Tissue-specific expression pattern of vascular endothelial growth factor isoforms in the malignant transformation of lung and colon

How VEGF-A and its splice variants affect breast cancer development - clinical implications

BACKGROUND

Altered expression levels and structural variations in the vascular endothelial growth factor (VEGF) have been found to play important roles in cancer development and to be associated with the overall survival and therapy response of cancer patients. Particularly VEGF-A and its splice variants have been found to affect physiological and pathological angiogenic processes, including tumor angiogenesis, correlating with tumor progression, mostly caused by overexpression. This review focuses on the expression and impact of VEGF-A splice variants under physiologic conditions and in tumors and, in particular, the distribution and role of isoform VEGF165b in breast cancer.

CONCLUSIONS AND PERSPECTIVES

Many publications already highlighted the importance of VEGF-A and its splice variants in tumor therapy, especially in breast cancer, which are summarized in this review. Furthermore, we were able to demonstrate that cytoplasmatic VEGFA/165b expression is higher in invasive breast cancer tumor cells than in normal tissues or stroma. These examples show that the detection of VEGF splice variants can be performed also on the protein level in formalin fixed tissues. Although no quantitative conclusions can be drawn, these results may be the starting point for further studies at a quantitative level, which can be a major step towards the design of targeted antibody-based (breast) cancer therapies.

Evaluation of recombinant human vascular endothelial growth factor VEGF121-loaded poly-l-lactide microparticles as a controlled release delivery system

Vascular endothelial growth factor A (VEGF-A) is an important growth factor that plays a major role in angiogenesis. With different isoforms distributed in various tissues, the shortest isoform of VEGF-A is VEGF121, one of the physiologically functional variants next to VEGF165. It is well known that VEGF has a shorter half-life, and the stability of the protein must be considered in therapeutic aspects. Poly-l-lactide (PLA) microparticles can release the encapsulated protein in a sustained release mode. In this study, the VEGF121 gene was cloned and expressed in a prokaryotic expression system (Escherichia coli). The recombinant VEGF121 was encapsulated with PLA microparticles and studied in vitro  and ex ovo  for the sustained release mechanism. The PLA-VEGF microparticles and the recombinant VEGF121 were explored for their bioactivity in human umbilical vein endothelial cells (HUVEC). VEGF released in vitro  from PLA microparticles on days 1, 20, and 30 showed remarkable biological activity compared to PBS-loaded PLA microparticles such as the ability of the cells to proliferate, migrate, and form tubes similar to recombinant VEGF121. Besides, PLA-VEGF microparticles and the recombinant VEGF121 were also tested for their proangiogenic action in embryonated eggs by chicken chorioallantoic membrane assay (CAM), and the effect was observed in both forms. This study suggests that PLA-loaded VEGF microparticles in a sustainable release format can be effectively used in proangiogenic therapy and reduce the adverse effects caused due to multiple dosages.

Tissue differences revealed by gene expression profiles of various cell lines

Mechanisms through which tissues are formed and maintained remain unknown but are fundamental aspects in biology. Tissue-specific gene expression is a valuable tool to study such mechanisms. But in many biomedical studies, cell lines, rather than human body tissues, are used to investigate biological mechanisms Whether or not cell lines maintain their tissue-specific characteristics after they are isolated and cultured outside the human body remains to be explored. In this study, we applied a novel computational method to identify core genes that contribute to the differentiation of cell lines from various tissues. Several advanced computational techniques, such as Monte Carlo feature selection method, incremental feature selection method, and support vector machine (SVM) algorithm, were incorporated in the proposed method, which extensively analyzed the gene expression profiles of cell lines from different tissues. As a result, we extracted a group of functional genes that can indicate the differences of cell lines in different tissues and built an optimal SVM classifier for identifying cell lines in different tissues. In addition, a set of rules for classifying cell lines were also reported, which can give a clearer picture of cell lines in different issues although its performance was not better than the optimal SVM classifier. Finally, we compared such genes with the tissue-specific genes identified by the Genotype-tissue Expression project. Results showed that most expression patterns between tissues remained in the derived cell lines despite some uniqueness that some genes show tissue specificity.

Altered VEGF Splicing Isoform Balance in Tumor Endothelium Involves Activation of Splicing Factors Srpk1 and Srsf1 by the Wilms' Tumor Suppressor Wt1

Angiogenesis is one hallmark of cancer. Vascular endothelial growth factor (VEGF) is a known inducer of angiogenesis. Many patients benefit from antiangiogenic therapies, which however have limitations. Although VEGF is overexpressed in most tumors, different VEGF isoforms with distinct angiogenic properties are produced through alternative splicing. In podocytes, the Wilms' tumor suppressor 1 (WT1) suppresses the Serine/arginine-rich protein-specific splicing factor kinase (SRPK1), and indirectly Serine/arginine-rich splicing factor 1 (Srsf1) activity, and alters VEGF splicing. We analyzed VEGF isoforms, Wt1, Srpk1, and Srsf1 in normal and tumor endothelium. Wt1, Srpk1, Srsf1, and the angiogenic VEGF164a isoform were highly expressed in tumor endothelium compared to normal lung endothelium. Nuclear expression of Srsf1 was detectable in the endothelium of various tumor types, but not in healthy tissues. Inducible conditional vessel-specific knockout of Wt1 reduced Wt1, Srpk1, and Srsf1 expression in endothelial cells and induced a shift towards the antiangiogenic VEGF120 isoform. Wt1(-KTS) directly binds and activates both the promoters of Srpk1 and Srsf1 in endothelial cells. In conclusion, Wt1 activates Srpk1 and Srsf1 and induces expression of angiogenic VEGF isoforms in tumor endothelium.

Quantification of VEGF Isoforms and VEGFR Transcripts by qRT-PCR and Their Significance in Acute Myeloid Leukemia

Vascular endothelial growth factor (VEGF) and its receptors are known to play an important role in normal and pathological hematopoiesis but the prognostic impact of VEGF isoform transcripts in acute myeloid leukemia (AML) has not been addressed. We conducted a single-institution prospective study to analyze the impact of these angiogenic factors and the expression of their receptors on the survival of adult patients newly diagnosed with AML. We investigated the levels of VEGF transcript isoforms VEGF121, -145, -165, -189 and -206 and their receptors, VEGFR-1 and VEGFR-2, using quantitative reverse transcriptase polymerase chain reaction assays in peripheral blood mononuclear cells (PBMCs) of 67 consecutive AML patients at diagnosis. VEGF total protein was measured for comparison with mRNA levels in PBMCs. The VEGF121 splice variant transcript in AML PBMCs was significantly higher than in the normal controls. VEGF transcripts were quantified in all samples while its protein was detected in 42/67 (63%) of AML samples. High levels of VEGF121, VEGF165 transcripts and VEGF protein in AML were significantly related to a worse prognosis when analyzing overall survival (p<0.0001, p=0.019 and p=0.012, respectively) or event-free survival (p<0.0001, p=0.010 and p=0.047) using univariate analysis. In multivariable analysis only VEGF121 expression remained an independent prognostic factor for either event-free survival or overall survival [aHR=8.83 (3.48–22.4), p<0.0001, and aHR=9.52 (3.41–26.6), p<0.0001]. No prognostic value was observed for the other isoforms and the two receptors. Our findings show that the level of VEGF121 mRNA in circulating cells from AML patients is a strong independent prognostic parameter, which could be useful in the management of unselected AML patients.

