Inhibition of ALDH1A1 Activity in Cisplatin-Resistant Ovarian Cancer Cells Alters Their Cancer Stemness, Cell Cycle Profile and Mitochondrial Respiration Rate

Introduction: Ovarian cancer is one of the leading cause of morbidity and death among women, with a five-year relative survival rate of only 30% in patients diagnosed with distant metastasis. The ovarian cancer cells initially respond to first-line platinum drug cisplatin [cis-diamminedichloroplatinum(II) (CDDP)] treatment. But, they subsequently develop resistance to CDDP and eventually exhibit chemoresistance. Aldehyde dehydrogenase 1 family member A1 (ALDH1A1) is one of the key functional markers of ovarian cancer stem cells (CSCs) that confers cancer stemness and therapeutic resistance, and is associated with poor prognosis and patient survival. In this study, we have assessed the anticancer effects of the ALDH1A1 inhibitor, A37, in CDDP-resistant ovarian cancer cells in vitro. Experimental Methods: SK-OV-3-CDDP, cisplatin-resistant ovarian cancer cells were treated with different concentrations of the small molecule inhibitor of ALDH1A1, A37. We determined the cell proliferation using water-soluble tetrazolium salt (WST-1) assay at 24 and 48 h. The distribution of cell division phases by cell cycle analysis and oxygen consumption rate (OCR) via seahorse extracellular flux analysis were assessed by flow cytometry and seahorse XFe24 analyzer, respectively. Furthermore, we examined the protein expression of key signaling molecules by western blot analysis and cancer stemness by tumorsphere formation assay. Results: Treatment of SK-OV-3-CDDP cells with A37 significantly reduced the ovarian cancer cell proliferation. Interestingly, A37 induced cell cycle arrest as observed by an increase in G₁ phase of the cell cycle. Additionally, A37 reduced the mitochondrial respiration of ovarian cancer cells as observed by the decrease in basal OCR. Moreover, A37 treatment markedly decreased the expression of WW domain containing transcription regulator 1 (WWTR1) protein [also called as transcriptional co-activator with PDZ-binding motif (TAZ)], which is a key downstream effector of mammalian Hippo signaling pathway that promotes cancer stemness, metastasis and chemoresistance. Importantly, A37 reduced the number and size of the tumorspheres. Conclusions: Our study suggests that inhibiting the ALDH1A1 activity using A37 reduced the cell proliferation and induced cell cycle arrest in CDPP-resistant ovarian cancer cells. The mechanism by which A37 elicits its anticancer effects on ovarian cancer cells include impairment in mitochondrial respiration that could alter cancer cell metabolism, and a decrease in WWTR1/TAZ expression and tumorsphere formation that could suppress cancer stemness. Our findings demonstrate that inhibition of ALDH1A1 could effectively eliminate the chemoresistant ovarian cancer cells, and therefore, new strategies targeting ALDH1A1 could lead to the development of novel therapeutics for aggressive chemoresistant ovarian cancer.

Role of Inflammation in the Development of Colorectal Cancer

Chronic inflammation can lead to the development of many diseases, including cancer. Inflammatory bowel disease (IBD) that includes both ulcerative colitis (UC) and Crohnmp's disease (CD) are risk factors for the development of colorectal cancer (CRC). Many cytokines produced primarily by the gut immune cells either during or in response to localized inflammation in the colon and rectum are known to stimulate the complex interactions between the different cell types in the gut environment resulting in acute inflammation. Subsequently, chronic inflammation, together with genetic and epigenetic changes, have been shown to lead to the development and progression of CRC. Various cell types present in the colon, such as enterocytes, Paneth cells, goblet cells, and macrophages, express receptors for inflammatory cytokines and respond to tumor necrosis factor-alpha (TNF-α), interleukin-1 beta (IL-1β), IL-6, and other cytokines. Among the several cytokines produced, TNF-α and IL-1β are the key pro-inflammatory molecules that play critical roles in the development of CRC. The current review is intended to consolidate the published findings to focus on the role of pro-inflammatory cytokines, namely TNF-α and IL-1β, on inflammation (and the altered immune response) in the gut, to better understand the development of CRC in IBD, using various experimental model systems, preclinical and clinical studies. Moreover, this review also highlights the current therapeutic strategies available (monotherapy and combination therapy) to alleviate the symptoms or treat inflammation-associated CRC by using monoclonal antibodies or aptamers to block pro-inflammatory molecules, inhibitors of tyrosine kinases in the inflammatory signaling cascade, competitive inhibitors of pro-inflammatory molecules, and the nucleic acid drugs like small activating RNAs (saRNAs) or microRNA (miRNA) mimics to activate tumor suppressor or repress oncogene/pro-inflammatory cytokine gene expression.

MON-513 Suppressing the Growth of Human Medullary Thyroid Cancer Cells Using FDA-Approved Drug

Medullary thyroid carcinoma (MTC) is a solid tumor of the parafollicular cells in the thyroid gland. MTC has worse prognosis, when compared with other differentiated thyroid cancers, and MTC patients with distant metastases have a low survival rate unless thyroidectomy is performed at an early stage. Furthermore, conventional treatments have only marginal benefits. Therefore, there is a need to develop novel therapeutics for MTC. Several drugs that are developed and tested in preclinical trials fail in clinical trials. Therefore, repurposing the already US Food and Drug Administration (FDA)-approved drugs towards the treatment of cancers may have potential benefits, like saving the lives of cancer patients and lowering the investment cost of drug development. Here, we explored a novel precision treatment for thyroid cancers by repurposing the FDA-approved small molecule anti-parasitic drug Nitazoxanide (NTZ). In our study, we examined the anticancer effects of NTZ on human MTC cells using the TT cell line. We treated the TT cells with different concentrations of NTZ and assessed the cell proliferation by water-soluble tetrazolium salt (WST-1) assay and oxygen consumption rate (OCR) by Seahorse extracellular flux analysis (Seahorse XFe24 Analyzer). Additionally, we determined the effects of NTZ on the protein expression of key signaling molecules that regulate MTC cell growth by western blot analysis. Our results indicated that NTZ significantly suppressed the growth of TT cells at 24 h treatment. Very importantly, NTZ reduced the basal OCR demonstrating the inhibition of mitochondrial respiration. Moreover, protein expression studies revealed that NTZ markedly reduced the key Hippo signaling pathway effector molecule TAZ and the oncogene c-myc. Interestingly, NTZ decreased the expression of epidermal growth factor receptor (EGFR) that plays an important role for RET activation in MTC. Importantly, NTZ increased the expression of p53 upregulated modulator of apoptosis (Puma). Taken together, our findings demonstrate for the first time that NTZ inhibits the growth of MTC cells and decreases the cancer cell metabolism. The mechanisms by which NTZ targets the MTC cells involve the suppression of key oncogenic proteins and upregulation of tumor suppressor molecule. Thus, our study highlights that repurposing this FDA-approved currently used drug may have a greater advantage of being tested in preclinical models of MTC, and therefore, for the rapid consideration of NTZ as a potential therapeutic drug to treat MTC patients in the near future.

The role of the redox/miR-6855-3p/PRDX5A axis in reversing SLUG-mediated BRCA2 silencing in breast cancer cells

BACKGROUND

We have previously shown that the zinc finger transcription repressor SNAI2 (SLUG) represses tumor suppressor BRCA2-expression in non-dividing cells by binding to the E2-box upstream of the transcription start site. However, it is unclear how proliferating breast cancer (BC) cells that has higher oxidation state, overcome this repression. In this study, we provide insight into the mechanism of de-silencing of BRCA2 gene expression by PRDX5A, which is the longest member of the peroxiredoxin5 family, in proliferating breast cancer cells.

METHODS

We used cell synchronization and DNA affinity pulldown to analyze PRDX5A binding to the BRCA2 silencer. We used oxidative stress and microRNA (miRNA) treatments to study nuclear localization of PRDX5A and its impact on BRCA2-expression. We validated our findings using mutational, reporter assay, and immunofluorescence analyses.

