RNA m6A reader YTHDF2 facilitates precursor miR-126 maturation to promote acute myeloid leukemia progression

As the most common internal modification of mRNA, N6-methyladenosine (m6A) and its regulators modulate gene expression and play critical roles in various biological and pathological processes including tumorigenesis. It was reported previously that m6A methyltransferase (writer), methyltransferase-like 3 (METTL3) adds m6A in primary microRNAs (pri-miRNAs) and facilitates its processing into precursor miRNAs (pre-miRNAs). However, it is unknown whether m6A modification also plays a role in the maturation process of pre-miRNAs and (if so) whether such a function contributes to tumorigenesis. Here, we found that YTHDF2 is aberrantly overexpressed in acute myeloid leukemia (AML) patients, especially in relapsed patients, and plays an oncogenic role in AML. Moreover, YTHDF2 promotes expression of miR-126-3p (also known as miR-126, as it is the main product of precursor miR-126 (pre-miR-126)), a miRNA that was reported as an oncomiRNA in AML, through facilitating the processing of pre-miR-126 into mature miR-126. Mechanistically, YTHDF2 recognizes m6A modification in pre-miR-126 and recruits AGO2, a regulator of pre-miRNA processing, to promote the maturation of pre-miR-126. YTHDF2 positively and negatively correlates with miR-126 and miR-126's downstream target genes, respectively, in AML patients, and forced expression of miR-126 could largely rescue YTHDF2/Ythdf2 depletion-mediated suppression on AML cell growth/proliferation and leukemogenesis, indicating that miR-126 is a functionally important target of YTHDF2 in AML. Overall, our studies not only reveal a previously unappreciated YTHDF2/miR-126 axis in AML and highlight the therapeutic potential of targeting this axis for AML treatment, but also suggest that m6A plays a role in pre-miRNA processing that contributes to tumorigenesis.

MYC acetylated lysine residues drive oncogenic cell transformation and regulate select genetic programs for cell adhesion-independent growth and survival

The MYC oncogenic transcription factor is acetylated by the p300 and GCN5 histone acetyltransferases. The significance of MYC acetylation and the functions of specific acetylated lysine (AcK) residues have remained unclear. Here, we show that the major p300-acetylated K148(149) and K157(158) sites in human (or mouse) MYC and the main GCN5-acetylated K323 residue are reversibly acetylated in various malignant and nonmalignant cells. Oncogenic overexpression of MYC enhances its acetylation and alters the regulation of site-specific acetylation by proteasome and deacetylase inhibitors. Acetylation of MYC at different K residues differentially affects its stability in a cell type-dependent manner. Lysine-to-arginine substitutions indicate that although none of the AcK residues is required for MYC stimulation of adherent cell proliferation, individual AcK sites have gene-specific functions controlling select MYC-regulated processes in cell adhesion, contact inhibition, apoptosis, and/or metabolism and are required for the malignant cell transformation activity of MYC. Each AcK site is required for anchorage-independent growth of MYC-overexpressing cells in vitro, and both the AcK148(149) and AcK157(158) residues are also important for the tumorigenic activity of MYC transformed cells in vivo. The MYC AcK site-specific signaling pathways identified may offer new avenues for selective therapeutic targeting of MYC oncogenic activities.

SRC2 controls CD4+ T cell activation via stimulating c-Myc-mediated upregulation of amino acid transporter Slc7a5

T cell activation stimulates substantially increased protein synthesis activity to accumulate sufficient biomass for cell proliferation. The protein synthesis is fueled by the amino acids transported from the environment. Steroid nuclear receptor coactivator 2 (SRC2) is a member of a family of transcription coactivators. Here, we show that SRC2 recruited by c-Myc enhances CD4+ T cell activation to stimulate immune responses via upregulation of amino acid transporter Slc7a5. Mice deficient of SRC2 in T cells (SRC2fl/fl/CD4Cre) are resistant to the induction of experimental autoimmune encephalomyelitis (EAE) and susceptible to Citrobacter rodentium (C. rodentium) infection. Adoptive transfer of naive CD4+ T cells from SRC2fl/fl/CD4Cre mice fails to elicit EAE and colitis in Rag1/ recipients. Further, CD4+ T cells from SRC2fl/fl/CD4Cre mice display defective T cell proliferation, cytokine production, and differentiation both in vitro and in vivo. Mechanically, SRC2 functions as a coactivator to work together with c-Myc to stimulate the expression of amino acid transporter Slc7a5 required for T cell activation. Slc7a5 fails to be up-regulated in CD4+ T cells from SRC2fl/fl/CD4Cre mice, and forced expression of Slc7a5 rescues proliferation, cytokine production, and the ability of SRC2fl/fl/CD4Cre CD4+ T cells to induce EAE. Therefore, SRC2 is essential for CD4+ T cell activation and, thus, a potential drug target for controlling CD4+ T cell-mediated autoimmunity.

