Inverse correlation between the metastasis suppressor RKIP and the metastasis inducer YY1: Contrasting roles in the regulation of chemo/immuno-resistance in cancer.

Several gene products have been postulated to mediate inherent and/or acquired anticancer drug resistance and tumor metastasis. Among these, the metastasis suppressor and chemo-immuno-sensitizing gene product, Raf Kinase Inhibitor Protein (RKIP), is poorly expressed in many cancers. In contrast, the metastasis inducer and chemo-immuno-resistant factor Yin Yang 1 (YY1) is overexpressed in many cancers. This inverse relationship between RKIP and YY1 expression suggests that these two gene products may be regulated via cross-talks of molecular signaling pathways, culminating in the expression of different phenotypes based on their targets. Analyses of the molecular regulation of the expression patterns of RKIP and YY1 as well as epigenetic, post-transcriptional, and post-translational regulation revealed the existence of several effector mechanisms and crosstalk pathways, of which five pathways of relevance have been identified and analyzed. The five examined cross-talk pathways include the following loops: RKIP/NF-κB/Snail/YY1, p38/MAPK/RKIP/GSK3ß/Snail/YY1, RKIP/Smurf2/YY1/Snail, RKIP/MAPK/Myc/Let-7/HMGA2/Snail/YY1, as well as RKIP/GPCR/STAT3/miR-34/YY1. Each loop is comprised of multiple interactions and cascades that provide evidence for YY1's negative regulation of RKIP expression and vice versa. These loops elucidate potential prognostic motifs and targets for therapeutic intervention. Chiefly, these findings suggest that targeted inhibition of YY1 by specific small molecule inhibitors and/or the specific induction of RKIP expression and activity are potential therapeutic strategies to block tumor growth and metastasis in many cancers, as well as to overcome anticancer drug resistance. These strategies present potential alternatives for their synergistic uses in combination with low doses of conventional chemo-immunotherapeutics and hence, increasing survival, reducing toxicity, and improving quality of life.

Raf-1 Kinase Inhibitory Protein (RKIP) Promotes Retinal Ganglion Cell Survival and Axonal Regeneration Following Optic Nerve Crush.

Raf-1 kinase inhibitory protein (RKIP), a member of the phosphatidylethanolamine-binding protein (PEBP) family, plays an important role in neuronal apoptosis and cognitive deficits associated with neurodegenerative diseases. However, the biological function of RKIP in the retina is still unclear. Therefore, in the present study, we investigated the expression of RKIP in mouse retina following optic nerve crush (ONC) and evaluated the effects of RKIP on retinal ganglion cells (RGCs) apoptosis and axonal regeneration after ONC. Our results showed that the expression of RKIP was markedly decreased in the injured retina. Overexpression of RKIP inhibits RGC apoptosis and promotes axonal regeneration after ONC. Furthermore, overexpression of RKIP significantly increased the phosphorylation in extracellular signal-related kinase (ERK)1/2 and AKT in the injured retina. Taken together, these results suggest that RKIP promotes RGCs survival and axonal regeneration following ONC through promoting the ERK signaling pathway, implying that RKIP may serve as a potential molecular target for the treatment of glaucoma.