Effects of raf kinase inhibitor protein expression on metastasis and progression of human breast cancer

Biological and therapeutic implications of RKIP in Gastrointestinal Stromal Tumor (GIST): an integrated transcriptomic and proteomic analysis

BACKGROUND

Gastrointestinal stromal tumors (GIST) represent a significant clinical challenge due to their metastatic potential and limited treatment options. Raf kinase inhibitor protein (RKIP), a suppressor of the MAPK signaling pathway, is downregulated in various cancers and acts as a metastasis suppressor. Our previous studies demonstrated low RKIP expression in GIST and its association with poor outcomes. This study aimed to expand on the previous findings and investigate the biological and therapeutic implications of RKIP loss on GIST.

METHODS

To validate the RKIP prognostic significance, its expression was evaluated by immunohistochemistry in 142 bona fide GIST cases. The functional role of RKIP was evaluated in vitro, using the GIST-T1 cell line, which was knocked out for RKIP. The biological and therapeutic implications of RKIP were evaluated by invasion, migration, apoptosis, and 2D / 3D viability assays. Additionally, the transcriptome and proteome of RKIP knockout cells were determined by NanoString and mass spectrometry, respectively.

RESULTS

Immunohistochemical analysis revealed the absence of RKIP in 25.3% of GIST cases, correlating with a tendency toward poor prognosis. Functional assays demonstrated that RKIP knockout increased GIST cells' invasion and migration potential by nearly 60%. Moreover, we found that RKIP knockout cells exhibited reduced responsiveness to Imatinib treatment and higher cellular viability in 2D and 3D in vitro models, as assessed by apoptosis-related protein expression. Through comprehensive genetic and proteomic profiling of RKIP knockout cells, we identified several putative RKIP-regulated proteins in GIST, such as COL3A1.

CONCLUSIONS

Using a multidimensional integrative analysis, we identified, for the first time in GIST, molecules and pathways modulated by RKIP that may potentially drive metastasis and, consequently, poor prognosis in this disease.

Identification of cuproptosis and immune-related gene prognostic signature in lung adenocarcinoma

Background

Cuproptosis is a novel form of programmed cell death that differs from other types such as pyroptosis, ferroptosis, and autophagy. It is a promising new target for cancer therapy. Additionally, immune-related genes play a crucial role in cancer progression and patient prognosis. Therefore, our study aimed to create a survival prediction model for lung adenocarcinoma patients based on cuproptosis and immune-related genes. This model can be utilized to enhance personalized treatment for patients.

Methods

RNA sequencing (RNA-seq) data of lung adenocarcinoma (LUAD) patients were collected from The Cancer Genome Atlas (TCGA) and Gene Expression Omnibus (GEO) databases. The levels of immune cell infiltration in the GSE68465 cohort were determined using gene set variation analysis (GSVA), and immune-related genes (IRGs) were identified using weighted gene coexpression network analysis (WGCNA). Additionally, cuproptosis-related genes (CRGs) were identified using unsupervised clustering. Univariate COX regression analysis and least absolute shrinkage selection operator (LASSO) regression analysis were performed to develop a risk prognostic model for cuproptosis and immune-related genes (CIRGs), which was subsequently validated. Various algorithms were utilized to explore the relationship between risk scores and immune infiltration levels, and model genes were analyzed based on single-cell sequencing. Finally, the expression of signature genes was confirmed through quantitative real-time PCR (qRT-PCR), immunohistochemistry (IHC), and Western blotting (WB).

Results

We have identified 5 Oncogenic Driver Genes namely CD79B, PEBP1, PTK2B, STXBP1, and ZNF671, and developed proportional hazards regression models. The results of the study indicate significantly reduced survival rates in both the training and validation sets among the high-risk group. Additionally, the high-risk group displayed lower levels of immune cell infiltration and expression of immune checkpoint compared to the low-risk group.

Manipulating RKIP reverses the metastatic potential of breast cancer cells

Breast cancer is a common tumor type among women, with a high fatality due to metastasis. Metastasis suppressors encode proteins that inhibit the metastatic cascade independent of the primary tumor growth. Raf kinase inhibitory protein (RKIP) is one of the promising metastasis suppressor candidates. RKIP is reduced or lost in aggressive variants of different types of cancer. A few pre-clinical or clinical studies have capitalized on this protein as a possible therapeutic target. In this article, we employed two breast cancer cells to highlight the role of RKIP as an antimetastatic gene. One is the low metastatic MCF-7 with high RKIP expression, and the other is MDA-MB-231 highly metastatic cell with low RKIP expression. We used high-throughput data to explore how RKIP is lost in human tissues and its effect on cell mobility. Based on our previous work recapitulating the links between RKIP and SNAI, we experimentally manipulated RKIP in the cell models through its novel upstream NME1 and investigated the subsequent genotypic and phenotypic changes. We also demonstrated that RKIP explained the uneven migration abilities of the two cell types. Furthermore, we identified the regulatory circuit that might carry the effect of an existing drug, Epirubicin, on activating gene transcription. In conclusion, we propose and test a potential strategy to reverse the metastatic capability of breast cancer cells by chemically manipulating RKIP expression.

RKIP Pleiotropic Activities in Cancer and Inflammatory Diseases: Role in Immunity

Simple Summary

The human body consists of tissues and organs formed by cells. In each cell there is a switch that allows the cell to divide or not. In contrast, cancer cells have their switch on which allow them to divide and invade other sites leading to death. Over two decades ago, Doctor Kam Yeung, University of Toledo, Ohio, has identified a factor (RKIP) that is responsible for the on/off switch which functions normally in healthy tissues but is inactive or absent in cancers. Since this early discovery, many additional properties have been ascribed to RKIP including its role in inhibiting cancer metastasis and resistance to therapeutics and its role in modulating the normal immune response. This review describes all of the above functions of RKIP and suggesting therapeutics to induce RKIP in cancers to inhibit their growth and metastases as well as inhibit its activity to treat non-cancerous inflammatory diseases.

Abstract

Several gene products play pivotal roles in the induction of inflammation and the progression of cancer. The Raf kinase inhibitory protein (RKIP) is a cytosolic protein that exerts pleiotropic activities in such conditions, and thus regulates oncogenesis and immune-mediated diseases through its deregulation. Herein, we review the general properties of RKIP, including its: (i) molecular structure; (ii) involvement in various cell signaling pathways (i.e., inhibition of the Raf/MEK/ERK pathway; the NF-kB pathway; GRK-2 or the STAT-3 pathway; as well as regulation of the GSK3Beta signaling; and the spindle checkpoints); (iii) regulation of RKIP expression; (iv) expression’s effects on oncogenesis; (v) role in the regulation of the immune system to diseases (i.e., RKIP regulation of T cell functions; the secretion of cytokines and immune mediators, apoptosis, immune check point inhibitors and RKIP involvement in inflammatory diseases); and (vi) bioinformatic analysis between normal and malignant tissues, as well as across various immune-related cells. Overall, the regulation of RKIP in different cancers and inflammatory diseases suggest that it can be used as a potential therapeutic target in the treatment of these diseases.

The RhoA dependent anti-metastatic function of RKIP in breast cancer

Raf-1 kinase inhibitor protein was initially discovered as a physiological kinase inhibitor of the MAPK signaling pathway and was later shown to suppress cancer cell invasion and metastasis. Yet, the molecular mechanism through which RKIP executes its effects is not completely defined. RhoA has both a pro- and anti-metastatic cell-context dependent functions. Given that Rho GTPases primarily function on actin cytoskeleton dynamics and cell movement regulation, it is possible that one way RKIP hinders cancer cell invasion/metastasis is by targeting these proteins. Here we show that RKIP inhibits cancer cell invasion and metastasis by stimulating RhoA anti-tumorigenic functions. Mechanistically, RKIP activates RhoA in an Erk2 and GEF-H1 dependent manner to enhance E-cadherin membrane localization and inhibit CCL5 expression.

Metastasis Suppressor Genes in Pancreatic Cancer: An Update

ABSTRACT

Pancreatic cancer, especially pancreatic ductal adenocarcinoma (PDAC), has for long remained a deadly form of cancer characterized by high mortality rates resulting from metastasis to multiple organs. Several factors, including the late manifestation of the disease, partly amplified by lack of efficient screening methods, have hampered the drive to design an effective therapeutic strategy to treat this deadly cancer. Understanding the biology of PDAC progression and identifying critical genes regulating these processes are essential to overcome the barriers toward effective treatment. Metastasis suppressor genes have been shown to inhibit multiple steps in the metastatic cascade without affecting primary tumor formation and are considered to hold promise for treating metastatic cancers. In this review, we catalog the bona fide metastasis suppressor genes reported in PDAC and discuss their known mechanism of action.

