Effects of raf kinase inhibitor protein expression on suppression of prostate cancer metastasis

Genetically predicted metabolites mediate the association between lipidome and malignant melanoma of skin

Objective

To investigate the causal relationship between lipidome and malignant melanoma of skin (MMOS), while identifying and quantifying the role of metabolites as potential mediators.

Methods

A two-sample Mendelian randomization (MR) analysis of lipid species (n=7174) and MMOS was performed using pooled data from genome-wide association studies (GWAS). In addition, we quantified the proportion of metabolite-mediated lipidome effects on MMOS by two-step MR.

Results

This study identified potential causal relationships between 11 lipids and MMOS, and 40 metabolites and MMOS, respectively. Phosphatidylethanolamine (18:0_18:2) levels mined from 179 lipids by MR Analysis increased the risk of MMOS (OR: 1.962; 95%CI:1.298,2.964; P=0.001). There is no strong evidence for a relationship between genetically predicted MMOS and phosphatidylethanolamine (18:0_18:2) levels (P=0.628). The proportion of gene predictions for phosphatidylethanolamine (18:0_18:2) levels mediated by 1-stearoyl-(glycosylphosphatidylinositol) GPI (18:0) levels was 12.40%.

Conclusion

This study identifies 1-stearoyl-GPI (18:0) levels as a potential mediator that may mediate the causal relationship between phosphatidylethanolamine (18:0_18:2) levels and MMOS, This provides direction for the investigation of MMOS, but further research of other possible potential mediators is still needed.

MEK inhibitors and DA-Raf, a dominant-negative antagonist of the Ras-ERK pathway, prevent the migration and invasion of KRAS-mutant cancer cells

The Ras-induced ERK pathway (Raf-MEK-ERK signaling cascade) regulates a variety of cellular responses including cell proliferation, survival, and migration. Activating mutations in RAS genes, particularly in the KRAS gene, constitutively activate the ERK pathway, resulting in tumorigenesis, cancer cell invasion, and metastasis. DA-Raf1 (DA-Raf) is a splicing isoform of A-Raf and contains the Ras-binding domain but lacks the kinase domain. Consequently, DA-Raf antagonizes the Ras-ERK pathway in a dominant-negative manner and can serve as a tumor suppressor that targets mutant Ras protein-induced tumorigenesis. We show here that MEK inhibitors and DA-Raf interfere with the in vitro collective cell migration and invasion of human KRAS-mutant carcinoma cell lines, the lung adenocarcinoma A549, colorectal carcinoma HCT116, and pancreatic carcinoma MIA PaCa-2 cells. DA-Raf expression was silenced in these cancer cell lines. All these cell lines had high collective migration abilities and invasion properties in Matrigel, compared with nontumor cells. Their migration and invasion abilities were impaired by suppressing the ERK pathway with the MEK inhibitors U0126 and trametinib, an approved anticancer drug. Expression of DA-Raf in MIA PaCa-2 cells reduced the ERK activity and hindered the migration and invasion abilities. Therefore, DA-Raf may function as an invasion suppressor protein in the KRAS-mutant cancer cells by blocking the Ras-ERK pathway when DA-Raf expression is induced in invasive cancer cells.

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.

Changes in Expression of Tumor Suppressor Gene RKIP Impact How Cancers Interact with Their Complex Environment

Tumor microenvironment (TME) is the immediate environment where cancer cells reside in a tumor. It is composed of multiple cell types and extracellular matrix. Microenvironments can be restrictive or conducive to the progression of cancer cells. Initially, microenvironments are suppressive in nature. Stepwise accumulation of mutations in oncogenes and tumor suppressor genes enables cancer cells to acquire the ability to reshape the microenvironment to advance their growth and metastasis. Among the many genetic events, the loss-of-function mutations in tumor suppressor genes play a pivotal role. In this review, we will discuss the changes in TME and the ramifications on metastasis upon altered expression of tumor metastasis suppressor gene RKIP in breast cancer cells.

Cancer resistance via the downregulation of the tumor suppressors RKIP and PTEN expressions: therapeutic implications

The Raf kinase inhibitor protein (RKIP) has been reported to be underexpressed in many cancers and plays a role in the regulation of tumor cells' survival, proliferation, invasion, and metastasis, hence, a tumor suppressor. RKIP also regulates tumor cell resistance to cytotoxic drugs/cells. Likewise, the tumor suppressor, phosphatase and tensin homolog (PTEN), which inhibits the phosphatidylinositol 3 kinase (PI3K)/AKT pathway, is either mutated, underexpressed, or deleted in many cancers and shares with RKIP its anti-tumor properties and its regulation in resistance. The transcriptional and posttranscriptional regulations of RKIP and PTEN expressions and their roles in resistance were reviewed. The underlying mechanism of the interrelationship between the signaling expressions of RKIP and PTEN in cancer is not clear. Several pathways are regulated by RKIP and PTEN and the transcriptional and post-transcriptional regulations of RKIP and PTEN is significantly altered in cancers. In addition, RKIP and PTEN play a key role in the regulation of tumor cells response to chemotherapy and immunotherapy. In addition, molecular and bioinformatic data revealed crosstalk signaling networks that regulate the expressions of both RKIP and PTEN. These crosstalks involved the mitogen-activated protein kinase (MAPK)/PI3K pathways and the dysregulated nuclear factor-kappaB (NF-κB)/Snail/Yin Yang 1 (YY1)/RKIP/PTEN loop in many cancers. Furthermore, further bioinformatic analyses were performed to investigate the correlations (positive or negative) and the prognostic significance of the expressions of RKIP or PTEN in 31 different human cancers. These analyses were not uniform and only revealed that there was a positive correlation between the expression of RKIP and PTEN only in few cancers. These findings demonstrated the existence of signaling cross-talks between RKIP and PTEN and both regulate resistance. Targeting either RKIP or PTEN (alone or in combination with other therapies) may be sufficient to therapeutically inhibit tumor growth and reverse the tumor resistance to cytotoxic therapies.

