Tumor suppressor p53 restricts Ras stimulation of RhoA and cancer cell motility

Many features of the cancer cell phenotype emerge as a result of cooperation between multiple oncogenic mutations. Here we show that activated Ras(V12) and loss of p53 function can cooperate to promote cell motility, a feature closely associated with cancer progression to malignancy. Our analysis indicates that Ras(V12) and loss of p53 synergistically induce RhoA activity, revealing a previously unknown role for p53 in tumor suppression. p53 prevents activation of RhoA and thus induction of cell motility by Ras(V12) through a simple signaling circuit, which integrates multiple inputs that converge on RhoA. Our data suggest that p53 suppresses cancer progression to malignancy by modulating the quality of Ras signaling.     

Effect of vasoactive intestinal peptide, peptide histidine isoleucine and growth hormone-releasing factor-40 on bombesin-like immunoreactivity, somatostatin and gastrin release from the perfused rat stomach

Bombesin-like immunoreactivity (BLI) has been demonstrated in neurons of the gastrointestinal tract and gastric BLI secretion can be demonstrated in response to the classical neurotransmitter acetylcholine. Since structurally related peptides VIP, PHI and GRF have to be considered as peptidergic neurotransmitters it was of interest to determine their effect on gastric BLI secretion. Additionally, somatostatin (SLI) and gastrin secretion was examined. The isolated stomach of overnight fasted rats was perfused with Krebs-Ringer buffer via the celiac artery and the effluent was collected via the portal vein. The gastric lumen was perfused with isotonic saline at pH7 or pH2. All four peptides were tested at a dose of 10(-11) M and 10(-8) M at both pH levels and in addition the effect of VIP and PHI was examined at 10(-14) M and 10(-12) M during luminal pH2. At luminal pH7 VIP and PHI stimulated SLI release at 10(-8) M but had no effect on BLI or gastrin secretion. rGRF and hpGRF were both ineffective on SLI and gastrin release while rGRF inhibited and hpGRF stimulated BLI secretion. This effect was not dose related. At luminal pH2 all four peptides stimulated BLI secretion. Stimulation by PHI was already observed at a dose of 10(-14) M while VIP elicited a stimulatory effect at 10(-12) M. PHI at the two lowest concentrations of 10(-14) and 10(-12) M elicited a stimulation of SLI and gastrin release while the same doses of VIP and the higher doses of all four peptides had no effect on SLI and gastrin secretion at an acidic intraluminal pH.(ABSTRACT TRUNCATED AT 250 WORDS)     

Loss of cell polarity drives tumor growth and invasion through JNK activation in Drosophila

Apparent defects in cell polarity are often seen in human cancer. However, the underlying mechanisms of how cell polarity disruption contributes to tumor progression are unknown. Here, using a Drosophila genetic model for Ras-induced tumor progression, we show a molecular link between loss of cell polarity and tumor malignancy. Mutation of different apicobasal polarity genes activates c-Jun N-terminal kinase (JNK) signaling and downregulates the E-cadherin/beta-catenin adhesion complex, both of which are necessary and sufficient to cause oncogenic Ras(V12)-induced benign tumors in the developing eye to exhibit metastatic behavior. Furthermore, activated JNK and Ras signaling cooperate in promoting tumor growth cell autonomously, as JNK signaling switches its proapoptotic role to a progrowth effect in the presence of oncogenic Ras. Our finding that such context-dependent alterations promote both tumor growth and metastatic behavior suggests that metastasis-promoting mutations may be selected for based primarily on their growth-promoting capabilities. Similar oncogenic cooperation mediated through these evolutionarily conserved signaling pathways could contribute to human cancer progression.     

