RKIP Expression Research Articles

Prognostic significance of RKIP, TGM2, and CMTM4 expression in oral squamous cell carcinoma.

The expression of RKIP, TGM2, and CMTM4 in oral squamous cell carcinoma (OSCC) and normal oral tissues was detected and their correlations were analyzed. The relationships between RKIP, TGM2, and CMTM4 and the clinicopathological parameters and prognosis of patients were analyzed. Seventy cancerous and adjacent normal tissue samples were selected, recorded in the pathology department, and embedded in paraffin. Protein expression was detected by immunohistochemistry. Statistical software (SPSS 25.0, IBM Corporation) was used for the statistical analysis. The chi-squared (χ2) test was used to analyze the expression of RKIP, TGM2, and CMTM4 proteins and their clinicopathological features. Differences in RKIP, TGM2, and CMTM4 protein levels between OSCC and normal tissues were compared using a χ2 test. Survival analysis was performed using the Kaplan-Meier method, and differences between survival curves were determined using the log-rank test. The effects of RKIP, TGM2, and CMTM4 expression on patient prognosis were analyzed using a multivariate Cox proportional hazards regression model. P < .05 was considered statistically significant. The expression level of RKIP correlated with age and clinical stage (P < .05). TGM2 was associated with clinical stage and lymph node metastasis (P < .05). The expression of CMTM4 increased with a decrease in cancer differentiation. Kaplan-Meier survival analysis suggested that the positive expression of TGM2 and CMTM4 may predict poor prognosis in patients with OSCC. The multivariate Cox proportional hazards regression model suggested that TGM2 could be an independent prognostic factor for patients with OSCC. Combined expression of TGM2 and CMTM4 can be used as an indicator to evaluate the risk of metastasis and prognosis of OSCC.

Didymin Suppresses Microglia Pyroptosis and Neuroinflammation Through the Asc/Caspase-1/GSDMD Pathway Following Experimental Intracerebral Hemorrhage.

Neuroinflammation has been proven to exert an important effect on brain injury after intracerebral hemorrhage (ICH). Previous studies reported that Didymin possessed anti-inflammatory properties after acute hepatic injury, hyperglycemia-induced endothelial dysfunction, and death. However, the role of Didymin in microglial pyroptosis and neuroinflammation after ICH is unclear. The current study aimed to investigate the effect of Didymin on neuroinflammation mediated by microglial pyroptosis in mouse models of ICH and shed some light on the underlying mechanisms. In this study, we observed that Didymin treatment remarkably improved neurobehavioral performance and decreased BBB disruption and brain water content. Microglial activation and neutrophil infiltration in the peri-hematoma tissue after ICH were strikingly mitigated by Didymin as well. At the molecular level, administration of Didymin significantly unregulated the expression of Rkip and downregulated the expression of pyroptotic molecules and inflammatory cytokines such as Nlrp3 inflammasome, GSDMD, caspase-1, and mature IL-1β, TNF-α, and MPO after ICH. Besides, Didymin treatment decreased the number of Caspase-1-positive microglia and GSDMD-positive microglia after ICH. Inversely, Locostatin, an Rkip-specific inhibitor, significantly abolished the anti-pyroptosis and anti-neuroinflammation effects of Didymin. Moreover, Rkip binding with Asc could interrupt the activation and assembly of the inflammasome. Mechanistically, inhibition of Caspase-1 by VX-765 attenuated brain injury and suppressed microglial pyroptosis and neuroinflammation by downregulation of GSDMD, mature IL-1β, TNF-α, and MPO based on Locostatin-treated ICH. Taken together, Didymin alleviated microglial pyroptosis and neuroinflammation, at least in part through the Asc/Caspase-1/GSDMD pathway via upregulating Rkip expression after ICH. Therefore, Didymin may be a potential agent to attenuate neuroinflammation via its anti-pyroptosis effect after ICH.

