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

The Divergence of Flowering Time Modulated by FT/TFL1 Is Independent to Their Interaction and Binding Activities

FLOWERING LOCUS T (FT) and TERMINAL FLOWER1 (TFL1) proteins share highly conserved amino acid residues but they play opposite regulatory roles in promoting and repressing the flowering response, respectively. Previous substitution models and functional analysis have identified several key amino acid residues which are critical for the promotion of flowering. However, the precise relationship between naturally occurring FT/TFL1 homologs and the mechanism of their role in flowering is still unclear. In this study, FT/TFL1 homologs from eight Rosaceae species, namely, Spiraea cantoniensis, Pyracantha fortuneana, Photinia serrulata, Fragaria ananassa, Rosa hybrida, Prunus mume, Prunus persica and Prunus yedoensis, were isolated. Three of these homologs were further characterized by functional analyses involving site-directed mutagenesis. The results showed that these FT/TFL1 homologs might have diverse functions despite sharing a high similarity of sequences or crystal structures. Functional analyses were conducted for the key FT amino acids, Tyr-85 and Gln-140. It revealed that TFL1 homologs cannot promote flowering simply by substitution with key FT amino acid residues. Mutations of the IYN triplet motif within segment C of exon 4 can prevent the FT homolog from promoting the flowering. Furthermore, physical interaction of FT homologous or mutated proteins with the transcription factor FD, together with their lipid-binding properties analysis, showed that it was not sufficient to trigger flowering. Thus, our findings revealed that the divergence of flowering time modulating by FT/TFL1 homologs is independent to interaction and binding activities.

Investigational serine/threonine kinase inhibitors against prostate cancer metastases

INTRODUCTION

Androgen deprivation therapy (ADT) is used as first therapeutic approach in prostate cancer (PCa) although castration resistant disease (CRPC) develops with high frequency. CRPC is the consequence of lack of apoptotic responses to ADT. Alternative targeting of the androgen axis with abiraterone and enzalutamide, as well as taxane-based chemotherapy were used in CRPC. Serine/threonine protein kinases (STKs) regulate different molecular pathways of normal and neoplastic cells and participate to development of CRPC as well as to the progression towards a bone metastatic disease (mCRPC). Areas covered: The present review provide data on STK expression and activity in the development of CRPC as well as summarize recent reports of different strategies to block STK activity for the control of PCa progression. Expert Opinion: Inhibitors for different STKs have been developed but clinical trials in PCa are comparatively rare and few exhibit satisfactory 'drug-like' properties. It is, however, necessary to intensify, when possible, the number of clinical trials with these drugs in order to insert new therapies or combinations with standard hormone- and chemo-therapies in the treatment guidelines of the mPCA.

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.

Regulation of the epithelial to mesenchymal transition and metastasis by Raf kinase inhibitory protein-dependent Notch1 activity

Raf kinase inhibitory protein (RKIP), an endogenous inhibitor of the extracellular signal-regulated kinase (ERK) pathway, has been implicated as a suppressor of metastasis and a prognostic marker in cancers. However, how RKIP acts as a suppressor during metastasis is not fully understood. Here, we show that RKIP activity in cervical and stomach cancer is inversely correlated with endogenous levels of the Notch1 intracellular domain (NICD), which stimulates the epithelial to mesenchymal transition (EMT) and metastasis. The levels of RKIP were significantly decreased in tumor tissues compared to normal tissues, whereas NICD levels were increased. Overexpression of RKIP in several cell lines resulted in a dramatic decrease of NICD and subsequent inhibition of several mesenchymal markers, such as vimentin, N-cadherin, and Snail. In contrast, knockdown of RKIP exhibited opposite results both in vitro and in vivo using mouse models. Nevertheless, knockdown of Notch1 in cancer cells had no effect on the expression of RKIP, suggesting that RKIP is likely an upstream regulator of the Notch1 pathway. We also found that RKIP directly interacts with Notch1 but has no influence on the intracellular level of the γ-secretase complex that is necessary for Notch1 activation. These data suggest that RKIP plays a distinct role in activation of Notch1 during EMT and metastasis, providing a new target for cancer treatment.

Locostatin, a disrupter of Raf kinase inhibitor protein, inhibits extracellular matrix production, proliferation, and migration in human uterine leiomyoma and myometrial cells

OBJECTIVE

To investigate the presence of Raf kinase inhibitor protein (RKIP) in human myometrium and leiomyoma as well as to determine the effect of locostatin (RKIP inhibitor) on extracellular matrix (ECM) production, proliferation, and migration in human myometrial and leiomyoma cells.

DESIGN

Laboratory study.

SETTING

Human myometrium and leiomyoma.

PATIENT(S)

Thirty premenopausal women who were admitted to the hospital for myomectomy or hysterectomy.

INTERVENTION(S)

Myometrial and leiomyoma tissues were used to investigate the localization and the expression level of RKIP through immunohistochemistry and Western blotting. Myometrial and leiomyoma cells were treated with locostatin (10 μM) to measure ECM expression by real-time polymerase chain reaction, GSK3β expression by Western blotting, cell migration by wound-healing assay, and cell proliferation by MTT assay and immunocytochemistry.

MAIN OUTCOME MEASURE(S)

The expression of RKIP in human myometrial and leiomyoma tissue; ECM components and GSK3β expression, migration, and proliferation in myometrial and leiomyoma cells.

RESULT(S)

RKIP is expressed in human myometrial and leiomyoma tissue. Locostatin treatment resulted in the activation of the mitogen-activated protein kinase (MAPK) signal pathway (ERK phosphorylation), providing a powerful validation of our targeting protocol. Further, RKIP inhibition by locostatin reduces ECM components. Moreover, the inhibition of RKIP by locostatin impaired cell proliferation and migration in both leiomyoma and myometrial cells. Finally, locostatin treatment reduced GSK3β expression. Therefore, even if the activation of MAPK pathway should increase proliferation and migration, the destabilization of GSK3β leads to the reduction of proliferation and migration of myometrial and leiomyoma cells.

CONCLUSION(S)

Our results indicate that RKIP may be involved in leiomyoma pathophysiology.

Effects of Raf kinase inhibitor protein expression on pancreatic cancer cell growth and motility: an in vivo and in vitro study

PURPOSE

Raf kinase inhibitor protein (RKIP) is a tumor suppressor that inhibits cell growth and metastasis of malignant tumors. Pancreatic cancer is a leading cause of cancer death with a low survival rate. RKIP expression and its role in tumorigenesis and metastasis in pancreatic cancer are poorly understood. The aims of our study were to assess the effects of RKIP on pancreatic carcinoma cells in vitro and in tumor tissues in vivo.

