Loss of Raf-1 kinase inhibitory protein in pancreatic ductal adenocarcinoma

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

BACKGROUND

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

METHODS

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

RESULTS

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

CONCLUSIONS

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

Multifaceted Effects of Kinase Inhibitors on Pancreatic Cancer Cells Reveals Pivotal Entities with Therapeutic Implications

Pancreatic cancer is one of the most aggressive forms of cancer and is the seventh leading cause of cancer deaths worldwide. Pancreatic ductal adenocarcinoma (PDAC) accounts for over 90% of pancreatic cancers. Most pancreatic cancers are recalcitrant to radiation, chemotherapy, and immunotherapy, highlighting the urgent need for novel treatment options for this deadly disease. To this end, we screened a library of kinase inhibitors in the PDAC cell lines PANC-1 and BxPC-3 and identified two highly potent molecules: Aurora kinase inhibitor AT 9283 (AT) and EGFR kinase inhibitor WZ 3146 (WZ). Both AT and WZ exhibited a dose-dependent inhibition of viability in both cell lines. Thus, we conducted an in-depth multilevel (cellular, molecular, and proteomic) analysis with AT and WZ in PANC-1 cells, which harbor KRAS mutation and exhibit quasimesenchymal properties representing pancreatic cancer cells as having intrinsic chemoresistance and the potential for differential response to therapy. Elucidation of the molecular mechanism of action of AT and WZ revealed an impact on the programmed cell death pathway with an increase in apoptotic, multicaspase, and caspase 3/7 positive cells. Additionally, the key survival molecule Bcl-2 was impacted. Moreover, cell cycle arrest was observed with both kinase inhibitors. Additionally, an increase in superoxide radicals was observed in the AT-treated group. Importantly, proteomic profiling revealed differentially regulated key entities with multifaceted effects, which could have a deleterious impact on PDAC. These findings suggest potential targets for efficacious treatment, including a possible increase in the efficacy of immunotherapy using PD-L1 antibody due to the upregulation of lactoferrin and radixin. Furthermore, combination therapy outcomes with gemcitabine/platinum drugs may also be more effective due to an increase in the NADH dehydrogenase complex. Notably, protein-protein interaction analysis (STRING) revealed possible enrichment of reactome pathway entities. Additionally, novel therapy options, such as vimentin-antibody--drug conjugates, could be explored. Therefore, future studies with the two kinases as monotherapy/combination therapy are warranted.

Alteration in Levels of Specific miRNAs and Their Potential Protein Targets between Human Pancreatic Cancer Samples, Adjacent Normal Tissue, and Xenografts Derived from These Tumors

Herein, we describe the global comparison of miRNAs in human pancreatic cancer tumors, adjacent normal tissue, and matched patient-derived xenograft models using microarray screening. RNA was extracted from seven tumor, five adjacent normal, and eight FI PDX tumor samples and analyzed by Affymetrix GeneChip miRNA 4.0 array. A transcriptome analysis console (TAC) was used to generate comparative lists of up- and downregulated miRNAs for the comparisons, tumor vs. normal and F1 PDX vs. tumor. Particular attention was paid to miRNAs that were changed in the same direction in both comparisons. We identified the involvement in pancreatic tumor tissue of several miRNAs, including miR4534, miR3154, and miR4742, not previously highlighted as being involved in this type of cancer. Investigation in the parallel mRNA and protein lists from the same samples allowed the elimination of proteins where altered expression correlated with corresponding mRNA levels and was thus less likely to be miRNA regulated. Using the remaining differential expression protein lists for proteins predicted to be targeted for differentially expressed miRNA on our list, we were able to tentatively ascribe specific protein changes to individual miRNA. Particularly interesting target proteins for miRs 615-3p, 2467-3p, 4742-5p, 509-5p, and 605-3p were identified. Prominent among the protein targets are enzymes involved in aldehyde metabolism and membrane transport and trafficking. These results may help to uncover vulnerabilities that could enable novel approaches to treating pancreatic cancer.