Abstract PO-030: Characterizing mechanisms for inhibiting metastasis in triple negative breast cancer

Abstract Tumor cell heterogeneity has been strongly implicated in metastatic progression of solid tumors such as breast cancer, leading to resistance and recurrence. We hypothesize that inhibiting metastasis will reduce tumor cell heterogeneity and thereby increase therapeutic sensitivity. To test this hypothesis, we expressed the metastasis suppressor Raf Kinase Inhibitory Protein (RKIP or PEBP1) in triple-negative breast cancer (TNBC) cells as a means of comparing the variation in gene expression between individual cells in metastatic versus non-metastatic tumors. Xenograft tumors with or without exogenous RKIP expression were dissociated into single cell suspensions. We removed mouse as well as dead cells, and the remaining cells were loaded onto a Fluidigm C1 high-throughput chip for separation and library preparation. For each condition we performed three independent experiments yielding a total of 1569 cells. We performed controls to ensure that differences were not due to batch effects, cell cycle stage or sample quality. Clustering of single cells across all samples indicated that gene expression profiles are similar, confirming reproducibility. Gene ontology analysis of differentially expressed genes between cells with and without RKIP overexpression reveals gene sets that are important in tumor cell transitions from metastatic to non-metastatic states. These data will allow us to specifically test whether metastatic tumors are more heterogeneous than non-metastatic tumors in TNBC. Citation Format: Dongbo Yang, Christopher Dann, Sebastian Pott, Marsha Rosner. Characterizing mechanisms for inhibiting metastasis in triple negative breast cancer [abstract]. In: Proceedings of the AACR Virtual Special Conference on Tumor Heterogeneity: From Single Cells to Clinical Impact; 2020 Sep 17-18. Philadelphia (PA): AACR; Cancer Res 2020;80(21 Suppl):Abstract nr PO-030.

Abstract 2697: Single cell RNA sequencing and tumor cell heterogeneity in metastatic triple-negative breast cancer

Abstract Tumor cell heterogeneity has been strongly implicated in metastatic progression of solid tumors such as breast cancer, leading to resistance and recurrence. We hypothesize that inhibiting metastasis will reduce tumor cell heterogeneity and thereby increase therapeutic sensitivity. To test this hypothesis, we expressed the metastasis suppressor Raf Kinase Inhibitory Protein (RKIP or PEBP1) in triple-negative breast cancer (TNBC) cells as a means of comparing the variation in gene expression between individual cells in metastatic versus non-metastatic tumors. Xenograft tumors with or without exogenous RKIP expression were dissociated into single cell suspensions. We removed mouse as well as dead cells, and the remaining cells were loaded onto a microfluidic device (Fluidigm C1) for separation and library preparation. For each condition we performed three independent experiments yielding a total of 1569 cells. Initially, we performed controls to ensure that differences were not due to batch effects, cell cycle stage or sample quality. Clustering of single cells across all samples indicated that gene expression profiles are similar, confirming reproducibility. Gene ontology analysis of differentially expressed genes between cells with and without RKIP overexpression reveals gene sets that are important in tumor cell transitions from metastatic to non-metastatic states. These data will allow us to specifically test whether metastatic tumors are more heterogeneous than non-metastatic tumors in TNBC. Citation Format: Dongbo Yang, Christopher Dann, Sebastian Pott, Marsha Rosner. Single cell RNA sequencing and tumor cell heterogeneity in metastatic triple-negative breast cancer [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr 2697.

Expression analysis of DUSP6, DAB2IP, and RKIP genes in patients with head and neck squamous cell carcinoma

