Fetuin-A Promotes 3-Dimensional Growth in LNCaP Prostate Cancer Cells by Sequestering Extracellular Vesicles to Their Surfaces to Act as Signaling Platforms

The present studies were conducted to evaluate key serum proteins and other components that mediate anchorage-independent growth (3-D growth) of LNCaP prostate cancer cells as spheroids. The cells were cultured on ultra-low attachment plates in the absence and presence of fetuin-A and with or without extracellular vesicles. The data show that fetuin-A (alpha 2HS glycoprotein) is the serum protein that mediates 3-D growth in these cells. It does so by sequestering extracellular vesicles of various sizes on the surfaces of rounded cells that grow as spheroids. These vesicles in turn transmit growth signals such as the activation of AKT and MAP kinases in a pattern that differs from the activation of these key growth signaling pathways in adherent and spread cells growing in 2-D. In the process of orchestrating the movement and disposition of extracellular vesicles on these cells, fetuin-A is readily internalized in adhered and spread cells but remains on the surfaces of non-adherent cells. Taken together, our studies suggest the presence of distinct signaling domains or scaffolding platforms on the surfaces of prostate tumor cells growing in 3-D compared to 2-D.

MicroRNA-21 deficiency suppresses prostate cancer progression through downregulation of the IRS1-SREBP-1 signaling pathway

Sterol regulatory element-binding protein 1 (SREBP-1), a master transcription factor in lipogenesis and lipid metabolism, is critical for disease progression and associated with poor outcomes in prostate cancer (PCa) patients. However, the mechanism of SREBP-1 regulation in PCa remains elusive. Here, we report that SREBP-1 is transcriptionally regulated by microRNA-21 (miR-21) in vitro in cultured cells and in vivo in mouse models. We observed aberrant upregulation of SREBP-1, fatty acid synthase (FASN) and acetyl-CoA carboxylase (ACC) in Pten/Trp53 double-null mouse embryonic fibroblasts (MEFs) and Pten/Trp53 double-null mutant mice. Strikingly, miR-21 loss significantly reduced cell proliferation and suppressed the prostate tumorigenesis of Pten/Trp53 mutant mice. Mechanistically, miR-21 inactivation decreased the levels of SREBP-1, FASN, and ACC in human PCa cells through downregulation of insulin receptor substrate 1 (IRS1)-mediated transcription and induction of cellular senescence. Conversely, miR-21 overexpression increased cell proliferation and migration; as well as the levels of IRS1, SREBP-1, FASN, and ACC in human PCa cells. Our findings reveal that miR-21 promotes PCa progression by activating the IRS1/SREBP-1 axis, and targeting miR-21/SREBP-1 signaling pathway can be a novel strategy for controlling PCa malignancy.

Identification of MAGEC2/CT10 as a High Calcium-Inducible Gene in Triple-Negative Breast Cancer

The expression of the melanoma/cancer-testis antigen MAGEC2/CT10 is restricted to germline cells, but like most cancer-testis antigens, it is frequently upregulated in advanced breast tumors and other malignant tumors. However, the physiological cues that trigger the expression of this gene during malignancy remain unknown. Given that malignant breast cancer is often associated with skeletal metastasis and co-morbidities such as cancer-induced hypercalcemia, we evaluated the effect of high Ca²⁺ on the calcium-sensing receptor (CaSR) and potential mechanisms underlying the survival of triple-negative breast cancer (TNBC) cells at high Ca²⁺. We show that chronic exposure of TNBC cells to high Ca²⁺ decreased the sensitivity of CaSR to Ca²⁺ but stimulated tumor cell growth and migration. Furthermore, high extracellular Ca²⁺ also stimulated the expression of early response genes such as FOS/FOSB and a unique set of genes associated with malignant tumors, including MAGEC2. We further show that the MAGEC2 proximal promoter is Ca²⁺ inducible and that FOS/FOSB binds to this promoter in a Ca²⁺- dependent manner. Finally, downregulation of MAGEC2 strongly inhibited the growth of TNBC cells in vitro. These data suggest for the first time that MAGEC2 is a high Ca²⁺ inducible gene and that aberrant expression of MAGEC2 in malignant TNBC tissues is at least in part mediated by an increase in circulating Ca²⁺via the AP-1 transcription factor.

The rapid endocytic uptake of fetuin-A by adherent tumor cells is mediated by Toll-like receptor 4 (TLR4)

Fetuin‐A is a serum glycoprotein synthesized and secreted into blood by the liver and whose main physiological function is the inhibition of ectopic calcification. However, a number of studies have demonstrated that it is a multifunctional protein. For example, endocytic uptake of fetuin‐A by tumor cells resulting in rapid cellular adhesion and spreading has been reported. The precise uptake mechanism, however, has been elusive. The present studies were done to determine whether Toll‐like receptor‐4 (TLR4), which has been previously shown to be a receptor for fetuin‐A and is commonly expressed in immune cells, could take part in the rapid uptake (< 3 min) of fetuin‐A by tumor cells. Rapid uptake of fetuin‐A was inhibited by the specific TLR4 inhibitor CLI‐095 and also attenuated in TLR4 knockdown prostate tumor cells. Inhibition of TLR4 by CLI‐095 also attenuated the rapid adhesion of tumor cells as well as invasion through a bed of Matrigel. The data suggest mechanisms by which TLR4 modulates the adhesion and growth of tumor cells.

Comparative strategic approaches to COVID-19 in Africa: Balancing public interest with civil liberties

As COVID-19 spreads rapidly across Africa, causing havoc to economies and disruption to already fragile healthcare systems, it is becoming clear that despite standardised global health strategies, national and local government responses must be tailored to their individual settings. Some African countries have adopted stringent measures such as national lockdown, quarantine or isolation, in combination with good hand hygiene, mandatory wearing of masks and physical distancing, to prevent an impending healthcare crisis. The impact of stringent measures in low- to middle-income African countries has bought time for healthcare facilities to prepare for the onslaught of COVID-19 cases, but some measures have been challenging to implement. In some settings, public health measures have been associated with serious violations of individual rights owing to abuse of power and gaps in implementation of well-intentioned policy. Collateral damage with regard to non-COVID-19 diseases that were suboptimally managed in pre-pandemic times may mean that lives lost from other diseases could exceed those saved from COVID-19. While individuals complying with lockdown regulations have embraced an acceptance of the concept of the common good, at a broad community level many are finding the transition from individualism to collective thinking required during a pandemic difficult to navigate. In this article, we look at government responses to the pandemic in six African countries (Malawi, South Africa, Uganda, Zambia, Zimbabwe and Botswana), and highlight ethical concerns arising in these contexts.

Diverse Roles of Annexin A6 in Triple-Negative Breast Cancer Diagnosis, Prognosis and EGFR-Targeted Therapies

The calcium (Ca2+)-dependent membrane-binding Annexin A6 (AnxA6), is a multifunctional, predominantly intracellular scaffolding protein, now known to play relevant roles in different cancer types through diverse, often cell-type-specific mechanisms. AnxA6 is differentially expressed in various stages/subtypes of several cancers, and its expression in certain tumor cells is also induced by a variety of pharmacological drugs. Together with the secretion of AnxA6 as a component of extracellular vesicles, this suggests that AnxA6 mediates distinct tumor progression patterns via extracellular and/or intracellular activities. Although it lacks enzymatic activity, some of the AnxA6-mediated functions involving membrane, nucleotide and cholesterol binding as well as the scaffolding of specific proteins or multifactorial protein complexes, suggest its potential utility in the diagnosis, prognosis and therapeutic strategies for various cancers. In breast cancer, the low AnxA6 expression levels in the more aggressive basal-like triple-negative breast cancer (TNBC) subtype correlate with its tumor suppressor activity and the poor overall survival of basal-like TNBC patients. In this review, we highlight the potential tumor suppressor function of AnxA6 in TNBC progression and metastasis, the relevance of AnxA6 in the diagnosis and prognosis of several cancers and discuss the concept of therapy-induced expression of AnxA6 as a novel mechanism for acquired resistance of TNBC to tyrosine kinase inhibitors.

