and mild PI3K/Akt pathway activation compared with adenomas from DMH-treated wild-type mice. Microarray hybridization and clustering analysis demonstrated different expression profiles in adenomas from DMH-treated wild-type and DMH-treated K-ras{Val12} mice, indicating involvement of different molecular mechanisms including Erk/MapK and PI3K/Akt signalling in K-ras{Val12}-expressing adenomas. Array-comparative genomic hybridization analysis showed chromosome stability in both cohorts, with only a very few tiny alterations observed in one adenoma from a DMH-treated K-ras{Val12} mouse. Taken together, these data show that mutant K-ras significantly promotes DMH-induced colorectal tumourigenesis, resulting in distinct changes in cell signalling and proliferation, but does not alter chromosome stability in the tumours.

K-ras exon 4A has a tumour suppressor effect on carcinogen-induced murine colonic adenoma formation

K-ras encodes two isoforms, K-ras 4A and 4B, that are jointly affected by K-ras activating mutations, which are prevalent in colorectal cancer (CRC). CRC shows alterations in the expressed K-ras 4A : 4B isoform ratio in favour of K-ras 4B, in tumours both with and without K-ras mutations. The present study evaluated whether K-ras 4A expression can suppress colonic adenoma development in the absence of its oncogenic allele. Mice with homozygous targeted deletions of K-ras exon 4A (K-ras(tmDelta4A/tmDelta4A)) that can express the K-ras 4B isoform only, along with heterozygous K-ras(tmDelta4A/+) and wild-type mice, were given ten weekly 1,2-dimethylhydrazine (DMH) treatments to induce colonic adenomas. There was a significant increase in both the number and the size of colonic adenomas in DMH-treated K-ras(tmDelta4A/tmDelta4A) mice, with reduced survival, compared with heterozygous and wild-type mice. No K-ras mutations were found in any of the 30 tumours tested from the three groups. Lack of expression of K-ras 4A transcripts was confirmed, whereas the relative expression levels of K-ras 4B transcripts were significantly increased in the adenomas of K-ras(tmDelta4A/tmDelta4A) mice compared with K-ras(tmDelta4A/+) and wild-type mice. Immunohistochemical studies showed that adenomas of K-ras(tmDelta4A/tmDelta4A) mice had significantly increased cell proliferation and significantly decreased apoptosis with evidence of activation of MapKinase and Akt pathways, with increased phospho-Erk1/2 and both phospho-Akt-Thr308 and phospho-Akt-Ser473 immunostaining, compared with adenomas from K-ras(tmDelta4A/+) and wild-type mice. In conclusion, following DMH treatment, K-ras exon 4A deletion promoted increased number and size of colonic adenomas showing increased K-ras 4B expression, increased proliferation, decreased apoptosis, and activation of MapKinase and Akt pathways, in the absence of K-ras mutations. Therefore, K-ras 4A expression had a tumour suppressor effect on carcinogen-induced murine colonic adenoma formation, explaining the selective advantage of the altered K-ras 4A : 4B isoform ratio found in human colorectal cancer.

Mutated K-ras(Asp12) promotes tumourigenesis in Apc(Min) mice more in the large than the small intestines, with synergistic effects between K-ras and Wnt pathways

Summary K-ras mutations are found in 40-50% of human colorectal adenomas and carcinomas, but their functional contribution remains incompletely understood. Here, we show that a conditional mutant K-ras mouse model (K-ras(Asp12)/Cre), with transient intestinal Cre activation by beta-Naphthoflavone (beta-NF) treatment, displayed transgene recombination and K-ras(Asp12) expression in the murine intestines, but developed few intestinal adenomas over 2 years. However, when crossed with Apc(Min/+) mice, the K-ras(Asp12)/Cre/Apc(Min/+) offspring showed acceleration of intestinal tumourigenesis with significantly changed average lifespan (P < 0.05) decreased to 18.4 +/- 5.4 weeks from 20.9 +/- 4.7 weeks (control Apc(Min/+) mice). The numbers of adenomas in the small intestine and large intestine were significantly (P < 0.01) increased by 1.5-fold and 5.7-fold, respectively, in K-ras(Asp12)/Cre/Apc(Min/+) mice compared with Apc(Min/+) mice, with the more marked increase in adenoma prevalence in the large intestine. To explore possible mechanisms for K-ras(Asp12) and Apc(Min) co-operation, the Mitogen-activated protein kinase (Mapk), Akt and Wnt signalling pathways, including selected target gene expression levels, were evaluated in normal large intestine and large intestinal tumours. K-ras(Asp12) increased activation of Mapk and Akt signalling pathway targets phospho-extracellular signal-regulated kinase (pErk) and pAkt, and increased relative expression levels of Wnt pathway targets vascular endothelial growth factor (VEGF), gastrin, cyclo-oxygenase 2 (Cox2) and T-cell lymphoma invasion and metastasis 1 (Tiam1) in K-ras(Asp12)/Cre/Apc(Min/+) adenomas compared with that of Apc(Min/+) adenomas, although other Wnt signalling pathway target genes such as Peroxisome proliferator-activated receptor delta (PPARd), matrix metalloproteinase 7 (MMP7), protein phosphatase 1 alpha (PP1A) and c-myc remained unchanged. In conclusion, intestinal expression of K-ras(Asp12) promotes mutant Apc-initiated intestinal adenoma formation in vivo more in the large intestine than the small intestine, with evidence of synergistic co-operation between mutant K-ras and Apc involving increased expression of some Wnt-pathway target genes.

Oncogene AF1q enhances doxorubicin-induced apoptosis through BAD-mediated mitochondrial apoptotic pathway

AF1q is an oncogenic factor involved in leukemia development, thyroid tumorigenesis, and breast cancer metastasis. In the present study, AF1q was found to be down-regulated in a doxorubicin-resistant subline of human squamous carcinoma A431 cells. Knockdown of AF1q decreased the apoptosis induced by doxorubicin, Taxol, gamma-radiation, IFN-alpha, and IFN-gamma in A431 cells. On the other hand, overexpression of AF1q increased the doxorubicin-induced apoptosis in A431 cells as well as in HepG2 and HL60 cells. Both exogenous and ectopic expression of AF1q in A431 cells increased the mRNA and protein levels of BAD, a proapoptotic BCL-2 family protein. Gene silencing of BAD by small interfering RNA suppressed the AF1q enhancement of apoptosis, suggesting that BAD is downstream of AF1q in regulation of apoptosis. Furthermore, AF1q enhanced the mitochondrial membrane depolarization, mitochondrial cytochrome c release, and activation of caspase-9 and caspase-3 on doxorubicin treatment. Collectively, AF1q increases doxorubicin-induced apoptosis in cells through activation of BAD-mediated apoptotic pathway. The study provides the first evidence that AF1q plays a critical role in the regulation of apoptosis and drug resistance.

