Signaling crossroads: The function of Raf kinase inhibitory protein in cancer, the central nervous system and reproduction

Department of Molecular Biology Cell Biology and Biochemistry, Brown University, Providence, RI 02912, United States.
Cellular Signalling (Impact Factor: 4.47). 02/2008; 20(1):1-9. DOI: 10.1016/j.cellsig.2007.07.003
Source: PubMed

ABSTRACT The Raf kinase inhibitory protein 1 (RKIP-1) and its orthologs are conserved throughout evolution and widely expressed in eukaryotic organisms. In its non-phosphorylated form RKIP-1 negatively regulates the Raf/MEK/ERK pathway by interfering with the activity of Raf-1. In its phosphorylated state, RKIP-1 dissociates from Raf-1 and inhibits GRK-2, a negative regulator of G-protein coupled receptors (GPCRs). Available data indicate that the phosphorylation of RKIP-1 by PKC can stimulate both the Raf/MEK/ERK and GPCR pathways. RKIP-1 has also been implicated as a negative regulator of the NF-kappaB pathway. Recent studies have shown that phosphorylated RKIP-1 binds to the centrosomal and kinetochore regions of metaphase chromosomes, where it may be involved in regulating the partitioning of chromosomes and the progression through mitosis. The collective evidence indicates that RKIP-1 regulates the activity and mediates the crosstalk between several important cellular signaling pathways. A variety of ablative interventions suggest that reduced RKIP-1 function may influence metastasis, angiogenesis, resistance to apoptosis, and genome integrity. Attenuation of RKIP-1 may also affect cardiac and neurological functions, spermatogenesis, sperm decapacitation, and reproductive behavior. In this review, the role of RKIP-1 in cellular signaling, and especially its functions revealed using a mouse knockout model, are discussed.


Available from: Steven Theroux, May 26, 2015
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    ABSTRACT: In the present study, we investigated whether Raf-1 kinase inhibitory protein (RKIP) is important for neural cell apoptosis induced by microwave exposure and explored the role of MEK/ERK/CREB pathway regulated by RKIP in the apoptosis. Differentiated PC12 cells were exposed to continuous microwave radiation at 2.856 GHz for 5 min with average power density of 30 mW/cm(2). RKIP sense and anti-sense recombinant plasmids were constructed and transfected into PC12 cells, respectively. Terminal deoxynucleotidyl transferase (TdT)-mediated dUTP nick end labeling (TUNEL) staining and caspase-3 activity assay were used to detect cell apoptosis. The results showed that RKIP was downregulated after microwave exposure while the MEK/ERK/CREB signaling pathway was activated excessively. Moreover, the ratio of Bcl-2/Bax decreased, activity of caspase-3 increased, and thus apoptotic DNA fragmentation increased. RKIP overexpression significantly inhibited the phosphorylation of MEK, ERK, and CREB, while RKIP downregulation had the reverse effect. Furthermore, U0126 was found to antagonize the changes caused by RKIP downregulation after exposure to radiation. In conclusion, RKIP plays an important role in the neural cell apoptosis induced by microwave radiation, and the regulation of cell apoptosis by RKIP is partly through the MEK/ERK/CREB pathway. This suggests that RKIP may act as a key regulator of neuronal damage caused by microwave radiation.
    Molecular Neurobiology 08/2014; DOI:10.1007/s12035-014-8831-5 · 5.29 Impact Factor
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    ABSTRACT: 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.RESULTSEndogenous 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 © 2014 Wiley Periodicals, Inc.
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