MTBP inhibits migration and metastasis of hepatocellular carcinoma

Hepatocellular carcinoma (HCC) is one of the most common cancers worldwide with increasing incidence. Despite curative surgical resection and advanced chemotherapy, its survival rate remains low. The presence of microvascular invasion and occult metastasis is one of the major causes for this poor outcome. MDM2 Binding Protein (MTBP) has been implicated in the suppression of cell migration and cancer metastasis. However, clinical significance of MTBP, particularly in human cancer, is poorly understood. Specifically, clinical relevance of MTBP in human HCC has never been investigated. Here we demonstrated that expression of MTBP was significantly reduced in human HCC tissues compared to adjacent non-tumor tissues. MTBP expression was negatively correlated with capsular/vascular invasion and lymph node metastasis. Overexpression of MTBP resulted in the suppression of the migratory and metastatic potential of HCC cells, while its downregulation increased the migration. Consistent with the previous report, MTBP endogenously bound to alpha-actinin 4 (ACTN4) and suppressed ACTN4-mediated cell migration in multiple HCC cell lines. However, MTBP also inhibited migratory potential of PLC/PRF/5 HCC cells whose migration was not altered by manipulation of ACTN4 expression. These results suggest that mechanisms behind MTBP-mediated migration suppression may not be limited to the pathway involving ACTN4 in certain cellular contexts. Additionally, as a potential mechanism for reduced MTBP expression in tumors, we found that MTBP expression was increased following the treatment with histone deacetylase inhibitors (HDIs). Our study, for the first time, provides clinical relevance of MTBP in the suppression of HCC metastasis.

Abstract 135: Phosphorylation and furin-mediated processing are critical posttranslational modifications of the KISS1 metastasis suppressor

Originally discovered as a metastasis suppressor, KISS1 has since been defined as a neurotransmittor and regulator of diverse cellular functions and has been implicated in pathologies such as hypogonadism and Alzheimer's disease. Several laboratories are actively developing therapies based upon KISS1 biology. KISS1 is secreted and processed into small peptides (called kisspeptins (KP)) in the extracellular milieu. However, the enzyme(s) responsible for generation of KP from nascent KISS1 is unknown, although sequence analysis (cleavage at KR or RR dibasic sites) suggests that proprotein convertases (PC) are responsible. We hypothesized that enzyme(s) belonging to the PC family processes KISS1 to generate KP. KISS1 processing was completely inhibited by treatment with PC inhibitors Dec-RVKR-CMK and a1-PDX in these cells multiple tumor cell lines. Further, mRNA expression of the seven members of the PC family showed consistent expression of only three proteases - furin, PCSK5 and PCSK7 narrowing the candidate proteases. Only shRNA-mediated knockdown of furin (i.e., not PCSK5 or PCSK7) blocked KISS1 processing. Thus furin is the essential enzyme responsible for KP generation. Even when cells were exposed to Dec-RVKR-CMK or shRNA targeting furin, two bands (Mr∼15.9 kDa and Mr ∼17 kDa) were consistently detected in SDS-PAGE of conditioned medium. This observation suggested KISS1 could either be alternatively post-translationally modified or that another protease (family) might also cleave KISS1. To investigate the possibility that KISS1 may be post-translationally modified, potential sites of O-glycosylation (NetOGlyc 4.0) or serine/threonine phosphorylation (NetPhos 2.0) were analyzed in silico. Three amino acid residues (T69, S70, and S72)of the native KISS1 protein showed highest scores as being either O-glycosylated or phosphorylated. Further, mutation of these three residues to alanine resulted in the loss of the higher molecular weight band which was co-localized to a band detected using anti-phospho Ser/Thr strongly suggesting that KISS1 is indeed phosphorylated. This is the first report of phosphorylation of KISS1. Studies are underway to identify the kinase(s) and phosphatase(s) involved as well as the functional significance of the phosphorylation. Support: CA134981, National Foundation for Cancer Research, Steiner Family Fellowship in Metastasis Research, Susan G. Komen for the Cure SAC110037.

Citation Format: Sitaram Harihar, Kelsey R. Hampton, Tomoo Iwakuma, Nabil G. Seidah, Danny R. Welch. Phosphorylation and furin-mediated processing are critical posttranslational modifications of the KISS1 metastasis suppressor. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 135. doi:10.1158/1538-7445.AM2014-135

Abstract LB-191: Astrocytes promote colonization of human brain with breast cancer cells via inhibition of KISS1 expression

Introduction: KISS1 metastatic suppressor is a negative regulator of tumor progression. Recently, we described that breast cancer metastatic cells to the brain exhibit much lower level of KISS1 expression detected by real time PCR and IHC. However little is known about the mechanism that regulates KISS1 in the brain metastatic cells and promotes brain metastases. We hypothesized that loss of KISS1 allows persistence of metastatic cells in the brain.

Results: Given the fact that some migrating breast cancer cells possess stem cells (CSC) properties, we stained the primary breast cancer and brain metastatic clinical specimens contain breast cancer cells using CD24, CD44, ESA1 and KISS1 markers. We observed that in the brain metastases, the CSC exhibit low/lack of KISS1 expression, whereas in the MDA-MB-231 model, blood derived circulating cells express comparative to primary xenografts level of KiSS1 expression. Then we co-cultured MDA-231-Br or CN34Br cells with either human microglia (HM) or human astrocytes (HA) to determine the conditions that affect KISS1 expression. We observed that primary human astrocytes downregulate the expression of KISS1, whereas HM conditional media had little effect. Furthermore, we detected that inhibition of KISS1 expression in breast metastatic cells is dependent on the expression of chemokines such CCL2 and CXCL12. This effect was dose dependent and required activation of cellular signaling in the tumor cells. Our data demonstrate that interaction of breast cancer cells with astrocytes inhibits KISS1 metastatic suppressor and contributes to tumorigenesis.