Fatty acid oxidation protects cancer cells from apoptosis by increasing mitochondrial membrane lipids

Overcoming resistance to chemotherapies remains a major unmet need for cancers, such as triple-negative breast cancer (TNBC). Therefore, mechanistic studies to provide insight for drug development are urgently needed to overcome TNBC therapy resistance. Recently, an important role of fatty acid β-oxidation (FAO) in chemoresistance has been shown. But how FAO might mitigate tumor cell apoptosis by chemotherapy is unclear. Here, we show that elevated FAO activates STAT3 by acetylation via elevated acetyl-coenzyme A (CoA). Acetylated STAT3 upregulates expression of long-chain acyl-CoA synthetase 4 (ACSL4), resulting in increased phospholipid synthesis. Elevating phospholipids in mitochondrial membranes leads to heightened mitochondrial integrity, which in turn overcomes chemotherapy-induced tumor cell apoptosis. Conversely, in both cultured tumor cells and xenograft tumors, enhanced cancer cell apoptosis by inhibiting ASCL4 or specifically targeting acetylated-STAT3 is associated with a reduction in phospholipids within mitochondrial membranes. This study demonstrates a critical mechanism underlying tumor cell chemoresistance.

Epigenetic Dysregulation of KCNK9 Imprinting and Triple-Negative Breast Cancer

Simple Summary

Genomic imprinting is an inherited form of parent-of-origin specific epigenetic gene regulation that is dysregulated by poor prenatal nutrition and environmental toxins. Here, we showed that KCNK9 is imprinted in breast tissue and identified the differentially methylated region (DMR) controlling its imprint status. Hypomethylation at the DMR, coupled with biallelic expression of KCNK9, occurred in 63% of triple-negative breast cancers (TNBC). The association between hypomethylation and TNBC status was highly significant in African-Americans (p = 0.006), but not in Caucasians (p = 0.70). The high frequency of KCNK9 DMR hypomethylation in TNBC and non-cancerous breast tissue from high-risk women provides evidence that hypomethylation of the KNCK9 DMR/TASK3 overexpression may provide a new target for prevention of TNBC.

Abstract

Genomic imprinting is an inherited form of parent-of-origin specific epigenetic gene regulation that is dysregulated by poor prenatal nutrition and environmental toxins. KCNK9 encodes for TASK3, a pH-regulated potassium channel membrane protein that is overexpressed in 40% of breast cancer. However, KCNK9 gene amplification accounts for increased expression in <10% of these breast cancers. Here, we showed that KCNK9 is imprinted in breast tissue and identified a differentially methylated region (DMR) controlling its imprint status. Hypomethylation at the DMR, coupled with biallelic expression of KCNK9, occurred in 63% of triple-negative breast cancers (TNBC). The association between hypomethylation and TNBC status was highly significant in African-Americans (p = 0.006), but not in Caucasians (p = 0.70). KCNK9 hypomethylation was also found in non-cancerous tissue from 77% of women at high-risk of developing breast cancer. Functional studies demonstrated that the KCNK9 gene product, TASK3, regulates mitochondrial membrane potential and apoptosis-sensitivity. In TNBC cells and non-cancerous mammary epithelial cells from high-risk women, hypomethylation of the KCNK9 DMR predicts for increased TASK3 expression and mitochondrial membrane potential (p < 0.001). This is the first identification of the KCNK9 DMR in mammary epithelial cells and demonstration that its hypomethylation in breast cancer is associated with increases in both mitochondrial membrane potential and apoptosis resistance. The high frequency of hypomethylation of the KCNK9 DMR in TNBC and non-cancerous breast tissue from high-risk women provides evidence that hypomethylation of the KNCK9 DMR/TASK3 overexpression may serve as a marker of risk and a target for prevention of TNBC, particularly in African American women.

R-2-hydroxyglutarate attenuates aerobic glycolysis in leukemia by targeting the FTO/m6A/PFKP/LDHB axis

R-2-hydroxyglutarate (R-2HG), a metabolite produced by mutant isocitrate dehydrogenases (IDHs), was recently reported to exhibit anti-tumor activity. However, its effect on cancer metabolism remains largely elusive. Here we show that R-2HG effectively attenuates aerobic glycolysis, a hallmark of cancer metabolism, in (R-2HG-sensitive) leukemia cells. Mechanistically, R-2HG abrogates fat-mass- and obesity-associated protein (FTO)/N6-methyladenosine (m6A)/YTH N6-methyladenosine RNA binding protein 2 (YTHDF2)-mediated post-transcriptional upregulation of phosphofructokinase platelet (PFKP) and lactate dehydrogenase B (LDHB) (two critical glycolytic genes) expression and thereby suppresses aerobic glycolysis. Knockdown of FTO, PFKP, or LDHB recapitulates R-2HG-induced glycolytic inhibition in (R-2HG-sensitive) leukemia cells, but not in normal CD34+ hematopoietic stem/progenitor cells, and inhibits leukemogenesis in vivo; conversely, their overexpression reverses R-2HG-induced effects. R-2HG also suppresses glycolysis and downregulates FTO/PFKP/LDHB expression in human primary IDH-wild-type acute myeloid leukemia (AML) cells, demonstrating the clinical relevance. Collectively, our study reveals previously unrecognized effects of R-2HG and RNA modification on aerobic glycolysis in leukemia, highlighting the therapeutic potential of targeting cancer epitranscriptomics and metabolism.

