The p90 ribosomal S6 kinase (Rsk) family comprises four mammalian serine/threonine kinases (Rsk14). In the past, S6K1 and S6K2 were thought to be the predominant operating S6 kinases, however RSK 1 and 2 have been shown to phosphorylate S6 in response to the ERK pathway, or otherwise known as the extra cellular signal-regulated kinases pathway. RSK 1 in particular is very multifunctional as it participates in nuclear signaling, regulates nuclear factors, regulates several transcription factors like c-Fos, and interacts with the transcriptional coactivator CREB-binding protein. As a result, RSK1 seems to have an important role in cellular growth control and proliferation. (1-5).