Implications For Tumor Biology Research Articles

PATH-21. GPX4 IS CRUCIALLY IMPLICATED IN THE PATHOBIOLOGY OF GLIOBLASTOMA AND A PUTATIVE ACTIONABLE TARGET

Abstract BACKGROUND Glioblastoma(GBM) is the most common malignant primary brain tumor with a dismal prognosis. Glutathione-mediated inhibition of the ferroptotic form of cell death is crucially implicated in various malignancies, which is principally regulated by glutathione peroxidase 4 (GPX4). However, there is limited data on GBM. The present study evaluated the expression of GPX4 in GBM and its implications in tumor biology, clinical outcome, and therapeutic potentials. METHODS The mRNA and protein expression was assessed by qRT-PCR and immunohistochemistry, respectively, in 75 cases of adult hemispheric GBMs (IDH wild type). For comparison, 21 lower-grade astrocytomas (IDH-mutant, grade-2/3) [LGA] and 20 cases were also evaluated. In-vitro analysis was performed on U87MG and LN229 glioma cell line. RESULTS The mRNA expression of GPX-4 was significantly higher in GBM than LGA, and normal brain (NB) [p-values 0.028, and 0.001, respectively]. Normal brain cases were negative for GPX4. Almost half of the GBMs (49.3%) showed strong immunoreactivity, which was higher than LGAs (23.8%) [p-value -0.04]. Inhibition of GPX-4 in-vitro by 1S-RSL3 & FIN56 was associated with decreased cell survival, proliferation, migration, invasion, and increased cell death. GPX-4 expression was not significantly associated with overall survival in GBM. CONCLUSION GPX-4 is crucial for the tumor cells' survival and aggressive biological behavior. Considering its immune-positivity only in the neoplastic cell and strong positivity in GBM it may be a useful adjunct to the diagnosis. The present study emphasized its role as a potential therapeutic target in the form of 1S-RSL3 & FIN56.

Exploring Ribosome Code: Unveiling A Novel Dimension of Gene Regulation in Carcinogenesis

The central dogma of molecular biology has traditionally viewed ribosomes as uniform entities translating mRNA into proteins with mechanical precision. Recent findings challenge this perspective, revealing unexpected ribosome heterogeneity within cells, thus proposing a novel mechanism for diversifying protein synthesis. This concept parallels the “histone code” hypothesis, leading to the proposition of a “ribosome code” that suggests variations in ribosomal protein stoichiometry, paralogs, and modifications may preferentially translate certain mRNA populations. The role of ribosome heterogeneity in cancer pathogenesis, however, remains a subject of debate. Evidence suggests that alterations in ribosome composition, structure, and activity could influence abnormal protein synthesis, thus contributing to tumorigenesis. This is supported by the correlation between enhanced ribosome biogenesis, protein synthesis, and tumor growth, as well as the observed modifications in cancer ribosomes. Examining the nuances of ribosome heterogeneity, its influence on translational biases, and implications for tumor biology could significantly deepen our understanding of cancer’s molecular landscape, potentially unveiling novel therapeutic targets.

Elevated expression of cholesterol transporter LRP-1 is crucially implicated in the pathobiology of glioblastoma.