Cancer Chemoprevention Using Nanotechnology-Based Approaches

Cancer research in pursuit of better diagnostic and treatment modalities has seen great advances in recent years. However, the incidence rate of cancer is still very high. Almost 40% of women and men are diagnosed with cancer during their lifetime. Such high incidence has not only resulted in high mortality but also severely compromised patient lifestyles, and added a great socioeconomic burden. In view of this, chemoprevention has gained wide attention as a method to reduce cancer incidence and its relapse after treatment. Among various stems of chemoprevention research, nanotechnology-based chemoprevention approaches have established their potential to offer better efficacy and safety. This review summarizes recent advances in nanotechnology-based chemoprevention strategies for various cancers with emphasis on lung and bronchial cancer, colorectal, pancreatic, and breast cancer and highlights the unmet needs in this developing field towards successful clinical translation.

Peroxisome proliferator-activated receptor gamma controls prostate cancer cell growth through AR-dependent and independent mechanisms

BACKGROUND

Prostate cancer (PC) remains a leading cause of cancer mortality and the most successful chemopreventative and treatment strategies for PC come from targeting the androgen receptor (AR). Although AR plays a key role, it is likely that other molecular pathways also contribute to PC, making it essential to identify and develop drugs against novel targets. Recent studies have identified peroxisome proliferator-activated receptor gamma (PPARγ), a nuclear receptor that regulates fatty acid (FA) metabolism, as a novel target in PC, and suggest that inhibitors of PPARγ could be used to treat existing disease. We hypothesized that PPARγ acts through AR-dependent and independent mechanisms to control PC development and growth and that PPARγ inhibition is a viable PC treatment strategy.

METHODS

Immunohistochemistry was used to determine expression of PPARү in a cohort of patients with PC. Standard molecular techniques were used to investigate the PPARү signaling in PC cells as well a xenograft mouse model to test PPARү inhibition in vivo. Kaplan-Meier curves were created using cBioportal.

RESULTS

We confirmed the expression of PPARү in human PC. We then showed that small molecule inhibition of PPARγ decreases the growth of AR-positive and -negative PC cells in vitro and that T0070907, a potent PPARγ antagonist, significantly decreased the growth of human PC xenografts in nude mice. We found that PPARγ antagonists or small interfering RNA (siRNA) do not affect mitochondrial activity nor do they cause apoptosis; instead, they arrest the cell cycle. In AR-positive PC cells, antagonists and siRNAs reduce AR transcript and protein levels, which could contribute to growth inhibition. AR-independent effects on growth appear to be mediated by effects on FA metabolism as the specific FASN inhibitor, Fasnall, inhibited PC cell growth but did not have an additive effect when combined with PPARγ antagonists. Patients with increased PPARү target gene expression, but not alterations in PPARү itself, were found to have significantly worse overall survival.

CONCLUSIONS

Having elucidated the direct cancer cell effects of PPARγ inhibition, our studies have helped to determine the role of PPARγ in PC growth, and support the hypothesis that PPARγ inhibition is an effective strategy for PC treatment.

Loratadine self-microemulsifying drug delivery systems (SMEDDS) in combination with sulforaphane for the synergistic chemoprevention of pancreatic cancer

Pancreatic cancer (PC), currently the third leading cause of cancer-related deaths in the USA, is projected to become the second leading cause, behind lung cancer, by 2020. The increasing incidence, low survival rate, and limited treatment opportunities necessitate the use of alternative approaches such as chemoprevention, to tackle PC. In this study, we report significant synergistic chemoprevention efficacy for the first time from a low-dose combination of a classical antihistaminic drug, Loratadine (LOR) and a neutraceutical compound, Sulforaphane (SFN) using a self-microemulsifying drug delivery system (SMEDDS) formulation. The formulation was developed using Quality by Design approach (globule size, 95.13 ± 7.9 nm; PDI, 0.17 ± 0.04) and revealed significant (p < 0.05) enhancement in the in vitro dissolution profile confirming the enhanced solubility of BCS class II drug LOR with SMEDDS formulation. The LOR-SFN combination revealed ~ 40-fold reduction in IC50 concentration compared to LOR alone in MIA PaCa-2 and Panc-1 cell lines respectively, confirming the synergistic enhancement in chemoprevention. Further, the nanoformulation resulted in ~ 7-fold and ~ 11-fold reduction in IC50 values compared to LOR-SFN combination. Hence, our studies successfully demonstrate that a unique low-dose combination of LOR encapsulated within SMEDDs with SFN shows significantly enhanced chemopreventive efficacy of PC.