METHODS

This study included 84 patients with histologically confirmed pancreatic adenocarcinoma. The expression levels of RKIP were measured in pancreatic cancer tissues and adjacent normal tissues using real-time PCR and immunohistochemistry. Overexpression plasmid of RKIP was transfected into SW1990 and AsPC-1 cell lines, and the effects on cell proliferation were studied using a Cell Counting Kit-8 assay. MEK1/2 and ERK1/2 were detected by Western blot and immunofluorescence assay.

RESULTS

Results showed a reduced expression of RKIP in pancreatic carcinoma tissues compared with adjacent normal tissues, which closely correlated with patient outcomes. Overexpression of RKIP suppressed cell proliferation and promoted apoptosis in cultured SW1990 and AsPC-1 cell lines. Transwell assay showed RKIP can inhibit cell migration and invasion, and in vivo RKIP can suppress tumorigenesis by diminishing the volume of the tumors.

CONCLUSIONS

In conclusion, expression of RKIP is closely correlated with the survival of pancreatic cancer patients. RKIP can inhibit pancreatic adenocarcinoma cells proliferation, activities of migration and invasion, through downregulating Raf-1-MEK1/2-ERK1/2 signaling pathway.

Reduction of RKIP expression promotes nasopharyngeal carcinoma invasion and metastasis by activating Stat3 signaling

The role and underlying mechanism of Raf kinase inhibitory protein (RKIP) in nasopharyngeal carcinoma (NPC) metastasis remain unclear. Here, we showed that RKIP was downregulated in the NPC with high metastatic potentials, and its decrement correlated with NPC metastasis and poor patient survival, and was an independent predictor for reduced overall survival. With a combination of loss-of-function and gain-of-function approaches, we observed that high expression of RKIP reduced invasion, metastasis and epithelial to mesenchymal transition (EMT) marker alternations of NPC cells. We further showed that RKIP overexpression attenuated while RKIP knockdown enhanced Stat3 phosphorylation and activation in NPC cells; RKIP reduced Stat3 phosphorylation through interacting with Stat3; Stattic attenuated NPC cell migration, invasion and EMT marker alternations induced by RKIP knockdown, whereas Stat3 overexpression restored NPC cell migration, invasion and EMT marker alternations reduced by RKIP overexpression. In addition, there was an inverse correlation between RKIP and phospho-Stat3 expression in the NPC tissues and xenograft metastases. Our data demonstrate that RKIP is a metastatic suppressor and predictor for metastasis and prognosis in NPC, and RKIP downregulation promotes NPC invasion, metastasis and EMT by activating Stat3 signaling, suggesting that RKIP/Stat3 signaling could be used as a therapeutic target for NPC metastasis.

BACH1, the master regulator gene: A novel candidate target for cancer therapy

BACH1 (BTB and CNC homology 1, basic leucine zipper transcription factor 1) is a transcriptional factor and a member of cap 'n' collar (CNC) and basic region leucine zipper factor family. In contrast to other bZIP family members, BACH1 appeared as a comparatively specific transcription factor. It acts as transcription regulator and is recognized as a recently hypoxia regulator and functions as an inducible repressor for the HO-1 gene in many human cell types in response to stress oxidative. In regard to studies lately, although, BACH1 has been related to the regulation of oxidative stress and heme oxidation, it has never been linked to invasion and metastasis. Recent studies have showed that BACH1 is involved in bone metastasis of breast cancer by up-regulating vital metastatic genes like CXCR4 and MMP1. This newly discovered aspect of BACH1 gene provides new insight into cancer progression study and stands on its master regulator role in metastasis process, raising the possibility of considering it as a potential target for cancer therapy.

Increased Expression of miR-23a Mediates a Loss of Expression in the RAF Kinase Inhibitor Protein RKIP

RAF kinase inhibitor protein (RKIP) is a seminal regulator of intracellular signaling and exhibits both antimetastatic and antitumorigenic properties. Decreased expression of RKIP has been described in several human malignancies, including acute myelogenous leukemia (AML). As the mechanisms leading to RKIP loss in AML are still unclear, we aimed to analyze the potential involvement of miRNAs within this study. miRNA microarray and qPCR data of more than 400 AML patient specimens revealed correlation between decreased expression of RKIP and increased expression of miR-23a, a member of the miR-23a/27a/24-2 cluster. In functional experiments, overexpression of miR-23a decreased RKIP mRNA and protein expression, whereas miR-23a inhibition caused the opposite effect. By using an RKIP 3'-untranslated region luciferase reporter construct with and without mutation or deletion of the putative miR-23a-binding site, we could show that RKIP modulation by miR-23a is mediated via direct binding to this region. Importantly, miR-23a overexpression induced a significant increase of proliferation in hematopoietic cells. Simultaneous transfection of an RKIP expression construct lacking the miR-23a-binding sites reversed this phenotype, indicating that this effect is truly mediated via downregulation of RKIP. Finally, by analyzing more than 4,300 primary patient specimens via database retrieval from The Cancer Genome Atlas, we could highlight the importance of the miR-23a/RKIP axis in a broad range of human cancer entities. In conclusion, we have identified miR-23a as a negative regulator of RKIP expression in AML and have provided data that suggest the importance of our observation beyond this tumor entity. Cancer Res; 76(12); 3644-54. ©2016 AACR.

Inverse association between Bmi-1 and RKIP affecting clinical outcome of gastric cancer and revealing the potential molecular mechanisms underlying tumor metastasis and chemotherapy resistance

BACKGROUND

B-cell-specific Moloney murine leukemia virus integration site 1 (Bmi-1) and Raf kinase inhibitory protein (RKIP) are involved in cancer metastasis and chemotherapeutic resistance, respectively. In this study, we evaluated the association between Bmi-1 and RKIP and outcome of gastric cancer through clinical data analysis and in vitro experiments.

METHODS

Bmi-1 expression and RKIP expression were observed in 107 cases of gastric cancer through use of tissue microarray technology to identify their correlations with clinicopathological parameters, patient survival, and susceptibility to chemotherapy. The correlation was confirmed in gastric cancer cell lines, analyzed further by gene overexpression and silencing analysis, a cell invasion assay, and a chemosensitivity test.

RESULTS

Positive expression of Bmi-1 was highly correlated with T classification and clinical stage. Diminished or lost expression of RKIP was significantly associated with T classification, lymph node metastasis, distant metastasis, and clinical stage. Bmi-1 is negatively and RKIP is positively related to patient survival. Positive expression of Bmi-1 and negative expression of RKIP are associated with poor patient survival and modest efficacy of postoperative chemotherapy. A meaningfully inverse association between Bmi-1 and RKIP was found in tissue microarray studies, and was verified further in gastric cancer cell lines. Moreover, gene overexpression and silencing analysis indicated that RKIP might be regulated by Bmi-1. Furthermore, the impacts of Bmi-1 on cell invasion and chemotherapy resistance were rescued by knockdown of RKIP.