Glioblastoma (GBM) is the most common primary malignant brain tumor with a grave prognosis. The present study evaluated the expression of Cholesterol transporter [importer -Lipoprotein Receptor-related Protein-1 (LRP-1) and exporter -ATP-binding cassette transporters-1 (ABCA-1)] in GBM and their implications in tumor-biology, clinical outcome and therapeutic potentials. The mRNA and protein expression was assessed by qRT-PCR and immunohistochemistry, respectively, in 85 GBMs. For comparison, 25 lower-grade astrocytomas (IDH-mutant, grade-2/3) [LGA] 16 cases of high-grade astrocytomas (IDH-mutant, grade-4) [HGA] were also evaluated. In-vitro analysis was performed on U87MG and LN229 glioma cell line. The expression of LRP-1 (mRNA and protein) was significantly higher in GBM than LGA, HGA and normal brain (NB) [p-values 0.007, 0.003 and <0.001 for mRNA; 0.024, <0.001 and <0.001 for immunohistochemistry]. Majority of the GBMs (82.4%) showed strong immunoreactivity for LRP-1, and all tumor cases were positive while the normal brain was negative. LRP-1 immunoreactivity positively correlated with the MIB-1 labeling index (p-value-0.013). LRP-1 knockdown in-vitro was associated with decreased cell survival, proliferation, migration, invasion, and increased apoptosis. Similar effect was also demonstrated by Receptor Associated Protein (RAP), a LRP-1 inhibitory drug. The silencing of LRP-1 was also associated with decreased cholesterol level. The ABCA-1 expression was higher in GBM than LGA and NB (p-value 0.011 and <0.001), however there was no significant association with other parameters. LRP-1 showed a positive correlation with ABCA-1 and associated with decreased expression with LRP-1 knock-down in-vitro. The expression of LRP-1 and ABCA-1 didn't correlate with overall survival in GBMs. Hence, LRP-1 is crucial for the tumor cells' survival and aggressive biological behavior which is maintain through the regulation of high intracellular cholesterol import. Its expression is significantly higher in GBMs and also implicated in the regulation of ABCA-1 expression. Considering its immune-positivity only in the neoplastic cell and strong positivity in GBM it may be a useful adjunct to the diagnosis. For the first time, the present study emphasized its role as a potential therapeutic target in the form of RAP which is presently being used in other neurological diseases under clinical trials.

Abstract 3663: Allostatic load, tumor genomics, and outcomes in NSCLC

Abstract Introduction: Allostatic load (AL) is a multi-system measure of chronic stress shown to be an emerging framework for understanding disparities in cancer outcomes, but there have been no AL studies in lung cancer. Methods: We conducted a retrospective review of patients diagnosed with stage IV lung adenocarcinoma from 2016 - 2020 at the University of Illinois Hospital and Health System. An AL index included 9 biomarkers (systolic blood pressure, diastolic blood pressure, resting heart rate, BMI, albumin, eGFR, creatinine, glucose, and use of medications for hypertension, diabetes, or hypocholesteremia) with 1 point assigned for each biomarker meeting a pre-determined cutoff. AL was dichotomized between AL-high (5-9) and AL-low (0-4) with median progression-free survival of first-line therapy (mPFS1) and median overall survival (mOS) estimated for both groups with Kaplan-Meier curves. Rates of clinically actionable driver mutations (driver-POS), including EGFR, ALK, ROS1, BRAF V600e, RET, MET, NTRK, and KRAS G12C, were compared for both groups using chi-squared test. Mean AL was compared between those who were driver-POS and those who did not have a clinically actionable driver mutation (driver-NEG) using independent samples t-test. Results: A total of 61 patients were identified with 56% female and 74% former or current tobacco users. The cohort was 49% Black, 21% White, and 13% Hispanic or Latino. Mean AL at diagnosis was 3.3 (+/- 1.4). AL-high patients comprised 20% (12) of the cohort compared with 80% (49) AL-low. Between AL-high and AL-low cohorts, there was no statistically significant difference in mPFS1 (15 vs. 13 months, P = 0.98) and mOS (34 vs. 18 months, P = 0.33). Rates of driver-POS were lower in AL-high compared with AL-low (25% vs 69%, P &amp;lt;0.01). Mean AL was higher in the driver-NEG population compared with driver-POS population (3.79 vs 3.03, P = 0.04). Conclusions: Patients whose tumors did not have a clinically actionable driver mutation were associated with a higher AL, suggestive of higher chronic stress playing a role in more aggressive tumor biology. No statistically significant survival difference was observed in AL-high versus AL-low populations for mPFS1 and mOS. Larger, prospective trials are planned to correlate AL at diagnosis with clinical and biomarker data. AL, which serves as a measure of physiological dysfunction due to chronic stress associated with social disadvantage, may have implications for tumor biology and clinical outcomes in lung cancer. Citation Format: Ryan H. Nguyen, Michael Weinfeld, Mary Pasquinelli, Frank Weinberg, Natalie Reizine, Lawrence Feldman, Vijayakrishna K. Gadi. Allostatic load, tumor genomics, and outcomes in NSCLC [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 3663.