Lapatinib-induced annexin A6 upregulation as an adaptive response of triple-negative breast cancer cells to EGFR tyrosine kinase inhibitors

The epidermal growth factor receptor (EGFR) is a major oncogene in triple-negative breast cancer (TNBC), but the use of EGFR-targeted tyrosine kinase inhibitors (TKI) and therapeutic monoclonal antibodies is associated with poor response and acquired resistance. Understanding the basis for the acquired resistance to these drugs and identifying biomarkers to monitor the ensuing resistance remain a major challenge. We previously showed that reduced expression of annexin A6 (AnxA6), a calcium-dependent membrane-binding tumor suppressor, not only promoted the internalization and degradation of activated EGFR but also sensitized TNBC cells to EGFR-TKIs. Here, we demonstrate that prolong (>3 days) treatment of AnxA6-low TNBC cells with lapatinib led to AnxA6 upregulation and accumulation of cholesterol in late endosomes. Basal extracellular signal-regulated kinase 1 and 2 (ERK1/2) activation was EGFR independent and significantly higher in lapatinib-resistant MDA-MB-468 (LAP-R) cells. These cells were more sensitive to cholesterol depletion than untreated control cells. Inhibition of lapatinib-induced upregulation of AnxA6 by RNA interference (A6sh) or withdrawal lapatinib from LAP-R cells not only reversed the accumulation of cholesterol in late endosomes but also led to enrichment of plasma membranes with cholesterol, restored EGFR-dependent activation of ERK1/2 and sensitized the cells to lapatinib. These data suggest that lapatinib-induced AnxA6 expression and accumulation of cholesterol in late endosomes constitute an adaptive mechanism for EGFR-expressing TNBC cells to overcome prolong treatment with EGFR-targeted TKIs and can be exploited as an option to inhibit and/or monitor the frequently observed acquired resistance to these drugs.

Reciprocal expression of Annexin A6 and RasGRF2 discriminates rapidly growing from invasive triple negative breast cancer subsets

Actively growing tumors are often histologically associated with Ki67 positivity, while the detection of invasiveness relies on non-quantitative pathologic evaluation of mostly advanced tumors. We recently reported that reduced expression of the Ca2+-dependent membrane-binding annexin A6 (AnxA6) is associated with increased expression of the Ca2+ activated RasGRF2 (GRF2), and that the expression status of these proteins inversely influence the growth and motility of triple negative breast cancer (TNBC) cells. Here, we establish that the reciprocal expression of AnxA6 and GRF2 is at least in part, dependent on inhibition of non-selective Ca2+ channels in AnxA6-low but not AnxA6-high TNBC cells. Immunohistochemical staining of breast cancer tissues revealed that compared to non-TNBC tumors, TNBC tumors express lower levels of AnxA6 and higher Ki67 expression. GRF2 expression levels strongly correlated with high Ki67 in pretreatment biopsies from patients with residual disease and with residual tumor size following chemotherapy. Elevated AnxA6 expression more reliably identified patients who responded to chemotherapy, while low AnxA6 levels were significantly associated with shorter distant relapse-free survival. Finally, the reciprocal expression of AnxA6 and GRF2 can delineate GRF2-low/AnxA6-high invasive from GRF2-high/AnxA6-low rapidly growing TNBCs. These data suggest that AnxA6 may be a reliable biomarker for distant relapse-free survival and response of TNBC patients to chemotherapy, and that the reciprocal expression of AnxA6 and GRF2 can reliably delineate TNBCs into rapidly growing and invasive subsets which may be more relevant for subset-specific therapeutic interventions.

Implication of calcium activated RasGRF2 in Annexin A6-mediated breast tumor cell growth and motility

The role of AnxA6 in breast cancer and in particular, the mechanisms underlying its contribution to tumor cell growth and/or motility remain poorly understood. In this study, we established the tumor suppressor function of AnxA6 in triple negative breast cancer (TNBC) cells by showing that loss of AnxA6 is associated with early onset and rapid growth of xenograft TNBC tumors in mice. We also identified the Ca²⁺ activated RasGRF2 as an effector of AnxA6 mediated TNBC cell growth and motility. Activation of Ca²⁺ mobilizing oncogenic receptors such as epidermal growth factor receptor (EGFR) in TNBC cells or pharmacological stimulation of Ca²⁺ influx led to activation, subsequent degradation and altered effector functions of RasGRF2. Inhibition of Ca²⁺ influx or overexpression of AnxA6 blocked the activation/degradation of RasGRF2. We also show that AnxA6 acts as a scaffold for RasGRF2 and Ras proteins and that its interaction with RasGRF2 is modulated by GTP and/or activation of Ras proteins. Meanwhile, down-regulation of RasGRF2 and treatment of cells with the EGFR-targeted tyrosine kinase inhibitor (TKI) lapatinib strongly attenuated the growth of otherwise EGFR-TKI resistant AnxA6 high TNBC cells. These data not only suggest that AnxA6 modulated Ca²⁺ influx and effector functions of RasGRF2 underlie at least in part, the AnxA6 mediated TNBC cell growth and/or motility, but also provide a rationale to target Ras-driven TNBC with EGFR targeted therapies in combination with inhibition of RasGRF2.

Extracellular histones are the ligands for the uptake of exosomes and hydroxyapatite-nanoparticles by tumor cells via syndecan-4

The mechanisms by which exosomes (nano-vesicular messengers of cells) are taken up by recipient cells are poorly understood. We hypothesized that histones associated with these nanoparticles are the ligands which facilitate their interaction with cell surface syndecan-4 (SDC4) to mediate their uptake. We show that the incubation with fetuin-A (exosome-associated proteins) and histones mediates the uptake of exosomes that are normally not endocytosed. Similarly, hydroxyapatite-nanoparticles incubated with fetuin-A and histones (FNH) are internalized by tumor cells, while nanoparticles incubated with fetuin-A alone (FN) are not. The uptake of exosomes and FNH, both of which move to the perinuclear region of the cell, is attenuated in SDC4-knockdown cells. Data show that FNH can compete with exosomes for uptake and that both use SDC4 as uptake receptors.

Association of calcium sensing receptor polymorphisms at rs1801725 with circulating calcium in breast cancer patients

BACKGROUND

Breast cancer (BC) patients with late-stage and/or rapidly growing tumors are prone to develop high serum calcium levels which have been shown to be associated with larger and aggressive breast tumors in post and premenopausal women respectively. Given the pivotal role of the calcium sensing receptor (CaSR) in calcium homeostasis, we evaluated whether polymorphisms of the CASR gene at rs1801725 and rs1801726 SNPs in exon 7, are associated with circulating calcium levels in African American and Caucasian control subjects and BC cases.

METHODS

In this retrospective case-control study, we assessed the mean circulating calcium levels, the distribution of two inactivating CaSR SNPs at rs1801725 and rs1801726 in 199 cases and 384 age-matched controls, and used multivariable regression analysis to determine whether these SNPs are associated with circulating calcium in control subjects and BC cases.

RESULTS

We found that the mean circulating calcium levels in African American subjects were higher than those in Caucasian subjects (p < 0.001). As expected, the mean calcium levels were higher in BC cases compared to control subjects (p < 0.001), but the calcium levels in BC patients were independent of race. We also show that in BC cases and control subjects, the major alleles at rs1801725 (G/T, A986S) and at rs1801726 (C/G, Q1011E) were common among Caucasians and African Americans respectively. Compared to the wild type alleles, polymorphisms at the rs1801725 SNP were associated with higher calcium levels (p = 0.006) while those at rs1801726 were not. Using multivariable linear mixed-effects models and adjusting for age and race, we show that circulating calcium levels in BC cases were associated with tumor grade (p = 0.009), clinical stage (p = 0.003) and more importantly, with inactivating mutations of the CASR at the rs1801725 SNP (p = 0.038).

CONCLUSIONS

These data suggest that decreased sensitivity of the CaSR to calcium due to inactivating polymorphisms at rs1801725, may predispose up to 20% of BC cases to high circulating calcium-associated larger and/or aggressive breast tumors.