Distinct roles for the RNA-binding protein Staufen1 in prostate cancer

BACKGROUND

Prostate cancer is one of the most common malignant cancers with the second highest global rate of mortality in men. During the early stages of disease progression, tumour growth is local and androgen-dependent. Despite treatment, a large percentage of patients develop androgen-independent prostate cancer, which often results in metastases, a leading cause of mortality in these patients. Our previous work on the RNA-binding protein Staufen1 demonstrated its novel role in cancer biology, and in particular rhabdomyosarcoma tumorigenesis. To build upon this work, we have focused on the role of Staufen1 in other forms of cancer and describe here the novel and differential roles of Staufen1 in prostate cancer.

METHODS

Using a cell-based approach, three independent prostate cancer cell lines with different characteristics were used to evaluate the expression of Staufen1 in human prostate cancer relative to control prostate cells. The functional impact of Staufen1 on several key oncogenic features of prostate cancer cells including proliferation, apoptosis, migration and invasion were systematically investigated.

RESULTS

We show that Staufen1 levels are increased in all human prostate cancer cells examined in comparison to normal prostate epithelial cells. Furthermore, Staufen1 differentially regulates growth, migration, and invasion in the various prostate cancer cells assessed. In LNCaP prostate cancer cells, Staufen1 regulates cell proliferation through mTOR activation. Conversely, Staufen1 regulates migration and invasion of the highly invasive, bone metastatic-derived, PC3 prostate cells via the activation of focal adhesion kinase.

CONCLUSIONS

Collectively, these results show that Staufen1 has a direct impact in prostate cancer development and further demonstrate that its functions vary amongst the prostate cancer cell types. Accordingly, Staufen1 represents a novel target for the development of much-needed therapeutic strategies for prostate cancer.

PKCδ mediates mitochondrial ROS generation and oxidation of HSP60 to relieve RKIP inhibition on MAPK pathway for HCC progression

Both protein kinase C (PKC) and reactive oxygen species (ROS) are well-known signaling messengers cross-talking with each other to activate mitogen-activated protein kinases (MAPKs) for progression of hepatocellular carcinoma (HCC). However, the underlying mechanisms are not well elucidated. Especially, whether mitochondrial ROS (mtROS) is involved and how it triggers MAPK signaling are intriguing. In this study, we found mtROS generation and phosphorylation of MAPKs were mediated by PKCδ in HCCs treated with the tumor promoter 12-O-tetradecanoyl-phorbol-13-acetate (TPA). Heat shock protein 60 (HSP60), one of the chaperones in mitochondria was the major protein oxidized in TPA-treated HCCs. Moreover, depletion of HSP60 or expression of HSP60 cysteine mutant prevented TPA-induced phosphorylation of MAPKs. To delineate how HSP60 mediated MAPK activation, the role of Raf kinase inhibitor protein (RKIP), a negative regulator of MAPK, was investigated. TPA dissociated RKIP from HSP60 in both mitochondria and cytosol, concurrently with translocation of HSP60 and MAPK from mitochondria to cytosol, which was associated with robust phosphorylation of MAPKs in the cytosol. Moreover, TPA induced opposite phenotypical changes of HCCs, G1 cell cycle arrest, and cell migration, which were prevented by mtROS scavengers and depletion of PKCδ and HSP60. Consistently, TPA increased the migration-related genes, hydrogen peroxide inducible clone5, matrix metalloproteinase-1/3, lamininγ2, and suppressed the cell cycle regulator cyclin E1 (CCNE1) via PKCδ/mtROS/HSP60/MAPK-axis. Finally, c-jun and c-fos were required for TPA-induced expression of the migration-related genes and a novel microRNA, miR-6134, was responsible for TPA-induced suppression of CCNE1. In conclusion, PKCδ cross-talked with mtROS to trigger HSP60 oxidation for release of RKIP to activate MAPK, regulating gene expression for migration, and G1 cell cycle arrest in HCC. Targeted therapy aiming at key players like PKCδ, RKIP, and HSP60 is promising for preventing HCC progression.

Resveratrol binds and activates RKIP protein in colorectal cancer

Raf-1 kinase inhibitory protein (RKIP) acts as a tumor cell metastasis suppressor and prognostic indicator for survival in various cancers. Its use is predicted to improve therapy for various malignancies, including colorectal cancer (CRC). RKIP, frequently denoted as phosphatidylethanolamine-binding protein 1, is expressed in all normal mammalian tissues. RKIP functions as an inhibitor of the Raf-1, PI-3K, and MAP kinase (MAPK) pathways. In this study, we found that resveratrol induced the expression of RKIP at protein levels. To elucidate the structural basis of the interaction between resveratrol and RKIP, we performed computational studies that explore the binding affinity and ligand efficacy of resveratrol against RKIP. This study reveals the prognostic significance of RKIP metastasis suppressor activity against CRC and its structural arrangements during drug-target interactions.

Current Status of Raf Kinase Inhibitor Protein (RKIP) in Lung Cancer: Behind RTK Signaling

Lung cancer is the most deadly neoplasm with the highest incidence in both genders, with non-small cell lung cancer (NSCLC) being the most frequent subtype. Somatic mutations within the tyrosine kinase domain of the epidermal growth factor receptor (EGFR) gene are key drivers of NSCLC progression, with EGFR inhibitors being particularly beneficial for patients carrying the so-called “EGFR-sensitizing mutations”. However, patients eventually acquire resistance to these EGFR inhibitors, and a better knowledge of other driven and targetable proteins will allow the design of increasingly accurate drugs against patients’ specific molecular aberrations. Raf kinase inhibitory protein (RKIP) is an important modulator of relevant intracellular signaling pathways, including those controlled by EGFR, such as MAPK. It has been reported that it has metastasis suppressor activity and a prognostic role in several solid tumors, including lung cancer. In the present review, the potential use of RKIP in the clinic as a prognostic biomarker and predictor of therapy response in lung cancer is addressed.

α-Ketoglutaric Acid-Modified Carbonate Apatite Enhances Cellular Uptake and Cytotoxicity of a Raf- Kinase Inhibitor in Breast Cancer Cells through Inhibition of MAPK and PI-3 Kinase Pathways

AZ628 is a hydrophobic Raf-kinase inhibitor (rapidly accelerated fibrosarcoma) currently in clinical trial of various cancer. The physicochemical properties of hydrophobic drugs that affect the drug-particle interactions and cause aggregation of drugs and particles might be the key aspect to impede effective drug delivery. Retaining smaller particle size is the prerequisite to overcome the opsonization and improve cytotoxicity in the targeted region. Carbonate apatite (CA), an attractive biodegradable vector, has been used to carry both hydrophilic and hydrophobic drugs and release the payloads inside the cells following endocytosis. We incorporated AZ628 into CA and also modified it with α-ketoglutaric acid (α-KA) for reducing particle growth kinetics and increasing total surface area to improve the delivery of AZ628 by enhancing cellular uptake by breast cancer cells. AZ628-loaded nanoparticles of CA and α-KA-modified CA (α-KAMCA) were synthesized and evaluated in MCF-7 and 4T1 cell lines by measuring cytotoxicity and cellular uptake analysis. HPLC (high-performance liquid chromatography) assay was performed to quantify the binding affinity of the nanocarriers towards the drug. Western blot analysis was done to see the activation and expression levels of Akt, MAPK (mitogen-activated protein kinase) pathways and Caspase-3. Zetasizer was used to measure the particle size along with the surface charge. α-KAMCA showed almost 88% encapsulation efficacy for AZ628 with around 21% enhanced cellular uptake of the drug in two different breast cancer cell lines. These findings suggest that α-KAMCA could be a promising therapeutic tool to carry AZ628 for breast cancer treatment.

RKIP: A Key Regulator in Tumor Metastasis Initiation and Resistance to Apoptosis: Therapeutic Targeting and Impact

RAF-kinase inhibitor protein (RKIP) is a well-established tumor suppressor that is frequently downregulated in a plethora of solid and hematological malignancies. RKIP exerts antimetastatic and pro-apoptotic properties in cancer cells, via modulation of signaling pathways and gene products involved in tumor survival and spread. Here we review the contribution of RKIP in the regulation of early metastatic steps such as epithelial–mesenchymal transition (EMT), migration, and invasion, as well as in tumor sensitivity to conventional therapeutics and immuno-mediated cytotoxicity. We further provide updated justification for targeting RKIP as a strategy to overcome tumor chemo/immuno-resistance and suppress metastasis, through the use of agents able to modulate RKIP expression in cancer cells.