Conclusions: Our results provide a new insight into the mechanism that promotes brain metastases, and may have implications for the treatment and prevention of brain metastases.

Citation Format: Ilya V. Ulasov, Natalya V. Kaverina, JG Yoon, Hwahyung Lee, Purvaba Sarvaiya, Dmitry Malin, Vincent L. Cryns, Danny R. Welch, Charles K. Cobbs. Astrocytes promote colonization of human brain with breast cancer cells via inhibition of KISS1 expression. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr LB-191. doi:10.1158/1538-7445.AM2014-LB-191

Abstract 1990: Identification and biochemical characterization of HMP19, a tumor/metastasis suppressor in pancreatic cancer

The overwhelming majority of pancreatic cancer is not diagnosed until the cancer has metastasized, which leads to an abysmal average life expectancy (3 to 6 months post-diagnosis). Earlier detection and more effective treatments have been hampered by inadequate understanding of the underlying molecular mechanisms controlling metastasis. Metastasis suppressors inhibit metastasis without blocking orthotopic tumor growth and represent powerful new targets and biomarkers. We hypothesize that metastasis suppressors are involved in controlling metastasis in pancreatic cancer. Using an unbiased genome wide shRNA screen, we identified HMP19 as a putative metastasis suppressor in pancreatic ductal adenocarcinoma (PDAC). Functional validation was carried out by manipulating expression in PDAC cell lines. Knockdown of HMP19 in S2-028 cells increased orthotopic tumor growth and liver metastasis, while over-expression in S2-007 cells slowed tumor growth and suppressed metastasis in xenographs. HMP19 expression inversely correlated with in vitro migration, colony formation, proliferation, and cyclin E1 expression. In clinical samples, HMP19 expression inversely correlated with tumor size, plexus invasion, liver metastasis, and patient survival (p<0.05). HMP19 is essentially uncharacterized, except for reported sub-cellular localization in the Golgi apparatus in neuronal cells (Saberan-Djoneidi et al. 1994). HMP19 is localized throughout the secretory/endocytic pathways (fluorescence microscopy), including at the plasma membrane (surface biotinylation). HMP19 is predicted to be a type II, single-pass transmembrane protein with 3 domains (cytoplasmic; transmembrane; extracellular). However, the ability to biotinylate HMP19 in intact S2-028 cells expressing the predicted cytoplasmic+transmembrane domains suggest that HMP19 might be a type I transmembrane protein. The cytoplasmic tail and transmembrane domains are important for protein stability, while the presence of multiple bands in immunoblots (16, 19, 21, and 25 kDa) suggests that HMP19 is post-translationally modified by an as-yet defined mechanism. Interestingly, we found that HMP19 co-immunoprecipitates with and suppresses phospho-ERK nuclear localization. Here we describe the discovery and characterization of a novel PDAC metastasis suppressor and potential mechanism of action, which is in support of our hypothesis that metastasis suppressors control metastasis in pancreatic cancer.

Support: National Foundation for Cancer Research, Hall Family Foundation, Kansas Bioscience Authority, and CA134981

Citation Format: Christopher R. Bohl, Hiroshi Kurahara, Shoji Natsugoe, Yuka Nishizono, Sitaram Harihar, Tomoo Iwakuma, Danny R. Welch. Identification and biochemical characterization of HMP19, a tumor/metastasis suppressor in pancreatic cancer. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 1990. doi:10.1158/1538-7445.AM2014-1990

Abstract 126: The KISS1 metastasis suppressor appears to integrate glycolysis, mitochondrial biogenesis and metastasis via regulation of a PGC1α pathway

Considering the enormous energy requirements and stresses of the metastatic cascade, an interrelationship with aerobic glycolysis seems intuitive, but has not been definitively established. The purpose of these studies was to determine whether there is a relationship between KISS1 metastasis suppression and metabolism. Wild-type KISS1 expressed in human melanoma cells were metastasis suppressed and took up less glucose and produced less lactate, corresponding to higher pH[Ex]. Metabolism and metastasis changes did not occur when KISS1 was missing the secretion signal peptide (ΔSS). Changes in glucose transport and key glycolytic enzymes did not consistently correlate with metabolic changes; however, V-ATPase, which promotes extracellular acidification, invasion and metastasis, appears to be involved in KISS1-mediated metabolic changes. Also corresponding with the shift from glycolysis to oxidative phosphorylation, KISS1-expressing cells have 30-50% more mitochondrial mass accompanied increased higher expression of PPARγ co-activator 1α (PGC1α), a master regulator of mitochondrial biogenesis. PGC1α-mediated downstream pathways (i.e. fatty acid synthesis and β-oxidation) are differentially regulated by KISS1, apparently reliant upon direct KISS1 interaction with Nuclear Respiratory Factor 1 (NRF1), a major transcription factor involved in mitochondrial biogenesis. KISS1 does not affect PGC1α mRNA expression but stabilizes the protein through interaction with the ubiquitin-like protein, UBQLN1. To test whether a KISS1- PGC1α axis is critical for metastasis suppressor function, shRNA to KISS1 or PGC1α was introduced into KISS1-expressing cells. Metabolic changes and suppression of invasion and migration were reversed. Importantly, knock-down of PGC1α abolished KISS1-mediated metastasis suppression in vivo, strongly suggesting that PGC1α is an essential downstream mediator of KISS1 as a metastasis suppressor. Taken together, these data define a novel signaling pathway controlling metabolism and metastasis. Moreover, these data appear to directly connect changes in aerobic glycolysis, mitochondrial metabolism, and cancer metastasis.