Mutant Allele Imbalance in Cancer

The search for somatic mutations that drive the initiation and progression of human tumors has dominated recent cancer research. While much emphasis has been placed on characterizing the prevalence and function of driver mutations, comparatively less is known about their serial genetic evolution. Indeed, study of this phenomenon has largely focused on tumor-suppressor genes recessive at the cellular level or mechanisms of resistance in tumors with mutant oncogenes targeted by therapy. There is, however, a growing appreciation that despite a decades-old presumption of heterozygosity, changes in mutant oncogene zygosity are common and drive dosage and stoichiometry changes that lead to selective growth advantages. Here, we review the recent progress in understanding mutant allele imbalance and its implications for tumor biology, cancer evolution, and response to anticancer therapy.

Novel Insights Into Epigenetic Reprogramming and Destabilization of Pericentromeric Heterochromatin in Cancer.

Pericentromeric heterochromatin is maintained in a condensed structure by repressive epigenetic control mechanisms and perturbation of these may cause diseases. The chromosome 1q12 region harbors the largest pericentromeric heterochromatin domain in the genome and is among the most common breakpoints in both solid and hematopoietic cancers. Furthermore, the 1q arm is frequently amplified in cancer and this may support tumorigenesis by increasing the dosage of the many oncogenes of this genomic region. Recent studies have provided insight into the mechanisms leading to loss of 1q12 stability and 1q amplification and DNA hypomethylation seems to play a prominent role. This may be the result of decreased activity of DNA methyltransferases and instrumental for 1q12 destabilization or arise secondary to perturbation of other important epigenetic mechanisms that control repression of pericentromeric heterochromatin. Polycomb proteins were recently demonstrated to epigenetically reprogram demethylated 1q12 pericentromeric heterochromatin in premalignant and malignant cells to form large subnuclear structures known as polycomb bodies. This may influence the regulation and stability of 1q12 pericentromeric heterochromatin and/or the distribution of polycomb factors to support tumorigenesis. This review will discuss recent insight into the epigenetic perturbations causing the destabilization of 1q12 pericentromeric heterochromatin and its possible implications for tumor biology.

Interaction between Polycomb and SSX Proteins in Pericentromeric Heterochromatin Function and Its Implication in Cancer.

The stability of pericentromeric heterochromatin is maintained by repressive epigenetic control mechanisms, and failure to maintain this stability may cause severe diseases such as immune deficiency and cancer. Thus, deeper insight into the epigenetic regulation and deregulation of pericentromeric heterochromatin is of high priority. We and others have recently demonstrated that pericentromeric heterochromatin domains are often epigenetically reprogrammed by Polycomb proteins in premalignant and malignant cells to form large subnuclear structures known as Polycomb bodies. This may affect the regulation and stability of pericentromeric heterochromatin domains and/or the distribution of Polycomb factors to support tumorigeneses. Importantly, Polycomb bodies in cancer cells may be targeted by the cancer/testis-related SSX proteins to cause derepression and genomic instability of pericentromeric heterochromatin. This review will discuss the interplay between SSX and Polycomb factors in the repression and stability of pericentromeric heterochromatin and its possible implications for tumor biology.

A Previously Unrecognized Monocytic Component of Pheochromocytoma and Paraganglioma.

We describe a consistently present, previously unrecognized, population of monocytes in pheochromocytomas and paragangliomas. Although sustentacular cells are generally recognized as a common component of these tumors, differential immunohistochemical staining for CD163 and S100 shows that monocytes can in factbe more numerous. These cells frequently resemble sustentacular cells topographically and cytologically, possibly explaining why they have not been previously noticed. They contribute to the tumor proteome and may have implications for tumor biology. No correlations were identifiable between the presence of these cells and any clinical characteristics of the tumors in the present study. A possible association with genotype is suggested by immunoblot showing high expression of CD163 protein in tumors with succinate dehydrogenase mutations.

