Negative Regulator Of Tumor Growth Research Articles

Abstract 6811: IL-9 enhances lung tumor growth through intrinsic and ARG1-dependent transcriptomic changes in interstitial macrophages

Abstract A defining characteristic of cancer is its ability to evade detection by immune cells through the generation of a myeloid cell-dependent immunosuppressive tumor microenvironment. Arginine is utilized by Arginase 1 (ARG1) or nitric oxide synthase in tumor-associated macrophages to respectively elicit pro-tumor or anti-tumor activity. The balance between these enzymes is regulated by extracellular cytokines including Interleukin 9 (IL-9), a pleiotropic cytokine that can be a positive or negative regulator of tumor growth. Our lab identified that IL-9 promotes tumor development in the lung by expanding interstitial macrophage populations and inducing ARG1. Lung tumor growth is attenuated in mice with myeloid cell deficiency of Arg1. Similarly, macrophage-targeting nanoparticles containing Arg1 siRNA can therapeutically reduce tumor burden and alter macrophage populations in the lung toward an immunostimulatory phenotype. However, an understanding of the mechanism by which IL-9R/ARG1+ interstitial macrophages drive tumor progression remains incomplete. Here, using a B16F10 lung metastasis model in mixed-bone marrow chimeric mice, we demonstrate that IL-9-responsive interstitial macrophages are intrinsically altered at the transcriptomic level toward an ARG1-dependent immunosuppressive phenotype. Furthermore, our research shows that the absence of IL-9 signaling or ARG1 expression in macrophages has a notable impact on the levels of arginine and its metabolites in the lung tissue and bronchoalveolar lavage fluid of tumor-bearing mice. These alterations subsequently lead to an enhanced anti-tumoral immune response, reflected by changes in Interferon-gamma expression in both lung macrophages and T cells. Thus, our work suggests that the IL-9R/ARG1/interstitial macrophage axis promotes lung tumor development by altering intrinsic arginine metabolism and reprogramming immune cell populations toward an immunosuppressive phenotype. Citation Format: Anthony Cannon, Mark H. Kaplan. IL-9 enhances lung tumor growth through intrinsic and ARG1-dependent transcriptomic changes in interstitial macrophages [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 6811.

The expression of Duffy antigen receptor for chemokines by epithelial ovarian cancer decreases growth potential.

Epithelial ovarian cancer (EOC) is one of the main causes of cancer-associated mortality in females with gynecological malignancies. Duffy antigen receptor for chemokines (DARC) has previously been reported to be involved in tumor growth and the inhibition of tumor metastasis. However, the association between DARC and EOC remains unknown. The aim of the present study was to investigate the expression of DARC in the SKOV3 human epithelial ovarian cancer cell line with the establishment of a subcutaneous model in nude mice. To investigate the effects of DARC on the tumorigenesis of human epithelial ovarian cancer cells, GV287-DARC-L.V lentiviral vectors containing a DARC overexpression construct were transfected into SKOV3 cells. The present study revealed that transfection with DARC reduced the viability of SKOV3 cells in vitro by performing an MTT assay. SKOV3-DARC and SKOV3-negative control (NC) cells cultured in vitro were injected into nude mice to establish a subcutaneous model. The ovarian tumor volumes and the tumor weights were observed. Immunohistochemistry to detect CD31 expression was used to determine the microvessel density (MVD) in SKOV3-DARC and SKOV3-NC tumors. The results of the present study revealed that DARC-induced inhibition of tumor growth was associated with MVD in xenograft tumors. This suggested that DARC was a negative regulator of tumor growth in EOC, primarily via the inhibition of tumor angiogenesis.

Identification and frequency of the rs12516 and rs8176318 BRCA1 gene polymorphisms among different populations.