Myc-Induced Liver Tumors in Transgenic Zebrafish Can Regress in tp53 Null Mutation

Hepatocellular carcinoma (HCC) is currently one of the top lethal cancers with an increasing trend. Deregulation of MYC in HCC is frequently detected and always correlated with poor prognosis. As the zebrafish genome contains two differentially expressed zebrafish myc orthologs, myca and mycb, it remains unclear about the oncogenicity of the two zebrafish myc genes. In the present study, we developed two transgenic zebrafish lines to over-express myca and mycb respectively in the liver using a mifepristone-inducible system and found that both myc genes were oncogenic. Moreover, the transgenic expression of myca in hepatocytes caused robust liver tumors with several distinct phenotypes of variable severity. ~5% of myca transgenic fish developing multinodular HCC with cirrhosis after 8 months of induced myca expression. Apoptosis was also observed with myca expression; introduction of homozygous tp53^-/- mutation into the myca transgenic fish reduced apoptosis and accelerated tumor progression. The malignant status of hepatocytes was dependent on continued expression of myca; withdrawal of the mifepristone inducer resulted in a rapid regression of liver tumors, and the tumor regression occurred even in the tp53^-/- mutation background. Thus, our data demonstrated the robust oncogenicity of zebrafish myca and the requirement of sustained Myc overexpression for maintenance of the liver tumor phenotype in this transgenic model. Furthermore, tumor regression is independent of the function of Tp53.     

Acquisition order of Ras and p53 gene alterations defines distinct adrenocortical tumor phenotypes

Sporadic adrenocortical carcinomas (ACC) are rare endocrine neoplasms with a dismal prognosis. By contrast, benign tumors of the adrenal cortex are common in the general population. Whether benign tumors represent a separate entity or are in fact part of a process of tumor progression ultimately leading to an ACC is still an unresolved issue. To this end, we have developed a mouse model of tumor progression by successively transducing genes altered in adrenocortical tumors into normal adrenocortical cells. The introduction in different orders of the oncogenic allele of Ras (H-Ras(G12V)) and the mutant p53(DD) that disrupts the p53 pathway yielded tumors displaying major differences in histological features, tumorigenicity, and metastatic behavior. Whereas the successive expression of Ras(G12V) and p53(DD) led to highly malignant tumors with metastatic behavior, reminiscent of those formed after the simultaneous introduction of p53(DD) and Ras(G12V), the reverse sequence gave rise only to benign tumors. Microarray profiling revealed that 157 genes related to cancer development and progression were differentially expressed. Of these genes, 40 were up-regulated and 117 were down-regulated in malignant cell populations as compared with benign cell populations. This is the first evidence-based observation that ACC development follows a multistage progression and that the tumor phenotype is directly influenced by the order of acquisition of genetic alterations.     

Dual-wavelength imaging of tumor progression by activatable and targeting near-infrared fluorescent probes in a bioluminescent breast cancer model

Bioluminescence imaging (BLI) has shown its appeal as a sensitive technique for in vivo whole body optical imaging. However, the development of injectable tumor-specific near-infrared fluorescent (NIRF) probes makes fluorescence imaging (FLI) a promising alternative to BLI in situations where BLI cannot be used or is unwanted (e.g., spontaneous transgenic tumor models, or syngeneic mice to study immune effects).In this study, we addressed the questions whether it is possible to detect tumor progression using FLI with appropriate sensitivity and how FLI correlates with BLI measurements. In addition, we explored the possibility to simultaneously detect multiple tumor characteristics by dual-wavelength FLI (~700 and ~800 nm) in combination with spectral unmixing. Using a luciferase-expressing 4T1-luc2 mouse breast cancer model and combinations of activatable and targeting NIRF probes, we showed that the activatable NIRF probes (ProSense680 and MMPSense680) and the targeting NIRF probes (IRDye 800CW 2-DG and IRDye 800CW EGF) were either activated by or bound to 4T1-luc2 cells. In vivo, we implanted 4T1-luc2 cells orthotopically in nude mice and were able to follow tumor progression longitudinally both by BLI and dual-wavelength FLI. We were able to reveal different probe signals within the tumor, which co-localized with immuno-staining. Moreover, we observed a linear correlation between the internal BLI signals and the FLI signals obtained from the NIRF probes. Finally, we could detect pulmonary metastases both by BLI and FLI and confirmed their presence histologically.Taken together, these data suggest that dual-wavelength FLI is a feasible approach to simultaneously detect different features of one tumor and to follow tumor progression with appropriate specificity and sensitivity. This study may open up new perspectives for the detection of tumors and metastases in various experimental models and could also have clinical applications, such as image-guided surgery.     