Conditional expression of mutated K-ras accelerates intestinal tumorigenesis in Msh2-deficient mice

K-ras mutation occurs in 40-50% of human colorectal adenomas and carcinomas, but its contribution to intestinal tumorigenesis in vivo is unclear. We developed K-ras(V12) transgenic mice that were crossed with Ah-Cre mice to generate K-ras(V12)/Cre mice, which showed beta-naphthoflavone-induction of Cre-mediated LoxP recombination that activated intestinal expression of K-ras(V12) 4A and 4B transcripts and proteins. Only very occasional intestinal adenomas were observed in beta-naphthoflavone-treated K-ras(V12)/Cre mice aged up to 2 years, suggesting that mutated K-ras expression alone does not significantly initiate intestinal tumourigenesis. To investigate the effects of mutated K-ras on DNA mismatch repair (MMR)-deficient intestinal tumour formation, these mice were crossed with Msh2(-/-) mice to generate K-ras(V12)/Cre/Msh2(-/-) offspring. After beta-naphthoflavone treatment, K-ras(V12)/Cre/Msh2(-/-) mice showed reduced average lifespan of 17.3+/-5.0 weeks from 26.9+/-6.8 (control Msh2(-/-) mice) (P<0.01). They demonstrated increased adenomas in the small intestine from 1.41 (Msh2(-/-) controls) to 7.75 per mouse (increased fivefold, P<0.01). In the large intestine, very few adenomas were found in Msh2(-/-) mice (0.13 per mouse) whereas K-ras(V12)/Cre/Msh2(-/-) mice produced 2.70 adenomas per mouse (increased 20-fold, P<0.01). Over 80% adenomas from K-ras(V12)/Cre/Msh2(-/-) mice showed transgene recombination with expression of K-ras(V12) 4A and 4B transcripts and proteins. Sequencing of endogenous murine K-ras showed mutations in two out of 10 tumours examined from Msh2(-/-) mice, but no mutations in 17 tumours from K-ras(V12)/Cre/Msh2(-/-) mice. Expression of K-ras(V12) in tumours caused activation of the mitogen-activated protein kinase and Akt/protein kinase B signaling pathways, demonstrated by phosphorylation of p44MAPK, Akt and GSK3beta, as well as transcriptional upregulation of Pem, Tcl-1 and Trap1a genes (known targets of K-ras(V12) expression in stem cells). Thus, mutated K-ras cooperates synergistically with MMR deficiency to accelerate intestinal tumorigenesis, particularly in the large intestine.

Stem cell gene expression changes induced specifically by mutated K-ras

K-Ras proteins transduce signals from membrane-bound receptors via multiple downstream effector pathways and thereby regulate fundamental stem cell processes that affect neoplasia, including proliferation, apoptosis, and differentiation, but their contribution to tumourigenesis is unclear. Because cancers develop from stem cells, we set out to determine the characteristic changes in gene expression brought about by mutated K-ras (without interference from normal K-ras) in otherwise normal stem cells. cDNA microarrays were used to analyze gene expression profiles comparing wild-type murine embryonic stem (ES) cells with K-ras(Val12) expressing ES cells (previously made null for both endogenous K-ras alleles and transfected with K-ras(Val12), with valine for glycine at codon 12). K-ras(Val12) was expressed at 1.2-fold normal K-ras levels and produced transcripts for both activated K-Ras4A and 4B isoforms. The array expression data were confirmed by real-time quantitative PCR analysis of selected genes expressed both in the K-ras(Val12) expressing ES cells (R = 0.91 with array data) and in the normal intestinal tissues of K-ras(Val12) transgenic mice (R = 0.91 with array data). Changes in gene expression were correlated with the effects of K-ras(Val12) expression on ES cells of enhancing self-renewal in an undifferentiated state, increasing susceptibility to DNA damage-induced apoptosis, and increased proliferation. These expression data may explain, at least in part, some neoplasia-related aspects of the phenotypic changes brought about in this ES cell line by mutated K-ras, in that upregulation of cell growth-related proteins and DNA-associated proteins is consistent with increased proliferation; upregulation of certain apoptosis-related proteins is consistent with a greater susceptibility to DNA damage-induced apoptosis; and downregulation of structural proteins, extracellular matrix components, secretory proteins and receptors is consistent with a less differentiated phenotype.

Molecular biological design of novel antineoplastic therapies

Novel therapies represent a new strategy for the development of anticancer agents. New targets derived from the knowledge of the molecular structure and genetic defects has been useful in developing anticancer drugs that prolong or stabilise the progression of tumours with minimal systemic toxicities. In this review, the mechanism of action and the most significant trials regarding monoclonal antibodies, tyrosine kinase inhibitors, angiogenesis and cyclooxygenase inhibitor-based therapies, farnesyl transferase inhibitors and proteasome inhibitors are discussed. The potential biological end points and toxicities are also described. In conclusion, novel therapies present a promising class of anticancer agents, acting through different mechanisms and offering a new perspective in the treatment of cancer.

Tamoxifen increases apoptosis but does not influence markers of proliferation in an MCF-7 xenograft model of breast cancer

Twenty-four nude mice bearing MCF-7 breast cancer cells grown as xenografts and treated with tamoxifen (2.5 mg slow-release pellet) were studied for up to 35 days. Tumour size was measured in 2 dimensions at regular time-intervals and tumours were harvested on each of days 2, 4, 7, 14, 28 and 35 after the start of treatment. Control animals (8) received no treatment and the tumours were harvested after 0 or 35 days. Tumour sections were assessed for prevalence of apoptosis and mitosis and examined immunocytochemically for Ki(67)(MIB-1) and bcl-2 expression. Tumours increased in size during tamoxifen-treatment, but at a significantly slower rate (max. 2.6-fold) than in the untreated control animals; thus tumours not actually regressing may, nevertheless, be responding significantly to tamoxifen. MIB-1 and bcl-2 immunostaining and mitosis failed to show any consistent change over the period of study. Apoptosis, however, increased progressively and significantly to day-28 in tamoxifen-treated tumours, reaching approximately a 5-fold increase over day-0 values, then decreasing again to nearly 3-fold by day-35 (P= 0.0002). The apoptosis: mitosis ratio in treated tumours also increased to approximately 10-fold on day-28 over day-0 values, decreasing to nearly 4-fold by day-35 (P= 0.037). Within the treated group, apoptosis was significantly inversely correlated with both mitosis (R = -0.38, P= 0.03) and expression of bcl-2 (R = -0.48, P= 0.0056) and strongly positively correlated with both time on tamoxifen (R = +0.63, P= 0.0003) and the % inhibition of growth by tamoxifen (R = +0.58,P = 0.0012) in the 28 individual, treated tumours (estimated relative to the mean growth rate in the controls). The apoptosis: mitosis ratio was also inversely correlated with bcl-2 expression (R = -0.56, P= 0.0021) and positively correlated with both time on tamoxifen (R = +0.50, P= 0.0068) and % inhibition of growth (R = +0.56, P= 0.0019). In this hormone-sensitive tumour model for breast cancer, in which tamoxifen caused inhibition rather than regression, it was not possible to detect significant changes in the marker proteins Ki(67)and bcl-2, or in the prevalence of mitosis in relation to treatment; these factors may therefore not be accurate indices of response to tamoxifen in all situations. By contrast, however, tamoxifen induced a significant, early increase in the prevalence of apoptosis associated with inhibition of tumour growth and an inverse relationship in both mitosis and bcl-2 expression, suggesting that apoptosis may be an accurate and sensitive early marker of even a moderate response to tamoxifen.