Regulation of Kinase Signaling Pathways by α6β4-Integrins and Plectin in Prostate Cancer

Hemidesmosomes (HDs) are adhesive structures that ensure stable anchorage of cells to the basement membrane. They are formed by α6β4-integrin heterodimers and linked to intermediate filaments via plectin. It has been reported that one of the most common events during the pathogenesis of prostate cancer (PCa) is the loss of HD organization. While the expression levels of β4-integrins are strongly reduced, the expression levels of α6-integrins and plectin are maintained or even elevated, and seem to promote tumorigenic properties of PCa cells, such as proliferation, invasion, metastasis, apoptosis- and drug-resistance. In this review, we discuss the potential mechanisms of how HD components might contribute to various cellular signaling pathways to promote prostate carcinogenesis. Moreover, we summarize the current knowledge on the involvement of α6β4-integrins and plectin in PCa initiation and progression.

Development of a ferroptosis-based model to predict prognosis, tumor microenvironment, and drug response for lung adenocarcinoma with weighted genes co-expression network analysis

Objective: The goal of this study was to create a risk model based on the ferroptosis gene set that affects lung adenocarcinoma (LUAD) patients' prognosis and to investigate the potential underlying mechanisms. Material and Methods: A cohort of 482 LUAD patients from the TCGA database was used to develop the prognostic model. We picked the module genes from the ferroptosis gene set using weighted genes co-expression network analysis (WGCNA). The least absolute shrinkage and selection operator (LASSO) and univariate cox regression were used to screen the hub genes. Finally, the multivariate Cox analysis constructed a risk prediction score model. Three other cohorts of LUAD patients from the GEO database were included to validate the prediction ability of our model. Furthermore, the differentially expressed genes (DEG), immune infiltration, and drug sensitivity were analyzed. Results: An eight-gene-based prognostic model, including PIR, PEBP1, PPP1R13L, CA9, GLS2, DECR1, OTUB1, and YWHAE, was built. The patients from the TCGA database were classified into the high-RS and low-RS groups. The high-RS group was characterized by poor overall survival (OS) and less immune infiltration. Based on clinical traits, we separated the patients into various subgroups, and RS had remarkable prediction performance in each subgroup. The RS distribution analysis demonstrated that the RS was significantly associated with the stage of the LUAD patients. According to the study of immune cell infiltration in both groups, patients in the high-RS group had a lower abundance of immune cells, and less infiltration was associated with worse survival. Besides, we discovered that the high-RS group might not respond well to immune checkpoint inhibitors when we analyzed the gene expression of immune checkpoints. However, drug sensitivity analysis suggested that high-RS groups were more sensitive to common LUAD agents such as Afatinib, Erlotinib, Gefitinib, and Osimertinib. Conclusion: We constructed a novel and reliable ferroptosis-related model for LUAD patients, which was associated with prognosis, immune cell infiltration, and drug sensitivity, aiming to shed new light on the cancer biology and precision medicine.

Circular RNA circPOLR2A promotes clear cell renal cell carcinoma progression by facilitating the UBE3C-induced ubiquitination of PEBP1 and, thereby, activating the ERK signaling pathway

Background

Increasing evidence has demonstrated that circular RNAs (circRNAs) are implicated in cancer progression. However, the aberrant expression and biological functions of circRNAs in clear cell renal cell carcinoma (cRCC) remain largely elusive.

Method

Differentially expressed circRNAs in cRCC were filtered via bioinformatics analysis. Aberrant circPOLR2A expression was validated in cRCC tissues and cell lines via qRT-PCR. Sanger sequencing was used to identify the backsplicing site of circPOLR2A. In vitro and in vivo functional experiments were performed to evaluate the role of circPOLR2A in cRCC malignancy. RNA pull-down, mass spectrometry, RIP, FISH and immunofluorescence assays were used to identify and validate the circPOLR2A-interacting proteins. Ubiquitination modification and interaction between proteins were detected via Co-IP and western blotting. The m6A modification in circPOLR2A was validated by the meRIP assay.

Results

Bioinformatics analysis revealed that circPOLR2A was highly expressed in cRCC tissues and metastatic cRCC tissues. CircPOLR2A expression was associated with tumor size and TNM stage in cRCC patients. In vitro and in vivo functional assays revealed that circPOLR2A accelerated cRCC cell proliferation, migration, invasion and angiogenesis, while inhibiting apoptosis. Further mechanistic research suggested that circPOLR2A could interact with UBE3C and PEBP1 proteins, and that UBE3C could act as a specific ubiquitin E3 ligase for the PEBP1 protein. The UBE3C/circPOLR2A/PEBP1 protein-RNA ternary complex enhanced the UBE3C-mediated ubiquitination and degradation of the PEBP1 protein which could inactivate the ERK signaling pathway. Rescue experiments revealed that the PEBP1 protein was the functional downstream target of circPOLR2A. Furthermore, m6A modification in circPOLR2A was confirmed, and the m6A reader YTHDF2 could regulate circPOLR2A expression.

Conclusion

Our study demonstrated that circPOLR2A modulated the UBE3C-mediated ubiquitination and degradation of the PEBP1 protein, and further activated the ERK pathway during cRCC progression and metastasis. The m6A reader, YTHDF2, regulated circPOLR2A expression in cRCC. Hence, circPOLR2A could be a potential target for the diagnosis and treatment of cRCC.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12943-022-01607-8.

A Stochastic Binary Model for the Regulation of Gene Expression to Investigate Responses to Gene Therapy

In this manuscript, we use an exactly solvable stochastic binary model for the regulation of gene expression to analyze the dynamics of response to a treatment aiming to modulate the number of transcripts of a master regulatory switching gene. The challenge is to combine multiple processes with different time scales to control the treatment response by a switching gene in an unavoidable noisy environment. To establish biologically relevant timescales for the parameters of the model, we select the RKIP gene and two non-specific drugs already known for changing RKIP levels in cancer cells. We demonstrate the usefulness of our method simulating three treatment scenarios aiming to reestablish RKIP gene expression dynamics toward a pre-cancerous state: (1) to increase the promoter's ON state duration; (2) to increase the mRNAs' synthesis rate; and (3) to increase both rates. We show that the pre-treatment kinetic rates of ON and OFF promoter switching speeds and mRNA synthesis and degradation will affect the heterogeneity and time for treatment response. Hence, we present a strategy for reaching increased average mRNA levels with diminished heterogeneity while reducing drug dosage by simultaneously targeting multiple kinetic rates that effectively represent the chemical processes underlying the regulation of gene expression. The decrease in heterogeneity of treatment response by a target gene helps to lower the chances of emergence of resistance. Our approach may be useful for inferring kinetic constants related to the expression of antimetastatic genes or oncogenes and for the design of multi-drug therapeutic strategies targeting the processes underpinning the expression of master regulatory genes.