CONCLUSIONS

Our study implies that detection of Bmi-1 and RKIP is valuable in predicting patient survival and therapeutic response in gastric cancer, and the inverse association between Bmi-1 and RKIP reveals the potential molecular mechanisms underlying tumor metastasis and chemotherapy resistance.

Polo-like kinase 1 induces epithelial-to-mesenchymal transition and promotes epithelial cell motility by activating CRAF/ERK signaling

Polo-like kinase 1 (PLK1) is a key cell cycle regulator implicated in the development of various cancers, including prostate cancer. However, the functions of PLK1 beyond cell cycle regulation remain poorly characterized. Here, we report that PLK1 overexpression in prostate epithelial cells triggers oncogenic transformation. It also results in dramatic transcriptional reprogramming of the cells, leading to epithelial-to-mesenchymal transition (EMT) and stimulation of cell migration and invasion. Consistently, PLK1 downregulation in metastatic prostate cancer cells enhances epithelial characteristics and inhibits cell motility. The signaling mechanisms underlying the observed cellular effects of PLK1 involve direct PLK1-dependent phosphorylation of CRAF with subsequent stimulation of the MEK1/2-ERK1/2-Fra1-ZEB1/2 signaling pathway. Our findings highlight novel non-canonical functions of PLK1 as a key regulator of EMT and cell motility in normal prostate epithelium and prostate cancer. This study also uncovers a previously unanticipated role of PLK1 as a potent activator of MAPK signaling.

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.

Nitric oxide-mediated sensitization of resistant tumor cells to apoptosis by chemo-immunotherapeutics

The generation of NO by the various NO synthases in normal and malignant tissues is manifested by various biological effects that are involved in the regulation of cell survival, differentiation and cell death. The role of NO in the cytotoxic immune response was first revealed by demonstrating the induction of iNOS in target cells by immune cytokines (e.g. IFN-γ, IL-1, TNF-α, etc.) and resulting in the sensitization of resistant tumor cells to death ligands-induced apoptosis. Endogenous/exogenous NO mediated its immune sensitizing effect by inhibiting NF-κΒ activity and downstream, inactivating the repressor transcription factor YY1, which inhibited both Fas and DR5 expressions. In addition, NO-mediated inhibition of NF-κΒ activity and inhibition downstream of its anti-apoptotic gene targets sensitized the tumor cells to apoptosis by chemotherapeutic drugs. We have identified in tumor cells a dysregulated pro-survival/anti-apoptotic loop consisting of NF-κB/Snail/YY1/RKIP/PTEN and its modification by NO was responsible, in large, for the reversal of chemo and immune resistance and sensitization to apoptotic mechanisms by cytotoxic agents. Moreover, tumor cells treated with exogenous NO donors resulted in the inhibition of NF-κΒ activity via S-nitrosylation of p50 and p65, inhibition of Snail (NF-κΒ target gene), inhibition of transcription repression by S-nitrosylation of YY1 and subsequent inhibition of epithelial-mesenchymal transition (EMT), induction of RKIP (inhibition of the transcription repressor Snail), and induction of PTEN (inhibition of the repressors Snail and YY1). Further, each gene product modified by NO in the loop was involved in chemo-immunosensitization. These above findings demonstrated that NO donors interference in the regulatory circuitry result in chemo-immunosensitization and inhibition of EMT. Overall, these observations suggest the potential anti-tumor therapeutic effect of NO donors in combination with subtoxic chemo-immuno drugs. This combination acts on multiple facets including reversal of chemo-immune resistance, and inhibition of both EMT 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.

Metastasis Suppressors Regulate the Tumor Microenvironment by Blocking Recruitment of Prometastatic Tumor-Associated Macrophages

Triple-negative breast cancer (TNBC) patients have the highest risk of recurrence and metastasis. Because they cannot be treated with targeted therapies, and many do not respond to chemotherapy, they represent a clinically underserved group. TNBC is characterized by reduced expression of metastasis suppressors such as Raf kinase inhibitory protein (RKIP), which inhibits tumor invasiveness. Mechanisms by which metastasis suppressors alter tumor cells are well characterized; however, their ability to regulate the tumor microenvironment and the importance of such regulation to metastasis suppression are incompletely understood. Here, we use species-specific RNA sequencing to show that RKIP expression in tumors markedly reduces the number and metastatic potential of infiltrating tumor-associated macrophages (TAM). TAMs isolated from nonmetastatic RKIP(+) tumors, relative to metastatic RKIP(-) tumors, exhibit a reduced ability to drive tumor cell invasion and decreased secretion of prometastatic factors, including PRGN, and shed TNFR2. RKIP regulates TAM recruitment by blocking HMGA2, resulting in reduced expression of numerous macrophage chemotactic factors, including CCL5. CCL5 overexpression in RKIP(+) tumors restores recruitment of prometastatic TAMs and intravasation, whereas treatment with the CCL5 receptor antagonist Maraviroc reduces TAM infiltration. These results highlight the importance of RKIP as a regulator of TAM recruitment through chemokines such as CCL5. The clinical significance of these interactions is underscored by our demonstration that a signature comprised of RKIP signaling and prometastatic TAM factors strikingly separates TNBC patients based on survival outcome. Collectively, our findings identify TAMs as a previously unsuspected mechanism by which the metastasis-suppressor RKIP regulates tumor invasiveness, and further suggest that TNBC patients with decreased RKIP activity and increased TAM infiltration may respond to macrophage-based therapeutics.

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.

Clinicopathological features and prognostic implications of Raf kinase inhibitor protein downregulation in tongue squamous cell carcinoma

Raf kinase inhibitor protein (RKIP) is recognized as a suppressor of metastasis, and the downregulation of RKIP is associated with aggressive events and a poor outcome in a variety of solid tumors. However, the clinical relevance of RKIP expression in tongue squamous cell carcinoma (TSCC) remains unclear. In the present study, the expression of RKIP in 85 pairs of TSCC and corresponding adjacent non-cancerous tissues, 30 matched metastatic lesions from the cervical lymph nodes and 32 oral leukoplakia samples were assessed using immunohistochemical methods. The association between RKIP expression and clinicopathological features was then evaluated. Kaplan-Meier survival analysis and Cox proportional hazards model were used to estimate the effect of RKIP expression on the survival time of patients with TSCC. The results revealed that RKIP expression was dramatically downregulated in TSCC, and to an even greater extent in metastatic lesions. RKIP downregulation was significantly associated with the presence of lymphatic metastasis and the clinical stage of TSCC. Furthermore, patients with low RKIP expression demonstrated a significantly shorter overall survival time. Multivariate analysis indicated that RKIP expression may be an independent prognostic factor in TSCC. In conclusion, the present findings indicate that the lack of RKIP expression is of clinical significance and may serve as a prognostic biomarker in TSCC.