Natural history of colorectal nonpolypoid adenomas: a prospective colonoscopic study and relation with cell kinetics and K-ras mutations

OBJECTIVE

Serial colonoscopic observations were prospectively conducted to elucidate the natural history of nonpolypoid tumors. Furthermore, to clarify whether cell kinetic status affects the tumor development, proliferative indices, apoptotic indices, and K-ras codon 12 point mutations on biopsy specimens were investigated.

METHODS

Seventy-five colorectal tumors, 13 polypoid and 62 nonpolypoid type (56 flat elevated and six depressed type) were studied. Proliferating and apoptotic cells were detected with anti-Ki-67 antibody and the terminal deoxynucleotidyl transferase-mediated dUTP nick-end labeling method, respectively. Point mutations at K-ras codon 12 were examined by enriched polymerase chain reaction-based restriction fragment length polymorphism assay.

RESULTS

The average follow-up period was 22 months (range 1-50). The lesions of subsequent exophytic growth, unchanged shape, depressed growth, and disappearance were observed in 0%, 92%, 0%, and 8% of polypoid type, in 39%, 39%, 13%, and 9% of flat elevated type, and in 33%, 67%, 0%, and 0% of depressed type, respectively. There was no significant difference in tumor size between initial and follow-up colonoscopy. Nonpolypoid tumors apparently changed to the exophytic growth during 2 yr or more. The tumors with exophytic growth had significantly higher proliferative indices/apoptotic indices ratios than those with unchanged morphology and disappearance/depressed growth (p < 0.05, respectively). K-ras codon 12 point mutations did not correlate with tumor development.

CONCLUSIONS

Cell kinetic status plays an important role in determining minute colorectal tumor development, but not K-ras codon 12 mutations. Minute nonpolypoid adenomas frequently tend to grow slowly, and nearly 40% of those become the exophytic growth with time. Most of minute nonpolypoid tumors seem to follow the adenoma-carcinoma sequence.

Action of an HMG CoA reductase inhibitor, lovastatin, on apoptosis of untransformed and ts-SV40 transformed human smooth muscle cells derived from saphenous vein

The effect of lovastatin, an inhibitor of 3-hydroxymethyl-3-glutaryl coenzyme A (HMG CoA) reductase, was examined on human vascular smooth muscle cells (HVSMC). Untransformed HVSMC were obtained from saphenous vein and in addition an SV-40 transformed immortalized cell line (HVTs-SM1) derived from saphenous vein smooth muscle was also used. HVTs-SM1 cell proliferation and DNA synthesis were measured, and cell cycle analysis was performed by flow cytometry. Apoptosis in both cell types was assessed by a combination of flow cytometry, terminal deoxynucleotidyl transferase (TUNEL) reagent-based immunocytochemistry, DAPI staining, and DNA agarose gel electrophoresis. Lovastatin had no effect on apoptosis of HVSMC over 96 h in serum-free conditions or after stimulation with platelet-derived growth factor (PDGF-BB), although PDGF-BB increased apoptosis in HVSMC, and this was prevented by lovastatin. In HVTs-SM1 cells lovastatin inhibited cell proliferation and DNA synthesis and induced apoptosis in a time- and concentration-dependent manner. The effects of lovastatin on cell proliferation, DNA synthesis, and apoptosis were prevented by coincubation with mevalonate and geranylgeranyl pyrophosphate, but not by farnesyl pyrophosphate. Lovastatin does not induce apoptosis in saphenous vein HVSMC in culture and inhibits PDGF-BB-induced DNA synthesis and apoptosis. In contrast, in SV40 transformed immortalized HVTs-SM1 cells, lovastatin induces apoptosis and inhibits cell proliferation and DNA synthesis. The pro-apoptotic effects of lovastatin in SV40 transformed HVTs-SM1 cells may be related to the enhanced rate of proliferation or deregulation of the cell cycle in this cell line.

Mutant K-ras enhances apoptosis in embryonic stem cells in combination with DNA damage and is associated with increased levels of p19(ARF)

The roles of K-ras in neoplasia are not entirely understood, although there is evidence that K-ras affects susceptibility to apoptosis, modulating survival of DNA damaged cells which would otherwise be eliminated. In this study, we investigated the effects of mutant K-ras on apoptosis in vitro following DNA damage. To avoid complications resulting from mutations in other cancer-related genes and from the presence of endogenous K-ras, we derived K-ras null embryonic stem cells. Expression of either wild-type or mutant K-ras was reconstructed by stable plasmid transfection. The cell lines were treated with etoposide, cisplatin and UV radiation and apoptosis measured flow cytometrically. Mutant K-ras potentiated the effect of etoposide-derived DNA damage by increasing apoptosis, whereas absence of K-ras had the opposite effect. This pattern was similar but less marked with cisplatin, whereas UV yielded no difference in apoptosis with regard to K-ras status, suggesting that the effect of K-ras on apoptosis is dependent on the nature of the DNA damage. To investigate possible mechanisms, we examined the expression of p19(ARF) mRNA by RT-PCR. Cells expressing mutant K-ras produced elevated levels of p19(ARF) mRNA, which could link K-ras status with p53 expression and hence susceptibility to DNA damage-induced apoptosis.

Current concepts in cell toxicity

This overview provides a basic definition of cellular death and the mechanisms that are associated with cell death: apoptosis and necrosis. It includes a description of structural changes and macromolecular degradation and the roles of signaling, mitochondria, and genetic changes in the two forms of cell death.

Ras biochemistry and farnesyl transferase inhibitors: a literature survey

Over the last decades, knowledge on the genetic defects involved in tumor formation and growth has increased rapidly. This has launched the development of novel anticancer agents, interfering with the proteins encoded by the identified mutated genes. One gene of particular interest is ras, which is found mutated at high frequency in a number of malignancies. The Ras protein is involved in signal transduction: it passes on stimuli from extracellular factors to the cell nucleus, thereby changing the expression of a number of growth regulating genes. Mutated Ras proteins remain longer in their active form than normal Ras proteins, resulting in an overstimulation of the proliferative pathway. In order to function, Ras proteins must undergo a series of post-translational modifications, the most important of which is farnesylation. Inhibition of Ras can be accomplished through inhibition of farnesyl transferase, the enzyme responsible for this modification. With this aim, a number of agents, designated farnesyl transferase inhibitors (FTIs), have been developed that possess antineoplastic activity. Several of them have recently entered clinical trials. Even though clinical testing is still at an early stage, antitumor activity has been observed. At the same time, knowledge on the biochemical mechanisms through which these drugs exert their activity is expanding. Apart from Ras, they also target other cellular proteins that require farnesylation to become activated, e.g. RhoB. Inhibition of the farnesylation of RhoB results in growth blockade of the exposed tumor cells as well as an increase in the rate of apoptosis. In conclusion, FTIs present a promising class of anticancer agents, acting through biochemical modulation of the tumor cells.