RESULTS

Under oxidative stress, proliferating BC cells express PRDX5 isoform A (PRDX5A). In the nucleus, PRDX5A binds to the BRCA2 silencer near the E2-box, displacing SLUG and enhancing BRCA2-expression. Nuclear PRDX5A is translated from the second AUG codon in frame to the first AUG codon in the PRDX5A transcript that retains all exons. Mutation of the first AUG increases nuclear localization of PRDX5A in MDA-MB-231 cells, but mutation of the second AUG decreases it. Increased mitronic hsa-miRNA-6855-3p levels under oxidative stress renders translation from the second AUG preferable. Mutational analysis using reporter assay uncovered a miR-6855-3p binding site between the first and second AUG codon in the PRDX5A transcript. miR-6855-3p mimic increases accumulation of nuclear PRDX5A and inhibits reporter gene translation.

CONCLUSION

Oxidative stress increases miR-6855-3p expression and binding to the inter-AUG sequence of the PRDX5A transcript, promoting translation of nuclear PRDX5A. Nuclear PRDX5A relieves SLUG-mediated BRCA2 silencing, resulting in increased BRCA2-expression.

Carbon monoxide sensitizes cisplatin-resistant ovarian cancer cell lines toward cisplatin via attenuation of levels of glutathione and nuclear metallothionein

Cisplatin resistance remains a major impediment to effective treatment of ovarian cancer. Despite initial platinum responsiveness, thiol-containing peptides and proteins, glutathione (GSH) and metallothionein (MT), bind and inactivate cisplatin in cancer cells. Indeed, high levels of GSH and MT in ovarian cancers impart cisplatin resistance and are predictive of poor prognosis. Cystathionine β-synthase (CBS), an enzyme involved in sulfur metabolism, is overexpressed in ovarian cancer tissues and is itself associated with cisplatin resistance. Treatment with exogenous carbon monoxide (CO), a known inhibitor of CBS, may mitigate cisplatin resistance in ovarian cancer cells by attenuation of GSH and MT levels. Using a photo-activated CO-releasing molecule (photoCORM), [Mn(CO)₃(phen)(PTA)]CF₃SO₃ (phen = 1,10-phenanthroline, PTA = 1,3,5-triza-7-phosphaadamantane) we assessed the ability of CO to sensitize established cisplatin-resistant ovarian cancer cell lines to cisplatin. Cisplatin-resistant cells, treated with both cisplatin and CO, exhibited significantly lower cell viability and increased poly (ADP-ribose) polymerase (PARP) cleavage versus those treated with cisplatin alone. These cisplatin-resistant cell lines overexpressed CBS and had increased steady state levels of GSH and expression of nuclear MT. Both CO treatment and lentiviral-mediated silencing of CBS attenuated GSH and nuclear MT expression in cisplatin resistant cells. We have demonstrated that CO, delivered from a photoCORM, sensitizes established cisplatin-resistant cell lines to cisplatin. Furthermore, we have presented strong evidence that the effects of CO in circumventing chemotherapeutic drug resistance is at least in part mediated by the inactivation of endogenous CBS.

Abstract A12: Characterization of the mitronic tsmiR miR6855-3p as a DNA damage repair regulator in the SLUG-high metastatic breast cancer cells

The precursor of the human microRNA hsa-miR-6855-3p is a 5-tailed mitronic pre-miRNA that is coded by intron #13 of the deubiquitinase USP20 gene. Our preliminary data suggest that the biosynthesis of this miRNA is upregulated by oxidative stress in the SLUG-high metastatic breast cancer cells, promoting DNA double-strand break repair (DSBR) through the indirect enhancement of BRCA2 gene expression. We found that miR-6855-3p favors BRCA2 biosynthesis through the enhancement of the level of an alternately translated form of the BRCA2 gene enhancer protein SPRDX5. We hypothesize that BRCA2 gene silencer acts as a scaffolding to co-recruit SLUG and SPRDX5 and promote SPRDX5-mediated oxidative inactivation of the BRCA2 negative regulator protein SLUG. Here, we present evidence that (a) the expression of miR-6855-3p is essential for the expression of BRCA2 in the SLUG-high metastatic breast cancer cells; (b) knockdown of miR-6855-3p affects DSBR in these cells; and (c) the miR-6855-3p knocked-down cells are susceptible to the synthetic lethality by the PARP inhibitors. Our study reveals a novel mechanism of regulation of BRCA2 gene expression in the aggressive breast cancer cells, offering an alternative strategy to chemically intervene in the progression of hard-to-cure, highly aggressive SLUG-high breast cancer. We propose that the inhibition of miR-6855-3p will induce BRCA2 deficiency in the BLBC cells, thus increasing their susceptibility to standard chemotherapy as well as to PARP inhibitors as has been described for other BRCA2-deficient cells. Supported in part by DOD-CDMRP IDEA Expansion Grant #BC103645 and NIH/NCI grant 1R21CA181920-01 to GC and 1U54RR026140 to SM.

Note: This abstract was not presented at the conference.

Citation Format: Marshall JD Ellison, Smita Misra, Gautam Chaudhuri. Characterization of the mitronic tsmiR miR6855-3p as a DNA damage repair regulator in the SLUG-high metastatic breast cancer cells [abstract]. In: Proceedings of the AACR Special Conference: Advances in Breast Cancer Research; 2017 Oct 7-10; Hollywood, CA. Philadelphia (PA): AACR; Mol Cancer Res 2018;16(8_Suppl):Abstract nr A12.

Abstract 4486: Redox regulation of the biosynthesis of mitronic tsmiR miR6855 in the basal like breast cancer cells

Radiation and chemotherapeutic agents eradicate tumors by inducing irreparable DNA damage. However, cancer cells often develop resistance to therapy by manipulating the DNA repair machinery. Conversely, a dividing cell constantly exposed to environmental and endogenous DNA damaging agents can transform into a tumor due to incorrect repair. Therefore the expression level of DNA repair proteins is critical both for cancer therapy and tumorigenesis. Our preliminary studies implied a unique mechanism involving an miRNA miR-6855-3p that promotes the biosynthesis of the transcriptional regulator protein SPRDX5 which enhances the expression of the tumor suppressor protein BRCA2 leading to the genotoxin and radiation-resistance of aggressive SLUG-high basal-like breast cancer (BLBC) cells. The miRNA miR-6855-3p thus acts as a tumor suppressor miRNA (tsmiR). Interestingly, the gene for the miRNA miR-6855-3p is mitronic and is nested within the intron#13 of the USP20 gene which is a deubiquitinase. Thus, the transcription of miR-6855-3p gene is regulated through the USP20 gene promoter. We present evidence here that USP20 and miR-6855 gene transcriptions are up regulated by oxidative stress. Tert-butylhydroperoxide was used for oxidative stress. Under the oxidative stress conditions tested, NRF2 level and the levels of several NRF2-regulated proteins are increased, indicating activation of NRF2 in the stressed BLBC cells. Under the stress conditions the levels of USP20 and miR-6855-3p are increased significantly. Knockdown of NRF2 prevented stress-induced elevation of USP20 and miR-6855-3p RNA level in the BLBC cells indicating the involvement of NRF2 in this process. The binding of NRF2 to the USP20 gene promoter and its function were characterized by ChIP analysis, site-directed mutagenesis and using the promoter-luciferase reporter constructs. We conclude that the biosynthesis of the tsmiR miR-6855-3p in the BLBC cells is regulated by oxidative stress and involves NRF2. Since oxidative stress is a hallmark in the etiology and progression of metastatic breast cancer, understanding the redox regulation of a tsmiR that positively influences BRCA2 gene expression in the BLBC cells could be clinically significant. Supported in part by DOD-CDMRP IDEA Expansion Grant# BC103645 and NIH/NCI grant 1R21CA181920-01 to GC and 1U54RR026140 to SM.