Genetic mutation of breast cancer 1 (BRCA1) is one of the most notable factors responsible for a proportion of breast cancer cases. BRCA1 encodes a 1,863-amino acid protein and functions as a negative regulator of tumor growth. Thus, investigation of the underlying mechanisms that regulate BRCA1 gene expression provide further insight into possible targets for breast cancer therapy. Previous studies have demonstrated that the genetic variants in the BRCA1 3' untranslated region (3'UTR), in addition to the cytosine-phosphate-guanine (CpG) islands in the promoter region, are significantly associated with breast cancer risk; however, the role of single nucleotide polymorphisms (SNPs) in the BRCA1 3'UTR remains unclear. The present study aimed to investigate the association between SNPs and BRCA1 mRNA expression levels. Bioinformatics analysis demonstrated that 2 SNPs in the BRCA1 3'UTR (rs12516 and rs8176318 with putative microRNA binding sites) were significantly correlated with mRNA expression in lymphoblastoid cell lines (P=2.55×10-4 and P=8.78×10-5, respectively). Furthermore, the genotype frequency distribution varied between populations worldwide. In addition, 3 CpG islands and several transcription factor binding sites in the BRCA1 promoter region were established. The identification of such polymorphisms and CpG islands may aid in designing improved therapeutic strategies to treat patients with BRCA1-associated breast cancer.

P53 deficiency linked to B cell translocation gene 2 (BTG2) loss enhances metastatic potential by promoting tumor growth in primary and metastatic sites in patient-derived xenograft (PDX) models of triple-negative breast cancer

BackgroundDespite advances in early diagnosis and treatment of cancer patients, metastasis remains the major cause of mortality. TP53 is one of the most frequently mutated genes in human cancer, and these alterations can occur during the early stages of oncogenesis or as later events as tumors progress to more aggressive forms. Previous studies have suggested that p53 plays a role in cellular pathways that govern metastasis. To investigate how p53 deficiency contributes to late-stage tumor growth and metastasis, we developed paired isogenic patient-derived xenograft (PDX) models of triple-negative breast cancer (TNBC) differing only in p53 status for longitudinal analysis.MethodsPatient-derived isogenic human tumor lines differing only in p53 status were implanted into mouse mammary glands. Tumor growth and metastasis were monitored with bioluminescence imaging, and circulating tumor cells (CTCs) were quantified by flow cytometry. RNA-Seq was performed on p53-deficient and p53 wild-type tumors, and functional validation of a lead candidate gene was performed in vivo.ResultsIsogenic p53 wild-type and p53-deficient tumors metastasized out of mammary glands and colonized distant sites with similar frequency. However, p53-deficient tumors metastasized earlier than p53 wild-type tumors and grew faster in both primary and metastatic sites as a result of increased proliferation and decreased apoptosis. In addition, greater numbers of CTCs were detected in the blood of mice engrafted with p53-deficient tumors. However, when normalized to tumor mass, the number of CTCs isolated from mice bearing parental and p53-deficient tumors was not significantly different. Gene expression profiling followed by functional validation identified B cell translocation gene 2 (BTG2), a downstream effector of p53, as a negative regulator of tumor growth both at primary and metastatic sites. BTG2 expression status correlated with survival of TNBC patients.ConclusionsUsing paired isogenic PDX-derived metastatic TNBC cells, loss of p53 promoted tumor growth and consequently increased tumor cell shedding into the blood, thus enhancing metastasis. Loss of BTG2 expression in p53-deficient tumors contributed to this metastatic potential by enhancing tumor growth in primary and metastatic sites. Furthermore, clinical data support conclusions generated from PDX models and indicate that BTG2 expression is a candidate prognostic biomarker for TNBC.Electronic supplementary materialThe online version of this article (doi:10.1186/s13058-016-0673-9) contains supplementary material, which is available to authorized users.

Abstract 1201: Characterization of the effects of IDH2 mutations and (R)-2-HG in cancer progression

