Glutathione-conjugate transport by RLIP76 is required for clathrin-dependent endocytosis and chemical carcinogenesis

Rlip76 in ageing and Alzheimer's disease: Focus on oxidative stress and mitochondrial mechanisms

RLIP76 (Rlip), a stress-responsive protein, plays a multifaceted role in cellular function. This protein acts primarily as a glutathione-electrophile conjugate (GS-E) transporter, crucial for detoxifying hazardous compounds and converting them into mercapturic acids. RLIP76 also modulates cytoskeletal motility and membrane plasticity through its role in the Ral-signaling pathway, interacting with RalA and RalB, key small GTPases involved in growth and metastasis. Beyond its ATP-dependent transport functions in various tissues, RLIP76 also demonstrates GTPase Activating Protein (GAP) activity towards Rac1 and Cdc42, with a preference for Ral-GTP over Ral-GDP. Its functions span critical physiological processes including membrane dynamics, oxidative stress response, and mitochondrial dynamics. The protein's widespread expression and evolutionary conservation underscore its significance. Our lab discovered that Rlip interacts with Alzheimer's disease (AD) proteins, amyloid beta and phosphorylated and induce oxidative stress, mitochondrial dysfnction and synaptic damage in AD. Our in vitro studies revealed that overexpression of Rlip reduces mitochondrial abnormalities. Further, our in vivo studies (Rlip+/- mice) revealed that a partial reduction of Rlip in mice (Rlip+/-), leads to mitochondrial abnormalities, elevated oxidative stress, and cognitive deficits resembling late-onset AD, emphasizing the protein's crucial role in neuronal health and disease. Finally, we discuss the experimental cross-breedings of overexpression of mice Rlip TG/TG or Rlip + /- mice with Alzheimer's disease models - earlyonset 5XFAD, late-onset APPKI and Tau transgenic mice, providing new insights into RLIP76's role in AD progression and development. This review summarizes RLIP76's structure, function, and cellular pathways, highlighting its implications in AD and its potential as a therapeutic target.

The potential role of Ral-interacting protein 76 and vascular endothelial growth factor on angiogenesis in the tumor and ovarian corpus luteum microenvironment

Tumors and the ovarian corpus luteum have complex mechanisms in the growth microenvironment. Angiogenesis is especially important for demonstrating the molecular mechanism of dynamic cellular function in tumors and corpus luteum. Angiogenesis in tumors and corpus luteum seems to have a similar function, and Ral-interacting protein 76 (RLIP76) and vascular endothelial growth factor (VEGF) are expressed in the tissues of tumors and ovarian corpus luteum. RLIP76 is a potential factor with VEGF in the tumor and corpus luteum angiogenesis. RLIP76 regulates a small GTPase (R-Ras) in cell survival, spreading, and migration. VEGF activates angiogenic functions in tumor and endothelial cells. Hypoxia-inducible factor-1 (HIF-1) is important in tumor growth, tumor angiogenesis, and corpus luteum. VEGF and HIF-1 regulate the angiogenic function of RLIP76, and RLIP76 controls vascular growth in endothelial and tumor cells. RLIP76, R-Ras, VEGF, and HIF-1 may be useful in the research of corpus luteum and cancer therapy and the study of mechanisms of tumor and corpus luteum angiogenesis. This review will help to elucidate the roles of RLIP76 and VEGF in tumor and corpus luteum angiogenesis, tumorigenesis, and the specific regulation of RLIP76 and VEGF. Thus, we reviewed the potential role of RLIP76 and VEGF in the angiogenesis of the tumor and corpus luteum in the tumor and ovarian microenvironment.

Enhancing carboplatin sensitivity in ovarian cancer cells by blocking the mercapturic acid pathway transporter

Ral-binding/interacting protein (RLIP) acts as a transporter that responds to stress and provides protection, specifically against glutathione-electrophile conjugates and xenobiotic toxins. Its increased presence in malignant cells, especially in cancer, emphasizes its crucial antiapoptotic function. This is achieved by selectively regulating the cellular levels of proapoptotic oxidized lipid byproducts. Suppressing the progression of tumors in human xenografts can be achieved by effectively inhibiting RLIP, a transporter in the mercapturic acid pathway, without involving chemotherapy. Utilizing ovarian cancer (OC) cell lines (MDAH2774, OVCAR4, and OVCAR8), we observed that agents targeting RLIP, such as RLIP antisense and RLIP antibodies, not only substantially impeded the viability of OC cells but also remarkably increased their sensitivity to carboplatin. To delve further into the cytotoxic synergy between RLIP antisense, RLIP antibodies, and carboplatin, we conducted investigations in both cell culture and xenografts of OC cells. The outcomes revealed that RLIP depletion via phosphorothioate antisense led to rapid and sustained remissions in established subcutaneous human ovary xenografts. Furthermore, RLIP inhibition by RLIP antibodies exhibited comparable efficacy to antisense and enhanced the effectiveness of carboplatin in MDAH2774 OC xenografts. These investigations underscore RLIP as a central carrier crucial for supporting the survival of cancer cells, positioning it as a suitable focus for cancer treatment.

The role of RLIP76 in oxidative stress and mitochondrial dysfunction: Evidence based on autopsy brains from Alzheimer's disease patients

Several converging lines of evidence from our group support a potential role of RLIP76 (AKA Rlip) in neurodegenerative disorders, including Alzheimer's Disease (AD). However, the role of Rlip in Alzheimer's and other neurodegenerative diseases is not well understood. The purpose of the present study is to determine the role of Rlip in the brains of AD patients and control subjects. To achieve our goals, we used frozen tissues and formalin-fixed paraffin-embedded postmortem brains from AD patients of different Braak stages and age-matched control subjects. Our immunohistology and immunoblotting blotting analysis revealed that expression of Rlip protein gradually and significantly decreased (p = 0.0001) with AD progression, being lowest in Braak stage IV-V. Rlip was colocalized with Amyloid beta (Aβ) and phosphorylated tau (p-Tau) as observed by IHC staining and co-immunoprecipitation studies. Lipid peroxidation (4-HNE generation) and H2O2 production were significantly higher (p = 0.004 and 0.0001 respectively) in AD patients compared to controls, and this was accompanied by lower ATP production in AD (p = 0.0009). Oxidative DNA damage was measured by 8-Hydroxyguanosine (8-OHdG) in tissue lysates by ELISA and COMET assay. AD 8-OHdG levels were significantly higher (p = 0.0001) compared to controls. COMET assay was performed in brain cells, isolated from frozen postmortem samples. The control samples showed minimal DNA in comets representing few DNA strand breaks (<20 %), (score-0-1). However, the AD group showed an average of 50 % to 65 % of DNA in comet tails (score-4-5) indicating numerous DNA strand breaks. The difference between the two groups was significant (p = 0.001), as analyzed by Open Comet by ImageJ. Elevated DNA damage was further examined by western blot analysis for phosphorylated histone variant H2AX (γH2AX). Induction of γH2AX was very significant (p < 0.0001) and confirmed the presence of double-strand breaks in DNA. Overall, our results indicate an important role for Rlip in maintaining neuronal health and homeostasis by suppressing cellular oxidative stress and DNA damage. Based on our findings, we cautiously conclude that Rlip is a promising therapeutic target for Alzheimer's disease.

Regression of ovarian cancer xenografts by depleting or inhibiting RLIP

Ovarian cancer (OC) is the most prevalent and deadly cancer of the female reproductive system. Women will continue to be impacted by OC-related morbidity and mortality. Despite the fact that chemotherapy with cisplatin is the main component as the first-line anticancer treatment for OC, chemoresistance and unfavorable side effects are important obstacles to effective treatment. Targets for effective cancer therapy are required for cancer cells but not for non-malignant cells because they are expressed differently in cancer cells compared to normal cells. Targets for cancer therapy should preferably be components that already exist in biochemical and signalling frameworks and that significantly contribute to the development of cancer or regulate the response to therapy. RLIP is an important mercapturic acid pathway transporter that is crucial for survival and therapy resistance in cancers, therefore, we examined the role of RLIP in regulating essential signalling proteins involved in relaying the inputs from upstream survival pathways and mechanisms contributing to chemo-radiotherapy resistance in OC. The findings of our research offer insight into a novel anticancer effect of RLIP depletion/inhibition on OC and might open up new therapeutic avenues for OC therapy.

RLIP: A necessary transporter protein for translating oxidative stress into pro-obesity and pro-carcinogenic signaling

Previously, we showed that knockout mice homozygous for deficiency of the mercapturic acid pathway (MAP) transporter protein, RLIP (RLIP^-/-), are resistant to chemical carcinogenesis, inflammation, and metabolic syndrome (MetS). We also found that RLIP^-/- mice are highly resistant to obesity caused by a high-fat diet (HFD). Interestingly, these studies showed that kinase, cytokine, and adipokine signaling that are characteristics of obesity were blocked despite the presence of increased oxidative stress in RLIP^-/- mice. The deficiencies in obesity-inducing kinase, cytokine, and adipokine signaling were attributable to a lack of clathrin-dependent endocytosis (CDE), a process that is severely deficient in RLIP^-/- mice. Because CDE is also necessary for carcinogenic signaling through EGF, WNT, TGFβ and other cancer-specific peptide hormones, and because RLIP^-/- mice are cancer-resistant, we reasoned that depletion of RLIP by an antisense approach should cause cancer regression in human cancer xenografts. This prediction has been confirmed in studies of xenografts from lung, kidney, prostate, breast, and pancreatic cancers and melanoma. Because these results suggested an essential role for RLIP in carcinogenesis, and because our studies have also revealed a direct interaction between p53 and RLIP, we reasoned that if RLIP played a central role in carcinogenesis, that development of lymphoma in p53^-/- mice, which normally occurs by the time these mice are 6 months old, could be delayed or prevented by depleting RLIP. Recent studies described herein have confirmed this hypothesis, showing complete suppression of lymphomagenesis in p53^-/- mice treated with anti-RLIP antisense until the age of 8 months. All control mice developed lymphoma in the thymus or testis as expected. These findings lead to a novel paradigm predicting that under conditions of increased oxidative stress, the consequent increased flux of metabolites in the MAP causes a proportional increase in the rate of CDE. Because CDE inhibits insulin and TNF signaling but promotes EGF, TGFβ, and Wnt signaling, our model predicts that chronic stress-induced increases in RLIP (and consequently CDE) will induce insulin-resistance and enhance predisposition to cancer. Alternatively, generalized depletion of RLIP would antagonize the growth of malignant cells, and concomitantly exert therapeutic insulin-sensitizing effects. Therefore, this review focuses on how targeted depletion or inhibition of RLIP could provide a novel target for treating both obesity and cancer.