Granulocyte-colony stimulating factor induced intranuclear endonuclease in murine leukemia cell line

We have reported that murine leukemia cell line (C2M-A5) induced apoptosis by G-CSF. To clarify the mechanism, mRNA expression of apoptosis-related genes was studied. It revealed transient over-expression of c-myc, H-ras and p53 and down-expression of bcl-2. These changes were known as triggers of endonuclease induction. After 96 h culture with G-CSF, apoptosis was occurred simultaneously with endonuclease (37 kd) activation. This endonuclease induced the digestion of double-strand DNA and might be associated with caspase3. Although G-CSF accelerates cell growth and prevents apoptosis in general, it is a contradictory effect. We concluded that G-CSF induced endogenous endonuclease activity in C2M-A5.

Loss of p21WAF1/CIP1 accelerates Ras oncogenesis in a transgenic/knockout mammary cancer model

Upregulation of the cyclin-dependent kinase inhibitor p21WAF1/CIP1 and subsequent cell growth arrest or senescence is one mechanism by which normal cells are believed to respond to stress induced by the constitutively activated GTPase Ras. We hypothesize that in the absence of p21, the onset of Ras-dependent oncogenesis is accelerated. To test this hypothesis, we crossed MMTV/v-Ha-ras transgenic mice into a p21-deficient background. By 63 days of age, all 8 ras/p21-/- mice developed either malignant (mammary and/or salivary adenocarcinomas) or benign (Harderian hyperplasia) tumors. In contrast, by the same age, only one out of nine of the ras/p21+/+ mice developed a tumor. Furthermore, by 94 days of age, half of the ras/p21-/- mice, but none of the ras/p21+/+ mice, developed mammary tumors. p21-deficiency also accelerated the development of salivary (T50=66 days for ras/p21-/- vs T50=136 days for ras/p21+/+) and Harderian (T50=52 days for ras/p21-/- vs T50>221 days for ras/p21+/+) tumors. Furthermore, two out of the eight ras/p21-/- mice had metastatic lesions, one in its lungs, the other in its abdomen. None of the nine ras/p21+/+ mice had metastatic lesions. By 4 months of age, the mammary tumor multiplicity was 10-fold greater in ras/p21-/- (average 3.40 tumors/mouse) than in ras/p21+/+ (average 0.33 tumor/mouse) mice. However, once the tumors appeared, their growth rate, apoptosis level, and mitotic index were not affected by the loss of p21, suggesting that loss of p21 is critical in early but not late events of Ras oncogenesis. Altogether, the results show that tumor onset in MMTV/v-Ha-ras mice is p21-dependent with loss of p21 associated with earlier tumor appearance and increased tumor multiplicity and aggressiveness.

Suppression of P-gp induced multiple drug resistance in a drug resistant gastric cancer cell line by overexpression of Fas

AIM: To observe the drug sensitizing effect and related mechanisms of fas gene transduction on human drug-resistant gastric cancer cell SGC7901/VCR (resistant to Vincristine).

METHODS: The cell cycle alteration was observed by FACS. The sensitivity of gastric cancer cells to apoptosis was determined by in vitro apoptosis assay. The drug sensitization of cells to several anti-tumor drugs was observed by MTT assay. Immunochemical method was used to show expression of P-gp and Topo II in gastric cancer cells.

RESULTS: Comparing to SGC7901 and pBK-SGC7901/VCR, fas-SGC7901/VCR showed decreasing G2 cells and increasing S cells, the G2 phase fraction of pBK-SGC7901/VCR was about 3.0 times that of fas-SGC7901/VCR, but S phase fraction of fas-SGC7901/VCR was about 1.9 times that of pBK-SGC7901/VCR, indicating S phase arrest of fas-SGC7901/VCR. FACS also suggested apoptosis of fas-SGC7901/VCR. fas-SGC7901/VCR was more sensitive to apoptosis inducing agent VM-26 than pBK-SGC7901/VCR. MTT assay showed increased sensitization of fas-SGC7901/VCR to DDP, MMC and 5-FU, but same sensitization to VCR according to pBK-SGC7901/VCR. SGC7901, pBK-SGC7901/VCR and fas-SGC7901/VCR had positively stained Topo II equally. P-gp staining in pBK-SGC7901/VCR was stronger than in SGC7901, but there was little staining of Pgp in fas-SGC7901/VCR.

CONCLUSION: fas gene transduction could reverse the MDR of human drug-resistant gastric cancer cell SGC7901/VCR to a degree, possibly because of higher sensitization to apoptosis and decreased expression of P-gp.

Restricted 12p amplification and RAS mutation in human germ cell tumors of the adult testis

Human testicular germ-cell tumors of young adults (TGCTs), both seminomas and nonseminomas, are characterized by 12p overrepresentation, mostly as isochromosomes, of which the biological and clinical significance is still unclear. A limited number of TGCTs has been identified with an additional high-level amplification of a restricted region of 12p including the K-RAS proto-oncogene. Here we show that the incidence of these restricted 12p amplifications is approximately 8% in primary TGCTs. Within a single cell formation of i(12p) and restricted 12p amplification is mutually exclusive. The borders of the amplicons cluster in short regions, and the amplicon was never found in the adjacent carcinoma in situ cells. Seminomas with the restricted 12p amplification virtually lacked apoptosis and the tumor cells showed prolonged in vitro survival like seminoma cells with a mutated RAS gene. However, no differences in proliferation index between these different groups of seminomas were found. Although patients with a seminoma containing a homogeneous restricted 12p amplification presented at a significantly younger age than those lacking it, the presence of a restricted 12p amplification/RAS mutation did not predict the stage of the disease at clinical presentation and the treatment response of primary seminomas. In 55 primary and metastatic tumors from 44 different patients who failed cisplatinum-based chemotherapy, the restricted 12p amplification and RAS mutations had the same incidence as in the consecutive series of responding patients. These data support the model that gain of 12p in TGCTs is related to invasive growth. It allows tumor cells, in particular those showing characteristics of early germ cells (ie, the seminoma cells), to survive outside their specific microenvironment. Overexpression of certain genes on 12p probably inhibits apoptosis in these tumor cells. However, the copy numbers of the restricted amplification of 12p and K-RAS mutations do not predict response to therapy and survival of the patients.

Cooperation of bcl-2 and myc in the neoplastic transformation of normal rat liver epithelial cells is related to the down-regulation of gap junction-mediated intercellular communication

The objectives of this study were to isolate several rat liver epithelial cell clones containing the human bcl-2 and myc/bcl-2 genes in order to study their potential cooperative effect on neoplastic transformation and gap junction-mediated intercellular communication (GJIC) and to test the hypothesis that the loss of GJIC leads to tumorigenesis. Using anchorage-independent growth as a surrogate marker for neoplastic transformation, we transfected both normal rat liver epithelial cells, WB-F344, and a WB-F344 cell line overexpressing v-myc with human bcl-2 cDNA. Those cell lines that only expressed v-myc or human bcl-2 were unable to form colonies in soft agar. However, those cell lines that overexpressed both v-myc and human bcl-2 showed varying ability to form colonies in soft agar, which did not correlate with their human bcl-2 expression level. In order to test if there was a correlation between cell line growth in soft agar and the ability to communicate through gap junctions, we performed scrape load dye transfer and fluorescence recovery after photobleaching assays. Our results show that v-myc and human bcl-2 can cooperate in the transformation of normal cells, but the degree to which the cells are transformed is dependent on the cells' ability to communicate through gap junctions.

