RSK2-Mediated ELK3 Activation Enhances Cell Transformation and Breast Cancer Cell Growth by Regulation of c-fos Promoter Activity

Abstract

Ribosomal S6 kinase 2 (RSK2), regulated by Ras/Raf/MEKs/ERKs, transmits upstream activation signals to downstream substrates including kinases and transcription and epigenetic factors. We observed that ELK members, including ELK1, 3, and 4, highly interacted with RSK2. We further observed that the RSK2-ELK3 interaction was mediated by N-terminal kinase and linker domains of RSK2, and the D and C domains of ELK3, resulting in the phosphorylation of ELK3. Importantly, RSK2-mediated ELK3 enhanced c-fos promoter activity. Notably, chemical inhibition of RSK2 signaling using kaempferol (a RSK2 inhibitor) or U0126 (a selective MEK inhibitor) suppressed EGF-induced c-fos promoter activity. Moreover, functional deletion of RSK2 by knockdown or knockout showed that RSK2 deficiency suppressed EGF-induced c-fos promoter activity, resulting in inhibition of AP-1 transactivation activity and Ras-mediated foci formation in NIH3T3 cells. Immunocytofluorescence assay demonstrated that RSK2 deficiency reduced ELK3 localization in the nucleus. In MDA-MB-231 breast cancer cells, knockdown of RSK2 or ELK3 suppressed cell proliferation with accumulation at the G1 cell cycle phase, resulting in inhibition of foci formation and anchorage-independent cancer colony growth in soft agar. Taken together, these results indicate that a novel RSK2/ELK3 signaling axis, by enhancing c-Fos-mediated AP-1 transactivation activity, has an essential role in cancer cell proliferation and colony growth.

Silencing of ELK3 Induces S-M Phase Arrest and Apoptosis and Upregulates SERPINE1 Expression Reducing Migration in Prostate Cancer Cells

“…Our current study demonstrated that ELK3 acts as a positive regulator on PCa cell growth, migration, and EMT, and which knockdown results in cell migration inhibition may partly due to upregulation of SERPINE1 via the activation of AKT. ELK3 belongs to the ETS oncogene family and plays an important role in many biological processes such as cell proliferation, migration, invasion, and angiogenesis [11][12][13][14], which has been proved to promote the progression of several types of tumors including breast cancer, liver cancer, and squamous cell carcinomas [11-13, 15, 31]. On the contrary, some researchers reported that ELK3 was less expressed in cervical cancer and pancreatic cancer, and its ectopic expression inhibited the growth of these cancer cells [32][33][34].…”

“…Wasylyk et al identified a novel pyrazole XRP44X that inhibited fibroblast growth factor 2-induced ELK3 phosphorylation by the Ras-Erk signaling and led to G2-M cell cycle arrest in NIH3T3 fibroblasts and HUVEC endothelial cells [36]. Recently, Yoo et al reported that knockdown of ELK3 suppressed cell proliferation with accumulation at the G1 cell cycle phase in MDA-MB-231 breast cancer cells [11]. However, in contrast, ELK3 overexpression inhibited the cell cycle progression of pancreatic carcinoma cells, resulting in an increase in G0/G1 phase fraction and a decrease in S phase fraction [34].…”

“…ELK3 (also called Net, SAP-2, or ERP) is an ETS domaincontaining transcription factor that forms a ternary complex transcription factor (TCF) together with ELK-1 and serum response factor accessory protein-1 (SAP-1) and binds to a specific DNA sequence through a purine-rich GGA core sequence to regulate the expression of many genes including proto-oncogenes [6,7]. Under basal conditions, ELK3 is a transcriptional repressor, which converts to a transcriptional activator in response to ratsarcoma viral oncogene homolog/ extracellular regulated protein kinases (RAS/ERK) signaling and p38 mitogen-activated protein kinase (MAPK) pathway [8][9][10], and is involved in cell migration, angiogenesis, and malignant progression [11][12][13][14]. Several studies have showed that ELK3 is overexpressed in some cancer cells and correlates with cell migration and invasion [13][14][15].…”

Prognostic signature composed of transcription factors accurately predicts the prognosis of gastric cancer patients

“…Under basic conditions, ELK3 is a transcriptional repressor, but it can be activated by RAS/ERK signals and mitogen-activated protein kinase (Mitogen-Activated Protein Kinase, MAPK) pathways to turn it into a transcription activator [ 28 , 29 ]. In recent years, ELK3 has been proven to play an important role in the occurrence and development of breast cancer, liver cancer, lung cancer, and other malignant tumors [ 30 – 33 ]. In prostate cancer studies, it has been shown that inhibition of ELK3 can promote cycle arrest and apoptosis of tumor cells [ 34 ].…”

<p>Parthenolide Inhibits Angiogenesis in Esophageal Squamous Cell Carcinoma Through Suppression of VEGF</p>

“…25 c-Fos has been shown to interfere with cell proliferation and induce cell transformation. 53,54 c-Jun is a member of Ap-1, as well as the most potent transcriptional activator of Ap-1. 55 c-Jun was shown to regulate cellular proliferation and apoptosis.…”