Abstract The isocitrate dehydrogenase (IDH) family of enzymes is central to cellular metabolism, catalyzing the oxidative decarboxylation of isocitrate to α-ketoglutarate (α-KG) and production of NADPH. Recently, cancer-associated heterozygous somatic mutations in family members IDH1 and IDH2 were discovered and present predominantly in glioblastoma multiforme and acute myeloid leukemia. The major consequence of these point mutations is the biochemical production of the ‘oncometabolite’ (R)-2-hydroxyglutarate [(R)-2-HG] from α-KG. Recent studies indicate that unalike mutations of IDH2 produce different intracellular levels of (R)-2-HG, suggesting that IDH2 mutations may differentially influence tumorigenesis. Contrasting clinical studies find IDH mutations to be associated either with increased metastatic potential, or higher survival and enhanced chemosensitivity probabilities. Nevertheless, these studies failed to indicate specifically which of the various IDH mutations were found in each of the patients’ tumors. This raises important questions as to whether specific IDH mutations contribute differently to tumorigenesis. In this study, specific IDH2 mutations were evaluated and compared for their chemosensitivity, tumorigenic activity, and production of (R)-2-HG- all notable determinants for their potential use as tumor biomarkers. Three individual clinically relevant IDH2 mutations (IDH2-R172K, -R172M, and -R140Q) or IDH2-WT were expressed in human U87MG glioblastoma cells. We observed distinct changes in cell morphology, proliferation, migration, invasion, anchorage-independent growth and response to chemotherapeutic agents. Differences in base-line activation of various stress pathways were also observed, lending a plausible explanation to the differing phenotypic outcomes. Interestingly, the variable levels of endogenous (R)-2-HG produced by the cell panel inversely correlated with their respective growth rates, implicating (R)-2-HG as a negative regulator of tumor growth. Indeed, treatment of tumor cell lines, expressing IDH2-WT, with exogenous (R)-2-HG induced a decrease in cell proliferation in a dose-dependent manner. When tested in vivo, treatment of tumor-bearing mice with (R)-2-HG significantly reduced tumor volume. These in vivo results complement the results of soft-agar colony forming assays, demonstrating again that (R)-2-HG inhibits tumor growth. In contrast, immortalized cells subjected to long-term (R)-2-HG treatment showed enhanced cell proliferation. Their response to (R)-2-HG, however, could be switched from growth promotion to that of growth inhibition through expression of oncogenic Ras. Thus, these findings demonstrate conclusively that IDH2 mutations are not alike and that oncometabolite (R)-2-HG plays dual roles in tumorigenesis. Citation Format: Kevin Kotredes, Ana M. Gamero. Characterization of the effects of IDH2 mutations and (R)-2-HG in cancer progression. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 1201. doi:10.1158/1538-7445.AM2015-1201

The DUSP26 phosphatase activator adenylate kinase 2 regulates FADD phosphorylation and cell growth.

Adenylate kinase 2 (AK2), which balances adenine nucleotide pool, is a multi-functional protein. Here we show that AK2 negatively regulates tumour cell growth. AK2 forms a complex with dual-specificity phosphatase 26 (DUSP26) phosphatase and stimulates DUSP26 activity independently of its AK activity. AK2/DUSP26 phosphatase protein complex dephosphorylates fas-associated protein with death domain (FADD) and regulates cell growth. AK2 deficiency enhances cell proliferation and induces tumour formation in a xenograft assay. This anti-growth function of AK2 is associated with its DUSP26-stimulating activity. Downregulation of AK2 is frequently found in tumour cells and human cancer tissues showing high levels of phospho-FADDSer194. Moreover, reconstitution of AK2 in AK2-deficient tumour cells retards both cell proliferation and tumourigenesis. Consistent with this, AK2+/− mouse embryo fibroblasts exhibit enhanced cell proliferation with a significant alteration in phospho-FADDSer191. These results suggest that AK2 is an associated activator of DUSP26 and suppresses cell proliferation by FADD dephosphorylation, postulating AK2 as a negative regulator of tumour growth.

Caveolin-1 is a negative regulator of tumor growth in glioblastoma and modulates chemosensitivity to temozolomide

Caveolin-1 (Cav-1) is a critical regulator of tumor progression in a variety of cancers where it has been shown to act as either a tumor suppressor or tumor promoter. In glioblastoma multiforme, it has been previously demonstrated to function as a putative tumor suppressor. Our studies here, using the human glioblastoma-derived cell line U-87MG, further support the role of Cav-1 as a negative regulator of tumor growth. Using a lentiviral transduction approach, we were able to stably overexpress Cav-1 in U-87MG cells. Gene expression microarray analyses demonstrated significant enrichment in gene signatures corresponding to downregulation of MAPK, PI3K/AKT and mTOR signaling, as well as activation of apoptotic pathways in Cav-1-overexpressing U-87MG cells. These same gene signatures were later confirmed at the protein level in vitro. To explore the ability of Cav-1 to regulate tumor growth in vivo, we further show that Cav-1-overexpressing U-87MG cells display reduced tumorigenicity in an ectopic xenograft mouse model, with marked hypoactivation of MAPK and PI3K/mTOR pathways. Finally, we demonstrate that Cav-1 overexpression confers sensitivity to the most commonly used chemotherapy for glioblastoma, temozolomide. In conclusion, Cav-1 negatively regulates key cell growth and survival pathways and may be an effective biomarker for predicting response to chemotherapy in glioblastoma.

