Ribosomal s6 kinase
# Ribosomal s6 kinase

In molecular biology, ribosomal s6 kinase (rsk) is a family of protein kinases involved in signal transduction. There are two subfamilies of rsk, $p90^{rsk},$ also known as MAPK-activated protein kinase-1 (MAPKAP-K1), and $p70^{rsk},$ also known as S6-H1 Kinase or simply S6 Kinase. There are three variants of $p90^{rsk}$ 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.

## Substrates

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 $p90^{rsk}$ 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.

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.

$p90^{rsk}$ also regulates transcription factors including cAMP response element-binding protein (CREB); estrogen receptor-α (ERα); IκBα/NF-κB; and c-Fos.

## Genomics

p90 Rsk-1 is located at 1p.

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.

p90 Rsk-3 is located at 6q27.

## Proteomics

The main distinguishing feature between $p90^{rsk}$ and $p70^{rsk}$ is that the 90 kDa family contain two non-identical kinase domains, while the 70 kDa family contain only one kinase domain.

## Research history

Rsk was first identified in Xenopus laevis eggs by Erikson and Maller in 1985.