Citation Format: Smita Misra, Gautam Chaudhuri. Redox regulation of the biosynthesis of mitronic tsmiR miR6855 in the basal like breast cancer cells [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 4486. doi:10.1158/1538-7445.AM2017-4486

Abstract 1472: Alternate translation initiation regulation of PRDX5 mRNA by miR6855<->3p in basal<->like breast cancer cells

Human peroxiredoxins (PRDXs) are a superfamily of six thiol<->dependent peroxidases that are able to reduce hydrogen peroxide, alkyl hydroperoxides and peroxynitrite. Apart from the classical, apparently redundant function of mitochondrial and often peroxisomal peroxide neutralization shared by other peroxiredoxins, PRDX5 was initially discovered as a DNA binding transcriptional repressor regulating the biosynthesis of cytotoxic Alu RNAs through a mitochondrial<->localization signal<->truncated mature form (SPRDX5] of this protein that is accumulated in the nucleus and binds to a 60 bp nucleotide sequence at the Alu gene promoters. Our data suggest that SPRDX5 also binds to the Alu<->sequence<->containing BRCA2 gene silencer to prevent the binding of SLUG at the silencer thus enhancing the BRCA2 gene expression leading to the genotoxin and radiation<->resistance of aggressive SLUG<->high basal<->like breast cancer cells. PRDX5 mRNA contains two in<->frame start codons (AUGs) that are conditionally used as alternate translation initiation sites. Translation from the first AUG would result in the synthesis of a larger 214<->residue protein (LPRDX5) whereas the use of the second AUG would result in the production of a shorter 162<->residue polypeptide (SPRDX5). Since SPRDX5 lacks the mitochondrial localization signal, it is accumulated in the nucleus via its C<->terminal bipartite nuclear localization signal. We present evidence here that a miRNA, miR<->6855<->3p, binds the primary PRDX5 transcript between the two AUG codons and prevents the translation of the mRNA from the first AUG codon but not that from the second AUG codon thus favoring the initiation of translation from the second AUG codon. To characterize the effect of miR<->6855<->3p on Prdx5 mRNA translation, we developed three different PRDX5<->FLAG constructs in pCV3XFLAG14 (Sigma) that has Prdx5 ORF with or without mutation on the first or second AUG codon. Transfection of these constructs into BT549 cells followed by treatments with miR<->6855<->3p mimic or antagomiR and subcellular fractionation further supported our notion. We propose here that miR<->6855<->3p acts as a tsmiR by promoting the biosynthesis of the transcriptional regulator protein SPRDX5 which enhances the expression of the tumor suppressor protein BRCA2 leading to the genotoxin and radiation<->resistance of aggressive SLUG<->high basal<->like breast cancer cells. Supported in part by DOD-CDMRP IDEA Expansion Grant# BC103645 and NIH/NCI grant 1R21CA181920 01 to GC and 1U54RR026140 to SM.

Citation Format: Gautam Chaudhuri, Smita Misra. Alternate translation initiation regulation of PRDX5 mRNA by miR6855<->3p in basal<->like breast cancer cells [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 1472. doi:10.1158/1538-7445.AM2017-1472

The Role of Epithelial to Mesenchymal Transition in Human Amniotic Membrane Rupture

CONTEXT

Biochemical weakening of the amnion is a major factor preceding preterm premature rupture of membranes (PPROMs), leading to preterm birth. Activation of matrix metalloproteinases (MMPs) is known to play a key role in collagen degradation of the amnion; however, epithelial to mesenchymal transition (EMT) that is also induced by MMP activation has not been investigated as a mechanism for amnion weakening.

OBJECTIVE

To measure amniotic EMT associated with vaginal delivery (VD) compared with unlabored cesarean sections (CSs), and to assess changes in amniotic mechanical strength with pharmacologic inhibitors and inducers of EMT, thus testing the hypothesis that EMT is a key biochemical event that promotes amniotic rupture.

FINDINGS

(1) Amnions taken from VD contained a significantly increased number of mesenchymal cells relative to epithelial cells compared with unlabored CS by fluorescence-activated cell sorting analysis (60% vs 10%); (2) tumor necrosis factor (TNF)-α stimulation of amniotic epithelial cells increased expression of the mesenchymal marker vimentin after 2 days; (3) EMT inhibitor, etodolac, significantly increased the time and mechanical pressure required to rupture the amnion; and (4) TNF-α and another pharmacologic EMT inducer, ethacridine, decreased the time and mechanical pressure required for amnion rupture, further confirming that the mesenchymal phenotype significantly weakens the amnion.

CONCLUSIONS

This work demonstrated amniotic cell EMT was associated with labor and EMT decreased the tensile strength of the amnion. These findings suggest a role for EMT in the pathophysiology of PPROM and may provide a basis for development of therapies to prevent preterm labor.

Increased sensitivity of African American triple negative breast cancer cells to nitric oxide-induced mitochondria-mediated apoptosis

Background

Breast cancer is a complex heterogeneous disease where many distinct subtypes are found. Younger African American (AA) women often present themselves with aggressive form of breast cancer with unique biology which is very difficult to treat. Better understanding the biology of AA breast tumors could lead to development of effective treatment strategies. Our previous studies indicate that AA but not Caucasian (CA) triple negative (TN) breast cancer cells were sensitive to nitrosative stress-induced cell death. In this study, we elucidate possible mechanisms that contribute to nitric oxide (NO)-induced apoptosis in AA TN breast cancer cells.

Methods

Breast cancer cells were treated with various concentrations of long-acting NO donor, DETA-NONOate and cell viability was determined by trypan blue exclusion assay. Apoptosis was determined by TUNEL and caspase 3 activity as well as changes in mitochondrial membrane potential. Caspase 3 and Bax cleavage, levels of Cu/Zn superoxide dismutase (SOD) and Mn SOD was assessed by immunoblot analysis. Inhibition of Bax cleavage by Calpain inhibitor, and levels of reactive oxygen species (ROS) as well as SOD activity was measured in NO-induced apoptosis. In vitro and in vivo effect of NO treatment on mammary cancer stem cells (MCSCs) was assessed.

Results and discussion

NO induced mitocondria-mediated apoptosis in all AA but not in CA TN breast cancer cells. We found significant TUNEL-positive cells, cleavage of Bax and caspase-3 activation as well as depolarization mitochondrial membrane potential only in AA TN breast cancer cells exposed to NO. Inhibition of Bax cleavage and quenching of ROS partially inhibited NO-induced apoptosis in AA TN cells. Increase in ROS coincided with reduction in SOD activity in AA TN breast cancer cells. Furthermore, NO treatment of AA TN breast cancer cells dramatically reduced aldehyde dehydrogenase1 (ALDH1) expressing MCSCs and xenograft formation but not in breast cancer cells from CA origin.

Conclusions

Ethnic differences in breast tumors dictate a need for tailoring treatment options more suited to the unique biology of the disease.

Abstract 1927: Myc-induced suppression of the RNA-binding protein ZAR2 in breast cancer cells

Our objective is to verify the hypothesis that c-Myc-regulated oncomiR miR-130a-5p suppresses the level of the RNA-binding tumor suppressor protein ZAR2 in the cMyc-high aggressive breast cancer cells. We experimentally validated the binding of miR130a-5p miRISC to ZAR2 mRNA in vivo and inhibition of the translation of this mRNA by this binding. We used three commercially available c-Myc-high ZAR2-low breast cancer cell lines BT549, MDA-MB-453 and MDA-MB-231 and two c-Myc-low ZAR2-high breast cancer cells MCF7 and HCC38 for our studies. We cloned the full length 3′-UTR (179 bp) of human ZAR2 mRNA immediately downstream of the firefly luciferase open reading frame sequence contained in the reporter plasmid. We also have created different mutants of the 3’-UTR, each having mutation in each of the putative miR130a-5p binding sites. We transiently transfected the recombinant plasmid and miR130a-5p miRNA mimic into breast cancer cells and assessed luciferase activity or fluorescence 24-48 hours after transfection. We also have transfected just the reporter construct into breast cancer cells which express the endogenous miR130a-5p miRNAs, along with vectors which express mutant versions of the miRNA binding sites. In this experimental system the wild-type reporters had less activity than their respective mutants. To evaluate the functional importance of miR130a-5p miRNA/ZAR2 mRNA pair, we transiently over-expressed a miR130a-5p miRNA mimic in the cMyc-low breast cancer breast cancer cells and subsequently analyzed the level of ZAR2 protein levels. Our data showed that ZAR2 protein levels are decreased by the mimic increasing the in vitro invasiveness of these cells. Our results thus reveal a novel mechanism for the induction of aggressiveness by cMyc in the breast cancer cells. This research is supported in part by DOD-CDMRP IDEA Expansion Grant# BC103645 and NIH/NCI grant 1R21CA181920-01 to GC and NIH grant 1U54RR026140 TO SM

Citation Format: Smita Misra, Gautam Chaudhuri. Myc-induced suppression of the RNA-binding protein ZAR2 in breast cancer cells. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 1927.