Citation Format: Wen Liu, Benjamin Beck, Kedar S. Vaidya, Kevin T. Nash, Scott W. Ballinger, Danny R. Welch. The KISS1 metastasis suppressor appears to integrate glycolysis, mitochondrial biogenesis and metastasis via regulation of a PGC1α pathway. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 126. doi:10.1158/1538-7445.AM2014-126

Abstract 130: Deadly KISS, Kisspeptin10 interaction with osteoblasts and breast cancer metastastic cells

Current cancer research focuses on blockading metastasis with the hope of increasing patient survival and prognoses. This research has spurred an interest in metastasis suppressor genes, such as KISS-1, whose role in breast cancer remains controversial. This study focuses on the interactions among one of the proteolytic processing products of the Kiss1 protein (kisspeptin10, KP10), its receptor, KISS1R (GPR54, AXOR12), osteoblasts (bone forming cells), and bone-metastatic breast cancer cells, MDA-MB-231. Previous research suggests that treatment with KP10 reduces the ability of the cancer cells to invade a reconstituted basement membrane (Matrigel) and to migrate in response to osteosarcoma cells. The aim of this present study was to determine if KP10 affected the interaction of MC3T3-E1 osteoblasts and bone-metastatic breast cancer cells.

Our laboratory had previously determined that osteoblasts exhibit an inflammatory response when treated with conditioned medium from breast cancer cells. This inflammatory response may contribute to cancer cell proliferation in the bone. This response has not yet been characterized in the presence of KP10. I hypothesized that KP10 would down regulate the inflammatory response of osteoblasts to breast cancer cells. MDA-MB-231 breast cancer cells express theKISS1R; therefore, these cells were treated with KP10 (10-100 nM, 2hr), the medium was collected, and the osteoblasts were treated with it. KP10 significantly decreased the inflammatory response of osteoblasts to breast cancer conditioned media indicated by decreased levels of IL-6 as determined by ELISA. This research has important implications because it provides insight into how KP10 may be acting on either the breast cancer cells or the bone cells. In my future research, I will continue to characterize how KP10 can be used to prevent proliferation or activation of breast cancer metastases in the bone.

This work was supported by an undergraduate research grant from the Eberly College of Science of Penn State University.

Citation Format: Kaitlyn E. Leahey, Danny R. Welch, Yu-Chi Chen, Karen M. Bussard, Andrea M. Mastro. Deadly KISS, Kisspeptin10 interaction with osteoblasts and breast cancer metastastic cells. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 130. doi:10.1158/1538-7445.AM2014-130

Abstract 4326: Mitochondrial genetics and cellular metabolism regulate tumorigenicity and metastatic potential

Current paradigms of carcinogenic risk suggest that genetic, hormonal, and environmental factors combine to influence an individual's predilection for breast cancer and related metastatic tumor formation. The genetic component, in particular, has become the focus of many emergent studies. A renewed focus on cancer metabolism and the Warburg Effect has similarly cast a spotlight on the role, if any, of the mitochondrion in directing disease progression. Analysis of the direct contribution of mitochondrial DNA on tumorigenicity is made possible through the use of mitochondrial-nuclear exchange (MNX) mice in which nuclei from normal FVB mice (the background strain of the tg: MMTV-PyMT) were transferred onto cytoplasms containing C57BL/6 or BALB/c mitochondria. Crossing male FVB:tg:MMTV:PyMT mice with FVB(nDNA)C57BL/6(mtDNA) or FVB(nDNA)BALB/c(mtDNA) females maintained nuclear FVB nDNA and takes advantage of maternal inheritance of mtDNA. These PyMT transgene positive female progeny are then scored for primary tumor onset and pulmonary metastatic density. Present data indicate primary tumor latency segregating by mitochondrial DNA as PyMT-FVB wild-type animals develop primary tumors in 57 days compared to PyMT-FVB(n)C57BL/6(mt) which develop primary tumors in 65 days and PyMT-FVB(n)BALB/c(mt) animals having detectable tumors in 52 days. One group of animals were aged 40 days following primary tumor detection and a second group were sacrificed when aged to 70 days, allowing for evaluation of metastatic severity and confirmation of differential primary tumor growth, respectively. This work hypothesizes that the pre-existent “normal” mitochondrial haplotype harbored by an individual conveys risk in determining tumor latency and metastatic susceptibility. Furthermore, these changes in susceptibility will be accompanied by altered mitochondrial functional characteristics that can be attributed to differences in mitochondrial haplotype. To address those mitochondrial differences, primary mammary epithelial cells were isolated from resected tumors which were then assessed for Complex I and Complex IV activity. In addition, isolated mammary epithelial cells from tumor and healthy animals had bioenergetic profiles generated using the Seahorse XF24 analyzer. Markers of ROS production will also be assessed as they too have been implicated increasingly frequently in cancer aggressiveness.

