Abstract LB-356: An siRNA screen identifies Rsk1 as a key modulator of lung cancer metastasis

Lung cancer is the commonest cancer killer worldwide. The appearance of distant metastasis is one of the main reasons for failing to cure patients with this disease. To address the underlying molecular mechanisms that regulate cancer cell motility, we performed an automated kinome-based RNA interference screen in the non-small cell lung cancer (NSCLC) cell line A549. We studied changes in cell migration patterns using timelapse microscopy and automatic tracking. Mathematical analysis of the obtained cell tracks provided information on migration speed and distance. 48 kinases were identified that were previously unknown to regulate cell motility. Among our candidates, were several members of the ribosomal S6 kinase (Rsk) family. In particular, Rsk1 silencing increased, while Rsk2 and 4 downregulation decreased, cell motility. These effects correlated with changes to the actin cytoskeleton as well as decreased E-cadherin and increased Vimentin expression levels. A secondary 3-dimensional invasion screen for our candidates confirmed that Rsk1 downregulation increased the invasiveness of A549 cells. In silico analysis and biochemical experimentation revealed that Rsk1 interacted with the actin regulators Vasp and Mena. This correlated with the ability of Rsk1 to phosphorylate Vasp on Thr-278, a site regulating Vasp-mediated actin dynamics. Moreover, Rsk1 silencing enhanced the metastatic behaviour of A549 cells in vivo using a zebrafish xenograft model. Importantly, immunohistochemical staining validated Rsk1 down regulation in metastatic lung cancer samples compared to isogenically matched primary tumours. Moreover, patients with Rsk1-negative lung primary tumours showed an increased number of metastatic lesions as well as an increase in Rsk2 and/or Rsk4 staining establishing Rsk family members as strong determinants of lung cancer cell metastasis and potential predictive markers for the progression of this disease. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr LB-356. doi:10.1158/1538-7445.AM2011-LB-356