The KRAS-variant and its impact on normal breast epithelial cell biology

MicroRNA (miRNA)-binding site variants in 3' untranslated regions (3'UTRs) are a novel class of germ-line, functional mutations, which are now recognized as powerful biomarkers of human cancer risk and biology. The first mutation discovered in this class is the KRAS-variant, a let-7-binding site mutation in the 3'UTR of the KRAS oncogene. The KRAS-variant predicts increased cancer risk for certain populations, is a predictive biomarker of cancer treatment response across cancer types, leads to conserved tumor biology and elevated AKT signaling in KRAS-variant patient tumors, and was recently found to predict elevated TGF-β and immunosuppression in cancer patients. Based on the functional biology of the KRAS-variant in cancer patients, here we chose to investigate altered normal cellular biology in the presence of the KRAS-variant, through interrogation of an isogenic normal breast epithelial cell line model with and without the KRAS-variant. We find that KRAS-variant normal breast epithelial cells exhibit a mesenchymal phenotype, which appears to be due to numerous molecular changes, including miRNA dysregulation and autocrine pathway alterations, including elevated TGF-β, resulting in ZEB and SNAIL upregulation. Our findings support the hypothesis that the KRAS-variant has a fundamental biological impact on normal cellular biology, that is conserved in these patients when they develop cancer.

Pancreatic Cancer: Recent Advances in Nanoformulation-Based Therapies

Pancreatic cancer is the fourth leading cause of death in the United States and has a 5-year life expectancy of ~8%. Currently, only a few drugs have been approved by the United States Food and Drug Administration for pancreatic cancer treatment. Despite available drug therapy and ongoing clinical investigations, the high prevalence and mortality associated with pancreatic cancer mean that there is an unmet chemopreventive and therapeutic need. From ongoing studies with various novel formulations, it is evident that the development of smart drug delivery systems will improve delivery of drug cargo to the pancreatic target site to ensure and enhance the therapeutic/chemoprevention efficacy of existing drugs and newly designed drugs in the future. With this in view, nanotechnology is emerging as a promising avenue to enhance drug delivery to the pancreas via both passive and active targeting mechanisms. Research in this field has grown extensively over the past decade, as is evident from available scientific literature. This review summarizes the recent advances that have brought nanotechnology-based formulations to the forefront of pancreatic cancer treatment.

Novel nano-drug combination therapeutic regimen demonstrates significant efficacy in the transgenic mouse model of pancreatic ductal adenocarcinoma

The current work studied the chemopreventive efficacy of orally administered chitosan coated solid-lipid nanoparticle (c-SLN) encapsulated aspirin (ASP), curcumin (CUR) and free sulforaphane (SFN), ACS-cSLN, in the LSL-Kras ^G12D/+; Pdx-1 ^Cre/+ transgenic mouse model of pancreatic ductal adenocarcinoma (PDAC). In vitro uptake study and intracellular localization of ODA-FITC labeled ASP and CUR c-SLNs were performed in Panc-1 and MIA PaCa-2 cells by fluorescence microscopy. LSL-Kras ^G12D/+; Pdx-1 ^Cre/+ transgenic mice (n = 30) were randomly divided into 5 groups. Treatment groups were orally gavaged with ACS c-SLNs in three doses: low (2 + 4.5 + 0.16 mg/kg), medium (20 + 45 + 1.6 mg/kg) and high (60 + 135 + 4.8 mg/kg), respectively. After 20 weeks of treatment, mice pancreas were harvested, stained with dye and scored according to various pancreatic intraepithelial neoplasms (PanIN) categories by an independent observer. In vitro, cellular uptake evaluated on Panc-1 and MIA PaCa-2 cells resulted in higher fluorescence intensities, indicating increased cellular uptake of ASP and CUR c-SLNs. For further evidence, the addition of lysoID (red fluorescence) demonstrated location and uptake of ASP and CUR c-SLNs into the lysosome. In vivo, treatment with ACS c-SLN for 20-weeks did not cause obvious adverse effects on growth and no statistically significant differences in body weight were observed between groups. However, the weight (mean ± SEM) of pancreas at the end of the study was higher in blank c-SLN group (223.6 ± 42.2 mg) compared to low (138.0 ± 26.0 mg; not significant [NS]), medium (145.0 ± 9.0 mg; NS), and high (133.8 ± 20.3 mg; NS) ACS c-SLN treated groups, demonstrating the efficacy of ACS c-SLN nanoformulations. The low, medium and high dose of ACS c-SLN combinations exhibited a reduction in tumor incidence (PanIN count) by 16.6% (P < 0.01), 66.8% (P < 0.01), and 83.4% (P < 0.01), respectively. These studies provide further proof for the use of an oral, low dose nanotechnology-based combinatorial regimen for the chemoprevention of PDAC.