Citation Format: Kyle P. Feeley, Alexander W. Bray, Jessica L. Fetterman, David G. Westbrook, Larry W. Johnson, Robert A. Kesterson, Danny R. Welch, Scott W. Ballinger. Mitochondrial genetics and cellular metabolism regulate tumorigenicity and metastatic potential. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 4326. doi:10.1158/1538-7445.AM2014-4326

Abstract SY20-03: Nuclear-mitochondrial cross-talk: A key determinant of cancer metastasis

Despite the well known energy requirements and stresses of metastasis, the relationships between metabolism, mitochondrial genetics and metastasis are still underdeveloped. Two lines of investigation point to more intimate involvement of mtDNA than is widely appreciated. First, recent data demonstrate that the metastasis suppressor KISS1 essentially reverses the so-called Warburg Effect by regulating mitochondrial biogenesis. KISS1 re-expression results in higher pH[Ex] due to reduced lactate secretion concomitant with reduced glycolysis and a shift toward oxidative phosphorylation. KISS1-expressing cells have 30-50% more mitochondrial mass, which appears to be due to higher expression of PPARγ co-activator 1α (PGC1α), a master regulator of mitochondrial biogenesis. shRNA-mediated knockdown of KISS1 and PGC1α establish a pathway between these molecules, mitochondrial biogenesis and metastatic potential. Second, genetic crosses with a newly described MNX (mitochondrial-nuclear exchange) mice suggest that mitochondrial polymorphisms (haplotypes) may control susceptibility to metastasis. Transgenic FVB/N-tg:MMTV-PyMT which spontaneously develop mammary tumors and lung metastasis with high penetrance were crossed with female MNX mice having the same nuclear background (FVB - wild-type) but with C57BL/6 and BALB/c mitochondrial backgrounds. Using this strategy, the mtDNA contributions to metastasis can be discriminated. Results demonstrate that tumor and metastasis incidence do not appear to be significantly different. However, metastasis size is greatly affected. Taken together, these data strongly support the concept that mitochondrial-nuclear cross-talk is a more significant determinant of metastasis than generally appreciated. SUPPORT: NCI-CA134981; Natl Fndn Cancer Res, Susan G. Komen SAC11037, Hall Family Fndn, KS Bioscience Auth.

Citation Format: Danny R. Welch, Wen Liu, Kyle P. Feeley, Scott W. Ballinger. Nuclear-mitochondrial cross-talk: A key determinant of cancer metastasis. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr SY20-03. doi:10.1158/1538-7445.AM2014-SY20-03

Abstract A090: Mitochondrial genetics in the regulation of tumorigenicity and metastatic potential

Current paradigms of carcinogenic risk suggest that genetic, hormonal, and environmental factors combine to influence an individual's predilection for breast cancer and related metastatic tumor formation. The genetic component, in particular, has become the focus of emergent studies which have determined a role for nuclear genetic differences directing breast cancer susceptibility. Studies examining tumor latency and metastatic formation in mice have demonstrated clear differences between inbred strains. However, these studies fail to exclude the possibility that mitochondrial genetic inheritance is responsible for the observed changes in tumor onset and metastatic spread due to maternal inheritance of the mitochondrial genome. Although mitochondrial mutations within the tumor cell have recently been implicated as contributing to metastatic potential, studies have not directly addressed the effects of the mitochondrial DNA (mtDNA) background of the host on disease susceptibility. This work hypothesizes that the pre-existent “normal” mitochondrial haplotype harbored by an individual conveys risk in determining tumor latency and metastatic susceptibility. Furthermore, these changes in susceptibility will be accompanied by altered mitochondrial functional characteristics that can be attributed to differences in mitochondrial haplotype. Analysis of the direct contribution of mitochondrial DNA on tumorigenicity is made possible through the use of mitochondrial-nuclear exchange (MNX) mice in which nuclei from normal FVB mice (the background strain of the tg: MMTV-PyMT) were transferred onto cytoplasms containing C57BL/6 or BALB/c mitochondria. Crossing male FVB:tg:MMTV:PyMT mice with FVB(nDNA)C57BL/6(mtDNA) or FBV(nDNA)BALB/c(mtDNA) females maintained nuclear FVB nDNA and takes advantage of maternal inheritance of mtDNA. Present data indicate primary tumor latency segregating by mitochondrial DNA as PyMT-FVB wild-type animals develop primary tumors in 57 days compared to PyMT-FVB(n)C57BL/6(mt) which develop primary tumors in 65 days. Bioenergetic analyses using the Seahorse XF-24 as well as electron transport complex enzymatic assays will be conducted to more precisely delineate the functional metabolic differences contributing to altered tumorigenicity. MNX crosses suggest that cross-talk between mtDNA and nDNA has a greater influence on metastasis than previously appreciated and that mtDNA may be used clinically to improve patient prognosis.

Citation Format: Kyle P. Feeley, Alexander W. Bray, Jessica L. Fetterman, David G. Westbrook, Larry W. Johnson, Robert A. Kesterson, Danny R. Welch, Scott W. Ballinger. Mitochondrial genetics in the regulation of tumorigenicity and metastatic potential. [abstract]. In: Proceedings of the AACR Special Conference on Advances in Breast Cancer Research: Genetics, Biology, and Clinical Applications; Oct 3-6, 2013; San Diego, CA. Philadelphia (PA): AACR; Mol Cancer Res 2013;11(10 Suppl):Abstract nr A090.