Transcriptional repression of VEGF by ZNF24: mechanistic studies and vascular consequences in vivo

AbstractVEGF is a key regulator of normal and pathologic angiogenesis. Although many trans-activating factors of VEGF have been described, the transcriptional repression of VEGF remains much less understood. We have previously reported the identification of a SCAN domain–containing C2H2 zinc finger protein, ZNF24, that represses the transcription of VEGF. In the present study, we identify the mechanism by which ZNF24 represses VEGF transcription. Using reporter gene and electrophoretic mobility shift assays, we identify an 11-bp fragment of the proximal VEGF promoter as the ZNF24-binding site that is essential for ZNF24-mediated repression. We demonstrate in 2 in vivo models the potent inhibitory effect of ZNF24 on the vasculature. Expression of human ZNF24 induced in vivo vascular defects consistent with those induced by VEGF knockdown using a transgenic zebrafish model. These defects could be rescued by VEGF overexpression. Overexpression of ZNF24 in human breast cancer cells also inhibited tumor angiogenesis in an in vivo tumor model. Analyses of human breast cancer tissues showed that ZNF24 and VEGF levels were inversely correlated in malignant compared with normal tissues. These data demonstrate that ZNF24 represses VEGF transcription through direct binding to an 11-bp fragment of the VEGF proximal promoter and that it functions as a negative regulator of tumor growth by inhibiting angiogenesis.

STAT3 negatively regulates thyroid tumorigenesis

Although tyrosine-phosphorylated or activated STAT3 (pY-STAT3) is a well-described mediator of tumorigenesis, its role in thyroid cancer has not been investigated. We observed that 63 of 110 (57%) human primary papillary thyroid carcinoma (PTC) cases expressed nuclear pY-STAT3 in tumor cells, preferentially in association with the tumor stroma. An inverse relationship between pY-STAT3 expression with tumor size and the presence of distant metastases was observed. Using human thyroid cancer-derived cell lines [harboring rearranged during transfection (RET)/PTC, v-RAF murine sarcoma viral oncogene homolog B (BRAF), or rat sarcoma virus oncogene (RAS) alterations], we determined that IL-6/gp130/JAK signaling is responsible for STAT3 activation. STAT3 knockdown by shRNA in representative thyroid cancer cell lines that express high levels of pY-STAT3 had no effect on in vitro growth. However, xenografted short hairpin STAT3 cells generated larger tumors than control cells. Similarly, STAT3 deficiency in a murine model of BRAFV600E-induced PTC led to thyroid tumors that were more proliferative and larger than those tumors expressing STAT3wt. Genome expression analysis revealed that STAT3 knockdown resulted in the down-regulation of multiple transcripts, including the tumor suppressor insulin-like growth factor binding protein 7. Furthermore, STAT3 knockdown led to an increase in glucose consumption, lactate production, and expression of Hypoxia-inducible factor 1 (HIF1α) target genes, suggesting that STAT3 is a negative regulator of aerobic glycolysis. Our studies show that, in the context of thyroid cancer, STAT3 is paradoxically a negative regulator of tumor growth. These findings suggest that targeting STAT3 in these cancers could enhance tumor size and highlight the complexities of the role of STAT3 in tumorigenesis.

Abstract 5133: Transcriptional repression of VEGF by ZNF24: Mechanistic studies and vascular consequences in vivo