JAK/STAT3-Regulated Fatty Acid β-Oxidation Is Critical for Breast Cancer Stem Cell Self-Renewal and Chemoresistance

Cancer stem cells (CSCs) are critical for cancer progression and chemoresistance. How lipid metabolism regulates CSCs and chemoresistance remains elusive. Here, we demonstrate that JAK/STAT3 regulates lipid metabolism, which promotes breast CSCs (BCSCs) and cancer chemoresistance. Inhibiting JAK/STAT3 blocks BCSC self-renewal and expression of diverse lipid metabolic genes, including carnitine palmitoyltransferase 1B (CPT1B), which encodes the critical enzyme for fatty acid β-oxidation (FAO). Moreover, mammary-adipocyte-derived leptin upregulates STAT3-induced CPT1B expression and FAO activity in BCSCs. Human breast-cancer-derived data suggest that the STAT3-CPT1B-FAO pathway promotes cancer cell stemness and chemoresistance. Blocking FAO and/or leptin re-sensitizes them to chemotherapy and inhibits BCSCs in mouse breast tumors in vivo. We identify a critical pathway for BCSC maintenance and breast cancer chemoresistance.

PD-L1/CD80 interaction differentially regulates CD8+ T cell metabolism, survival and GVHD capacity in the presence or absence of PD-1

Purified alloreactive CD8+ T cells induce no acute GVHD, but the mechanisms remain unknown. PD-L1 interacts with PD-1 and CD80. Here we show that, sorted C57BL/6 donor CD8+ T cells (1.25 ×106) expanded in wild-type MHC-mismatched BALB/c recipients but induced no acute GVHD. In PD-L1−/− recipients, donor CD8+ T cells expanded and induced lethal acute GVHD. PD-1−/−CD8+ T cells induced lethal acute GVHD in wild-type recipients. Blockade of PD-L1/CD80 interactions on days 0 and 2 prevented expansion of wild-type and PD-1−/− CD8+ T cells in wild type recipients and prevented acute GVHD caused by PD-1−/− CD8+ T cells. On the other hand, blockade of PD-L1/CD80 interaction after CD8+ T activation on day 5 caused lethal acute GVHD in wild-type recipients that usually have no acute GVHD. Naïve CD8+ T cells express much higher levels of CD80 than PD-1, whereas activated CD8+ T cells express higher levels of PD-1 than CD80. PD-L1/CD80 interaction augmented glycolysis in naïve WT and PD-1−/− CD8+T cells. This interaction was associated with increased phosphorylation of PLC-γ and activation of the AKT/mTOR pathway in a CD28-dependent manner. This interaction increased mitochondrial numbers and volume and augmented ROS production and apoptosis at the peak of CD8+ T cell activation, such that CD8+T cells did not over-expand to cause GVHD. Conversely, blockade of PD-L1/CD80 after CD8+ T activation in the presence of high PD-1 expression led to increased mitophagy, reduced apoptosis and overexpansion of CD8+ T cells, resulting in lethal GVHD. These results indicate that PD-L1/ CD80 interaction is dependent on PD-1 expression to differentially regulate glycolysis and mitophagy as well as expansion, survival and acute GVHD capacity of alloreactive CD8+ T cells.

Elevated HMGA2 expression is associated with cancer aggressiveness and predicts poor outcome in breast cancer

High mobility group AT-hook 2 (HMGA2) is involved in a wide spectrum of biological processes and is upregulated in several tumors. Here, we collected 273 breast cancer (BC) specimens as a training set and 310 specimens as a validation set to examine the expression of HMGA2 by immunohistochemical staining. It was found that HMGA2 expression was significantly positively correlated with advanced tumor grade and poor survival. Subgroup analysis indicated that high level of HMGA2 was significantly correlated with poor prognosis, especially in the subgroups of stage II-III, low pathological grade and non-triple negative breast cancer cases. Gene set enrichment analysis (GSEA) demonstrated a significant positive correlation between HMGA2 level and the gene expression signature of metaplastic and mesenchymal phenotype. Importantly, we also observed that ectopic expression of HMGA2 promoted the migration and invasion of breast cancer cells, and protected cancer cells against genotoxic stress from agents stimulating P53 (Ser15) phosphorylation. As a conclusion, expression of HMGA2 might indicate more advanced malignancy of breast cancer. Thus we believe HMGA2 could serve as a biomarker of poor prognosis and a novel target in treating BC tumors.

A Peptide mimicking a region in proliferating cell nuclear antigen specific to key protein interactions is cytotoxic to breast cancer

Proliferating cell nuclear antigen (PCNA) is a highly conserved protein necessary for proper component loading during the DNA replication and repair process. Proteins make a connection within the interdomain connector loop of PCNA, and much of the regulation is a result of the inherent competition for this docking site. If this target region of PCNA is modified, the DNA replication and repair process in cancer cells is potentially altered. Exploitation of this cancer-associated region has implications for targeted breast cancer therapy. In the present communication, we characterize a novel peptide (caPeptide) that has been synthesized to mimic the sequence identified as critical to the cancer-associated isoform of PCNA. This peptide is delivered into cells using a nine-arginine linking mechanism, and the resulting peptide (R9-cc-caPeptide) exhibits cytotoxicity in a triple-negative breast cancer cell line, MDA-MB-436, while having less of an effect on the normal counterparts (MCF10A and primary breast epithelial cells). The novel peptide was then evaluated for cytotoxicity using various in vivo techniques, including ATP activity assays, flow cytometry, and clonogenetic assays. This cytotoxicity has been observed in other breast cancer cell lines (MCF7 and HCC1937) and other forms of cancer (pancreatic and lymphoma). R9-cc-caPeptide has also been shown to block the association of PCNA with chromatin. Alanine scanning of the peptide sequence, combined with preliminary in silico modeling, gives insight to the disruptive ability and the molecular mechanism of action of the therapeutic peptide in vivo.