A novel graph convolutional neural network for predicting interaction sites on protein kinase inhibitors in phosphorylation

Protein kinase-inhibitor interactions are key to the phosphorylation of proteins involved in cell proliferation, differentiation, and apoptosis, which shows the importance of binding mechanism research and kinase inhibitor design. In this study, a novel machine learning module (i.e., the WL Box) was designed and assembled to the Prediction of Interaction Sites of Protein Kinase Inhibitors (PISPKI) model, which is a graph convolutional neural network (GCN) to predict the interaction sites of protein kinase inhibitors. The WL Box is a novel module based on the well-known Weisfeiler-Lehman algorithm, which assembles multiple switch weights to effectively compute graph features. The PISPKI model was evaluated by testing with shuffled datasets and ablation analysis using 11 kinase classes. The accuracy of the PISPKI model with the shuffled datasets varied from 83 to 86%, demonstrating superior performance compared to two baseline models. The effectiveness of the model was confirmed by testing with shuffled datasets. Furthermore, the performance of each component of the model was analyzed via the ablation study, which demonstrated that the WL Box module was critical. The code is available at https://github.com/feiqiwang/PISPKI .

Insights of RKIP-Derived Suppression of Prostate Cancer

Simple Summary

Despite an intensive research effort in the past few decades, prostate cancer (PC) remains a top cause of cancer death in men, particularly in the developed world. The major cause of fatality is the progression of local prostate cancer to metastasis disease. Treatment of patients with metastatic prostate cancer (mPC) is generally ineffective. Based on the discovery of mPC relying on androgen for growth, many patients with mPC show an initial response to the standard of care: androgen deprivation therapy (ADT). However, lethal castration resistant prostate cancers (CRPCs) commonly develop. It is widely accepted that intervention of metastatic progression of PC is a critical point of intervention to reduce PC death. Accumulative evidence reveals a role of RKIP in suppression of PC progression towards mPC. We will review current evidence and discuss the potential utilization of RKIP in preventing mPC progression.

Abstract

Prostate cancer (PC) is a major cause of cancer death in men. The disease has a great disparity in prognosis. Although low grade PCs with Gleason scores ≤ 6 are indolent, high-risk PCs are likely to relapse and metastasize. The standard of care for metastatic PC (mPC) remains androgen deprivation therapy (ADT). Resistance commonly occurs in the form of castration resistant PC (CRPC). Despite decades of research efforts, CRPC remains lethal. Understanding of mechanisms underpinning metastatic progression represents the overarching challenge in PC research. This progression is regulated by complex mechanisms, including those regulating PC cell proliferation, epithelial–mesenchymal transition (EMT), and androgen receptor (AR) signaling. Among this PC metastatic network lies an intriguing suppressor of PC metastasis: the Raf kinase inhibitory protein (RKIP). Clinically, the RKIP protein is downregulated in PC, and showed further reduction in mPC. In xenograft mouse models for PC, RKIP inhibits metastasis. In vitro, RKIP reduces PC cell invasion and sensitizes PC cells to therapeutic treatments. Mechanistically, RKIP suppresses Raf-MEK-ERK activation and EMT, and modulates extracellular matrix. In return, Snail, NFκB, and the polycomb protein EZH2 contribute to inhibition of RKIP expression. In this review, we will thoroughly analyze RKIP’s tumor suppression actions in PC.

Pheno-SELEX: Engineering Anti-Metastatic Aptamers through Targeting the Invasive Phenotype Using Systemic Evolution of Ligands by Exponential Enrichment

Multiple methods (e.g., small molecules and antibodies) have been engineered to target specific proteins and signaling pathways in cancer. However, many mediators of the cancer phenotype are unknown and the ability to target these phenotypes would help mitigate cancer. Aptamers are small DNA or RNA molecules that are designed for therapeutic use. The design of aptamers to target cancers can be challenging. Accordingly, to engineer functionally anti-metastatic aptamers we used a modification of systemic evolution of ligands by exponential enrichment (SELEX) we call Pheno-SELEX to target a known phenotype of cancer metastasis, i.e., invasion. A highly invasive prostate cancer (PCa) cell line was established and used to identify aptamers that bound to it with high affinity as opposed to a less invasive variant to the cell line. The anti-invasive aptamer (AIA1) was found to inhibit in vitro invasion of the original highly invasive PCa cell line, as well as an additional PCa cell line and an osteosarcoma cell line. AIA1 also inhibited in vivo development of metastasis in both a PCa and osteosarcoma model of metastasis. These results indicate that Pheno-SELEX can be successfully used to identify aptamers without knowledge of underlying molecular targets. This study establishes a new paradigm for the identification of functional aptamers.

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 Therapeutic Potential of MAPK/ERK Inhibitors in the Treatment of Colorectal Cancer

The MAPK/ERK signaling pathway regulates cancer cell proliferation, apoptosis, inflammation, angiogenesis, metastasis and drug resistance. Mutations and up-regulation of components of the MAPK/ERK signaling pathway, as well as over-activation of this critical signaling pathway, are frequently observed in colorectal carcinomas. Targeting the MAPK/ERK signaling pathway, using specific pharmacological inhibitors, elicits potent anti-tumor effects, supporting the therapeutic potential of these inhibitors in the treatment of CRC. Several drugs have recently been developed for the inhibition of the MEK/ERK pathway in preclinical and clinical settings, such as MEK162 and MK-2206. MEK1/2 inhibitors demonstrate promising efficacy and anticancer activity for the treatment of this malignancy. This review summarizes the current knowledge on the role of the MAPK/ERK signaling pathway in the pathogenesis of CRC and the potential clinical value of synthetic inhibitors of this pathway in preventing CRC progression for a better understanding, and hence, better management of colorectal cancer.

