Anchorage-independent Growth Phenotype Research Articles

SLC4A2 anion exchanger promotes tumour cell malignancy via enhancing net acid efflux across golgi membranes

Proper functioning of each secretory and endocytic compartment relies on its unique pH micro-environment that is known to be dictated by the rates of V-ATPase-mediated H+ pumping and its leakage back to the cytoplasm via an elusive “H+ leak” pathway. Here, we show that this proton leak across Golgi membranes is mediated by the AE2a (SLC4A2a)-mediated bicarbonate-chloride exchange, as it is strictly dependent on bicarbonate import (in exchange for chloride export) and the expression level of the Golgi-localized AE2a anion exchanger. In the acidic Golgi lumen, imported bicarbonate anions and protons then facilitate a common buffering reaction that yields carbon dioxide and water before their egress back to the cytoplasm via diffusion or water channels. The flattened morphology of the Golgi cisternae helps this process, as their high surface-volume ratio is optimal for water and gas exchange. Interestingly, this net acid efflux pathway is often upregulated in cancers and established cancer cell lines, and responsible for their markedly elevated Golgi resting pH and attenuated glycosylation potential. Accordingly, AE2 knockdown in SW-48 colorectal cancer cells was able to restore these two phenomena, and at the same time, reverse their invasive and anchorage-independent growth phenotype. These findings suggest a possibility to return malignant cells to a benign state by restoring Golgi resting pH.

Abstract A095: Metabolic rewiring in African-American prostate cancer: A role for adenosine-inosine axis in tumor progression

Abstract Introduction: Prostate cancer (PCa) prevalence and mortality are remarkably higher in African-American (AA)men compared to European-American (EA) men. In addition to known differences in socioeconomic status and access to health care, there is increasing evidence to suggest biological differences between AA and EA PCa. Our lab has pioneered the understanding of reprogrammed metabolism, a hallmark of tumor progression, in AA and EA PCa. Analysis of a compendium of 190 metabolites in ancestry verified, pathologically confirmed AA and EA PCa tissues followed by validation of key pathway components in plasma and urine revealed high inosine to adenosine ratio in AA PCa compared to EA PCa. Consistent with this, the enzyme adenosine deaminase (ADA), which converts adenosine to inosine was also found to be elevated in AA PCa. The current study will address the role of adenosine-inosine axis in AA PCa progression and attempt to delineate its significance in the clinical setting. Methods: Analysis of metabolites in tissues, plasma and urine was done using LC/MS. Tissue microarray analysis (TMA) was done to check the expression of ADA in tissues and correlate it to clinical outcomes. To determine the function of ADA in PCa progression, the gene was overexpressed in MDA-PCa-2A (AA) and LNCaP (EA) cells using lentiviral transduction (termed ADA OE). In vitro invasion was assessed using Boyden chamber assay and in vivo tumorigenic properties were examined in nude mice. Molecular studies were performed using qPCR, ELISA and western blotting. Results: Overexpression of the enzyme ADA in PCa cells confers an anchorage-independent growth phenotype (a.k.a. Anoikis Resistance) associated with a reduction in Integrin β1 (ITGB1) levels. Anoikis resistance is a key prerequisite for metastasis and a hallmark of circulating tumor cells (CTCs). ADA OE AA cells exhibited higher invasive potential compared to the EA cells. Molecular analysis revealed downregulation E-cadherin (epithelial marker) and Bim (pro-apoptotic marker), and upregulation of XIAP (anti-apoptotic marker), all of which support anoikis resistance phenotype in these cells. ADA OE cells had reduced cAMP levels, and addition of external cAMP resulted in reversal of anoikis resistance, increased cell adhesion and rescued ITGB1 levels. Mechanistically, it is postulated that high inosine upon ADA OE activates adenosine receptors A1 and A3, which causes a decrease in cAMP levels. Decreased cAMP affects the Epac-Rap1 signaling, a key regulator of integrin-mediated adhesion. Concomitantly, ADA OE cells also showed a decrease in Rap1 levels. Conclusion: Elevated inosine to adenosine ratio associated with increased expression of ADA is a metabolic hallmark in AA PCa, associated with anoikis resistance and possibly increased CTCs. Our findings also strongly support the potential of using inosine to adenosine ratio in plasma or urine as a predictive marker for PCa incidence or progression in AA men. In addition, ADA could serve as a potential therapeutic target for AA PCa. Citation Format: Christy Charles, Jie Gohlke, Stacy Lloyd, James Henderson, Balasubramaniam Karanam, Nora Navone, Rick Kittles, Stefan Ambs, George Michailidis, Nagireddy Putluri, Arun Sreekumar. Metabolic rewiring in African-American prostate cancer: A role for adenosine-inosine axis in tumor progression [abstract]. In: Proceedings of the Twelfth AACR Conference on the Science of Cancer Health Disparities in Racial/Ethnic Minorities and the Medically Underserved; 2019 Sep 20-23; San Francisco, CA. Philadelphia (PA): AACR; Cancer Epidemiol Biomarkers Prev 2020;29(6 Suppl_2):Abstract nr A095.