Wnt modulates MCL1 to control cell survival in triple negative breast cancer

BACKGROUND

Triple negative breast cancer (TNBC) has higher rates of recurrence and distant metastasis, and poorer outcome as compared to non-TNBC. Aberrant activation of WNT signaling has been detected in TNBC, which might be important for triggering oncogenic conversion of breast epithelial cell. Therefore, we directed our focus on identifying the WNT ligand and its underlying mechanism in TNBC cells.

METHODS

We performed large-scale analysis of public microarray data to screen the WNT ligands and the clinical significance of the responsible ligand in TNBC. WNT5B was identified and its overexpression in TNBC was confirmed by immunohistochemistry staining, Western blot and ELISA. ShRNA was used to knockdown WNT5B expression (shWNT5B). Cellular functional alteration with shWNT5B treatment was determined by using wound healing assay, mammosphere assay; while cell cycle and apoptosis were examined by flowcytometry. Mitochondrial morphology was photographed by electron microscope. Biological change of mitochondria was detected by RT-PCR and oxygen consumption assay. Activation of WNT pathway and its downstream targets were evaluated by liciferase assay, immunohistochemistry staining and immunoblot analysis. Statistical methods used in the experiments besides microarray analysis was two-tailed t-test.

RESULTS

WNT5B was elevated both in the tumor and the patients' serum. Suppression of WNT5B remarkably impaired cell growth, migration and mammosphere formation. Additionally, G0/G1 cell cycle arrest and caspase-independent apoptosis was observed. Study of the possible mechanism indicated that these effects occurred through suppression of mitochondrial biogenesis, as evidenced by reduced mitochondrial DNA (MtDNA) and compromised oxidative phosphorylation (OXPHOS). In Vivo and in vitro data uncovered that WNT5B modulated mitochondrial physiology was mediated by MCL1, which was regulated by WNT/β-catenin responsive gene, Myc. Clinic data analysis revealed that both WNT5B and MCL1 are associated with enhanced metastasis and decreased disease-free survival.

CONCLUSIONS

All our findings suggested that WNT5B/MCL1 cascade is critical for TNBC and understanding its regulatory apparatus provided valuable insight into the pathogenesis of the tumor development and the guidance for targeting therapeutics.

Abstract 1724: Inhibition of the PI3K and mTOR pathways reverses gemcitabine resistance in pancreatic cancer

BACKGROUND: Despite chemotherapy, survival for most patients with pancreatic cancer is less than one year. These dismal statistics reflect the lack of effective therapy. Understanding the molecular pathways that drive cancer growth may help target our therapy. Over 90% of pancreatic cancers are K-ras mutant which activates the PI3K/AKT pathway and signals downstream to mTOR leading to cell growth, proliferation and survival. We explored the combination of gemcitabine and BEZ235, a novel dual PI3K/mTOR inhibitor, in pancreatic cancer cell lines.

METHODS: Cytotoxicity assays were performed utilizing the CellTiter-96-Aqueous-One-Solution-Cell-Proliferation-Assay-(MTS) from Promega in K-ras mutant MIA PaCa-2 pancreatic cancer cell lines. We generated gemcitabine resistant cell lines by serial passage of cells with increasing concentrations of drug. We utilized the CalcuSyn program by Biosoft to quantify synergism or antagonism with drug combinations. We also collected cells 6 hours after drug treatment for analysis of phosphorylated proteins.

RESULTS: MIA PaCa-2 wild-type and gemcitabine resistant cells were treated with 100, 50 and 25 nM of either gemcitabine, BEZ235 or the combination of both. At the 100 nM dose, cell viability of the wild-type cells was 66%, 55% and 39% respectively. In the gemcitabine resistant cells, cell viability was 84%, 63% and 44%. The combination index was 0.51 in the wild-type cells and 0.46 in the gemcitabine resistant cells indicating synergy in both cell lines. In both cell lines, p-S6K and p-AKT levels increased with gemcitabine treatment which was abrogated by treatment with BEZ-235. Interestingly, in the gemcitabine resistant cells, there appeared to be significantly increased levels of p-MEK1 compared to control.

CONCLUSION: Because pancreatic cancer remains resistant to current therapies despite recent advances in the development of molecular targeted therapies, there is an urgency to understand these pathways. We showed that the combination of gemcitabine and BEZ235 is synergistic in both cell lines but cell viability still remains high at 39% and 44% respectively. Combination with a MEK inhibitor may help to increase cell apoptosis and studies are on-going.