γ-Aminobutyric Acid Is Synthesized and Released by the Endothelium: Potential Implications

RATIONALE

Gamma aminobutyric acid (GABA), a neurotransmitter of the central nervous system, is found in the systemic circulation of humans at a concentration between 0.5 and 3 μmol/L. However, the potential source of circulating GABA and its significance on the vascular system remains unknown. We hypothesized that endothelial cells (ECs) may synthesize and release GABA to modulate some functions in the EC and after its release into the circulation.

OBJECTIVE

To assess whether GABA is synthesized and released by the EC and its potential functions.

METHODS AND RESULTS

Utilizing the human umbilical vein ECs and aortic ECs, we demonstrated for the first time that ECs synthesize and release GABA from [1-(14)C]glutamate. Localization of GABA and the presence of the GABA-synthesizing enzyme, glutamic acid decarboxylase in EC were confirmed by immunostaining and immunoblot analysis, respectively. The presence of GABA was further confirmed by immunohistochemistry in the EC lining the human coronary vessel. EC-derived GABA regulated the key mechanisms of ATP synthesis, fatty acid, and pyruvate oxidation in EC. GABA protected EC by inhibiting the reactive oxygen species generation and prevented monocyte adhesion by attenuating vascular cell adhesion molecule -1 and monocyte chemoattractant protein-1 expressions. GABA had no relaxing effect on rat aortic rings. GABA exhibited a dose-dependent fall in blood pressure. However, the fall in BP was abolished after pretreatment with pentolinium.

CONCLUSIONS

Our findings indicate novel potential functions of endothelium-derived GABA.

Role of cystathionine β-synthase in human breast Cancer

Cystathionine β-synthase (CBS) is an enzyme in the transulfuration pathway that can catalyze the condensation of homocysteine (Hcy) and cysteine (Cys) to hydrogen sulfide (H2S) and cystathionine (CTH). CBS-derived H2S is important in angiogenesis and drug resistance in colon and ovarian cancers, respectively. However, the mechanisms by which cancer cell-derived H2S is utilized by cancer cells as a protective agent against host-derived activated macrophages are not yet investigated. This study investigated the mechanistic role of CBS-derived H2S in the protection of human breast cancer (HBC) cells against activated macrophages. HBC patient-derived tissue arrays and immunoblot analysis of HBC cells exhibited significantly increased levels of CBS when compared with their normal counterparts. This was associated with increased levels of H2S and CTH. Silencing of CBS in HBC cells caused a significant decrease in the levels of H2S and CTH but did not affect the growth of these cells per se, in in vitro cultures. However CBS-silenced cells exhibited significantly reduced growth in the presence of activated macrophages and in xenograft models. This was associated with an increase in the steady state levels of reactive aldehyde-derived protein adducts. Exogenous addition of H2S countered the effects of CBS silencing in the presence of macrophages. Conversely overexpression of CBS in human breast epithelial (HBE) cells (which do not naturally express CBS) protected them from activated macrophages, which were otherwise susceptible to the latter.

Abstract 183: Oncogenic miRNA miR-130a-induced inhibition of the growth regulator protein ZAR2 in TNBC cells

ZAR2 is C4-type zinc-finger protein that we found to suppress the growth of breast tumor cells. In the dividing breast cancer cells ZAR2 is primarily located in the cytosol. It probably inhibits the growth of the tumor cells through sequence-specific capture and degradation of certain mRNAs which are critical for the growth of the cells. We found that the level of ZAR2 protein is significantly lower in the highly aggressive breast cancer cells of the triple negative subtype (TNBC). Forced expression of ZAR2 in the TNBC cells prevented the proliferation and invasiveness of these cells. Major objective of the research presented here is to understand the mechanism of suppression of ZAR2 level in the TNBC cells. As ZAR2 mRNA levels are very similar in the TNBC and non-TNBC cells, we postulated that ZAR2 protein levels are down-regulated in the TNBC cells due to the induction of a ZAR2-targeting miRNA in these cells. We used computational prediction to identify potential microRNAs down-regulating ZAR2 in the TNBC cells. One of the major miRNAs that is predicted by DIANA-Tools (http://diana.imis.athena-innovation.gr/DianaTools/index.php?r = MicroT_CDS/index) to target ZAR2 mRNA is hsa-miR-130a-5p. We found that the level of miR-130a-5p in the TNBC cells is inversely related to the level of ZAR2 protein in the TNBC cells. We validated the binding of miR130a-5p miRISC to several specific locations at the 3′-UTR of ZAR2 mRNA and the inhibition of translation of ZAR2 mRNA by this miRNA. We propose that targeted knockdown of miR130a-5p in the TNBC cells will elevate the level of ZAR2 protein resulting in the inhibition of the growth of these cells. This research is supported in part by NIH/NCIgrant1R21CA181920-01 to GC and NIH grant 1U54RR026140 to SM.

Citation Format: Smita Misra, Ashutosh Snghal, Gautam Chaudhuri. Oncogenic miRNA miR-130a-induced inhibition of the growth regulator protein ZAR2 in TNBC cells. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 183. doi:10.1158/1538-7445.AM2015-183

Acid gradient across plasma membrane can drive phosphate bond synthesis in cancer cells: acidic tumor milieu as a potential energy source

Aggressive cancers exhibit an efficient conversion of high amounts of glucose to lactate accompanied by acid secretion, a phenomenon popularly known as the Warburg effect. The acidic microenvironment and the alkaline cytosol create a proton-gradient (acid gradient) across the plasma membrane that represents proton-motive energy. Increasing experimental data from physiological relevant models suggest that acid gradient stimulates tumor proliferation, and can also support its energy needs. However, direct biochemical evidence linking extracellular acid gradient to generation of intracellular ATP are missing. In this work, we demonstrate that cancer cells can synthesize significant amounts of phosphate-bonds from phosphate in response to acid gradient across plasma membrane. The noted phenomenon exists in absence of glycolysis and mitochondrial ATP synthesis, and is unique to cancer. Biochemical assays using viable cancer cells, and purified plasma membrane vesicles utilizing radioactive phosphate, confirmed phosphate-bond synthesis from free phosphate (P_i), and also localization of this activity to the plasma membrane. In addition to ATP, predominant formation of pyrophosphate (PP_i) from P_i was also observed when plasma membrane vesicles from cancer cells were subjected to trans-membrane acid gradient. Cancer cytosols were found capable of converting PP_i to ATP, and also stimulate ATP synthesis from P_i from the vesicles. Acid gradient created through glucose metabolism by cancer cells, as observed in tumors, also proved critical for phosphate-bond synthesis. In brief, these observations reveal a role of acidic tumor milieu as a potential energy source and may offer a novel therapeutic target.

Abstract 3159: ZAR2 transcriptionally represses the ATPase ATP6V0A4 to negatively regulate invasiveness of breast cancer cells

ZAR2 is a recently characterized RNA-dependent transcriptional repressor protein that is implicated in the cell cycle-dependent regulation of BRCA2 gene expression. We have shown previously that ZAR2 mRNA is transcribed from the overlapping bi-directional promoter of the BRCA2 gene, binds to the overlapping promoter and prevents the expression of BRCA2 through chromatin remodeling. ZAR2 level is significantly low in the invasive breast cancer cells and tissues as compared to the non-invasive cells. Knockdown of ZAR2 in the non-invasive breast cancer cells increased the in vitro invasiveness of these cells whereas forced expression of ZAR2 in the invasive breast cancer cells prevented their invasiveness. To understand the possible mechanism of ZAR2-mediated regulation of invasiveness of the breast cancer cells we studied differential gene expression in the ZAR2 knocked down non-invasive breast cancer cells by RNA-seq analysis. One of the genes that are significantly elevated in the ZAR2 knocked down cells is the invasion determining enzyme ATP6V0A4. ATP6V0A4 is transcribed from an overlapping bi-directional promoter along with its partner TMEM213 in the breast cancer cells. We found that both ATP6V0A4 and TMEM213 levels are increased in the ZAR2 knocked down cells whereas cells with forced expression of ZAR2 have a significant decrease in the levels of these proteins. ZAR2 cell cycle dependently binds to the ATP6V0A4/TMEM213 gene promoter to repress the activity of this bi-directional promoter. This study thus reports a new pathway for the regulation of the invasiveness of breast cancer cells. Supported in part by DOD grants BC990678 and BC050641 to GC and NIH grant 1U54RR026140 to SM.