Regulation on tumor metastasis by Raf kinase inhibitory protein: New insight with reactive oxygen species signaling

Targeted therapy aiming at the metastatic signal pathway, such as that triggered by receptor tyrosine kinase (RTK), for the prevention of tumor progression is promising. However, RTK-based targeted therapy frequently suffered from drug resistance due to the co-expression of multiple growth factor receptors that may raise compensatory secondary signaling and acquired mutations after treatment. One alternative strategy is to manipulate the common negative regulators of the RTK signaling. Among them, Raf kinase inhibitory protein (RKIP) is highlighted and focused on this review. RKIP can associate with Raf-1, thus suppressing the downstream mitogen-activated protein kinase (MAPK) cascade. RKIP also negatively regulates other metastatic signal molecules including NF-κB, STAT3, and NOTCH1. In general, RKIP achieves this task via associating and blocking the activity of the critical molecules on upstream of the aforementioned pathways. One novel RKIP-related signaling involves reactive oxygen species (ROS). In our recent report, we found that PKCδ-mediated ROS generation may interfere with the association of RKIP with heat shock protein 60 (HSP60)/MAPK complex via oxidation of HSP60 triggered by the tumor promoter 12-O-tetradecanoyl-phorbol-13-acetate. The departure of RKIP may impact the downstream MAPK in two aspects. One is to trigger the Mt→cytosol translocation of HSP60 coupled with MAPKs. The other is to change the conformation of HSP60, favoring more efficient activation of the associated MAPK by upstream kinases in cytosol. It is worthy of investigating whether various RTKs capable of generating ROS can drive metastatic signaling via affecting RKIP in the same manner.

RAF-MEK-ERK pathway in cancer evolution and treatment

The RAF-MEK-ERK signaling cascade is a well-characterized MAPK pathway involved in cell proliferation and survival. The three-layered MAPK signaling cascade is initiated upon RTK and RAS activation. Three RAF isoforms ARAF, BRAF and CRAF, and their downstream MEK1/2 and ERK1/2 kinases constitute a coherently orchestrated signaling module that directs a range of physiological functions. Genetic alterations in this pathway are among the most prevalent in human cancers, which consist of numerous hot-spot mutations such as BRAF^V600E. Oncogenic mutations in this pathway often override otherwise tightly regulated checkpoints to open the door for uncontrolled cell growth and neoplasia. The crosstalk between the RAF-MEK-ERK axis and other signaling pathways further extends the proliferative potential of this pathway in human cancers. In this review, we summarize the molecular architecture and physiological functions of the RAF-MEK-ERK pathway with emphasis on its dysregulations in human cancers, as well as the efforts made to target the RAF-MEK-ERK module using small molecule inhibitors.

Molecular mediators of breast cancer metastasis

Breast cancer has the highest incidence rate of malignancy in women worldwide. A major clinical challenge faced by patients with breast cancer treated by conventional therapies is frequent relapse. This relapse has been attributed to the cancer stem cell (CSC) population that resides within the tumor and possess stemness properties. Breast CSCs are generated when breast cancer cells undergo epithelial-mesenchymal transition resulting in aggressive, highly metastatic, and invasive phenotypes that exhibit resistance towards chemotherapeutics. Metastasis, a phenomenon that aids in the migration of breast CSCs, occurs through any of three different routes: hematogenous, lymphatic, and transcoelomic. Hematogenous dissemination of breast CSCs leads to metastasis towards distant unrelated organs like lungs, liver, bone, and brain causing secondary tumor generation. Activation of metastasis genes or silencing of metastasis suppressor genes often leads to the advancement of metastasis. This review focuses on various genes and molecular factors that have been implicated to regulate organ-specific breast cancer metastasis by defying the available therapeutic interventions.

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.

Role of the PI3K/Akt pathway in cadmium induced malignant transformation of normal prostate epithelial cells

This study investigated the role of the PI3K/Akt pathway in cadmium (Cd) induced malignant transformation of normal prostate epithelial (PWR1E and RWPE1) cells. Both PWR1E and RWPE1 cells were exposed to 10 μM Cd for one year and designated as Cd-PWR1E and Cd-RWPE1. Cd-RWPE1 cells robustly formed tumors in athymic nude mice. Functionally, Cd-exposure induced tumorigenic attributes indicated by increased wound healing, migration and invasion capabilities in both cell lines. RT²-array analysis revealed many oncogenes including P110α, Akt, mTOR, NFKB1 and RAF were induced whereas tumor suppressor (TS) genes were attenuated in Cd-RWPE1. This was validated by individual quantitative-real-time-PCR at transcriptional and by immunoblot at translational levels. These results were consistent in Cd-PWR1E vs parental PWR1E cells. Gene Set Enrichment Analysis revealed that five prostate cancer (PCa) related pathways were enriched in Cd-exposed cells compared to their normal controls. These pathways include the KEGG- Pathways in cancer, Prostate Cancer Pathway, ERBB, Apoptosis and MAPK pathways. We selected up- and down-regulated genes randomly from the PI3K/Akt pathway array and profiled these in the TCGA/GDC prostate-adenocarcinoma (PRAD) patient cohort. An upregulation of oncogenes and downregulation of TS genes was observed in PCa compared to their normal controls. Taken together, our study reveals that the PI3K/Akt signaling is one of the main molecular pathways involved in Cd-driven transformation of normal prostate epithelial cells to malignant form. Understanding the molecular mechanisms involved in the Cd-driven malignant transformation of normal prostate cells will provide a significant insight to develop better therapeutic strategies for Cd-induced prostate cancer.

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.

Activation of the Erk/MAPK signaling pathway is a driver for cadmium induced prostate cancer

PURPOSE

Cadmium (Cd) is reported to be associated with carcinogenesis. The molecular mechanisms associated with Cd-induced prostate cancer (PCa) remain elusive.

MATERIALS AND METHODS

RWPE1, PWR1E and DU 145 cells were used. RT2 Profiler Array, real-time-quantitative-PCR, immunofluorescence, cell cycle, apoptosis, proliferation and colony formation assays along with Gene Set Enrichment Analysis (GSEA) were performed.