Inhibition of RKIP aggravates thioacetamide-induced acute liver failure in mice

Accumulating evidence has indicated that Raf kinase inhibitor protein (RKIP) is involved in several intracellular signaling pathways; its abnormal expression is associated with tumor progression and metastasis in several human neoplasms. However, the role of RKIP in acute liver injury has remained elusive. In the present study, acute liver failure was induced by thioacetamide in mice, and locostatin was used to interfere with RKIP expression. It was found that RKIP expression was significantly inhibited by locostatin. Down-regulation of RKIP expression resulted in severe liver injury and extensive release of alanine aminotransferase and aspartate aminotransferase. In addition, reduced RKIP expression significantly enhanced the levels of reactive oxygen species and the content of pro-inflammatory factors such as tumor necrosis factor-α as well as interleukin-6 and −1β, and decreased the levels of nuclear factor E2-related factor-2 and heme oxygenase-1. Furthermore, down-regulation of RKIP promoted the activation of the nuclear factor-κB and extracellular signal-regulated kinase signaling pathways. In conclusion, the present study indicates an inverse correlation between RKIP level and the degree of hepatic injury, that is, a decrease in RKIP expression may exacerbate acute liver failure.

Molecular mechanism of hepatitis B virus (HBV) on suppression of raf kinase inhibitor protein (RKIP) expression

Raf kinase inhibitor protein (RKIP) has been shown to be a suppressor of the mitogen-activated protein kinase pathway and is reported to be involved in human malignancy. However, the molecular mechanism of hepatitis B virus (HBV) in regulating RKIP expression is not yet clarified. In this study, we compared RKIP expression in 107 pairs of matched liver cancer and adjacent non-cancerous liver tissues. Among seven HBV-encoded proteins, we found HBV X (HBX) protein could significantly inhibit the expression level of RKIP, indicating that HBV could suppress RKIP expression through regulating HBX. To further elucidate the mechanism, analyses on transcriptional regulation and promoter methylation inhibition were conducted in Huh7 cells. Our results showed that HBX can interact with AP1 protein to inhibit the RKIP transcription. Moreover, we observed that the promoter methylation level of RKIP could be enhanced by HBV. In conclusion, our study revealed that RKIP could act as a molecular marker for HBV-infected liver cancer, but had no tumor-suppressing effect.

Reduced RKIP Expression is Associated With Breast Neoplastic Progression and is Correlated With Poor Outcomes and Aberrant Methylation in Breast Carcinoma

Raf kinase inhibitor protein's (RKIP) downregulation can predict poor outcome in patients with various types of malignancy. In this study, we aimed to assess the potential involvement of RKIP in breast carcinogenesis and to evaluate its association with outcome variables and aberrant promoter methylation in breast carcinoma (BC). Tissue microarray sections were immunostained for RKIP in 26 normal breasts, 25 usual ductal hyperplasia, 76 ductal carcinoma in situ, and 198 BC specimens. The methylation status of RKIP was also determined in BC. In addition, the mRNA and protein level of RKIP was analyzed in 8 pairs of BC tissues and surrounding normal tissues by quantitative real-time polymerase chain reaction and Western blot analysis, respectively. RKIP mRNA and protein expression was significantly downregulated in BC tissues compared with the surrounding normal tissues (P<0.05 and P<0.01, respectively). Reduced RKIP expression seemed to increase progressively from normal breast to BC (P<0.001). Reduced RKIP expression was significantly associated with metastatic relapse (P<0.001) and was identified as an independent adverse prognostic indicator for disease-free survival (P=0.003). Reduced RKIP expression in BC was significantly correlated with its aberrant promoter methylation (P<0.05). In conclusion, downregulation of RKIP plays an important role in the breast neoplastic progression and correlates with poor prognosis in patients with BC. Aberrant RKIP methylation is one of the mechanisms that lead to downregulation of RKIP in BC.

Crosstalks between Raf-kinase inhibitor protein and cancer stem cell transcription factors (Oct4, KLF4, Sox2, Nanog)

Raf-kinase inhibitor protein has been reported to inhibit both the Raf/mitogen extracellular signal-regulated kinase/extracellular signal-regulated kinase and nuclear factor kappa-light-chain of activated B cells pathways. It has also been reported in cancers that Raf-kinase inhibitor protein behaves as a metastatic suppressor as well as a chemo-immunosensitizing factor to drug/immune-mediated apoptosis. The majority of cancers exhibit low or no levels of Raf-kinase inhibitor protein. Hence, the activities of Raf-kinase inhibitor protein contrast, in part, to those mediated by several cancer stem cell transcription factors for their roles in resistance and metastasis. In this review, the existence of crosstalks in the signaling pathways between Raf-kinase inhibitor protein and several cancer stem cell transcription factors (Oct4, KLF4, Sox2 and Nanog) was assembled. Oct4 is induced by Lin28, and Raf-kinase inhibitor protein inhibits the microRNA binding protein Lin28. The expression of Raf-kinase inhibitor protein inversely correlates with the expression of Oct4. KLF4 does not interact directly with Raf-kinase inhibitor protein, but rather interacts indirectly via Raf-kinase inhibitor protein's regulation of the Oct4/Sox2/KLF4 complex through the mitogen-activated protein kinase pathway. The mechanism by which Raf-kinase inhibitor protein inhibits Sox2 is via the inhibition of the mitogen-activated protein kinase pathway by Raf-kinase inhibitor protein. Thus, Raf-kinase inhibitor protein's relationship with Sox2 is via its regulation of Oct4. Inhibition of extracellular signal-regulated kinase by Raf-kinase inhibitor protein results in the upregulation of Nanog. The inhibition of Oct4 by Raf-kinase inhibitor protein results in the failure of the heterodimer formation of Oct4 and Sox2 that is necessary to bind to the Nanog promoter for the transcription of Nanog. The findings revealed that there exists a direct correlation between the expression of Raf-kinase inhibitor protein and the expression of each of the above transcription factors. Based on these analyses, we suggest that the expression level of Raf-kinase inhibitor protein may be involved in the regulation of the cancer stem cell phenotype.

RKIP regulates CCL5 expression to inhibit breast cancer invasion and metastasis by controlling macrophage infiltration

Accumulating evidence suggests that presence of macrophages in the tumor microenvironment add to the invasive and tumor-promoting hallmarks of cancer cells by secreting angiogenic and growth factors. RKIP is a known metastasis suppressor and interferes with several steps of metastasis. However, the mechanistic underpinnings of its function as a broad metastasis suppressor remain poorly understood. Here, we establish a novel pathway for RKIP regulation of metastasis inhibition through the negative regulation of RANTES/CCL5 thereby limiting tumor macrophage infiltration and inhibition of angiogenesis. Using a combination of loss- and gain-of-function approaches, we show that RKIP hinders breast cancer cell invasion by inhibiting expression of the CC chemokine CCL5 in vitro. We also show that the expression levels of RKIP and CCL5 are inversely correlated among clinical human breast cancer samples. Using a mouse allograft breast cancer transplantation model, we highlight that ectopic expression of RKIP significantly decreases tumor vasculature, macrophage infiltration and lung metastases. Mechanistically, we demonstrate that the inhibition of the CCL5 expression is the cause of the observed effects resulting from RKIP expression. Taken together, our results underscore the significance of RKIP as important negative regulator of tumor microenvironment.

A novel long non-coding RNA lnc-GNAT1-1 is low expressed in colorectal cancer and acts as a tumor suppressor through regulating RKIP-NF-κB-Snail circuit

Background

The role of long non-coding RNAs (lncRNAs) in colorectal cancer (CRC) progression has not fully been elucidated. This study was designed to report the identification of a novel lncRNA, lnc-GNAT1-1, and its functional role in CRC progression.

Methods

lncRNA expression profile microarray was performed in three paired primary and liver metastatic tissues of CRC, and a novel lncRNA, lnc-GNAT1-1, was identified to be a potential functional lncRNA. Quantitative real-time PCR was used to detect its expression in CRC tissues, cell lines, and patients’ plasma, cell fractionation was used to evaluate its subcellular location. lnc-GNAT1-1 was knockdown by siRNA or overexpressed by a lentivirus vector, then in vitro an vivo experiments were performed to evaluate its biological role and the underlying mechanisms in CRC.