Citation Format: Smita Misra, Gautam Chaudhuri. ZAR2 transcriptionally represses the ATPase ATP6V0A4 to negatively regulate invasiveness of breast cancer 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 3159. doi:10.1158/1538-7445.AM2014-3159

Proteomic identification of mitochondrial targets of arginase in human breast cancer

We have previously reported arginase expression in human breast cancer cells and demonstrated that the inhibition of arginase by N^ω hydroxy L-arginine (NOHA) in MDA-MB-468 cells induces apoptosis. However, arginase expression and its possible molecular targets in human breast tumor samples and potential clinical implications have not been fully elucidated. Here, we demonstrate arginase expression in human breast tumor samples, and several established breast cancer cell lines, in which NOHA treatment selectively inhibits cell proliferation. The over-expression of Bcl2 in MDA-MB-468 cells abolished NOHA-induced apoptosis, suggesting that the mitochondria may be the main site of NOHA’s action. We, therefore, undertook a proteomics approach to identify key mitochondrial targets of arginase in MDA-MB-468 cells. We identified 54 non-mitochondrial and 13 mitochondrial proteins that were differentially expressed in control and NOHA treated groups. Mitochondrial serine hydroxymethyltransferase (mSHMT) was identified as one of the most promising targets of arginase. Both arginase II (Arg II) and mSHMT expressions were higher in human breast tumor tissues compared to the matched normal and there was a strong correlation between Arg II and mSHMT protein expression. MDA-MB-468 xenografts had significant upregulation of Arg II expression that preceded the induction of mSHMT expression. Small inhibitory RNA (siRNA)-mediated inhibition of Arg II in MDA-MB-468 and HCC-1806 cells led to significant inhibition of both the mSHMT gene and protein expression. As mSHMT is a key player in folate metabolism, our data provides a novel link between arginine and folate metabolism in human breast cancer, both of which are critical for tumor cell proliferation.

A light-activated NO donor attenuates anchorage independent growth of cancer cells: Important role of a cross talk between NO and other reactive oxygen species

It is established that high concentrations of nitric oxide(1) (NO), as released from activated macrophages, induce apoptosis in breast cancer cells. In this study, we assessed the potential of a light-activated NO donor [(Me2bpb)Ru(NO)(Resf)], a recently reported apoptototic agent, in suppressing the anchorage independent growth potentials of an aggressive human breast cancer cell line. Our results demonstrated the down regulation of anchorage independent growth by light activated NO treatment in the aggressive human breast cancer cell line MDA-MB-231 and afforded insight into the associated mechanism(s). The investigation revealed an up-regulation of the bioactivity of catalase with an accompanied reduction in the endogenous levels of H2O2, a direct substrate of catalase and a recently identified endogenous growth modulator in breast cancer cells. An earlier publication reported that endogenous superoxide (O2(-)) in human breast cancer cells constitutively inhibits catalase bioactivity (at the level of its protein), resulting in increased H2O2 levels. Interestingly in this study, O2(-) was also found to be down- regulated following NO treatment providing a basis for the observed increase in catalase bioactivity. Cells silenced for the catalase gene exhibited compromised reduction in anchorage independent growth upon light activated NO treatment. Collectively this study detailed a mechanistic cross talk between exogenous NO and endogenous ROS in attenuating anchorage independent growth.

Induction of a feed forward pro-apoptotic mechanistic loop by nitric oxide in a human breast cancer model

We have previously demonstrated that relatively high concentrations of NO [Nitric Oxide] as produced by activated macrophages induced apoptosis in the human breast cancer cell line, MDA-MB-468. More recently, we also demonstrated the importance of endogenous H₂O₂ in the regulation of growth in human breast cancer cells. In the present study we assessed the interplay between exogenously administered NO and the endogenously produced reactive oxygen species [ROS] in human breast cancer cells and evaluated the mechanism[s] in the induction of apoptosis. To this end we identified a novel mechanism by which NO down regulated endogenous hydrogen peroxide [H₂O₂] formation via the down-regulation of superoxide [O₂^.−] and the activation of catalase. We further demonstrated the existence of a feed forward mechanistic loop involving protein phosphatase 2A [PP2A] and its downstream substrate FOXO1 in the induction of apoptosis and the synthesis of catalase. We utilized gene silencing of PP2A, FOXO1 and catalase to assess their relative importance and key roles in NO mediated apoptosis. This study provides the potential for a therapeutic approach in treating breast cancer by targeted delivery of NO where NO donors and activators of downstream players could initiate a self sustaining apoptotic cascade in breast cancer cells.

Abstract B39: Methylation of BRCA2 gene promoter CpG units through ZAR2-dependent DNMT1 recruitment

BRCA2 gene expression is stringently regulated during the cell cycle. BRCA2 expression is proportional to the rate of cell proliferation. Looking at the human BRCA2 gene minimal promoter sequence we found that it has over 45 CpG units which could be potentially methylated regulating the recruitment of different transcription factors affecting BRCA2 gene expression. We discovered that BRCA2 gene promoter has bi-directional activity and the product of the reverse activity (a ZAR1-like protein, we named ZAR2) silences the forward promoter (for BRCA2). ZAR2 is a C4-type zinc finger-containing transcription factor that regulates BRCA2 in a cell cycle dependent manner. We found that ZAR2 enters the nucleus of the G0/G1 cells binds to the promoter of BRCA2 and silences the BRCA2 gene expression. ZAR2 has a dsRNA binding domain. We report here that BRCA2 gene promoter, through its bidirectional activity, produces two partially overlapping transcripts (BRCA2 and ZAR2) in the breast cells forming a 111 bp RNA duplex. We postulate that endogenous transcriptional gene silencing RNAs (tgsRNAs) against BRCA2 gene promoter are thus formed from the overlapping RNA duplex in the cell nucleus. These tgsRNAs in turn contribute towards promoter methylation. Our data suggest that ZAR2 upon binding to the tgsRNAs binds to specific locations of BRCA2 gene promoter and recruits DNMT1 which in turn perform CpG methylation. This study will contribute towards the understanding of the epigenetic regulation of BRCA2 gene expression in different cell cycle stages as well as in sporadic cases of breast and other cancer. Supported in part by the DOD-CDMRP IDEA Grants BC990678 and BC050641 to GC and MeTRC pilot project grant 1U54RR026140-01 to SM

Citation Format: Smita Misra, Mukul K. Mittal, Sheetal V. Khedkar, Gautam Chaudhuri. Methylation of BRCA2 gene promoter CpG units through ZAR2-dependent DNMT1 recruitment. [abstract]. In: Proceedings of the AACR Special Conference on Chromatin and Epigenetics in Cancer; Jun 19-22, 2013; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2013;73(13 Suppl):Abstract nr B39.