RESULT

Chronic Cd exposure of non-malignant RWPE1 and PWR1E cells promoted cell survival, proliferation and colony formation with inhibition of apoptosis. Even a two-week Cd exposure of PCa cell line (DU 145) significantly increased the proliferation and decreased apoptosis. RT2 profiler array of 84 genes involved in the Erk/MAPK pathway revealed induction of gene expression in Cd-RWPE1 cells compared to RWPE1. This was confirmed by individual TaqMan gene expression analysis in both Cd-RWPE1 and Cd-PWR1E cell lines. GSEA showed an enrichment of the Erk/MAPK pathway along with other pathways such as KEGG-ERBB, KEGG-Cell Cycle, KEGG-VEGF, KEGG-Pathways in cancer and KEGG-prostate cancer pathway. We randomly selected upregulated genes from Erk/MAPK pathway and performed profile analysis in a PCa data set from the TCGA/GDC data base. We observed upregulation of these genes in PCa compared to normal samples. An increase in phosphorylation of the Erk1/2 and Mek1/2 was observed in Cd-RWPE1 and Cd-PWR1E cells compared to parental cells, confirming that Cd-exposure induces activation of the Erk/MAPK pathway.

CONCLUSION

This study demonstrates that Erk/MAPK signaling is a major pathway involved in Cd-induced malignant transformation of normal prostate cells. Understanding these dominant oncogenic pathways may help develop optimal therapeutic strategies for PCa.

Small Ones to Fight a Big Problem-Intervention of Cancer Metastasis by Small Molecules

Metastasis represents the most lethal attribute of cancer and critically limits successful therapies in many tumor entities. The clinical need is defined by the fact that all cancer patients, who have or who will develop distant metastasis, will experience shorter survival. Thus, the ultimate goal in cancer therapy is the restriction of solid cancer metastasis by novel molecularly targeted small molecule based therapies. Biomarkers identifying cancer patients at high risk for metastasis and simultaneously acting as key drivers for metastasis are extremely desired. Clinical interventions targeting these key molecules will result in high efficiency in metastasis intervention. In result of this, personalized tailored interventions for restriction and prevention of cancer progression and metastasis will improve patient survival. This review defines crucial biological steps of the metastatic cascade, such as cell dissemination, migration and invasion as well as the action of metastasis suppressors. Targeting these biological steps with tailored therapeutic strategies of intervention or even prevention of metastasis using a wide range of small molecules will be discussed.

RKIP Regulates Differentiation-Related Features in Melanocytic Cells

Raf Kinase Inhibitor Protein (RKIP) has been extensively reported as an inhibitor of key signaling pathways involved in the aggressive tumor phenotype and shows decreased expression in several types of cancers. However, little is known about RKIP in melanoma or regarding its function in normal cells. We examined the role of RKIP in both primary melanocytes and malignant melanoma cells and evaluated its diagnostic and prognostic value. IHC analysis revealed a significantly higher expression of RKIP in nevi compared with early-stage (stage I–II, AJCC 8th) melanoma biopsies. Proliferation, wound healing, and collagen-coated transwell assays uncovered the implication of RKIP on the motility but not on the proliferative capacity of melanoma cells as RKIP protein levels were inversely correlated with the migration capacity of both primary and metastatic melanoma cells but did not alter other parameters. As shown by RNA sequencing, endogenous RKIP knockdown in primary melanocytes triggered the deregulation of cellular differentiation-related processes, including genes (i.e., ZEB1, THY-1) closely related to the EMT. Interestingly, NANOG was identified as a putative transcriptional regulator of many of the deregulated genes, and RKIP was able to decrease the activation of the NANOG promoter. As a whole, our data support the utility of RKIP as a diagnostic marker for early-stage melanomas. In addition, these findings indicate its participation in the maintenance of a differentiated state of melanocytic cells by modulating genes intimately linked to the cellular motility and explain the progressive decrease of RKIP often described in tumors.

GRK2 enforces androgen receptor dependence in the prostate and prostate tumors

Metastatic tumors that have become resistant to androgen deprivation therapy represent the major challenge in treating prostate cancer. Although these recurrent tumors typically remain dependent on the androgen receptor (AR), non-AR-driven tumors that also emerge are particularly deadly and becoming more prevalent. Here, we present a new genetically engineered mouse model for non-AR-driven prostate cancer that centers on a negative regulator of G protein-coupled receptors that is downregulated in aggressive human prostate tumors. Thus, prostate-specific expression of a dominant-negative G protein-coupled receptor kinase 2 (GRK2-DN) transgene diminishes AR and AR target gene expression in the prostate, and confers resistance to castration-induced involution. Further, the GRK2-DN transgene dramatically accelerates oncogene-initiated prostate tumorigenesis by increasing primary tumor size, potentiating visceral organ metastasis, suppressing AR, and inducing neuroendocrine marker mRNAs. In summary, GRK2 enforces AR-dependence in the prostate, and the loss of GRK2 function in prostate tumors accelerates disease progression towards the deadliest stage.

Primary prostate cancer educates bone stroma through exosomal pyruvate kinase M2 to promote bone metastasis

Prostate cancer (PCa) metastasizes selectively to bone through unknown mechanisms. In the current study, we identified exosome-mediated transfer of pyruvate kinase M2 (PKM2) from PCa cells into bone marrow stromal cells (BMSCs) as a novel mechanism through which primary tumor-derived exosomes promote premetastatic niche formation. We found that PKM2 up-regulates BMSC CXCL12 production in a HIF-1α-dependent fashion, which subsequently enhances PCa seeding and growth in the bone marrow. Furthermore, serum-derived exosomes from patients with either primary PCa or PCa metastasis, as opposed to healthy men, reveal that increased exosome PKM2 expression is associated with metastasis, suggesting clinical relevance of exosome PKM2 in PCa. Targeting the exosome-induced CXCL12 axis diminished exosome-mediated bone metastasis. In summary, primary PCa cells educate the bone marrow to create a premetastatic niche through primary PCa exosome-mediated transfer of PKM2 into BMSCs and subsequent up-regulation of CXCL12. This novel mechanism indicates the potential for exosome PKM2 as a biomarker and suggests therapeutic targets for PCa bone metastasis.

