In molecular biology, ribosomal s6 kinase (rsk) is a family of protein kinases involved in signal transduction. There are two subfamilies of rsk, p90rsk, also known as MAPK-activated protein kinase-1 (MAPKAP-K1), and p70rsk, also known as S6-H1 Kinase or simply S6 Kinase. There are three variants of p90rsk in humans, rsk 1-3. Rsks are serine/threonine kinases and are activated by the MAPK/ERK pathway. There are two known mammalian homologues of S6 Kinase: S6K1 and S6K2.
Both p90 and p70 Rsk phosphorylate ribosomal protein s6, part of the translational machinery, but several other substrates have been identified, including other ribosomal proteins. Cytosolic substrates of p90rsk include protein phosphatase 1; glycogen synthase kinase 3 (GSK3); L1 CAM, a neural cell adhesion molecule; Son of Sevenless, the Ras exchange factor; and Myt1, an inhibitor of cdc2. [1]
RSK phosphorylation of SOS1 (Son of Sevenless) at Serines 1134 and 1161 creates 14-3-3 docking site. This interaction of phospho SOS1 and 14-3-3 negatively regulates Ras-MAPK pathway. [2]
p90rsk also regulates transcription factors including cAMP response element-binding protein (CREB); estrogen receptor-α (ERα); IκBα/NF-κB; and c-Fos. [1]
p90 Rsk-1 is located at 1p. [3]
p90 Rsk-2 is located at Xp22.2 and contains 22 exons. Mutations in this gene have been associated with Coffin–Lowry syndrome, a disease characterised by severe psychomotor retardation and other developmental abnormalities. [4]
The main distinguishing feature between p90rsk and p70rsk is that the 90 kDa family contain two non-identical kinase domains, while the 70 kDa family contain only one kinase domain.
Rsk was first identified in Xenopus laevis eggs by Erikson and Maller in 1985. [7]
Cell cycle checkpoints are control mechanisms in the eukaryotic cell cycle which ensure its proper progression. Each checkpoint serves as a potential termination point along the cell cycle, during which the conditions of the cell are assessed, with progression through the various phases of the cell cycle occurring only when favorable conditions are met. There are many checkpoints in the cell cycle, but the three major ones are: the G1 checkpoint, also known as the Start or restriction checkpoint or Major Checkpoint; the G2/M checkpoint; and the metaphase-to-anaphase transition, also known as the spindle checkpoint. Progression through these checkpoints is largely determined by the activation of cyclin-dependent kinases by regulatory protein subunits called cyclins, different forms of which are produced at each stage of the cell cycle to control the specific events that occur therein.
The MAPK/ERK pathway is a chain of proteins in the cell that communicates a signal from a receptor on the surface of the cell to the DNA in the nucleus of the cell.
In molecular biology, extracellular signal-regulated kinases (ERKs) or classical MAP kinases are widely expressed protein kinase intracellular signalling molecules that are involved in functions including the regulation of meiosis, mitosis, and postmitotic functions in differentiated cells. Many different stimuli, including growth factors, cytokines, virus infection, ligands for heterotrimeric G protein-coupled receptors, transforming agents, and carcinogens, activate the ERK pathway.
A serine/threonine protein kinase is a kinase enzyme that phosphorylates the OH group of serine or threonine. At least 125 of the 500+ human protein kinases are serine/threonine kinases (STK).
Son of sevenless homolog 1 is a protein that in humans is encoded by the SOS1 gene.
Mitogen-activated protein kinase 1, also known as MAPK1, p42MAPK, and ERK2, is an enzyme that in humans is encoded by the MAPK1 gene.
Mitogen-activated protein kinase 14, also called p38-α, is an enzyme that in humans is encoded by the MAPK14 gene.
Mitogen-activated protein kinase 3, also known as p44MAPK and ERK1, is an enzyme that in humans is encoded by the MAPK3 gene.
AKT2, also known as RAC-beta serine/threonine-protein kinase, is an enzyme that in humans is encoded by the AKT2 gene. It influences metabolite storage as part of the insulin signal transduction pathway.
Ribosomal protein S6 kinase alpha-1 is an enzyme that in humans is encoded by the RPS6KA1 gene.
protein S6 kinase, 90kDa, polypeptide 3, also s RPS6KA3, is an enzyme that in humans is encoded by the RPS6KA3 gene.
Ribosomal protein S6 kinase beta-1 (S6K1), also known as p70S6 kinase, is an enzyme that in humans is encoded by the RPS6KB1 gene. It is a serine/threonine kinase that acts downstream of PIP3 and phosphoinositide-dependent kinase-1 in the PI3 kinase pathway. As the name suggests, its target substrate is the S6 ribosomal protein. Phosphorylation of S6 induces protein synthesis at the ribosome.
5'-AMP-activated protein kinase catalytic subunit alpha-1 is an enzyme that in humans is encoded by the PRKAA1 gene.
Ribosomal protein S6 kinase alpha-5 is an enzyme that in humans is encoded by the RPS6KA5 gene. This kinase, together with RPS6KA4, are thought to mediate the phosphorylation of histone H3, linked to the expression of immediate early genes.
Ribosomal protein S6 kinase alpha-2 is an enzyme that in humans is encoded by the RPS6KA2 gene.
Protein Tob1 is a protein that in humans is encoded by the TOB1 gene.
Ribosomal protein S6 kinase beta-2 is an enzyme that in humans is encoded by the RPS6KB2 gene.
Ribosomal protein S6 kinase alpha-4 is an enzyme that in humans is encoded by the RPS6KA4 gene.
MAP kinase-activated protein kinase 5 is an enzyme that in humans is encoded by the MAPKAPK5 gene. The protein encoded by this gene is a member of the serine/threonine kinase family. In response to cellular stress and proinflammatory cytokines, this kinase is activated through its phosphorylation by MAP kinases, including MAPK1/ERK, MAPK14/p38-alpha, and MAPK11/p38-beta. In vitro, this kinase phosphorylates heat shock protein HSP27 at its physiologically relevant sites. Two alternately-spliced transcript variants of this gene encoding distinct isoforms have been reported.
Tuberous sclerosis proteins 1 and 2, also known as TSC1 (hamartin) and TSC2 (tuberin), form a protein-complex. The encoding two genes are TSC1 and TSC2. The complex is known as a tumor suppressor. Mutations in these genes can cause tuberous sclerosis complex. Depending on the grade of the disease, mental retardation, epilepsy and tumors of the skin, retina, heart, kidney and the central nervous system can be symptoms.