Imaging of epidermal growth factor receptor on single breast cancer cells using surface-enhanced Raman spectroscopy

Epidermal growth factor receptor (EGFR) is widely used as a biomarker for pathological grading and therapeutic targeting of human cancers. This study investigates expression, spatial distribution as well as the endocytosis of EGFR in single breast cancer cells using surface-enhanced Raman spectroscopy (SERS). By incubating anti-EGFR antibody conjugated SERS nanoprobes with an EGFR-over-expressing cancer cell line, A431, EGFR localization was measured over time and found to be located primarily at the cell surface. To further validate the constructed SERS probes, we applied this SERS probes to detect the EGFR expression on breast cancer cells (MDA-MB-435, MDA-MB-231) and their counterpart cell lines in which EGFR expression was down-regulated by breast cancer metastasis suppressor 1 (BRMS1). The results showed that SERS method not only confirms immunoblot data measuring EGFR levels, but also adds new insights regarding EGFR localization and internalization in living cells which is impossible in immunoblot method. Thus, SERS provides a powerful new tool to measure biomarkers in living cancer cells.

Toward a drug development path that targets metastatic progression in osteosarcoma

Despite successful primary tumor treatment, the development of pulmonary metastasis continues to be the most common cause of mortality in patients with osteosarcoma. A conventional drug development path requiring drugs to induce regression of established lesions has not led to improvements for patients with osteosarcoma in more than 30 years. On the basis of our growing understanding of metastasis biology, it is now reasonable and essential that we focus on developing therapeutics that target metastatic progression. To advance this agenda, a meeting of key opinion leaders and experts in the metastasis and osteosarcoma communities was convened in Bethesda, Maryland. The goal of this meeting was to provide a "Perspective" that would establish a preclinical translational path that could support the early evaluation of potential therapeutic agents that uniquely target the metastatic phenotype. Although focused on osteosarcoma, the need for this perspective is shared among many cancer types. The consensus achieved from the meeting included the following: the biology of metastatic progression is associated with metastasis-specific targets/processes that may not influence grossly detectable lesions; targeting of metastasis-specific processes is feasible; rigorous preclinical data are needed to support translation of metastasis-specific agents into human trials where regression of measurable disease is not an expected outcome; preclinical data should include an understanding of mechanism of action, validation of pharmacodynamic markers of effective exposure and response, the use of several murine models of effectiveness, and where feasible the inclusion of the dog with naturally occurring osteosarcoma to define the activity of new drugs in the micrometastatic disease setting.

Furin is the major proprotein convertase required for KISS1-to-Kisspeptin processing

KISS1 is a broadly functional secreted proprotein that is then processed into small peptides, termed kisspeptins (KP). Since sequence analysis showed cleavage at KR or RR dibasic sites of the nascent protein, it was hypothesized that enzyme(s) belonging to the proprotein convertase family of proteases process KISS1 to generate KP. To this end, cell lines over-expressing KISS1 were treated with the proprotein convertase inhibitors, Dec-RVKR-CMK and α1-PDX, and KISS1 processing was completely inhibited. To identify the specific enzyme(s) responsible for KISS1 processing, mRNA expression was systematically analyzed for six proprotein convertases found in secretory pathways. Consistent expression of the three proteases – furin, PCSK5 and PCSK7 – were potentially implicated in KISS1 processing. However, shRNA-mediated knockdown of furin – but not PCSK5 or PCSK7 – blocked KISS1 processing. Thus, furin appears to be the essential enzyme for the generation of kisspeptins.

Metastasis suppressor KISS1 seems to reverse the Warburg effect by enhancing mitochondrial biogenesis

Cancer cells tend to utilize aerobic glycolysis even under normoxic conditions, commonly called the "Warburg effect." Aerobic glycolysis often directly correlates with malignancy, but its purpose, if any, in metastasis remains unclear. When wild-type KISS1 metastasis suppressor is expressed, aerobic glycolysis decreases and oxidative phosphorylation predominates. However, when KISS1 is missing the secretion signal peptide (ΔSS), invasion and metastasis are no longer suppressed and cells continue to metabolize using aerobic glycolysis. KISS1-expressing cells have 30% to 50% more mitochondrial mass than ΔSS-expressing cells, which are accompanied by correspondingly increased mitochondrial gene expression and higher expression of PGC1α, a master coactivator that regulates mitochondrial mass and metabolism. PGC1α-mediated downstream pathways (i.e., fatty acid synthesis and β-oxidation) are differentially regulated by KISS1, apparently reliant upon direct KISS1 interaction with NRF1, a major transcription factor involved in mitochondrial biogenesis. Since the downstream effects could be reversed using short hairpin RNA to KISS1 or PGC1α, these data appear to directly connect changes in mitochondria mass, cellular glucose metabolism, and metastasis.

MCF-7 cells expressing nuclear associated lysyl oxidase-like 2 (LOXL2) exhibit an epithelial-to-mesenchymal transition (EMT) phenotype and are highly invasive in vitro

LOXL2 is a copper- and lysine tyrosylquinone-dependent amine oxidase that has been proposed to function both extracellularly and intracellularly to activate oncogenic signaling pathways leading to EMT and invasion of breast cancer cells. In this study, we selected MCF-7 cells that stably express forms of recombinant LOXL2 differing in their subcellular localizations and catalytic competencies. This enabled us to dissect the molecular functions of intracellular and extracellular LOXL2s and examine their contributions to breast cancer metastasis/invasion. We discovered that secreted LOXL2 (~100-kDa) is N-glycosylated at Asn-455 and Asn-644, whereas intracellular LOXL2 (~75-kDa) is nonglycosylated and N-terminally processed, and is primarily associated with the nucleus. Both forms of LOXL2 can oxidize lysine in solution. However, we found that expression of intracellular LOXL2 is more strongly associated with EMT and invasiveness than secreted LOXL2 in vitro. The results indicate that nuclear associated LOXL2 contributes to the stabilization of Snail1 transcription factor at the protein level to induce EMT and promote invasion in vitro, through repression of E-cadherin, occludin, and estrogen receptor-α, and up-regulation of vimentin, fibronectin, and MT1-MMP.