Abstract 3928: Association of calcium sensing receptor polymorphisms at rs1801725 with circulating calcium in breast cancer patients

Patients with metastatic or end-stage breast cancer (BC) inevitably develop hypercalcemia, while up to 30% of BC patients develop cancer-induced hypercalcemia (CIH) in the absence of metastases or bone diseases. The commonly diagnosed mild increase in circulating calcium activates the calcium sensing receptor (CaSR) and has been shown to be associated with larger and more aggressive breast tumors in postmenopausal and premenopausal patients respectively. Whether differences in circulating calcium and/or specific inactivating CaSR variants play any role in disparities in BC outcomes remains unclear. DESIGN METHODS: We identified 199 BC cases and 384 age and genetic ancestry-matched controls with calcium assay and genotyping data from the Vanderbilt University DNA biorepository (BioVU) linked to de-identified electronic medical records. The linear mixed effects and codominant models were used to assess the relationship between inactivating CaSR mutations at rs1801725 (codon 986) and rs1801726 (codon 1011) and either circulating calcium levels or risk of high calcium-driven aggressive BC outcomes. RESULTS: We observed that circulating calcium levels were significantly higher in BC cases compared to control subjects (p=0.001) and interestingly, in subjects of African ancestry compared to Caucasians (p=0.001). The A986S mutant CaSR is common among Caucasians while the Q1011E mutant receptor is common among African Americans. However, only inactivating mutations at rs1801725 locus were significantly associated with higher calcium levels (p=0.006) and a higher (69%) risk of high calcium-driven aggressive BC outcomes compared to the wild type receptor. We also demonstrate that invasive BC cells are tolerant to sustained high calcium and that their adaptation to high calcium occurs via up-regulation of calcium-activated early response and malignancy-associated genes. CONCLUSION: These data suggest that inactivating CaSR polymorphisms at rs1801725 predispose BC patients to hypercalcemia and that high circulating calcium-driven aggressive disease outcomes occur via calcium modulated malignancy-associated genes such as MAGEC2/CT10.

Citation Format: Diva Whalen, Li Wang, Sarrah Widatalla, Josiah Ochieng, Ann Richmond, Amos Sakwe. Association of calcium sensing receptor polymorphisms at rs1801725 with circulating calcium in breast cancer patients [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 3928. doi:10.1158/1538-7445.AM2017-3928

Fetuin-A (alpha 2HS glycoprotein) modulates growth, motility, invasion, and senescence in high-grade astrocytomas

Glioblastomas (high-grade astrocytomas) are highly aggressive brain tumors with poor prognosis and limited treatment options. In the present studies, we have defined the role of fetuin-A, a liver-derived multifunctional serum protein, in the growth of an established glioblastoma cell line, LN229. We hereby demonstrate that these cells synthesize ectopic fetuin-A which supports their growth in culture in the absence of serum. We have demonstrated that a panel of tissue microarray (TMA) of glioblastomas also express ectopic fetuin-A. Knocking down fetuin-A using shRNA approach in LN229, significantly reduced their in vitro growth as well as growth and invasion in vivo. The fetuin-A knockdown subclones of LN229 (A and D) also had reduced motility and invasive capacity. Treatment of LN229 cells with asialofetuin (ASF), attenuated their uptake of labeled fetuin-A, and induced senescence in them. Interestingly, the D subclone that had ~90% reduction in ectopic fetuin-A, underwent senescence in serum-free medium which was blunted in the presence of purified fetuin-A. Uptake of labeled exosomes was attenuated in fetuin-A knockdown subclones A and D. Taken together, the studies demonstrate the impact of fetuin-A as significant node of growth, motility, and invasion signaling in glioblastomas that can be targeted for therapy.

Identification and characterization of EGF receptor in individual exosomes by fluorescence-activated vesicle sorting

Exosomes are small, 40–130 nm secreted extracellular vesicles that recently have become the subject of intense focus as agents of intercellular communication, disease biomarkers and potential vehicles for drug delivery. It is currently unknown whether a cell produces different populations of exosomes with distinct cargo and separable functions. To address this question, high-resolution methods are needed. Using a commercial flow cytometer and directly labelled fluorescent antibodies, we show the feasibility of using fluorescence-activated vesicle sorting (FAVS) to analyse and sort individual exosomes isolated by sequential ultracentrifugation from the conditioned medium of DiFi cells, a human colorectal cancer cell line. EGFR and the exosomal marker, CD9, were detected on individual DiFi exosomes by FAVS; moreover, both markers were identified by high-resolution stochastic optical reconstruction microscopy on individual, approximately 100 nm vesicles from flow-sorted EGFR/CD9 double-positive exosomes. We present evidence that the activation state of EGFR can be assessed in DiFi-derived exosomes using a monoclonal antibody (mAb) that recognizes “conformationally active” EGFR (mAb 806). Using human antigen-specific antibodies, FAVS was able to detect human EGFR and CD9 on exosomes isolated from the plasma of athymic nude mice bearing DiFi tumour xenografts. Multicolour FAVS was used to simultaneously identify CD9, EGFR and an EGFR ligand, amphiregulin (AREG), on human plasma-derived exosomes from 3 normal individuals. These studies demonstrate the feasibility of FAVS to both analyse and sort individual exosomes based on specific cell-surface markers. We propose that FAVS may be a useful tool to monitor EGFR and AREG in circulating exosomes from individuals with colorectal cancer and possibly other solid tumours.

Abstract B09: Fetuin-A, an emerging biomarker for breast and prostate cancer

We hypothesized that fetuin-A, a liver derived glycoprotein would be a useful biomarker to follow for the progression of prostate and breast cancer particularly in African American patients. For many years, conflicting reports have appeared in the literature regarding the role of fetuin-A in the progression of a number of solid tumors. The majority of the studies have reported that the serum levels of fetuin-A drops as tumors progress, suggesting a tumor suppressive role for the protein. We on the other hand, demonstrated that it is a significant tumor growth promoter in vitro. In the recent past, a number of laboratories, including ours, have indicated that fetuin-A is actively synthesized by high grade tumors.

In the present study, we investigated the appearance of fetuin-A autoantibodies in the sera of 12 prostate and breast cancer patients, 60% of whom were African Americans. We demonstrated the presence of fetuin-A auto antibodies in all except two of the tumor serum specimens. Blood of normal tumor free individuals do not show fetuin-A autoantibodies. We also subjected tissue microarrays of prostate and breast tumors to immune-histochemical analysis of fetuin-A. Our data show a dramatic increase in the synthesis of fetuin-A in the TMA particularly in high grade tumors. Taken together, these results suggest that as tumors become more aggressive they may synthesize fetuin-A which then presents as a new antigen in the blood that provokes the synthesis of auto-antibodies, which could be a biomarker of advanced or metastatic disease. Furthermore, the study suggests that fetuin-A itself could be a significant surrogate marker of aggressive tumors of the prostate or breast particularly in African Americans.

Citation Format: Gladys Nangami, Josiah Ochieng, Ebenezer Appah, Philip E. Lammers. Fetuin-A, an emerging biomarker for breast and prostate cancer. [abstract]. In: Proceedings of the Eighth AACR Conference on The Science of Health Disparities in Racial/Ethnic Minorities and the Medically Underserved; Nov 13-16, 2015; Atlanta, GA. Philadelphia (PA): AACR; Cancer Epidemiol Biomarkers Prev 2016;25(3 Suppl):Abstract nr B09.

Assessing the carcinogenic potential of low-dose exposures to chemical mixtures in the environment: the challenge ahead

Low-dose exposures to common environmental chemicals that are deemed safe individually may be combining to instigate carcinogenesis, thereby contributing to the incidence of cancer. This risk may be overlooked by current regulatory practices and needs to be vigorously investigated.

Lifestyle factors are responsible for a considerable portion of cancer incidence worldwide, but credible estimates from the World Health Organization and the International Agency for Research on Cancer (IARC) suggest that the fraction of cancers attributable to toxic environmental exposures is between 7% and 19%. To explore the hypothesis that low-dose exposures to mixtures of chemicals in the environment may be combining to contribute to environmental carcinogenesis, we reviewed 11 hallmark phenotypes of cancer, multiple priority target sites for disruption in each area and prototypical chemical disruptors for all targets, this included dose-response characterizations, evidence of low-dose effects and cross-hallmark effects for all targets and chemicals. In total, 85 examples of chemicals were reviewed for actions on key pathways/mechanisms related to carcinogenesis. Only 15% (13/85) were found to have evidence of a dose-response threshold, whereas 59% (50/85) exerted low-dose effects. No dose-response information was found for the remaining 26% (22/85). Our analysis suggests that the cumulative effects of individual (non-carcinogenic) chemicals acting on different pathways, and a variety of related systems, organs, tissues and cells could plausibly conspire to produce carcinogenic synergies. Additional basic research on carcinogenesis and research focused on low-dose effects of chemical mixtures needs to be rigorously pursued before the merits of this hypothesis can be further advanced. However, the structure of the World Health Organization International Programme on Chemical Safety ‘Mode of Action’ framework should be revisited as it has inherent weaknesses that are not fully aligned with our current understanding of cancer biology.