Expression, purification and functionality of bioactive recombinant human vascular endothelial growth factor VEGF165 in E. coli

Vascular endothelial growth factor (VEGF) is associated with tumour growth and metastasis. Because VEGF is the major player in both angiogenesis and vascular permeability and the most explored factor in angio-inhibitory therapies, many expression procedures have been developed to produce functional VEGF₁₆₅ in convenient yield. In this study, recombinant human VEGF₁₆₅ was cloned and expressed in Escherichia coli (BL21)-DE3 cells and large scale production was performed by fermentation. A high yield of active soluble protein was obtained after protein extraction employing both lysozyme and sonication treatment. Inclusion bodies were also isolated from the cell lysate and subjected to a simple protocol of solubilisation and refolding. Single-step purification was performed using nickel affinity chromatography and the purified proteins were able to recognize monoclonal Anti-poly-His antibody. The biological activity of the VEGF₁₆₅ was successfully tested using the Chicken chorioallantoic membrane assay, wound-healing migration and proliferation assay on human umbilical vein endothelial cells (HUVEC).

Alternative splicing of VEGFA, APP and NUMB genes in colorectal cancer

AIM

To investigate alternative splicing in vascular endothelial growth factor A (VEGFA), amyloid beta precursor protein (APP), and Numb homolog (NUMB) in colorectal cancer (CRC).

METHODS

Real-time quantitative reverse transcriptase polymerase chain reaction (qRT-PCR) and PCR-restriction fragment length polymorphism analyses were performed to detect the expression of VEGFA, APP, and NUMB mRNA in 20 CRC tissues and matched adjacent normal tissues, as well as their alternative splicing variants.

RESULTS

qRT-PCR analysis revealed that the expression of APP, NUMB, and VEGFA165b mRNA were significantly downregulated, while VEGFA mRNA was upregulated, in CRC tissues (all P < 0.05). PCR-restriction fragment length polymorphism analysis revealed that the expression of VEGFA165a/b in CRC tissues was significantly higher than in adjacent normal tissues (P < 0.05). Compared with adjacent normal tissues, the expression of NUMB-PRR(S) in CRC tissues was significantly decreased (P < 0.05), and the expression of NUMB-PRR(L) was increased (P < 0.05).

CONCLUSION

Alternative splicing of VEGFA, APP, and NUMB may regulate the development of CRC, and represent new targets for its diagnosis, prognosis, and treatment.

VEGFA isoforms play a vital role in oral cancer progression

Angiogenesis plays an important role in tumor growth and prognostication. A key angiogenesis stimulator is vascular endothelial growth factor (VEGF). The present investigation aimed to study contribution of VEGFA isoforms in oral cancer progression. Reverse transcription polymerase chain reaction and ELISA were employed to analyze tissue VEGFA isoforms and serum VEGF levels, respectively, in 109 oral cancer cases and 50 controls. VEGF183 and VEGF165 were significantly downregulated in malignant tissues as compared to adjacent normal tissues. VEGF183 and VEGF189 were significantly associated with tumor differentiation and tumor size. VEGF165 was significantly higher in recurrent early stage tumors. Serum VEGF levels were significantly higher in cases as compared to the controls and were associated with tumor differentiation. Serum VEGF levels were significantly higher in patients with recurrent advanced stage tumors. Further, patients with high levels of VEGF165 and serum VEGF levels had the worst prognosis. VEGFA isoform status and serum VEGF levels play a significant role in the progression as well as prognosis of oral cancer.

Microfluidic source-sink model reveals effects of biophysically distinct CXCL12 isoforms in breast cancer chemotaxis

Chemokines critically regulate chemotaxis in normal and pathologic states, but there is limited understanding of how multicellular interactions generate gradients needed for cell migration. Previous studies of chemotaxis of CXCR4+ cells toward chemokine CXCL12 suggest the requirement of cells expressing scavenger receptor CXCR7 in a source-sink system. We leveraged an established microfluidic device to discover that chemotaxis of CXCR4 cells toward distinct isoforms of CXCL12 required CXCR7 scavenging only under conditions with higher than optimal levels of CXCL12. Chemotaxis toward CXCL12-β and -γ isoforms, which have greater binding to extracellular molecules and have been largely overlooked, was less dependent on CXCR7 than the more commonly studied CXCL12-α. Chemotaxis of CXCR4+ cells toward even low levels of CXCL12-γ and CXCL12-β still occurred during treatment with a FDA-approved inhibitor of CXCR4. We also detected CXCL12-γ only in breast cancers from patients with advanced disease. Physiological gradient formation within the device facilitated interrogation of key differences in chemotaxis among CXCL12 isoforms and suggests CXCL12-γ as a biomarker for metastatic cancer.

Compartment model predicts VEGF secretion and investigates the effects of VEGF trap in tumor-bearing mice

Angiogenesis, the formation of new blood vessels from existing vasculature, is important in tumor growth and metastasis. A key regulator of angiogenesis is vascular endothelial growth factor (VEGF), which has been targeted in numerous anti-angiogenic therapies aimed at inhibiting tumor angiogenesis. Systems biology approaches, including computational modeling, are useful for understanding this complex biological process and can aid in the development of novel and effective therapeutics that target the VEGF family of proteins and receptors. We have developed a computational model of VEGF transport and kinetics in the tumor-bearing mouse, which includes three-compartments: normal tissue, blood, and tumor. The model simulates human tumor xenografts and includes human (VEGF121 and VEGF165) and mouse (VEGF120 and VEGF164) isoforms. The model incorporates molecular interactions between these VEGF isoforms and receptors (VEGFR1 and VEGFR2), as well as co-receptors (NRP1 and NRP2). We also include important soluble factors: soluble VEGFR1 (sFlt-1) and α-2-macroglobulin. The model accounts for transport via macromolecular transendothelial permeability, lymphatic flow, and plasma clearance. We have fit the model to available in vivo experimental data on the plasma concentration of free VEGF Trap and VEGF Trap bound to mouse and human VEGF in order to estimate the rates at which parenchymal cells (myocytes and tumor cells) and endothelial cells secrete VEGF. Interestingly, the predicted tumor VEGF secretion rates are significantly lower (0.007-0.023 molecules/cell/s, depending on the tumor microenvironment) than most reported in vitro measurements (0.03-2.65 molecules/cell/s). The optimized model is used to investigate the interstitial and plasma VEGF concentrations and the effect of the VEGF-neutralizing agent, VEGF Trap (aflibercept). This work complements experimental studies performed in mice and provides a framework with which to examine the effects of anti-VEGF agents, aiding in the optimization of such anti-angiogenic therapeutics as well as analysis of clinical data. The model predictions also have implications for biomarker discovery with anti-angiogenic therapies.

Predicting the effects of anti-angiogenic agents targeting specific VEGF isoforms

Vascular endothelial growth factor (VEGF) is a key mediator of angiogenesis, whose effect on cancer growth and development is well characterized. Alternative splicing of VEGF leads to several different isoforms, which are differentially expressed in various tumor types and have distinct functions in tumor blood vessel formation. Many cancer therapies aim to inhibit angiogenesis by targeting VEGF and preventing intracellular signaling leading to tumor vascularization; however, the effects of targeting specific VEGF isoforms have received little attention in the clinical setting. In this work, we investigate the effects of selectively targeting a single VEGF isoform, as compared with inhibiting all isoforms. We utilize a molecular-detailed whole-body compartment model of VEGF transport and kinetics in the presence of breast tumor. The model includes two major VEGF isoforms, VEGF(121) and VEGF(165), receptors VEGFR1 and VEGFR2, and co-receptors Neuropilin-1 and Neuropilin-2. We utilize the model to predict the concentrations of free VEGF, the number of VEGF/VEGFR2 complexes (considered to be pro-angiogenic), and the receptor occupancy profiles following inhibition of VEGF using isoform-specific anti-VEGF agents. We predict that targeting VEGF(121) leads to a 54% and 84% reduction in free VEGF in tumors that secrete both VEGF isoforms or tumors that overexpress VEGF(121), respectively. Additionally, 21% of the VEGFR2 molecules in the blood are ligated following inhibition of VEGF(121), compared with 88% when both isoforms are targeted. Targeting VEGF(121) reduces tumor free VEGF and is an effective treatment strategy. Our results provide a basis for clinical investigation of isoform-specific anti-VEGF agents.