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 1724. doi:10.1158/1538-7445.AM2011-1724

p53R2 inhibits the proliferation of human cancer cells in association with cell-cycle arrest

Deregulation of the expression of p53R2, a p53-inducible homologue of the R2 subunit of ribonucleotide reductase, has been found in various human cancer tissues; however, the roles p53R2 plays in cancer progression and malignancy remain controversial. In the present study, we examined changes in gene expression profiles associated with p53R2 in cancer cells, using the analysis of cDNA microarray. Gene set enrichment analysis identified that the gene set regulating cell-cycle progression was significantly enriched in p53R2-silencing human oropharyngeal carcinoma KB cells. Attenuation of p53R2 expression significantly reduced p21 expression and moderately increased cyclin D1 expression in both wild-type p53 cancer cells (KB and MCF-7) and mutant p53 cancer cells (PC3 and MDA-MB-231). Conversely, overexpression of p53R2-GFP resulted in an increase in the expression of p21 and decrease in the expression of cyclin D1, which correlated with reduced cell population in S-phase in vitro and suppressed growth in vivo. Furthermore, the MAP/ERK kinase inhibitor PD98059 partially abolished modulation of p21 and cyclin D1 expression by p53R2. Moreover, under the conditions of nonstress and adriamycin-induced genotoxic stress, attenuation of p53R2 in KB cells significantly increased phosphorylated H2AX, which indicates that attenuation of p53R2 may enhance DNA damage induced by adriamycin. Overall, our study shows that p53R2 may suppress cancer cell proliferation partially by upregulation of p21 and downregulation of cyclin D1; p53R2 plays critical roles not only in DNA damage repair but also in proliferation of cancer cells.

Effects of KGF on alveolar epithelial cell transdifferentiation are mediated by JNK signaling

Rat alveolar epithelial cells (AEC) in primary culture transdifferentiate from a type II (AT2) toward a type I (AT1) cell-like phenotype, a process that can be both prevented and reversed by keratinocyte growth factor (KGF). Microarray analysis revealed that these effects of KGF are associated with up-regulation of key molecules in the mitogen-activated protein kinase (MAPK) pathway. To further explore the role of three key MAPK (i.e., extracellular signal-related kinase [ERK] 1/2, c-Jun N-terminal kinase [JNK] and p38) in mediating effects of KGF on AEC phenotype, primary rat AEC cultivated in minimal defined serum-free medium (MDSF) were treated with KGF (10 ng/ml) from Day 4 for intervals up to 48 hours. Exposure to KGF activated all three MAPK, JNK, ERK1/2, and p38. Inhibition of JNK, but not of ERK1/2 or p38, abrogated the ability of KGF to maintain the AT2 cell phenotype, as evidenced by loss of expression of lamellar membrane protein (p180) and increased reactivity with the AT1 cell-specific monoclonal antibody VIIIB2 by Day 6 in culture. Overexpression of JNKK2, upstream kinase of JNK, increased activation of endogenous c-Jun in association with increased expression of p180 and abrogation of AQP5, suggesting that activation of c-Jun promotes retention of the AT2 cell phenotype. These results indicate that retention of the AT2 cell phenotype by KGF involves c-Jun and suggest that activation of c-Jun kinase may be an important determinant of maintenance of AT2 cell phenotype.

Recombinant arginine deiminase as a potential anti-angiogenic agent

Arginine deiminase (ADI), isolated from Mycoplasma cell extracts, has been suggested to inhibit endothelial cell growth in vitro. However, anti-angiogenic activity by ADI has not yet been demonstrated. In this study, we investigated the in vitro effect of recombinant ADI (rADI) on the growth, migration, and tube formation of human umbilical vein endothelial (HUVE) cells. Mycoplasma arginine deiminase was cloned by PCR and the rADI was expressed in Escherichia coli. and purified to near homogeneity. The purified recombinant protein was found to have characteristics similar to those of the native enzyme: molecular weight (48 kDa) and specific enzymatic activity of converting L-arginine into citrulline (32.7 U/mg). This recombinant enzyme also exhibited an inhibitory effect on the growth of HUVE cells. The anti-angiogenic activity was demonstrated by in vitro inhibition of migration into the scratch wounded area in HUVE cell monolayers and the inhibition of microvessel tube-like formation of HUVE cells on Matrigel-coated surfaces. These results suggest that arginine deiminase is a potential inhibitor for angiogenesis, and that arginine concentrations may play an important role in regulating neovascularization.