WNT7B mediates autocrine Wnt/β-catenin signaling and anchorage-independent growth in pancreatic adenocarcinoma

Developmental and cancer models show Wnt/β-catenin-dependent signaling mediates diverse phenotypic outcomes in the pancreas that are dictated by context, duration and strength of activation. While generally assumed to be pro-tumorigenic, it is unclear to what extent dysregulation of Wnt/β-catenin signaling impacts tumor progression in pancreatic adenocarcinoma (PDAC). In the present study, Wnt/β-catenin activity was characterized across a spectrum of PDAC cell lines and primary tumors. Reporter and gene expression based assays revealed wide heterogeneity in Wnt/β-catenin transcriptional activity across PDAC cell lines and patient tumors, as well as variable responsiveness to exogenous Wnt ligand stimulation. An experimentally-generated, pancreas-specific gene expression signature of Wnt/β-catenin transcriptional activation was used to stratify pathway activation across a cohort of resected, early stage PDAC tumors (N=41). In this cohort, higher Wnt/β-catenin activation was found to significantly correlate with lymphvascular invasion and worse disease specific survival (median survival time 20.3 versus 43.9 months, log rank P=0.03). Supporting the importance of Wnt ligand in mediating autocrine Wnt signaling, Wnt/β-catenin activity was significantly inhibited in PDAC cell lines by WLS gene silencing and the small molecule inhibitor IWP-2, both of which functionally block Wnt ligand processing and secretion. Transcriptional profiling revealed elevated expression of WNT7B occurred in PDAC cell lines with high levels of cell autonomous Wnt/β-catenin activity. Gene knockdown studies in AsPC-1 and HPAF-2 cell lines confirmed WNT7B mediated cell autonomous Wnt/β-catenin activation, as well as an anchorage-independent growth phenotype. Our findings indicate WNT7B can serve as a primary determinant of differential Wnt/β-catenin activation in PDAC. Disrupting the interaction between Wnt ligands and their receptors may be a particularly suitable approach for therapeutic modulation of Wnt/β-catenin signaling in PDAC and other cancer contexts where Wnt activation is mediated by ligand expression rather than mutations in canonical pathway members.

Adverse Cell Culture Conditions Mimicking the Tumor Microenvironment Upregulate ABCG2 to Mediate Multidrug Resistance and a More Malignant Phenotype

ABCG2 is an efflux transporter commonly found to overexpress in multidrug resistant (MDR) cancer cells. It is also believed to be a survival factor for cancer stem cells to drive tumor growth. Tumor microenvironment represents an attractive new drug target because it allows complex interaction between a tumor and its surrounding normal cells, molecules, and blood vessels, which all participate in tumor progression. Hypoxia, glucose deprivation and acidosis are the hallmarks of tumor microenvironment. This study investigated the upregulation of ABCG2 by these adverse growth conditions within the tumor microenvironment. Reporter gene assay revealed that a region within the ABCG2 promoter close to the reported HIF-1α response element is responsible for ABCG2 upregulation. Increased ABCG2 efflux activity was observed under the same conditions, subsequently leading to reduced response to ABCG2 substrate anticancer drug. Importantly, glucose deprivation and hypoxia were also found to enhance the resistance level of ABCG2-overexpressing resistant cells with pre-existing genetic and epigenetic MDR mechanisms. Hypoxia was further demonstrated to cause a more malignant anchorage-independent growth phenotype in the resistant cells, which can be abolished by knocking down ABCG2. A better understanding of ABCG2 regulation by the tumor microenvironment may help design novel strategies to improve treatment outcome.

Abstract 1468: MTA2 enhances breast cancer metastasis via regulation of the cytoskeleton and rho signaling pathways

Abstract Metastasis tumor associated (MTA) 2 is a component of the nucleosome remodeling and histone deacetylation complex and is implicated in regulating gene expression through its associated histone deacetylase activity. We have previously found that MTA2 enhanced the anchorage independent growth phenotype of estrogen receptor alpha (ER)-positive cells, implicating a potential role in metastasis. As MTA2-overexpression in these cells also resulted in an estrogen independent phenotype, we hypothesized that MTA2-overexpression may similarly enhance the aggressiveness of ER-negative cells. We found that MTA2-overexpressing MDA-MB-231 cells were more invasive through Matrigel, had enhanced soft-agar colony formation activity compared with vector controls, and demonstrated increased migration in wound healing assays. Furthermore, we found that MTA2 overexpression resulted in rapid systemic metastases when grown as orthotopic xenografts, while vector control cells failed to form metastases, in the same time period. Microarray analysis revealed enrichment for genes regulating the cytoskeleton and cell-environment interactions, which was validated using a previously published microarray dataset. We found that the negative regulator of the Rho pathway, Rho GDP dissociation inhibitor alpha (RhoGDI-alpha), was also decreased in expression at the protein level in the MTA2-overexpressing MDA-MB-231 cells. We found that blocking signaling through the Rho pathway by either using a Rho Kinase inhibitor or by overexpressing RhoGDI-alpha significantly reduced the soft-agar colony forming ability of MTA2-overexpressing cells. We examined the effect of MTA2 and RhoGDI-alpha expression in a retrospective breast cancer microarray dataset and found that patients classified as MTA2-high and RhoGDI-alpha-low had significantly earlier recurrence compared with all other patients. These data indicate that MTA2-overexpression results in an increase in the metastatic potential of breast cancer cells. These results have potential clinical implications as patients who have the MTA2-high/RhoGDI-alpha-low phenotype are at increased risk for early recurrence. In conclusion, our data show that MTA2 and RhoGDI-alpha enhances breast cancer metastasis possibly by promoting invasiveness and anchorage independent growth and survival. 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 1468. doi:10.1158/1538-7445.AM2011-1468