The impact of low-dose carcinogens and environmental disruptors on tissue invasion and metastasis

The purpose of this review is to stimulate new ideas regarding low-dose environmental mixtures and carcinogens and their potential to promote invasion and metastasis. Whereas a number of chapters in this review are devoted to the role of low-dose environmental mixtures and carcinogens in the promotion of invasion and metastasis in specific tumors such as breast and prostate, the overarching theme is the role of low-dose carcinogens in the progression of cancer stem cells. It is becoming clearer that cancer stem cells in a tumor are the ones that assume invasive properties and colonize distant organs. Therefore, low-dose contaminants that trigger epithelial-mesenchymal transition, for example, in these cells are of particular interest in this review. This we hope will lead to the collaboration between scientists who have dedicated their professional life to the study of carcinogens and those whose interests are exclusively in the arena of tissue invasion and metastasis.

Abstract 5306: Shotgun proteomic analysis of human head and neck squamous cell carcinoma cell line SQ20B with diminished AHSG expression

The Alpha-Heremans-Schmid Glycoprotein (AHSG) has tumor promoting properties in animal models of breast cancer and lung cancer (1, 2). These cancer cells do not synthesize AHSG, instead utilizing the liver-generated glycoprotein that is abundant in serum. We have reported that head and neck squamous cell carcinoma (HNSCC) cell lines synthesize AHSG (in press) and have also detected abundant AHSG in primary HNSCC tumors (unpublished). Growth in serum-free medium and in vitro tumorigenic properties, including proliferation, adhesion and migration, are diminished in the HNSCC SQ20B cell line modified with AHSG-specific shRNA to express only twenty percent of the wild-type SQ20B cell line (SQ20B-AH20) compared to SQ20B modified with empty vector alone and expressing the wild-type amount of AHSG (SQ20B-EV) (in press). Here we have used shotgun proteomic analysis to identify additional proteins whose expression may also affect these in vitro properties of tumorigenesis associated with AHSG.

The two cell lines were cultured in serum-free medium to avoid the contribution of exogenous AHSG in serum. Cell lysates were obtained, and the proteins were separated in polyacrylamide gels in duplicate. Each full protein lane was cut into 10 pieces, in-gel digested with trypsin and analyzed with tandem liquid chromatography mass spectrometry (LC-MS). MS data were analyzed against a recent human protein database. Proteins differentially expressed were quantified using a spectral counting approach.

A total of 1386 distinct protein groups were identified in the two samples. Forty-eight proteins were differentially expressed in these samples (z score &gt; 3, which corresponds to p ≤ 0.001, and Benjamini-Hochberg [statistical] FDR &lt; 0.05). Proteins associated with the cytoskeleton, adhesion and apoptosis were over-represented in the group of differentially expressed proteins. Here we have shown that the human HNSCC cell line SQ20B exhibits changes in the proteome when AHSG expression is diminished. These proteins are critical for the tumorigenic properties of adhesion and migration. These data will help to identify mechanisms of tumorigenesis associated with AHSG in HNSCC.

References

1. B. Guillory, A.M. Sakwe, M. Saria, P. Thompson, C. Adhiambo, R. Koumangoye, B. Ballard, A. Binhazim, C. Cone, W. Jahanen-Dechent, J. Ochieng, Lack of fetuin-A (alpha2-HS-glycoprotein) reduces mammary tumor incidence and prolongs tumor latency via the transforming growth factor-beta signaling pathway in a mouse model of breast cancer, The American Journal of Pathology 177 (2010) 2635-2644.

2. M.N. Kundranda, M. Henderson, K.J. Carter, L. Gorden, A. Binhazim, S. Ray, T. Baptiste, M. Shokrani, M.L. Leite-Browning, W. Jahnen-Dechent, L.M. Matrisian, J. Ochieng, The serum glycoprotein fetuin-A promotes Lewis lung carcinoma tumorigenesis via adhesive-dependent and adhesive-independent mechanisms, Cancer Res 65 (2005) 499-506.

Citation Format: Dana R. Marshall, Victor Paramov, Siddharth Pratap, Georgina Iyamu, Amos Sakwe, Pamela Thompson, Josiah Ochieng. Shotgun proteomic analysis of human head and neck squamous cell carcinoma cell line SQ20B with diminished AHSG 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 5306. doi:10.1158/1538-7445.AM2014-5306

Fetuin-A associates with histones intracellularly and shuttles them to exosomes to promote focal adhesion assembly resulting in rapid adhesion and spreading in breast carcinoma cells

The present analyses were undertaken to define the mechanisms by which fetuin-A modulates cellular adhesion. FLAG-tagged fetuin-A was expressed in breast carcinoma and HEK-293T cells. We demonstrated by confocal microscopy that fetuin-A co-localizes with histone H2A in the cell nucleus, forms stable complexes with histones such as H2A and H3 in solution, and shuttles histones to exosomes. The rate of cellular adhesion and spreading to either fibronectin or laminin coated wells was accelerated significantly in the presence of either endogenous fetuin-A or serum derived protein. More importantly, the formation of focal adhesion complexes on surfaces coated by laminin or fibronectin was accelerated in the presence of fetuin-A or histone coated exosomes. Cellular adhesion mediated by histone coated exosomes was abrogated by heparin and heparinase III. Heparinase III cleaves heparan sulfate from cell surface heparan sulfate proteoglycans. Lastly, the uptake of histone coated exosomes and subsequent cellular adhesion, was abrogated by heparin. Taken together, the data suggest a mechanism where fetuin-A, either endogenously synthesized or supplied extracellularly can extract histones from the nucleus or elsewhere in the cytosol/membrane and load them on cellular exosomes which then mediate adhesion by interacting with cell surface heparan sulfate proteoglycans via bound histones.

Reduced annexin A6 expression promotes the degradation of activated epidermal growth factor receptor and sensitizes invasive breast cancer cells to EGFR-targeted tyrosine kinase inhibitors

Background

The expression of annexin A6 (AnxA6) in AnxA6-deficient non-invasive tumor cells has been shown to terminate epidermal growth factor receptor (EGFR) activation and downstream signaling. However, as a scaffolding protein, AnxA6 may stabilize activated cell-surface receptors to promote cellular processes such as tumor cell motility and invasiveness. In this study, we investigated the contribution of AnxA6 in the activity of EGFR in invasive breast cancer cells and examined whether the expression status of AnxA6 influences the response of these cells to EGFR-targeted tyrosine kinase inhibitors (TKIs) and/or patient survival.

Results

We demonstrate that in invasive BT-549 breast cancer cells AnxA6 expression is required for sustained membrane localization of activated (phosho-Y1068) EGFR and consequently, persistent activation of MAP kinase ERK1/2 and phosphoinositide 3-kinase/Akt pathways. Depletion of AnxA6 in these cells was accompanied by rapid degradation of activated EGFR, attenuated downstream signaling and as expected enhanced anchorage-independent growth. Besides inhibition of cell motility and invasiveness, AnxA6-depleted cells were also more sensitive to the EGFR-targeted TKIs lapatinib and PD153035. We also provide evidence suggesting that reduced AnxA6 expression is associated with a better relapse-free survival but poorer distant metastasis-free and overall survival of basal-like breast cancer patients.

Conclusions

Together this demonstrates that the rapid degradation of activated EGFR in AnxA6-depleted invasive tumor cells underlies their sensitivity to EGFR-targeted TKIs and reduced motility. These data also suggest that AnxA6 expression status may be useful for the prediction of the survival and likelihood of basal-like breast cancer patients to respond to EGFR-targeted therapies.

Knowledge about the research and ethics committee at Makerere University, Kampala

BACKGROUND

All research involving human participants should be reviewed by a competent and independent institutional research and ethics committee. Research conducted at Makerere University College of Health Sciences should be subjected to a rigorous review process by the ethics committee in order to protect human participants' interests, rights and welfare.

OBJECTIVE

To evaluate researchers' knowledge about the functions and ethical review process of the College of Health Sciences research and ethics committee.

METHODS

A cross sectional study. 135 researchers consented to participate in the study, but 70 questionnaires were answered giving a 52% response.

RESULTS

Age ranged between 30 to 61 years, majority of participants 30-39 years. Most of the respondents do agree that the REC functions include Protocol review 86%, protection of research participants 84.3%, and monitoring of ongoing research. During ethical review, the RECpays special attention to scientific design [79.7%] and ethical issues [75.3%], but less to the budget and literature review. More than 97% of the respondents believe that the REC is either average or very good, while 2.8% rank it below average.

