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

Abstract

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.

miR-19b promotes breast cancer metastasis through targeting MYLIP and its related cell adhesion molecules

“…Once the metastasis occurred in distant organs, the survival rate and prognostic effect for cancer patients will be greatly reduced. The molecular events for metastasis are as follows: 1) the dysregulation of metastasis related genes, such as Ras, Mtsl, Nm23, TIAM-1, KAI1/CD82, RKIP, Kiss1, BRMS1, RhoGDI, MKK4, Drg-1 and so on [ 18 – 21 ]; 2) the abnormal expression of cell adhesion molecules, such as Integrins, Cadherins, Selectins, ICAM-1, VCAM-1, CD44 and so on [ 22 – 24 ]; 3) the abnormal expression of protein degrading enzymes, such as MMPs, t-PA, u-PA, Heparinase and so on [ 25 ]; 4) the over activation of tumor angiogenesis, and the key factors involved in this process including VEGF, bFGF, CD105 and so on [ 26 ]; 5) the imbalance of immune system states, and the major immune cells involved in anti-cancer immunity including NK cells, CTL cells, mononuclear macrophage cells, TIL cells and so on [ 27 ].…”

Current Status of Raf Kinase Inhibitor Protein (RKIP) in Lung Cancer: Behind RTK Signaling

“…Furthermore, it was demonstrated that RKIP acts as a physiological inhibitor of NOTCH1, a major player in EMT and metastases [98]. Using H1299 cells, transfected to overexpress RKIP, the authors demonstrated that RKIP directly interacts with the full-length of NOTCH1, preventing its proteolytic cleavage and NICD release (Figure 1), decreasing EMT markers like Vimentin, N-cadherin and Snail.…”

“…Using H1299 cells, transfected to overexpress RKIP, the authors demonstrated that RKIP directly interacts with the full-length of NOTCH1, preventing its proteolytic cleavage and NICD release (Figure 1), decreasing EMT markers like Vimentin, N-cadherin and Snail. As a consequence, the migratory and invasive capacity of the cells also decreased, a phenotype that was reverted in vivo by RKIP knockdown in A549 cells [98].…”

A New Linkage between the Tumor Suppressor RKIP and Autophagy: Targeted Therapeutics

“…136 RKIP-dependent Notch1 deactivation and cytoplasmic sequestration repress the expression of Notch1 target genes such as CDH2 , SNAI1 , and VIM in hypoxic conditions. 36 RKIP’s capacity to counteract the prometastatic effect of hypoxia and pro-EMT protein expressions highlights its role as a metastasis suppressor. 137 Previous reports also described a potential for RKIP to suppress cancer cell stemness via regulation of stem cell factors Oct4, Sox2, KLF2, and Nanog.…”

“…32–34 Similar interactions with other proto-oncogenes [i.e., Notch1 and melanoma differentiation–associated gene-9 (MDA-9)] reiterate the attenuation of EMT in cells expressing high levels of RKIP. 35,36 Given RKIP’s eponymous function in the Ras/Raf/MEK signaling axis and the characterization of various nodes of convergence between the MAPK pathway and the PI3K/Akt/mTOR pathway, it makes sense that RKIP should directly or indirectly influence autophagic activity in cancer cells. 37 Indeed, it was recently shown that RKIP acts as a gatekeeper of autophagy by binding to LC3, an essential protein in autophagosome formation, thus halting autophagy.…”