Expression of metastasis suppressor BRMS1 in breast cancer cells results in a marked delay in cellular adhesion to matrix

Metastatic dissemination is a multi-step process that depends on cancer cells' ability to respond to microenvironmental cues by adapting adhesion abilities and undergoing cytoskeletal rearrangement. Breast Cancer Metastasis Suppressor 1 (BRMS1) affects several steps of the metastatic cascade: it decreases survival in circulation, increases susceptibility to anoikis, and reduces capacity to colonize secondary organs. In this report, BRMS1 expression is shown to not significantly alter expression levels of integrin monomers, while time-lapse and confocal microscopy revealed that BRMS1-expressing cells exhibited reduced activation of both β1 integrin and focal adhesion kinase, and decreased localization of these molecules to sites of focal adhesions. Short-term plating of BRMS1-expressing cells onto collagen or fibronectin markedly decreased cytoskeletal reorganization and formation of cellular adhesion projections. Under 3D culture conditions, BRMS1-expressing cells remained rounded and failed to reorganize their cytoskeleton and form invasive colonies. Taken together, BRMS1-expressing breast cancer cells are greatly attenuated in their ability to respond to microenvironment changes. © 2013 Wiley Periodicals, Inc.

Breast cancer metastasis suppressor-1 promoter methylation in primary breast tumors and corresponding circulating tumor cells

Breast cancer metastasis suppressor-1 (BRMS1) differentially regulates the expression of multiple genes, leading to metastasis suppression without affecting orthotopic tumor growth. For the first time, BRMS1 promoter methylation was evaluated as a prognostic biomarker in primary breast tumors and a subset of corresponding circulating tumor cells (CTC). Formalin-fixed paraffin embedded samples were analyzed for BRMS1 methylation status using methylation-specific PCR in a human specimen cohort consisting of noncancerous tissues, benign fibroadenomas, and primary breast tumors, including some with adjacent noncancerous tissues. Peripheral blood mononuclear cells from a large subset of these patients were fixed in cytospins and analyzed. In addition, BRMS1 expression in cytospins was examined by double-immunofluorescence using anti-BRMS1 and pan-cytokeratin antibodies. BRMS1 promoter methylation was not detected in noncancerous breast tissues or benign fibroadenomas; however, methylation was observed in more than a third of primary breast tumors. Critically, BRMS1 promoter methylation in primary tumors was significantly associated with reduced disease-free survival with a trend toward reduced overall survival. Similarly, a third of cytospin samples were positive for the presence of CTCs, and the total number of detected CTCs was 41. Although a large fraction of CTCs were negative or maintained low expression of BRSM1, promoter methylation was observed in a small fraction of samples, implying that BRSM1 expression in CTCs was either downregulated or heterogeneous. In summary, these data define BRMS1 promoter methylation in primary breast tumors and associated CTCs.

IMPLICATIONS

This study indicates that BRSM1 promoter methylation status has biomarker potential in breast cancer.

Abstract 3860: Furin is required for processing KISS1 to kisspeptins

KISS1 is a broadly functional metastatic suppressor that is secreted and processed in the extracellular milieu into small peptides (called kisspeptins (KP)). The enzyme(s) responsible for generation of KP from nascent KISS1 is unknown, although sequence analysis (cleavage at KR or RR dibasic sites) suggests that members of the proprotein convertase family may be involved. We, therefore, hypothesized that enzyme(s) belonging to the proprotein convertase family process KISS1 to generate kisspeptins. To this end, we treated multiple melanomas and breast carcinoma cells overexpressing KISS1 with the proprotein convertase inhibitor Dec-RVKR-CMK and found that KISS1 processing was completely inhibited, strongly consistent with a role for proprotein convertases. To identify specific proprotein convertases responsible for KISS1 processing, we systematically analyzed the mRNA expression of the nine members of this family across numerous cell lines. We found a consistent expression of the three proteases - furin, PC5 and PC7 -suggesting one or combination of these three enzymes to be involved in KISS1 processing. shRNA-mediated knockdown of furin, PC5 and PC7 (individually and in combination) resulted in complete loss of KISS1 processing only in furin knockdown cells; whereas, no effect on processing was observed in PC5 or PC7 knockdown cells. Thus, when combined with previous studies showing post-secretion processing, extracellular furin was identified as the essential enzyme responsible for KISS1 proteolytic cleavage into kisspeptins. [Support: CA134981, Komen SAC110037, National Foundation for Cancer Research, Steiner Family Fellowship in Metastasis Research]

Citation Format: Sitaram Harihar, Keke M. Pounds, Tomoo Iwakuma, N G. Seidah, Danny R. Welch. Furin is required for processing KISS1 to kisspeptins. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 3860. doi:10.1158/1538-7445.AM2013-3860

Abstract 1864: Mitochondrial bioenergetics of metastatic breast cancer cells in response to decreasing oxygen tension

