Ribosomal protein S6 kinase alpha-2, also known as 90 kDa ribosomal protein S6 kinase 2, MAP kinase-activated protein kinase 1c, MAPK-activated protein kinase 1c, Ribosomal S6 kinase 3, RSK-3, RPS6KA2 and MAPKAPK1C, is a nucleus protein which belongs to the protein kinase superfamily, AGC Ser/Thr protein kinase family and S6 kinase subfamily. RPS6KA2 / RSK-3 is expressed in many tissues. Highest expression is in lung and skeletal muscle. The expression of RPS6KA2 reduced proliferation, caused G1 arrest, increased apoptosis, reduced levels of phosphorylated extracellular signal-regulated kinase and altered other cell cycle proteins. RPS6KA2 / RSK-3 contains one AGC-kinase C-terminal domain and two protein kinase domains. It forms a complex with either ERK1 or ERK2 in quiescent cells. It transiently dissociates following mitogenic stimulation. RPS6KA2 / RSK-3 is a serine/threonine kinase that may play a role in mediating the growth-factor and stress induced activation of the transcription factor CREB. RPS6KA1, RPS6KA2, RPS6KB1, RPS6KB2, and PDK1 are involved in several pathways central to the carcinogenic process, including regulation of cell growth, insulin, and inflammation.