Treatment of acromegaly in the era of personalized and predictive medicine

Acromegaly is a chronic disorder usually diagnosed late in the disease evolution. Such delayed diagnosis, together with the inability to achieve the treatment goals of normalizing biochemical disease markers and controlling tumour mass may result in substantial morbidity and mortality. Somatostatin analogues (SSA) are accepted as first-line medical therapy or as second-line therapy in patients undergoing unsuccessful surgery and are considered a cornerstone in the treatment of acromegaly. However, because a high percentage of patients experience SSA medical treatment failure, the identification of biomarkers associated with a successful or unsuccessful response to all classes of medical therapy would help in the choice of treatment and potentially allow for a quicker normalization of biochemical parameters. The current treatment algorithms for acromegaly are based upon a "trial-and-error" approach with additional treatment options provided when disease is not controlled. In many other diseases, therapeutic algorithms have been evolving towards personalized treatment with the medication that best matches individual disease characteristics, using biomarkers that identify therapeutic response. Additionally, a personalized approach to complementary treatment of comorbidities present in the acromegalic patient is also required. This review will discuss the development of a potential treatment algorithm for acromegaly addressing the biochemical control of the disease as well of its associated comorbidities, under a personalized approach based upon markers of prognostic and predictive significance, such as tumour size, MRI adenoma signal, GH value after acute octreotide test, granular adenoma pattern, Ki-67, somatostatin receptor phenotype, aryl hydrocarbon-interacting protein expression, gsp mutations, RAF kinase activity, E-cadherin and beta-arrestin-1.

RKIP-mediated chemo-immunosensitization of resistant cancer cells via disruption of the NF-κB/Snail/YY1/RKIP resistance-driver loop

Cancer remains one of the most dreadful diseases. Whereas most treatment regimens for various cancers have resulted in improved clinical responses and sometimes cures, unfortunately, subsets of cancer patients are either pretreatment resistant or develop resistance following therapy. These subsets of patients develop cross-resistance to unrelated therapeutics and usually succumb to death. Thus, delineating the underlying molecular mechanisms of resistance of various cancers and identifying molecular targets for intervention are the current main focus of research investigations. One approach to investigate cancer resistance has been to identify pathways that regulate resistance and develop means to disrupt these pathways in order to override resistance and sensitize the resistant cells to cell death. Hence, we have identified one pathway that is dysregulated in cancer, namely, the NF-κB/Snail/YY1/RKIP loop, that has been shown to regulate, in large part, tumor cell resistance to apoptosis by chemotherapeutic and immunotherapeutic cytotoxic drugs. The dysregulated resistant loop is manifested by the overexpression of NF-κB, Snail, and YY1 activities and the underexpression of RKIP. The induction of RKIP expression results in the downregulation of NF-κB, Snail, and YY1 and the sensitization of resistant cells to drug-induced apoptosis. These findings identified RKIP, in addition to its antiproliferative and metastatic suppressor functions, as an anti-resistance factor. This brief review describes the role of RKIP in the regulation of drug sensitivity via disruption of the NF-κB/Snail/ YY1/RKIP loop that regulates resistance in cancer cells.

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.

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.

Molecular regulation of bone marrow metastasis in prostate and breast cancer

Metastasis is a multistep process, which refers to the ability to leave a primary tumor through circulation toward the distant tissue and form a secondary tumor. Bone is a common site of metastasis, in which osteolytic and osteoblastic metastasis are observed. Signaling pathways, chemokines, growth factors, adhesion molecules, and cellular interactions as well as miRNAs have been known to play an important role in the development of bone metastasis. These factors provide an appropriate environment (soil) for growth and survival of metastatic tumor cells (seed) in bone marrow microenvironment. Recognition of these factors and determination of their individual roles in the development of metastasis and disruption of cellular interactions can provide important therapeutic targets for treatment of these patients, which can also be used as prognostic and diagnostic biomarkers. Thus, in this paper, we have attempted to highlight the molecular regulation of bone marrow metastasis in prostate and breast cancers.

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.

Promoter methylation of Raf kinase inhibitory protein: A significant prognostic indicator for patients with gastric adenocarcinoma

DNA methylation has an important role in the development of carcinomas. As a metastasis suppressor gene, Raf kinase inhibitory protein (RKIP) suppresses tumor cell invasion and metastasis. In the present study, the associations between RKIP protein expression and promoter methylation with clinicopathological parameters, prognosis and survival rates in gastric adenocarcinoma were investigated. RKIP protein expression and promoter methylation were measured in 135 cases of surgically resected gastric adenocarcinoma specimens and corresponding normal tissues using immunohistochemistry and methylation-specific polymerase chain reaction, respectively. Kaplan-Meier analyses were performed to analyze the patient survival rate. Prognostic factors were determined using multivariate Cox analysis. RKIP promoter methylation was detected in 48.9% of gastric carcinoma tissues and 5.17% of adjacent tissues (P<0.05). RKIP protein expression was detected in 43.0% of gastric carcinoma tissues and 91.1% of adjacent tissues (P<0.05). The protein expression levels and promoter methylation of RKIP were shown to correlate with pathological staging, Union for International Cancer Control-stage, tumor differentiation and lymph node metastasis (P<0.05). In addition, the protein expression of RKIP in gastric carcinomas was demonstrated to be associated with promoter methylation of RKIP. Survival analysis of gastric carcinoma patients revealed that promoter methylation in RKIP-positive tumors correlated with a significantly shorter survival time when compared with RKIP-negative tumors (P=0.0002, using the log-rank test). Using multivariate Cox analysis, promoter methylation of RKIP was shown to be an independent prognostic factor (P=0.033). These results indicated that abnormal promoter methylation of RKIP may be one cause of downregulated RKIP expression. Downregulation of RKIP expression was shown to correlate with the incidence and development of gastric carcinomas. Thus, abnormal promoter methylation of RKIP may be a valuable biomarker for estimating gastric carcinoma prognosis.

