Abstract
Alterations of the EGFR/ERK and Hippo/YAP pathway have been found in non-small cell lung cancer (NSCLC). Herein, we show that ERK1 and ERK2 have an effect on the Hippo/YAP pathway in human NSCLC cells. Firstly, inhibition of ERK1/2 by siRNA or small-molecular inhibitors decreased the YAP protein level, the reporter activity of the Hippo pathway, and the mRNA levels of the Hippo downstream genes, CTGF, Gli2, and BIRC5. Secondly, degradation of YAP protein was accelerated after ERK1/2 depletion in NSCLC cell lines, in which YAP mRNA level was not decreased. Thirdly, forced over-expression of the ERK2 gene rescued the YAP protein level and Hippo reporter activity after siRNA knockdown targeting 3'UTR of the ERK2 gene in NSCLC cells. Fourthly, depletion of ERK1/2 reduced the migration and invasion of NSCLC cells. Combined depletion of ERK1/2 had a greater effect on cell migration than depletion of either one separately. Finally, the MEK1/2 inhibitor Trametinib decreased YAP protein level and transcriptional activity of the Hippo pathway in NSCLC cell lines. Our results suggest that ERK1/2 inhibition participates in reducing YAP protein level, which in turn down-regulates expression of the downstream genes of the Hippo pathway to suppress migration and invasion of NSCLC cells.
Highlights
Non-small cell lung cancer (NSCLC), a common malignancy, has a known association with mitogen-activated protein kinase (MAPK) signal transduction pathways [1,2,3]
We found that Yes-associated protein (YAP) protein level decreased after ERK1/2 knockdown by small interfering RNA (siRNA) (Figure 1B)
The results showed that YAP expression decreased in a dose-dependent manner in both cell lines treated with either CAY10561 or FR180204, in contrast to what occurred after control treatment with DMSO (Figure 1C)
Summary
Non-small cell lung cancer (NSCLC), a common malignancy, has a known association with mitogen-activated protein kinase (MAPK) signal transduction pathways [1,2,3]. Extracellular signal regulated kinases (ERK1/2) are important components of the MAPK signal pathway, which is mediated by Epidermal Growth Factor Receptor (EGFR). Amplification of genes that encode ERK and overexpression of ERK have been found in human NSCLC [5, 6]. In clinical and pre-clinical studies, disrupting the MAPK/ERK pathway in cancer cells through inhibiting Raf or MEK often induced negative feedback or paradoxical activation of ERK and resulted in drug resistance [7,8,9]. Direct inhibition of ERK1/2 is becoming a new strategy in cancer treatment [10,11,12]
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