Solid tumors are characterized by regions of low oxygen tension, which play a central role in tumor progression and resistance to therapy. The major organelle affected by reduced oxygen tension is the mitochondrion, which has to functionally adapt to maintain cellular bioenergetics for the cell survival. In the present study, a novel experimental approach was developed to examine the real-time bioenergetic changes during adaptation to various oxygen tensions ranging from 20% to < 1% oxygen using highly sensitive extracellular flux technology. Oxygen was gradually removed from the culture medium, and bioenergetic changes were measured in normal breast epithelial (MCF10A) and metastatic cancer cell lines (MDA-MB-231 and MCF10CA clones). We found that breast cancer cells, but not MCF10A cells, rapidly responded to low oxygen tension by stabilizing HIF-1α, increasing hypoxia responsive gene expression, and stimulating cellular uptake of glucose, confirming previous observations. In addition, breast cancer cells increased extracellular acidification rate (ECAR) or glycolysis during adaptation to low oxygen tension, and this effect was markedly lower in MCF10A cells. Interestingly, breast cancer cells exhibited a biphasic response in oxygen consumption rate (OCR) as the oxygen tension was reduced gradually from 20% to <1.0%, a response not previously described. This effect is HIF-1α-dependent, as silencing HIF-1α function in cancer cells completely abolished the biphasic response in OCR and increase in ECAR. Moreover, cancer cells demonstrated the ability to restore and maintain its OCR steadily at specific oxygen tension either during deoxygenation or reoxygenation, an effect not observed in HIF-1α silenced cells. Additional studies confirmed that the initial stimulation of OCR is due to increased mitochondrial respiration. In conclusion, our results suggest that HIF-1α provides high degree of bioenergetic flexibility under different oxygen tensions which may confer an adaptive advantage in the ever-changing tumor microenvironment as well as during invasion and metastasis. Moreover, these differences may be useful in screening novel therapeutic agents that target the bioenergetics of cancer cells in response to low oxygen tension.

Citation Format: Praveen K. Vayalil, Anne R. Diers, Claudia R. Olivia, Corinne E. Griguer, Victor Darley-Usmar, Douglas R. Hurst, Danny R. Welch, Aimee Landar. Mitochondrial bioenergetics of metastatic breast cancer cells in response to decreasing oxygen tension. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 1864. doi:10.1158/1538-7445.AM2013-1864

Abstract 3866: The KISS1 metastasis suppressor appears to reverse the Warburg effect by enhancing mitochondria biogenesis

Cancer cells tend to utilize aerobic glycolysis even under normoxic conditions, which is commonly called the “Warburg Effect.” Aerobic glycolysis often directly correlates with malignant potential. Though its purpose remains unclear, the “Warburg Effect” is thought to confer advantages to proliferation, survival and dissemination to cancer cells by increasing uptake of nutrients into biomass. KISS1 protein is secreted and proteolytically cleaved into kisspeptins (KP) that block the colonization of disseminated metastatic C8161.9 human melanoma cells at secondary sites. In this study, we hypothesized that KISS1 metastasis suppression occurs via regulation of aerobic glycolysis. Comparison of bioenergetic and metabolic aspects of glucose metabolism showed that all KISS1-secreting clones were less invasive, took up less glucose, produced less lactate which corresponds to higher pH[Ex], effects which were reversed when cells were transduced with shRNA to KISS1. The metabolism, invasion, and metastasis changes did not occur when KISS1 was missing the signal peptide (ΔSS). Utilizing a Seahorse bioanalyzer, KISS1, but not ΔSS cells showed significantly decreased extracellular acidification rates, increased O2 consumption and elevated mitochondria reserve capacity, an indicator of mitochondrial condition and a parameter thought to improve the cells’ ability to cope with oxidative stress. KISS1-expressing cells have 30-50% more mitochondria compared to vector or ΔSS-expressing cells. Increased mitochondrial mass was accompanied by significantly increased expression of mitochondrial genes involved in apoptosis and mitophagy, protein processing and trafficking. Increased mitochondrial mass correlated with higher PGC1α considered to be a master co-activator that regulates mitochondrial mass and metabolism. Interestingly, KISS1 differentially affects PGC1α-mediated downstream pathways, i.e. fatty acid synthesis and β-oxidation. KISS1-mediated up-regulation of mitochondria biogenesis appears to rely on KISS1 interaction with NRF1, a major transcription factor of mitochondria biogenesis. KP10 (which can activate the KISS1 receptor) does not alter pH[Ex] since the metastatic tumor cells do not express KISS1R. This paradox - metastasis and metabolic changes require secretion, but responding cells do not have the receptor - raises questions regarding the mechanism. Nonetheless, these data appear to directly connect changes in mitochondria mass, cellular glucose metabolism and metastasis. [Support: CA134581, Natl. Fndn. Cancer Res., Komen SAC110037].

Citation Format: Wen Liu, Benjamin H. Beck, Kedar S. Vaidya, Kevin T. Nash, Anne R. Diers, Kyle P. Feeley, Aimee Landar, Scott W. Ballinger, Danny R. Welch. The KISS1 metastasis suppressor appears to reverse the Warburg effect by enhancing mitochondria biogenesis. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 3866. doi:10.1158/1538-7445.AM2013-3866

Unraveling the 'TGF-β paradox' one metastamir at a time

Transforming growth factor beta (TGF-β) has received noteworthy attention in the recent past due to its unique characteristic of functionally switching roles from tumor suppressor to metastasis promoter. To uncover the black box surrounding the mechanisms of TGF-β, Taylor and colleagues performed global miRNA expression analyses using a murine mammary carcinoma progression model. They discovered multiple miRNA regulated by TGF-β and matrix stiffness. Focusing on miR-181a, they uncovered an intricate pathway regulating breast cancer metastasis that sheds new insight into metastasis regulation that may prove useful in clinical settings.

