The p70 ribosomal S6 kinases (S6K) and p90 ribosomal S6 kinases (RSK) are distinct families of Ser/Thr kinases (EC 2.7.11.1) that regulate diverse cellular processes by phosphorylation of ribosomal protein S6 (Rps6). They transduces anabolic signals that indicate nutritional status to regulate cell size and growth and metabolism through various mechanisms. These include effects on the translational machinery and on cellular energy levels through the activity of adenosine monophosphate (AMP)-activated protein kinase (AMPK)[1].
RSKs are downstream effectors of the Ras–extracellular signal-regulated kinase (ERK)/mitogen-activated protein kinase (MAPK) signaling cascade, and IGF-1 (IIS) and mTOR signaling pathways[2]. RSK phosphorylates a variety of proteins, including transcription factors, immediate-early gene products, translational regulators, enzymes, and structural proteins, that potentially link it to many biological processes such as cell proliferation, cell differentiation, and survival. The ribosomal protein S6 kinase 1 (S6K1) is one of two mammalian p70-RSK proteins, acting as a downstream mediator of mammalian target of rapamycin (mTOR) in the phosphoinositide 3-kinase (PI3K) pathway and/or the Ras-MAPK pathway. It acts to converge growth factor, hormonal, nutrient and energy signals in order to maintain cellular homeostasis[3]. It has been hypothesized that the mTORC1-S6K1 is a master determinant in longevity control[4].

RSK subclasses listed: p70-RSK, p90-RSK