Rlip76: An Unexplored Player in Neurodegeneration and Alzheimer’s Disease?

Alzheimer’s disease (AD) is a progressive neurodegenerative disorder and is the most common cause of dementia in older people. AD is associated with the loss of synapses, oxidative stress, mitochondrial structural and functional abnormalities, microRNA deregulation, inflammatory responses, neuronal loss, accumulation of amyloid-beta (Aβ) and phosphorylated tau (p-tau). AD occurs in two forms: early onset, familial AD and late-onset, sporadic AD. Causal factors are still unknown for a vast majority of AD patients. Genetic polymorphisms are proposed to contribute to late-onset AD via age-dependent increases in oxidative stress and mitochondrial abnormalities. Recent research from our lab revealed that reduced levels of Rlip76 induce oxidative stress, mitochondrial dysfunction and synaptic damage, leading to molecular and behavioral phenotypes resembling late-onset AD. Rlip76 is a multifunctional 76 kDa protein encoded by the RALBP1 gene, located on chromosome 18. Rlip is a stress-protective ATPase of the mercapturic acid pathway that couples clathrin-dependent endocytosis with the efflux of glutathione–electrophile conjugates. Rlip is evolutionarily highly conserved across species and is ubiquitously expressed in all tissues, including AD-affected brain regions, the cerebral cortex and hippocampus, where highly active neuronal metabolisms render the cells highly susceptible to intracellular oxidative damage. In the current article, we summarize molecular and cellular features of Rlip and how depleted Rlip may exacerbate oxidative stress, mitochondrial dysfunction and synaptic damage in AD. We also discuss the possible role of Rlip in aspects of learning and memory via axonal growth, dendritic remodeling, and receptor regulation. We conclude with a discussion of the potential for the contribution of genetic polymorphisms in Rlip to AD progression and the potential for Rlip-based therapies.

Rlip Depletion Alters Oncogene Transcription at Multiple Distinct Regulatory Levels

Simple Summary

Rlip76 is a multifunctional membrane protein that facilitates cancer growth, and its depletion kills cancer cells. We recently found that Rlip depletion also results in broad changes to oncogene and tumor suppressor transcription. The present studies were designed to decipher the unknown downstream signaling pathways and transcriptional regulatory mechanisms driving the effect. Building on prior findings that Rlip depletion induces broad methylomic changes, we found using bioluminescence reporter assays that depletion of Rlip also exerts transcriptional control over several cancer genes through methylation-independent changes in transcription factor-mediated activation of their promoter regions and through additional as yet unidentified mechanisms. These findings have important implications for Rlip-targeted cancer therapy.

Abstract

Rlip76 (Rlip) is a multifunctional membrane protein that facilitates the high metabolic rates of cancer cells through the efflux of toxic metabolites and other functions. Rlip inhibition or depletion results in broad-spectrum anti-cancer effects in vitro and in vivo. Rlip depletion effectively suppresses malignancy and causes global reversion of characteristic CpG island methylomic and transcriptomic aberrations in the p53-null mouse model of spontaneous carcinogenesis through incompletely defined signaling and transcriptomic mechanisms. The methylome and transcriptome are normally regulated by the concerted actions of several mechanisms that include chromatin remodeling, promoter methylation, transcription factor interactions, and miRNAs. The present studies investigated the interaction of Rlip depletion or inhibition with the promoter methylation and transcription of selected cancer-related genes identified as being affected by Rlip depletion in our previous studies. We constructed novel promoter CpG island/luciferase reporter plasmids that respond only to CpG methylation and transcription factors. We found that Rlip depletion regulated expression by a transcription factor-based mechanism that functioned independently of promoter CpG methylation, lipid peroxidation, and p53 status.

Anticancer Activity of Ω-6 Fatty Acids through Increased 4-HNE in Breast Cancer Cells

Simple Summary

Epidemiological evidence suggests that breast cancer risk is lowered by Ω-3 and increased by Ω-6 polyunsaturated fatty acids (PUFAs). Paradoxically, the Ω-6 PUFA metabolite 4-hydroxynonenal (4-HNE) inhibits cancer cell growth. This duality prompted us to study whether arachidonic acid (AA) would enhance doxorubicin (dox) cytotoxicity towards breast cancer cells. We found that supplementing AA or inhibiting 4-HNE metabolism potentiated doxorubicin (dox) toxicity toward Her2-dependent breast cancer but spared myocardial cells. Our results suggest that Ω-6 PUFAs could improve outcomes of dox chemotherapy in Her2-overexpressing breast cancer.

Abstract

Her2-amplified breast cancers resistant to available Her2-targeted therapeutics continue to be a challenge in breast cancer therapy. Dox is the mainstay of chemotherapy of all types of breast cancer, but its usefulness is limited by cumulative cardiotoxicity. Because oxidative stress caused by dox generates the pro-apoptotic Ω-6 PUFA metabolite 4-hydroxynonenal (4-HNE), we surmised that Ω-6 PUFAs would increase the effectiveness of dox chemotherapy. Since the mercapturic acid pathway enzyme RALBP1 (also known as RLIP76 or Rlip) that limits cellular accumulation of 4-HNE also mediates dox resistance, the combination of Ω-6 PUFAs and Rlip depletion could synergistically improve the efficacy of dox. Thus, we studied the effects of the Ω-6 PUFA arachidonic acid (AA) and Rlip knockdown on the antineoplastic activity of dox towards Her2-amplified breast cancer cell lines SK-BR-3, which is sensitive to Her2 inhibitors, and AU565, which is resistant. AA increased lipid peroxidation, 4-HNE generation, apoptosis, cellular dox concentration and dox cytotoxicity in both cell lines while sparing cultured immortalized cardiomyocyte cells. The known functions of Rlip including clathrin-dependent endocytosis and dox efflux were inhibited by AA. Our results support a model in which 4-HNE generated by AA overwhelms the capacity of Rlip to defend against apoptosis caused by dox or 4-HNE. We propose that Ω-6 PUFA supplementation could improve the efficacy of dox or Rlip inhibitors for treating Her2-amplified breast cancer.

RALBP1 in Oxidative Stress and Mitochondrial Dysfunction in Alzheimer's Disease

The purpose of our study is to understand the role of the RALBP1 gene in oxidative stress (OS), mitochondrial dysfunction and cognition in Alzheimer's disease (AD) pathogenesis. The RALPB1 gene encodes the 76 kDa protein RLIP76 (Rlip). Rlip functions as a stress-responsive/protective transporter of glutathione conjugates (GS-E) and xenobiotic toxins. We hypothesized that Rlip may play an important role in maintaining cognitive function. The aim of this study is to determine whether Rlip deficiency in mice is associated with AD-like cognitive and mitochondrial dysfunction. Brain tissue obtained from cohorts of wildtype (WT) and Rlip+/- mice were analyzed for OS markers, expression of genes that regulate mitochondrial fission/fusion, and synaptic integrity. We also examined mitochondrial ultrastructure in brains obtained from these mice and further analyzed the impact of Rlip deficiency on gene networks of AD, aging, stress response, mitochondrial function, and CREB signaling. Our studies revealed a significant increase in the levels of OS markers and alterations in the expression of genes and proteins involved in mitochondrial biogenesis, dynamics and synapses in brain tissues from these mice. Furthermore, we compared the cognitive function of WT and Rlip+/- mice. Behavioral, basic motor and sensory function tests in Rlip+/- mice revealed cognitive decline, similar to AD. Gene network analysis indicated dysregulation of stress-activated gene expression, mitochondrial function and CREB signaling genes in the Rlip+/- mouse brain. Our results suggest that Rlip deficiency-associated increases in OS and mitochondrial dysfunction could contribute to the development or progression of OS-related AD processes.

Acrolein but not its metabolite, 3-Hydroxypropylmercapturic acid (3HPMA), activates vascular transient receptor potential Ankyrin-1 (TRPA1): Physiological to toxicological implications

Acrolein, an electrophilic α,β-unsaturated aldehyde, is present in foods and beverages, and is a product of incomplete combustion, and thus, reaches high ppm levels in tobacco smoke and structural fires. Exposure to acrolein is linked with cardiopulmonary toxicity and cardiovascular disease risk. The hypothesis of this study is the direct effects of acrolein in isolated murine blood vessels (aorta and superior mesenteric artery, SMA) are transient receptor potential ankyrin-1 (TRPA1) dependent. Using isometric myography, isolated aorta and SMA were exposed to increasing levels of acrolein. Acrolein inhibited phenylephrine (PE)-induced contractions (approximately 90%) in aorta and SMA of male and female mice in a concentration-dependent (0.01-100 μM) manner. The major metabolite of acrolein, 3-hydroxypropylmercapturic acid (3HPMA), also relaxed PE-precontracted SMA. As the SMA was 20× more sensitive to acrolein than aorta (SMA EC50 0.8 ± 0.2 μM; aorta EC50 > 29.4 ± 4.4 μM), the mechanisms of acrolein-induced relaxation were studied in SMA. The potency of acrolein-induced relaxation was inhibited significantly by: 1) mechanically-impaired endothelium; 2) Nω-Nitro-L-arginine methyl ester hydrochloride (L-NAME); 3) guanylyl cyclase (GC) inhibitor (ODQ); and, 4) a TRPA1 antagonist (A967079). TRPA1 positive immunofluorescence was present in the endothelium. Compared with other known TRPA1 agonists, including allyl isothiocyanate (AITC), cinnamaldehyde, crotonaldehyde, and formaldehyde, acrolein stimulated a more potent TRPA1-dependent relaxation. Acrolein, at high concentration [100 μM], induced tension oscillations (spasms) independent of TRPA1 in precontracted SMA but not in aorta. In conclusion, acrolein is vasorelaxant at low levels (physiological) yet vasotoxic at high levels (toxicological).