Results

Expression of lnc-GNAT1-1 was decreased in liver metastasis than the primary tumor, while the later one is lower than the paired normal mucosa. Decreased lnc-GNAT1-1 expression was associated unfavorable clinicopathological features and a poor prognosis of CRC patients. In multivariate analysis, lnc-GNAT1-1 was proved to be an independent prognostic factor. In plasma, lnc-GNAT1-1 was significant decreased in CRC patients than healthy donors, and with the TNM stages advanced, the plasma lnc-GNAT1-1 level decreased; Receiver operating characteristic curve (ROC curve) showed that plasma lnc-GNAT1-1 had a moderate to well diagnostic efficiency for CRC. In vitro experiments showed that knockdown of lnc-GNAT1-1 could inhibit the aggressive phenotypes of CRC cell lines. In vivo study showed that overexpression of lnc-GNAT1-1 could suppress the liver metastasis of CRC cells. Finally, we explored the underlying mechanism of the role lnc-GNAT1-1 plays in CRC, and found a positive correlation between lnc-GNAT1-1 and Raf kinase inhibitor protein (RKIP) expression both in cells and in patients’ tissues. We further found that lnc-GNAT1-1 could regulate the RKIP-NF-κB-Snail circuit in CRC.

Conclusions

We have demonstrated in this study that a novel lncRNA, lnc-GNAT1-1, is low expressed in colorectal cancer tissues and plasma, and acts as a tumor suppressor through regulating RKIP-NF-κB-Snail circuit.

Electronic supplementary material

The online version of this article (doi:10.1186/s13046-016-0467-z) contains supplementary material, which is available to authorized users.

Didymin ameliorates hepatic injury through inhibition of MAPK and NF-κB pathways by up-regulating RKIP expression

A flavone was isolated from Origanum vulgare and identified as didymin (O. vulgare didymin, OVD). The protective effect and mechanism of OVD on acute liver injury was then assessed in vivo and in vitro. Our results showed that OVD significantly alleviated CCl₄-induced liver injury in mice and markedly decreased serum ALT and AST activities. OVD treatment significantly reduced CYP2E1 activity, lipid peroxidation level, ROS generation, NO production and pro-inflammatory cytokines (such as TNF-α, IL-6 and IL-1β) in liver tissues and RAW 264.7 cells, but enhanced the hepatic antioxidative enzymes activities. Further study showed that OVD significantly inhibited the NF-κB and MAPK pathways. Interestingly, OVD notably enhanced Raf kinase inhibitor protein (RKIP) expression, and the effects of OVD on histological changes, oxidative stress and inflammation was largely abolished by the RKIP specific inhibitor locostatin. Our findings indicate that OVD can ameliorate CCl₄-induced liver injury, which may be ascribed to its radical scavenging action, antioxidant activity, and modulation of MAPK and NF-κB signaling pathways.

Loss of Raf kinase inhibitor protein is associated with malignant progression in hepatic fibrosis

Raf kinase inhibitory protein (RKIP), besides regulating important intracellular signaling cascades, was described to be associated with progression, metastasis and prognosis in several human neoplasms. But its role in hepatic fibrogenesis remains unclear. In the present study, we found that the absence of RKIP expression significantly enhanced the proliferation of HSC-T6 cells. Reduced RKIP expression promoted the activation of HSCs and the accumulation of collagen, as evidenced by the increases in the levels of collagen I and α-smooth muscle actin. Moreover, down-regulating RKIP expression led to severe histopathological changes and collagen accumulation in hepatic tissues of rats with liver fibrosis. Furthermore, the absence of RKIP promoted the activation of ERK/MAPK pathway in vitro and in vivo. Our findings clearly demonstrate an inverse correlation between RKIP level and the degree of the liver injury and fibrosis. Loss of RKIP may be associated with malignant progression in hepatic fibrosis.

RKIP Inhibits Local Breast Cancer Invasion by Antagonizing the Transcriptional Activation of MMP13

Raf Kinase Inhibitory Protein or RKIP was initially identified as a Raf-1 binding protein using the yeast 2-hybrid screen. RKIP inhibits the activation phosphorylation of MEK by Raf-1 by competitively inhibiting the binding of MEK to Raf-1 and thus exerting an inhibitory effect on the Raf-MEK-Erk pathway. RKIP has been identified as a metastasis suppressor gene. Expression of RKIP is low in cancer metastases. Although primary tumor growth remains unaffected, re- expression of RKIP inhibits cancer metastasis. Mechanistically, RKIP constrains metastasis by inhibiting angiogenesis, local invasion, intravasation, and colonization. The molecular mechanism of how RKIP inhibits these individual steps remains undefined. In our present study, using an unbiased PCR based screening and by analyzing DNA microarray expression datasets we observe that the expression of multiple metalloproteases (MMPs) including MMP1, MMP3, MMP10 and MMP13 are negatively correlated with RKIP expression in breast cancer cell lines and clinical samples. Since expression of MMPs by cancer cells is important for cancer metastasis, we hypothesize that RKIP may mediate suppression of breast cancer metastasis by inhibiting multiple MMPs. We show that the expression signature of RKIP and MMPs is better at predicting high metastatic risk than the individual gene. Using a combination of loss- and gain-of-function approaches, we find that MMP13 is the cause of RKIP-mediated inhibition of local cancer invasion. Interestingly expression of MMP13 alone is not sufficient to reverse the inhibition of breast cancer cell metastasis to the lung due to the expression of RKIP. We find that RKIP negatively regulates MMP13 through the Erk2 signaling pathway and the repression of MMP13 by RKIP is transcription factor AP-1 independent. Together, our findings indicate that RKIP inhibits cancer cell invasion, in part, via MMP13 inhibition. These data also implicate RKIP in the regulation of MMP transcription, suggesting a potential mechanism by which RKIP inhibits tumor progression and metastasis.

Common reduction of the Raf kinase inhibitory protein in clear cell renal cell carcinoma

Despite the recent progress in our understanding of clear cell renal cell carcinomas (ccRCCs), the etiology of ccRCC remains unclear. We reported here a prevailing reduction of the raf kinase inhibitory protein (RKIP) in ccRCC. In our examination of more than 600 ccRCC patients by western blot and immunohistochemistry, RKIP was significantly reduced in 80% of tumors. Inhibition of RKIP transcription in ccRCC occurs to greater levels than VHL transcription based on the quantification analysis of their transcripts in six large datasets of DNA microarray available in Oncomine™ with the median rank of suppression being 582 and 2343 for RKIP and VHL, respectively. Collectively, the magnitude of RKIP reduction and the levels of its downregulation match those of VHL. Furthermore, RKIP displays tumor suppressing activity in ccRCC. While modulation of RKIP expression did not affect the proliferation of A498 and 786-0 ccRCC cells and neither their ability to form xenograft tumors in NOD/SCID mice, ectopic expression or knockdown of RKIP inhibited or enhanced A498 and 786-0 ccRCC cell invasion, respectively. This was associated with robust changes in vimentin expression, a marker of EMT. Taken together, we demonstrate here that downregulation of RKIP occurs frequently at a rate that reaches that of VHL, suggesting RKIP being a critical tumor suppressor for ccRCC. This is consistent with RKIP being a tumor suppressor for other cancers.

Effect of Raf kinase inhibitor protein expression on malignant biological behavior and progression of colorectal cancer

The Raf kinase inhibitor protein (RKIP) is a novel metastasis suppressor. RKIP was previously found to have low expression in a colorectal cancer (CRC) patient cohort by immunohistochemistry. However, the role of RKIP in CRC remains undetermined. In the present study, immunohistochemistry was performed to compare RKIP expression between 129 paired stage II CRC and adjacent non-tumorous tissues. The correlations between clinical parameters, prognosis and RKIP expression were evaluated. To investigate the effect of RKIP on proliferation and metastasis, RKIP was overexpressed and knocked down in colon cancer cell lines. 3-(4,5-Dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT), Transwell and wound-healing assays were performed. Murine models were established to confirm the influence of RKIP on malignant tumor phenotypes in vivo. Our results showed that RKIP expression was significantly decreased in the CRC tissues compared to the adjacent non‑cancerous tissues (p<0.001) and was correlated with the risk of relapse in stage II CRC (p<0.05). Overexpression of RKIP suppressed HCT116 cell metastasis in vitro and in vivo, whereas knockdown of RKIP expression in SW480 cells and its murine model increased metastatic ability (p<0.05). No effect of RKIP on cell proliferation in CRC was observed. These data suggest that RKIP is an important metastasis-suppressor gene in CRC. The re-expression of RKIP could be a potential therapeutic target for antimetastatic strategies for CRC.

Role of Raf-kinase inhibitor protein in colorectal cancer and its regulation by hydroxycamptothecine

Background

Recently accumulated evidence suggests that Raf kinase inhibitor protein (RKIP) participates in regulation of many signaling pathways and plays an important role in tumorigenesis and tumor metastasis. However, studies investigating the role of RKIP in colorectal cancer have not been reported. The aim of this study was to investigate the role of RKIP on colorectal cancer cell differentiation, progression and its correlation with chemosensitivity.