Microenvironmental Influences on Metastasis Suppressor Expression and Function during a Metastatic Cell's Journey

Metastasis is the process of primary tumor cells breaking away and colonizing distant secondary sites. In order for a tumor cell growing in one microenvironment to travel to, and flourish in, a secondary environment, it must survive a series of events termed the metastatic cascade. Before departing the primary tumor, cells acquire genetic and epigenetic changes that endow them with properties not usually associated with related normal differentiated cells. Those cells also induce a subset of bone marrow-derived stem cells to mobilize and establish pre-metastatic niches [1]. Many tumor cells undergo epithelial-to-mesenchymal transition (EMT), where they transiently acquire morphologic changes, reduced requirements for cell-cell contact and become more invasive [2]. Invasive tumor cells eventually enter the circulatory (hematogenous) or lymphatic systems or travel across body cavities. In transit, tumor cells must resist anoikis, survive sheer forces and evade detection by the immune system. For blood-borne metastases, surviving cells then arrest or adhere to endothelial linings before either proliferating or extravasating. Eventually, tumor cells complete the process by proliferating to form a macroscopic mass [3].Up to 90 % of all cancer related morbidity and mortality can be attributed to metastasis. Surgery manages to ablate most primary tumors, especially when combined with chemotherapy and radiation. But if cells have disseminated, survival rates drop precipitously. While multiple parameters of the primary tumor are predictive of local or distant relapse, biopsies remain an imperfect science. The introduction of molecular and other biomarkers [4, 5] continue to improve the accuracy of prognosis. However, the invasive procedure introduces new complications for the patient. Likewise, the heterogeneity of any tumor population [3, 6, 7] means that sampling error (i.e., since it is impractical to examine the entire tumor) necessitates further improvements.In the case of breast cancer, for example, women diagnosed with stage I diseases (i.e., no evidence of invasion through a basement membrane) still have a ~30 % likelihood of developing distant metastases [8]. Many physicians and patients opt for additional chemotherapy in order to "mop up" cells that have disseminated and have the potential to grow into macroscopic metastases. This means that ~ 70 % of patients receive unnecessary therapy, which has undesirable side effects. Therefore, improving prognostic capability is highly desirable.Recent advances allow profiling of primary tumor DNA sequences and gene expression patterns to define a so-called metastatic signature [9-11], which can be predictive of patient outcome. However, the genetic changes that a tumor cell must undergo to survive the initial events of the metastatic cascade and colonize a second location belie a plasticity that may not be adequately captured in a sampling of heterogeneous tumors. In order to tailor or personalize patient treatments, a more accurate assessment of the genetic profile in the metastases is needed. Biopsy of each individual metastasis is not practical, safe, nor particularly cost-effective. In recent years, there has been a resurrection of the notion to do a 'liquid biopsy,' which essentially involves sampling of circulating tumor cells (CTC) and/or cell free nucleic acids (cfDNA, including microRNA (miRNA)) present in blood and lymph [12-16].The rationale for liquid biopsy is that tumors shed cells and/or genetic fragments into the circulation, theoretically making the blood representative of not only the primary tumor but also distant metastases. Logically, one would predict that the proportion of CTC and/or cfDNA would be proportionate to the likelihood of developing metastases [14]. While a linear relationship does not exist, the information within CTC or cfDNA is beginning to show great promise for enabling a global snapshot of the disease. However, the CTC and cfDNA are present at extremely low levels. Nonetheless, newer technologies capture enough material to enrich and sequence the patient's DNA or quantification of some biomarkers.Among the biomarkers showing great promise are metastasis suppressors which, by definition, block a tumor cell's ability to complete the metastatic process without prohibiting primary tumor growth [17]. Since the discovery of the first metastasis suppressor, Nm23, more than 30 have been functionally characterized. They function at various stages of the metastatic cascade, but their mechanisms of action, for the most part, remain ill-defined. Deciphering the molecular interactions of functional metastasis suppressors may provide insights for targeted therapies when these regulators cease to function and result in metastatic disease.In this brief review, we summarize what is known about the various metastasis suppressors and their functions at individual steps of the metastatic cascade (Table 1). Some of the subdivisions are rather arbitrary in nature, since many metastasis suppressors affect more than one step in the metastatic cascade. Nonetheless what emerges is a realization that metastasis suppressors are intimately associated with the microenvironments in which cancer cells find themselves [18].

Raf kinase inhibitor protein (RKIP) blocks signal transducer and activator of transcription 3 (STAT3) activation in breast and prostate cancer

Raf kinase inhibitor protein (RKIP) is a member of the phosphatidylethanolamine-binding-protein (PEBP) family that modulates the action of many kinases involved in cellular growth, apoptosis, epithelial to mesenchymal transition, motility, invasion and metastasis. Previously, we described an inverse association between RKIP and signal transducers and activators of transcription 3 (STAT3) expression in gastric adenocarcinoma patients. In this study, we elucidated the mechanism by which RKIP regulates STAT3 activity in breast and prostate cancer cell lines. RKIP over expression inhibited c-Src auto-phosphorylation and activation, as well as IL-6-, JAK1 and 2-, and activated Raf-mediated STAT3 tyrosine and serine phosphorylation and subsequent activation. In MDA-231 breast cancer cells that stably over express RKIP, IL-6 treatment blocked STAT3 phosphorylation and transcriptional activation. Conversely, in RKIP knockdown MDA-231 cells: STAT3 phosphorylation and activation increased in comparison to parental MDA-231 cells. RKIP over expression resulted in constitutive physical interaction with STAT3 and blocked c-Src and STAT3 association. The treatment of DU145 prostate, but not PC3 prostate or MDA-231 breast, cancer cell lines with ENMD-1198 or MKC-1 dramatically increased expression of RKIP. Overexpression of RKIP sensitized PC3 and MDA-231 cells to MTI-induced apoptosis. Moreover, MTI treatment resulted in a decrease in Src-mediated STAT3 tyrosine phosphorylation and activation, an effect that was significantly enhanced by RKIP over expression. In stable RKIP over expressing MDA-231 cells, tumor xenograft growth induced by activated STAT3 is inhibited. RKIP synergizes with MTIs to induce apoptosis and inhibit STAT3 activation of breast and prostate cancer cells. RKIP plays a critical role in opposing the effects of pro-oncogenic STAT3 activation.