Abstract IA15: Lung cancer genomics

Abstract Lung cancer remains the most common cause of cancer related deaths in the United States. The primary reason for the high mortality rate is the advanced stage of the disease at the time of diagnosis. Racial disparities in incidence and mortality have been observed in the United States, with higher rate among African-Americans, particularly males. In recent years genetic alterations that bestow a proliferative and survival advantage, so called ‘driver' genetic alterations, have been identified in a subset of cancers including Non-Small Cell Lung Cancer (NSCLC). Molecular changes resulting from these genetic alterations can be targeted for therapeutic benefit and such targeted therapy has become standard of care for the management of NSCLC patients. These data have generated an interested in assessing and understanding lung cancer genomics. Several studies have been conducted and results of these studies have allowed the characterization of lung cancer into genomically distinct categories that may have implications for tumor biology and possibly for cancer therapeutics. Racial and ethnic variations in the incidence of specific ‘driver' genetic alterations have been observed. Thus the incidence of EGFR (epidermal growth factor receptor) mutation positive NSCLC is higher in Asian population compared to North American population. Such differences have not been observed for ALK (anaplastic lymphoma kinase) gene rearrangement positive NSCLC. These observations have generated an interest in evaluating lung cancer genomics to explain the observed racial differences in both incidence and mortality. Ongoing efforts will attempt to define racial and ethnic differences, if any in lung cancer genomics and the implications of the same. Citation Format: Shirish M. Gadgeel. Lung cancer genomics. [abstract]. In: Proceedings of the Ninth AACR Conference on the Science of Cancer Health Disparities in Racial/Ethnic Minorities and the Medically Underserved; 2016 Sep 25-28; Fort Lauderdale, FL. Philadelphia (PA): AACR; Cancer Epidemiol Biomarkers Prev 2017;26(2 Suppl):Abstract nr IA15.

Cancer Stem Cells and Macrophages: Implications in Tumor Biology and Therapeutic Strategies.

Cancer stem cells (CSCs) are a unique subset of cells within tumors with stemlike properties that have been proposed to be key drivers of tumor initiation and progression. CSCs are functionally defined by their unlimited self-renewal capacity and their ability to initiate tumor formation in vivo. Like normal stem cells, CSCs exist in a cellular niche comprised of numerous cell types including tumor-associated macrophages (TAMs) which provides a unique microenvironment to protect and promote CSC functions. TAMs provide pivotal signals to promote CSC survival, self-renewal, maintenance, and migratory ability, and in turn, CSCs deliver tumor-promoting cues to TAMs that further enhance tumorigenesis. Studies in the last decade have aimed to understand the molecular mediators of CSCs and TAMs, and recent advances have begun to elucidate the complex cross talk that occurs between these two cell types. In this review, we discuss the molecular interactions that define CSC-TAM cross talk at each stage of tumor progression and examine the clinical implications of targeting these interactions.

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The tumor microenvironment includes a complicated network of physiological gradients contributing to plasticity of tumor cells and heterogeneity of tumor tissue. Hypoxia is a key component generating intratumoral oxygen gradients, which affect the cellular expression program and lead to therapy resistance and increased metastatic propensity of weakly oxygenated cell subpopulations. One of the adaptive responses of tumor cells to hypoxia involves the increased expression and functional activation of carbonic anhydrase IX (CA IX), a cancer-related cell surface enzyme catalyzing the reversible conversion of carbon dioxide to bicarbonate ion and proton. Via its catalytic activity, CA IX participates in regulation of intracellular and extracellular pH perturbations that result from hypoxia-induced changes in cellular metabolism producing excess of acid. Through the ability to regulate pH, CA IX also facilitates cell migration and invasion. In addition, CA IX has non-catalytic function in cell adhesion and spreading. Thus, CA IX endows tumor cells with survival advantages in hypoxia/acidosis and confers an increased ability to migrate, invade and metastasize. Accordingly, CA IX is expressed in a broad range of tumors, where it is associated with prognosis and therapy outcome. Its expression pattern and functional implications in tumor biology make CA IX a promising therapeutic target, which can be hit either by immunotherapy with monoclonal antibodies or with compounds inhibiting its enzyme activity. The first strategy has already reached the clinical trials, whereas the second one is still in preclinical testing. Both strategies indicate that CA IX can become a clinically useful anticancer target, but urge further efforts toward better selection of patients for immunotherapy and deeper understanding of tumor types, clinical situations and synthetic lethality interactions with other treatment approaches.

DNA methylation plasticity contributes to the natural history of metastasis

DNA methylation plasticity contributes to the natural history of metastasis

Impact of estrogen receptor (ER) and human epidermal growth factor receptor-2 (HER2) co-expression on breast cancer disease characteristics: implications for tumor biology and research.