Genetic determinants of response to chemotherapy in transgenic mouse mammary and salivary tumors

Several transgenic mouse tumor models were utilized to explore how specific genetic alterations affect the tumor cell response to chemotherapeutic agents in vivo. Specifically, MMTV-ras transgenic mice were interbred to p53 knock-out mice to create a model for assessing the role of p53 in chemotherapeutic responses. In addition, MMTV-ras tumors were compared to MMTV-myc and MMTV-ras/myc tumors. Mice of each genotype reproducibly develop mammary and/or salivary tumors, but tumor growth dynamics vary considerably between genotypes. MMTV-ras/p53-/- tumors exhibit higher S phase fractions than MMTV-ras/p53+/+ tumors, although both tumor types display very low apoptosis levels. In contrast, MMTV-myc tumors exhibit both high S phase fractions and spontaneous apoptosis levels. Tumor-bearing mice of each genotype were treated with either doxorubicin or paclitaxel, and effects on overall tumor growth, cell cycle distribution and apoptosis were evaluated. Surprisingly, neither agent efficiently induced apoptosis in any of the tumor models, including those with wildtype p53. Rather, tumor responses were mediated primarily by changes in cell cycle distribution. However, the spontaneous apoptosis levels did serve as a predictor of tumor growth response, in that only those tumors with high pretreatment apoptosis levels underwent significant regression following treatment with either agent.

Autocrine signaling through Ras prevents apoptosis in vascular smooth muscle cells in vitro

Vascular smooth muscle cell (SMC) apoptosis contributes to physiological and pathological vascular remodeling. Autocrine fibroblast growth factor (FGF) signaling promotes survival in SMC in vitro. Interruption of autocrine FGF signaling results in apoptosis that can be rescued by other growth factors such as PDGF (platelet-derived growth factor) or EGF (epidermal growth factor). Such heterologous growth factor rescue is prevented by pharmacological inhibition of MAPK, implicating signaling through Ras in mediating survival. This study was designed to test the hypothesis that signaling through Ras is both necessary and sufficient to mediate SMC survival in vitro. Recombinant adenoviruses encoding dominant-negative (Ras(N17)) and constitutively active (Ras(L61)) mutants of Ras were used. Ras(N17) blocks growth factor-mediated MAPK activation and can itself induce SMC apoptosis. Ras(N17) is synergistic with inhibition of autocrine FGF signaling in triggering apoptosis and prevents heterologous growth factor rescue. Conversely, Ras(L61) prevents apoptosis resulting from inhibition of autocrine FGF signaling. Rescue by Ras(L61) can be partially prevented by pharmacological inhibition of MEK or phosphatidylinositol 3-kinase, two downstream effectors of Ras. These results suggest that Ras signaling is both necessary and sufficient to mediate survival in SMC in vitro. Further work is required to determine how these signaling events are regulated in the context of vascular remodeling in vivo.

Alternative effects of RAS and RAF oncogenes on the proliferation and apoptosis of factor-dependent FDC-P1 cells

Despite the fact that RAF-1 lies immediately downstream of p21RAS in the MAP kinase-signalling cascade, recent evidence in non-haematopoietic environments suggest that RAS and RAF can transduce signals through alternative pathways specific to a particular cell type. Since mutational activation of RAS occurs at high frequency in human leukaemia, we have investigated the contribution of signalling from mutant RAF in mediating the transforming effects of the N-RAS oncogene in the growth factor-dependent cell line, FDC-P1. Independent activation of N-RAS extended the period of exponential growth leading to an increased saturating density under optimal growth conditions. Under conditions of growth factor withdrawal, cells expressing mutant RAS, but not control cells, demonstrated protection against apoptotic death. Although RAF promoted cell proliferation in a similar manner to that observed in FDCP-RAS cells, expression of mutant RAF was not as effective at protecting these cells against apoptotic death following growth factor withdrawal. The results suggest that RAS utilises RAF-dependent signals in promoting the proliferation of FDC-P1 cells but the anti-apoptotic effects of this oncogene are mediated through a RAF- and BCL-2-independent pathway.

A molecular model for the development of germ cell cancer

Human germ cell tumors comprise a heterogeneous group of neoplasms. Those of the adult testis, known as TGCTs, originate from carcinoma in situ (CIS), which are initiated during intra-uterine development. We present here a molecular model for the development of TGCTs, including various parameters, such as apoptosis, chromosomal constitution, as well as genomic imprinting. We assume that TGCTs originate from a pluripotent, erased embryonic germ cell, of which aneuploidization is one of the early events. Subsequently, net loss and gain of specific chromosomal regions result in the consistent pattern of chromosomal aberrations that are observed in these tumors, including gain of 12p-sequences. By means of analysis of a relatively small region of the short arm of chromosome 12, we are in the process of identifying the relevant genes. Possibly, this gene(s) suppresses apoptosis outside the specific micro-environment of the seminiferous tubule.

Induction of mammary gland hyperplasia in transgenic mice over-expressing human Cdc25B

Cdc25 A and B are dual-specificity phosphatases which have been implicated in neoplastic transformation. Although Cdc25A and Cdc25B have been found to be over-expressed in many cancer cell lines and primary tumors, the physiological roles of Cdc25A and B in vivo are largely undefined. To investigate the roles of these proteins in the oncogenic transformation of the mammary gland we used the mouse mammary tumor virus (MMTV) promoter to target over-expression of the Cdc25B transgene in the mammary glands of transgenic mouse lines. Here we report that the over-expression of Cdc25B enhances the proliferation of mammary epithelial cells resulting in the formation of precocious alveolar hyperplasia. At the molecular level, marked increases in cyclin D1 protein have been found in transgenic mammary epithelial cells. The accelerated growth rate of the mammary epithelial cells could also be attributed to the increased levels of cyclin E/cdk2 activity. In addition, a pronounced decrease in apoptosis was also observed during the involution of mammary gland. The reduction of apoptosis during involution correlated well with the reduced expression of c-myc and p53, both of which have been implicated in apoptosis. Taken together, our results clearly indicate that the deregulated expression of Cdc25B generates mammary gland hyperplasia.

B-Raf inhibits programmed cell death downstream of cytochrome c release from mitochondria by activating the MEK/Erk pathway

Growth factor-dependent kinases, such as phosphatidylinositol 3-kinase (PI 3-kinase) and Raf kinases, have been implicated in the suppression of apoptosis. We have recently established Rat-1 fibroblast cell lines overexpressing B-Raf, leading to activation of the MEK/Erk mitogen-activated protein kinase pathway. Overexpression of B-Raf confers resistance to apoptosis induced by growth factor withdrawal or PI 3-kinase inhibition. This is accompanied by constitutive activation of Erk without effects on the PI 3-kinase/Akt pathway. The activity of MEK is essential for cell survival mediated by B-Raf overexpression, since either treatment with the specific MEK inhibitor PD98059 or expression of a dominant inhibitory MEK mutant blocks the antiapoptotic activity of B-Raf. Activation of MEK is not only necessary but also sufficient for cell survival because overexpression of constitutively activated MEK, Ras, or Raf-1, like B-Raf, prevents apoptosis after growth factor deprivation. Overexpression of B-Raf did not interfere with the release of cytochrome c from mitochondria after growth factor deprivation. However, the addition of cytochrome c to cytosols of cells overexpressing B-Raf failed to induce caspase activation. It thus appears that the B-Raf/MEK/Erk pathway confers protection against apoptosis at the level of cytosolic caspase activation, downstream of the release of cytochrome c from mitochondria.