Results

Immunohistochemical analysis revealed that RKIP expression was higher in non-neoplastic colorectal tissue (NCRCT) and colorectal cancer tissue (CRCT) than that in metastatic lymph node tissue (MLNT) (P <0.05). P-ERK protein expression was higher in MLNT and CRCT than that in NCRCT (P = 0.02). Immunocytochemical analysis further revealed that RKIP expression was higher in the well differentiated cell line SW1116 as compared to that in the poorly differentiated cell line LoVo. Matrigel invasive assay demonstrated that the inhibition of RKIP by short hairpin RNA (shRNA) 271 transfection significantly increased the number of migrated cells (90.67 ± 4.04 vs. 37.33 ± 2.51, P <0.05), whereas over-expression of RKIP by PEBP-1 plasmid transfection significantly suppressed the number of migrated cells (79.24 ± 5.18 vs. 154.33 ± 7.25, P <0.05). Meanwhile, down-regulation of RKIP induced an increase in the cell survival rate by inhibiting apoptosis induced by hydroxycamptothecine.

Conclusions

RKIP was also found to be associated with cell differentiation, with a higher activity in well differentiated colorectal cancer cells than in poorly differentiated ones. The upregulated expression of RKIP in colorectal cancer cells inhibited cell invasion and metastasis, while downregulation of RKIP reduced chemosensitivity by inhibiting apoptosis induced by HCPT.

Raf kinase inhibitor protein (RKIP) deficiency decreases latency of tumorigenesis and increases metastasis in a murine genetic model of prostate cancer

BACKGROUND

Raf kinase inhibitor protein (RKIP) has been shown to act as a metastasis suppressor gene in multiple models of cancer. Loss of RKIP expression promotes invasion and metastasis in cell transplantation animal models. However, it is unknown if RKIP expression can impact the progression of cancer in an autochthonous model of cancer. The goal of this study was to determine if loss of RKIP expression in a genetic mouse model of prostate cancer (PCa) impacts metastasis.

METHODS

Endogenous RKIP expression was measured in the primary tumors and metastases of transgenic adenocarcinoma of the mouse prostate (TRAMP(+) ) mice. RKIP knockout mice (RKIP(-/-) ) were crossbred with (TRAMP(+) ) mice to create RKIP(-/-) TRAMP(+) mice. Mice were euthanized at 10, 20, and 30 weeks for evaluation of primary and metastatic tumor development. To determine if loss of RKIP alone promotes metastasis, RKIP was knocked down in the low metastatic LNCaP prostate cancer cell line.

RESULTS

Endogenous RKIP expression decreased in TRAMP(+) mice as tumors progressed. Primary tumors developed earlier in RKIP(-/-) TRAMP(+) compared to TRAMP(+) mice. At 30 weeks of age, distant metastases were identified only the RKIP(-/-) TRAMP(+) mice. While prostate epithelial cell proliferation rates were higher at 10 and 20 weeks in RKIP(-/-) TRAMP(+) compared to TRAMP(+) mice, by 30 weeks there was no difference. Apoptosis rates in both groups were similar at all timepoints. Decreased RKIP expression did not impact the metastatic rate of LNCaP in an orthotopic PCa model.

CONCLUSIONS

These results demonstrate that loss of RKIP decreases latency of tumor development and promotes distant metastasis in the TRAMP mouse model in the context of a pro-metastatic background; but loss of RKIP alone is insufficient to promote metastasis. These findings suggest that in addition to its known metastasis suppressor activity, RKIP may promote tumor progression through enhancing tumor initiation. Prostate 75:292-302, 2015. © 2014 Wiley Periodicals, Inc.

RARRES3 suppresses breast cancer lung metastasis by regulating adhesion and differentiation

In estrogen receptor-negative breast cancer patients, metastatic relapse usually occurs in the lung and is responsible for the fatal outcome of the disease. Thus, a better understanding of the biology of metastasis is needed. In particular, biomarkers to identify patients that are at risk of lung metastasis could open the avenue for new therapeutic opportunities. Here we characterize the biological activity of RARRES3, a new metastasis suppressor gene whose reduced expression in the primary breast tumors identifies a subgroup of patients more likely to develop lung metastasis. We show that RARRES3 downregulation engages metastasis-initiating capabilities by facilitating adhesion of the tumor cells to the lung parenchyma. In addition, impaired tumor cell differentiation due to the loss of RARRES3 phospholipase A1/A2 activity also contributes to lung metastasis. Our results establish RARRES3 downregulation as a potential biomarker to identify patients at high risk of lung metastasis who might benefit from a differentiation treatment in the adjuvant programme.

RKIP promotes cisplatin-induced gastric cancer cell death through NF-κB/Snail pathway

The objectives of this study were to explore the expression profiles of Raf kinase inhibitor protein (RKIP) in human gastric cancer cell line (SGC-7901) and cisplatin-resistant cell line (SGC-7901/DDP) and investigate the role of RKIP in the sensitivity of human gastric cancer cells to cisplatin and its signaling pathways, with an attempt to identify new approaches and strategies for the management of gastric cancer. The human gastric cancer cell line (SGC-7901) and cisplatin-resistant cell line (SGC-7901/DDP) were separately cultured in vitro. The expression profiles of RKIP in these two cell lines were detected by Western blotting. Forty-eight hours after the transfection of RKIP siRNA in SGC-7901 cells, the change of RKIP expression in the cells was detected using Western blotting, and the change of cell viability after the interference of RKIP expression was determined using 3-(4,5)-dimethylthiahiazo (-z-y1)-3,5-di-phenytetrazoliumromide (MTT) method. The effect of the ectopic expression of RKIP on the cisplatin-induced viability of gastric cancer cell was detected using MTT method. The effect of the ectopic expression of RKIP on the cisplatin-induced apoptosis of gastric cancer cell was detected using flow cytometry after having been double stained with Annexin V/PI. The effect of the ectopic expression of RKIP on the NF-κB and Snail expressions in cisplatin-induced gastric cancer cells was detected using Western blotting. As shown by the Western blotting, the expression of RKIP in SGC-7901/DDP cells significantly decreased when compared with that in SGC-7901 cells (P < 0.05). Compared with the control group, the expression of RKIP in SGC-7901 cells significantly decreased 48 h after the transfection of RKIP siRNA (P < 0.01). After the SGC-7901 cells were transfected with RKIP siRNA, the cell viability was significantly increased (P < 0.05); after the SGC-7901/DDP cells were transfected with RKIP recombinant plasmid, the cell viability was significantly decreased (P < 0.05). After the RKIP expression was suppressed in the cisplatin-treated SGC-7901 cells, the cell viability significantly increased (P < 0.05), and the amount of apoptotic cells significantly decreased (P < 0.05). In contrast, after the RKIP overexpression in the cisplatin-treated SGC-7901/DDP cells, the cell viability significantly decreased (P < 0.05), and the amount of apoptotic cells significantly increased (P < 0.05). The suppression of RKIP expression in SGC-7901 cells could significantly promote the increase of NF-κB expression (P < 0.05); in contrast, the increased expression of RKIP in SGC-7901/DDP cells significantly inhibited the expression of Snail (P < 0.05). The expression of RKIP is downregulated in cisplatin-resistant cell line (SGC-7901/DDP). The overexpression of RKIP can enhance the sensitivity of human gastric cancer cells to cisplatin, which may be achieved via the NF-κB/Snail signaling pathway.