Targeting the mercapturic acid pathway for the treatment of melanoma

The treatment of metastatic melanoma is greatly hampered by the simultaneous dysregulation of several major signaling pathways that suppress apoptosis and promote its growth and invasion. The global resistance of melanomas to therapeutics is also supported by a highly active mercapturic acid pathway (MAP), which is responsible for the metabolism and excretion of numerous chemotherapy agents. The relative importance of the MAP in melanoma survival was not recognized until demonstrated that B16 melanoma undergoes dramatic apoptosis and regression upon the depletion or inhibition of the MAP transporter protein RLIP. RLIP is a multi-functional protein that couples ATP hydrolysis with the movement of substances. As the rate-limiting step of the MAP, the primary function of RLIP in the plasma membrane is to catalyze the ATP-dependent efflux of unmetabolized drugs and toxins, including glutathione (GSH) conjugates of electrophilic toxins (GS-Es), which are the precursors of mercapturic acids. Clathrin-dependent endocytosis (CDE) is an essential mechanism for internalizing ligand-receptor complexes that promote tumor cell proliferation through autocrine stimulation (Wnt5a, PDGF, βFGF, TNFα) or paracrine stimulation by hormones produced by fibroblasts (IGF1, HGF) or inflammatory cells (IL8). Aberrant functioning of these pathways appears critical for melanoma cell invasion, metastasis, and evasion of apoptosis. This review focuses on the selective depletion or inhibition of RLIP as a highly effective targeted therapy for melanoma that could cause the simultaneous disruption of the MAP and critical peptide hormone signaling that relies on CDE.

Prevention of mammary carcinogenesis in MMTV-neu mice by targeting RLIP

The overexpression and amplification of the protooncogene neu (ERBB2) play an important role in the development of aggressive breast cancer (BC) in humans. Ral-interacting protein (RLIP), a modular stress-response protein with pleiotropic functions, is overexpressed in several types of cancer, including BC. Here, we show that blocking RLIP attenuates the deleterious effects caused by the loss of the tumor suppressor p53 and inhibits the growth of human BC both in vitro and in vivo in MMTV-neu mice. In addition, we show that treatment with the diet-derived, RLIP-targeting chemotherapeutic 2'-hydroxyflavanone (2HF), alone or in combination with RLIP-specific antisense RNA or antibodies, significantly reduced the cumulative incidence and/or burden of mammary hyperplasia and carcinoma in MMTV-neu mice. 2HF treatment correlated with reduced tumor cell proliferation and increased apoptosis, and the average number of Ki67-positive (proliferating) cells was significantly lower in the tumors of 2HF-treated mice than in the tumors of control mice. Furthermore, targeting RLIP also resulted in the overexpression of E-cadherin and the infiltration of CD3+ T cells into mammary tumors. Taken together, these results underscore the translational potential of RLIP-targeting agents and provide a strong rationale to validate them in the clinic.

RLIP depletion induces apoptosis associated with inhibition of JAK2/STAT3 signaling in melanoma cells

The incidence of malignant melanoma, a neoplasm of melanocytic cells, is increasing rapidly. The lymph nodes are often the first site of metastasis and can herald systemic dissemination, which is almost uniformly fatal. RLIP, a multi-specific ATP-dependent transporter that is over-expressed in several types of cancers, plays a central role in cancer cell resistance to radiation and chemotherapy. RLIP appears to be necessary for cancer cell survival because both in vitro cell culture and in vivo animal tumor studies show that the depletion or inhibition of RLIP causes selective toxicity to malignant cells. RLIP depletion/inhibition triggers apoptosis in cancer cells by inducing the accumulation of endogenously formed glutathione-conjugates. In our in vivo studies, we administered RLIP antibodies or antisense oligonucleotides to mice bearing subcutaneous xenografts of SKMEL2 and SKMEL5 melanoma cells and demonstrated that both treatments caused significant xenograft regression with no apparent toxic effects. Anti-RLIP antibodies and antisense, which respectively inhibit RLIP-mediated transport and deplete RLIP expression, showed similar tumor regressing activities, indicating that the inhibition of RLIP transport activity at the cell surface is sufficient to achieve anti-tumor activity. Furthermore, RLIP antisense treatment reduced levels of RLIP, pSTAT3, pJAK2, pSrc, Mcl-1 and Bcl2, as well as CDK4 and cyclin B1, and increased levels of Bax and phospho 5' AMP-activated protein kinase (pAMPK). These studies indicate that RLIP serves as a key effector in the survival of melanoma cells and is a valid target for cancer therapy. Overall, compounds that inhibit, deplete or downregulate RLIP will function as wide-spectrum agents to treat melanoma, independent of common signaling pathway mutations.

Targeting RLIP with CRISPR/Cas9 controls tumor growth

Breast cancer (BC) remains one of the major causes of cancer deaths in women. Over half of all BCs carry genetic defects in the gene encoding p53, a powerful tumor suppressor. P53 is known as the 'guardian of the genome' because it is essential for regulating cell division and preventing tumor formation. Ral-interacting protein (RLIP) is a modular protein capable of participating in many cellular functions. Blocking this stress-responsive protein, which is overexpressed during malignancy, enables BC cells to overcome the deleterious effects of p53 loss more effectively. In the clustered regularly interspaced short palindromic repeats/CRISPR-associated protein (CRISPR/Cas9) system, a single-guide RNA (sgRNA) recognizes a specific DNA sequence and directs the endonuclease Cas9 to make a double-strand break, which enables editing of targeted genes. Here, we harnessed CRISPR/Cas9 technology to target the RLIP gene in BC cells. We screened sgRNAs using a reporter system and lentivirally delivered them, along with Cas9, to BC cells for validation. We then assessed the survival, proliferation, and tumorigenicity of BC cells in vitro and the growth of tumors in vivo after CRISPR-mediated knockdown of RLIP. Doxycycline-inducible expression of Cas9 in BC cells transduced with lentiviral vectors encoding the sgRNAs disrupted the RLIP gene, leading to inhibition of BC cell proliferation both in vitro and in vivo, with resected tumors showing reduced levels of the survival and proliferation markers Ki67, RLIP, pAkt, and survivin, the cell cycle protein CDK4, and the mesenchymal marker vimentin, as well as elevated levels of the differentiation protein E-cadherin and pro-apoptotic protein Bim. Inducible Cas9/sgRNA-transduced BC cells without doxycycline treatment did not exhibit altered cell survival or proliferation in vitro or in vivo. Our study provides proof-of-concept that the CRISPR/Cas9 system can be utilized to target RLIP in vitro and in vivo.

Activating p53 function by targeting RLIP

Aberrations in RLIP, p53, and PKCα represent essentially the entire spectrum of all human neoplasms. Elevated PKCα expression, failure of the cell cycle checkpoint (p53 dysfunction), and abnormal glutathione (GSH) metabolism are fundamental hallmarks of carcinogenesis and drug/radiation resistance. However, a lack of investigations into the interactions between these important regulatory nodes has fundamentally limited our understanding of carcinogenesis and the development of effective interventions for cancer prevention and therapy. Loss of p53, perhaps the most powerful tumor suppressor gene, predisposes rodents to spontaneous cancer and humans to familial, as well as acquired, cancers. Until recently, no genetic manipulation of any oncogene had been reported to abrogate spontaneous carcinogenesis in p53^-/- rodent models. However, the overexpression of RLIP, a GSH-electrophile conjugate (GS-E) transporter, has been found to enhance cancer cell proliferation and confer drug/radiation resistance, whereas its depletion causes tumor regression, suggesting its importance in cancer and drug/radiation resistance. Indeed, RLIP is an essential effector of p53 that is necessary for broad cancer-promoting epigenetic remodeling. Interestingly, through a haploinsufficiency mechanism, the partial depletion of RLIP in p53^-/- mice provides complete protection from neoplasia. Furthermore, RLIP^-/- mice exhibit altered p53 and PKCα function, marked deficiency in clathrin-dependent endocytosis (CDE), and almost total resistance to chemical carcinogenesis. Based on these findings, in this review, we present a novel and radical hypothesis that expands our understanding of the highly significant cross-talk between p53, PKCα, and GSH signaling by RLIP in multiple tumor models.