ER and HER2 are critical drivers of breast cancer biology and can interact when co-expressed, but less data describe the impact of ER/HER2 co-expression on clinical disease characteristics. We studied the impact of ER and HER2 (co)-expression ina cohort of 1,187 patients with invasive breast cancer and compared disease characteristics among different groups according to ER and HER2 status. Age, tumor size, grade, nodal status, TNM stage, and metastatic sites were compared and significance determined using the appropriate t tests. All p values were two-tailed. Compared to ER-negative/HER2-negative disease as the control group, ER expression was associated with older age, smaller tumors, lower grade, earlier TNM stage, and increased bone involvement in de novo metastasis, while HER2 had no significant impact on these characteristics. ER and HER2 co-expression wasassociated with lower grade and higher bone involvement in de novo metastasis, reflecting a retained impact for ER. HER2 impact on ER-positive disease was reflected by younger age, higher grade andTNM stage, and increased frequency of visceral involvement in de novo metastasis. Within the ER-positive/HER2-positive group, triple positive breast cancer (ER+/PgR+/HER2+) was associated with younger age compared to ER+/PgR-/HER2+ disease (mean age of 50.8 vs. 56years, p=0.0226). PgR was also associated with younger age in ER+/HER2- disease with a mean age of 57.6years in ER+/PgR+/HER2- disease vs. 63.4years in ER+/PgR-/HER2- disease (p<0.0001). In conclusion,ER has a profound impact on breast cancer characteristics, including a retained impact when co-expressed with HER2. Similarly, HER2 dramatically modulates ER-positive breast cancer making it more aggressive. PgR association with young age may be related to hormonal levels of the premenopausal state, with HER2 providing an earlier growth advantage in triple positive disease, suggesting a specific dependence for this subset on high estrogen levels.

Galectin-8: a matricellular lectin with key roles in angiogenesis.

Galectin-8 (gal-8) is a "tandem-repeat"-type galectin, containing two carbohydrate recognition domains connected by a linker peptide. gal-8 is expressed both in the cytoplasm and nucleus in vascular endothelial cells (ECs) from normal and tumor-associated blood vessels, and in lymphatic endothelial cells. Herein, we describe a novel role for gal-8 in the regulation of vascular and lymphatic angiogenesis and provide evidence of its critical implications in tumor biology. Functional assays revealed central roles for gal-8 in the control of capillary-tube formation, EC migration and in vivo angiogenesis. So far, two endothelial ligands have been described for gal-8, namely podoplanin in lymphatic vessels and CD166 (ALCAM, activated leukocyte cell adhesion molecule) in vascular ECs. Other related gal-8 functions are also summarized here, including cell adhesion and migration, which collectively demonstrate the multi-functionality of this complex lectin. Thus, gal-8 is an important component of the angiogenesis network, and an essential molecule in the extracellular matrix by providing molecular anchoring to this surrounding matrix. The implications of gal-8 in tumor angiogenesis remain to be further explored, but it is exciting to speculate that modulating gal-8-glycan interactions could be used to block lymphatic-vascular connections vital for metastasis.

Mnk kinase pathway: Cellular functions and biological outcomes.

The mitogen-activated protein kinase (MAPK) interacting protein kinases 1 and 2 (Mnk1 and Mnk2) play important roles in controlling signals involved in mRNA translation. In addition to the MAPKs (p38 or Erk), multiple studies suggest that the Mnk kinases can be regulated by other known kinases such as Pak2 and/or other unidentified kinases by phosphorylation of residues distinct from the sites phosphorylated by the MAPKs. Several studies have established multiple Mnk protein targets, including PSF, heterogenous nuclear ribonucleoprotein A1, Sprouty 2 and have lead to the identification of distinct biological functions and substrate specificity for the Mnk kinases. In this review we discuss the pathways regulating the Mnk kinases, their known substrates as well as the functional consequences of engagement of pathways controlled by Mnk kinases. These kinases play an important role in mRNA translation via their regulation of eukaryotic initiation factor 4E (eIF4E) and their functions have important implications in tumor biology as well as the regulation of drug resistance to anti-oncogenic therapies. Other studies have identified a role for the Mnk kinases in cap-independent mRNA translation, suggesting that the Mnk kinases can exert important functional effects independently of the phosphorylation of eIF4E. The role of Mnk kinases in inflammation and inflammation-induced malignancies is also discussed.