Pharmacokinetics and pharmacodynamics of VEGF-neutralizing antibodies

Background

Vascular endothelial growth factor (VEGF) is a potent regulator of angiogenesis, and its role in cancer biology has been widely studied. Many cancer therapies target angiogenesis, with a focus being on VEGF-mediated signaling such as antibodies to VEGF. However, it is difficult to predict the effects of VEGF-neutralizing agents. We have developed a whole-body model of VEGF kinetics and transport under pathological conditions (in the presence of breast tumor). The model includes two major VEGF isoforms VEGF₁₂₁ and VEGF₁₆₅, receptors VEGFR1, VEGFR2 and co-receptors Neuropilin-1 and Neuropilin-2. We have added receptors on parenchymal cells (muscle fibers and tumor cells), and incorporated experimental data for the cell surface density of receptors on the endothelial cells, myocytes, and tumor cells. The model is applied to investigate the action of VEGF-neutralizing agents (called "anti-VEGF") in the treatment of cancer.

Results

Through a sensitivity study, we examine how model parameters influence the level of free VEGF in the tumor, a measure of the response to VEGF-neutralizing drugs. We investigate the effects of systemic properties such as microvascular permeability and lymphatic flow, and of drug characteristics such as the clearance rate and binding affinity. We predict that increasing microvascular permeability in the tumor above 10^-5 cm/s elicits the undesired effect of increasing tumor interstitial VEGF concentration beyond even the baseline level. We also examine the impact of the tumor microenvironment, including receptor expression and internalization, as well as VEGF secretion. We find that following anti-VEGF treatment, the concentration of free VEGF in the tumor can vary between 7 and 233 pM, with a dependence on both the density of VEGF receptors and co-receptors and the rate of neuropilin internalization on tumor cells. Finally, we predict that free VEGF in the tumor is reduced following anti-VEGF treatment when VEGF₁₂₁ comprises at least 25% of the VEGF secreted by tumor cells.

Conclusions

This study explores the optimal drug characteristics required for an anti-VEGF agent to have a therapeutic effect and the tumor-specific properties that influence the response to therapy. Our model provides a framework for investigating the use of VEGF-neutralizing drugs for personalized medicine treatment strategies.

VEGF-A and its isoform VEGF₁₂₁ mRNA expression measured by quantitative real-time RT-PCR: correlation with F-18 FDG uptake and aggressiveness of lung adenocarcinoma: preliminary study

OBJECTIVE

To investigate the correlation of vascular endothelial growth factor (VEGF) A and its isoform VEGF₁₂₁ mRNA expression with F-18 fluorodeoxyglucose (FDG) uptake and aggressiveness in lung adenocarcinoma.

METHODS

Twenty-three patients with lung adenocarcinoma underwent FDG PET before surgery. As semi-quantitative analysis for FDG uptake, partial volume corrected standardized uptake value (PVC-SUV) of the tumor was calculated. Total RNA from lung adenocarcinoma tissue was prepared from the frozen specimens. Using the real-time reverse transcription polymerase chain reaction method, we analyzed the mRNA level of VEGF-A and VEGF-A isoform VEGF₁₂₁ mRNA level. 18S ribosomal RNA was used as an endogenous control.

RESULTS

VEGF-A and VEGF₁₂₁ mRNA levels had significantly positive correlation with PVC-SUV in lung adenocarcinoma (r = 0.477, p = 0.021, r = 0.539, p = 0.008, respectively), while they were not correlated with tumor size (≤3 or >3 cm). VEGF-A and VEGF₁₂₁ mRNA levels of the low FDG uptake group were significantly lower than those of the high FDG uptake group (p = 0.005 and p = 0.004, respectively). FDG uptake (PCV-SUV) of aggressive lung adenocarcinoma was higher than that of non-aggressive lung adenocarcinoma (p = 0.01). VEGF-A and VEGF₁₂₁ mRNA levels of aggressive lung adenocarcinoma were higher than those of non-aggressive lung adenocarcinoma (p = 0.0001 and p = 0.0001, respectively).

CONCLUSION

VEGF-A and VEGF₁₂₁ mRNA levels may correlate with FDG uptake and aggressiveness in lung adenocarcinoma. These findings support the hypothesis that VEGF-A and VEGF₁₂₁ may help in predicting the outcome in patients with lung adenocarcinoma.

The transcription factor E2F1 and the SR protein SC35 control the ratio of pro-angiogenic versus antiangiogenic isoforms of vascular endothelial growth factor-A to inhibit neovascularization in vivo

The transcription factor E2F1 has a crucial role in the control of cell growth and has been shown to regulate neoangiogenesis in a p53-dependent manner through inhibition of activity of the VEGF-A (vascular endothelial growth factor) promoter. Besides being regulated by transcription, VEGF-A is also highly regulated by pre-mRNA alternative splicing, resulting in the expression of several VEGF isoforms with either pro-(VEGF(xxx)) or anti-(VEGF(xxx)b) angiogenic properties. Recently, we identified the SR (Ser-Rich/Arg) protein SC35, a splicing factor, as a new transcriptional target of E2F1. Here, we show that E2F1 downregulates the activity of the VEGF-A promoter in tumour cells independently of p53, leading to a strong decrease in VEGF(xxx) mRNA levels. We further show that, strikingly, E2F1 alters the ratio of pro-VEGF(xxx) versus anti-VEGF(xxx)b angiogenic isoforms, favouring the antiangiogenic isoforms, by a mechanism involving the induction of SC35 expression. Finally, using lung tumour xenografts in nude mice, we provide evidence that E2F1 and SC35 proteins increase the VEGF(165)b/VEGF ratio and decrease tumour neovascularization in vivo. Overall, these findings highlight E2F1 and SC35 as two regulators of the VEGF(xxx)/VEGF(xxx)b angiogenic switch in human cancer cells, a role that could be crucial during tumour progression, as well as in tumour response to antiangiogenic therapies.

Nerve growth factor promotes breast cancer angiogenesis by activating multiple pathways

Background

Although several anti-angiogenic therapies have been approved in the treatment of cancer, the survival benefits of such therapies are relatively modest. Discovering new molecules and/or better understating signaling pathways of angiogenesis is therefore essential for therapeutic improvements. The objective of the present study was to determine the involvement of nerve growth factor (NGF) in breast cancer angiogenesis and the underlying molecular mechanisms.

Results

We showed that both recombinant NGF and NGF produced by breast cancer cells stimulated angiogenesis in Matrigel plugs in immunodeficient mice. NGF strongly increased invasion, cord formation and the monolayer permeability of endothelial cells. Moreover, NGF-stimulated invasion was under the control of its tyrosine kinase receptor (TrkA) and downstream signaling pathways such as PI3K and ERK, leading to the activation of matrix metalloprotease 2 and nitric oxide synthase. Interestingly, NGF increased the secretion of VEGF in both endothelial and breast cancer cells. Inhibition of VEGF, with a neutralizing antibody, reduced about half of NGF-induced endothelial cell invasion and angiogenesis in vivo.