RKIP inhibits gastric cancer cell survival and invasion by regulating the expression of HMGA2 and OPN

The objective of this study was to explore the mechanism via which Raf kinase inhibitor protein (RKIP) suppresses the invasion of gastric cancer cells and promote apoptosis, with an attempt to provide evidences for the application of RKIP in treating gastric cancer. The recombinant plasmid pcDNA3.1-RKIP or RKIP-shRNA was transfected into the gastric cancer cell line SGC-7901 using liposome. Then, the messenger RNA (mRNA) and protein expressions of RKIP, HMGA2, and OPN were detected using qPCR and Western blotting. The effects of HMGA2 on the proliferation, apoptosis, and invasion of SGC-7901 cells were detected using flow cytometry and Transwell assay. To further explore the regulatory effect of PKIP on the biological activities of HMGA2, we over-expressed or knock down RKIP and HMGA2 simultaneously and detected its effects on the proliferation, apoptosis, and invasion of SGC-7901 cells. As shown by qPCR and Western blotting, after over-expression of RKIP in SGC-7901 cells, the mRNA and protein expressions of RKIP significantly increased (P < 0.01), whereas the mRNA and protein expressions of HMGA2 and OPN significantly decreased (P < 0.01). In contrast, the transfection of RKIP-shRNA in the SGC-7901 cells resulted in opposite results. After over-expression of HMGA2 in SGC-7901 cells, the protein expression of HMGA2 significantly increased (P < 0.01); however, it significantly decreased after the transfection of HMGA2-shRNA (P < 0.01). As shown by Transwell assay and flow cytometry, After the over-expression of HMGA2 in SGC-7901 cells, the (G2 + S) phase fraction significantly increased (P < 0.01); also, the percentage of the apoptotic cells significantly declined (P < 0.05) and the number of invasive cells significantly increased (P < 0.05). However, the interference of the expression of HMGA2 resulted in opposite results. The simultaneous over-expression of RKIP and HMGA2 in SGC-7901 cells or the simultaneous interference of RKIP and HMGA2 showed no significant difference with the control group in terms of (G2 + S) phase fraction, percentage of apoptotic cells, and number of invasive cells (P > 0.05). In conclusion, RKIP can inhibit the survival and invasion of gastric cancer cells and promote apoptosis, possibly by regulating the expression of HMGA2 or OPN.

RKIP suppresses gastric cancer cell proliferation and invasion and enhances apoptosis regulated by microRNA-224

The purposes of this study were to determine the expression profile of Raf kinase inhibitor protein (RKIP) in human gastric cancer cells and its effect on the biological characteristics of SGC-7901 cell lines, to examine the modulatory effect of microRNA-224 (miR-224) on RKIP. The research will provide novel strategies for gastric cancer treatment in the future. Quantitative real-time reverse transcription PCR (qRT-PCR) was employed to determine the expression profile of RKIP in gastric cancer cell lines (SGC-7901, MGC80-3, and MKN45). A eukaryotic expression vector, pcDNA3.1-RKIP, was constructed and transfected into SGC-7901 cells. Changes in RKIP protein expression were examined by Western blot assays, and the effect of RKIP overexpression on SCG-7901 cell viability was determined by 3-(4,5)-dimethylthiahiazo(-z-y1)-3,5-diphenytetrazoliumromide (MTT) assays. The effect of RKIP overexpression on SGC-7901 cell proliferation and apoptosis was analyzed by flow cytometry and that on the migration of SGC-7901 cells was investigated by Transwell migration assays. RKIP was identified to be a regulatory target gene of miR-224 using a luciferase reporter gene system, and the effect of miR-224 on intracellular RKIP protein expression was examined by Western blot assays. The regulatory effect of miR-224 on the biological characteristics of RKIP was investigated by MTT, flow cytometry, and Transwell invasion chamber assays. The expression of RKIP in gastric cancer cells was decreased significantly in comparison to that of normal gastric mucosal epithelial cells (GES-1) (p < 0.01), as demonstrated by qRT-PCR assays. Compared with the control group, the up-regulation of RKIP intracellular expression was observed in SGC-7901 cells after transfection of pcDNA3.1-RKIP for 48 h (p < 0.01). There were significant decreases in cell viability and the S-phase fraction (p < 0.05), concomitant with a significant increase in apoptosis (p < 0.01), as well as a significant reduction in cells migrating through Transwell chambers (p < 0.05), as shown by MTT, flow cytometry, and Transwell invasion chamber assays. A significant decrease in luciferase activities in cells transfected with a miR-224 mimic was observed compared with that of the control group (p < 0.05), as suggested by the luciferase reporter gene system. As shown by Western blot assays, there was a significant decrease in RKIP expression in SGC-7901 cells transfected with the miR-224 mimic for 48 h compared with the control group (p < 0.05). As shown by MTT, flow cytometry, and Transwell invasion chamber assays, the changes in biological characteristics induced by RKIP overexpression could be suppressed in SGC-7901 cells after transfection of the miR-224 mimic. In conclusion, the down-regulation of RKIP expression was observed in human gastric cell lines, and miR-224 could negatively regulate the expression and biological characteristics of RKIP, contributing to suppress the proliferation and invasion of gastric cells.

Clinical significance of RKIP mRNA expression in non-small cell lung cancer

Raf-1 kinase inhibitor protein (RKIP) expression was associated with the onset, development, invasion, and metastasis of numerous tumor types including prostate cancer, melanoma, colorectal cancer, liver cancer, and breast cancer. However, RKIP mRNA expression and the clinical significance in non-small cell lung cancers (NSCLC) remain unresolved. Real-time PCR was performed to detect the expression of RKIP mRNA in 126 pairs of lung tumor tissues (TT) and surrounding normal tissues (sNT). Correlations between RKIP mRNA expression and clinicopathological features were evaluated by statistical analysis. In the 126 patients examined, RKIP mRNA expression was significantly lower in lung TT than the sNT (p < 0.05). Our results indicated that downregulation of RKIP mRNA expression was associated with a poorer N-stage (p = 0.019) and poorer pathological TNM stage (p = 0.015). However, no significant association was observed between the expression status of RKIP mRNA and clinicopathologic factors, such as gender, age, histological type, and the size of the tumor (p > 0.05). The level of RKIP mRNA expression was found to be significantly downregulated in NSCLC, and the lower mRNA levels correlated with poorer differentiation, advanced pathologic TNM stage in patients with NSCLC.

[Expression and significance of Raf kinase inhibitory protein in lung cancer]

背景与目的

Raf激酶抑制蛋白（Raf kinase inhibitor protein, RKIP）属于磷脂酰乙醇胺结合蛋白家族的成员，RKIP参与ERK/MAPK、G蛋白偶联受体和NF-κΒ等信号传导过程，且RKIP的表达减弱或丢失与多种肿瘤的发生发展及侵润转移相关。本研究旨在探讨RKIP在非小细胞肺癌（non-small cell lung cancer, NSCLC）组织中的表达及其与NSCLC临床病理特征的相关性。

方法

应用RT-PCR、Western blot及免疫组化方法检测83例NSCLC及其癌旁组织标本中RKIP的表达，并结合临床病理学资料进行统计学分析，所有病例均经病理诊断确诊，均无其它部位原发肿瘤，术前无化疗、放疗和免疫治疗史。

结果

NSCLC中RKIP mRNA及蛋白的表达明显低于癌旁组织，差异有统计学意义（P < 0.05）。RKIP与肿瘤分化程度、TNM分期、有无淋巴结转移及生存期有关（P < 0.05），但与患者的性别、吸烟、年龄及肿瘤的大小无关（P > 0.05）。

结论

RKIP的低表达与NSCLC的发生及侵袭转移有关，可作为NSCLC预测及预后评估的指标。

cis-Acting elements and trans-acting factors in the transcriptional regulation of raf kinase inhibitory protein expression

The Raf kinase inhibitory protein (RKIP) is down-regulated in multiple types of human cancers. Decreased RKIP transcription activity may be one of the major mechanisms responsible for the downregulation of RKIP expression in human diseases. To test this hypothesis, we need to gain basic knowledge of the transcriptional regulation of RKIP. To achieve this objective, we made a systematic effort to identify cis-acting elements and trans-acting factors that control RKIP promoter activity. We found that full RKIP promoter activity requires the region −56 to +261 relative to the transcription start site. Within the full promoter region, there are two motifs rich in G/C that responded to transcription factor Sp1, one cAMP-responsive element that responded to the transcription factor CREB, and one docking site for the histone acetylase p300. In human melanoma A375 cells and human cervical cancer HeLa cells, mutation or deletion of each of these cis-acting elements decreased promoter activity. In A375 cells, knockdown of the corresponding transcription factors Sp1, CREB, or p300 decreased RKIP promoter activity, whereas overexpression of CREB and p300 increased RKIP promoter activity. The results obtained with HeLa cells also supported the idea that Sp1 and CREB play positive roles in the regulation of RKIP transcription. These findings suggest that regulators of the expression or activity of Sp1, CREB, and p300 are involved in regulating RKIP transcription.