Simulations of magnetic field generation in unmagnetized plasmas via beat-wave current drive

This work describes the scientific basis and associated simulation results for the magnetization of an unmagnetized plasma via beat-wave current drive. Two-dimensional electromagnetic particle-in-cell simulations have been performed for a variety of angles between the injected waves to demonstrate beat-wave generation in agreement with theoretical predictions of the beat-wave wave vector and saturation time, revealing new 2D effects. The simulations clearly demonstrate electron acceleration by the beat waves and resultant current drive and magnetic field generation. The basic process depends entirely on the angle between the parent waves and the ratio of the beat-wave phase velocity to the electron thermal velocity. The wave to magnetic energy conversion efficiency of the cases examined is as high as 0.2%. The technique could enable novel plasma experiments in which the use of magnetic coils is infeasible.

Pre-osteoblastic MC3T3-E1 cells promote breast cancer growth in bone in a murine xenograft model

The bones are the most common sites of breast cancer metastasis. Upon arrival within the bone microenvironment, breast cancer cells coordinate the activities of stromal cells, resulting in an increase in osteoclast activity and bone matrix degradation. In late stages of bone metastasis, breast cancer cells induce apoptosis in osteoblasts, which further exacerbates bone loss. However, in early stages, breast cancer cells induce osteoblasts to secrete inflammatory cytokines purported to drive tumor progression. To more thoroughly evaluate the role of osteoblasts in early stages of breast cancer metastasis to the bones, we used green fluorescent protein-labeled human breast cancer cell lines MDA-MB-231 and MDA-MB-435, which both induce osteolysis after intra-femoral injection in athymic mice, and the murine pre-osteoblastic cell line MC3T3-E1 to modulate osteoblast populations at the sites of breast cancer metastasis. Breast cancer cells were injected directly into the femur with or without equal numbers of MC3T3-E1 cells. Tumors grew significantly larger when co-injected with breast cancer cells and MC3T3-E1 cells than injected with breast cancer cells alone. Osteolysis was induced in both groups, indicating that MC3T3-E1 cells did not block the ability of breast cancer cells to cause bone destruction. MC3T3-E1 cells promoted tumor growth out of the bone into the extraosseous stroma. These data suggest that breast cancer cells and osteoblasts communicate during early stages of bone metastasis and promote tumor growth.

Allelic variation and differential expression of the mSIN3A histone deacetylase complex gene Arid4b promote mammary tumor growth and metastasis

Accumulating evidence suggests that breast cancer metastatic progression is modified by germline polymorphism, although specific modifier genes have remained largely undefined. In the current study, we employ the MMTV-PyMT transgenic mouse model and the AKXD panel of recombinant inbred mice to identify AT-rich interactive domain 4B (Arid4b; NM_194262) as a breast cancer progression modifier gene. Ectopic expression of Arid4b promoted primary tumor growth in vivo as well as increased migration and invasion in vitro, and the phenotype was associated with polymorphisms identified between the AKR/J and DBA/2J alleles as predicted by our genetic analyses. Stable shRNA-mediated knockdown of Arid4b caused a significant reduction in pulmonary metastases, validating a role for Arid4b as a metastasis modifier gene. ARID4B physically interacts with the breast cancer metastasis suppressor BRMS1, and we detected differential binding of the Arid4b alleles to histone deacetylase complex members mSIN3A and mSDS3, suggesting that the mechanism of Arid4b action likely involves interactions with chromatin modifying complexes. Downregulation of the conserved Tpx2 gene network, which is comprised of many factors regulating cell cycle and mitotic spindle biology, was observed concomitant with loss of metastatic efficiency in Arid4b knockdown cells. Consistent with our genetic analysis and in vivo experiments in our mouse model system, ARID4B expression was also an independent predictor of distant metastasis-free survival in breast cancer patients with ER+ tumors. These studies support a causative role of ARID4B in metastatic progression of breast cancer.

Abstract 3416: Ubiquitous Brms1 expression is critical for mammary carcinoma metastasis suppression via promotion of apoptosis

Morbidity and mortality in breast cancer patients are drastically increased when primary tumor cells are able to spread to distant sites and proliferate to become secondary lesions. Effective treatment of metastatic disease has been limited; therefore, increased molecular understanding to identify biomarkers and targets is needed. We have previously shown that breast cancer metastasis suppressor 1 (Brms1) can suppress development of pulmonary metastases when expressed in a variety of cancer types, including metastatic mammary carcinoma. Our lab has developed two transgenic Brms1 mouse models, one which expresses murine Brms1 cDNA specifically in mammary tissue (expression by the mouse mammary tumor virus (MMTV) promoter) and a ubiquitous Brms1 expression model (expression by the chicken beta actin promoter). The goal of this study was to investigate mechanisms of Brms1-mediated metastasis suppression in transgenic mice that express Brms1 using a polyoma middle T (PyMT) oncogene-induced model. Brms1 expression, either ubiquitously or predominantly in the mammary gland, did not significantly alter growth of the primary tumor, confirming earlier studies. When expressed ubiquitously, Brms1 suppressed pulmonary metastasis and promoted tumor cell apoptosis in the lung but not in the mammary gland. However, selective expression of Brms1 in the mammary gland using the MMTV promoter did not significantly block metastasis nor did it promote apoptosis in mammary glands or lungs despite increased expression within primary tumors and the lungs. These results suggest tissue- or cell-type specific expression of Brms1 is a critical determinant for Brms1-mediated metastasis suppression.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 3416. doi:1538-7445.AM2012-3416