Prostate-specific expression of p53(R172L) differentially regulates p21, Bax, and mdm2 to inhibit prostate cancer progression and prolong survival

Loss of heterozygosity or mutation at the p53 tumor suppressor gene locus is frequently associated with advanced human prostate cancer. Hence, replacement p53 gene therapy may prove to be efficacious for this disease. While many mutations result in p53 molecules with oncogenic properties, other variants may possess wild-type properties with increased tumor suppressor activity. We have chosen to investigate the activity of a naturally occurring variant p53 molecule, p53(R172L), carrying an arginine-to-leucine mutation at codon 172. We demonstrate that p53(R172L) can differentially activate expression of genes involved in cell cycle control and apoptosis in vitro. Transgenic mice expressing a subphysiological level of a p53(R172L) minigene (PB-p53(R172L)) in the prostate epithelium were generated and bred to the transgenic adenocarcinoma mouse prostate (TRAMP) model of prostate cancer. While PB-p53(R172L) transgenic mice developed normally with no detectable prostate gland phenotype, we observed a significant increase in the apoptotic index in the prostate glands of TRAMP x PB-p53(R172L) F1 mice. We noted an increase in the expression of Bax in the bigenic mice concomitant with the reduced incidence and rate of tumor growth and increased survival. While low-level expression of the p53(R172L) variant had no obvious influence on normal prostate tissue, it was able to significantly inhibit prostate cancer progression in the context of a genetically predisposed model system. This suggests that additional tumor-related events specifically influence the ability of the variant p53(R172L) molecule to inhibit tumor growth. These studies support gene therapy strategies employing specific p53 variants.     

No Requirement for V(D)J Recombination in p53-Deficient Thymic Lymphoma

The p53 tumor suppressor is activated in response to a variety of cellular stress signals, although specific in vivo signals that trigger tumor suppression are unknown. In mouse thymocytes, where p53 inactivation leads to tumorigenesis, several observations suggest that V(D)J recombination of T-cell receptor (TCR) loci could provide a DNA damage signal triggering p53-dependent apoptosis and tumor suppression. Inactivation of p53 would allow V(D)J driven mutation of additional cancer genes, facilitating tumorigenesis. Here, we show that mice with a p53 deficiency in thymocytes and unable to carry out V(D)J recombination are not impaired in the development of thymoma. Recombination-activating gene (RAG) deficiencies were introduced into both p53^−/− mice and TgTΔN transgenic mice, a strain in which 100% of the mice develop thymoma due to thymocyte-specific inactivation of p53 by a simian virus 40 T-antigen variant. V(D)J recombination was dispensable for tumorigenesis since thymomas developed with or without the RAG-1 or RAG-2 gene, although some delay was observed. When V(D)J recombination was suppressed by expression of rearranged TCR transgenes, 100% of the TgTΔN mice developed thymoma, surprisingly with reduced latency. Further introduction of a RAG deficiency into these mice had no impact on the timing or frequency of tumorigenesis. Finally, karyotype and chromosome painting analyses showed no evidence for TCR gene translocations in p53-deficient thymomas, although abundant aneuploidy involving frequent duplication of certain chromosomes was present. Thus, contrary to the current hypothesis, these studies indicate that signals other than V(D)J recombination promote p53 tumor suppression in thymocytes and that the mechanism of tumorigenesis is distinct from TCR translocation oncogene activation.     

Regulation of cellular senescence by p53.

Many normal cells respond to potentially oncogenic stimuli by undergoing cellular senescence, a state of irreversibly arrested proliferation and altered differentiated function. Cellular senescence very likely evolved to suppress tumorigenesis. In support of this idea, it is regulated by several tumor suppressor genes. At the heart of this regulation is p53. p53 is essential for the senescence response to short telomeres, DNA damage, oncogenes and supraphysiological mitogenic signals, and overexpression of certain tumor suppressor genes. Despite the well-documented central role for p53 in the senescence response, many questions remain regarding how p53 senses senescence-inducing stimuli and how it elicits the senescent phenotype.     

