P70-S6 Kinase 1

Ribosomal protein S6 kinase beta-1 (S6K1), also known as p70S6 kinase (p70S6K, p70-S6K), is an enzyme (specifically, a protein kinase) that in humans is encoded by the RPS6KB1 gene.[5][6] It is a serine/threonine kinase that acts downstream of PIP3 and phosphoinositide-dependent kinase-1 in the PI3 kinase pathway.[7] As the name suggests, its target substrate is the S6 ribosomal protein.[8] Phosphorylation of S6 induces protein synthesis at the ribosome.

RPS6KB1
Available structures
PDBOrtholog search: PDBe RCSB
Identifiers
AliasesRPS6KB1, PS6K, S6K, S6K-beta-1, S6K1, STK14A, p70 S6KA, p70(S6K)-alpha, p70-S6K, p70-alpha, P70-S6 Kinase 1, ribosomal protein S6 kinase B1, p70S6K, p70S6 kinase
External IDsOMIM: 608938 MGI: 1270849 HomoloGene: 81703 GeneCards: RPS6KB1
Orthologs
SpeciesHumanMouse
Entrez

6198

72508

Ensembl

ENSG00000108443

ENSMUSG00000020516

UniProt

P23443

Q8BSK8

RefSeq (mRNA)

NM_001272042
NM_001272043
NM_001272044
NM_001272060
NM_003161

NM_001114334
NM_028259
NM_001363162

RefSeq (protein)

NP_001107806
NP_082535
NP_001350091

Location (UCSC)Chr 17: 59.89 – 59.95 MbChr 11: 86.5 – 86.54 Mb
PubMed search[3][4]
Wikidata
View/Edit HumanView/Edit Mouse

The phosphorylation of p70S6K at threonine 389 has been used as a hallmark of activation by mTOR and correlated with autophagy inhibition in various situations. However, several recent studies suggest that the activity of p70S6K plays a more positive role in the increase of autophagy.[9][10]

Function

This gene encodes a member of the S6K family of serine/threonine kinases, which phosphorylate several residues of the S6 ribosomal protein. The kinase activity of this protein leads to an increase in protein synthesis and cell proliferation. Amplification of the region of DNA encoding this gene and overexpression of this kinase are seen in some breast cancer cell lines. Alternate translational start sites have been described and alternate transcriptional splice variants have been observed but have not been thoroughly characterized.

mTOR

The p70S6 kinase is a downstream target of mTOR (mammalian target of rapamycin) signaling, specifically mTORC1, an mTOR-containing complex characterized by the inclusion of Raptor rather than Rictor (mTORC2). mTOR can be activated via an AND-gate-like mechanism at the lysosome, integrating signals about growth factors and bioavailability of important molecules. For instance, amino acids such as arginine and leucine can trigger lysosomal recruitment of mTORC1. Once at the lysosome, mTOR can be activated by Rheb, a small, lysosomal-resident GTPase, in its GTP-bound state. Rheb GTPase activity is stimulated (and therefore capacity to activate mTOR diminished) by the upstream TSC complex, which is inhibited by IGF signalling. Thus, the AND gate consists of proper localization by sufficiency of amino acids and activation by growth factors. Once mTOR has been properly localized and activated, it can phosphorylate downstream targets such as p70S6K, 4EBP, and ULK1 which are important for regulating protein anabolic/catabolic balance.

Physical exercise activates protein synthesis via phosphorylation (activation) of p70S6K in a pathway that is dependent on mTOR, specifically mTORC1. This has been demonstrated by using an inhibitor of mTOR, rapamycin, to block an increase in muscle mass, despite increases in load (e.g., exercise). Exercise has been shown to increase levels of IGF-1 in muscle, thus inducing the IGF-1/PI3K/Akt/p70S6K signaling pathway, and thereby increasing the protein synthesis is required to build muscle.

Clinical significance

Inhibition of the S6K1 protein, or a lack of it, slows the production of adipose (fat) cells by disrupting and retarding the initial "commitment stage" of their formation. The study could have implications for the treatment of obesity.[11]

Amplification of the region of DNA encoding this gene and overexpression of this kinase are seen in some breast cancer cell lines.

Another pathway for which P70 has proposed involvement is in muscle lengthening and growing. P70 is phosphorylated by passive stretch in the soleus muscle. This may be one of many protein kinases involved in muscle building.[12]

In its inactive state, S6K1 is bound to eIF3 and detaches following phosphorylation by mTOR/Raptor. Free S6K1 is then able to phosphorylate a number of its targets, including eIF4B.[13]

Interactions

P70-S6 Kinase 1 has been shown to interact with:

See also

References
  1. GRCh38: Ensembl release 89: ENSG00000108443 - Ensembl, May 2017
  2. GRCm38: Ensembl release 89: ENSMUSG00000020516 - Ensembl, May 2017
  3. "Human PubMed Reference:". National Center for Biotechnology Information, U.S. National Library of Medicine.
  4. "Mouse PubMed Reference:". National Center for Biotechnology Information, U.S. National Library of Medicine.
  5. Grove JR, Banerjee P, Balasubramanyam A, Coffer PJ, Price DJ, Avruch J, Woodgett JR (Nov 1991). "Cloning and expression of two human p70 S6 kinase polypeptides differing only at their amino termini". Molecular and Cellular Biology. 11 (11): 5541–50. doi:10.1128/mcb.11.11.5541. PMC 361924. PMID 1922062.
  6. "Entrez Gene: RPS6KB1 ribosomal protein S6 kinase, 70kDa, polypeptide 1".
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  • Overview of all the structural information available in the PDB for UniProt: P23443 (Ribosomal protein S6 kinase beta-1) at the PDBe-KB.
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