Fully phosphorothioate-modified CpG ODN with PolyG motif inhibits the adhesion of B16 melanoma cells in vitro and tumorigenesis in vivo

Adhesion to the extracellular matrix and endothelial lining of blood vessels is critical for tumor cells to grow at original or metastatic sites. Inhibition of tumor cell adhesion can be an antitumor strategy. Guanosine-rich (G-rich) oligodeoxynucleotides (ODNs) can inhibit the adhesion of certain tumor cells. However, no data exist on how inclusion of the CpG motif in the G-rich sequence influences tumor cell adhesion and subsequent tumorigenesis. In this study, in vitro and in vivo assays were used to evaluate how a panel of ODN-containing contiguous guanosines and the CpG motif influenced adhesion of B16 melanoma cells. The results showed that a self-designed ODN, named BW001, containing the polyG motif and a full phosphorothioate modification backbone could inhibit B16 melanoma cell adhesion on a culture plate or on a plate coated with various substances. In vivo data revealed that B16 melanoma cells co-administered with BW001 and intraperitoneally injected into mice formed fewer tumor colonies in peritoneal cavities. This effect was related to the polyG motif and the full phosphorothioate modification backbone and enhanced by the existence of the CpG motif. Additional in vivo data showed that survival of tumor-bearing mice in the BW001 group was significantly prolonged, subcutaneous melanoma developed much more slowly, and lung dissemination colonies formed much less often than in mice inoculated with B16 melanoma cells only. The effect was CpG motif-dependent. These results suggest that BW001 may exert an integrated antitumor effect.

Raf kinase inhibitor protein inhibits esophageal cancer cell invasion through downregulation of matrix metalloproteinase expression

Esophageal cancer is the eighth most common malignant tumor in the world and is a common cause of tumor-related death. The development of esophageal cancer is a complex process involving many pathogenetic factors, multiple stages and accumulation of multiple gene mutations and interactions. This study aimed to investigate the effects of Raf kinase inhibitor protein (RKIP) on the proliferation, apoptosis and invasion of TE-1 esophageal cancer cells. Surgical specimens from esophageal cancer patients were classified into esophageal cancer tissues, tumor-adjacent tissues and normal esophageal tissues. The tissues were fixed in 4% paraformaldehyde solution for hematoxylin and eosin and immunohistochemical staining. RKIP expression in esophageal tissues was detected by immunohistochemical staining. The esophageal cancer cell line TE-1 was exposed to four different viruses: RKIP-RNAi-AD, NC-RNAi-GFP-AD, RKIP-AD and GFP-AD. Cell proliferation was detected by MTT assay and cell apoptosis was detected by flow cytometry. Cell invasion was determined by a Transwell coated with Matrigel. RKIP, phospho-RKIP, Raf-1, phospho-Raf-1, ERK1/2, phospho-ERK1/2, GRK-2 and GAPDH expression was assayed by western blotting. LIN28 and MMP-14 mRNA was assayed by qPCR. The results showed that RKIP expression was reduced in esophageal cancer tissues in comparison with expression in normal esophageal epithelium tissues and tumor-adjacent tissues. Reduced RKIP expression was associated with lymph node or distant metastasis in esophageal cancer. RKIP inhibited the invasive and metastatic abilities of esophageal cancer cell line TE-1 by downregulating mRNA expression of LIN28 and MMP-14. RKIP had no effect on the MAPK signaling pathway in the esophageal cancer cell line TE-1, but was involved in the G protein-coupled signaling pathway. Our findings clearly demonstrate that RKIP inhibits esophageal cancer cell invasion by downregulating the expression of GRK-2, LIN28 and MMP-14.

RKIP inhibition in cervical cancer is associated with higher tumor aggressive behavior and resistance to cisplatin therapy

Cervical cancer is one of the most common cancers in women worldwide, being high-risk group the HPV infected, the leading etiological factor. The raf kinase inhibitory protein (RKIP) has been associated with tumor progression and metastasis in several human neoplasms, however its role on cervical cancer is unclear. In the present study, 259 uterine cervix tissues, including cervicitis, cervical intraepithelial lesions and carcinomas, were analyzed for RKIP expression by immunohistochemistry. We found that RKIP expression was significantly decreased during malignant progression, being highly expressed in non-neoplastic tissues (54% of the samples; 73/135), and expressed at low levels in the cervix invasive carcinomas (∼15% (19/124). Following in vitro downregulation of RKIP, we observed a viability and proliferative advantage of RKIP-inhibited cells over time, which was associated with an altered cell cycle distribution and higher colony number in a colony formation assay. An in vitro wound healing assay showed that RKIP abrogation is associated with increased migratory capability. RKIP downregulation was also associated with an increased vascularization of the tumors in vivo using a CAM assay. Furthermore, RKIP inhibition induced cervical cancer cells apoptotic resistance to cisplatin treatment. In conclusion, we described that RKIP protein is significantly depleted during the malignant progression of cervical tumors. Despite the lack of association with patient clinical outcome, we demonstrate, in vitro and in vivo, that loss of RKIP expression can be one of the factors that are behind the aggressiveness, malignant progression and chemotherapy resistance of cervical cancer.

RKIP and 14-3-3ε exert an opposite effect on human gastric cancer cells SGC7901 by regulating the ERK/MAPK pathway differently

BACKGROUND

Raf-1 kinase inhibitor protein (RKIP) inhibits Raf (a key element in the ERK/MAPK pathway) and is regarded as anti-tumoral. In contrast, 14-3-3 is considered protumoral. However, the pathogenetic role of RKIP and 14-3-3ε in gastric cancer is unclear.

AIM

The purpose of this study was to examine the influence of 14-3-3ε and RKIP on SGC7901, the regulation of the ERK/MAKP pathway by both, and the interaction between the two proteins.

METHODS

RKIP and 14-3-3ε genes were introduced into SGC7901 cells using gene cloning technique, then, the bioactivities including the proliferation, migration and invasion of the cells were assessed by MTT and migration assays. ERK/MAKP pathway's activity was examined using real-time quantitative RT-PCR, western blot, immunoprecipitation and 3D-immunolocalization techniques.

RESULTS

Our results showed that RKIP inhibited SGC7901 cells' bioactivities whereas 14-3-3ε upregulated them through the involvement of the ERK/MAPK pathway. RKIP inactivated this pathway, but 14-3-3ε activated it. RKIP and 14-3-3ε were co-localized in the cells and interacted with each other; this attributed to their opposite influence on the ERK/MAPK pathway and the cells bioactivities.

CONCLUSIONS

The ERK/MAPK pathway is involved in the pathogenesis of gastric cancer; RKIP and 14-3-3ε exert an opposite effect on this pathway and the cells possibly via both direct and indirect reactions with the elements in this pathway. The interaction between RKIP and 14-3-3ε may also contribute to their pathogenetic roles in gastric cancer.

Positive effect of high RKIP expression on reduced distant metastasis by chemotherapy when combined with radiotherapy in locoregionally advanced nasopharyngeal carcinoma: a prospective study

The purpose of this prospective study is to investigate the predictive and prognostic significance of the Raf kinase inhibitory protein (RKIP) in locoregionally advanced nasopharyngeal carcinoma (NPC). Immunohistochemical assays were performed to detect the RKIP protein expression of samples from 212 patients with locoregionally advanced NPC. All patients were assigned randomly into the inductive chemotherapy plus radiation therapy (IC + RT) group, the concurrent chemoradiotherapy (CCRT) group, the inductive chemotherapy plus concurrent chemoradiotherapy (IC + CCRT) group, and the radiation therapy alone (RT) group. The patients in the IC + RT group were treated with IC using 2-3 cycles of cisplatin (80 mg/m(2)) and fluorouracil (500 mg/m(2)), repeated every 3 weeks, followed by radiotherapy. Those in the CCRT group were treated with weekly cisplatin (40 mg/m(2)) for 6-7 cycles during radiotherapy. In the IC + CCRT group, the chemotherapy prior to radiation was similar to the cisplatin-fluorouracil regimen in the IC + RT group, whereas it cisplatin regimen was identical to that in the CCRT group. The results show that RKIP is an independent prognostic factor for 5-year distant metastasis-free survival (DMFS), overall survival (OS), and progression-free survival (PFS). Patients with high RKIP expression benefited more from reduced metastasis in the IC + RT and the IC + CCRT group, with improved OS and PFS in each treatment group compared with that among patients with low RKIP expression. In the high RKIP expression subgroup, chemotherapy combined with radiotherapy improved the DMFS when compared with the RT group, but this effect was not observed in the low RKIP expression subgroup. RKIP was predictive of distant metastasis with good sensitivity and specificity. Clinically, high RKIP expression inhibited distant metastasis in advanced NPC, and its detection might be used to predict distant metastasis with good sensitivity and specificity. The effect of chemotherapy on distant metastasis in combined chemoradiotherapy might be related to the RKIP expression level. Patients with high RKIP expression showed more improved OS and PFS than their low RKIP expression counterparts. Higher RKIP expression improves the DMFS of patients who receive inductive high-dose cisplatin-based chemoradiotherapy, with or without concurrent cisplatin. Low RKIP expression is also a predictive marker for cancer progression and metastasis, which could be used to stratify patients with high risk of metastasis and death.