Abstract Vascular endothelial growth factor (VEGF) is a key regulator of both normal and pathological angiogenesis. It plays critical roles in physiological processes such as maintaining vascular stability and promoting skeletal muscle differentiation. Under pathological conditions such as cancer, VEGF serves as a principle proangiogenic factor to facilitate tumor angiogenesis. To date, although many trans-activating factors of VEGF have been well described, transcriptional repression of VEGF remains much less understood. We have previously reported the identification of a SCAN domain-containing C2H2 zinc finger protein, ZNF24, which functions to repress the transcription of VEGF via direct binding to the proximal VEGF promoter. In the current study, we have focused on mapping the ZNF24 binding site within the VEGF promoter and exploring its functions in vivo. Utilizing electrophoretic mobility shift assays, we have identified an 11bp fragment of the proximal VEGF promoter as the ZNF24 binding site and show that it is essential for ZNF24-mediated repression. In addition, this fragment can modulate VEGF transcription as a decoy for ZNF24 when introduced into human breast cancer cells. Using transgenic zebrafish as an in vivo model system, we have demonstrated that expression of human ZNF24 induces vascular defects similar to those induced by VEGF knockdown. Importantly, these defects can be rescued by overexpression of VEGF. Analysis of human breast cancer tissues has shown that ZNF24 protein levels are significantly decreased in malignant tissues compared to normal adjacent tissues. Our data support the conclusion that ZNF24 represses VEGF transcription through direct binding to an 11bp fragment of the VEGF proximal promoter and that it may function as a negative regulator of tumor growth by inhibiting tumor angiogenesis. (Supported by NIH P01 CA045548 and The Breast Cancer Research Foundation) Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr 5133. doi:10.1158/1538-7445.AM2011-5133

A novel role for the T‐box transcription factor Tbx1 as a negative regulator of tumor cell growth in mice

The T-box transcription factor, Tbx1, an important regulatory gene in development, is highly expressed in hair follicle (HF) stem cells in adult mice. Because mouse models of skin carcinogenesis have demonstrated that HF stem cells are a carcinogen target population and contribute significantly to tumor development, we investigated whether Tbx1 plays a role in skin carcinogenesis. We first assessed Tbx1 expression levels in mouse skin tumors, and found down-regulation in all tumors examined. To study the effect of Tbx1 expression on growth and tumorigenic potential of carcinoma cells, we transfected mouse Tbx1 cDNA into a mouse spindle cell carcinoma cell line that did not express endogenous Tbx1. Following transfection, two cell lines expressing different levels of the Tbx1/V5 fusion protein were selected for further study. Intradermal injection of the cell lines into mice revealed that Tbx1 expression significantly suppressed tumor growth, albeit with no change in tumor morphology. In culture, ectopic Tbx1 expression resulted in decreased cell growth and reduced development into multilayered colonies, compared to control cells. Tbx1-transfectants exhibited a reduced proliferative rate compared to control cells, with fewer cells in S and G2/M phases. The Tbx1 transfectants developed significantly fewer colonies in soft agar, demonstrating loss of anchorage-independent growth. Taken together, our data show that ectopic expression of Tbx1 restored contact inhibition to the skin tumor cells, suggesting that this developmentally important transcription factor may have a novel dual role as a negative regulator of tumor growth. © 2011 Wiley Periodicals, Inc.

007 The tumour suppressor Ras-association domain family 1 isoform A (RASSF1A): a novel modulator of hypertrophic signalling pathway in the heart

Myocardial hypertrophy is an important pathological process that can lead to heart failure, therefore understanding the molecular mechanisms of cardiac hypertrophy is key in elucidating the pathogenesis of this disease. One important signalling pathway which has been associated with cardiac hypertrophy is the Ras pathway. It is known that mutations in genes of the Ras signalling pathway are associated with syndromes (eg, Noonan and Costelloe) that are characterised by tumour formation and cardiac hypertrophy. This lead us to hypothesise that negative regulators of the Ras pathway may also limit cardiac growth in common conditions such as pressure overload. One such negative regulator of tumour growth is the recently described tumour suppressor protein RASSF1A (Ras-association domain family 1 isoform A). Although we and others have detected RASSF1A expression in the heart, little is known about its functions. Here we investigate the role of this molecule in regulating myocardial hypertrophy. We used mice with genetic ablation of the Rassf1a gene and isolated neonatal rat cardiomyocytes with adenoviral mediated overexpression of RASSF1A to investigate the role of RASSF1A in the heart. Induction of pressure overload hypertrophy by transverse aortic constriction (TAC) resulted in enhanced myocardial hypertrophy in knock out (KO) mice compared to wild type (WT) controls (64.7% increase in heart weight/body weight ratio in RASSF1A KO mice compared to 30.6% in WT, n=10, p In conclusion, our data establish RASSF1A as a potent inhibitor of cardiac hypertrophy by modulating the Ras-Raf1-ERK1/2 pathway. This may provide opportunities for the development of novel therapeutic strategies for heart failure in the future.