Abstract LB-112: Increase in glutaminase (GLS1) levels through SLUG-induced repression of hsa-miR-23a in triple negative breast cancer cells

Aggressive breast cancers of the triple negative type (TNBC) are often characterized by their high rate of proliferation and dissemination to other organs. One hallmark of this type of cancer cells is their adaptation to rely upon an altered metabolic scheme that includes changes in the glycolytic pathway, known as the Warburg effect, and elevated glutamine metabolism. Glutamine is taken up in a high rate by the proliferating cells and metabolized to provide a major source of energy and nitrogen for biosynthesis of nucleic acids. It is also used as a carbon substrate for anabolic processes in the cancer cells but the regulation of glutamine metabolism in the TNBC cells is not studied in details. Glutamine metabolism is thus implicated as a viable target for anticancer chemotherapy. Here we report that the transcriptional repressor protein SLUG, which is highly expressed in the most of the subtypes of the TNBC cells, indirectly up regulates the level of the glutaminase GLS1 through the repression of hsa-miR-23a gene. Knockdown of SLUG in the SLUG-high TNBC cells increases the hsa-miR-23a levels with subsequent decrease in the GLS1 levels. SLUG binds to the E2-box sequences at the hsa-miR-23a gene promoter and heterochromatinizes the promoter DNA through chromatin remodeling. A specific double-stranded DNA decoy against SLUG also alleviates the SLUG repression of the hsa-miR-23a gene promoter and thus decreases the glutaminase levels in the TNBC cells inhibiting the tumor cell growth. We postulate that maintenance of normal levels of GLS1 in the TNBC cells through the inhibition of the functions of SLUG will control aggressiveness and multiplication of breast tumors. Supported in parts by the DOD-CDMRP grants BC050641, BC086542 and BC103645 to GC.

Citation Format: Mukul K. Mittal, Gautam Chaudhuri. Increase in glutaminase (GLS1) levels through SLUG-induced repression of hsa-miR-23a in triple negative breast cancer cells. [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 LB-112. doi:10.1158/1538-7445.AM2013-LB-112

Mitochondrial-associated nitric oxide synthase activity inhibits cytochrome c oxidase: implications for breast cancer

Nitric oxide (NO) is produced and nitric oxide synthase (NOS) activity is expressed in many types of tumor cells, but their precise role in tumor proliferation has not been clearly elucidated. Recently, it has been observed that patients with triple-negative breast tumors expressing NOS have a significantly worse prognosis compared to those that do not express any NOS. We observed that NOS activity was associated with the mitochondria in two breast cancer cell lines, ZR-75-30 and BT-474, compared with another NO-producing benign breast epithelial cell line, MCF-12F, in which no significant mitochondrial-associated NOS activity was detected. The rate of proliferation of the malignant cells expressing mitochondrial-associated NOS was decreased in the presence of an inhibitor of NO synthesis, but it had no effect on the normal breast epithelial cells, MCF-12F, which also expressed NOS, but not associated with mitochondria. The basal rate of proliferation was not affected by ODQ, an inhibitor of soluble guanylate cyclase, indicating that the effects of the endogenous NO produced by the malignant cell lines on proliferation are cGMP independent. Our results indicate that mitochondrial-associated NOS activity exhibited by the cancer cell lines ZR-75-30 and BT-474 inhibited cytochrome c oxidase, resulting in increased production of hydrogen peroxide (H2O2), which inhibited protein phosphatase 2A activity. This resulted in the maintenance of Akt and ERK1/2 in a phosphorylated state, leading to cell proliferation.

Down-regulation of vitamin D receptor in mammospheres: implications for vitamin D resistance in breast cancer and potential for combination therapy

Vitamin D signaling in mammary cancer stem cells (MCSCs), which are implicated in the initiation and progression of breast cancer, is poorly understood. In this study, we examined vitamin D signaling in mammospheres which are enriched in MCSCs from established breast cancer cell lines. Breast cancer cells positive for aldehyde dehydrogenase (ALDH(+)) had increased ability to form mammospheres compared to ALDH(-) cells. These mammospheres expressed MCSC-specific markers and generated transplantable xenografts in nude mice. Vitamin D receptor (VDR) was significantly down-regulated in mammospheres, as well as in ALDH(+) breast cancer cells. TN aggressive human breast tumors as well as transplantable xenografts obtained from SKBR3 expressed significantly lower levels of VDR but higher levels of CD44 expression. Snail was up-regulated in mammospheres isolated from breast cancer cells. Inhibition of VDR expression by siRNA led to a significant change in key EMT-specific transcription factors and increased the ability of these cells to form mammospheres. On the other hand, over-expression of VDR led to a down-regulation of Snail but increased expression of E-cad and significantly compromised the ability of cells to form mammospheres. Mammospheres were relatively insensitive to treatment with 1,25-dihydroxyvitamin D (1,25D), the active form of vitamin D, compared to more differentiated cancer cells grown in presence of serum. Treatment of H-Ras transformed HMLE(HRas) cells with DETA NONOate, a nitric oxide (NO)-donor led to induction of MAP-kinase phosphatase -1 (MKP-1) and dephosphorylation of ERK1/2 in the mammospheres. Combined treatment of these cells with 1,25D and a low-concentration of DETA NONOate led to a significant decrease in the overall size of mammospheres and reduced tumor volume in nude mice. Our findings therefore, suggest that combination therapy using 1,25D with drugs specifically targeting key survival pathways in MCSCs warrant testing in prospective clinical trial for treatment of aggressive breast cancer.

Maintenance of higher H₂O₂ levels, and its mechanism of action to induce growth in breast cancer cells: important roles of bioactive catalase and PP2A

We assessed the catalase bioactivity and hydrogen peroxide (H₂O₂) production rate in human breast cancer (HBC) cell lines and compared these with normal human breast epithelial (HBE) cells. We observed that the bioactivity of catalase was decreased in HBC cells when compared with HBE cells. This was also accompanied by an increase in H₂O₂ steady-state levels in HBC cells. Silencing the catalase gene led to a further increase in the steady-state level of H₂O₂ which was also accompanied by an increase in growth rate of HBC cells. Catalase activity was up regulated on treatment with superoxide (O₂⁻) scavengers such as pegylated SOD (PEG-SOD, indicating inhibition of catalase by the increased O₂⁻ produced by HBC cells. Transfection of either catalase or glutathione peroxidase to HBC cells decreased intracellular H₂O₂ levels and led to apoptosis of these cells. The H₂O₂ produced by HBC cells inhibited PP2A activity accompanied by increased phosphorylation of Akt and ERK1/2. The importance of catalase bioactivity in breast cancer was further confirmed as its bioactivity was also decreased in human breast cancer tissues when compared to normal breast tissues. We conclude that inhibition of catalase bioactivity by O₂⁻ leads to an increase in steady-state levels of H₂O₂ in HBC cells, which in turn inhibits PP2A activity, leading to phosphorylation of ERK 1/2 and Akt and resulting in HBC cell proliferation.

Abstract 1287: High mobility of triple-negative breast cancer cells is due to repression of plakoglobin gene by SLUG

One of highly pathogenic breast cancer cell types are the SLUG-high claudin-low triple negative (negative in the expression of estrogen, progesterone and ERBB2 receptors) breast cancer (TNBC) cells. These cells are highly metastatic and have low levels of the motility regulatory catenin plakoglobin. In order to link high levels of the transcriptional repressor SLUG in the TNBC cells with low levels of plakoglobin we found that SLUG inhibits the expression of plakoglobin gene directly in these cells and thus, among other downstream effects, help disseminating these tumor cells. Overexpression of SLUG in the SLUG-deficient cancer cells significantly decreased the levels of mRNA and protein of plakoglobin. On the contrary, knockdown of SLUG in SLUG-high cancer cells elevated the levels of plakoglobin. Overexpression of SLUG in the SLUG-deficient cells elevated the invasiveness and motility of these cells. On the other hand, knockdown of plakoglobin in these low motility non-invasive breast cancer cells did not affect the ability of the cancer cells to penetrate Matrigel matrix but increase the growth and migration rates of these cells. This study thus implicates high levels of SLUG and low levels of plakoglobin as determinants in the progression of highly disseminating breast cancer. Supported in parts by the DOD-CDMRP grants BC050641, BC086542 and BC103645 to GC.