CONCLUSION

Respondents knew the major functions of the committee including protection of the rights and welfare of research participants, protocol review and monitoring of on going research, and the elements of protocol review that are given more attention include ;scientific design and ethical issues. Overall performance of the REC was ranked as average by respondents. The committee should limit delays in approval and effectively handle all functions of the committee.

Abstract C37: Reduced annexin A6 expression enhances EGFR degradation and sensitizes invasive breast cancer cells to EGFR-targeted tyrosine kinase inhibitors

The role of annexin A6 (AnxA6), a calcium-dependent phospholipid binding protein, in breast carcinogenesis remains poorly understood. Some reports suggest that AnxA6 inhibits the activation and down-stream signaling of epidermal growth factor receptor (EGFR). On the contrary, other studies have shown that AnxA6 not only stabilizes activated receptors on the cell surface but also promotes the expression of differentiation markers in chondrocytes. Together with our recent study showing that AnxA6 expression is reduced in breast cancer, we investigated whether AnxA6 expression status influences breast cancer outcome in patients and whether this may be attributed to its modulation of EGFR expression. We show that low AnxA6 expression correlates with reduced distant metastasis-free and overall survival, but is associated with a higher probability for recurrence-free survivalof patients with basal-like breast cancer. To determine whether these effects are mediated via EGFR, a predictive marker of basal-like breast cancer, we examined the effects of altered expression of AnxA6 in AnxA6-high invasive triple negative breast cancer cells. Interestingly, depletion of AnxA6 in invasive BT-549 cells was accompanied by decreased expression of EGFR protein and mRNA. We also show that in invasive breast cancer cells, AnxA6 expression is required for sustained membrane localization of activated EGFR and persistent downstream signaling. Consequently, AnxA6-depleted cells exhibited decreased cell motility, and increased sensitivity to the tyrosine kinase inhibitors (TKIs), lapatinib and PD153035. On the contrary, over-expression of AnxA6 in AnxA6-low HCC1806 cells did not affect their motility but as expected, inhibited their growth in 3D matrigel cultures. These data suggest that AnxA6-modulation of EGFR expression and activity underlies at least in part, the changes in proliferation, metastatic potentials and sensitivity to EGFR-targeted TKIs of invasive breast cancer cells. Our data also suggest that AnxA6 expression status may predict the survival and likelihood to respond to EGFR-targeted therapies of patients with basal-like breast cancer.

Citation Format: Rainelli B. Koumangoye, Josiah Ochieng, Amos M. Sakwe. Reduced annexin A6 expression enhances EGFR degradation and sensitizes invasive breast cancer cells to EGFR-targeted tyrosine kinase inhibitors. [abstract]. In: Proceedings of the Third AACR International Conference on Frontiers in Basic Cancer Research; Sep 18-22, 2013; National Harbor, MD. Philadelphia (PA): AACR; Cancer Res 2013;73(19 Suppl):Abstract nr C37.

In vitro and in vivo evaluation of novel anticancer agents in triple negative breast cancer models

Triple negative breast cancer (TNBC) is subtype of breast disease devoid of the estrogen, progesterone, and Her2/neu receptors which are targets for pharmacological intervention. There is a need for novel anti-breast cancer agents that target TNBC. Therefore, novel isochalcone DJ52 was evaluated using the alamar blue dye exclusion assay, the luciferase colony assay, and xenograft models to determine its efficacy and potency. DJ52 significantly decreased proliferation of cells measured by using the alamar blue dye method and produced IC50 values of DJ52, DJ56, and DJ82 at 10-6M, 10-5M, and 10-5M, respectively. In vivo studies were conducted by injecting MDA-MB-231 cells into SCID mice to determine tumor regression was measured over 20 days. DJ52 at 50 mg/kg caused significant decrease in tumor volume (p value <.05) by nearly 50% compared with the control with vehicle alone. These data suggest that DJ52 has merit for further evaluation as a novel anticancer agent.

Abstract 3788: Alpha-2 Heremans Schmid glycoprotein (AHSG) promotes migration in head and neck squamous cell carcinoma (HNSCC) cell lines

Head and neck squamous cell carcinoma (HNSCC) is the eighth most common tumor in the world. Approximately 30,000 new cases of HNSCC are reported each year and 8,000 related deaths, in the United States. HNSCC of the oral cavity is highly metastatic and has a recurrence rate of 20%-50%, with a dismal 5-year survival rate of ∼50%. African-American males have a 5-year survival rate of ∼42% while the survival rate for Caucasian males is 52%. To date, there is no consistent means for early detection or a reliable biomarker for HNSCC, thus perpetuating the lack of improvement in mortality despite advances in delivery of treatment and surgical reconstruction. In a proteomic study seeking possible biomarkers for HNSCC, AHSG was detected at elevated levels in serum. Interestingly, we have found that some HNSCC cell lines synthesize and secrete AHSG. We have also shown in earlier studies, that the lack of AHSG reduces mammary tumor incidence and prolongs tumor latency in a mouse model for breast cancer. Together, this suggests that this hepatocellular glycoprotein that is found in most body fluids including serum could be a potential biomarker for HNSCC. AHSG is a negative acute phase response protein, which makes the findings of elevated levels of AHSG in the proteomic study most intriguing. In order to evaluate the role of AHSG in HNSCC progression (proliferation and metastatic properties) in vitro, we depleted AHSG in the HNSCC cell lineSQ20B. Thus far, we show that depletion of AHSG does not affect the proliferation of SQ20B cells. However, the depletion of AHSG mediates a decrease in migration and invasion of SQ20B cells. We are currently elucidating the molecular mechanisms of AHSG-mediated motility.

This work was supported by grants from the NIH-NCI-Score 1 SC1 CA134018-01 (JO); DOD W81XWH-07-1-0254 (J.O); 5 T32 HL007735-15 (SA) and U54 CA091408 (subproject, DM).

Citation Format: Pamela D. Thompson, Kurt Watson, Amos Sakwe, Josiah Ochieng, Dana Marshall. Alpha-2 Heremans Schmid glycoprotein (AHSG) promotes migration in head and neck squamous cell carcinoma (HNSCC) cell lines. [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 3788. doi:10.1158/1538-7445.AM2013-3788

Induction of tumorigenicity by galectin-3 in a nontumorigenic human breast-carcinoma cell-line

The human galectin-3 is a galactoside-binding protein of 31 kDa which functions as a receptor for glycoproteins containing poly N-acetyllactosamine side chains and as a substrate for matrix metalloproteinases-2 and -9. We studied its expression by flow cytoflourimetry, Western, Northern and Southern analyses, in five cultured human breast carcinoma cell lines previously characterized as nontumorigenic, poorly metastatic or metastatic in nude mice. The expression of galectin-3 correlated with the reported tumorigenicity of the cells. The introduction of recombinant galectin-3 into the null expressing non-tumorigenic BT-549 cells resulted in the acquisition of anchorage-independent growth properties in all and tumorigenicity in 3/4 sense transfected cell clones. The data indicate a relationship between galectin-3 expression and malignancy of human breast carcinoma cell lines.

Abstract 5313: Sustained hypercalcemia primes non-invasive breast cancer cells for metastasis to high calcium microenvironments

Breast cancer frequently spreads to calcium-rich organs/metastatic sites such as skeletal tissues but the role of hypercalcemia in breast cancer progression remains poorly understood. While patients with metastatic or end-stage cancer are likely to become hypercalcemic, up to 30% of breast cancer patients develop cancer-induced hypercalcemia (CIH) in the absence of metastases or bone diseases. The resulting high extracellular ionized calcium (Ca2+) activates the calcium sensing receptor (CaSR) that not only promotes the proliferation of breast cancer cells but also the secretion of parathyroid hormone-related protein by the tumor cells. This suggests that CIH may promote both the vicious osteolytic cycle and breast cancer progression. In this study, we examined whether sustained hypercalcemia primes breast cancer cells for metastasis to high Ca2+ microenvironments. We demonstrate that sustained hypercalcemia enables Ca2+-sensitive non invasive breast cancer cells such as MCF-7 to become high Ca2+-adapted and that this adaptation is accompanied by increased motility and more aggressive growth (increased proliferation). Consistent with this observation, invasive and metastatic breast cancer cells are high Ca2+-adapted cells that efficiently grow over a wide range of Ca2+ concentrations (up to 10 mM). Interestingly, we also show that at high Ca2+ (5 mM) breast cancer cells expressing the Q1011E CaSR variant that is common among African Americans proliferate faster than those expressing the A986S CaSR variant that is common among Caucasians. These data suggest that differences in the adaptation of breast cancer cells to hypercalcemia due in part to the expression of distinct CaSR variants underlie the distinct race-related breast cancer outcomes. This work is funded by the following grants made available to JO: DOD-W81XWH-07-1-0254 and 1SC1CA134018-01