Abstract 2392: Transcriptional repression of VEGF by Znf24, a C2H2 zinc finger protein

Abstract Vascular endothelial growth factor (VEGF) is a key regulator during the formation of new blood vessels during angiogenesis. It functions to promote the proliferation and migration of endothelial cells under both physiological conditions such as embryogenesis and pathological conditions such as tumor growth. VEGF has been shown to play an important role in the development and metastasis of breast as well as other human cancers. To date, many trans-activating factors of VEGF have been described, whereas transcriptional repression of VEGF remains less studied. We have previously reported the identification of a SCAN-domain containing C2H2 zinc finger protein, Znf24, which functions to repress the transcription of VEGF. In this study we explore the mechanism by which Znf24 represses VEGF transcription. We have generated a series of VEGF promoter constructs bearing deletions from the 5′ end. Reporter gene assays in the breast cancer cell line MDA-MB-231 have revealed a proximal region of the VEGF promoter essential for Znf24-induced repression. To determine whether Znf24 represses VEGF transcription through direct binding to the VEGF promoter, we have performed electrophoretic mobility shift assays (EMSA) using the VEGF proximal promoter region as a probe. We have found that Znf24 protein binds to this proximal region, suggesting that VEGF is a direct downstream target of Znf24. To begin to investigate Znf24 functions in vivo, we have conducted immunohistochemistry assays using human breast cancer tissue microarrays representing different stages of disease progression and tumor sizes, as well as matched normal breast tissues. We have determined that Znf24 protein levels are significantly decreased in malignant tissues compared to normal adjacent tissues. A potential negative correlation between Znf24 protein levels and tumor sizes is also observed, suggesting that Znf24 may serve as a negative regulator of tumor growth. Our data suggest that Znf24 represses VEGF transcription through direct binding to the VEGF promoter and that it may function as a negative regulator of tumor growth by inhibiting tumor angiogenesis. (Supported by NIH P01 CA045548 and the Simeon J. Fortin Charitable Foundation) Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 2392.

Correction: Vascular Endothelial Growth Factor–A Positive and Negative Regulator of Tumor Growth

Correction: Vascular Endothelial Growth Factor–A Positive and Negative Regulator of Tumor Growth

Vascular Endothelial Growth Factor—A Positive and Negative Regulator of Tumor Growth

Over the past decade, the well-documented role of vascular endothelial growth factor (VEGF) in tumor angiogenesis has led it to become one of the leading therapeutic targets for the treatment of cancer. Emerging evidence from genetically modified animal models, however, suggests that elevated levels of VEGF, or a proangiogenic phenotype, may impede, rather than promote, early tumor development and progression. For example, hypermorph VEGF transgenic mice display delayed progression of a retroviral-induced murine leukemia, and knockdown of VEGF expression within the myeloid compartment accelerates tumor progression. Several mechanisms have been proposed to explain this paradox, whereby VEGF induces changes within the hematopoietic compartment and tumor microenvironment through recruitment of tumor inhibitory monocytic cells and the negative regulation of tumor angiogenesis. Thus, it is apparent that the levels of VEGF expression in both tumor and nontumor tissues, as well as the context and timing of its modulation relative to cancer induction, play an important role in determining the effects of VEGF expression on tumorigenicity. In light of these recent findings, the various mechanisms underlying the negative role of VEGF during early tumor development, progression, and metastasis will be discussed.

P140Cap protein suppresses tumour cell properties, regulating Csk and Src kinase activity

We recently identified p140Cap as a novel adaptor protein, expressed in epithelial-rich tissues and phosphorylated upon cell matrix adhesion and growth factor treatment. Here, we characterise p140Cap as a novel Src-binding protein, which regulates Src activation via C-terminal Src kinase (Csk). p140Cap silencing increases cell spreading, migration rate and Src kinase activity. Accordingly, increased expression of p140Cap activates Csk, leading to inhibition of Src and downstream signalling as well as of cell motility and invasion. Moreover, cell proliferation and "in vivo" breast cancer cell growth are strongly impaired by high levels of p140Cap, providing the first evidence that p140Cap is a novel negative regulator of tumour growth.