Structure, function, and molecular modeling approaches to the study of the intestinal dipeptide transporter PepT1

The proton-coupled intestinal dipeptide transporter, PepT1, has 707 amino acids, 12 putative transmembrane domains (TMD), and is of importance in the transport of nutritional di- and tripeptides and structurally related drugs, such as penicillins and cephalosporins. By using a combination of molecular modeling and site-directed mutagenesis, we have identified several key amino acid residues that effect catalytic transport properties of PepT1. Our molecular model of the transporter was examined by dividing it into four sections, parallel to the membrane, starting from the extracellular side. The molecular model revealed a putative transport channel and the approximate locations of several aromatic and charged amino acid residues that were selected as targets for mutagenesis. Wild type or mutagenized human PepT1 cDNA was transfected into human embryonic kidney (HEK293) cells, and the uptake of tritiated glycylsarcosine [3H]-(Gly-Sar) was measured. Michaelis-Menton analysis of the wild-type and mutated transporters revealed the following results for site-directed mutagenesis. Mutation of Tyr-12 or Arg-282 into alanine has only a very modest effect on Gly-Sar uptake. By contrast, mutation of Trp-294 or Glu-595 into alanine reduced Gly-Sar uptake by 80 and 95%, respectively, and mutation of Tyr-167 reduced Gly-Sar uptake to the level of mock-transfected cells. In addition, preliminary data from fluorescence microscopy following the expression of N-terminal-GFP-labeled PepT1Y167A in HEK cells indicates that the Y167A mutation was properly inserted into the plasma membrane but has a greatly reduced Vmax.

Phospholipid peroxidation induces cytosolic phospholipase A2 activity: membrane effects versus enzyme phosphorylation

Cytosolic phospholipase A2 (cPLA2) is a signal-responsive enzyme that is highly selective to the nature of phospholipid substrates. A mechanism for cPLA2 activity regulation through a signal transduction pathway has been proposed and this signaling appears to be influenced by oxidants. Oxidant-mediated signaling of PLA2 may serve as an alternative mechanism for enzyme regulation; however, the manner of regulation has yet to be delineated. In this report we demonstrate that there is a direct effect of membrane oxidation on cPLA2 phosphorylation and activity. A simple in vitro system consisting of purified cPLA2 and phospholipid vesicles was used to facilitate protein kinase C (PKC) activity and provide substrates for cPLA2. Using these vesicles we found that the activity of cPLA2 was enhanced twofold when the vesicles contained as little as 5 mol% phosphatidylcholine hydroperoxides (PLPCOOH). The order of hydrolytic preference for fatty acyl species was 20:4 > 18:2 > 18:1 > 16:0, and the presence of PLPCOOH stimulated hydrolysis largely of phosphatidylcholine containing 20:4. The Ca2+ concentrations required for stimulated hydrolytic activity were also twofold lower for oxidized compared to unoxidized vesicles. Using phospholipid micelles as substrates, PKC-mediated phosphorylation of cPLA2 increased hydrolytic activity 71% compared to preparations lacking PKC. Using phospholipid vesicles as substrates, PKC-mediated phosphorylation resulted in an 85% increase in cPLA2 activity compared to preparations without PKC. PKC-mediated phosphorylation of cPLA2, therefore, stimulates catalytic activity toward membrane phospholipids and the extent of activation is enhanced directly by peroxidation of membrane phospholipids and involves a peroxide-induced stimulation of cPLA2 phosphorylation.

Characterization of human and rat immortalized clones parotid acinar cells with respect to specific proteins and their mRNAs, and receptor-linked adenylate cyclase

This study reports the isolation and characterization of a rat nontumorigenic parotid acinar cell clone (2RSG), a human nontumorigenic parotid acinar cell clone (2HPC8), and a human tumorigenic acinar clone (2HP1G). The levels of alpha-amylase mRNAs detected when using alpha-amylase cDNA of 1176 and 702 bp for hybridization were higher in 2RSG and 2HPC8 cells than their respective whole parotid glands. The level of these mRNAs decreased in 2HP1G cells. In contrast to alpha-amylase mRNAs levels, the alpha-amylase activity in cultured acinar cells was extremely low in comparison to whole glands, irrespective of species or cell status. The levels of proline-rich protein (PRP) mRNA and parotid secretory protein (PSP) mRNA detected when using PRP cDNA of 600 bp and PSP cDNA of 805 bp for hybridization were higher in 2RSG cells than those in rat parotid glands; the reverse was observed in 2HPC8 cells and human parotid glands. The levels of PRP mRNA and PSP mRNA in 2HPC8 and 2PH1G acinar cells were similar. The level of mRNA was not detectable in murine neuroblastoma cells (NBP2) using the same alpha-amylase cDNA, PRP cDNA and PSP cDNA for hybridization. The PSP level in rat parotid gland was lower than that found in 2RSG cells; the reverse was observed in 2HPC8 cells and human parotid glands. The level of PSP in 2HP1G cells was higher than that found in 2HPC8 cells. Isoproterenol increased the cAMP level in 2RSG, 2HPC8, and 2HP1G clones, being most effective in 2RSG cells, and least effective in 2HPG cells. Prostaglandin E1 (PGE1) also increased cAMP level, being most effective in 2HPC8 cells and ineffective in 2HP1G cells, suggesting that the PGE1 receptor-linked adenylate cyclase becomes inactive upon transformation. These results suggest that the three clonal acinar cells from rat and human parotid glands reported here can be useful in comparative studies on regulation of growth, differentiation, and transformation.