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 1287. doi:1538-7445.AM2012-1287

Abstract 286: Development and evaluation of a molecular decoy against SLUG function in the breast cancer cells

SLUG, also known as SNAI2, is a member of the SNAI superfamily of zinc-finger transcriptional repressors. It is a C2H2-type zinc finger transcription factor that binds to E2-box motif (5′-CAGGTG-3′/5′-CACCTG-3′), and silences gene expression by chromatin remodeling. More than ninety genes are shown to bind tightly to SLUG as was revealed by ChIP-on-chip analysis, showing the large regulatory network involving SLUG. It is recently implicated as the major mediator of the master transcriptional regulator protein TWIST. SLUG represses several genes to directly contribute towards the metastatic transformation of several epithelial cancer cells. Specific inhibitor against SLUG is not known. We describe here the development and evaluation of a nuclease resistant double-stranded DNA decoy that specifically inhibit the repressor activity of SLUG in the human breast cancer cells. The decoy is designed from the VDR gene promoter which is repressed by SLUG. This decoy has two SLUG-binding E2-box sequences. EMSA analysis showed in vitro binding of SLUG to the wild-type decoy but not to the E2-box mutated decoy. In vitro pull down analysis also showed high affinity binding of SLUG to the decoy. Biotin-tagged wild-type decoy DNA could immunopull down SLUG but little SNAIL from the extracts from decoy-transfected cells. The decoy increased the mRNA and protein levels of several SLUG target genes in MDA-MB-231 cells. The decoy also alleviated the repressive activity of SLUG on the SLUG target gene promoters in MDA-MB-231 cells. Since SLUG overexpression is implicated in the drug-resistance and antiapoptosis development in breast cancer cells, the SLUG decoy we developed should be useful to combat breast cancer progression when used with classical anticancer drugs. Supported in parts by the DOD-CDMRP grants BC050641, BC086542 and BC103645 to GC.

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 286. doi:1538-7445.AM2012-286

Abstract 2114: Trypanosoma brucei: A model to evaluate joint contribution of BRCA2 and PARP in DNA damage repair

The DNA repair protein BRCA2, initially discovered as a tumor suppressor for familial breast cancer cases, is now found to play critical role in the biology of many eukaryotes. The extracellular protozoan parasite Trypanosoma brucei significantly relies on its BRCA2 protein for stress management as well as surviving from host humoral immunity during its mammalian stage of its complex digenetic life cycle. An interesting aspect of BRCA2 deficiency in cancer cells is that these cells are ultra-sensitive to the inhibitors of the chromatin modifying enzyme poly(ADP-ribose) polymerase (PARP). In the absence of PARP, spontaneous single-strand breaks collapse replication forks and trigger homologous recombination for repair. Thus, PARP activity is essential in homologous recombination-deficient BRCA2-mutant cancer cells. BRCA2 and PARP are not only expressed in the mammalian cells but also present in high levels in many other eukaryotic cells including the parasitic protozoan T. brucei. To evaluate the universality of the importance of these two proteins in the management of DNA damage, we determined the effect of PARP inhibitors such as 3-AB, Veliparib, PF-01367338, Olaparib and Iniparib in BRCA2 knocked down T. brucei cells treated with the DNA damaging agent cisplatin. Our in vitro data strongly suggest that a combination of a BRCA2 inhibitor (e.g. BRCA2 BRC peptide), a PARP inhibitor and a DNA damaging agent (e.g. cisplatin) will be a chemical regimen for the management of trypanosomiasis and similar protozoan infections. Supported by NIH grants 2SC1GM081146-05 to MC, 1U54RR026140-01 to SM and NIH grants R01AI042327, R21AI076757 to GC.

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 2114. doi:1538-7445.AM2012-2114

High motility of triple-negative breast cancer cells is due to repression of plakoglobin gene by metastasis modulator protein SLUG

One of highly pathogenic breast cancer cell types are the triple negative (negative in the expression of estrogen, progesterone, and ERBB2 receptors) breast cancer cells. These cells are highly motile and metastatic and are characterized by high levels of the metastasis regulator protein SLUG. Using isogenic breast cancer cell systems we have shown here that high motility of these cells is directly correlated with the levels of the SLUG in these cells. Because epithelial/mesenchymal cell motility is known to be negatively regulated by the catenin protein plakoglobin, we postulated that the transcriptional repressor protein SLUG increases the motility of the aggressive breast cancer cells through the knockdown of the transcription of the plakoglobin gene. We found that SLUG inhibits the expression of plakoglobin gene directly in these cells. Overexpression of SLUG in the SLUG-deficient cancer cells significantly decreased the levels of mRNA and protein of plakoglobin. On the contrary, knockdown of SLUG in SLUG-high cancer cells elevated the levels of plakoglobin. Blocking of SLUG function with a double-stranded DNA decoy that competes with the E2-box binding of SLUG also increased the levels of plakoglobin mRNA, protein, and promoter activity in the SLUG-high triple negative breast cancer cells. Overexpression of SLUG in the SLUG-deficient cells elevated the motility of these cells. Knockdown of plakoglobin in these low motility non-invasive breast cancer cells rearranged the actin filaments and increased the motility of these cells. Forced expression of plakoglobin in SLUG-high cells had the reverse effects on cellular motility. This study thus implicates SLUG-induced repression of plakoglobin as a motility determinant in highly disseminating breast cancer.

Protein phosphatase 2A promotes endothelial survival via stabilization of translational inhibitor 4E-BP1 following exposure to tumor necrosis factor-α

OBJECTIVE

Tumor necrosis factor-α (TNFα) may change from a stimulator of reversible activation of endothelial cells (ECs) to a killer when combined with cycloheximide (CHX). The means by which endothelial cells are destined to either the survival pathway or the apoptotic pathway are not fully understood. We investigated the role of p38 mitogen-activated protein kinase (MAPK) and protein phosphatase 2A (PP2A) activation and their regulation of 4E-BP1 stability in ECs to determine whether this pathway contributes to apoptosis induced by TNFα and CHX.

METHODS AND RESULTS

Apoptosis was induced in human umbilical vein ECs (HUVECs) by treating them with a combination of TNFα and CHX (TNFα/CHX). Activation of p38 MAPK was increased in HUVECs undergoing apoptosis, which was associated with degradation of eukaryotic initiation factor 4A regulator 4E-BP1 in a p38 MAPK-dependent manner. CHX attenuated a TNFα-stimulated increase in the expression and activity of PP2A. Silencing PP2A expression with small interfering RNA transfection mimicked CHX sensitization, increasing HUVEC apoptosis with TNFα stimulation and suggesting a protective role for PP2A in the apoptotic process.

CONCLUSION

Our data suggest that (1) TNFα stimulates PP2A and HUVECs elude apoptosis by PP2A-dependent dephosphorylation of p38 MAPK, and (2) CHX-induced inhibition of PP2A leads to maintenance of p38 activity and degradation of 4E-BP1, resulting in enhanced TNFα-induced apoptosis.

Abstract B36: Development of calcitrol-resistance in triple-negative breast cancer cells through SLUG-mediated coordinate repression of CYP2R1, CYP27B1, and VDR gene promoters

Metastatic breast and other cancers are often found to be refractory to vitamin D therapy. Vitamin D is synthesized from 7-dehydrocholesterol, an intermediate metaboltie in cholesterol synthesis. Ultraviolet irradiation in sunlight-exposed skin induces a photochemical reaction of 7–25-position by vitamin D 25-hydroxylase (CYP2R1), to yield 25-hydroxyvitamin D3 (cholecalciferol). Vitamin D3 is hydroxylated at the 25-position by vitamin D 25-hydroxylase (CYP2R1), to yield 25-hydroxyvitamin D3 (25(OH)D3; 25-hydroxycholecalciferol), the major form of vitamin D in the circulation. 25(OH)D3 is further hydroxylated at the 1 -position by the 25-hydroxyvitamin D 1 -hydroxylase (CYP27B1) to produce calcitrol (VD3). VD3 exhibits physiological and pharmacological effects by binding to the vitamin D receptor (VDR), a transcription factor of the nuclear receptor superfamily. Although photoactivated cholecalciferol is mainly hydroxylated in the liver and kidney, many other cells including breast cells have significant expressions of CYP2R1, CYP27B1 and VDR. Breast cells thus should be able to activate and utilize cholecalciferol if these proteins are not suppressed. We report here that the metastasis modulator protein SLUG, which is often overexpressed in metastatic triple negative breast cancer cells, coordinately repressse the levels of CYP2R1, CYP27B1 and VDR proteins in the breast cancer cells to induce vitamin D-resistance in these cells. SLUG inhibited CYP2R1, CYP27B1 and VDR gene promoter activities in these cells. ChIP assays revealed that SLUG is recruited at the CYP2R1, CYP27B1 and VDR gene promoters. Knockdown of SLUG in highly invasive MDA-MB-231 and BT549 cells increased their CYP2R1, CYP27B1 and VDR gene expression and decreased their resistance their resistance to VD3 in vitro. Our data established that SLUG regulates vitamin D metabolism and contributes to the induction of VD3-resistance in human breast cancer cells through the inhibition of CYP2R1, CYP27B1 and VDR gene promoters epigenetically through chromatin remodeling.