The biology of gonadotropin hormone-releasing hormone: role in the control of tumor growth and progression in humans

It is now well known that different forms of GnRH coexist in the same vertebrate species. In humans, two forms of GnRH have been identified so far. The first form corresponds to the hypophysiotropic decapeptide, and is now called GnRH-I. The second form has been initially identified in the chicken brain, and it is referred to as GnRH-II. GnRH-I binds to and activates specific receptors, belonging to the 7 transmembrane (7TM) domain superfamily, present on pituitary gonadotropes. These receptors (type I GnRH receptors) are coupled to the Gq/11/PLC intracellular signalling pathway. A receptor specific for GnRH-II (type II GnRH receptor) has been identified in non-mammalian vertebrates as well as in primates, but not yet in humans. In the last 10–15 years experimental evidence has been accumulated indicating that GnRH-I is expressed, together with its receptors, in tumors of the reproductive tract (prostate, breast, ovary, and endometrium). In these hormone-related tumors, activation of type I GnRH receptors consistently decreases cell proliferation, mainly by interfering with the mitogenic activity of stimulatory growth factors (e.g., EGF, IGF). Recent data seem to suggest that GnRH-I might also reduce the migratory and invasive capacity of cancer cells, possibly by affecting the expression and/or activity of cell adhesion molecules and of enzymes involved in the remodelling of the extracellular matrix. These observations point to GnRH-I as an autocrine negative regulatory factor on tumor growth progression and metastatization. Extensive research has been performed to clarify the molecular mechanisms underlying the peculiar antitumor activity of GnRH-I. Type I GnRH receptors in hormone-related tumors correspond to those present at the pituitary level in terms of cDNA nucleotide sequence and protein molecular weight, but do not share the same pharmacological profile in terms of binding affinity for the different synthetic GnRH-I analogs. Moreover, the classical intracellular signalling pathway mediating the stimulatory activity of the decapeptide on gonadotropin synthesis and secretion is not involved in its inhibitory activity on hormone-related tumor growth. In these tumors, type I GnRH receptors are coupled to the Gi-cAMP, rather than the Gq/11-PLC, signal transduction pathway. Recently, we have reported that GnRH-I and type I GnRH receptors are expressed also in tumors not related to the reproductive system, such as melanoma. Also in melanoma cells, GnRH-I behaves as a negative regulator of tumor growth and progression. Interestingly, the biochemical and pharmacological profiles of type I GnRH receptors in melanoma seem to correspond to those of the receptors at pituitary level. The data so far reported on the expression and on the possible functions of GnRH-II in humans are still scanty. The decapeptide has been identified, together with a ‘putative’ type II GnRH receptor, both in the central nervous system and in peripheral structures, such as tissues of the reproductive tract (both normal and tumoral). The specific biological functions of GnRH-II in humans are presently under investigation.

Effect of interleukin-1 and dexamethasone on interleukin-6 production and growth in human meningiomas.

Interleukin-6 (IL-6) has been shown to be released by cultured human meningioma cells and may be a positive or negative regulator of tumour growth. IL-6 protein and mRNA levels have been examined in a series of meningiomas. In 14 cases, the results are compared with the effects of IL-6 and dexamethasone on growth and IL-6 secretion in vitro. Tumours with the highest in vivo IL-6 mRNA expression also showed maximum induction of IL-6 and increased cellular proliferation on IL-1 stimulation in vitro. Dexamethasone decreased the IL-1-stimulated IL-6 release in all cases. Meningiomas which had little or no IL-6 message were refractory to IL-1 control of IL-6. Remarkably, these formed the group of meningiomas that increased their growth rate in response to dexamethasone.

Effects of interleukin-1 and dexamethasone on interleukin-6 production and growth in human meningiomas

Interleukin-6 (IL-6) has been shown to be released by cultured human meningioma cells and may be a positive or negative regulator of tumour growth. IL-6 protein and mRNA levels have been examined in a series of meningiomas. In 14 cases, the results are compared with the effects of IL-6 and dexamethasone on growth and IL-6 secretion in vitro. Tumours with the highest in vivo IL-6 mRNA expression also showed maximum induction of IL-6 and increased cellular proliferation on IL-1 stimulation in vitro. Dexamethasone decreased the IL-1-stimulated IL-6 release in all cases. Meningiomas which had little or no IL-6 message were refractory to IL-1 control of IL-6. Remarkably, these formed the group of meningiomas that increased their growth rate in response to dexamethasone. © 1997 John Wiley & Sons, Ltd.