Conclusions

Our findings provided direct evidence that NGF could be an important stimulator for breast cancer angiogenesis. Thus, NGF, as well as the activated signaling pathways, should be regarded as potential new targets for anti-angiogenic therapy against breast cancer.

Endothelial heparan sulfate in angiogenesis

Heparan sulfate (HS) is a linear polysaccharide composed of 50-200 glucosamine and uronic acid (glucuronic acid or iduronic acid) disaccharide repeats with epimerization and various sulfation modifications. HS is covalently attached to core proteins to form HS-proteoglycans. Most of the functions of HS-proteoglycans are mediated by their HS moieties. The biosynthesis of HS is initiated by chain polymerization and is followed by stepwise modification reactions, including sulfation and epimerization. These modifications generate ligand-binding sites that modulate cell functions and activities of proteinases and/or proteinase inhibitors. HS is abundantly expressed in developing and mature vasculature, and understanding its roles in vascular biology and related human diseases is an area of intense investigation. In this chapter, we summarize the significant recent advances in our understanding of the roles of HS in developmental and pathological angiogenesis with a major focus on studies using transgenic as well as gene knockout/knockdown models in mice and zebrafish. These studies have revealed that HS critically regulates angiogenesis by playing a proangiogenic role, and this regulatory function critically depends on HS fine structure. The latter is responsible for facilitating cell-surface binding of various proangiogenic growth factors that in turn mediate endothelial growth signaling. In cancer, mouse studies have revealed important roles for endothelial cell-surface HS as well as matrix-associated HS, wherein signaling by multiple growth factors as well as matrix storage of growth factors may be regulated by HS. We also discuss important mediators that may fine-tune such regulation, such as heparanase and sulfatases; and models wherein targeting HS (or core protein) biosynthesis may affect tumor growth and vascularization. Finally, the importance of targeting HS in other human diseases wherein angiogenesis may play pathophysiologic (or even therapeutic) roles is considered.

Identification of an exonic splicing silencer in exon 6A of the human VEGF gene

Background

The different isoforms of vascular endothelial growth factor (VEGF) play diverse roles in vascular growth, structure and function. Alternative splicing of the VEGF gene results in the expression of three abundant isoforms: VEGF121, VEGF165 and VEGF189. The mRNA for VEGF189 contains the alternatively spliced exon 6A whereas the mRNA for VEGF165 lacks this exon. The objective of this study was to identify the cis elements that control utilization of exon 6A. A reporter minigene was constructed (pGFP-E6A) containing the coding sequence for GFP whose translation was dependent on faithful splicing for removal of the VEGF exon 6A. To identify cis-acting splicing elements, sequential deletions were made across exon 6A in the pGFP-E6A plasmid.

Results

A candidate cis-acting exonic splicing silencer (ESS) comprising nucleotides 22-30 of exon 6A sequence was identified corresponding to the a silencer consensus sequence of AAGGGG. The function of this sequence as an ESS was confirmed in vivo both in the context of the reporter minigene as a plasmid and in the context of a longer minigene with VEGF exon 6A in its native context in an adenoviral gene transfer vector. Further mutagenesis studies resulted in the identification of the second G residue of the putative ESS as the most critical for function.

Conclusion

This work establishes the identity of cis sequences that regulate alternative VEGF splicing and dictate the relative expression levels of VEGF isoforms.

The importance of -460 C/T and +405 G/C single nucleotide polymorphisms to the function of vascular endothelial growth factor A in colorectal cancer

PURPOSE

The present study investigated the functional influence of the single nucleotide polymorphisms (SNPs) -460 C/T and +405 G/C at vascular endothelial growth factor A (VEGF-A), mRNA and protein levels in colorectal cancer (CRC) and normal colorectal tissue.

METHODS

Blood and tissue were collected from 113 patients surgically resected for colorectal cancer. SNPs were analysed from genomic DNA by PCR, the VEGF-A gene expression analysis was performed by RT-PCR and protein analysis by ELISA.

RESULTS

The T-allele in the -460 C/T SNP and the C-allele in the +405 G/C SNP were associated with significantly lower VEGF-A protein levels in normal colorectal tissue. There were no differences in protein levels in the malignant tissue according to genotypes. No differences were observed at the gene expression levels either.

CONCLUSION

The results indicate that the two SNPs have a functional influence on the VEGF-A protein levels in normal colorectal tissue. The possible clinical implications of the findings need further investigation.

Molecular diversity of VEGF-A as a regulator of its biological activity

The vascular endothelial growth factor (VEGF) family of proteins regulates blood flow, growth, and function in both normal physiology and disease processes. VEGF-A is alternatively spliced to form multiple isoforms, in two subfamilies, that have specific, novel functions. Alternative splicing of exons 5-7 of the VEGF gene generates forms with differing bioavailability and activities, whereas alternative splice-site selection in exon 8 generates proangiogenic, termed VEGF(xxx), or antiangiogenic proteins, termed VEGF(xxx)b. Despite its name, emerging roles for VEGF isoforms on cell types other than endothelium have now been identified. Although VEGF-A has conventionally been considered to be a family of proangiogenic, propermeability vasodilators, the identification of effects on nonendothelial cells, and the discovery of the antiangiogenic subfamily of splice isoforms, has added further complexity to their regulation of microvascular function. The distally spliced antiangiogenic isoforms are expressed in normal human tissue, but downregulated in angiogenic diseases, such as cancer and proliferative retinopathy, and in developmental pathologies, such as Denys Drash syndrome and preeclampsia. Here, we examine the molecular diversity of VEGF-A as a regulator of its biological activity and compare the role of the pro- and antiangiogenic VEGF-A splice isoforms in both normal and pathophysiological processes.

Alternative splicing in lung cancer

Alterations in alternative splicing affect essential biologic processes and are the basis for a number of pathologic conditions, including cancer. In this review we will summarize the evidence supporting the relevance of alternative splicing in lung cancer. An example that illustrates this relevance is the altered balance between Bcl-xL and Bcl-xS, two splice variants of the apoptosis regulator Bcl-x. Splice modifications in cancer-related genes can be associated with modifications either in cis-acting splicing regulatory sequences or in trans-acting splicing factors. In fact, lung tumors show abnormal expression of splicing regulators such as ASF/SF2 or some members of the heterogeneous nuclear ribonucleoprotein family. The potential significance of alternative splicing as a target for lung cancer diagnosis or treatment will also be discussed.

The positive correlation between gene expression of the two angiogenic factors: VEGF and BMP-2 in lung cancer patients

Lung cancer is a particular challenge in oncology. More than 1 million new cases occur worldwide every year and despite many clinical trials and modern diagnostic techniques, long-term survival rate has only marginally improved. The aim of the current research is to explore new molecular prognostic factors and identify new targets for anticancer therapy. Current evidence shows that angiogenesis is controlled by several angiogenic factors including VEGF and BMP-2. It has been also demonstrated that VEGF plays a key role in this process that is essential in carcinogenesis. Our study has shown that the expressions of the VEGF, BMP-2 and BMP-4 mRNAs were significantly higher (7.1-fold, 25.6-fold and 2.3-fold, respectively) in lung cancer samples than in adjacent normal lung tissues (real-time RT-PCR). Analysis based on the Pearson's correlation coefficient indicated the positive correlation between VEGF and BMP-2 gene expression, whereas no significant correlation between VEGF and BMP-4 gene expression was found. The mean+/-standard deviation serum level of VEGF was 423+/-136 pg/ml. Significant differences in the serum levels of VEGF between patients with T1 tumors and patients with T2, T3 or T4 tumors were observed. Patients with T2, T3 and T4 tumors, respectively, had 1.6-fold, 1.8-fold and 2.3-fold greater serum levels of VEGF than their peers with T1 tumors. In current study patients homozygous for the 936T allele of the +936C/T VEGF gene polymorphism had 12-fold lower VEGF gene expression and 1.3-fold lower VEGF serum level than patients homozygous for the 936C allele. In conclusion, our findings underline the importance of the two angiogenic factors namely VEGF and BMP-2 as well as +936C/T VEGF gene polymorphism in the evaluation of lung cancer patients.