Rlip Depletion Suppresses Growth of Breast Cancer

RLIP76 (RAL-binding protein-1, Rlip) is a stress-protective mercapturic-acid-pathway transporter protein that also plays a key role in regulating clathrin-dependent endocytosis as a Ral effector. Targeted inhibition or depletion of Rlip causes regression of xenografts of many cancers and is capable of abrogating tumor formation in p53-null mice. This is associated with the reversion of the abnormal methylomic profile of p53-null mice to wild-type. In a query of The Cancer Genome Atlas (TCGA) databases, we found that Rlip expression was associated with poor survival and with significant differences in the frequencies of PIK3CA mutation, MYC amplification, and CDKN2A/B deletion, which were the most commonly mutated, amplified, and deleted genes, respectively, among TCGA breast cancer patients. We conducted the present study to further examine the effects of Rlip inhibition and to evaluate the in vitro and in vivo efficacy in breast cancer. Using immunogold electron microscopy, we found that plasma-membrane Rlip was accessible to cell-surface antibodies in the MCF7 (ER+) breast cancer cell line. Rlip depletion resulted in decreased survival of MCF7 and MDA-MB-231 cells and increased terminal deoxynucleotidyl transferase dUTP nick end labeling (TUNEL) positivity and DNA laddering, indicating apoptotic cell death. Additionally, in vitro knockdown of Rlip inhibited EGF endocytosis and WNT/MAPK signaling. Xenograft studies in nude mice showed regression of breast cancer via antisense-mediated depletion of Rlip mRNA as well as by anti-Rlip antibody. Finally, knockdown of Rlip by antisense locked nucleic acid oligonucleotides increased markers for apoptotic signaling and decreased markers for proliferation, angiogenesis, and cell cycling in MCF7 and MDA-MB-231luc xenografts. Our findings validate Rlip as an attractive target in breast cancer.

RLIP controls receptor-ligand signaling by regulating clathrin-dependent endocytosis

RLIP (Ral-interacting protein) is a multifunctional protein that couples ATP hydrolysis with the movement of substances. Its primary function appears to be in the plasma membrane, where it catalyzes the ATP-dependent efflux of glutathione-conjugates (GS-Es), as well as un-metabolized drugs and toxins. In the plasma membrane, its interaction with the clathrin adaptor protein AP2 localizes it to endocytic vesicle, where its GS-E-stimulated ATPase and transport activity are required for clathrin-dependent endocytosis (CDE). CDE is an essential mechanism for internalizing ligand-receptor complexes that signal proliferation (EGF, insulin, IGF1), apoptosis (TNFα, TRAIL, Fas-L), and differentiation and morphogenesis (TGFβ, WNT, Notch, SHH). Aberrant functioning of these pathways appears crucial for most cancer cells to evade apoptosis, invade surrounding tissues, and metastasize. Internalization of receptor-ligand complexes by CDE begins a sequence of events that can terminate, initiate, or modulate downstream signaling; the consequences of signaling through these downstream pathways may be inherently different in cancer and normal cells, a view supported by numerous basic and clinical observations. In this review, we will discuss the GS-E transport activity of RLIP, which determines the rate of ligand endocytosis, and how the inhibition and/or depletion of RLIP globally disrupts in ligand-receptor signaling.

Topical 2'-Hydroxyflavanone for Cutaneous Melanoma

2′-hydroxyflavanone (2HF) is a dietary flavonoid with anticancer activity towards multiple cancers. Here, we report that topically applied 2HF inhibits the growth of intradermal implants of melanoma in immunocompetent mice. 2HF induced apoptosis and inhibited the growth of the human SK-MEL-24 as well as murine B16-F0 and B16-F10 melanoma cell lines in vitro. Apoptosis was associated with depletion of caspase-3, caspase-9, and PARP1 in B16-F0 and SK-MEL-24 cells. Caspase-9 and MEKK-15 were undetected even in untreated B16-F10 cells. Signaling proteins TNFα, and phospho-PDGFR-β were depleted in all three cell lines; MEKK-15 was depleted by 2HF in SK-MEL-24 cells. 2HF enhanced sunitinib (an MEK and PDGFR-β inhibitor) and AZD 2461 (a PARP1 inhibitor) cytotoxicity. 2HF also depleted the Ral-regulated, stress-responsive, antiapoptotic endocytic protein RLIP76 (RALBP1), the inhibition of which has previously been shown to inhibit B16-F0 melanoma growth in vivo. Functional inhibition of RLIP76 was evident from inhibition of epidermal growth factor (EGF) endocytosis by 2HF. We found that topically applied 2HF–Pluronic Lecithin Organogel (PLO) gel inhibited B16-F0 and B16-F10 tumors implanted in mice and caused no overt toxicity despite significant systemic absorption. 2HF treatment reduced phospho-AKT, vimentin, fibronectin, CDK4, cyclinB1, and BCL2, whereas it increased BIM and phospho-AMPK in excised tumors. Several cancer signals are controlled by endocytosis, a process strongly inhibited by RLIP76 depletion. We conclude that 2HF–PLO gel may be useful for topical therapy of cutaneous metastases of melanoma and could enhance the antineoplastic effects of sunitinib and PARP1 inhibitors. The mechanism of action of 2HF in melanoma overlaps with RLI76 inhibitors.

Synergistic efficacy of RLIP inhibition and 2'-hydroxyflavanone against DMBA-induced mammary carcinogenesis in SENCAR mice

Substantial evidence suggests that 7,12-dimethylbenzanthracene (DMBA)-induced mammary carcinogenesis in mice mimics human breast cancer (BC) in many respects. Therefore, it has been used extensively to evaluate preventive and therapeutic agents for human BC. Mammary carcinogenesis induced by DMBA administration in female SENsitive to CARcinogen (SENCAR) mice was characterized by histopathological analysis of the mammary glands and alterations to the phosphatidylinositol 3-kinase/protein kinase B/cyclin-dependent kinase 1 (PI3K/Akt/CDK1) pathway. We recently reported that 2'-hydroxyflavanone (2HF) is a promising diet-derived chemotherapeutic agent that suppresses BC growth in vitro and in vivo by targeting a 76 kDa ral-interacting protein (RLIP). The objective of the current study was to investigate the synergistic anticarcinogenic effects of RLIP inhibition/depletion and 2HF in an in vivo model of DMBA-induced mammary carcinogenesis in SENCAR mice. Mice were given 2HF (50 mg/kg, bw, orally on alternate days), RLIP antibody (Rab; 5 mg/kg, bw, ip weekly), RLIP antisense (RAS; 5 mg/kg, b.w., ip weekly), or a combination of 2HF + Rab + RAS. Animals were monitored daily, and 7 days after the first appearance of moribund behavior, tissues were harvested for morphological and immunohistological analysis. Western blot analyses were performed to determine the expression of anti- and proapoptotic proteins in the mammary glands. Our results reveal that 2HF, RAS, and Rab significantly prevented the carcinogenic effects of DMBA administration in the mammary glands and other organs. Further, mice treated with a combination of 2HF + RAS + Rab exhibited no carcinogenic effect of DMBA as compared to either or the single agent-treated mice. This study demonstrates for the first time the anticarcinogenic effects of 2HF and RLIP inhibition/depletion in vivo in a novel DMBA-induced model of BC in SENCAR mice and provides the rationale for further clinical investigation.

A potential function of RLIP76 in the ovarian corpus luteum

Ral interacting protein of 76 kDa (RLIP76) is multifunctional protein localized and distributed in the plasma membrane, cytosol, and nucleus of the cell. In tumorigenesis, RLIP76 emerges as a common feature for the solid tumor growth. RLIP76 is ubiquitously expressed in various tissues including the ovary. Interestingly, the similar physiological events in obtaining an adequate supply of nutrient by gaining access to the host vascular system are required either for corpus luteum formation or tumor development. In addition, the identical angiogenesis modulators were found in neoplastic and normal ovaries. Our previous study involving RLIP76−/− mice implanted with melanoma or carcinoma cell conclusively demonstrated that RLIP76 is necessary for angiogenesis and neovascularization of primary solid tumors. RLIP76 plays an essential role in tumor angiogenesis through the regulation of pro-angiogenic factors such as vascular endothelial growth factor (VEGF) and hypoxia-inducible factor-1 (HIF-1). In certain previous studies, those pro-angiogenic factors were found significantly to be upregulated during the corpus luteum formation. To that, the following review will discuss the likelihood of RLIP76 role in ovarian corpus luteum.

RLIP: An existential requirement for breast carcinogenesis

Breast cancer (BC) is the most common cancer among women worldwide. Due to its complexity in nature, effective BC treatment can encounter many challenges. The human RALBP1 gene encodes a 76-kDa splice variant protein, RLIP (ral-binding protein1, RalBP1), a stress-protective mercapturic acid pathway (MAP) transporter protein, that also plays a key role in regulating clathrin-dependent endocytosis (CDE) as a Ral effector. Growing evidence shows that targeting RLIP may be an effective strategy in cancer therapy, as RLIP is over-expressed in multiple cancers and is known to induce resistance to apoptosis and chemotherapeutic drugs. Recent studies demonstrated that RLIP is expressed in human BC tissues, as well as BC cell lines. Knockdown of RLIP resulted in apoptotic death of BC cells in vitro, and targeted inhibition and depletion of RLIP resulted in regression of BC in xenograft studies of nude mice. Signaling studies showed that RLIP depletion inhibited endocytosis and differentially regulated signaling to Akt, Myc, and ERK1/2. However, the proliferation and multi-specific transport mechanisms that promote RLIP-mediated cell death in BC are not well understood. In this review, we will discuss a missing but an essentially determining and connecting piece of the puzzle on the understanding of proliferation and transport mechanisms by focused analyses of the apoptotic, drug- and radiation-sensitivity regulated by RLIP, a stress-responsive non-ATP-binding cassette (ABC), high capacity MAP transporter, in breast cancer.