Gene set enrichment analysis of the NF-κB/Snail/YY1/RKIP circuitry in multiple myeloma

The presence of a dysregulated NF-κB/Snail/YY1/RKIP loop was recently established in metastatic prostate cancer cells and non-Hodgkin's lymphoma; however, its involvement in multiple myeloma (MM) has yet to be investigated. Aim of the study was to investigate the role of the NF-κB/Snail/YY1/RKIP circuitry in MM and how each gene is correlated with the remaining genes of the loop. Using gene set enrichment analysis and gene neighbours analysis in data received from four datasets included in the Multiple Myeloma Genomics Portal of the Multiple Myeloma Research Consortium, we identified various enriched gene sets associated with each member of the NF-κB/Snail/YY1/RKIP circuitry. In each dataset, the 20 most co-expressed genes with the circuitry genes were isolated subjected to Gene Ontology and Kyoto Encyclopedia of Genes and Genomes enrichment. Among many, we highlighted on FNDC3B, TPD52, BBX, MBNL1 and MFAP2. Many co-expressed genes participated in the regulation of metabolic processes and nucleic acid binding, or were transcription factor binding genes and genes with metallopeptidase activity. The transcription factors FOXO4, GATA binding factor, Sp1 and AP4 most likely affect the expression of the NF-κB/Snail/YY1/RKIP circuitry genes. Computational analysis of various GEO datasets revealed elevated YY1 and RKIP levels in MM vs. the normal plasma cells, as well as elevated RKIP levels in MM vs. normal B lymphocytes. The present study highlights the relationships of the NF-κB/Snail/YY1/RKIP circuitry genes with specific cancer-related gene sets in multiple myeloma.

A new p53 target gene, RKIP, is essential for DNA damage-induced cellular senescence and suppression of ERK activation

p53, a strong tumor suppressor protein, is known to be involved in cellular senescence, particularly premature cellular senescence. Oncogenic stresses, such as Ras activation, can initiate p53-mediated senescence, whereas activation of the Ras-mitogen-activated protein kinase (MAPK) pathway can promote cell proliferation. These conflicting facts imply that there is a regulatory mechanism for balancing p53 and Ras-MAPK signaling. To address this, we evaluated the effects of p53 on the extracellular signal-regulated kinase (ERK) activation and found that p53 could suppress ERK activation through de novo synthesis. Through several molecular biologic analyses, we found that RKIP, an inhibitor of Raf kinase, is responsible for p53-mediated ERK suppression and senescence. Overexpression of RKIP can induce cellular senescence in several types of cell lines, including p53-deficient cells, whereas the elimination of RKIP by siRNA or forced expression of ERK blocks p53-mediated cellular senescence. These results suggested that RKIP is an essential protein for cellular senescence. Moreover, modification of the p53 serine 46 residue was critical for RKIP induction and ERK suppression as well as cellular senescence. These results indicated that RKIP is a novel p53 target gene that is responsible for p53-mediated cellular senescence and tumor suppressor protein expression.

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.

Network of mutually repressive metastasis regulators can promote cell heterogeneity and metastatic transitions

The sources and consequences of nongenetic variability in metastatic progression are largely unknown. To address these questions, we characterized a transcriptional regulatory network for the metastasis suppressor Raf kinase inhibitory protein (RKIP). We previously showed that the transcription factor BACH1 is negatively regulated by RKIP and promotes breast cancer metastasis. Here we demonstrate that BACH1 acts in a double-negative (overall positive) feedback loop to inhibit RKIP transcription in breast cancer cells. BACH1 also negatively regulates its own transcription. Analysis of the BACH1 network reveals the existence of an inverse relationship between BACH1 and RKIP involving both monostable and bistable transitions that can potentially give rise to nongenetic variability. Single-cell analysis confirmed monostable and bistable-like behavior. Treatment with histone deacetylase inhibitors or depletion of the polycomb repressor enhancer of zeste homolog 2 altered relative RKIP and BACH1 levels in a manner consistent with a prometastatic state. Together, our results suggest that the mutually repressive relationship between metastatic regulators such as RKIP and BACH1 can play a key role in determining metastatic progression in cancer.

Loss of Raf-1 kinase inhibitor protein (RKIP) is strongly associated with high-grade tumor budding and correlates with an aggressive phenotype in pancreatic ductal adenocarcinoma (PDAC)

BACKGROUND

Raf-1 kinase inhibitor protein (RKIP) has emerged as a significant metastatic suppressor in a variety of human cancers and is known to inhibit Ras/Raf/MEK/ERK signaling. By suppressing the activation of the NFkB/SNAIL circuit, RKIP can regulate the induction of epithelial-mesenchymal transition (EMT). The aim of this study was to evaluate RKIP expression and to determine its association with clinicopathological features, including EMT in form of tumor budding in pancreatic ductal adenocarcinoma (PDAC).

METHODS

Staining for RKIP was performed on a multipunch Tissue Microarray (TMA) of 114 well-characterized PDACs with clinico-pathological, follow-up and adjuvant therapy information. RKIP-expression was assessed separately in the main tumor body and in the tumor buds. Another 3 TMAs containing normal pancreatic tissue, precursor lesions (Pancreatic Intraepithelial Neoplasia, PanINs) and matched lymph node metastases were stained in parallel. Cut-off values were calculated by receiver operating characteristic (ROC) curve analysis.

RESULTS

We found a significant progressive loss of RKIP expression between normal pancreatic ductal epithelia (average: 74%), precursor lesions (PanINs; average: 37%), PDAC (average 20%) and lymph node metastases (average 8%, p<0.0001). RKIP expression was significantly lower in tumor buds (average: 6%) compared to the main tumor body (average 20%; p<0.005). RKIP loss in the tumor body was marginally associated with advanced T-stage (p=0.0599) as well as high-grade peritumoral (p=0.0048) and intratumoral budding (p=0.0373). RKIP loss in the buds showed a clear association with advanced T stage (p=0.0089).

CONCLUSIONS

The progressive loss of RKIP seems to play a major role in the neoplastic transformation of pancreas, correlates with aggressive features in PDAC and is associated with the presence of EMT in form of tumor budding.

Overexpression of RKIP inhibits cell invasion in glioma cell lines through upregulation of miR-98

Raf-1 kinase inhibitor protein (RKIP) is a tumor and metastasis suppressor in cancer cells. MicroRNAs (miRNAs) have been suggested to play a vital role in tumor initiation and progression by negatively regulating oncogenes and tumor suppressors. Quite recently, studies have identified some miRNAs operating to promote or suppress tumor invasion or metastasis via regulating metastasis-related genes, providing potential therapeutic targets on antimetastasis strategy. In this study, we found that the expression of RKIP and miR-98 in glioma tissues were significantly lower than that in normal brain tissues. Overexpression of RKIP upregulated miR-98 expression and inhibited glioma cell invasion and miR-98 target gene HMGA2 but had no effect in glioma cell proliferation. Moreover, forced expression of miR-98 accelerated the inhibition of glioma cell invasion and the expression of HMGA2 also had no effect in glioma cell proliferation. Our findings newly described RKIP/miR-98 to HMGA2 link and provided a potential mechanism for glioma cell invasion. RKIP and miR-98 may illustrate the potential therapeutic utility of signaling pathway signatures.

