Abstract 2342: RSK2 phosphorylates and activates CREB to promote HNSCC cell invasion through upregulation of pro-metastatic MCAM and Fascin-1
Authors: Jin Lingtao , Kim Young-Mee , Zhou Wei , Taunton Jack , Chen Georgia Z. , Shin Dong M. , Khuri Fadlo R. , Kang Sumin 
Published: June 2012

Abstract
Head and neck squamous cell carcinoma (HNSCC) is one of the most common types of human cancer and clinically effective treatment of HNSCC remains difficult due to metastasis. Therefore, it is of immerse clinical interest to identify metastasis-promoting genes in HNSCC tumors to improve prognosis and define targets for therapy. We recently reported that continued expression of p90 Ribosomal S6 kinase 2 (RSK2) contributes to the maintenance of the invasive and metastatic potential of HNSCC cells in vitro and in vivo, respectively. By a phospho-proteomics based study using a phospho-antibody microarray, we identified a spectrum of pro-metastatic proteins whose phosphorylation levels are regulated by RSK2 in HNSCC cells, including CREB, Hsp27, c-Jun, Elk-1, FAK, IRS-1, Jun-B, c-MET, and Stathmin.
CREB is a transcription factor and RSK2 activates CREB by phosphorylating CREB Ser133. To explore the molecular mechanism underlying the RSK2→CREB pathway-mediated pro-invasive signals, we surveyed potential links between RSK2 and known CREB transcription targets that are implied in cell invasion and tumor metastasis, including HPSE-1, IRS-2, MMP2, VEGF, CNN/Cyr61, MCAM, and Fascin-1. RT-PCR results showed that stable knockdown of RSK2 in highly invasive HNSCC cells results in decreased mRNA levels of VEGF, MCAM and Fascin-1. MCAM (melanoma cell adhesion molecule) is one of the immunoglobulin superfamily which is known to be involved in focal adhesion assembly and cell migration. Fascin-1 is a critical hallmark of the invasive phenotype in cancer cells which bundles F-actin and contributes to cell migration and invasion. Using real-time RT-PCR, we confirmed that stable knockdown of RSK2 result in significant decrease in mRNA levels of MCAM and Fascin-1 in the RSK2-expressing, highly invasive HNSCC M4e, 212LN and 37B cells. Moreover, targeting MCAM and Fascin-1 by shRNA in 212LN cells led to significantly increased cell sensitivity to detachment-induced anoikis, which correlated with attenuated cell invasive potential of these cells. In addition, overexpression of MCAM and Fascin-1 in 212LN cells with stable knockdown of RSK2 rescued phenotypes due to lack of RSK2, resulting in increased cell invasion and reduced cell sensitivity to anoikis, compared to RSK2 knockdown cells.
These data together suggest a transcription-dependent mechanism in which RSK2 may signal through CREB to provide anti-anoikis signals and promote HNSCC cell invasion, in part by up-regulated pro-metastatic proteins such as MCAM and Fascin-1. Our studies may shed new insights into understanding of molecular mechanisms underlying HNSCC metastasis and development of novel therapeutic strategies to treat metastatic HNSCC.
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 2342. doi:10.1158/1538-7445.AM2011-2342