Non steroidal anti-inflammatory drugs and colorectal cancer: is there a way forward?

Non steroidal anti-inflammatory drugs (NSAIDs) have diverse clinical applications through modulation of oxidative processes and cell signalling. Observations that these agents may inhibit human colorectal carcinogenesis have produced great excitement. However, comparative data relating to their chemopreventative effectiveness or to relevant mechanisms of action remains unclear. This review considers the clinical and epidemiological evidence for colorectal tumour prevention by NSAIDs against current concepts of drug mechanisms. We also propose areas of further research for potential therapeutic advancement.

Increased tumor cell proliferation in murine tumors with decreasing dosage of wild-type p53

A number of transgenic animal model systems have addressed the mechanistic role of p53 loss in tumor progression. However, many of these tumor models have analyzed p53 function in the context of other transgenes expressing activated oncogenes or defective tumor suppressor genes generated by gene targeting. To examine the role of p53 loss independent of other exogenous oncogenic influences, we analyzed some of the biological aspects of tumor formation and progression in p53-knockout mice containing a null germline p53 allele. We analyzed tumors from p53-/-, p53+/-, and p53+/+ littermates. Some of the p53+/- tumors had lost the remaining p53 allele (p53+/- loss of heterozygosity), whereas others retained the allele (p53+/-). In this report, we show that loss or absence of p53 conferred a tumor growth advantage by increasing the rate of cellular proliferation in a p53 dosage-dependent manner. The apoptotic levels in tumor tissue were found to be modest and not significantly dependent on p53 status. These results contrast with those from some other p53-deficient tumor models, in which p53 loss was associated with more rapid tumor progression through abrogated apoptosis. Finally, as p53 has been shown to regulate certain angiogenic factors, we examined the levels of angiogenesis in p53-containing and p53-deficient tumors. We found no p53-dependent differences in the levels of tumor angiogenesis measured by intratumoral microvessel density.

Autocrine FGF signaling is required for vascular smooth muscle cell survival in vitro

Expression of both basic fibroblast growth factor (bFGF) and FGF receptors (FGFR) by vascular smooth muscle cells suggests that autocrine FGF signaling mechanisms may have important functions. Inhibition of smooth muscle cell bFGF expression provokes apoptosis, suggesting that endogenous bFGF generates an anti-apoptotic signal. The purpose of this study was to determine whether the survival function of endogenous bFGF requires signaling through FGFR. A recombinant adenovirus encoding a truncated murine FGFR-1 lacking the kinase domain (DN-FGFR) efficiently expressed the transgene in cultured rat aortic smooth muscle cells. The truncated receptor acted in a dominant negative fashion to effectively prevent receptor-mediated signaling, assessed by phosphorylation of p42/p44 MAP kinase. Expression of DN-FGFR provoked apoptosis of SMC in a dose-dependent fashion that was insensitive to recombinant bFGF but could be rescued by platelet derived growth factor or epidermal growth factor. Heterologous growth factor rescue was inhibited by PD98059, an inhibitor of MEK (MAP kinase-kinase). These data demonstrate that inhibition of FGF receptor activation results in apoptosis and suggest that an intact autocrine FGF signaling loop is required for vascular smooth muscle cell survival in vitro. These findings also implicate the Ras/Raf/MEK/MAP kinase cascade in generating or sustaining the survival signal. The functional significance of an autocrine FGF signaling loop in non-transformed cells has important implications for cardiovascular development, remodeling and disease.

3-Hydroxy-3-methylglutaryl coenzyme a reductase and isoprenylation inhibitors induce apoptosis of vascular smooth muscle cells in culture

Recent evidence suggests that apoptosis may be involved in the control of vascular smooth muscle cell (VSMC) number in atherosclerotic lesions. 3-Hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase inhibitors have been reported to induce apoptosis in a variety of tumor cell lines. To evaluate whether these agents also induce apoptosis of VSMCs, cultured rat VSMCs were treated with increasing doses of atorvastatin in the presence of FBS as a survival factor. The presence of apoptosis was evaluated by morphological criteria, annexin V binding, and DNA fragmentation and quantified as the proportion of hypodiploid cells by flow cytometry. Atorvastatin induced apoptosis in a dose-dependent manner, an effect also seen with simvastatin and lovastatin, but not with the hydrophilic drug pravastatin. The proapoptotic effect of statins was seen only when the inhibition of acetate incorporation into sterols was >95% and was fully reversed by mevalonate, farnesyl pyrophosphate, and geranylgeranyl pyrophosphate but not by isopentenyl adenosine, ubiquinone, or squalene, suggesting a role for prenylated proteins in the regulation of VSMC apoptosis. To further assess the role of protein prenylation, VSMCs were exposed to the prenyl transferase inhibitors perillic acid and manumycin A. Both agents induced VSMC apoptosis as evaluated by the above-mentioned criteria. Finally, VSMC treatment with lipophilic statins was associated with decreased prenylation of p21-Rho B, further supporting the role of protein prenylation inhibition in statin-induced VSMC apoptosis. The present data suggest that interference with protein prenylation by HMG-CoA reductase inhibitors or other agents may provide new strategies for the prevention of neointimal thickening.

ras mutation and platinum resistance in human ovarian carcinomas in vitro

A panel of 16 human ovarian carcinoma cell lines comprising cisplatin naive as well as those with acquired cisplatin resistance was studied to determine if there was a relationship between ras status and cisplatin sensitivity. From the ras expression studies alongside data produced by direct DNA sequencing, there was very little to suggest that ras overexpression or mutation plays a role in the cisplatin sensitivity of the panel of human ovarian carcinoma cell lines tested. A weak correlation (r2 = 0.53) was found between total Ras protein levels and resistance to cisplatin. No relationship was found between Kirsten-Ras protein levels and cisplatin sensitivity (r2 = 0.0). Only one ras mutation (codon 13, Kirsten exon 1, glycine --> aspartate in the HX62 cell line) was observed in the cisplatin naive cell lines from the panel which comprised both cisplatin sensitive and resistant models. Of interest, however, was that the HX62 cell line was the most resistant to cisplatin. No ras mutations were found in those cell lines which had repeatedly been exposed, and acquired resistance, to cisplatin. The A2780 and CH1 human ovarian carcinoma cell lines were transfected with activated, mutant Harvey-ras and, as a result, were shown to display elevated MAP kinase phosphorylation in low serum concentration growth medium. No changes in cisplatin sensitivity were found following transfection with activated Harvey-ras in these 2 human ovarian carcinoma tumor cell models which, importantly, differed greatly in their expression of Bcl-2. Therefore, when conducted under similar conditions to previously published studies, very little evidence was found to support Harvey-ras activation as a factor which can either sensitize or confer resistance to cisplatin in human ovarian carcinoma cell lines.