Dihydroartemisinin induces apoptosis of cervical cancer cells via upregulation of RKIP and downregulation of bcl-2

Treatment of recurrent and metastatic cervical cancer remains a challenge, especially in developing countries, which lack efficient screening programs. In recent years, artemisinin and its derivatives, such as dihydroartemisinin (DHA), which were traditionally used as anti-malarial agent, have been shown to inhibit tumor growth with low toxicity to normal cells. In this study, we investigated mechanisms underlying the anti-tumor effect of DHA in cervical cancer. We evaluated the role of DHA on the expression of bcl-2 and Raf kinase inhibitor protein (RKIP), which is a suppressor of metastasis. The MTT assay was used to compare the proliferation of untreated and DHA-treated Hela and Caski cervical cancer cells. Flow cytometry was used to determine the percentage of cells at each stage of the cell cycle in untreated and DHA-treated cells. We used RT-PCR and western blots to determine the expression of bcl-2 and RKIP mRNA and proteins. We evaluated the effect of DHA treatment in nude mice bearing Hela or Caski tumors. DHA-treated cells showed a time- and dose-dependent inhibition of proliferation and a significant increase in apoptosis. The expression of RKIP was significantly upregulated and the expression of bcl-2 was significantly downregulated in DHA-treated cells compared with control cells. DHA treatment caused (1) a significant inhibition of tumor growth and (2) a significant increase in the apoptotic index in nude mice bearing Hela or Caski tumors. Our data suggest that DHA inhibits cervical cancer growth via upregulation of RKIP and downregulation of bcl-2.

Metastasis suppressors in breast cancers: mechanistic insights and clinical potential

For the most part, normal epithelial cells do not disseminate to other parts of the body and proliferate, as do metastatic cells. Presumably, a class of molecules-termed metastasis suppressors-are involved in this homeostatic control. Metastasis suppressors are, by definition, cellular factors that, when re-expressed in metastatic cells, functionally inhibit metastasis without significantly inhibiting tumor growth. In this brief review, we catalog known metastasis suppressors, what is known about their mechanism(s) of action, and experimental and clinical associations to date.

Mapping the interactome of overexpressed RAF kinase inhibitor protein in a gastric cancer cell line

BACKGROUND

Gastric cancer (GC) is a threat to human health with increasing incidence and mortality worldwide. Down-regulation or absence of RAF kinase inhibitor protein (RKIP) was associated with the occurrence, differentiation, invasion, and metastasis of GC. This study aims to investigate the molecular mechanisms and biological functions of RKIP in the GC biology.

METHODS

The fusion expression plasmid pcDNA3.1-RKIP-3xFLAG was transfected into SGC7901 cells, the RKIP fusion proteins were purified with anti-flag M2 magnetic beads, and the RKIP-interacting proteins were identified with tandem mass spectrometry (MS/MS), and were analyzed with bioinformatics tools. Western blot and co-immunoprecipitation were used to confirm the interaction complex.

RESULTS

A total of 72 RKIP-interacting proteins were identified by MS/MS. Those proteins play roles in enzyme metabolism, molecular chaperoning, biological oxidation, cytoskeleton organization, signal transduction, and enzymolysis. Three RKIP-interaction protein network diagrams were constructed with Michigan Molecular Interactions, functional linage network, and Predictome analysis to address the molecular pathways of the functional activity of RKIP. The MS/MS-characterized components of the existing interaction complex (RKIP, HSP90, 14-3-3ε, and keratin 8) were confirmed by Western blot analysis and co-immunoprecipitation.

CONCLUSION

This study is the first discovery of the interaction of RKIP with HSP90, 14-3-3, and keratin. The present data would provide insight into the molecular mechanisms of how RKIP inhibits the occurrence and development of GC.

Cabozantinib inhibits prostate cancer growth and prevents tumor-induced bone lesions

PURPOSE

Cabozantinib, an orally available multityrosine kinase inhibitor with activity against mesenchymal epithelial transition factor (MET) and VEGF receptor 2 (VEGFR2), induces resolution of bone scan lesions in men with castration-resistant prostate cancer bone metastases. The purpose of this study was to determine whether cabozantinib elicited a direct antitumor effect, an indirect effect through modulating bone, or both.

EXPERIMENTAL DESIGN

Using human prostate cancer xenograft studies in mice, we determined the impact of cabozantinib on tumor growth in soft tissue and bone. In vitro studies with cabozantinib were performed using (i) prostate cancer cell lines to evaluate its impact on cell growth, invasive ability, and MET and (ii) osteoblast cell lines to evaluate its impact on viability and differentiation and VEGFR2.

RESULTS

Cabozantinib inhibited progression of multiple prostate cancer cell lines (Ace-1, C4-2B, and LuCaP 35) in bone metastatic and soft tissue murine models of prostate cancer, except for PC-3 prostate cancer cells in which it inhibited only subcutaneous growth. Cabozantinib directly inhibited prostate cancer cell viability and induced apoptosis in vitro and in vivo and inhibited cell invasion in vitro. Cabozantinib had a dose-dependent biphasic effect on osteoblast activity and inhibitory effect on osteoclast production in vitro that was reflected in vivo. It blocked MET and VEGFR2 phosphorylation in prostate cancer cells and osteoblast-like cells, respectively.

CONCLUSION

These data indicate that cabozantinib has direct antitumor activity, and that its ability to modulate osteoblast activity may contribute to its antitumor efficacy.

Raf kinase inhibitor protein (RKIP) and phospho-RKIP expression in melanomas

Melanoma, a cancer notorious for its high potential to metastasize, arises from melanocytes, cells dedicated to melanin production and located in the basal layer of the epidermis. Raf-1 kinase inhibitor protein (RKIP) is an inhibitory molecule that down-regulates the effects of the Ras/Raf/MEK/ERK signaling pathway. The aim of this study was to examine the expression of RKIP and pRKIP in melanomas at different stages. We evaluated the RKIP and pRKIP protein by immunohistochemistry in control skin, pigmented nevi and melanomas, and through Western blotting in human normal melanocytes and in four different melanoma-derived cell lines (WM35, A375, M14, and A2058). Our results demonstrated a correlation between the expression of RKIP and pRKIP, and metastatic ability in melanoma cells. This raises the possibility to analyze both RKIP and pRKIP in all melanomas. Down-regulation of both RKIP and pRKIP expression could represent a useful marker of metastatic melanoma. On the contrary for non-metastatic melanoma, especially in Clark I and II, low RKIP and high pRKIP expression could be indicative. In conclusion, the observed negative correlation of the RKIP and pRKIP expression in metastatic melanomas indicates that expression of these proteins may become a prognostic marker for the progression of human cutaneous melanoma. We propose that the investigation of both RKIP and pRKIP may provide a useful tool indicative for metastatic or non-metastatic melanoma in different Clark's level melanomas. Further studies are required to verify the molecular background of the observed RKIP and pRKIP variations.