RKIP as an Inflammatory and Immune System Modulator: Implications in Cancer

Raf kinase inhibitor protein (RKIP), an important modulator of intracellular signalling pathways, is commonly downregulated in multiple cancers. This reduction, or loss of expression, is correlated not only with the presence of metastasis, contributing to RKIP’s classification as a metastasis suppressor, but also with tumour aggressiveness and poor prognosis. Recent findings suggest a strong involvement of RKIP in the modulation of tumour microenvironment components, particularly by controlling the infiltration of specific immune cells and secretion of pro-metastatic factors. Additionally, RKIP interaction with multiple signalling molecules seems to potentiate its function as a regulator of inflammatory processes, mainly through stimulation of anti- or pro-inflammatory cytokines. Furthermore, RKIP is involved in the modulation of immunotherapeutic drugs response, through diverse mechanisms that sensitize cells to apoptosis. In the present review, we will provide updated information about the role of RKIP as an inflammatory and immune modulator and its potential implications in cancer will be addressed.

RAF Kinase Inhibitor Protein in Myeloid Leukemogenesis

RAF kinase inhibitor protein (RKIP) is an essential regulator of intracellular signaling. A somatic loss of RKIP expression is a frequent event in solid human cancers, and a role of RKIP as metastasis-suppressor is widely accepted nowadays. Recently, RKIP loss has been described in acute myeloid leukemia (AML) and a series of other myeloid neoplasias (MNs). Functional in vitro and in vivo experiments revealed that RKIP is an essential player within the development of these liquid tumors; however, the respective role of RKIP seems to be complex and multi-faceted. In this review, we will summarize the current knowledge about RKIP in myeloid leukemogenesis. We will initially describe its involvement in physiologic hematopoiesis, and will then proceed to discuss its role in the development of AML and other MNs. Finally, we will discuss potential therapeutic implications arising thereof.

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.

TROY interacts with RKIP to promote glioma development

TROY is a component of the Nogo receptor complex and plays the key role in neuronal survival, migration, and differentiation. Here, we show the up-regulation of TROY in human glioma tissues and cells. Inhibition of TROY expression slowed glioma development in vivo and in vitro. Raf kinase inhibitor (RKIP) was found to interact with TROY. The physical interaction of TROY/RKIP was confirmed via co-immunoprecipitation (co-IP) assays. Furthermore, we found that the TROY/RKIP interaction was enhanced by fetal bovine serum (FBS) exposure, and TROY knockdown also led to down-regulation of NF-κB. Finally, disruption of the TROY/RKIP interaction using the TAT-TROY (234–371 aa) protein reduced the glioma development in xenografted mice. This suggests the TROY/RKIP interaction is a potential target for therapy of gliomas.

Targeting Raf Kinase Inhibitory Protein Regulation and Function

Raf Kinase Inhibitory Protein (RKIP) is a highly conserved kinase inhibitor that functions as a metastasis suppressor in a variety of cancers. Since RKIP can reprogram tumor cells to a non-metastatic state by rewiring kinase networks, elucidating the mechanism by which RKIP acts not only reveals molecular mechanisms that regulate metastasis, but also represents an opportunity to target these signaling networks therapeutically. Although RKIP is often lost during metastatic progression, the mechanism by which this occurs in tumor cells is complex and not well understood. In this review, we summarize our current understanding of RKIP regulation in tumors and consider experimental and computational strategies for recovering or mimicking its function by targeting mediators of metastasis.

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.

Clinical and prognostic significance of Raf kinase inhibitory protein expression in gastrointestinal stromal tumors

AIM

To detect the expression of Raf kinase inhibitory protein (RKIP) in gastrointestinal stromal tumors (GISTs) and to analyze its relationship with clinicopatholgical characteristics and prognosis of this disease.

METHODS

Sixty-three patients with pathologically diagnosed GISTs who underwent surgical resection at the Shengjing Hospital of China Medical University from January 2011 to January 2015 and had complete clinical, pathological, and follow-up data were included. Immunohistochemical method was used to detect the expression of RKIP in GIST tissue samples from these patients. Kaplan-Meier method was used to calculate the survival rate of 60 patients with complete follow-up data, and Cox regression analysis was performed to identify factors affecting the prognosis of patients GISTs to evaluate further the diagnostic and prognostic value of RKIP in GISTs.

RESULTS

In GIST tissues, RKIP positive signals, manifesting as brownish yellow or brown granules, were located in the cytoplasm or on the membrane. Of 63 tissue samples included in this study, 34 (54%) were positive and 29 (46%) were negative for RKIP expression. Statistical analysis showed that RKIP expression in GISTs was significantly associated with tumor size, National Institutes of Health (NIH) risk grade, and mucosal invasion, but had no significant association with age, gender, tumor location, or the number of mitotic figures. Univariate Kaplan-Meier analysis revealed that the 1-, 3-, and 5-year survival rates were 94.4%, 89.2%, and 80.5% for patients with positive RKIP expression, and 88.6%, 68.2%, and 48.2% for patients with negative RKIP expression, suggesting that patients with high RKIP expression had significantly higher survival rates than those with low expression (Log-rank test, P = 0.0015). Cox regression analysis demonstrated that NIH risk grade was significantly associated with the prognosis of GISTs (P = 0.037), suggesting that NIH risk grade is a significant predictor of the prognosis of GISTs. RKIP expression had a tendency to predict the survival of GISTs (P = 0.122), suggesting that RKIP expression may have appreciated value to predict the prognosis of GISTs.

CONCLUSION

This study demonstrated that: (1) RKIP expression in GISTs is associated with tumor size, NIH risk grade, and mucosal invasion, and low or no expression of RKIP predicts a high malignancy potential; (2) high RKIP correlates positively with the survival of patients with GISTs; and (3) RKIP expression has appreciated value for predicting the survival of patients with GISTs, although it is not an independent prognostic factor in GISTs.

A survey of metastasis suppressors in Metazoa

Metastasis suppressors are genes/proteins involved in regulation of one or more steps of the metastatic cascade while having little or no effect on tumor growth. The list of putative metastasis suppressors is constantly increasing although thorough understanding of their biochemical mechanism(s) and evolutionary history is still lacking. Little is known about tumor-related genes in invertebrates, especially non-bilaterians and unicellular relatives of animals. However, in the last few years we have been witnessing a growing interest in this subject since it has been shown that many disease-related genes are already present in simple non-bilateral animals and even in their unicellular relatives. Studying human diseases using simpler organisms that may better represent the ancestral conditions in which the specific disease-related genes appeared could provide better understanding of how those genes function. This review represents a compilation of published literature and our bioinformatics analysis to gain a general insight into the evolutionary history of metastasis-suppressor genes in animals (Metazoa). Our survey suggests that metastasis-suppressor genes emerged in three different periods in the evolution of Metazoa: before the origin of metazoans, with the emergence of first animals and at the origin of vertebrates.