Additional evidence that the K-ras protooncogene is a candidate for the major mouse pulmonary adenoma susceptibility (Pas-1) gene

A locus for mouse pulmonary adenoma susceptibility, Pas-1, has been mapped on distal chromosome 6, where the K-ras gene is located. Allele-specific activation and expression of the K-ras allele from the susceptible parent has been observed in lung tumors from F1 hybrid mice. We report here genetic mapping of lung tumor susceptibility genes in urethane-treated A x B and B x A recombinant inbred (RI) mice using microsatellite markers to seek further evidence for the K-ras gene as candidate for Pas-1. The K-ras genotype differs between the A/J and C57BL/6J progenitors of the RI strains, and distal chromosome 6 contained a major lung tumor susceptibility determinant in the RI mice. Additional evidence that Pas-1 is K-ras involved linkage analysis of (A/JOLaHsd x BALB/ cOLaHsd) F2 intercross mice whose parents shared the same K-ras genotype. In contrast to the results with the A x B and B x A RI strains, no distal chromosome 6 site was significantly associated with tumor development in these F2 mice. In addition to this major locus, linkage analysis of the RI mice revealed additional quantitative trait loci for susceptibility on chromosomes 10, 17, and 19. These loci may serve as modifiers of Pas-1. The relationship between the K-ras genotype and the frequency of K-ras mutations in urethane-induced lung tumors from the RI mice was also explored. All 18 tumor DNAs from RI mice with high susceptibility contained an AT-->TA transversion at the second base of K-ras codon 61. This was also true for DNAs from 27 of 27 (100%) tumors in mice with high intermediate susceptibility. In RI strains with a low intermediate susceptibility, the DNA from 39 of 47 (83%) tumors contained an AT-->TA transversion at codon 61, and only 13 of 21 (62%) tumors had this mutation in the most resistant group. This reflects a positive correlation between the frequency of K-ras mutations in lung tumors of A x B or B x A RI strains and their susceptibility to lung carcinogenesis. Since K-ras appears to be Pas-1, these results suggest that some RI mice that have the resistant K-ras or Pas-1 allele undergo tumor development by a K-ras-independent route.

Apoptotic death of pancreatic cancer cells induced by polyunsaturated fatty acids varies with double bond number and involves an oxidative mechanism

Polyunsaturated fatty acids (PUFAs), reported to be cytotoxic at micromolar concentrations for cancer cells in vitro and in vivo, are currently being tested in clinical trials as anti-cancer agents. This study has shown that seven PUFAs all inhibited the growth in vitro of three pancreatic cancer cell lines and the HL-60 leukaemic cell line. Five PUFAs induced cell death within 20-30 h, but two less potent PUFAs induced death between 50 and 75 h. Apoptosis was demonstrated to be the mode of cell death by light, UV fluorescence, and electron microscopy, together with studies of DNA fragmentation. In a time-course study of PUFA-treated Mia-Pa-Ca-2 cells, apoptosis accounted for an average of 80 per cent of the loss of viability, with 'secondary necrosis', a feature of late apoptosis, apparently accounting for the remainder. Correlations were found between the number of fatty acid double bonds and the proportion of cells undergoing apoptosis induced in both Mia-Pa-Ca-2 cells (R = 0.88, P = 0.0001) and HL-60 cells (R = 0.85, P = 0.0001) and inversely with the micromolar concentrations of PUFAs required for 50 per cent inhibition of growth (IC50) of Mia-Pa-Ca-2 cells (R = -0.73, P = 0.05). Cell death was preceded by progressively increasing lipid peroxidation. The extent of PUFA-induced lipid peroxidation, measured as malondialdehyde (MDA), also correlated with the proportion of apoptosis induced in Mia-Pa-Ca-2 cells (R = 0.69, P = 0.025) or HL-60 cells (R = 0.64, P = 0.043), as well as with the number of fatty acid double bonds (R = 0.82, P = 0.0015). PUFA-induced apoptosis was oxidative, being blocked by both vitamin E acetate and sodium selenite, the latter in a critically time-dependent manner. The cytotoxic effects of exposure to a PUFA and to gamma-irradiation simultaneously with, or prior to, the addition of PUFA.

Dying enterocytes downregulate signaling pathways converging on Ras: rescue by protease inhibition

Organ and cell cultures of the small intestine serve as excellent in vitro models for programmed cell death (PCD). Cells cultured in serum-free, minimal medium rapidly died, as evidenced by histological changes, internucleosomal DNA cleavage, and TdT-mediated dUTP nick end labeling. Cell death was pervasive, although nonepithelial cells within the fibrovascular villus core were spared. PCD did not require a functional p53 gene. Serine and cysteine protease inhibitors, but not FCS, suppressed it. Relative to structural and functional proteins, dying enterocytes rapidly downregulated Ras-convergent proteins, including epidermal growth factor receptor, Erb-B2, and the son of sevenless guanine nucleotide exchangers. Reductions in the steady-state levels of both protein and mRNA were observed. These reductions were prevented by a combination of death-defying serine and caspase inhibitors, indicating a requirement for the initiation of death. Thus, during catastrophic PCD, intestinal epithelial cells delete cell surface signaling pathways responsible for Ras activation.

Nitrogen-containing bisphosphonates inhibit the mevalonate pathway and prevent post-translational prenylation of GTP-binding proteins, including Ras

Bisphosphonates are currently the most important class of antiresorptive drugs used for the treatment of metabolic bone diseases. Although the molecular targets of bisphosphonates have not been identified, these compounds inhibit bone resorption by mechanisms that can lead to osteoclast apoptosis. Bisphosphonates also induce apoptosis in mouse J774 macrophages in vitro, probably by the same mechanisms that lead to osteoclast apoptosis. We have found that, in J774 macrophages, nitrogen-containing bisphosphonates (such as alendronate, ibandronate, and risedronate) inhibit post-translational modification (prenylation) of proteins, including the GTP-binding protein Ras, with farnesyl or geranylgeranyl isoprenoid groups. Clodronate did not inhibit protein prenylation. Mevastatin, an inhibitor of 3-hydroxy-3-methylglutatyl (HMG)-CoA reductase and hence the biosynthetic pathway required for the production of farnesyl pyrophosphate and geranylgeranyl pyrophosphate, also caused apoptosis in J774 macrophages and murine osteoclasts in vitro. Furthermore, alendronate-induced apoptosis, like mevastatin-induced apoptosis, could be suppressed in J774 cells by the addition of farnesyl pyrophosphate or geranylgeranyl pyrophosphate, while the effect of alendronate on osteoclast number and bone resorption in murine calvariae in vitro could be overcome by the addition of mevalonic acid. These observations suggest that nitrogen-containing bisphosphonate drugs cause apoptosis following inhibition of post-translational prenylation of proteins such as Ras. It is likely that these potent antiresorptive bisphosphonates also inhibit bone resorption by preventing protein prenylation in osteoclasts and that enzymes of the mevalonate pathway or prenyl protein transferases are the molecular targets of the nitrogen-containing bisphosphonates. Furthermore, the data support the view that clodronate acts by a different mechanism.