Alternative splicing and disease

Almost all protein-coding genes are spliced and their majority is alternatively spliced. Alternative splicing is a key element in eukaryotic gene expression that increases the coding capacity of the human genome and an increasing number of examples illustrates that the selection of wrong splice sites causes human disease. A fine-tuned balance of factors regulates splice site selection. Here, we discuss well-studied examples that show how a disturbance of this balance can cause human disease. The rapidly emerging knowledge of splicing regulation now allows the development of treatment options.

Usefulness of contrast-enhanced magnetic resonance imaging for evaluating solitary pulmonary nodules

Evaluation of solitary pulmonary nodules (SPNs) poses a challenge to radiologists. Chest computed tomography (CT) is considered the standard technique for assessing morphologic findings and intrathoracic spread of an SPN. Although the clinical role of magnetic resonance imaging (MRI) for SPNs remains limited, considerable experience has been gained with MRI of thoracic diseases. Dynamic MRI and dynamic CT are useful for differentiating between malignant and benign SPNs (especially tuberculomas and hamartomas). Furthermore, dynamic MRI is useful for assessing tumor vascularity, interstitium, and vascular endothelial growth factor expression, and for predicting survival outcome among patients with peripheral pulmonary carcinoma. These advantages make dynamic MRI a promising method and a potential biomarker for characterizing tumor response to anti-angiogenic treatment as well as for predicting survival outcomes after treatment.

Overexpression of vascular endothelial growth factor 189 in breast cancer cells leads to delayed tumor uptake with dilated intratumoral vessels

Vascular endothelial growth factor (VEGF) is essential for breast cancer progression and is a relevant target in anti-angiogenesis. Although VEGF121 and VEGF165, the fully or partially secreted isoforms, respectively, have been the focus of intense studies, the role of the cell-associated VEGF189 isoform is not understood. To clarify the contribution of VEGF189 to human mammary carcinogenesis, we established several clones of MDA-MB-231 cells stably overexpressing VEGF189 (V189) and VEGF165 (V165). V189 and V165 clones increased tumor growth and angiogenesis in vivo. Remarkably, V165 induced the most rapid tumor uptake, whereas V189 increased vasodilation. In vitro overexpression of VEGF165 and VEGF189 increases the proliferation and chemokinesis of these cancer cells. Interestingly, overexpression of VEGF189 increased cell adhesion on fibronectin (1.9-fold) and vitronectin (1.6-fold), as compared to VEGF165, through alpha5beta1 and alphavbeta5 integrins. Using the BIACore system we demonstrated for the first time that VEGF189 binds directly to neuropilin-1, which is strongly expressed in MDA-MB-231 cells. In contrast, VEGF-R2 was not significantly expressed and VEGF-R1 was expressed at low level. Our in vitro results suggest an autocrine effect of VEGF189 on breast cancer cells, probably through neuropilin-1. In conclusion, our data indicate that VEGF189 participates in mammary tumor growth through both angiogenesis and nonangiogenic functions. Whether VEGF189 overexpression is correlated to prognosis in human breast tumors remains to be established.

Quantitative real-time reverse transcription PCR study of the expression of vascular endothelial growth factor (VEGF) splice variants and VEGF receptors (VEGFR-1 and VEGFR-2) in non small cell lung cancer

BACKGROUND

Vascular endothelial growth factor (VEGF) is a major regulator of angiogenesis and its expression is increased in non-small cell lung cancer (NSCLC). We aimed to determine the expression pattern of VEGF splice variants in NSCLC and its correlation with the clinicopathological characteristics of tumors.

METHODS

We used real-time reverse transcription PCR to quantify the mRNA expression of total VEGF, 4 VEGF splice variants (VEGF(121), VEGF(165), VEGF(183), and VEGF(189)), and 2 VEGF receptors (VEGFR-1 and VEGFR-2) in 27 pairs of cancerous and adjacent noncancerous tissues originating from patients with NSCLC.

RESULTS

Total VEGF, VEGF(121), and VEGF(165) were expressed in all specimens, whereas VEGF(183) and VEGF(189) were present in small amounts in certain samples. Total VEGF, VEGF(121), and VEGF(165) mRNA was upregulated in cancerous compared with healthy tissues, whereas VEGF(183) and VEGF(189) expression tended to be higher in healthy tissues. The expression of VEGFRs was similar between matched specimens. No correlation was found between the expression of total VEGF or VEGF splice variants and the clinicopathological characteristics of tumors. The expression patterns of VEGF splice variants differed between tissue pairs. VEGF(121) was the major variant expressed in all samples; however, its relative expression was higher in cancerous tissues. The relative expression of VEGF(183) and VEGF(189) was upregulated in healthy lung tissues, whereas the ratio of VEGF(165) to total VEGF was similar between matched specimens.

CONCLUSIONS

The expression pattern of certain VEGF splice variants is altered during tumorigenesis. Our data support the hypothesis that during malignant progression an angiogenic switch favoring the shorter diffusible isoforms occurs.

Increased expression of VEGF121/VEGF165-189 ratio results in a significant enhancement of human prostate tumor angiogenesis

Vascular endothelial growth factor (VEGF) is a proangiogenic factor upregulated in many tumors. The alternative splicing of VEGF mRNA renders 3 major isoforms of 121, 165 and 189 amino-acids in humans (1 less amino-acid for each mouse VEGF isoform). We have designed isoform specific real time QRT-PCR assays to quantitate VEGF transcripts in mouse and human normal and malignant prostates. In the human normal prostate, VEGF(165) was the predominant isoform (62.8% +/- 5.2%), followed by VEGF(121) (22.5% +/- 6.3%) and VEGF(189) (p < 0.001) (14.6% +/- 2.1%). Prostate tumors showed a significant increase in the percentage of VEGF(121) and decreases in VEGF(165) (p < 0.01) and VEGF(189) (p < 0.05). However, the amount of total VEGF mRNA was similar between normal and malignant prostates. VEGF(164) was the transcript with the highest expression in the mouse normal prostate. Unlike human prostate cancer, tumors from TRAMP mice demonstrated a significant increase in total VEGF mRNA levels and in each of the VEGF isoforms, without changes in the relative isoform ratios. Morpholino phosphorodiamide antisense oligonucleotide technology was used to increase the relative amount of VEGF(121) while proportionally decreasing VEGF(165) and VEGF(189) levels in human prostate cell lines, through the modification of alternative splicing, without changing transcription levels and total amount of VEGF. The increase in the VEGF(121)/VEGF(165-189) ratio in PC3 cells resulted in a dramatic increase in prostate tumor angiogenesis in vivo. Our results underscore the importance of VEGF(121) in human prostate carcinoma and demonstrate that the relative expression of the different VEGF isoforms has an impact on prostate carcinogenesis.

Hypoxia and angiogenesis in pancreatic cancer

BACKGROUND

Pancreatic cancer remains one of the most lethal of all solid tumours of the gastrointestinal tract. It is characterized by late diagnosis, aggressive local invasion, early metastasis and resistance to chemoradiotherapy. Increasing knowledge regarding the molecular events behind the growth and invasion of pancreatic cancer may lead to new targets for intervention.