Ionizing Radiation and Glioblastoma Exosomes: Implications in Tumor Biology and Cell Migration

Exosomes are nanometer-sized lipid vesicles released ubiquitously by cells, which have been shown to have a normal physiological role, as well as influence the tumor microenvironment and aid metastasis. Recent studies highlight the ability of exosomes to convey tumor-suppressive and oncogenic mRNAs, microRNAs, and proteins to a receiving cell, subsequently activating downstream signaling pathways and influencing cellular phenotype. Here, we show that radiation increases the abundance of exosomes released by glioblastoma cells and normal astrocytes. Exosomes derived from irradiated cells enhanced the migration of recipient cells, and their molecular profiling revealed an abundance of molecules related to signaling pathways important for cell migration. In particular, connective tissue growth factor (CTGF) mRNA and insulin-like growth factor binding protein 2 (IGFBP2) protein levels were elevated, and coculture of nonirradiated cells with exosomes isolated from irradiated cells increased CTGF protein expression in the recipient cells. Additionally, these exosomes enhanced the activation of neurotrophic tyrosine kinase receptor type 1 (TrkA), focal adhesion kinase, Paxillin, and proto-oncogene tyrosine-protein kinase Src (Src) in recipient cells, molecules involved in cell migration. Collectively, our data suggest that radiation influences exosome abundance, specifically alters their molecular composition, and on uptake, promotes a migratory phenotype.

Tumor‐derived exosomes and microvesicles in head and neck cancer: Implications for tumor biology and biomarker discovery

Exosomes and microvesicles (MVs) are nanometer-sized, membranous vesicles secreted from many cell types into their surrounding extracellular space and into body fluids. These two classes of extracellular vesicles are regarded as a novel mechanism through which cancer cells, including virally infected cancer cells, regulate their micro-environment via the horizontal transfer of bioactive molecules: proteins, lipids, and nucleic acids (DNA, mRNA, micro-RNAs; oncogenic cargo hence often referred to as oncosomes). In head and neck cancer (HNC), exosomes and MVs have been described in Epstein Barr Virus (EBV)-associated nasopharyngeal cancer (NPC), as well as being positively correlated with oral squamous cell carcinoma (OSCC) progression. It has therefore been suggested that HNC-derived vesicles could represent a useful source for biomarker discovery, enriched in tumor antigens and cargo; hence fundamentally important for cancer progression. This current review offers an overall perspective on the roles of exosomes and MVs in HNC biology, focusing on EBV-associated NPC and OSCC. We also highlight the importance of saliva as a proximal and easily accessible bio-fluid for HNC detection, and propose that salivary vesicles might serve as an alternative model in the discovery of novel HNC biomarkers.

KSHV infection of endothelial cells manipulates CXCR7-mediated signaling: implications for Kaposi’s Sarcoma progression and intervention

CXCR7 was recently characterized as an alternative receptor for the chemokine CXCL12/SDF-1, previously thought to bind and signal exclusively through CXCR4. We recently identified CXCR7 as a key cellular factor in the endothelial cell (EC) dysfunction associated with KSHV infection. CXCL12 signaling is critically associated with tumor growth, angiogenesis and metastasis in several diverse tumors and is one of the most studied chemokine/chemokine receptor interactions in cancer systems. The tumorigenic activity of the CXCL12 signaling axis offers an attractive target for therapeutic intervention in multiple cancers including Kaposi’ sS arcoma (KS). However, most of the research to date was based on the assumption that CXCR4 was the sole CXCL12 receptor, and thus focused on the development of CXCR4-targeted treatments. CXCR4 participates in important homeostatic functions including hematopoiesis and mucosal immunity, while CXCR7 is rarely expressed in normal adult cells. As a result, CXCR7 may be a more specific chemotherapeutic target for tumor cells and tumor-associated vasculature with fewer adverse effects than treatments targeting CXCR4. CXCR7 is poorly studied throughout the cancer literature and although CXCR7 expression has been found in tumor-associated vasculature, no studies comprehensively examine the biology of CXCR7 in EC and its implications for tumor biology. We seek to define th er ole of CXCR7-mediated CXCL12 signaling in EC biology, and in the context of KSHV infection, in order to determine potential contributions of CXCR7 signaling to KSHV-mediated EC transformation and KS tumorigenesis. We demonstrate that CXCR7 is strongly expressed on LANA+ spindle cells in KS biopsy tissue at all stages of tumor progression. We further demonstrate that CXCR7 induction by KSHV in vitro is specific to lymphatic EC lineages and occurs coincident with the acquisition of spindle morphology. Detailed examination of CXCR7 functions in EC biology reveals multiple roles for CXCR7 that could impact KS tumorigenesis, including effects on cellular proliferation, junctional integrity, cell survival and metastatic capacity. Specifically, we determine that CXCR7 expression results in a loss of PECAM/CD31 expression, perturbing the formation and maintenance of EC monolayers. Moreover, CXCR7+ EC display significant SDF-1 dependent hypermotility, as measured via Electrical Cell-Substrate Impedence Sensing (ECIS). We also demonstrate that SDF-1 signaling through CXCR7 expression is enhanced in EC undergoing anchorage-deprivation, affecting EC cell survival and invasion into SDF-1 rich niches. Taken together, these results demonstrate that CXCR7 is a novel KSHV-induced oncogene with the capacity to influence multiple aspects of KS pathogenesis including tumor growth, seeding and metastasis.