Selective cytotoxicity of farnesylamine to pancreatic carcinoma cells and Ki-ras-transformed fibroblasts

Farnesyl protein transferase (FPTase) catalyses the post-translational modification of proteins by a farnesyl pyrophosphate. One of the substrates of this enzyme is p21ras, the product of the ras oncogene. We examined whether farnesylamine, one of the FPTase inhibitors (FTI), is selectively cytotoxic in pancreatic carcinoma cells and Ki-ras-transformed fibroblasts. Furthermore, we investigated whether the cytotoxicity of farnesylamine is caused by the induction of apoptosis in these cells. Using the FPTase assay, we found that farnesylamine inhibited FPTase in vitro. Immunoprecipitation showed that farnesylamine inhibited farnesylation of p21ras in vivo. In addition, 24 and 5 microM farnesylamine were required to achieve 50% cytotoxicity in pancreatic carcinoma cells containing activated Ki-ras and Ki-ras-transformed NIH/3T3 cells, respectively. The parental NIH/3T3 cells were resistant to the cytotoxic effect of farnesylamine at concentrations less than 100 microM. After incubation with farnesylamine, DNA fragmentation was observed in both pancreatic carcinoma cells and Ki-ras-transformed fibroblasts at cytotoxic doses of this compound but not in NIH/3T3 cells. These results indicate that the mechanism of cell death induced by farnesylamine is apoptosis, and this apoptosis occurred specifically in pancreatic carcinoma cells containing mutated Ki-ras and the Ki-ras-transformed cells. Because raf is downstream of ras (p21ras) in the ras-raf-mitogen-activated protein kinase signaling pathway, we used c-raf-1-transformed fibroblasts, which proved to be resistant to apoptosis induced by farnesylamine. This supports the theory that inhibition of ras signaling may be related to the induction of apoptosis. These data further suggest that farnesylamine could be useful as a chemotherapeutic agent in cancers that very frequently contain a Ki-ras oncogene mutation, e.g., pancreatic cancer.

Ras signalling and apoptosis

Activated Ras proteins have either positive or negative effects on the regulation of apoptosis depending on cell type and other factors. In part, this is due to the ability of Ras to control directly multiple effector pathways, including PI3-kinase, which provides a universal survival signal, and Raf, which can inhibit survival. The mechanisms remain partly unclear, however, especially with regard to Raf effects on apoptosis regulation. Recently Ras has been shown to be able to protect cells from apoptosis either through activation of PKB/Akt via PI3-kinase, or through activation of NF-kappa B.

A farnesyltransferase inhibitor induces tumor regression in transgenic mice harboring multiple oncogenic mutations by mediating alterations in both cell cycle control and apoptosis

The farnesyltransferase inhibitor L-744,832 selectively blocks the transformed phenotype of cultured cells expressing a mutated H-ras gene and induces dramatic regression of mammary and salivary carcinomas in mouse mammary tumor virus (MMTV)-v-Ha-ras transgenic mice. To better understand how the farnesyltransferase inhibitors might be used in the treatment of human tumors, we have further explored the mechanisms by which L-744,832 induces tumor regression in a variety of transgenic mouse tumor models. We assessed whether L-744,832 induces apoptosis or alterations in cell cycle distribution and found that the tumor regression in MMTV-v-Ha-ras mice could be attributed entirely to elevation of apoptosis levels. In contrast, treatment with doxorubicin, which induces apoptosis in many tumor types, had a minimal effect on apoptosis in these tumors and resulted in a less dramatic tumor response. To determine whether functional p53 is required for L-744,832-induced apoptosis and the resultant tumor regression, MMTV-v-Ha-ras mice were interbred with p53(-/-) mice. Tumors in ras/p53(-/-) mice treated with L-744,832 regressed as efficiently as MMTV-v-Ha-ras tumors, although this response was found to be mediated by both the induction of apoptosis and an increase in G1 with a corresponding decrease in the S-phase fraction. MMTV-v-Ha-ras mice were also interbred with MMTV-c-myc mice to determine whether ras/myc tumors, which possess high levels of spontaneous apoptosis, have the potential to regress through a further increase in apoptosis levels. The ras/myc tumors were found to respond nearly as efficiently to L-744,832 treatment as the MMTV-v-Ha-ras tumors, although no induction of apoptosis was observed. Rather, the tumor regression in the ras/myc mice was found to be mediated by a large reduction in the S-phase fraction. In contrast, treatment of transgenic mice harboring an activated MMTV-c-neu gene did not result in tumor regression. These results demonstrate that a farnesyltransferase inhibitor can induce regression of v-Ha-ras-bearing tumors by multiple mechanisms, including the activation of a suppressed apoptotic pathway, which is largely p53 independent, or by cell cycle alterations, depending upon the presence of various other oncogenic genetic alterations.

A sustained increase of cytosolic Ca2+ in gammadelta T cells triggered by co-stimulation via TCR/CD3 and LFA-1

We previously reported that co-stimulation with LFA-1 triggered apoptosis in gammadelta T cells but not in alphabeta T cells after TCR engagement. We extended our earlier study on TCR/LFA-1 triggered apoptosis to two autoreactive TCR gammadelta and TCR alphabeta T cell clones, which were derived from syngeneic mixed lymphocyte culture of BALB/c mice. A gammadelta T cell clone, KM1, expressed the Vgamma4 and Vdelta5 genes and CD4-CD8-CD45RB+ phenotype; and an alphabeta T cell clone, BASL1.1, expressed Vbeta6 and CD4+CD8-CD45RB+. Both clones produced Th-1-type cytokines in response to syngeneic BALB/c stimulator cells. KM1 underwent apoptosis upon stimulation with immobilized anti-CD3/LFA-1 mAbs, whereas BASL1.1 could proliferate successfully in response to stimulation with the immobilized mAbs. BASL1.1 was able to down-regulate the increased cytosolic Ca2+ after the simultaneous stimulation, but KM1 exhibited a sustained increase of cytosolic Ca2+ after stimulation via CD3 and LFA-1. Similar results with respect to the kinetics of cytosolic Ca2+ were obtained with normal heterogeneous gammadelta and alphabeta T cell populations after co-stimulation via CD3 and LFA-1. Our results suggested that persistently high levels of cytosolic Ca2+ might be related to apoptosis in gammadelta T cell clone triggered by co-stimulation via CD3 and LFA-1.

Endothelial apoptosis in Braf-deficient mice

Tyrosine kinase growth factor receptors and Ras/Raf/MEK/MAPK signalling have been implicated in the suppression as well as augmentation of programmed cell death. In addition, a Ras-independent role for Raf as a suppressor of programmed cell death has been suggested by the recent finding that Craf1 interacts with members of the Bcl-2 family at mitochondrial membranes. However, genetic studies of C. elegans and Drosophila, as well as the targeted mutagenesis of the murine Araf gene, have failed to support such a role. Here we show that mice with a targeted disruption in the Braf gene die of vascular defects during mid-gestation. Braf -/- embryos, unlike Araf -/- or Craf1 -/- embryos (L.W. et al., unpublished), show an increased number of endothelial precursor cells, dramatically enlarged blood vessels and apoptotic death of differentiated endothelial cells. These results establish Braf as a critical signalling factor in the formation of the vascular system and provide the first genetic evidence for an essential role of Raf gene in the regulation of programmed cell death.