BackgroundHead and neck squamous cell carcinoma (HNSCC) is recognized as one of the most common malignancies worldwide, representing high mortality and morbidity. Here, we attempted to study the expression levels of DUSP6, DAB2IP, and RKIP genes, as the critical hallmarks involved in various central mechanisms including Mitogen-activated protein kinases (MAPK) pathway, in patients with HNSCC. MethodsThe mRNA expression levels of mentioned genes were evaluated in 45 HNSCC tissues and normal adjacent samples by quantitative Real-time PCR. Samples were obtained from AmirAlam Hospital Complex in Tehran, Iran. We, also, examined the correlation coefficient and receiver operating characteristic (ROC) curve for our data. ResultsThe expression levels of DUSP6 and DAB2IP genes were significantly up-regulated and decreased, respectively, in HNSCC samples, compared with control (p < .05). However, RKIP expression levels did not differ between these two groups. Moreover, statistically significant correlations were observed between expression levels of these three genes, as well as considerable correlations between their expression and clinicopathological features including sex, age, smoking history, histological grade, and pathologic stage for DUSP6 and DAB2IP. Finally, ROC curve analysis depicted DAB2IP and DUSP6 genes as good predictive biomarkers with highest specificity. DiscussionGiven the dysregulated mRNA expression levels of DUSP6 and DAB2IP genes, along with exhibited correlations and ROC curve analysis, the pivotal importance of studied genes and their network can be suggested in patients with HNSCC. Recognizing such molecular dysregulations in central cellular pathways can pave the road to potential therapeutic interventions and to improve medical diagnosis.

Evaluation of RKIP gene expression changes of MDA-MB-231 breast cancer cell line after microgravity treatment

Introduction: Gravity is one of the most important forces exposed to the organisms on the earth which affects the cells, molecules and thus the entire of organism. The purpose of this study is to investigate the effect of the simulated microgravity on the changes of RKIP metastasis suppressor gene expression on MDA-MB-231 breast cancer cell line.Materials and Methods: In order to impose microgravity state, cancer cells were placed on clinostat for one and three days. Then RNA was extracted from the cells and RKIP gene expression changes were evaluated by qReal time PCR.Results: The findings showed that the microgravity during one day reduced the RKIP expression level, but with continuing up to three days, the expression returned to the control level.Conclusion: By optimizing the duration of microgravity, it can be likely observed the significant effects on the RKIP gene expression changes and so that useful steps can be taken to discover the cancer mechanisms and its treatment.

Potential Therapeutic Applications of MDA-9/Syntenin-NF-κB-RKIP Loop in Human Liver Carcinoma.

Overexpression of MDA-9/Syntenin occurs in multiple human cancer cell lines and is associated with higher grade of tumor classification, invasiveness and metastasis. In some cases, its role in cancer biology depends on relationships between MDA-9/Syntenin and NF-κB. This study aims to analyze the presence of a regulation loop like that between MDA-9/Syntenin - NF-κB - RKIP in human liver carcinoma. Transient transfection was performed with siRNA anti-MDA-9/Syntenin. Expression of different factors was evaluated by Real time-PCR and Western blotting, while NF-κB activation by TransAM assay. Invasion capacity was analyzed by Matrigel Invasion Assay and the effects of agents on cell viability were examined by MTS assay. We have examined basal expression of MDA-9/Syntenin in three cell lines of human liver carcinoma (HA22T/VGH, Hep3B and HepG2). In all cell lines there was an inverse relationship between MDA-9/Syntenin and RKIP expression levels, and a positive correlation between MDA-9/Syntenin expression and NF-κB activation levels. By silencing with a siRNA anti-MDA-9/Syntenin we observed in all cell lines a very strong increase of RKIP at mRNA level. Interestingly, in all cell lines, inhibition of MDA- 9/Syntenin expression induced NF-κB downregulation and contemporary a reduction in invasion ability MMP-2 dependent. Finally, we showed a good additive effect of MDA- 9/Syntenin siRNA when associated with Curcumin or Doxorubicin on cell growth inhibition. Our data confirm the key role of MDA-9/Syntenin in HCC biology. The presence of a regulation loop among MDA-9/Syntenin, NF-κB and RKIP provide new pharmacological approaches.

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.