Frequent Heterogeneous Missense Mutations of GGAP2 in Prostate Cancer: Implications for Tumor Biology, Clonality and Mutation Analysis

Prostate cancer is the most common visceral malignancy in Western men and a major cause of cancer deaths. Increased activation of the AKT and NFkB pathways have been identified as critical steps in prostate cancer initiation and progression. GGAP2 (GTP-binding and GTPase activating protein 2) is a multidomain protein that contains an N-terminal Ras homology domain (GTPase), followed by a PH domain, a C-terminal GAP domain and an ankyrin repeat domain. GGAP2 can directly activate signaling via both the AKT and NFkB pathways and acts as a node of crosstalk between these pathways. Increased GGAP2 expression is present in three quarters of prostate cancers. Mutations of GGAP2 have been reported in cell lines from other malignancies. We therefore analyzed 84 prostate cancer tissues and 43 benign prostate tissues for somatic mutations in GGAP2 by direct sequencing of individual clones derived from the GAP and GTPase domains of normal and tumor tissue. Overall, half of cancers contained mutant GAP domain clones and in 20% of cancers, 30% or more of clones were mutant in the GAP domain. Surprisingly, the mutations were heterogeneous and nonclonal, with multiple different mutations being present in many tumors. Similar findings were observed in the analysis of the GTPase domain. Mutant GGAP2 proteins had significantly higher transcriptional activity using AP-1 responsive reporter constructs when compared to wild-type protein. Furthermore, the presence of these mutations was associated with aggressive clinical behavior. The presence of high frequency nonclonal mutations of a single gene is novel and represents a new mode of genetic alteration that can promote tumor progression. Analysis of mutations in cancer has been used to predict outcome and guide therapeutic target identification but such analysis has focused on clonal mutations. Our studies indicate that in some cases high frequency nonclonal mutations may need to be assessed as well.

Dipeptidyl Peptidases as Survival Factors in Ewing Sarcoma Family of Tumors: IMPLICATIONS FOR TUMOR BIOLOGY AND THERAPY

Ewing sarcoma family of tumors (ESFT) is a group of aggressive pediatric malignancies driven by the EWS-FLI1 fusion protein, an aberrant transcription factor up-regulating specific target genes, such as neuropeptide Y (NPY) and its Y1 and Y5 receptors (Y5Rs). Previously, we have shown that both exogenous NPY and endogenous NPY stimulate ESFT cell death via its Y1 and Y5Rs. Here, we demonstrate that this effect is prevented by dipeptidyl peptidases (DPPs), which cleave NPY to its shorter form, NPY(3-36), not active at Y1Rs. We have shown that NPY-induced cell death can be abolished by overexpression of DPPs and enhanced by their down-regulation. Both NPY treatment and DPP blockade activated the same cell death pathway mediated by poly(ADP-ribose) polymerase (PARP-1) and apoptosis-inducing factor (AIF). Moreover, the decrease in cell survival induced by DPP inhibition was blocked by Y1 and Y5R antagonists, confirming its dependence on endogenous NPY. Interestingly, similar levels of NPY-driven cell death were achieved by blocking membrane DPPIV and cytosolic DPP8 and DPP9. Thus, this is the first evidence of these intracellular DPPs cleaving releasable peptides, such as NPY, in live cells. In contrast, another membrane DPP, fibroblast activation protein (FAP), did not affect NPY actions. In conclusion, DPPs act as survival factors for ESFT cells and protect them from cell death induced by endogenous NPY. This is the first demonstration that intracellular DPPs are involved in regulation of ESFT growth and may become potential therapeutic targets for these tumors.