Multi-modality imaging identifies key times for annexin V imaging as an early predictor of therapeutic outcome

Radiolabeled annexin V may provide an early indication of the success or failure of anticancer therapy on a patient-by-patient basis as an in vivo marker of tumor cell killing. An important question that remains is when, after initiation of treatment, should annexin V imaging be performed. To address this issue, we obtained simultaneous in vivo measurements of tumor burden and uptake of radiolabeled annexin V in the syngeneic orthotopic murine BCL1 lymphoma model using in vivo bioluminescence imaging (BLI) and small animal single-photon emission computed tomography (SPECT). BCL1 cells labeled for fluorescence and bioluminescence assays (BCL1-gfp/luc) were injected into mice at a dose that leads to progressive disease within two to three weeks. Tumor response was followed by BLI and SPECT before and after treatment with a single dose of 10 mg/kg doxorubicin. Biodistribution analyses revealed a biphasic increase of annexin V uptake within the tumor-bearing tissues of mice. An early peak occurring before actual tumor cells loss was observed between 1 and 5 hr after treatment, and a second longer sustained rise from 9 to 24 hr after therapy, which heralds the onset of tumor cell loss as confirmed by BLI. Multimodality imaging revealed the temporal patterns of tumor cell loss and annexin V uptake revealing a better understanding of the timing of radiolabeled annexin V uptake for its development as a marker of therapeutic efficacy.     

Comprehensive Evaluation of the Anti-Angiogenic and Anti-Neoplastic Effects of Endostar on Liver Cancer through Optical Molecular Imaging

Molecular imaging enables non-invasive monitoring of tumor growth, progression, and drug treatment response, and it has become an important tool to promote biological studies in recent years. In this study, we comprehensively evaluated the in vivo anti-angiogenic and anti-neoplastic effects of Endostar on liver cancer based on the optical molecular imaging systems including micro-computer tomography (Micro-CT), bioluminescence molecular imaging (BLI) and fluorescence molecular tomography (FMT). Firefly luciferase (fLuc) and green fluorescent protein (GFP) dual labeled human hepatocellular carcinoma cells (HCC-LM3-fLuc-GFP cells) were used to establish the subcutaneous and orthotopic liver tumor model. After the tumor cells were implanted 14∼18 days, Endostar (5 mg/kg/day) was administered through an intravenous tail vein injection for continuous 14 days. The computer tomography angiography (CTA) and BLI were carried out for the subcutaneous tumor model. FMT was executed for the orthotopic tumor model. The CTA data showed that tumor vessel formation and the peritumoral vasculature of subcutaneous tumor in the Endostar treatment group was significantly inhibited compared to the control group. The BLI data exhibited the obvious tumor inhibition day 8 post-treatment. The FMT detected the tumor suppression effects of Endostar as early as day 4 post-treatment and measured the tumor location. The above data confirmed the effects of Endostar on anti-angiogenesis and tumor suppression on liver cancer. Our system combined CTA, BLI, and FMT to offer more comprehensive information about the effects of Endostar on the suppression of vessel and tumor formation. Optical molecular imaging system enabled the non-invasive and reliable assessment of anti-tumor drug efficacy on liver cancer.     