RLIP inhibition suppresses breast-to-lung metastasis

Breast tumor metastasis is a leading cause of cancer-related deaths worldwide. Breast cancer (BC) cells frequently metastasize to the lungs, where they pose a formidable therapeutic challenge. In the current study, we evaluated the anti-proliferative and anti-metastatic effects of 2'-hydroxyflavanone (2HF) and RLIP inhibition in an array of triple-negative BC cell lines and an orthotopic mouse model of breast-to-lung metastasis. Compared to control treatment, RLIP inhibition reduced in-vitro cell viability and suppressed the migratory and invasive potential of BC cells. In-vitro studies showed that 2HF treatment reduced the expression of RLIP, KRAS, pERK, pSTAT3, and pP70S6K. Further, mice orthotopically implanted with lung-seeking luciferase-expressing TMD231 cells were treated with 2HF (50 mg/kg, b.w.), RLIP antisense (RAS; 5 mg/kg, b.w.), RLIP antibody (Rab; 5 mg/kg, b.w.) or a combination of 2HF + RAS + Rab. 2HF-, RAS-, and Rab-treated mice exhibited significantly lower primary tumor weight and reduced lung metastasis compared to control mice. Mice treated with a combination of 2HF + RAS + Rab exhibited no metastasis and significantly lower tumor weight than the single agent-treated mice. Collectively, our results suggest that 2HF has potential to be combined with RLIP inhibition/depletion to more effectively suppress primary breast tumor growth and metastasis to the lungs.

Anticancer activity of 2'-hydroxyflavanone towards lung cancer

In previous studies, we found that 2'-hydroxyflavonone (2HF), a citrus flavonoid, inhibits the growth of renal cell carcinoma in a VHL-dependent manner. This was associated with the inhibition of glutathione S-transferases (GSTs), the first step enzyme of the mercapturic acid pathway that catalyzes formation of glutathione-electrophile conjugates (GS-E). We studied 2HF in small cell (SCLC) and non-small cell (NSCLC) lung cancer cell lines for sensitivity to 2HF antineoplastic activity and to determine the role of the GS-E transporter Rlip (Ral-interacting protein; RLIP76; RALBP1) in the mechanism of action of 2HF. Our results show that 2HF induced apoptosis in both histological types of lung cancer and inhibited proliferation and growth through suppression of CDK4, CCNB1, PIK3CA, AKT and RPS6KB1 (P70S6K) signaling. Increased E-cadherin and reduced fibronectin and vimentin indicated inhibition of epithelial-mesenchymal transition. Additionally, 2HF inhibited efflux of doxorubicin and increased its accumulation in the cells, but did not add to the transport inhibitory effect of anti-Rlip antibodies alone. Binding of Rlip to 2HF was evident from successful purification of Rlip by 2HF affinity chromatography. Consistent with increased drug accumulation, combined treatment with 1-chloro-2, 4-dinitrobenzene, reduced the GI50 of 2HF by an order of magnitude. Results of in-vivo nude mouse xenograft studies of SCLC and NSCLC, which showed that orally administered 2HF inhibited growth of both histological types of lung cancer, confirmed in-vitro study results. Our result suggest that Rlip inhibition is likely a mechanism of action. Our findings are basis of proposing 2HF as therapeutic or preventative drug for lung cancer.

SMC1A is associated with radioresistance in prostate cancer and acts by regulating epithelial-mesenchymal transition and cancer stem-like properties

Prostate cancer is one of the most commonly diagnosed cancers and a pressing health challenge in men worldwide. Radiation therapy (RT) is widely considered a standard therapy for advanced as well as localized prostate cancer. Although this primary therapy is associated with high cancer control rates, up to one-third of patients undergoing radiation therapy becomes radio-resistant and/or has tumor-relapse/recurrence. Therefore, focus on new molecular targets and pathways is essential to develop novel radio-sensitizing agents for the effective and safe treatment of prostate cancer. Here, we describe functional studies that were performed to investigate the role of structural maintenance of chromosome-1 (SMC1A) in radioresistance of metastatic prostate cancer cells. Short hairpin RNA (shRNA) was used to suppress SMC1A in metastatic castration-resistant prostate cancer cells, DU145 and PC3. Clonogenic survival assays, Western blot, RT-PCR, and γ-H2AX staining were used to assess the effect of SMC1A knockdown on radiation sensitivity of these prostate cancer cells. We demonstrate that SMC1A is overexpressed in human prostate tumors compared to the normal adjacent tissue. SMC1A knockdown limits the clonogenic potential, epithelial-mesenchymal transition (EMT), and cancer stem-like cell (CSC) properties of DU145 and PC3 cells and enhanced efficacy of RT in these cells. Targeted inhibition of SMC1A not only plays a critical role in overcoming radio-resistance in prostate cancer cells, but also suppresses self-renewal and the tumor-propagating potential of x-irradiated cancer cells. We propose that SMC1A could be a potential molecular target for the development of novel radio-sensitizing therapeutic agents for management of radio-resistant metastatic prostate cancer.

2'-Hydroxyflavanone inhibits in vitro and in vivo growth of breast cancer cells by targeting RLIP76

Consumption of citrus-fruits is associated with reduced incidence of breast cancer (BC), the most common cancer diagnosed in women across the globe. In this study, we investigated the anticancer potential of 2-Hydroxyflavanone (2HF) in BC. 2HF, a citrus-bioflavonoid, has demonstrated anticancer properties in various cancers, but its anticancer role in BC has not been well studied. We investigated the in vitro and in vivo growth inhibitory effects of 2HF in an array of BC lines and in xenograft mouse models of ER-positive and HER2-positive BC cells. Compared to control, 2HF treatment reduced cell viability and suppressed migratory and invasive potential of BC cells, while, no growth inhibitory effects were observed in non-tumorigenic breast epithelial cells. Further, 2HF inhibited the expression of RLIP76, a stress-defensive and anti-apoptotic protein, which is over-expressed in BC cells and simultaneously reduced proliferation of BC cells. Nude mice bearing MCF7 or SKBR3 BC cells xenografts treated with either 2HF or targeting RLIP76 by RLIP76-antisense or RLIP76-antibody treatment had significantly lower tumor-weight as compared to corresponding controls. In addition, Western-blotting and immunohistochemical analysis of tumor tissue from control and treatment group mice showed that 2HF decreased protein expression levels of RLIP76, and the decrease was similar to those seen following RLIP76-antisense treatment. Furthermore, 2HF decreased expression of Ki67, CD31, vimentin, inhibited phosphorylation of Akt and expression of survivin and Bcl2, and increased levels of Bax, E-cadherin, and cleaved-PARP. Therefore, our results indicate that 2HF may suppress BC growth in vitro and in vivo by targeting RLIP76, and may serve as a potential adjuvant treatment in BC patients.

Metastasis of breast tumor cells to brain is suppressed by targeting RLIP alone and in combination with 2'-Hydroxyflavanone

Brain metastasis is an important cause of morbidity and mortality in cancer-patients. Breast tumor cells frequently metastasize to brain and initiate severe therapeutic complications. In the present study, we evaluated the anti-metastatic effects of 2'-hydroxyflavanone (2HF) alone and in combination with RLIP targeted therapy in a novel murine model of breast tumor metastasis. The MDA-MB231Br (brain-seeking) breast cancer (BC) cells stably-transfected with luciferase were injected into the left-ventricle of NSG mouse heart and the migration of cells to brain was monitored using a non-invasive bioluminescent imaging system. To evaluate the tumor growth suppressive effects, mice were given 2HF (50 mg/kg, b.w., alternate days orally), RLIP-antibody (Rab; 5 mg/kg, b.w., weekly i.p.) or combination of 2HF+Rab starting day1 after intra-cardiac injection. Our results reveal that 2HF and Rab significantly prevented the metastasis of BC cells to brain. Further, mice treated with combination of 2HF+Rab exhibited no metastasis as compared to either or the single agent-treated mice. This study for the first time demonstrates the anti-metastatic effects of 2HF and RLIP-inhibition in-vivo in a novel breast tumor metastasis model and provides the rationale for further clinical investigation.

2'-Hydroxyflavanone effectively targets RLIP76-mediated drug transport and regulates critical signaling networks in breast cancer

Breast cancer (BC) is the most common cancer in women. Estrogen, epidermal growth factor receptor 2 (ERBB2, HER2), and oxidative stress represent critical mechanistic nodes associated with BC. RLIP76 is a major mercapturic acid pathway transporter whose expression is increased in BC. In the quest of a novel molecule with chemopreventive and chemotherapeutic potential, we evaluated the effects of 2'-Hydroxyflavanone (2HF) in BC. 2HF enhanced the inhibitory effects of RLIP76 depletion and also inhibited RLIP76-mediated doxorubicin transport in BC cells. RNA-sequencing revealed that 2HF induces strong reversal of the gene expression pattern in ER⁺MCF7, HER2⁺ SKBR3 and triple-negative MDA-MB-231 BC cells with minimal effects on MCF10A normal breast epithelial cells. 2HF down regulated ERα and enhanced inhibitory effects of imatinib mesylate/Gleevec in MCF7 cells. 2HF also down regulated ERα and HER2 gene networks in MCF7 and SKBR3 cells, respectively. 2HF activated TP53 and inhibited TGFβ1 canonical pathway in MCF7 and MDA-MB-231 BC cells. 2HF also regulated the expression of a number of critical prognostic genes of MammaPrint panel and their upstream targets including TP53, CDKN2A and MYC. The collective findings from this study provide a comprehensive, direct and integrated evidence for the benefits of 2HF in targeting major and clinically relevant mechanistic regulators of BC.

Rlip depletion prevents spontaneous neoplasia in TP53 null mice

Mice that have homozygous deletion of the p53 tumor suppressor protein universally die of malignancy, generally before 6 months of age. We show that hemizygous deficiency of RALBP1 (RLIP76 or Rlip) confers a degree of protection from spontaneous malignancy that has never previously been observed. This discovery introduces a paradigm for p53 function, in which Rlip plays a central role as an effector that appears necessary for the cancer susceptibility of p53 null mice. Because p53 loss has a powerful effect on genomic instability that contributes to the initiation and promotion of cancers and to drug and radiation resistance in humans, our findings provide a method for prevention and therapy of p53-deficient cancer.