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 5313. doi:1538-7445.AM2012-5313

Abstract 2424: Conditioned media enhances proliferation and mobility in triple negative breast cancer cells

Background. Triple negative breast cancer (TNBC) is one of the most aggressive forms of breast cancer and disproportionally affects African American women. This subtype of breast cancer is characterized by the absence of the estrogen, progesterone, and HER2/neu receptors. Our research has provided insight on understanding that the microenvironment, specifically noncancerous cells, play in enhancing cancer progression and metastasis. However, the role of adjacent noncancerous cells in the metastatic phenomenon is poorly understood. Therefore, the aims of this project were: 1) to determine if conditioned media from MCF-10A cells would enhance proliferation of MDA-MB-231 and MDA-MB-468 cells and 2) to evaluate the ability of the effects of migration of the conditioned media on the MDA-MB-231 and MDA-MB-468 cells. Methods. Crystal violet and alamar blue dye exclusion assays were performed to measure proliferation in the different medias. The trans well migration assay was used to evaluate motility enhancement based on the media used, either conditioned media and the Cellometer was used to evaluate whether the MDA-MB-468 and MCF-10A cells shared the same microenvironment. Results. Conditioned media is made from base medium with a concentration of 1.0 g/L glucose with .5% FBS exposed to non-cancerous MCF-10A cells that have been driven into crisis. This conditioned media encouraged robust and continuous proliferation of the tumorigenic MDA-MB-231 and MDA-MB-468 cell lines. HGCM was extracted in our lab using sterile technique and reused to analyze the proliferative effects on cancerous and non-cancerous cells. MDA-MB-231 cells demonstrated significant proliferation when compared to the control. MDA-MB-468 cells demonstrated a similar response. The trans well migration assay demonstrated that the GFP labeled MDA-MB-468 cells had a higher percentage of motility than with MCF-10A cells in standard media. Conclusions: Taken together, these data indicate that factors secreted into the microenvironment from noncancerous cells may contribute to the mobility of TNBC cells and the conditioned media contains unknown factors that promote the cell mobility of the MDA-MB-231 and MDA-MB-468 cells.

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 2424. doi:1538-7445.AM2012-2424

Detachment of breast tumor cells induces rapid secretion of exosomes which subsequently mediate cellular adhesion and spreading

Exosomes are nano-vesicles secreted by a wide range of mammalian cell types. These vesicles are abundant in serum and other extracellular fluids and contain a large repertoire of proteins, mRNA and microRNA. Exosomes have been implicated in cell to cell communication, the transfer of infectious agents, and neurodegenerative diseases as well as tumor progression. However, the precise mechanisms by which they are internalized and/or secreted remain poorly understood. In order to follow their release and uptake in breast tumor cells in real time, cell-derived exosomes were tagged with green fluorescent protein (GFP)-CD63 while human serum exosomes were rhodamine isothiocynate-labeled. We show that detachment of adherent cells from various substrata induces a rapid and substantial secretion of exosomes, which then concentrate on the cell surfaces and mediate adhesion to various extracellular matrix proteins. We also demonstrate that disruption of lipid rafts with methyl-beta-cyclodextrin (MβCD) inhibits the internalization of exosomes and that annexins are essential for the exosomal uptake mechanisms. Taken together, these data suggest that cellular detachment is accompanied by significant release of exosomes while cellular adhesion and spreading are enhanced by rapid uptake and disposition of exosomes on the cell surface.

Abstract 2119: Role of annexin A6 in anchorage-independent growth of invasive breast cancer cells

Annexin A6 (AnxA6) is a member of the annexin family of Ca2+-dependent membrane binding proteins that is frequently detected in cell-derived exosomes and on the surface of some cell types. Although its extracellular functions remain unclear, AnxA6 may play important roles in cell-cell and/or cell-extracellular matrix (ECM) interactions via its interactions with chondroitin sulfate containing proteoglycans, the serum glycoprotein fetuin-A and other undefined extracellular matrix components. In support of this notion, recent studies have shown that depletion of AnxA6 in MDA-MB-436 breast cancer cells promoted anchorage-independent cell growth. Here we show that depletion of AnxA6 in BT-549 breast carcinoma cells not only led to impaired cell-cell cohesion and cell spreading onto collagen type IV but also inhibited cell motility and invasiveness. In 3D cultures in growth factor-reduced matrigel, AnxA6-depleted BT-549 cells formed spheroid colonies as opposed to stellate colonies formed by the parental BT-549 cells. We also show that N-cadherin is up-regulated in the motility-impaired AnxA6-depleted cells, suggesting that loss of AnxA6 may uncouple cadherin-based cell-cell interactions as part of the mechanism that determines anchorage-independent cell growth and therefore tumor growth in vivo. Our data also show that the loss of contact inhibition and invasive properties in AnxA6-depleted cells may be partly due to the formation of fewer, elongated and dispersed vinculin-based focal contacts. To verify that these focal contacts may be functionally defective, we show that whereas the MAP kinase (ERK1/2) pathway remained constitutively active, Ca2+-dependent activation of focal adhesion kinase and the phosphoinositide-3 kinase/Akt pathway were strongly inhibited in the AnxA6-depleted BT-549 cells. These data suggest that loss of AnxA6 may promote breast cancer progression via anchorage-independent cell growth due to disruption of functional focal contacts that maintain cell-cell and/or cell-ECM interactions. Supported by grants: 1 SC1 CA134018-01 and DOD W81XWH-07-1-0254

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 2119. doi:10.1158/1538-7445.AM2011-2119

Annexin A6 contributes to the invasiveness of breast carcinoma cells by influencing the organization and localization of functional focal adhesions

The interaction of annexin A6 (AnxA6) with membrane phospholipids and either specific extracellular matrix (ECM) components or F-actin suggests that it may influence cellular processes associated with rapid plasma membrane reorganization such as cell adhesion and motility. Here, we examined the putative roles of AnxA6 in adhesion-related cellular processes that contribute to breast cancer progression. We show that breast cancer cells secrete annexins via the exosomal pathway and that the secreted annexins are predominantly cell surface-associated. Depletion of AnxA6 in the invasive BT-549 breast cancer cells is accompanied by enhanced anchorage-independent cell growth but cell-cell cohesion, cell adhesion/spreading onto collagen type IV or fetuin-A, cell motility and invasiveness were strongly inhibited. To explain the loss in adhesion/motility, we show that vinculin-based focal adhesions in the AnxA6-depleted BT-549 cells are elongated and randomly distributed. These focal contacts are also functionally defective because the activation of focal adhesion kinase and the phosphoinositide-3 kinase/Akt pathway were strongly inhibited while the MAP kinase pathway remained constitutively active. Compared with normal human breast tissues, reduced AnxA6 expression in breast carcinoma tissues correlates with enhanced cell proliferation. Together this suggests that reduced AnxA6 expression contributes to breast cancer progression by promoting the loss of functional cell-cell and/or cell-ECM contacts and anchorage-independent cell proliferation.

Fetuin-A ({alpha}2HS-glycoprotein) is a major serum adhesive protein that mediates growth signaling in breast tumor cells

The identity of the cell adhesive factors in fetal bovine serum, commonly used to supplement growth media, remains a mystery due to the plethora of serum proteins. In the present analyses, we showed that fetuin-A, whose function in cellular attachment in tissue culture has been debated for many years, is indeed a major serum cell attachment factor particularly for tumor cells. We are able to report this because of a new purification strategy that has for the first time given us a homogeneous protein band in colloidal Coomassie-stained gels that retains biological activity. The tumor cells adhered to immobilized fetuin-A and not α(2)-macroglobulin, its major contaminant. The interaction of cells with fetuin-A was driven mainly by Ca(2+) ions, and cells growing in regular medium supplemented with fetal bovine serum were just as sensitive to loss of extracellular Ca(2+) ions as cells growing in fetuin-A. Fractionation of human serum revealed that cell attachment was confined to the fractions that had fetuin-A. Interestingly, the tumor cells also took up fetuin-A and secreted it back to the medium using an unknown mechanism that can be observed in live cells. The attachment of tumor cells to fetuin-A was accompanied by phosphatidylinositol 3-kinase/Akt activation that was down-regulated in cells that lack annexin-A6, one of the cell surface receptors for fetuin-A. Taken together, our data show the significance of fetuin-A in tumor cell growth mechanisms in vitro and open new research vistas for this protein.