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.

Epithelial-to-mesenchymal transition leads to disease-stage differences in circulating tumor cell detection and metastasis in pre-clinical models of prostate cancer

Metastasis is the cause of most prostate cancer (PCa) deaths and has been associated with circulating tumor cells (CTCs). The presence of ≥5 CTCs/7.5mL of blood is a poor prognosis indicator in metastatic PCa when assessed by the CellSearch^® system, the “gold standard” clinical platform. However, ~35% of metastatic PCa patients assessed by CellSearch^® have undetectable CTCs. We hypothesize that this is due to epithelial-to-mesenchymal transition (EMT) and subsequent loss of necessary CTC detection markers, with important implications for PCa metastasis. Two pre-clinical assays were developed to assess human CTCs in xenograft models; one comparable to CellSearch^® (EpCAM-based) and one detecting CTCs semi-independent of EMT status via combined staining with EpCAM/HLA (human leukocyte antigen). In vivo differences in CTC generation, kinetics, metastasis and EMT status were determined using 4 PCa models with progressive epithelial (LNCaP, LNCaP-C42B) to mesenchymal (PC-3, PC-3M) phenotypes. Assay validation demonstrated that the CellSearch^®-based assay failed to detect a significant number (~40-50%) of mesenchymal CTCs. In vivo, PCa with an increasingly mesenchymal phenotype shed greater numbers of CTCs more quickly and with greater metastatic capacity than PCa with an epithelial phenotype. Notably, the CellSearch^®-based assay captured the majority of CTCs shed during early-stage disease in vivo, and only after establishment of metastases were a significant number of undetectable CTCs present. This study provides important insight into the influence of EMT on CTC generation and subsequent metastasis, and highlights that novel technologies aimed at capturing mesenchymal CTCs may only be useful in the setting of advanced metastatic disease.

Metastasis suppressors: functional pathways

Metastasis is a complex process and a major contributor of death in cancer patients. Metastasis suppressor genes are identified by their ability to inhibit metastasis at a secondary site without affecting the growth of primary tumor. In this review, we have conducted a survey of the metastasis suppressor literature to identify common downstream pathways. The metastasis suppressor genes mechanistically target MAPK, G-protein-coupled receptor, cell adhesion, cytoskeletal, transcriptional regulatory, and metastasis susceptibility pathways. The majority of the metastasis suppressor genes are functionally multifactorial, inhibiting metastasis at multiple points in the cascade, and many operate in a context-dependent fashion. A greater understanding of common pathways/molecules targeted by metastasis suppressor could improve metastasis treatment strategies.

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.

KRAS promotes tumor metastasis and chemoresistance by repressing RKIP via the MAPK-ERK pathway in pancreatic cancer

Oncogenic KRAS plays a crucial role in pancreatic ductal adenocarcinoma (PDAC) development and progression. However, the mechanism has not been clearly elucidated. RKIP is a tumor repressor, and loss of RKIP has been shown in PDAC. Here, we found that KRAS expression was inversely correlated with RKIP expression in PDAC fresh tissue regardless of the KRAS mutant status. The negative correlation between KRAS and RKIP was further confirmed in our PDAC tissue microarray. KRAS overexpression and RKIP downregulation were associated with poor clinical outcomes. Knockdown or overexpression of KRAS in PDAC cell lines robustly increased or decreased, respectively, RKIP protein and mRNA levels. Furthermore, the MAPK-ERK pathway was involved in the regulation of RKIP. KRAS-regulated RKIP expression, which in turn affected the expression of pivotal epithelial-mesenchymal transition (EMT) and apoptosis factors. The biological function of the KRAS-RKIP axis was demonstrated in human pancreatic cancer cells in vitro and in vivo. KRAS knockdown increased RKIP expression and inhibited metastasis and chemoresistance. Moreover, the feature of metastasis and chemoresistance was rescued in the KRAS-knockdown cells through the inhibition of RKIP by RNA interference. In conclusion, our studies demonstrate how KRAS inhibits the tumor suppressor RKIP, thus offering novel justification for targeting RKIP as a strategy to overcome KRAS-induced tumor metastasis and chemoresistance in PDAC.

SEC-induced activation of ANXA7 GTPase suppresses prostate cancer metastasis

Annexin A7 (ANXA7) is a suppressor of tumorigenesis and metastasis in prostate cancer. Activated ANXA7 GTPase promotes prostate cancer cell apoptosis. However, the role and underlying mechanism of ANXA7 GTPase in prostate cancer metastasis have not been established. RKIP is a metastatic suppressor and downregulated in prostate cancer metastases. The binding of RKIP and its target proteins could inhibit the activation of its interactive partners. However, the effect of RKIP on ANXA7 GTPase activation is not clear. Here, we report that activation of ANXA7 GTPase by a small molecule SEC ((S)-ethyl 1-(3-(4-chlorophenoxy)-2-hydroxypropyl)-3- (4-methoxyphenyl)-1H-pyrazole-5-carboxylate) effectively inhibited prostate cancer metastasis. Mechanistically, activated ANXA7 promoted AMPK phosphorylation, leading to decreased mTORC1 activity, suppressed STAT3 nuclear translocation, and downregulation of pro-metastatic genes, including CCL2, APLN, and IL6ST. Conversely, RKIP interacted with ANXA7 and impaired activation of ANXA7 GTPase by SEC and its downstream signaling pathway. Notably, SEC treatment suppressed metastasis of prostate cancer cells in in vivo orthotopic analysis. Together, our findings provide a novel insight into how metastasis of prostate cancer with low RKIP expression is suppressed by SEC-induced activation of ANXA7 GTPase via the AMPK/mTORC1/STAT3 signaling pathway.