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

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

RKIP Regulates Differentiation-Related Features in Melanocytic Cells

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

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

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

RIPK4/PEBP1 axis promotes pancreatic cancer cell migration and invasion by activating RAF1/MEK/ERK signaling

Pancreatic cancer is a lethal disease with a high metastatic potential. In our previous study, we identified a specific subgroup of patients with pancreatic cancer with a serum signature of carcinoembryonic antigen (CEA)+/cancer antigen (CA)125+/CA19-9 ≥1,000 U/ml. In this study, by using high-throughput screening analysis, we found that receptor-interacting protein kinases 4 (RIPK4) may be a key molecule involved in the high metastatic potential of this subgroup of patients with pancreatic cancer. A high RIPK4 expression predicted a poor prognosis and promoted pancreatic cancer cell migration and invasion via the RAF1/MEK/ERK pathway. Moreover, RIPK4 activated the RAF1/MEK/ERK pathway by regulating proteasome-mediated phosphatidylethanolamine binding protein 1 (PEBP1) degradation. The suppression of PEBP1 degradation eliminated the RIPK4-induced activation of RAF1/MEK/ERK signaling and pancreatic cancer cell migration or invasion. Thus, on the whole, the findings of this study indicated that RIPK4 was upregulated in the subgroup of pancreatic cancer with a high metastatic potential. RIPK4 overexpression promoted pancreatic cancer cell migration and invasion via the PEBP1 degradation-induced activation of the RAF1/MEK/ERK pathway.

Down-regulation of osteoprotegerin expression as a novel biomarker for colorectal carcinoma

A better understanding of tumor biology is important in the identification of molecules that are down-regulated in malignancy and in determining their role in tumor suppression. The aim of this study was to analyze osteoprotegerin (OPG) expression in colorectal carcinoma (CRC) and to investigate the underlying mechanism for changes in the expression of OPG. OPG expression was assessed in CRC tissue samples and cell lines. The methylation status of the OPG promoter region was determined, and the effects of demethylation on OPG expression were analyzed. The effects of recombinant OPG (rOPG) administration on cellular functions were also investigated. Clinical and prognostic implications of OPG protein expression in CRC patients were analyzed. The CRC tissues and cells showed significantly lower OPG expression. Pyrosequencing of OPG-silenced CRC cells revealed that the OPG gene promoter was highly methylated. Treatment with demethylating agent significantly elevated OPG mRNA and protein expression. rOPG significantly decreased cell viability and MMP-2 and VEGF-A production in CRC cells. Reduced OPG immunoreactivity was associated with aggressive oncogenic behavior in CRC. Also, OPG expression was found to be an independent predictor of recurrent hepatic metastasis and independent prognostic factor for worse survival rates. We demonstrated that OPG silencing in CRC occurs through epigenetic repression, and is involved in the development and progression of CRC. Our data suggest that OPG is a novel prognostic biomarker and a new therapeutic target for the treatment of patients with CRC.

Tyr42 phosphorylation of RhoA GTPase promotes tumorigenesis through nuclear factor (NF)-κB

Dysregulation of reactive oxygen species (ROS) levels is implicated in the pathogenesis of several diseases, including cancer. However, the molecular mechanisms for ROS in tumorigenesis have not been well established. In this study, hydrogen peroxide activated nuclear factor-κB (NF-κB) and RhoA GTPase. In particular, we found that hydrogen peroxide lead to phosphorylation of RhoA at Tyr42 via tyrosine kinase Src. Phospho-Tyr42 (p-Tyr42) residue of RhoA is a binding site for Vav2, a guanine nucleotide exchange factor (GEF), which then activates p-Tyr42 form of RhoA. P-Tyr42 RhoA then binds to IκB kinase γ (IKKγ), leading to IKKβ activation. Furthermore, RhoA WT and phospho-mimic RhoA, RhoA Y42E, both promoted tumorigenesis, whereas the dephospho-mimic RhoA, RhoA Y42F suppressed it. In addition, hydrogen peroxide induced NF-κB activation and cell proliferation, along with expression of c-Myc and cyclin D1 in the presence of RhoA WT and RhoA Y42E, but not RhoA Y42F. Indeed, levels of p-Tyr42 Rho, p-Src, and p-65 are significantly increased in human breast cancer tissues and show correlations between each of the two components. Conclusively, the posttranslational modification of as RhoA p-Tyr42 may be essential for promoting tumorigenesis in response to generation of ROS.