Abstract B19: Modulation of MAPK and PI3K-AKT signaling pathways and poor prognosis are associated with loss of RKIP

Abstract RKIP was described as a metastasis suppressor gene, and it loss was associated with several aggressiveness features, such as with higher stage and/or recurrence, presence of vascular invasion and metastasis, and poor overall survival of cancer patients. RKIP is a member of the phosphatidyl-ethanolamine-binding protein (PEBP) family that negatively regulates not only the MAPK signalling, but also the NF-κ β, GPRC-2, and GSK3β pathway. Gastrointestinal stromal tumors (GIST) are the most common mesenchymal tumor on the gastrointestinal tract characterized by hotspot mutations in KIT and PDGFRA genes, which are predictive of imatinib-based therapy response. In GIST, it is reported that 9% of tumors have loss of expression in RKIP. Our main goal is to investigate the RKIP protein expression in a series of 72 bona-fide GIST and to correlate with patients' clinicopathologic characteristics. Moreover, we intended to assess in vitro role of RKIP gene depletion. We performed immunohistochemistry in 72 primary GIST previously characterized for CD117, S100, Desmin, and CD34 as well as molecularly for KIT (exons 9, 11, 13, 17), PDGFRA (exons 12, 14, 18), and BRAF (V600E). In a second step, we established a RKIP knockout GIST cell line (GIST-T1) by transfection of a pool of 3 different optimized gRNA constructs, targeting RKIP, cloned into the RKIP CRISPR/Cas9 system. The RKIP knockout was verified by Western blotting. The expression profile of RKIP KO cells was assessed using the nanostring Cancer Pathways platform, which contains a set of 800 cancer-related genes. We found that RKIP is absent or expressed at low levels in 16.7% (12/72) of GIST. RKIP reduction was significantly associated with tumor in small intestine, with tumor size increased, and patient death. The overall five-year survival to RKIP-negative cases was 41.7% versus 73.9% in RKIP-positive patients, yet not significant (p=0.07). The in vitro assays showed that RKIP protein levels were depleted in the RKIP KO cells, comparing with the nontransfected cells and with the negative control. The nanostring expression analysis showed 34 genes downregulated and 9 genes upregulated in RKIP-depleted cells. The downregulated genes are especially involved in PI3K-AKT signaling pathway and the upregulated genes in MAPK signaling pathway. In conclusion, we confirm that the lack of RKIP expression occurs in a subset of GISTs and is associated with poor prognosis. We also showed that in GIST loss of RKIP changes important cancer signaling pathways. Citation Format: Nathália Cristina Campanella, Matias Melendez, Lucas Abrahão-Machado, Cristovam Scapulatempo-Neto, Denise Peixoto Guimarães, Rui Reis. Modulation of MAPK and PI3K-AKT signaling pathways and poor prognosis are associated with loss of RKIP [abstract]. In: Proceedings of the AACR International Conference held in cooperation with the Latin American Cooperative Oncology Group (LACOG) on Translational Cancer Medicine; May 4-6, 2017; São Paulo, Brazil. Philadelphia (PA): AACR; Clin Cancer Res 2018;24(1_Suppl):Abstract nr B19.

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.

Highlights from Recent Cancer Literature

Highlights from Recent Cancer Literature

Raf kinase inhibitor protein mediates intestinal epithelial cell apoptosis and promotes IBDs in humans and mice

ObjectiveRaf kinase inhibitor protein (RKIP) appears to control cancer cell metastasis and its expression in colonic tissue is related to colonic cancer development. We sought to identify the roles of...

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.

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.

Genetic variants in RKIP are associated with clear cell renal cell carcinoma risk in a Chinese population.

BackgroundRaf-1 kinase inhibitor protein (RKIP) plays a critical role in tumor development by regulating cell functions such as invasion, apoptosis and differentiation. Down-regulation of RKIP expression has been implicated in the development and progression of renal cell carcinoma (RCC). Herein, we hypothesized that genetic polymorphisms in RKIP might be associated with susceptibility and progression of RCC.MethodsA total of 5 tagging single-nucleotide polymorphisms (tSNPs) in RKIP were selected and genotyped by SNapShot method in a case-control study of 859 RCC patients and 1004 controls. The logistic regression was used to evaluate the genetic association with occurrence and progression of RCC. The functionality of the important SNP was preliminary examined by qRT-PCR.ResultWe found that the rs17512051 in the promoter region of RKIP was significantly associated with decreased clear cell RCC (ccRCC) risk (TA/AA vs. TT: P = 0.039, OR = 0.78, 95%CI = 0.62–0.99). Another SNP (rs1051470) in the 3′UTR region of RKIP was marginally associated with increased ccRCC risk (TT vs. CC+CT: OR = 1.45, 95%CI = 1.01–2.09). In the stratified analysis, the protective effect of rs17512051 was more predominant in the subgroups of male, non-smokers, non-drinkers as well as subjects without history of diabetes. Furthermore, we observed higher RKIP mRNA levels in the presence of the rs17512051A allele in normal renal tissues.ConclusionOur results suggest that the potentially functional RKIP rs17512051 polymorphism may affect ccRCC susceptibility through altering the endogenous RKIP expression level. Risk effects and the functional impact of this polymorphism need further validation.

