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C-terminal catalytic domain of the Serine/Threonine Kinase, Ribosomal S6 kinase 4 (also called Ribosomal protein S6 kinase alpha-6 or 90kDa ribosomal protein S6 kinase 6) STKs catalyze the transfer of the gamma-phosphoryl group from ATP to serine/threonine residues on protein substrates. RSK4 is also called S6K-alpha-6, RPS6KA6, p90RSK6 or pp90RSK4. RSK4 is a substrate of ERK and is a modulator of p53-dependent proliferation arrest in human cells. Deletion of the RSK4 gene, RPS6KA6, frequently occurs in patients of X-linked deafness type 3, mental retardation and choroideremia. Studies of RSK4 in cancer cells and tissues suggest that it may be oncogenic or tumor suppressive depending on many factors. RSK4 is one of four RSK isoforms (RSK1-4) from distinct genes present in vertebrates. RSKs contain an N-terminal kinase domain (NTD) from the AGC family and a C-terminal kinase domain (CTD) from the CAMK family. They are activated by signaling inputs from extracellular regulated kinase (ERK) and phosphoinositide dependent kinase 1 (PDK1). ERK phosphorylates and activates the CTD of RSK, serving as a docking site for PDK1, which phosphorylates and activates the NTD, which in turn phosphorylates all known RSK substrates. RSKs act as downstream effectors of mitogen-activated protein kinase (MAPK) and play key roles in mitogen-activated cell growth, differentiation, and survival. The RSK4 subfamily is part of a larger superfamily that includes the catalytic domains of other STKs, protein tyrosine kinases, RIO kinases, aminoglycoside phosphotransferase, choline kinase, and phosphoinositide 3-kinase. |
Jiyao W et al.(2023). "The conserved domain database in 2023.",