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 inhibitory protein (RKIP): functional pleiotropy in the mammalian brain

In 1984, a cytosolic protein was isolated from bovine brain and coined phosphatidylethanolamine binding protein (PEBP) to describe its phospholipid-binding potential. Its cellular function remained elusive for more than a decade until it was discovered that PEBP had the ability to suppress the Raf1-mitogen activated protein kinase (MAPK) pathway, earning it the new name of Raf1 kinase inhibitory protein (RKIP). This milestone discovery has paved the way for numerous studies that have now extended the reach of RKIP's function to other signaling cascades, within the context of various physiological and pathophysiological systems. This review will summarize our current knowledge of the neurophysiological roles of RKIP in the mammalian brain, including its function in the circadian clock and synaptic plasticity. It will also discuss evidence for an involvement of RKIP and its derived neuropeptide, hippocampal cholinergic neurostimulating peptide (HCNP), in neural development and differentiation. Implications in certain pathologies such as Alzheimer's disease and brain cancer will be highlighted. By chronicling the diverse functions of RKIP in the brain, we hope that this review will serve as a timely resource that ignites future studies on this versatile, multifaceted protein in the nervous system.

Expression of phosphorylated extracellular signal-regulated kinase at the invasive front of hepatic colorectal metastasis

Raf-1 kinase inhibitory protein (RKIP), an endogenous inhibitor of the extracellular signal-regulated kinase (ERK) pathway, suppresses metastasis in a number of cancer types, including colorectal carcinoma (CRC); thus, RKIP downregulation significantly contributes to CRC invasiveness and metastatic potential. However, our previous study demonstrated that RKIP-positive tumors in CRC patients are predictive of hepatic colorectal metastases (HCMs). Based on the previous finding that the ERK pathway can be activated independently of RKIP, we hypothesized that RKIP-expressing HCMs may express significant levels of phosphorylated ERK (pERK). Thus, the present study evaluated the expression of RKIP and pERK in 68 HCM tissue samples using immunohistochemistry. RKIP expression was positive in 22 (32.4%) of the 68 samples, seven (31.8%) of which exhibited nuclear pERK immunoreactivity exclusively at the invasive tumor front. Furthermore, pERK expression at the invasive front was significantly associated with recurrent HCM following hepatic resection, and pERK expression observed at the invasive front of RKIP-expressing HCMs indicated that the activation of the ERK pathway may also be involved in the invasive process of these tumors, despite the presence of RKIP. A strong association between pERK expression and the presence of recurrent HCM may indicate that the ERK pathway is important in the metastatic recurrence of RKIP-positive HCM.

Antiprotease strategy in pancreatic cancer treatment: emergence from a preclinical study

OBJECTIVES

Resistance to gemcitabine is one of the main causes of treatment failure in pancreatic cancer. Compelling evidences have shown the involvement of nuclear factor κB (NF-κB) activation in such phenomenon. The protease inhibitor gabexate mesilate has been shown to inhibit NF-κB. We here investigated if combined treatment with this drug could improve gemcitabine antitumoral efficacy in pancreatic cancer cells.

METHODS

The effect of gabexate mesilate and gemcitabine, both used at concentrations achievable in human plasma, was assessed on in vitro pancreatic cancer cell growth, invasion, and tumor angiogenesis. The molecular mechanism at the basis of these effects was also investigated.