Dual-modality monitoring of tumor response to cyclophosphamide therapy in mice with bioluminescence imaging and small-animal positron emission tomography

The purpose of this study was to noninvasively monitor the therapeutic efficacy of cyclophosphamide (CTX) in a mouse model by dual-modality molecular imaging: positron emission tomography (PET) and bioluminescence imaging (BLI). Firefly luciferase (fLuc) transfected HCC-LM3-fLuc human hepatocellular carcinoma cells were injected subcutaneously into BALB/c nude mice to establish the experimental tumor model. Two groups of HCC-LM3-fLuc tumor-bearing mice (n = 7 per group) were treated with saline or CTX (100 mg/kg on days 0, 2, 5, and 7). BLI and (18)F-fluorodeoxyglucose ((18)F-FDG) PET scans were done to evaluate the treatment efficacy. CTX induced a 25.25 ± 13.13% and 35.91 ± 25.85% tumor growth inhibition rate on days 9 and 12 posttreatment, respectively, as determined by BLI. A good linear correlation was found between the tumor sizes measured by caliper and the BLI signals determined by optical imaging (R(2) = .9216). (18)F-FDG imaging revealed a significant uptake reduction in the tumors of the CTX-treated group compared to that in the saline control group (5.30 ± 1.97 vs 3.00 ± 2.11% ID/g) on day 16 after CTX treatment. Dual-modality molecular imaging using BLI and small-animal PET can play important roles in the process of chemotherapy and will provide noninvasive and reliable monitoring of the therapeutic response.     

In Vivo imaging of differences in early donor cell proliferation in graft-versus-host disease hosts with different pre-conditioning doses

Graft-versus-host disease (GVHD) results from immunemediated attacks on recipient tissues by donor-originated cells through the recognition of incompatible antigens expressed on host cells. The pre-conditioning irradiation dose is a risk factor influencing GVHD severity. In this study, using newly generated luciferase transgenic mice on a B6 background (B6.Luc^Tg) as bone marrow and splenocyte donors, we explored the effects of irradiation doses on donor cell dynamics in major histocompatibility complex (MHC)-matched allogeneic GVHD hosts via bioluminescence imaging (BLI). Results from BLI of GVHD hosts showed higher emission intensities of luminescence signals from hosts irradiated with 900 cGy as compared with those irradiated with 400 cGy. In particular, BLI signals from target organs, such as the spleen, liver, and lung, and several different lymph nodes fluctuated with similar time kinetics soon after transplantation, reflecting the synchronous proliferation of donor cells in the different organs in hosts irradiated with 900 cGy. The kinetic curves of the BLI signals were not synchronized between the target organs and the secondary organs in hosts irradiated with 400 cGy. These results demonstrate that pre-conditioning doses influence the kinetics and degree of proliferation in the target organs soon after transplantation. The results from this study are the first describing donor cell dynamics in MHC-matched allogeneic GVHD hosts and the influence of irradiation doses on proliferation dynamics, and will provide spatiotemporal information to help understand GVHD pathophysiology.     

Large E1B proteins of adenovirus types 5 and 12 have different effects on p53 and distinct roles in cell transformation.

The formation of complexes between oncoproteins of DNA tumor viruses and the cellular protein p53 is thought to result in inactivation of the growth suppressor function of p53. In cells transformed by nononcogenic human adenovirus type 5 (Ad5), the 55-kDa protein encoded by E1B forms a stable complex with p53 and sequesters it in the cytoplasm. However, the homologous 54-kDa protein of highly oncogenic Ad12 does not detectably associate with p53. Yet in Ad12-transformed cells, p53 is metabolically stable, is present at high levels in the nucleus, and contributes to the oncogenicity of the cells. Such properties have previously been described for mutant forms of p53. Here, we show that stable p53 in Ad12-transformed cells is wild type rather than mutant and that stabilization of p53 is a direct consequence of the expression of the Ad12 E1B protein. We also compared the effects of the E1B proteins on transformation of rodent cells by different combinations of oncogenes. A synergistic interaction was observed for the gene encoding the 54-kDa E1B protein of Ad12 with myc plus ras oncogenes, resembling the effect of mutant p53 on myc plus ras. In contrast, the Ad5 55-kDa E1B protein strongly inhibited transformation by myc plus ras but stimulated transformation by E1A plus ras. The data are explained in terms of different interactions of the two E1B proteins with endogenous p53. The results suggest that in cultured rat cells, endogenous wild-type p53 plays an essential role in cell proliferation, even in the presence of myc plus ras. The dependence on p53 is lost, however, when the adenovirus E1A oncogene is present.