TP53 (p53) is a tumor suppressor whose functions are lost or altered in most malignancies. p53 homozygous knockout (p53^−/−) mice uniformly die of spontaneous malignancy, typically T-cell lymphoma. RALBP1 (RLIP76, Rlip) is a stress-protective, mercapturic acid pathway transporter protein that also functions as a Ral effector involved in clathrin-dependent endocytosis. In stark contrast to p53^−/− mice, Rlip^−/− mice are highly resistant to carcinogenesis. We report here that partial Rlip deficiency induced by weekly administration of an Rlip-specific phosphorothioate antisense oligonucleotide, R508, strongly inhibited spontaneous as well as benzo(a)pyrene-induced carcinogenesis in p53^−/− mice. This treatment effectively prevented large-scale methylomic and transcriptomic abnormalities suggestive of inflammation found in cancer-bearing p53^−/− mice. The remarkable efficiency with which Rlip deficiency suppresses spontaneous malignancy in p53^−/− mice has not been observed with any previously reported pharmacologic or genetic intervention. These findings are supported by cross-breeding experiments demonstrating that hemizygous Rlip deficiency also reduces the spontaneous malignancy phenotype of p53^+/− mice. Rlip is found on the cell surface, and antibodies directed against Rlip were found to inhibit growth and promote apoptosis of cell lines as effectively as Rlip siRNA. The work presented here investigates several features, including oxidative DNA damage of the Rlip–p53 association in malignant transformation, and offers a paradigm for the mechanisms of tumor suppression by p53 and the prospects of suppressing spontaneous malignancy in hereditary cancer syndromes such as Li-Fraumeni.

Extracellular oxidation in cystic fibrosis airway epithelium causes enhanced EGFR/ADAM17 activity

The EGF receptor (EGFR)/a disintegrin and metalloproteinase 17 (ADAM17) signaling pathway mediates the shedding of growth factors and secretion of cytokines and is involved in chronic inflammation and tissue remodeling. Since these are hallmarks of cystic fibrosis (CF) lung disease, we hypothesized that CF transmembrane conductance regulator (CFTR) deficiency enhances EGFR/ADAM17 activity in human bronchial epithelial cells. In CF bronchial epithelial CFBE41o^- cells lacking functional CFTR (iCFTR^-) cultured at air-liquid interface (ALI) we found enhanced ADAM17-mediated shedding of the EGFR ligand amphiregulin (AREG) compared with genetically identical cells with induced CFTR expression (iCFTR⁺). Expression of the inactive G551D-CFTR did not have this effect, suggesting that active CFTR reduces EGFR/ADAM17 activity. This was confirmed in CF compared with normal differentiated primary human bronchial epithelial cells (HBEC-ALI). ADAM17-mediated AREG shedding was tightly regulated by the EGFR/MAPK pathway. Compared with iCFTR⁺ cells, iCFTR^- cells displayed enhanced apical presentation and phosphorylation of EGFR, in accordance with enhanced EGFR/ADAM17 activity in CFTR-deficient cells. The nonpermeant natural antioxidant glutathione (GSH) strongly inhibited AREG release in iCFTR and in primary HBEC-ALI, suggesting that ADAM17 activity is directly controlled by extracellular redox potentials in differentiated airway epithelium. Furthermore, the fluorescent redox probe glutaredoxin 1-redox-sensitive green fluorescent protein-glycosylphosphatidylinositol (Grx1-roGFP-GPI) indicated more oxidized conditions in the extracellular space of iCFTR^- cells, consistent with the role of CFTR in GSH transport. Our data suggest that in CFTR-deficient airway epithelial cells a more oxidized state of the extracellular membrane, likely caused by defective GSH secretion, leads to enhanced activity of the EGFR/ADAM17 signaling axis. In CF lungs this could contribute to tissue remodeling and hyperinflammation.

Ral signaling pathway in health and cancer

The Ral (Ras-Like) signaling pathway plays an important role in the biology of cells. A plethora of effects is regulated by this signaling pathway and its prooncogenic effectors. Our team has demonstrated the overactivation of the RalA signaling pathway in a number of human malignancies including cancers of the liver, ovary, lung, brain, and malignant peripheral nerve sheath tumors. Additionally, we have shown that the activation of RalA in cancer stem cells is higher in comparison with differentiated cancer cells. In this article, we review the role of Ral signaling in health and disease with a focus on the role of this multifunctional protein in the generation of therapies for cancer. An improved understanding of this pathway can lead to development of a novel class of anticancer therapies that functions on the basis of intervention with RalA or its downstream effectors.

Regulatory roles of glutathione-S-transferases and 4-hydroxynonenal in stress-mediated signaling and toxicity

Glutathione-S-Transferases (GSTs) have primarily been thought to be xenobiotic metabolizing enzymes that protect cells from toxic drugs and environmental electrophiles. However, in last three decades, these enzymes have emerged as the regulators of oxidative stress-induced signaling and toxicity. 4-Hydroxy-trans 2-nonenal (HNE) an end-product of lipid peroxidation, has been shown to be a major determinant of oxidative stress-induced signaling and toxicity. HNE is involved in signaling pathways, including apoptosis, proliferation, modulation of gene expression, activation of transcription factors/repressors, cell cycle arrest, and differentiation. In this article, available evidence for a major role of GSTs in the regulation of HNE-mediated cell signaling processes through modulation of the intracellular levels of HNE is discussed.

2'-Hydroxyflavanone: A novel strategy for targeting breast cancer

Breast cancer is the most common cancer in women that is driven by cross-talk with hormonal and cellular signaling pathways. The natural phytochemicals, due to broad-spectrum anti-inflammatory and anti-cancerous properties, present with novel opportunities for targeting breast cancer. Intake of citrus fruits is known to reduce the risk for incidence of breast cancer. Hence, we tested the efficacy of citrus flavonoid 2'-hydroxyflavanone (2HF) in breast cancer. 2HF inhibited survival, clonogenic ability, cell cycle progression and induced apoptosis in breast cancer cells. 2HF also decreased VEGF levels and inhibited migratory capacity of breast cancer cells. Administration of 2HF led to regression of triple-negative MDA-MB-231 tumors in the mice xenograft model. 2HF decreased the levels of RLIP76 both in vitro studies and in vivo MDA-MB-231 xenograft model of breast cancer. Western blot and histopathological analyses of resected tumors showed a decline in the levels of survival and proliferation markers Ki67, pAkt, survivin, and cell cycle proteins CDK4 and cyclin B1. 2HF treatment led to inhibition of angiogenesis as determined by decreased VEGF levels in vitro and angiogenesis marker CD31 in vivo. 2HF reversed the pro-/anti-apoptotic ratio of BAX/BCL-2 by decreasing anti-apoptotic protein BCL-2 and increasing pro-apoptotic proteins BAX and BIM in vivo. 2HF also decreased the mesenchymal markers vimentin and fibronectin along with causing a parallel increase in pro-differentiation protein E-cadherin. Collectively, the ability of 2HF to decrease RLIP76, VEGF and regulate critical proliferative, apoptotic and differentiation proteins together provides strong rationale to further develop 2HF based interventions for targeting breast cancer.

RalBP1 and p19-VHL play an oncogenic role, and p30-VHL plays a tumor suppressor role during the blebbishield emergency program

Cancer stem cells evade apoptotic death by blebbishield emergency program, which constructs blebbishields from apoptotic bodies and drives cellular transformation. Von Hippel-Lindau (VHL) plays both tumor suppressor and oncogenic roles, and the reason behind is poorly understood. Here we demonstrate that dimers and trimers of p19-VHL interact with RalBP1 to construct blebbishields. Expression of RalBP1, p19-VHL, and high-molecular weight VHL is required to evade apoptosis by blebbishield-mediated transformation. In contrast, p30-VHL plays a tumor suppressor role by inhibiting blebbishield-mediated transformation. Furthermore, target genes of VHL that suppress oxidative stress were elevated during blebbishield-mediated cellular transformation. Thus, RalBP1 and p19-VHL play an oncogenic role, whereas p30-VHL plays a tumor suppressor role during the blebbishield emergency program by regulating oxidative stress management genes.

Didymin: an orally active citrus flavonoid for targeting neuroblastoma

Neuroblastoma, a rapidly growing yet treatment responsive cancer, is the third most common cancer of children and the most common solid tumor in infants. Unfortunately, neuroblastoma that has lost p53 function often has a highly treatment-resistant phenotype leading to tragic outcomes. In the context of neuroblastoma, the functions of p53 and MYCN (which is amplified in ~25% of neuroblastomas) are integrally linked because they are mutually transcriptionally regulated, and because they together regulate the catalytic activity of RNA polymerases. Didymin is a citrus-derived natural compound that kills p53 wild-type as well as drug-resistant p53-mutant neuroblastoma cells in culture. In addition, orally administered didymin causes regression of neuroblastoma xenografts in mouse models, without toxicity to non-malignant cells, neural tissues, or neural stem cells. RKIP is a Raf-inhibitory protein that regulates MYCN activation, is transcriptionally upregulated by didymin, and appears to play a key role in the anti-neuroblastoma actions of didymin. In this review, we discuss how didymin overcomes drug-resistance in p53-mutant neuroblastoma through RKIP-mediated inhibition of MYCN and its effects on GRK2, PKCs, Let-7 micro-RNA, and clathrin-dependent endocytosis by Raf-dependent and -independent mechanisms. In addition, we will discuss studies supporting potential clinical impact and translation of didymin as a low cost, safe, and effective oral agent that could change the current treatment paradigm for refractory neuroblastoma.