RESULTS

Gabexate mesilate significantly increased gemcitabine anti-invasive and antiangiogenic efficacy. This effect was related to inhibition of gemcitabine-induced NF-κB activation by gabexate mesilate, which prevented RelA/p65 nuclear translocation and resulted in metalloproteinase 2, metalloproteinase 9, vascular endothelial growth factor, and interleukin 8 down-regulation. Combined treatment with gabexate mesilate also inhibited gemcitabine-induced extracellular-regulated kinase 1/2 and AKT activation by increased expression of Raf kinase inhibitor protein and phosphatase and tensin homolog.

CONCLUSIONS

Combined treatment with gabexate mesilate sensitizes pancreatic cancer cells to gemcitabine by inhibition of the NF-κB pathway. The efficacy of this therapeutic strategy in pancreatic cancer patients remains to be established and deserves future clinical investigation.

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.

Selective disruption of rb-raf-1 kinase interaction inhibits pancreatic adenocarcinoma growth irrespective of gemcitabine sensitivity

Inactivation of the retinoblastoma (Rb) tumor suppressor protein is widespread in human cancers. Inactivation of Rb is thought to be initiated by association with Raf-1 (C-Raf) kinase, and here we determined how RRD-251, a disruptor of the Rb-Raf-1 interaction, affects pancreatic tumor progression. Assessment of phospho-Rb levels in resected human pancreatic tumor specimens by immunohistochemistry (n = 95) showed that increased Rb phosphorylation correlated with increasing grade of resected human pancreatic adenocarcinomas (P = 0.0272), which correlated with reduced overall patient survival (P = 0.0186). To define the antitumor effects of RRD-251 (50 μmol/L), cell-cycle analyses, senescence, cell viability, cell migration, anchorage-independent growth, angiogenic tubule formation and invasion assays were conducted on gemcitabine-sensitive and -resistant pancreatic cancer cells. RRD-251 prevented S-phase entry, induced senescence and apoptosis, and inhibited anchorage-independent growth and invasion (P < 0.01). Drug efficacy on subcutaneous and orthotopic xenograft models was tested by intraperitoneal injections of RRD-251 (50 mg/kg) alone or in combination with gemcitabine (250 mg/kg). RRD-251 significantly reduced tumor growth in vivo accompanied by reduced Rb phosphorylation and lymph node and liver metastasis (P < 0.01). Combination of RRD-251 with gemcitabine showed cooperative effect on tumor growth (P < 0.01). In conclusion, disruption of the Rb-Raf-1 interaction significantly reduces the malignant properties of pancreatic cancer cells irrespective of their gemcitabine sensitivity. Selective targeting of Rb-Raf-1 interaction might be a promising strategy targeting pancreatic cancer.

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.

Geographic analysis of RKIP expression and its clinical relevance in colorectal cancer

Background:

This study evaluates the geographic expression pattern of Raf-1 Kinase Inhibitor Protein (RKIP) in colorectal cancer (CRC) in correlation with clinicopathological and molecular features, markers of epithelial-mesenchymal transition (EMT) and survival outcome.

Methods:

Whole-tissue sections of 220 well-characterised CRCs were immunostained for RKIP. NF-κB and E-Cadherin expression was assessed using a matched multi-punch tissue microarray. Analysis of mismatch repair (MMR) protein expression, B-Raf and KRAS mutations was performed. RKIP expression in normal mucosa, tumour centre, invasion front and tumour buds was each assessed for clinical relevance.

Results:

RKIP was diffusely expressed in normal mucosa and progressively lost towards tumour centre and front (P<0.0001). Only 0.9% of tumour buds were RKIP-positive. In the tumour centre, RKIP deficiency predicted metastatic disease (P=0.0307), vascular invasion (P=0.0506), tumour budding (P=0.0112) and an invasive border configuration (P=0.0084). Loss of RKIP correlated with NF-κB activation (P=0.0002) and loss of E-Cadherin (P<0.0001). Absence of RKIP was more common in MMR-deficient cancers (P=0.0191), while no impact of KRAS and B-Raf mutation was observed. RKIP in the tumour centre was identified as a strong prognostic indicator (HR (95% CI): 2.13 (1.27–3.56); P=0.0042) independently of TNM classification and therapy (P=0.0474).