LncRNA XIST acts as a tumor suppressor in prostate cancer through sponging miR-23a to modulate RKIP expression

Accumulating evidences have indicated that aberrant expression of long non-coding RNAs (LncRNAs) is tightly associated with cancer development. Previous studies have reported that lncRNA XIST regulates tumor malignancies in several cancers. However, the underlying mechanism of XIST in prostate cancer remains unclear. In the current study, we found that XIST was down-regulated in prostate cancer specimens and cell lines. Low expression of XIST was correlated with poor prognosis and advanced tumor stage in prostate cancer patients. In gain and loss of function assays, we confirmed that XIST suppressed cellular proliferation and metastasis in prostate cancer both in vitro and in vivo. Furthermore, we found that XIST negatively regulates the expression of miR-23a and subsequently promotes RKIP expression at post-transcriptional level. Consequently, we investigated the correlation between XIST and miR-23a, and identified miR-23a as a direct target of XIST. In addition, over-expression of miR-23a efficiently abrogated the up-regulation of RKIP induced by XIST, suggesting that XIST positively regulates the expression of RKIP by competitively binding to miR-23a. Taken together, our study indicated that lncRNA XIST acts as a tumor suppressor in prostate cancer, and this regulatory effect of XIST will shed new light on epigenetic diagnostics and therapeutics in prostate cancer.

Identification of 14‑3‑3ζ as a potential biomarker in gastric cancer by proteomics‑based analysis

The identification of tumor biomarkers to support early diagnosis and tumor progression monitoring may potentially reduce the mortality of gastric cancer (GC). The present study aimed to detect novel tumor‑associated antigens from the AGS GC cell line, and to identify their associated autoantibodies in sera from patients with GC by proteomics‑based approaches. Proteins from AGS cell lysates were isolated using two‑dimensional polyacrylamide gel electrophoresis, and western blotting was subsequently performed, to determine autoantibody responses in sera derived from patients with GC and healthy individuals. Positive protein spots were removed from gels stained with Coomassie blue, and were then evaluated by liquid chromatography‑tandem mass spectrometry. Sera from patients with GC produced numerous spots, one of which was identified as 14‑3‑3ζ. Autoantibody frequency to 14‑3‑3ζ was 17.6% (15/85) in patients with GC, which was significantly higher than that in healthy control individuals (2.4%; 2/85; P<0.01). These results suggested that the autoantibody against 14‑3‑3ζ may be a potential serological biomarker for the detection and diagnosis of GC.

Overexpression of RKIP and its cross-talk with several regulatory gene products in multiple myeloma

Multiple myeloma (MM) is a clonal plasma-cell neoplastic disorder arising from an indolent premalignant disease known as monoclonal gammopathy of undetermined significance (MGUS). MM is a biologically complex heterogeneous disease reflected by its variable clinical responses of patients receiving the same treatment. Therefore, a molecular identification of stage-specific biomarkers will support a more individualized precise diagnostic/prognostic approach, an effective therapeutic regime, and will assist in the identification of novel therapeutic molecular targets. The metastatic suppressor/anti-resistance factor Raf-1 kinase inhibitor protein (RKIP) is poorly expressed in the majority of cancers and is often almost absent in metastatic tumors. RKIP inhibits the Raf/MEK/ERK1/2 and the NF-κB pathways. Whereby all tumors examined exhibited low levels of RKIP, in contrast, our recent findings demonstrated that RKIP is overexpressed primarily in its inactive phosphorylated form in MM cell lines and patient-derived tumor tissues. The underlying mechanism of RKIP overexpression in MM, in contrast to other tumors, is not known. We examined transcriptomic datasets on Oncomine platform (Life Technologies) for the co-expression of RKIP and other gene products in both pre-MM and MM. The transcription of several gene products was found to be either commonly overexpressed (i.e., RKIP, Bcl-2, and DR5) or underexpressed (i.e., Bcl-6 and TNFR2) in both pre-MM and MM. Noteworthy, a significant inverse correlation of differentially expressed pro-apoptotic genes was observed in pre-MM: overexpression of Fas and TNF-α and underexpression of YY1 versus expression of anti-apoptotic genes in MM: overexpression of YY1 and underexpression of Fas and TNF-α. Based on the analysis on mRNA levels and reported studies on protein levels of the above various genes, we have constructed various schemes that illustrate the possible cross-talks between RKIP (active/inactive) and the identified gene products that underlie the mechanism of RKIP overexpression in MM. Clearly, such cross-talks would need to be experimentally validated in both MM cell lines and patient-derived tumor tissues. If validated, the differential molecular signatures between pre-MM and MM might lead to a more precise diagnosis/prognosis of the disease and disease stages and will also identify novel molecular therapeutic targets for pre-MM and MM.

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.

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.

Promoter methylation and expression of Raf kinase inhibitory protein in esophageal squamous cell carcinoma

Raf kinase inhibitory protein (RKIP) regulates multiple cellular processes, and its downregulation is associated with distinct human cancers. In the present study, the status of RKIP promoter methylation, as well as its expression and clinical significance in esophageal squamous cell carcinoma (ESCC), were examined. The promoter methylation status in the 5'-CpG island of the RKIP gene and the expression level of the RKIP protein were examined using a modified methylation-specific polymerase chain reaction (MSP) method and immunohistochemical staining, respectively, in 77 ESCC samples and matched paratumor normal tissues. The incidence of RKIP promoter methylation was significantly higher in tumor samples (75.3%) than in the matched normal tissues (27.3%; P<0.001). A higher incidence of promoter methylation was also detected in poorly differentiated cancers (93.5%) compared with well-differentiated cancers (50.0%; P<0.001), as well as in tumor samples with positive lymph node metastasis (86.7%) compared with those with negative lymph node metastasis (59.4%; P<0.001). Consistent with the promoter methylation status, the expression level of RKIP was significantly reduced in cancer tissues (36.4%) compared with matched normal tissues (76.6%; P<0.01), as well as in cancers with positive lymph node metastasis (24.4%) compared with those with negative lymph node metastasis (53.1%; P=0.01). Promoter methylation-induced gene silencing significantly correlated with the down regulation of RKIP and the development of ESCC. The results of the present study suggested that the methylation status of the RKIP promoter, when combined with its expression level, may serve as a biomarker for predicting the biological behaviors of ESCC.