RLIP76 Inhibition: A Promising Developmental Therapy for Neuroblastoma

Refractory and relapsed neuroblastoma (NB) present with significant challenges in clinical management. Though primary NBs largely with wild-type p53 respond well to interventions, dysfunctional signaling in the p53 pathways in a MYCN oncogene driven background is found in a number of children with NB. The p53-mutant NB is largely unresponsive to available therapies and p53-independent targeted therapeutics represents a vital need in pediatric oncology. We analyzed the findings on mercapturic acid pathway (MAP) transporter RLIP76, which has broad and critical effects on multiple pathways as essential for carcinogenesis, oxidative stress and drug-resistance, is over-expressed in NB. RLIP76 inhibition by antibodies or depletion by antisense causes apoptosis and sensitization to chemo-radiotherapy in many cancers. In addition, recent studies indicate that the interactions between p53, MYCN, and WNT regulate apoptosis resistance and protein ubiquitination. RLIP76 and p53 interact with each other and colocalize in NB cells. Targeted depletion/inhibition of RLIP76 causes apoptosis and tumor regression in NB irrespective of p53 status. In the present review, we discuss the mechanisms and the role of RLIP76 in oxidative stress, drug-resistance and clathrin-dependent endocytosis (CDE), and analyze the molecular basis for the role of RLIP76 targeted approaches in the context principal drivers of NB pathogenesis, progression and drug-resistance. The evidence from RLIP76 studies in other cancers, when taken in the context of our recent RLIP76 focused mechanistic studies in NB, provides strong basis for further characterization and development of RLIP76 targeted therapies for NB.

Targeting the mercapturic acid pathway and vicenin-2 for prevention of prostate cancer

Prostate cancer (CaP) is often androgen-sensitive malignancy and regresses upon inhibition of androgen signaling. However, CaP, nearly always develops androgen resistance and progresses to aggressive and lethal androgen-independent CaP, which lacks satisfactory therapy. For metastatic CaP, patients are often treated with Taxotere (docetaxel), a cytoskeleton-targeted chemotherapy drug, that provides transient palliative benefit but to which patients rapidly develop drug-resistance. Combination chemotherapy may be used instead, but is more toxic and adds little clinically relevant benefit over docetaxel. Therefore, novel strategies to enhance docetaxel efficacy are needed to effectively treat patients with metastatic CaP. The mercapturic acid pathway, which metabolizes genotoxic and pro-apoptotic toxins, is over-expressed in CaP and plays an important role in carcinogenesis, metastasis and therapy-resistance of CaP. Vicenin-2, a flavonoid derived from Tulsi (holy basil) as an active compound, inhibits the growth of CaP and increases the anti-tumor activity of docetaxel in-vitro and in-vivo. Taken together, the combination of vicenin-2 and docetaxel could be highly effective in the treatment of advanced and metastatic CaP due to their multi-targeting anti-tumor potential.

Antioxidant role of glutathione S-transferases: 4-Hydroxynonenal, a key molecule in stress-mediated signaling

4-Hydroxy-2-trans-nonenal (4HNE), one of the major end products of lipid peroxidation (LPO), has been shown to induce apoptosis in a variety of cell lines. It appears to modulate signaling processes in more than one way because it has been suggested to have a role in signaling for differentiation and proliferation. It has been known that glutathione S-transferases (GSTs) can reduce lipid hydroperoxides through their Se-independent glutathione-peroxidase activity and that these enzymes can also detoxify LPO end-products such as 4HNE. Available evidence from earlier studies together with results of recent studies in our laboratories strongly suggests that LPO products, particularly hydroperoxides and 4HNE, are involved in the mechanisms of stress-mediated signaling and that it can be modulated by the alpha-class GSTs through the regulation of the intracellular concentrations of 4HNE. We demonstrate that 4HNE induced apoptosis in various cell lines is accompanied with c-Jun-N-terminal kinase (JNK) and caspase-3 activation. Cells exposed to mild, transient heat or oxidative stress acquire the capacity to exclude intracellular 4HNE at a faster rate by inducing GSTA4-4 which conjugates 4HNE to glutathione (GSH), and RLIP76 which mediates the ATP-dependent transport of the GSH-conjugate of 4HNE (GS-HNE). The balance between formation and exclusion promotes different cellular processes - higher concentrations of 4HNE promote apoptosis; whereas, lower concentrations promote proliferation. In this article, we provide a brief summary of the cellular effects of 4HNE, followed by a review of its GST-catalyzed detoxification, with an emphasis on the structural attributes that play an important role in the interactions with alpha-class GSTA4-4. Taken together, 4HNE is a key signaling molecule and that GSTs being determinants of its intracellular concentrations, can regulate stress-mediated signaling, are reviewed in this article.

RLIP76 Targeted Therapy for Kidney Cancer

Despite recent improvements in chemotherapeutic approaches to treating kidney cancer, this malignancy remains deadly if not found and removed at an early stage of the disease. Kidney cancer is highly drug-resistant, which may at least partially result from high expression of transporter proteins in the cell membranes of kidney cells. Although these transporter proteins can contribute to drug-resistance, targeting proteins from the ATP-binding cassette transporter family has not been effective in reversing drug-resistance in kidney cancer. Recent studies have identified RLIP76 as a key stress-defense protein that protects normal cells from damage caused by stress conditions, including heat, ultra-violet light, X-irradiation, and oxidant/electrophilic toxic chemicals, and is crucial for protecting cancer cells from apoptosis. RLIP76 is the predominant glutathione-electrophile-conjugate (GS-E) transporter in cells, and inhibiting it with antibodies or through siRNA or antisense causes apoptosis in many cancer cell types. To date, blocking of RLIP76, either alone or in combination with chemotherapeutic drugs, as a therapeutic strategy for kidney cancer has not yet been evaluated in human clinical trials, although there is considerable potential for RLIP76 to be developed as a therapeutic agent for kidney cancer. In the present review, we discuss the mechanisms underlying apoptosis caused by RLIP76 depletion, the role of RLIP76 in clathrin-dependent endocytosis deficiency, and the feasibility of RLIP76-targeted therapy for kidney cancer.

Oncolytic adenovirus-mediated short hairpin RNA targeting MYCN gene induces apoptosis by upregulating RKIP in neuroblastoma

The amplification of MYCN is a typical characteristic of aggressive neuroblastomas, whereas acquired mutations of p53 lead to refractory and relapsed cases. We had previously examined the applicability of the replication-competent oncolytic adenovirus, ZD55-shMYCN, to deliver a short hairpin RNA targeting MYCN gene for p53-null and MYCN-amplified neuroblastoma cell line LA1-55N. Our data have shown that ZD55-shMYCN has an additive tumor growth inhibitory response through shRNA-mediated MYCN knockdown and ZD55-mediated cancer cell lysis. In this regard, ZD55-shMYCN can downregulate MYCN and perform anticancer effects, thereby acquiring significance in the administration of MYCN-amplified and p53-null neuroblastomas. Hence, we further investigated the anticancer properties of ZD55-shMYCN in neuroblastomas. Our data showed that ZD55-shMYCN induced G2/M arrest via decreasing the levels of cyclin D1 and cyclin B1 irrespective of p53 status. ZD55-shMYCN effectively induced apoptosis in neuroblastomas through activation of caspase-3 and enhancing PARP cleavage. Furthermore, ZD55-shMYCN could downregulate phosphoinositide 3-kinase and pAkt and upregulate RKIP levels. Similarly, pro-apoptosis was revealed by the histopathologic examination of paraffin-embedded section of resected tumors of mice xenograft. In vitro and in vivo studies, we elucidate the apoptosis properties and mechanisms of action of ZD55-shMYCN, which provide a promising approach for further clinical development.

Novel compound 1,3-bis (3,5-dichlorophenyl) urea inhibits lung cancer progression

The successful clinical management of lung cancer is limited by frequent loss-of-function mutations in p53 which cooperates with chronic oxidant-stress induced adaptations in mercapturic acid pathway (MAP) which in turn regulates critical intracellular signaling cascades that determine therapeutic refractoriness. Hence, we investigated the anti-cancer effects and mechanisms of action of a novel compound called 1,3-bis(3,5-dichlorophenyl) urea (COH-SR4) in lung cancer. Treatment with COH-SR4 effectively inhibited the survival and clonogenic potential along with inducing apoptosis in lung cancer cells. COH-SR4 treatment caused the inhibition of GST activity and G0/G1 cell cycle arrest and inhibited the expression of cell cycle regulatory proteins CDK2, CDK4, cyclin A, cyclin B1, cyclin E1, and p27. The COH-SR4 activated AMPK pathway and knock-down of AMPK partially reversed the cytotoxic effects of COH-SR4 in lung cancer. COH-SR4 treatment lead to regression of established xenografts of H358 lung cancer cells without any overt toxicity. The histopathology of resected tumor sections revealed an increase in pAMPK, a decrease in the nuclear proliferative marker Ki67 and angiogenesis marker CD31. Western-blot analyses of resected tumor lysates revealed a decrease in pAkt and anti-apoptotic protein Bcl2 along with an increase in pAMPK, pro-apoptotic protein Bax and cleaved PARP levels. Importantly, COH-SR4 lead to decrease in the mesenchymal marker vimentin and increase in the normal epithelial marker E-cadherin. The results from our in-vitro and in-vivo studies reveal that COH-SR4 represents a novel candidate with strong mechanistic relevance to target aggressive and drug-resistant lung tumors.

RLIP76 protein knockdown attenuates obesity due to a high-fat diet

Feeding a Western high-fat diet (HFD) to C57BL/6 mice induces obesity, associated with a chronic inflammatory state, lipid transport, and metabolic derangements, and organ system effects that particularly prominent in the kidneys. Here, we report that RLIP76 homozygous knock-out (RLIP76(-/-)) mice are highly resistant to obesity as well as these other features of metabolic syndrome caused by HFD. The normal increase in pro-inflammatory and fibrotic markers associated with HFD induced obesity in wild-type C57B mice was broadly and nearly completely abrogated in RLIP76(-/-) mice. This is a particularly striking finding because chemical markers of oxidative stress including lipid hydroperoxides and alkenals were significantly higher in RLIP76(-/-) mice. Whereas HFD caused marked suppression of AMPK in wild-type C57B mice, RLIP76(-/-) mice had baseline activation of AMP-activated protein kinase, which was not further affected by HFD. The baseline renal function was reduced in RLIP76(-/-) mice as compared with wild-type, but was unaffected by HFD, in marked contrast to severe renal impairment and glomerulopathy in the wild-type mice given HFD. Our findings confirm a fundamental role of RLIP76 in regulating the function of obesity-promoting pro-inflammatory cytokines, and provide a novel mechanism for targeted therapy of obesity and metabolic syndrome.