Conclusion:

The clinical relevance of RKIP expression as an independent prognostic factor is restricted to the tumour centre. Loss of RKIP predicts features of EMT and correlates with frequent distant metastasis.

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

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

Low RKIP expression associates with poor prognosis in bladder cancer patients

Urothelial bladder cancer (UBC) is a heterogeneous type of disease. It is urgent to screen biomarkers of tumour aggressiveness in order to clarify the clinical behaviour and to personalize therapy in UBC patients. Raf kinase inhibitory protein (RKIP) is a metastasis suppressor, and its downregulation is associated with metastatic events in an increasing number of solid tumours. We evaluated the clinical and prognostic significance of RKIP expression in patients with high risk of progression UBC. Using immunohistochemistry, we determined RKIP expression levels in a series of 81 patients with high-grade pT1/pTis or muscle-invasive UBC. Staining of CD31 and D2-40 was used to assess blood and lymphatic vessels, in order to distinguish between blood and lymphatic vessel invasion (LVI). We found that 90 % of pT1/pTis tumours, 94 % of non-muscle invasive papillary tumours and 76 % of the cases without LVI occurrence expressed RKIP in >10 % of cells. In this group, we observed a subgroup of tumours (42 %) in which the tumour centre was significantly more intensely stained than the invasion front. This heterogeneous pattern was observed in 63 % of the cases with LVI. Low RKIP expression was associated with poorer 5-year disease-free and overall survival rates, and remained as an independent prognostic factor for disease-free survival. Loss of RKIP expression may be an important prognostic factor for patients with high risk of progression bladder cancer.

MEK-1 activates C-Raf through a Ras-independent mechanism

C-Raf is a member of the Ras-Raf-MEK-ERK mitogen-activated protein kinase (MAPK) signaling pathway that plays key roles in diverse physiological processes and is upregulated in many human cancers. C-Raf activation involves binding to Ras, increased phosphorylation and interactions with co-factors. Here, we describe a Ras-independent in vivo pathway for C-Raf activation by its downstream target MEK. Using (32)P-metabolic labeling and 2D-phosphopeptide mapping experiments, we show that MEK increases C-Raf phosphorylation by up-to 10-fold. This increase was associated with C-Raf kinase activation, matching the activity seen with growth factor stimulation. Consequently, coexpression of wildtype C-Raf and MEK was sufficient for full and constitutive activation of ERK. Notably, the ability of MEK to activate C-Raf was completely Ras independent, since mutants impaired in Ras binding that are irresponsive to growth factors or Ras were fully activated by MEK. The ability of MEK to activate C-Raf was only partially dependent on MEK kinase activity but required MEK binding to C-Raf, suggesting that the binding results in a conformational change that increases C-Raf susceptibility to phosphorylation and activation or in the stabilization of the phosphorylated-active form. These findings propose a novel Ras-independent mechanism for activating the C-Raf and the MAPK pathway without the need for mutations in the pathway. This mechanism could be of significance in pathological conditions or cancers overexpressing C-Raf and MEK or in conditions where C-Raf-MEK interaction is enhanced due to the down-regulation of RKIP and MST2.

The role of Raf-1 kinase inhibitor protein in the regulation of pancreatic beta cell proliferation in mice

AIMS/HYPOTHESIS

Manoeuvres aimed at increasing beta cell mass have been proposed as regenerative medicine strategies for diabetes treatment. Raf-1 kinase inhibitor protein 1 (RKIP1) is a common regulatory node of the mitogen-activated protein kinase (MAPK) and nuclear factor κB (NF-κB) pathways and therefore may be involved in regulation of beta cell homeostasis. The aim of this study was to investigate the involvement of RKIP1 in the control of beta cell mass and function.