Novel biomarkers for the prediction of metastasis in colorectal cancer

INTRODUCTION

In patients with metastatic colorectal cancers, multimodal management and the use of biological agents such as monoclonal antibodies have had major positive effects on survival. The ability to predict which patients may be at 'high risk' of distant metastasis could have major implications on patient management. Histomorphological, immunohistochemical or molecular biomarkers are currently being investigated in order to test their potential value as predictors of metastasis.

AREAS COVERED

Here, the author reviews the clinical and functional data supporting the investigation of three novel promising biomarkers for the prediction of metastasis in patients with colorectal cancer: tumor budding, Raf1 kinase inhibitor protein (RKIP) and metastasis-associated in colon cancer-1 (MACC1).

EXPERT OPINION

The lifespan of most potential biomarkers is short as evidenced by the rare cases that have successfully made their way into daily practice such as KRAS or microsatellite instability (MSI) status. Although the three biomarkers reviewed herein have the potential to become important predictive biomarkers of metastasis, they have similar hurdles to overcome before they can be implemented into clinical management: standardization and validation in prospective patient cohorts.

Polypeptide N-acetylgalactosaminyltransferase 2 regulates cellular metastasis-associated behavior in gastric cancer

Aberrant glycosylation of cell surface glycoprotein due to specific alterations of glycosyltransferase activity is usually associated with invasion and metastasis of cancer, particularly of gastric carcinomas. Polypeptide N-acetylgalactosaminyltransferase 2 (ppGalNAc-T2), which catalyzes initiation of mucin-type O-glycosylation, is also involved in tumor migration and invasion. However, a comprehensive understanding of how ppGalNAc-T2 correlates with the metastasic potential of human gastric cancer is not currently available. In the present study, ppGalNAc-T2 was detected in a variety of human poorly differentiated tumor cells, and expression appeared to be higher in SGC7901 gastric cancer cells. In addition, we investigated the potential effects of ppGalNAc-T2 on growth and metastasis-associated behavior in SGC7901 cells after stable transfection with ppGalNAc-T2 sense and antisense vectors. We found that cell proliferation, adhesion and invasion were decreased in ppGalNAc-T2 overexpressed cells but increased in ppGalNAc-T2 downregulated cells. Therefore, we attempted to clarify the mechanisms underlying the anti-metastatic activities of ppGalNAc-T2. Further investigation indicated that overexpression of ppGalNAc-T2 is involved in the inhibition of matrix metalloproteinase (MMP)-2 expression at both the protein and mRNA levels, which may be associated with ppGalNAc-T2 suppressing the expression of transforming growth factor (TGF)-β1. However, it did not exhibit any apparent correlation with MMP-14 expression levels. Our data show the effect of ppGalNAc-T2 on proliferation, adhesion or invasion of SGC7901 gastric cancer cells, suggesting that ppGalNAc-T2 may exert anti-proliferative and anti-metastatic activity through the decrease of MMP-2 and TGF-β1. These results indicate that ppGalNAc‑T2 may be used as a novel therapeutic target for human gastric cancer treatment.

Decreased expression and aberrant methylation of Raf kinase inhibitory protein gene in esophageal squamous cell carcinoma

Raf kinase inhibitory protein (RKIP) gene is considered to be a suppressor of metastasis involved in various carcinomas. In the present study, we observed that promoter methylation repressed the expression of RKIP in TE-13 cell line. 5-Aza treatment and stable transfection of RKIP resulted in a significant inhibition of TE-13 cell proliferation. The promoter hypermethylation of RKIP was found to occur in dysplastic tissues and a close correlation was noted between RKIP methylation and the loss of mRNA and protein expression of the gene in ESCC specimens. In summary, RKIP may act as a tumor suppressor gene in esophageal cancer.

Raf kinase inhibitor RKIP inhibits MDA-9/syntenin-mediated metastasis in melanoma

Melanoma differentiation associated gene-9 (MDA-9), also known as syntenin, functions as a positive regulator of melanoma progression and metastasis. In contrast, the Raf kinase inhibitor, RKIP, a negative modulator of RAF-stimulated MEKK activation, is strongly downregulated in metastatic melanoma cells. In this study, we explored a hypothesized inverse relationship between MDA-9 and RKIP in melanoma. Tumor array and cell line analyses confirmed an inverse relationship between expression of MDA-9 and RKIP during melanoma progression. We found that MDA-9 transcriptionally downregulated RKIP in support of a suggested cross-talk between these two proteins. Furthermore, MDA-9 and RKIP physically interacted in a manner that correlated with a suppression of FAK and c-Src phosphorylation, crucial steps necessary for MDA-9 to promote FAK/c-Src complex formation and initiate signaling cascades that drive the MDA-9-mediated metastatic phenotype. Finally, ectopic RKIP expression in melanoma cells overrode MDA-9-mediated signaling, inhibiting cell invasion, anchorage-independent growth, and in vivo dissemination of tumor cells. Taken together, these findings establish RKIP as an inhibitor of MDA-9-dependent melanoma metastasis, with potential implications for targeting this process therapeutically.

The role of Raf kinase inhibitor protein in rheumatoid fibroblast-like synoviocytes invasiveness and cytokine and matrix metalloproteinase expression

Fibroblast-like synoviocytes (FLS) play an important role in the pathogenesis of rheumatoid arthritis. Raf kinase inhibitor protein (RKIP) negatively regulates the Raf/MEK/ERK and NF-κB pathway. The role of RKIP in rheumatoid FLS is unknown. The purpose of the present study was to investigate the function of RKIP in rheumatoid FLS. Rheumatoid FLS were transfected with either RKIP-expressing plasmids or RKIP small interfering RNA (siRNA). RKIP protein was detected in rheumatoid synovial tissue (ST) and FLS. RKIP overexpression significantly decreased IL-6 mRNA expression in TNF-α-stimulated rheumatoid FLS. RKIP overexpression also showed a decreased trend in IL-8, MMP-1, and MMP-3 mRNA expression in TNF-α-stimulated rheumatoid FLS. RKIP silencing resulted in significantly increased MMP-1 and MMP-3 mRNA expression in TNF-α-stimulated rheumatoid FLS. RKIP silencing also increased IL-6 and IL-8 mRNA expression in TNF-α-stimulated rheumatoid FLS, but this increase did not reach statistical significance. TNF-α-induced ERK and NF-κB activation was suppressed in FLS with RKIP overexpression. RKIP silencing resulted in a significantly higher invasion index in TNF-α-stimulated rheumatoid FLS compared to controls. These results suggest that RKIP might be a potential therapeutic target for rheumatoid arthritis.

Strategies for the discovery and development of therapies for metastatic breast cancer

Nearly all deaths caused by solid cancers occur as a result of metastasis--the formation of secondary tumours in distant organs such as the lungs, liver, brain and bone. A major obstruction to the development of drugs with anti-metastatic efficacy is our fragmented understanding of how tumours 'evolve' and metastasize, at both the biological and genetic levels. Furthermore, although there is significant overlap in the metastatic process among different types of cancer, there are also marked differences in the propensity to metastasize, the extent of metastasis, the sites to which the tumour metastasizes, the kinetics of the process and the mechanisms involved. Here, we consider the case of breast cancer, which has some marked distinguishing features compared with other types of cancer. Considerable progress has been made in the development of preclinical models and in the identification of relevant signalling pathways and genetic regulators of metastatic breast cancer, and we discuss how these might facilitate the development of novel targeted anti-metastatic drugs.

Prospective study of prognostic value of Raf kinase inhibitory protein and pretreatment plasma Epstein-Barr virus DNA for distant metastasis in locoregionally advanced nasopharyngeal carcinoma

BACKGROUND

The purpose of this prospective study was to investigate the predictive significance of Raf kinase inhibitory protein (RKIP) in locoregionally advanced nasopharyngeal carcinoma (NPC) and its effect on distant metastasis.

METHODS

The usual immunohistochemical stainings were performed to detect RKIP expression of cancer tissues from 210 patients with advanced NPC. After DNA samples from pretreatment plasma from these patients were extracted, real-time polymerase chain reaction (PCR) was performed to quantitatively analyze plasma Epstein-Barr virus (EBV) DNA.

RESULTS

RKIP expression was significantly different for different N classifications and WHO pathologic grades, respectively (p < .05). Cox regression confirmed RKIP and EBV DNA were independent prognostic markers for 5-year distant metastasis-free survival (DMFS). In the high RKIP expression group, chemotherapy had a positive effect on improved DMFS, but not in the low RKIP expression group.

CONCLUSIONS

RKIP could be identified as an independent prognostic factor on DMFS. For each combined treatment modality, the different impact of chemotherapy on distant metastasis might be related to the RKIP expression level.