Orphan G protein–coupled receptor GPR56 plays a role in cell transformation and tumorigenesis involving the cell adhesion pathway

GPR56 is an orphan G protein - coupled receptor, mutations of which have recently been associated with bilateral frontoparietal polymicrogyria, a rare neurologic disease that has implications in brain development. However, no phenotype beyond central nervous system has yet been described for the GPR56-null mutations despite abundant GPR56 expression in many non - central nervous system adult tissues. In the present study, we show that higher GPR56 expression is correlated with the cellular transformation phenotypes of several cancer tissues compared with their normal counterparts, implying a potential oncogenic function. RNA interference-mediated GPR56 silencing results in apoptosis induction and reduced anchorage-independent growth of cancer cells via increased anoikis, whereas cDNA overexpression resulted in increased foci formation in mouse fibroblast NIH3T3 cell line. When GPR56 silencing was induced in vivo in several xenograft tumor models, significant tumor responses (including regression) were observed, suggesting the potential of targeting GPR56 in the development of tumor therapies. The expression profiling of GPR56-silenced A2058 melanoma cell line revealed several genes whose expression was affected by GPR56 silencing, particularly those in the integrin-mediated signaling and cell adhesion pathways. The potential role of GPR56 in cancer cell adhesion was further confirmed by the observation that GPR56 silencing also reduced cell adhesion to the extracellular matrix, which is consistent with the observed increase in anoikis and reduction in anchorage-independent growth phenotypes. The oncogenic potential and apparent absence of physiologic defects in adult human tissues lacking GPR56, as well as the targetable nature of G protein - coupled receptor by small molecule or antibody, make GPR56 an attractive drug target for the development of cancer therapies.

CDX2 promotes anchorage-independent growth by transcriptional repression of IGFBP-3

CDX2 is a Drosophila caudal-related homeobox transcription factor that is important for the establishment and maintenance of intestinal epithelial cells. We have reported that CDX2 promotes tumorigenicity in a subset of human colorectal cancer cell lines. Here, we present evidence that CDX2 negatively regulates the well-documented growth inhibitor insulin-like growth factor binding protein-3 (IGFBP-3). Specifically, CDX2 binds to the IGFBP-3 gene promoter and can repress IGFBP-3 transcription, protein expression and secretion. Furthermore, inhibition of IGFBP-3 partially rescues the decreased anchorage-independent growth phenotype observed in CDX2 knockout cells. These data demonstrate for the first time that (1) CDX2 can function as a transcriptional repressor, and (2) one mechanism by which CDX2 promotes anchorage-independent growth is by transcriptional repression of IGFBP-3.

Loss of tumorigenic potential by human lung tumor cells in the presence of antisense RNA specific to the ectopically synthesized alpha subunit of human chorionic gonadotropin.

A clonal strain of human lung tumor cells in culture (ChaGo), derived from a bronchogenic carcinoma, synthesizes and secretes large amounts of alpha (alpha) and a comparatively lower level of beta (beta) subunit of the glycoprotein hormone, human chorionic gonadotropin (HCG). ChaGo cells lost their characteristic anchorage-independent growth phenotype in the presence of anti-alpha-HCG antibody. The effect of the antibody was partially reversed by addition of alpha-HCG to the culture medium. ChaGo cells were transfected with an expression vector (pRSV-anti-alpha-HCG), that directs synthesis of RNA complementary to alpha-HCG mRNA. The transfectants produced alpha-HCG antisense RNA which was associated with the reduced level of alpha-HCG. Transfectants also displayed several altered phenotypic properties, including altered morphology, less mitosis, reduced growth rate, loss of anchorage-independent growth, and loss of tumorigenicity in nude mice. Treatment of transfectants with 8,bromo-cAMP resulted in increased accumulation of alpha-HCG mRNA, no change in the level of alpha-HCG antisense RNA, release of the inhibition of [3H]thymidine incorporation, and restoration of anchorage-independent growth phenotype. The overexpression of c-myc, observed in ChaGo cells, was unaffected by the reduced level of alpha-HCG. These results suggest that ectopic synthesis of the alpha subunit of HCG plays a functional role in the transformation of these human lung cells.