CNK1 Promotes Invasion of Cancer Cells through NF-κB–Dependent Signaling

Abstract

Hallmarks of cancer cells are uncontrolled proliferation, evasion of apoptosis, angiogenesis, cell invasion, and metastasis, which are driven by oncogenic activation of signaling pathways. Herein, we identify the scaffold protein CNK1 as a mediator of oncogenic signaling that promotes invasion in human breast cancer and cervical cancer cells. Downregulation of CNK1 diminishes the invasiveness of cancer cells and correlates with reduced expression of matrix metalloproteinase 9 (MMP-9) and membrane-type 1 MMP (MT1-MMP). Ectopic expression of CNK1 elevates MT1-MMP promoter activity in a NF-κB-dependent manner. Moreover, CNK1 cooperates with the NF-κB pathway, but not with the extracellular signal-regulated protein kinase pathway, to promote cell invasion. Mechanistically, CNK1 regulates the alternative branch of the NF-κB pathway because knockdown of CNK1 interferes with processing of NF-κB2 p100 to p52 and its localization to the nucleus. In agreement with this, the invasion of CNK1-depleted cells is less sensitive to RelB downregulation compared with the invasion of control cells. Moreover, CNK1-dependent MT1-MMP promoter activation is blocked by RelB siRNA. Thus, CNK1 is an essential mediator of an oncogenic pathway involved in invasion of breast and cervical cancer cells and is therefore a putative target for cancer therapy. Mol Cancer Res; 8(3); 395-406. ©2010 AACR.

Smurf2 E3 ubiquitin ligase modulates proliferation and invasiveness of breast cancer cells in a CNKSR2 dependent manner

“…Recent studies have shown that downregulation of CNK (Connector enhancer of KSR) proteins which are scaffold proteins regulating mitogen-activated protein kinase pathways, diminishes the proliferation and invasiveness of cancer cells, particularly breast cancer cells [21,35]. Remarkably, we also observed that Smurf2 knockdown caused a considerable downregulation in the expression of CNKSR2, a CNK homolog, followed by a concomitant decrease in the proliferation of breast cancer cells (Figures  7 and 8).…”

“…Interestingly, knockdown of hCNK2 in PC12 prevented NGF-dependent ERK activation as well as neurite outgrowth. It thus appears that CNK proteins can mediate RTK-specific signals and that their function is not restricted to RAS/ERK signaling [35]. In our study we observed that downregulation of CNKSR2 expression following Smurf2 knockdown did not affect the MEK, ERK and NF-kB signaling cascades.…”

“…Increased levels of CNK homologs have been identified in various cancers including breast cancer [27]. CNK1 was identified as one of a few critical genes that mediate metastasis in breast cancer [35]. However, the functional significance and regulation of CNKSR2 which is specifically involved in neuronal differentiation has not been fully identified yet.…”

Optogenetic clustering of CNK1 reveals mechanistic insights in RAF and AKT signalling controlling cell fate decisions

“…Assays with secreted embryonic alkaline phosphatase (SEAP) as reporter under the control of the serum response factor (SRF) activated by ERK signalling were performed to monitor the RAF-MEK-ERK pathway20. Matrix metalloproteinase 14 (MMP14) promoter-controlled luciferase reporter assays were used to measure AKT signalling8. Inhibitor treatment confirmed that SRF reporter activation depends on ERK signalling and MMP14 promoter activation on AKT signalling (Supplementary Figure S1A,B).…”

“…CNK1 drives AKT-dependent cell proliferation and co-localizes with AKT at the plasma membrane in invasive breast cancer tumours7. In addition, CNK1 promotes invasion of cancer cells by AKT-dependent NFκB pathway activation8. Insulin recruits CNK1 complexed with ARF guanine nucleotide exchange factors of the cytohesin family to the plasma membrane facilitating PI3K/AKT signalling9.…”