Abstract 124: Effect of RKIP on MMP expression and regulation of breast cancer metastasis

Abstract 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. Metastasis is a complex multiple-step process. Expression of RKIP is low in cancer metastases. Although primary tumor growth was 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. Using an unbiased PCR based screening and by analyzing DNA microarray expression datasets we observed that the expression of multiple metalloproteases (MMP) including MMP1, MMP3, MMP10 and MMP13 were 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. In this study 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 found that MMP13 is the cause of RKIP-mediated inhibition of local cancer invasion. Interestingly expression of MMP13 alone was not sufficient to reverse the inhibition of breast cancer cells metastasis to the lung due to the expression of RKIP. We found that RKIP negatively regulated MMP13 through the Erk2-Fra1 transcriptional axis and the repression of MMP13 by RKIP requires the presence of the a TPA-responsive element in the MMP13 proximal promoter. Together, our findings indicate that RKIP inhibits cancer cell invasion, in part, via MMP13 inhibition. These data also implicate RKIP in the regulation of MMPs transcription, suggesting a potential mechanism by which RKIP inhibits tumor progression and metastasis. Citation Format: Ila J. Datar, Jingwei Feng, Gang Ren, Zehui Li, Xiaoliang Qiu, Fahd Al-Mulla, Milad S. Bitar, Miranda Yeung, Kam Yeung. Effect of RKIP on MMP expression and regulation of breast cancer metastasis. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 124. doi:10.1158/1538-7445.AM2014-124

Raf Kinase Inhibitory Protein Role in the Molecular Subtyping of Breast Cancer

In this study, we examined the association between the RKIP expression and the molecular subtypes of breast cancer. Microarray gene expression data of 2,333 human breast cancer from 26 different cohorts performed on Affymetrix U133A or U133Plus2 platforms were downloaded from Array Express and Gene Expression Omnibus and the molecular subtype of breast cancer for the samples was determined by single sample Gene Set Enrichment Analysis. Differences in recurrence-free survival (RFS) were tested using the Log-rank test in univariate analysis and displayed using Kaplan-Meier curves. Cox proportional-hazards model was used to calculate the hazard ratio using univariate and multivariate analysis. Loss or reduced RKIP expression was associated with reduced RFS in breast cancer using univariate and multivariate analyses, which was independent of lymph node (LN) metastasis status. Basal-like, Claudin-low, and Her-2-enriched tumors had significantly lower RKIP levels compared to other subclasses (P < 0.0001). Conversely, the Luminal subclass exhibited the highest expression levels of RKIP (P < 0.0001 for Luminal A and P = 0.0005 for Luminal B subtype), while in normal-like breast cancer subtype, RKIP expression was not informative. RKIP expression was prognostic in ER+ and ER- subgroups. RKIP expression had no significant prognostic power within Basal-like, Claudine-low, Luminal B, or Her-2-enriched breast cancer subtypes. However, its expression pinpointed excellent from intermediate-poor Luminal A survivors, in both ER+ (P = 0.035) and ER- (P = 0.012) subgroups, especially in LN negative breast cancers. In conclusion, RKIP expression adds significant value to the molecular subclassification of breast cancer especially for the Luminal A subtype.

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.

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-κB p50, and NF-κBp65 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-κB (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-κB (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.