Supported in parts by the DOD-CDMRP grants BC050641 and BC103645.

Citation Information: Cancer Epidemiol Biomarkers Prev 2011;20(10 Suppl):B36.

Abstract B34: Increase in EGFR level through SLUG-induced repression of dynactin 5 in triple-negative breast cancer cells

Aggressive breast cancers of the triple negative type (TNBCs) are often characterized with higher levels of receptor tyrosine kinases (RTKs; e.g. EGFR) and G-protein coupled receptors (GPCRs; e.g. PAR1). These receptors are activated by their agonists, induce signal transduction and then are attenuated by signal uncoupling and retrograde recycling endosome transport. We report here that the levels of several of these receptor proteins are elevated and hyperactivated on the surface of aggressive breast cancer cells that have high levels of the transcriptional repressor protein SLUG. Chip-on-chip analysis to identify genes that are repressed by SLUG in the breast cancer cells revealed one of the proteins that are critical for the retrograde recycling transport of the RTKs and GPCRs, namely dynactin 5 (DCTN5). DCTN5 (aka p25) is a member of the dynactin complex. DCTN5 is a subunit of the pointed-end subcomplex of dynactin that is thought to interact with membranous cargo. Interestingly, DCTN5 is expressed from the reverse activity of the bidirectional promoter of human PALB2 (partner and localizer of BRCA2) gene whose product regulates the functions of the tumor suppressor protein BRCA2. We found that SLUG inhibits both PALB2 and DCTN5 gene expression through chromatin remodeling in human breast cancer cells. We hypothesize that the malignant breast cancer cells acquire highly aggressive and metastatic characteristics in part due to the higher levels and hyperactivation of EGFR on their surface. The hyperactivity of EGFR occurs through the SLUG-mediated repression of DCTN5 which mediates the internalization and thus, degradation of activated receptors. We evaluated the role of DCTN5 in the determination of aggressiveness in TNBC cells. We postulate that maintenance of normal levels DCTN5 in the TNBC cells through the inhibition of the functions of SLUG will control the invasive growth of the breast tumors. Supported in parts by the DOD-CDMRP grants BC050641, BC086542 and BC103645.

Citation Information: Cancer Epidemiol Biomarkers Prev 2011;20(10 Suppl):B34.

Abstract B35: SLUG-induced plakoglobin gene repression in triplenegative breast cancer cells

Breast cancer with the triple-negative phenotype (TNBC) are ER-negative, PR-negative and ERBB2 (HER2)-negative and represent one of the most aggressive and difficult to treat subtypes of human breast cancer. TNBC is highly over-represented in African American breast cancer patients and determining the genetic and molecular basis for this incidence and the biological basis for the aggressiveness of TNBCs are largely unknown and of high priority. The transcription factor SLUG, which controls epithelial to mesenchymal transition, stem cell phenotypes and therapeutic responsiveness, is highly expressed in the basal-type TNBC cells, making it a candidate master regulator of the TNBC phenotype. Plakoglobin, also known as γ-catenin or JUP, is a member of the armadillo motifcontaining proteins. This protein is a critical component of the desmosomal structure conferring structural integrity and resistance from mechanical stress to epithelial cells in tissues. We report here that SLUG inhibits the expression of several desmosomal proteins including the plakoglobin gene directly and thus, among other downstream effects, help disseminating the TNBC cells. Overexpression of SLUG in the SLUG-deficient cancer cells significantly decreased the levels of mRNA and protein of plakoglobin. On the contrary, knockdown of SLUG in SLUG-high TNBC cells elevated the levels of plakoglobin. Inhibition of SLUG activity with a molecular decoy in the TNBC cells abrogated the inhibitory effect of SLUG on plakoglobin gene expression. Although overexpression of SLUG in the SLUG-deficient cells elevated the invasiveness and motility of these cells, knockdown of plakoglobin only affected the growth and migration rates of these cells. This study thus implicates high levels of SLUG and low levels of plakoglobin as determinants in the progression of highly disseminating breast cancer of the TNBC type.

Supported by the DOD-CDMRP BCRP Grants W81XWH-06-1-0466, W81XWH-08-1-0446, BC086542, and the Susan G. Komen Breast Cancer Foundation grant# BCTR0707627 to GC.

Citation Information: Cancer Epidemiol Biomarkers Prev 2011;20(10 Suppl):B35.

Reduced association of anti-apoptotic protein Mcl-1 with E3 ligase Mule increases the stability of Mcl-1 in breast cancer cells

Background:

Mechanisms that increase resistance to apoptosis help promote cellular transformation. Cancer cells have deregulated apoptotic pathways, where increased expression and stability of anti-apoptotic proteins Mcl-1 and Bcl-2 increases resistance to apoptosis. Pathways that increase the stability of proteins in cancer cells remain poorly understood.

Methods:

Using human mammary epithelial and established breast cancer cell lines, we assessed the mechanisms that increase the stability of anti-apoptotic proteins in breast cancer cells by caspase assay, western blot, small-inhibitory RNA treatment and immunoprecipitation.

Results:

While breast cancer cells were resistant to de novo inhibition of protein synthesis, a rapid proteosome-mediated degradation of Mcl-1 and Bcl-2 induced apoptosis in mammary epithelial cells. Although Mule, an E3 ligase that targets Mcl-1 for degradation was expressed in mammary epithelial and breast cancer cell lines, rapid increase of polyubiquitinated Mcl-1 and Bcl-2 was detected only in mammary epithelial cells. Only transient formation of the Mule–Mcl-1 complex was detected in breast cancer cells. Downregulation of pERK1/2 in breast cancer cells reduced Mcl-1 levels and increased Mcl-1/Mule complex.

Conclusion:

Our findings suggest that reduced Mule/Mcl-1 complex has a significant role in increasing the stability of Mcl-1 in breast cancer cells and increased resistance to apoptosis.

Chronic estradiol exposure in oophorectomized mice induces a systemic inflammatory disorder that is mediated via TNFα. (54.9)

Estradiol (E2) administration to oophorectomized (Ovx) mice has been shown to induce the expression of IL-1β, IL-6 and TNFα and inducible NO synthase mRNA in macrophages. Here, we investigated the effect of chronic E2 supplementation on immune responses and cytokines. We found that long-term E2 exposure in Ovx mice led to a marked increase in granulocytes in the liver and spleen. Although, E2 exposed Ovx mice had reduced total cellularity of thymus and spleen and reduced CD4+ and CD8+ T cells in the spleen, more splenic T cells from these mice produced IFN-γ and IL-17 as compared to sham-operated and placebo-treated Ovx mice. IFN-γ and IL-17 were also abundantly made by T, NK and NKT cells in the liver of E2-exposed Ovx mice compared to animals in the other two groups. Intriguingly, E2 exposure in Ovx mice led to significant weight loss as compared to sham-operated mice and placebo-treated Ovx mice. Strikingly, the pro-inflammatory cytokine (IFN-γ and IL-17) response, granulocyte accumulation in liver, and weight loss elicited by chronic E2 exposure in Ovx mice were largely abolished by TNFα deficiency. Finally, 54% of chronically E2-exposed Ovx wild-type B6 mice, as compared to none of sham and placebo-Ovx wild-type mice and none of E2-exposed Ovx TNFα-/- mice, died during the study period. Thus, chronic E2 exposure in Ovx mice elicits an inflammatory condition that is mediated, at least in part, by TNFα.