METHODS

Rkip1 (also known as Pebp1) knockout (Rkip1 (-/-)) mice were characterised in terms of pancreatic and glucose homeostasis, including morphological and functional analysis. Glucose tolerance and insulin sensitivity were examined, followed by assessment of glucose-induced insulin secretion in isolated islets and beta cell mass quantification through morphometry. Further characterisation included determination of endocrine and exocrine proliferation, apoptosis, MAPK activation and whole genome gene expression assays. Capacity to reverse a diabetic phenotype was assessed in adult Rkip1 (-/-) mice after streptozotocin treatment.

RESULTS

Rkip1 (-/-) mice exhibit a moderately larger pancreas and increased beta cell mass and pancreatic insulin content, which correlate with an overall improvement in whole body glucose tolerance. This phenotype is established in young postnatal stages and involves enhanced cellular proliferation without significant alterations in cell death. Importantly, adult Rkip1 (-/-) mice exhibit rapid reversal of streptozotocin-induced diabetes compared with control mice.

CONCLUSIONS/INTERPRETATION

These data implicate RKIP1 in the regulation of pancreatic growth and beta cell expansion, thus revealing RKIP1 as a potential pharmacological target to promote beta cell regeneration.

Reduced expression of Raf-1 kinase inhibitory protein predicts regional lymph node metastasis and shorter survival in esophageal squamous cell carcinoma

Raf-1 kinase inhibitory protein (RKIP), a suppressor of metastasis, is associated inversely with the progression and metastasis of human malignancies. The present study evaluated relationships between RKIP expression and metastatic potential, clinicopathological characteristics and patient outcome in esophageal squamous cell carcinoma (ESCC). We examined tissue specimens from 138 patients with thoracic ESCC. Using immunohistochemistry, RKIP expression was detected in ESCC in situ, primary ESCC and nodal metastatic ESCC. RKIP expression was reduced in 28.9% (13/45) of ESCC in situ, in 50.0% (69/138) of primary ESCC and in 71.4% (65/91) of nodal metastatic ESCC. These levels of RKIP down-regulation differed significantly. RKIP expression was associated inversely with histological grade (P=0.008), pathological T stage (P=0.044), lymphatic invasion (P=0.019), regional lymph node metastasis (LNM; P=0.002) and stage (P=0.041). Pathological T stage (P=0.001), lymphatic invasion (P<0.001) and reduced RKIP expression (P=0.039) were independent predictors of regional LNM in ESCC. In addition, the postoperative survival of patients with RKIP-reduced ESCC was significantly shorter than for patients with RKIP-positive ESCC (P=0.004). Reduced RKIP expression in ESCC correlated with advanced disease, regional LNM and poor prognosis. RKIP expression may serve as a novel clinical biomarker in patients with ESCC.

Downregulation of RKIP is associated with poor outcome and malignant progression in gliomas

Malignant gliomas are highly infiltrative and invasive tumors, which precludes the few treatment options available. Therefore, there is an urgent need to elucidate the molecular mechanisms underlying gliomas aggressive phenotype and poor prognosis. The Raf Kinase Inhibitory protein (RKIP), besides regulating important intracellular signaling cascades, was described to be associated with progression, metastasis and prognosis in several human neoplasms. Its role in the prognosis and tumourigenesis of gliomas remains unclear.

In the present study, we found that RKIP protein is absent in a low frequency (10%, 20/193) of glioma tumors. Nevertheless, the absence of RKIP expression was an independent prognostic marker in glioma. Additionally, by in vitro downregulation of RKIP, we found that RKIP inhibition induces a higher viability and migration of the cells, having no effect on cellular proliferation and angiogenesis, as assessed by in vivo CAM assay.

In conclusion, this is the largest series studied so far evaluating the expression levels of this important cancer suppressor protein in glioma tumors. Our results suggest that in a subset of tumors, the absence of RKIP associates with highly malignant behavior and poor survival of patients, which may be a useful biomarker for tailored treatment of glioma patients.