Lack of fetuin-A (alpha2-HS-glycoprotein) reduces mammary tumor incidence and prolongs tumor latency via the transforming growth factor-beta signaling pathway in a mouse model of breast cancer

The present analyses were done to define the role of fetuin-A (Fet) in mammary tumorigenesis using the polyoma middle T antigen (PyMT) transgenic mouse model. We crossed Fet-null mice in the C57BL/6 background with PyMT mice in the same background and after a controlled breeding protocol obtained PyMT/Fet+/+, PyMT/Fet+/-, and PyMT/Fet-/- mice that were placed in control and experimental groups. Whereas the control group (PyMT/Fet+/+) formed mammary tumors 90 days after birth, tumor latency was prolonged in the PyMT/Fet-/- and PyMT/Fet+/- mice. The majority of the PyMT/Fet-/- mice were tumor-free at the end of the study, at approximately 40 weeks. The pathology of the mammary tumors in the Fet-null mice showed extensive fibrosis, necrosis, and squamous metaplasia. The preneoplastic mammary tissues of the PyMT/Fet-/- mice showed intense phopho-Smad2/3 staining relative to control tissues, indicating that transforming growth factor-β signaling is enhanced in these tissues in the absence of Fet. Likewise, p19ARF and p53 were highly expressed in tumor tissues of PyMT/Fet-/- mice relative to the controls in the absence of Fet. The phosphatidylinositol 3-kinase/Akt signaling pathway that we previously showed to be activated by Fet, on the other hand, was unaffected by the absence of Fet. The data indicate that Fet is a powerful modulator of breast tumorigenesis in this model system and has the potential to modulate breast cancer progression in humans.

Cystatin superfamily

Cystatins, the classical inhibitors of C1 cysteine proteinases, have been extensively studied and reviewed in the literature. Over the last 20 years, however, proteins containing cystatin domains but lacking protease inhibitory activities have been identified, and most likely more will be described in the near future. These proteins together with family 1, 2, and 3 cystatins constitute the cystatin superfamily. Mounting evidence points to the new roles that some members of the superfamily have acquired over the course of their evolution. This review is focused on the roles of cystatins in: 1) tumorigenesis, 2) stabilization of matrix metalloproteinases, 3) glomerular filtration rate, 4) immunomodulation, and 5) neurodegenerative diseases. It is the goal of this review to get as many investigators as possible to take a second look at the cystatin superfamily regarding their potential involvement in serious human ailments.

Abstract B52: Annexin A6 promotes cellular attachment and invasiveness of breast cancer cells

Annexin A6 (ANXA6) is a member of a family of Ca2+-dependent phospholipid-binding proteins capable of associating with negatively charged membranes in its Ca2+-bound state. Although the functions of this protein are yet to be clearly defined, various physiological roles have been proposed, including a role in the regulation of cell growth and tumorigenesis. We previously showed that ANXA2, ANXA4 and ANXA6 are receptors of the serum factor fetuin-A on the surface of breast carcinoma cells. To determine which of these annexins is the bona fide cell surface receptor for fetuin-A, we have now examined the surface expression of ANXA2 and ANXA6 in the fetuin-A expressing hepatocellular carcinoma cell line HepG2 and in the invasive breast carcinoma cell line BT549. By glycerol gradient centrifugation of the post nuclear supernatants of HepG2 cells briefly cultivated at high extracellular Ca2+, we show that while ANXA2 predominantly associated with heavy membranes corresponding to the endogenous fetuin-A profile, the total membrane-associated ANXA6 on the contrary, diminished. Analysis of the EGTA-solubilized surface-associated proteins from HepG2 and BT549 cells revealed that ANXA6 is predominantly associated with the cell surface suggesting that it is externalized. Further analysis of the secreted proteins by differential velocity centrifugation and in particular the nanovesicle-associated (exosomal) secreted proteins confirmed that while secreted ANXA2 was barely detectable, ANXA6 was abundantly secreted via the exosomal pathway. From these data we hypothesized that the surface associated ANXA6 may be the major fetuin-A receptor on the surface of the invasive BT549 breast cancer cells and that it may be important in the growth, attachment and migration of these tumor cells. Using ANXA6 targeted shRNA we show that down regulation of ANXA6 inhibited the attachment of these cells to collagen Type I, Collagen Type IV and to the serum factor fetuin-A but attachment to and spreading on fibronectin was not affected. Based on the detection of vinculin and focal adhesion kinase, we demonstrate the complete absence of adhesion plaques in the ANXA6-depleted cells compared to the parental BT549 cells. This supports our observation that the ANXA6-depleted BT549 cells lost their ability to spread and hence are predominantly spindle-shaped; Moreover, the ANXA6-depleted BT549 cells proliferate faster than the parental cells; they grow in three-dimensional cultures as spheroid colonies resembling the ANXA6-negative MCF-10A acini rather than as stellate colonies produced by the parental cells. Finally, ANXA6 depletion in BT549 cells inhibited their migration and in vitro invasion of matrigel. Together our data demonstrate that ANXA6 expression in this metastatic breast cancer cells correlates with the invasive phenotype and that its association with the surface of these breast cancer cells modulates at least in part, attachment of these cells to the ECM and their overall morphology.

Citation Information: Cancer Res 2009;69(23 Suppl):B52.

Anchorage-independent growth of breast carcinoma cells is mediated by serum exosomes

We hereby report studies that suggest a role for serum exosomes in the anchorage-independent growth (AIG) of tumor cells. In AIG assays, fetal bovine serum is one of the critical ingredients. We therefore purified exosomes from fetal bovine serum and examined their potential to promote growth of breast carcinoma cells in soft agar and Matrigel after reconstituting them into growth medium (EEM). In all the assays, viable colonies were formed only in the presence of exosomes. Some of the exosomal proteins we identified, have been documented by others and could be considered exosomal markers. Labeled purified exosomes were up-taken by the tumor cells, a process that could be competed out with excess unlabeled vesicles. Our data also suggested that once endocytosed by a cell, the exosomes could be recycled back to the conditioned medium from where they can be up-taken by other cells. We also demonstrated that low concentrations of exosomes activate MAP kinases, suggesting a mechanism by which they maintain the growth of the tumor cells in soft agar. Taken together, our data demonstrate that serum exosomes form a growth promoting platform for AIG of tumor cells and may open a new vista into cancer cell growth in vivo.

Mechano-transduction mediated secretion and uptake of galectin-3 in breast carcinoma cells: implications in the extracellular functions of the lectin

In the following experiments, we sought to understand the triggering mechanism which propels galectin-3 to be secreted into the extracellular compartment from its intracellular stores in breast carcinoma cells. We also wanted to analyze in greater details the role of galectin-3 in cellular adhesion and spreading. To do this, we made use of two pairs of breast carcinoma cell lines where one of the pair has high expression of galectin-3 and the other low expression of the lectin. We determined that galectin-3 secreted into the conditioned medium of sub-confluent and spread cells in culture was quite low, almost negligible. However, once the cells were detached and rounded up, a mechano-sensing mechanism triggered the rapid secretion of galectin-3 into the conditioned medium. The secretion was constitutive as long as the cells remained detached. Galectin-3 was shown to be actively taken up from the conditioned medium by spreading cells. The cells which express and secrete high levels of galectin-3 adhered and spread much faster on plastic than those with reduced expression. The uptake of galectin-3 according to our data was important in cell spreading because if this process was compromised significantly, cells failed to spread. The data suggested that galectin-3 uptake modulates the adhesion plaques in that cells which express high levels of galectin-3 have thin-dot like plaques that may be suited for rapid adhesion and spreading while cells in which galectin-3 expression is reduced or knocked-down, have thick and elongated plaques which may be suited for a firmer adhesion to the substratum. Recombinant galectin-3 added exogenously reduced the thickness of the adhesion plaques of tumor cells with reduced galectin-3 expression. Taken together, the present data suggest that galectin-3 once externalized, is a powerful modulator of cellular adhesion and spreading in breast carcinoma cells.