METHODS

A search of Pubmed and Medline databases was undertaken using the keywords pancreatic cancer, gastrointestinal cancer, hypoxia, angiogenesis and anti-angiogenesis therapy.

RESULTS

Hypoxia is the driving force behind angiogenesis in pancreatic cancers. Research into angiogenesis has shown many different sites that can be targeted by agents such as tyrosine kinase inhibitors.

CONCLUSION

Anti-angiogenic therapy could be an important adjunct to conventional chemotherapy treatment of gastrointestinal neoplasia.

Alternative splicing and differential gene expression in colon cancer detected by a whole genome exon array

Background

Alternative splicing is a mechanism for increasing protein diversity by excluding or including exons during post-transcriptional processing. Alternatively spliced proteins are particularly relevant in oncology since they may contribute to the etiology of cancer, provide selective drug targets, or serve as a marker set for cancer diagnosis. While conventional identification of splice variants generally targets individual genes, we present here a new exon-centric array (GeneChip Human Exon 1.0 ST) that allows genome-wide identification of differential splice variation, and concurrently provides a flexible and inclusive analysis of gene expression.

Results

We analyzed 20 paired tumor-normal colon cancer samples using a microarray designed to detect over one million putative exons that can be virtually assembled into potential gene-level transcripts according to various levels of prior supporting evidence. Analysis of high confidence (empirically supported) transcripts identified 160 differentially expressed genes, with 42 genes occupying a network impacting cell proliferation and another twenty nine genes with unknown functions. A more speculative analysis, including transcripts based solely on computational prediction, produced another 160 differentially expressed genes, three-fourths of which have no previous annotation. We also present a comparison of gene signal estimations from the Exon 1.0 ST and the U133 Plus 2.0 arrays.

Novel splicing events were predicted by experimental algorithms that compare the relative contribution of each exon to the cognate transcript intensity in each tissue. The resulting candidate splice variants were validated with RT-PCR. We found nine genes that were differentially spliced between colon tumors and normal colon tissues, several of which have not been previously implicated in cancer. Top scoring candidates from our analysis were also found to substantially overlap with EST-based bioinformatic predictions of alternative splicing in cancer.

Conclusion

Differential expression of high confidence transcripts correlated extremely well with known cancer genes and pathways, suggesting that the more speculative transcripts, largely based solely on computational prediction and mostly with no previous annotation, might be novel targets in colon cancer. Five of the identified splicing events affect mediators of cytoskeletal organization (ACTN1, VCL, CALD1, CTTN, TPM1), two affect extracellular matrix proteins (FN1, COL6A3) and another participates in integrin signaling (SLC3A2). Altogether they form a pattern of colon-cancer specific alterations that may particularly impact cell motility.

Unique vascular phenotypes following over-expression of individual VEGFA isoforms from the developing lens

Formation of a correctly organised vasculature and subsequently embryonic survival is critically dependent on the dosage and site-specific expression of VEGF. Murine VEGF exists in three common isoforms (viz. 120, 164 and 188 amino acids) having different organ specific distribution levels. Gene knock-in studies show that expression of any of the individual isoforms of VEGF extends survival until birth, although each is associated with distinct organ-specific abnormalities. Comparison of the effects of VEGF isoform expression is complicated by the general lethality of mis-expression, in addition to cumulative effects of adjacent tissues from the inappropriately patterned vasculature. Here we investigate the effects of over-expression of individual VEGFA isoforms from the lens-specific alphaA-Crystallin promoter and characterise their effects on the vessel morphology of the hyaloid and developing retinal vasculature. Since the hyaloid vasculature is an anatomically distinct, transient vasculature of the eye, comprising 3 cell types (endothelium, pericytes and macrophages) it is possible to more readily interpret the role of individual VEGF-A isoforms in vascular pattern formation in this model. The severity of the vascular phenotype, characterised by a hyperplastic hyaloid at E13.5 and subsequently retinal vascular patterning and ocular defects, is most severe in transgenics over-expressing the more diffusible forms of VEGFA (120 and 164), whereas in VEGFA(188) transgenics the hyaloid vascular defects partially resolve post-natally. The results of this study indicate that individual isoforms of VEGFA induce distinct vascular phenotypes in the eye during embryonic development and that their relative doses provide instructive cues for vascular patterning.

Clinicopathological significance of stromal variables: angiogenesis, lymphangiogenesis, inflammatory infiltration, MMP and PINCH in colorectal carcinomas

Cancer research has mainly focused on alterations of genes and proteins in cancer cells themselves that result in either gain-of-function in oncogenes or loss-of-function in tumour-suppressor genes. However, stromal variables within or around tumours, including blood and lymph vessels, stromal cells and various proteins, have also important impacts on tumour development and progression. It has been shown that disruption of stromal-epithelial interactions influences cellular proliferation, differentiation, death, motility, genomic integrity, angiogenesis, and other phenotypes in various tissues. Moreover, stromal variables are also critical to therapy in cancer patients. In this review, we mainly focus on the clinicopathological significance of stromal variables including angiogenesis, lymphangiogenesis, inflammatory infiltration, matrix metalloproteinase (MMP), and the particularly interesting new cysteine-histidine rich protein (PINCH) in colorectal cancer (CRC).

Decline in angiogenic factors, such as interleukin-8, indicates response to chemotherapy of metastatic melanoma

Serum concentrations of angiogenic factors have been reported to correlate with tumour burden and prognosis in metastatic melanoma. The present study was performed to assess the value of angiogenic factors in serum in indicating response or failure to chemotherapy and immunochemotherapy in stage IV melanoma. Thirty-five patients suffering from stage IV melanoma according to the American Joint Committee on Cancer (AJCC) criteria were included in this prospective study. Before and following chemotherapy or immunochemotherapy, serum levels of vascular endothelial growth factor (VEGF), basic fibroblast growth factor (bFGF), platelet-derived growth factor (PDGF-AB), vascular cell adhesion molecule-1 (VCAM-1) and interleukin-8 (IL-8) were measured. Staging examinations following chemotherapy revealed 15 patients with response to therapy (complete response, partial response, stable disease), 14 patients with progressive disease and six patients with mixed response. Patients who responded to therapy showed a significant decrease in the serum level of IL-8 at the time of staging examinations, whereas patients with progressive disease did not. Following chemotherapy, serum concentrations of PDGF-AB had significantly decreased in both patients with response and patients with progressive disease. Comparing the VEGF and bFGF levels of responders and non-responders after a single administration of cytostatics showed significantly lower concentrations in patients with response to therapy. In all patients, a high intra- and inter-individual variability of serum values was observed during application of therapy. It can be concluded that low IL-8 serum levels after chemotherapy indicate response to chemotherapy in stage IV melanoma patients. The persistence of elevated serum levels of VEGF and bFGF following the initial cytostatic administration may help to identify patients resistant to chemotherapy. The distinct variability of serum levels indicates that processes other than tumour angiogenesis also influence the serum concentration of the examined angiogenic factors.