Role of SMC1 in overcoming drug resistance in triple negative breast cancer

Triple-negative breast cancer (TNBC) is one of the hardest subtypes of breast cancer to treat due to the heterogeneity of the disease and absence of well-defined molecular targets. Emerging evidence has shown the role of cohesin in the formation and progression of various cancers including colon and lung cancer but the role of cohesin in breast cancer remains elusive. Our data showed that structural maintenance of chromosome 1 (SMC1), a subunit of the cohesin protein complex, is differentially overexpressed both at RNA and protein level in a panel of TNBC cell lines as compared to normal epithelial or luminal breast cancer cells, suggesting that the amplified product of this normal gene may play role in tumorigenesis in TNBC. In addition, our results show that induced overexpression of SMC1 through transient transfection enhanced cell migration and anchorage independent growth while its suppression with targeted small interfering RNA (siRNA) reduced the migration ability of TNBC cells. Increased expression of SMC1 also lead to increase in the mesenchymal marker vimentin and decrease in the normal epithelial marker, E-cadherin. Immunocytochemical studies along with flow cytometry and cell fractionation showed the localization of SMC1 in the nucleus, cytoplasm and also in the plasma membrane. The knockdown of SMC1 by siRNA sensitized the TNBC cells towards a PARP inhibitor (ABT-888) and IC₅₀ was approximately three fold less than ABT-888 alone. The cytotoxic effect of combination of SMC1 suppression and ABT-888 was also confirmed by the colony propagation assay. Taken together, these studies report for the first time that SMC1 is overexpressed in TNBC cells where it plays a role in cell migration and drug sensitivity, and thus provides a potential therapeutic target for this highly invasive breast cancer subtype.

P300 regulates the human RLIP76 promoter activity and gene expression

A 76-kDa Ral-interacting protein (RLIP76) has been implicated in the pathogenesis of cancer and diabetes. It is often over expressed in human malignant cell lines and human tumor samples and has been associated with metastasis and chemoresistance. RLIP76 homozygous knockout mice exhibit increased insulin sensitivity, hypoglycemia, and hypolipidemia, and resist cancer development. Little is known about the mechanism by which the expression of RLIP76 is regulated. In the present study, we functionally characterized the RLIP76 promoter using deletion mapping and mutational analysis to investigate the regulation of RLIP76 transcription. We have identified the promoter regions important for RLIP76 transcription, including a strong cis-activating element in the proximal promoter containing overlapping consensus cMYB and cETS binding sites. Transcription factor cMYB and the coactivator p300 associated with RLIP76 gene promoter as shown by CHIP assay. Knockdown of p300 in HEK293 cells reduced the activity of the promoter fragment containing wild type cMYB/cETS binding site in comparison to that with deleted or mutated cMYB/cETS binding site. Knockdown of p300 also decreased the RLIP76 expression as indicated by immunoblotting, immunocytochemistry and flow cytometry analysis. Thus, we report for the first time that p300 associates with the RLIP76 promoter via an overlapping cMYB and cETS binding site and regulates RLIP76 promoter activity and its expression.

Emerging treatments in lung cancer - targeting the RLIP76 molecular transporter

Multidrug resistance in lung cancer cells is a significant obstacle in the treatment of lung cancer. Resistance to chemotherapeutic agents is often the result of efflux of the drugs from cancer cells, mediated by adenosine triphosphate (ATP)-dependent drug transport across the plasma membrane. Thus, identifying molecular targets in the cancer cell transport machinery could be a key factor in successful combinatorial therapy, along with chemotherapeutic drugs. The transport protein Ral-interacting protein of 76 kDa (RLIP76), also known as Ral-binding protein 1 (RalBP1), is a highly promising target for lung cancer treatment. RLIP76 is an ATP-dependent non-ATP-binding cassette (ABC) transporter, responsible for the major transport function in many cells, including many cancer cell lines, causing efflux of glutathione-electrophile conjugates of both endogenous metabolites and environmental toxins. RLIP76 is expressed in most human tissues, and is overexpressed in non-small-cell lung cancer cell lines and in many tumor types. The blockade of RLIP76 by various approaches has been shown to increase the sensitivity to radiation and chemotherapeutic drugs, and leads to apoptosis in cells. In xenograft tumor models in mice, RLIP76 blockade or depletion results in complete and sustained regression across many cancer cell types, including lung cancer cells. In addition to its transport function, RLIP76 has many other cellular and physiological functions based on its domain structure, which includes a unique Ral-binding domain and a Rho GTPase activating protein (RhoGAP)-catalytic domain as well as docking sites for multiple signaling proteins. As a Ral effector, RhoGAP, and adapter protein, RLIP76 has been shown to play important roles in endocytosis, mitochondrial fission, cell spreading and migration, actin dynamics during gastrulation, and Ras-induced tumorigenesis. Additionally, RLIP76 is also important for stromal cell function in tumors, as it was recently shown to be required for efficient endothelial cell function and angiogenesis in solid tumors. However, RLIP76 knockout mice are viable, and blockade effects appear to be selective for implanted tumors in mice, suggesting the possibility that RLIP76-targeting drugs may be successful in clinical trials. In this review, we outline the many cellular and physiological functions of RLIP76 in normal and cancer cells, and discuss the potential for RLIP76-based therapeutics in lung cancer treatment.

RALBP1/RLIP76 depletion in mice suppresses tumor growth by inhibiting tumor neovascularization

RalBP1/RLIP76 is a widely expressed multifunctional protein that binds the Ral and R-Ras small GTPases. In the mouse, RLIP76 is nonessential but its depletion or blockade promotes tumorigenesis and heightens the sensitivity of normal and tumor cells to radiation and cytotoxic drugs. However, its pathobiologic functions, which support tumorigenesis, are not well understood. Here, we show that RLIP76 is required for angiogenesis and for efficient neovascularization of primary solid tumors. Tumor growth from implanted melanoma or carcinoma cells was blunted in RLIP76(-/-) mice. An X-ray microcomputed tomography-based method to model tumor vascular structures revealed defects in both the extent and form of tumor angiogenesis in RLIP76(-/-) mice. Specifically, tumor vascular volumes were diminished and vessels were fewer in number, shorter, and narrower in RLIP76(-/-) mice than in wild-type mice. Moreover, we found that angiogenesis was blunted in mutant mice in the absence of tumor cells, with endothelial cells isolated from these animals exhibiting defects in migration, proliferation, and cord formation in vitro. Taken together, our results establish that RLIP76 is required for efficient endothelial cell function and angiogenesis in solid tumors.

RLIP76 regulates PI3K/Akt signaling and chemo-radiotherapy resistance in pancreatic cancer

Purpose

Pancreatic cancer is an aggressive malignancy with characteristic metastatic course of disease and resistance to conventional chemo-radiotherapy. RLIP76 is a multi-functional cell membrane protein that functions as a major mercapturic acid pathway transporter as well as key regulator of receptor-ligand complexes. In this regard, we investigated the significance of targeting RLIP76 on PI3K/Akt pathway and mechanisms regulating response to chemo-radiotherapy.

Research Design and Methods

Cell survival was assessed by MTT and colony forming assays. Cellular levels of proteins and phosphorylation was determined by Western blot analyses. The impact on apoptosis was determined by TUNEL assay. The anti-cancer effects of RLIP76 targeted interventions in vivo were determined using mice xenograft model of the pancreatic cancer. The regulation of doxorubicin transport and radiation sensitivity were determined by transport studies and colony forming assays, respectively.

Results

Our current studies reveal an encompassing model for the role of RLIP76 in regulating the levels of fundamental proteins like PI3K, Akt, E-cadherin, CDK4, Bcl2 and PCNA which are of specific importance in the signal transduction from critical upstream signaling cascades that determine the proliferation, apoptosis and differentiation of pancreatic cancer cells. RLIP76 depletion also caused marked and sustained regression of established human BxPC-3 pancreatic cancer tumors in nude mouse xenograft model. RLIP76 turned out to be a major regulator of drug transport along with contributing to the radiation resistance in pancreatic cancer.

Conclusions/Significance

RLIP76 represents a mechanistically significant target for developing effective interventions in aggressive and refractory pancreatic cancers.

Novel anti-cancer compounds for developing combinatorial therapies to target anoikis-resistant tumors

Anoikis, a cell death pathway induced by loss of normal cell-matrix attachment or upon adhesion to a non-native matrix, ensures the balance between proliferative potential of normal cells and maintenance of tissue integrity. Thereby, anoikis serves as a potential molecular barrier against oncogenic transformation of normal cells. Cancer cells acquire anoikis resistance for survival and distant metastatic progression. During the acquisition of anoikis resistance, tumors modulate multiple cell signaling parameters through changes in the expression of up-stream receptors and by dynamically calibrating the dependency on down-stream signaling cascades. Many compounds that target the tumor-acquired switches in integrins, tumor antigens, growth factors, metabolic pathways, oxidative and osmotic-stress signaling are in various phases of pre-clinical and clinical development. Combinatorial approaches maximize the therapeutic efficacy and minimize the activation of alternate signaling pathways, which will otherwise contribute to drug resistance. In this regard, an integrated analysis of the mechanisms of action of potential drugs and lead compounds that can target significant nodes of anoikis signaling networks will provide a rational frame-work for further development and clinical use of respective agents, by formulating more effective combinatorial therapies, in patients with distinct drug-sensitivity profiles.