Galectin-3 interacts with membrane lipids and penetrates the lipid bilayer

The precise mechanism by which galectin-3 and other cytosolic proteins that lack signal peptides are secreted is yet to be elucidated. In the present analyses, we determined that galectin-3, a beta-galactoside binding protein, can interact directly with membrane lipids in solid phase binding assays. More interestingly, we determined by spectrophotometric methods that it can spontaneously penetrate the lipid bilayer of liposomes in either direction. These findings suggest that galectin-3 on its own has the capacity to traverse the lipid bilayer. Whereas the situation is rather simplified in liposomes, the interaction of galectin-3 with the plasma membrane may involve cholesterol-rich membrane domains where galectin-3 can be concentrated and form multimers or interact covalently with other proteins.

The Serum Glycoprotein Fetuin-A Promotes Lewis Lung Carcinoma Tumorigenesis via Adhesive-Dependent and Adhesive-Independent Mechanisms

Fetuin-A is a serum glycoprotein in the cystatin family associated with the regulation of soft tissue calcification. We tested the role of systemic fetuin in tumor cell growth and metastasis by injecting Lewis lung carcinoma (LLC) cells into fetuin-A null and their wild-type (WT) littermate control C57BL/6 mice via the tail vein, s.c., and intrasplenic routes. In the experimental metastasis assay, the lungs of the WT mice were filled with metastatic nodules, whereas the lungs of the fetuin-A null mutant mice were virtually free of colonies at the end of 2 weeks. Lung colonization responded to the levels of serum fetuin-A in a dose-dependent manner, as observed by the formation of half as many colonies in mice heterozygous for the fetuin-A locus compared with homozygous WT mice and restoration of lung colonization by the administration of purified fetuin-A to fetuin-A-null mice. Serum fetuin-A also influenced the growth of LLC cells injected s.c.: fetuin-A-null mice developed small s.c. tumors only after a substantial delay. Similarly, intrasplenic injection of LLC cells resulted in rapid colonization of the liver with metastasis to the lungs within 2 weeks in the WT but not fetuin-A null mice. To examine the mechanism by which fetuin-A influences LLC colonization and growth, we showed that LLC tumor cells adhere to fetuin-A in a Ca2+-dependent fashion, resulting in growth of the tumor cells. These studies support the role of fetuin-A as a major growth promoter in serum that can influence tumor establishment and growth.

The serum glycoprotein fetuin-A promotes Lewis lung carcinoma tumorigenesis via adhesive-dependent and adhesive-independent mechanisms

Fetuin-A is a serum glycoprotein in the cystatin family associated with the regulation of soft tissue calcification. We tested the role of systemic fetuin in tumor cell growth and metastasis by injecting Lewis lung carcinoma (LLC) cells into fetuin-A null and their wild-type (WT) littermate control C57BL/6 mice via the tail vein, s.c., and intrasplenic routes. In the experimental metastasis assay, the lungs of the WT mice were filled with metastatic nodules, whereas the lungs of the fetuin-A null mutant mice were virtually free of colonies at the end of 2 weeks. Lung colonization responded to the levels of serum fetuin-A in a dose-dependent manner, as observed by the formation of half as many colonies in mice heterozygous for the fetuin-A locus compared with homozygous WT mice and restoration of lung colonization by the administration of purified fetuin-A to fetuin-A-null mice. Serum fetuin-A also influenced the growth of LLC cells injected s.c.: fetuin-A-null mice developed small s.c. tumors only after a substantial delay. Similarly, intrasplenic injection of LLC cells resulted in rapid colonization of the liver with metastasis to the lungs within 2 weeks in the WT but not fetuin-A null mice. To examine the mechanism by which fetuin-A influences LLC colonization and growth, we showed that LLC tumor cells adhere to fetuin-A in a Ca(2+)-dependent fashion, resulting in growth of the tumor cells. These studies support the role of fetuin-A as a major growth promoter in serum that can influence tumor establishment and growth.

Human galectin-3 promotes Trypanosoma cruzi adhesion to human coronary artery smooth muscle cells

Human galectin-3 binds to the surface of Trypanosoma cruzi trypomastigotes and human coronary artery smooth muscle (CASM) cells. CASM cells express galectin-3 on their surface and secrete it. Exogenous galectin-3 increased the binding of T. cruzi to CASM cells. Trypanosome binding to CASM cells was enhanced when either T. cruzi or CASM cells were preincubated with galectin-3. Cells stably transfected with galectin-3 antisense show a dramatic decrease in galectin-3 expression and very little T. cruzi adhesion to cells. The addition of galectin-3 to these cells restores their initial capacity to bind to trypanosomes. Thus, host galectin-3 expression is required for T. cruzi adhesion to human cells and exogenous galectin-3 enhances this process, leading to parasite entry.

Annexins expressed on the cell surface serve as receptors for adhesion to immobilized fetuin-A

Fetuin-A is a major constituent of the fetal bovine serum used extensively in cell culture media. We hereby present data demonstrating that breast carcinoma cells can adhere to immobilized fetuin-A in a calcium-dependent fashion. Interestingly, the cells can also divide and attain confluency under these conditions. Using a proteomic approach, we have identified annexin-II and -VI as the putative cell surface receptors for fetuin-A in the presence of Ca2+ ions. Biotinylation of cell surface proteins followed by immunoprecipitation revealed that annexin-VI was expressed on the extracytoplasmic surface of the cell membranes. Finally, to demonstrate that annexin-II and -VI were the adhesive receptors for fetuin-A, siRNA knockdown of expression of the annexins significantly reduced the calcium-mediated adhesion. Interestingly, we demonstrated that the tumor cells could also adhere to immobilized fetuin-A in the presence of magnesium ions, and that this adhesion was most likely mediated by integrins because neutralizing antibodies against beta1 integrins substantially reduced the adhesion. Our studies suggest that the expression of annexin-II and -VI and possibly other members of the family mediate novel adhesion and signaling mechanisms in tumor cells.

Alpha 2-HS glycoprotein (fetuin-A) modulates murine skin tumorigenesis

Fetuin, a major serum glycoprotein secreted by the liver, has been shown to play a role in bone development, calcium homeostasis and insulin sensitivity. In an earlier study, we demonstrated that bovine fetuin can bind to the plasma membrane of squamous and spindle-cell carcinoma cells. To test our hypothesis that fetuin plays a causal role in skin tumorigenesis, fetuin-A null and wild-type mice were challenged using a two-stage chemically-induced carcinogenesis protocol with DMBA (7,12-dimethylbenzo(a)anthracene) as the initiator, followed by twice weekly treatments with the tumor promoter TPA (12-O-tetradecanoylphorbol-13-acetate). Tumors that developed on fetuin-A null animals grew at a similar rate as those arising on their wild-type counterparts. Absence of fetuin-A did not alter tumor onset or conversion to squamous cell carcinoma, but reduced the number of tumors per mouse by 30%. This correlated with a decrease in tumor burden in fetuin-A null animals compared to wild-type weeks 18-22 from tumor onset. In addition, tumors arising on fetuin-A null mice had a diminished proliferative index with no change in cell survival or neovascularization in comparison with wild-type tumors. Our results suggest that fetuin-A contributes to early stages of skin tumorigenesis.

Members of the cystatin superfamily interact with MMP-9 and protect it from autolytic degradation without affecting its gelatinolytic activities

Matrix metalloproteinases (MMPs), like other proteinases, can undergo autolytic degradation once activated in vivo. Whereas the activities of these enzymes are tightly regulated by tissue inhibitors of matrix metalloproteinases (TIMPs), it is not clear mechanistically how these enzymes are protected from autolysis in their active state. We previously reported that MMPs particularly MMP-9 and MMP-2 interact with the serum glycoprotein fetuin-A [Arch. Biochem. Biophys. (1995) 322, 250], a member of the cystatin superfamily. In the present analyses, we demonstrate that this interaction protects MMP-9 from autolytic degradation without interfering with its enzymatic activity, allowing it to efficiently digest gelatin. Our data demonstrate that MMP-9 binds to members of the cystatin family with K(diss) ranging from 25 to 58 nM for fetuin-A and 1.5-1.9 microM for cystatin C. The ability of fetuin-A to protect MMP-9 from autolysis requires a molar ratio of at least 8:1 (fetuin-A/MMP-9). More interestingly, our data show that the other members of the cystatin also have the ability to protect MMP-9 from autolysis, provided they are in molar excess relative to MMP-9. Taken together, our data suggest that cystatins, particularly fetuin-A, in any cellular compartment including the circulatory system, efficiently protect MMP-9 and possibly other MMPs from autolysis. This mechanism ensures the digestion of the preferred substrate for MMP-9 without sacrificing the enzyme in the process.