Overexpression of vascular endothelial growth factor and its receptors in bronchial dypslasia demonstrated by quantitative RT-PCR analysis

Neoangiogenesis is required for the growth of invasive lung carcinoma, however, the role of angiogenesis in the progression of premalignant changes to carcinoma of the lung is less clear. We have evaluated vascular endothelial growth factor (VEGF) expression and microvessel densities (MVDs) in 62 bronchoscopic biopsies from normal, reactive (basal cell hyperplasia (BCH)) and dysplastic bronchial epithelium and in tissue from twenty-seven invasive lung carcinomas in an effort to demonstrate angiogenic activity in these preneoplastic lesions and determine whether it is associated with increased bronchial epithelial VEGF expression. MVDs and VEGF RNA expression measured by quantitative RT-PCR were found to be elevated in comparison to normal bronchial tissue in bronchial dysplasias and invasive lung carcinomas but not in basal cell hyperplasias. Immunohistochemical (IHC) analyses revealed that expression of VEGF arose predominantly from bronchial epithelium. ELISA analysis of lung tumor tissue showed that elevated VEGF protein expression correlated with VEGF RNA levels (r=0.59, p=0.004). Increased expression of VEGF RNA was also found in histologically normal bronchial mucosa from patients with either dysplasia at other sites or a history of heavy tobacco use suggesting a possible field effect in regard to the elaboration of VEGF. Furthermore, analysis of VEGF isoforms and VEGF receptors by semi-quantitative RT-PCR in dysplastic and invasive lesions revealed characteristic altered patterns of expression in dysplasia and early cancer as compared to normal tissue. These results indicate that angiogenesis develops early in lung carcinogenesis and is associated with overexpression of VEGF.

The induction of vascular endothelial growth factor by ultrafine carbon black contributes to the increase of alveolar-capillary permeability

Ultrafine carbon black (ufCB) can cause proinflammatory response and increase alveolar-capillary permeability. However, the mechanism underlying the increased permeability is not well characterized. Vascular endothelial growth factor (VEGF) is originally recognized as a vascular permeability factor. Oxidative stress generated by hydrogen peroxide (H2O2) stimulates VEGF gene expression. The purpose of this study was to explore the role of VEGF in ufCB-induced alveolar-capillary permeability. Intratracheal instillation of 200 microg ufCB in mice caused a significant and sustained increase of total proteins in bronchoalveolar lavage (BAL) fluid, with the maximal increase at 21 hr postinstillation. The influx of neutrophils did not significantly increase until 16 hr. It reached the highest level at 21 hr and returned to the basal level by 42 hr. Tumor necrosis factor-alpha was significantly elevated only at 4 hr. ufCB induced significant increases of VEGF in BAL fluid throughout the study period, with the peak increase at 16 hr. The nonsecreted isoform VEGF188 was not altered after 16 hr of exposure to ufCB. Moreover, there was a strong correlation between VEGF and total proteins in BAL fluid (R2 = 0.7352, p < 0.01). In vivo study supported the role of reactive oxygen species (ROSs) in ufCB-induced VEGF release and protein leakage. The involvement of ROSs was strengthened by the fact that interventions with N-acetylcysteine prevented ufCB-induced generation of ROSs and VEGF in vitro. Our study for the first time demonstrates that ufCB induces the production of VEGF, which is associated with the increase of alveolar-capillary permeability. The induction of VEGF by ufCB acts through an ROS-dependent pathway.

Preclinical data targeting vascular endothelial growth factor in colorectal cancer

Vascular endothelial growth factor (VEGF) is the driving force behind angiogenesis in most solid malignancies. This also holds true for colorectal cancer (CRC), where increased levels of VEGF in primary cancers are associated with increased microvessel density and poor prognosis. These findings have led to preclinical studies evaluating the efficacy of anti-VEGF therapy in inhibiting the growth of CRC in ectopic and orthotopic locations. In preclinical models, numerous approaches to inhibit VEGF activity led to decreased tumor growth and angiogenesis. These studies led to clinical trials in which, unfortunately, single-agent anti-VEGF therapy was relatively ineffective for patients with metastatic CRC. However, combinations of anti-VEGF therapies with chemotherapy have clearly demonstrated clinical benefit. Understanding the mechanisms of the role of VEGF in CRC angiogenesis and the effect of anti-VEGF therapy on the tumor vasculature will allow oncologists to optimize therapeutic regimens targeting VEGF and its receptors.

Aberrant and Alternative Splicing in Cancer

Pre-mRNA splicing is a sophisticated and ubiquitous nuclear process, which is a natural source of cancer-causing errors in gene expression. Intronic splice site mutations of tumor suppressor genes often cause exon-skipping events that truncate proteins just like classical nonsense mutations. Also, many studies over the last 20 years have reported cancer-specific alternative splicing in the absence of genomic mutations. Affected proteins include transcription factors, cell signal transducers, and components of the extracellular matrix. Antibodies against alternatively spliced products on cancer cells are currently in clinical trials, and competitive reverse transcription-PCR across regions of alternative splicing is being used as a simple diagnostic test. As well as being associated with cancer, the nature of the alternative gene products is usually consistent with an active role in cancer; therefore, the alternative splicing process itself is a potential target for gene therapy.

Up-regulation of the enzymes involved in prostacyclin synthesis via Ras induces vascular endothelial growth factor

BACKGROUND AND AIMS

The constitutive activation of Ras is an important step in the development and progression of several different cancers and is known to increase the level of cyclooxygenase 2 (COX-2). Prostaglandins are the downstream bioactive lipid mediators produced by the COX-2 enzyme. We sought to determine the role of Ras-induced up-regulation of the enzymes involved in prostacyclin biosynthesis in nontransformed rat intestinal epithelial cells (IECs).

METHODS

Messenger RNA (mRNA) and protein expression were analyzed by Northern and Western analysis, respectively, to determine the level of enzymes induced by Ras. In vitro assays were used to determine the production of vascular endothelial growth factor (VEGF) and prostaglandins as well as the promoter and enzymatic activation of the rate-limiting enzyme in prostaglandin production (phospholipase A(2) [cPLA(2)]).

RESULTS

The inducible expression of Ha-Ras(V12) increased the production of prostaglandin (PG)F(2alpha) and prostacyclin by 2- and 13-fold, respectively. The induction of Ha-Ras(V12) also up-regulated the mRNA and protein levels of cPLA(2), COX-2, and prostacyclin synthase, as well as the promoter and enzyme activity of cPLA(2). Furthermore, oncogenic Ras increased the production of the pro-angiogenic factor VEGF. The increase of VEGF was abolished after treatment with celecoxib, a selective COX-2 inhibitor. The addition of PGI 2 alone also induced the expression of VEGF.

CONCLUSIONS

Inducible Ha-Ras(V12) increases the production of PGI(2) through the coordinate up-regulation of cPLA(2), COX-2, and prostacyclin synthase (PGIS). The production of PGI(2) leads to an increase in the level of the pro-angiogenic factor VEGF, which is known to play a crucial role in the regulation of tumor-associated angiogenesis.

Angiogenesis in colorectal cancer: therapeutic implications and future directions

This article discusses the therapeutic implications and future directions of angiogenesis in colorectal cancer.

αCP-4, Encoded by a Putative Tumor Suppressor Gene at 3p21, But Not Its Alternative Splice Variant αCP-4a, Is Underexpressed in Lung Cancer

alpha CP-4 is an RNA-binding protein coded by PCBP4, a gene mapped to 3p21, a common deleted region in lung cancer. In this study we characterized the expression of alpha CP-4 and alpha CP-4a, an alternatively spliced variant of alpha CP-4, in lung cancer cell lines and non-small cell lung cancer (NSCLC) samples from early stage lung cancer patients. In NSCLC biopsies, an immunocytochemical analysis showed cytoplasmic expression of alpha CP-4 and alpha CP-4a in normal lung bronchiolar epithelium. In contrast, alpha CP-4 immunoreactivity was not found in 47% adenocarcinomas and 83% squamous cell carcinomas, whereas all of the tumors expressed alpha CP-4a. Besides, lack of alpha CP-4 expression was associated with high proliferation of the tumor (determined by Ki67 expression). By fluorescence in situ hybridization, >30% of NSCLC cell lines and tumors showed allelic losses at PCBP4, correlating with the absence of the protein. On the other hand, no mutations in the coding region of the gene were found in any of the 24 cell lines analyzed. By Northern blotting and real-time reverse transcription-PCR, we detected the expression of alpha CP-4 and alpha CP-4a messages in NSCLC and small cell lung cancer cell lines. Our data demonstrate an abnormal expression of alpha CP-4 in lung cancer, possibly associated with an altered processing of the alpha CP-4 mRNA leading to a predominant expression of alpha CP-4a. This may be considered as an example of alternative splicing involved in tumor suppressor gene inactivation. Finally, induction of alpha CP-4 expression reduced cell growth, in agreement with its proposed role as a tumor suppressor, and suggesting an association of this RNA-binding protein with lung carcinogenesis.