RKIP and HMGA2 regulate breast tumor survival and metastasis through lysyl oxidase and syndecan-2

Elucidating targets of physiological tumor metastasis suppressors can highlight key signaling pathways leading to invasion and metastasis. To identify downstream targets of the metastasis suppressor Raf Kinase Inhibitory Protein (RKIP/PEBP1), we utilized an integrated approach based upon statistical analysis of tumor gene expression data combined with experimental validation. Previous studies from our laboratory identified the architectural transcription factor and oncogene, HMGA2, as a target of inhibition by RKIP. Here we identify two signaling pathways that promote HMGA2-driven metastasis. Using both human breast tumor cells and an MMTV-Wnt mouse breast tumor model, we show that RKIP induces and HMGA2 inhibits expression of miR-200b; miR-200b directly inhibits expression of lysyl oxidase (LOX), leading to decreased invasion. RKIP also inhibits syndecan-2 (SDC2), which is aberrantly expressed in breast cancer, via down-regulation of HMGA2; but this mechanism is independent of miR-200. Depletion of SDC2 induces apoptosis and suppresses breast tumor growth and metastasis in mouse xenografts. RKIP, LOX, and SDC2 are coordinately regulated and collectively encompass a prognostic signature for metastasis-free survival in ER-negative breast cancer patients. Taken together, our findings reveal two novel signaling pathways targeted by the metastasis suppressor RKIP that regulate remodeling of the extracellular matrix and tumor survival.

A comparison of the biological features of prostate cancer with (PSA+, PSMA+) profile according to RKIP

PURPOSE

To investigate differences in the biological features of the most immunoexpressed prostate cancer (PC) profiles (PSA+, PSMA+) according to the RKIP.

METHODS

19 PC with dominant Gleason grade ≥ 8 were studied. Expression of PSA, PSMA, RKIP, Raf-1, MEK-1, ERK-1, ERK-2, p-Akt (T308), p-Akt (S473), NF- κ B p50, and NF- κ Bp65 were detected immunohistochemically.

RESULTS

. Loss of RKIP in the most immunoexpressed PC (PSA+, PSMA+) profile was associated with increased levels of PSA and PSMA expression. Intensities of immunoreactions to PSA and PSMA were higher in cancer cells negative for RKIP (12.51 ± 1.6 and 34.95 ± 1.92) compared to those positive for RKIP (4.68 ± 1.11 and 28.56 ± 0.91). In parallel, missing RKIP expression in PC patients with PSA+, PSMA+ profile was connected with increased components of both Raf-1/MEK/ERK and NF- κ B (p65/p50), whereas Akt is activated independently of RKIP.

CONCLUSIONS

Although characterized by the same (PSA+, PSMA+) profile, PC phenotype missing the RKIP related to invasive potential and greater biological aggressiveness reflected in overexpression of components of Raf-1/MEK/ERK and NF- κ B (p65/p50) in which Akt is activated independently of RKIP. Taking into account the PC phenotypes according to RKIP among PSA-PSMA profiles may improve distinguishing them from cancers that will become more aggressive and therefore adapt the therapeutic strategies in those patients.

Prostate cancer invasion and metastasis: insights from mining genomic data

Prostate cancer (PCa) is the second most commonly diagnosed malignancy in men in the Western world and the second leading cause of cancer-related deaths among men worldwide. Although most cancers have the potential to metastasize under appropriate conditions, PCa favors the skeleton as a primary site of metastasis, suggesting that the bone microenvironment is conducive to its growth. PCa metastasis proceeds through a complex series of molecular events that include angiogenesis at the site of the original tumor, local migration within the primary site, intravasation into the blood stream, survival within the circulation, extravasation of the tumor cells to the target organ and colonization of those cells within the new site. In turn, each one of these steps involves a complicated chain of events that utilize multiple protein-protein interactions, protein signaling cascades and transcriptional changes. Despite the urgent need to improve current biomarkers for diagnosis, prognosis and drug resistance, advances have been slow. Global gene expression methods such as gene microarrays and RNA sequencing enable the study of thousands of genes simultaneously and allow scientists to examine molecular pathways of cancer pathogenesis. In this review, we summarize the current literature that explored high-throughput transcriptome analysis toward the advancement of biomarker discovery for PCa. Novel biomarkers are strongly needed to enable more accurate detection of PCa, improve prediction of tumor aggressiveness and facilitate the discovery of new therapeutic targets for tailored medicine. Promising molecular markers identified from gene expression profiling studies include HPN, CLU1, WT1, WNT5A, AURKA and SPARC.

Solution structure and backbone dynamics of human Raf-1 kinase inhibitor protein

Human Raf-1 kinase inhibitor protein (hRKIP) is a small multi-functional protein of 187 residues. It contains a conserved pocket, which binds a wide range of ligands from various small molecules to distinct proteins. To provide a structural basis for the ligand diversity of RKIP, we herein determined the solution structure of hRKIP, and analyzed its structural dynamics. In solution, hRKIP mainly comprises two antiparallel β sheets, two α helices and two 3₁₀ helices. NMR dynamic analysis reveals that the overall structure of hRKIP is rigid, but its C-terminal helix which is close to the ligand-binding site is mobile. In addition, residues around the ligand-binding pocket exhibit significant conformational exchange on the μs-ms timescale. Conformational flexibility may allow the ligand-binding pocket and the C-terminal helix to adopt various conformations to interact with different substrates. This work may shed light on the underlying molecular mechanisms of how hRKIP recognizes and binds diverse substrate ligands.

RKIP: much more than Raf kinase inhibitory protein

From its discovery as a phosphatidylethanolamine-binding protein in bovine brain to its designation as a physiological inhibitor of Raf kinase protein, RKIP has emerged as a critical molecule for maintaining subdued, well-orchestrated cellular responses to stimuli. The disruption of RKIP in a wide range of pathologies, including cancer, Alzheimer's disease, and pancreatitis, makes it an exciting target for individualized therapy and disease-specific interventions. This review attempts to highlight recent advances in the RKIP field underscoring its potential role as a master modulator of many pivotal intracellular signaling cascades that control cellular growth, motility, apoptosis, genomic integrity, and therapeutic resistance. Specific biological and functional niches are highlighted to focus future research towards an enhanced understanding of the multiple roles of RKIP in health and disease.