Expression of neuropilin-1 in high-grade dysplasia, invasive cancer, and metastases of the human gastrointestinal tract

Neuropilin-1 (NRP-1) functions as an axonal guidance molecule in the developing nervous system, and recent work has identified NRP-1 up-regulation in several cancers, including neuroblastomas and breast carcinoma. We examined for the first time NRP-1 expression in a large variety of gastrointestinal carcinomas and precursor lesions to determine whether NRP-1 up-regulation correlated with invasive growth in this system. Protein expression and localization of NRP-1 were studied by immunolabeling and semiquantification in >300 dysplastic, invasive, and metastatic lesions of the gastrointestinal tract, and confirmation of NRP-1 protein expression was performed by Western blot analysis on pancreatic cancer cell lines. NRP-1 expression was limited within normal tissues of the gastrointestinal tract, with prominent labeling present only in endothelial cells, pancreatic islet cells, and the most apical colonic epithelium. Invasive cancer of the esophagus, gallbladder, ampulla of Vater, pancreas (endocrine and exocrine), and colon, however, all demonstrated striking NRP-1 expression. NRP-1 was also identified in precursor lesions of gastrointestinal adenocarcinomas, such as Barrett esophagus and colorectal adenomas. Within the spectrum of precursor lesions, a progressive increase in both intensity and area of expression was evident during histologic progression from low-grade to high-grade dysplasia. Notably, the most intense up-regulation of NRP-1 was apparent at or around the point of invasion, with focal expression of NRP-1 at levels equivalent to the invasive cancer (2- to 3-fold increase). Prominent labeling for NRP-1 was apparent in primary invasive cancers, liver metastases, and a subset of lymph node metastases, with a 2- to 3-fold increase of NRP-1 over dysplastic lesions. We conclude that increased expression of NRP-1 occurs in gastrointestinal adenocarcinomas and in a subset of high-grade precursor lesions. This up-regulation appears to parallel invasive behavior and may therefore be used as a potential marker for cancer aggressiveness in this system.

Angiogenesis and antiangiogenic therapy of colon cancer liver metastasis

The fact that tumor growth and metastatic spread relies on angiogenesis has been widely proven and accepted. The understanding of cancer biology and metastasis formation has led to the development of new therapeutic approaches that target tumor biology. The survival and establishment of metastatic lesions depend on a shift in the normal balance of proangiogenic and antiangiogenic factors that favor angiogenesis. Colorectal cancer is one of the leading cancer deaths worldwide. Angiogenesis has been associated with colon cancer progression and metastatic spread, thereby significantly affecting patient survival. New experimental approaches that inhibit angiogenic processes have demonstrated promising antineoplastic effects on metastatic colorectal cancer and are partially being investigated in clinical trials. This review focuses on angiogenesis in colorectal cancer metastasis formation as a target for antiangiogenic therapy, describing the experience from experimental studies and current clinical trials.

Small peripheral pulmonary carcinomas evaluated with dynamic MR imaging: correlation with tumor vascularity and prognosis

PURPOSE

To correlate the findings at contrast material-enhanced dynamic magnetic resonance (MR) imaging of small peripheral pulmonary carcinomas with tumor vascularity and prognosis.

MATERIALS AND METHODS

Ninety-four patients with small peripheral pulmonary carcinomas who underwent surgical resection were examined retrospectively. Pathologic specimens were stained with hematoxylin-eosin and elastin-van Gieson. CD34 and vascular endothelial growth factor (VEGF) were assessed immunohistochemically. Delineated CD34-positive cells were counted as microvessels. Dynamic MR imaging was performed prior to and at 1, 2, 3, 4, 5, 6, and 8 minutes after injection of a bolus of gadopentetate dimeglumine. The two observers reviewed all images, and two pathologists performed all histologic analyses; a decision was determined with consensus. The maximum enhancement ratio (MER), the time lapse between the completion of the injection and the point of maximum signal intensity (Tmax), the washout ratio, and the slope value of the time-signal intensity curve were correlated with the microvessel density. VEGF-positive and VEGF-negative tumors were compared. All statistical analyses were performed by using nonparametric methods.

RESULTS

The MER and the slope value were positively correlated, and the Tmax was negatively correlated (Spearman rank test, P <.0001, all comparisons) with the microvessel counts. The distribution of elastic and collagen fibers correlated with the washout ratio (Kruskal-Wallis test, P <.001). There was a statistically significant difference between the slope value of VEGF-positive tumors and that of VEGF-negative tumors (Mann-Whitney U test, P <.0001). Patients with VEGF-positive tumors had a significantly shorter overall survival than did those with VEGF-negative tumors (log-rank test, P <.0001).

CONCLUSION

Dynamic MR imaging findings correlate with tumor vascularity and may be helpful in the prediction of prognosis.

Requirement of different signaling pathways mediated by insulin-like growth factor-I receptor for proliferation, invasion, and VPF/VEGF expression in a pancreatic carcinoma cell line

Several oncogenes and growth factors are found to be mutated and overexpressed in adenocarcinoma of the pancreas, and may correlate with its highly aggressive nature. Insulin-like growth factor (IGF-I) and its receptor (IGF-IR) are highly expressed in this tumor type. We examined the IGF-IR-mediated signaling pathways in relation to cell proliferation, invasiveness, and expression pattern of vascular permeability factor/vascular endothelial growth factor (VPF/VEGF) in the pancreatic cancer line ASPC-1. Our findings show that IGF-IR is an important growth factor receptor for cell proliferation and invasion, and VPF/VEGF expression in ASPC-1. Further experiments indicate that IGF-IR mediates different signaling pathways to execute its functions. Activation of Ras by IGF-IR was found to be required for the cell invasion. On the other hand Src activation through IGF-IR is required for the cell proliferation, invasion, and also VPF/VEGF expression. Taken together, our data indicate the importance of IGF-IR in growth and invasiveness of the pancreatic cancer cell lines and also point out the multiple signaling pathways channeled through this receptor.

Angiogenesis in normal and neoplastic pituitary tissues

Angiogenesis, or the formation of new blood vessels, is a dynamic process needed for embryogenesis, post-natal growth, morphogenesis, tumorigenesis, and for other biological processes. Angiogenesis is very important for tumor development and progression. This review examines the activators and inhibitors of angiogenesis with emphasis on the pituitary gland and pituitary neoplasms. Some of the proteins regulating angiogenesis in pituitary tumors such as vascular endothelial growth factor (VEGF) and VEGF receptors, fibroblasts growth factors (FGF), transforming growth factor beta (TGFB), interleukins, interferons, and matrix metalloproteinases (MMPs) and inhibitors of MMPs have been examined in animal and human pituitary tumor models. However, many other significant regulators of angiogenesis including angiopoietins, angiostatin, and thrombospondins have not been studied extensively in pituitary tumors to date. Newer concepts and developments in angiogenesis such as vasculogenic mimicry and gene therapy approaches to angiogenesis in cancer treatment are also discussed.