ARAF

ARAF
Available structures
PDB	Ortholog search: PDBe RCSB
List of PDB id codes
	1WXM, 2MSE
Identifiers
Aliases	ARAF, A-Raf proto-oncogene, serine/threonine kinase, A-RAF, ARAF1, PKS2, RAFA1, Serine/threonine-protein kinase A-Raf
External IDs	OMIM: 311010; MGI: 88065; HomoloGene: 1249; GeneCards: ARAF; OMA:ARAF - orthologs
Gene location (Human)
Chr.	X chromosome (human)
End	47,571,908 bp
Gene location (Mouse)
Chr.	X chromosome (mouse)
End	20,726,758 bp
RNA expression pattern
	Top expressed in
	muscle of thigh; ; granulocyte; ; gastrocnemius muscle; ; body of stomach; ; apex of heart; ; body of pancreas; ; right lobe of liver; ; gastric mucosa; ; transverse colon; ; left uterine tube;
	Top expressed in
	dorsomedial hypothalamic nucleus; ; lateral hypothalamus; ; mammillary body; ; neural layer of retina; ; ventral tegmental area; ; paraventricular nucleus of hypothalamus; ; ventromedial nucleus; ; lateral septal nucleus; ; arcuate nucleus; ; dentate gyrus of hippocampal formation granule cell;
	More reference expression data
	More reference expression data
Gene ontology
Molecular function	transferase activity; protein kinase activity; nucleotide binding; metal ion binding; kinase activity; protein serine/threonine kinase activity; protein binding; ATP binding; MAP kinase kinase kinase activity; mitogen-activated protein kinase kinase binding;
Cellular component	mitochondrion; cytosol; cellular component;
Biological process	intracellular signal transduction; regulation of TOR signaling; phosphorylation; negative regulation of apoptotic process; positive regulation of peptidyl-serine phosphorylation; MAPK cascade; protein phosphorylation; regulation of proteasomal ubiquitin-dependent protein catabolic process; signal transduction; multicellular organism development; negative regulation of signal transduction; cell differentiation; positive regulation of ERK1 and ERK2 cascade;
	Sources:Amigo / QuickGO
Orthologs
	369
	11836
	ENSG00000078061
	ENSMUSG00000001127
	P10398; Q96II5
	P04627
	NM_001256196; NM_001256197; NM_001654
	NM_001159645; NM_009703
	NP_001243125; NP_001243126; NP_001645; NP_001243125.1
	NP_001153117; NP_033833
	Wikidata
View/Edit Human	View/Edit Mouse

Serine/threonine-protein kinase A-Raf or simply A-Raf is an enzyme that in humans is encoded by the ARAF gene.^[5] A-Raf is a member of the Raf kinase family of serine/threonine-specific protein kinases.^[6]

Compared to the other members of this family (Raf-1 and B-Raf), very little is known about A-Raf. It seems to share many of the properties of the other isoforms, but its biological functions are not as thoroughly researched. All three Raf proteins are involved in the MAPK signaling pathway.

There are several ways A-Raf is different from the other Raf kinases. A-Raf is the only steroid hormone-regulated Raf isoform.^[7] In addition, the A-Raf protein has amino acid substitutions in a negatively charged region upstream of the kinase domain (N-region). This could be responsible for its low basal activity.^[8]

Like Raf-1 and B-Raf, A-Raf activates MEK proteins which causes the activation of ERK and ultimately leads to cell cycle progression and cell proliferation. All three Raf proteins are located in the cytosol in their inactive state when bound to 14-3-3. In the presence of active Ras, they translocate to the plasma membrane.^[9] Among the Ras kinase family, A-Raf has the lowest kinase activity towards MEK proteins in the Raf kinase family.^[10] Thus, it is possible that A-Raf has other functions outside the MAPK pathway or that it helps the other Raf kinases activate the MAPK pathway. In addition to phosphorylating MEK, A-Raf also inhibits MST2, a tumor suppressor and proapoptotic kinase not found in the MAPK pathway. By inhibiting MST2, A-Raf can prevent apoptosis from occurring. However, this inhibition is only possible when the splice factor heterogenous nuclear ribonucleoprotein H (hnRNP H) maintains the expression of a full-length A-Raf protein. Tumorous cells often overexpress hnRNP H. When hnRNP H is downregulated, the A-RAF gene is alternatively spliced. This prevents the expression of full-length A-Raf protein.^[11] Thus, overexpression of hnRNP H in tumor cells leads to full-length expression of A-Raf which then inhibits apoptosis, allowing cancerous cells that should be destroyed to stay alive.

A-Raf also binds to pyruvate kinase M2 (PKM2), again outside the MAPK pathway. PKM2 is an isozyme of pyruvate kinase that is responsible for the Warburg effect in cancer cells.^[12] A-Raf upregulates the activity of PKM2 by promoting a conformational change in PKM2. This causes PKM2 to transition from its low-activity dimeric form to a highly active tetrameric form. In cancer cells, the ratio between dimeric and tetrameric forms of PKM2 determines what happens to glucose carbons. If PKM2 is in the dimeric form, glucose is channeled into synthetic processes such as nucleic acid, amino acid, or phospholipid synthesis. If A-Raf is present, PKM2 is more likely to be in the tetrameric form. This causes more glucose carbons to be converted to pyruvate and lactate, producing energy for the cell. Thus, A-Raf can be linked to energy metabolism regulation and cell transformation, both of which are very important in tumorigenesis.^[13]

In addition, researchers have proposed a model of how A-Raf is linked to endocytosis. Upstream of A-Raf, receptor tyrosine kinases (RTKs) are activated, leading to RAS-mediated activation of Raf kinases, including A-Raf. Once activated, A-Raf binds to membranes rich in Phosphatidylinositol 4,5-bisphosphate (PtdIns (4,5)P₂ and signals endosomes. This leads to activation of ARF6, a central regulator of endocytic trafficking.^[14]

Interactions

ARAF has been shown to interact with:

References

^ ^a ^b ^c GRCh38: Ensembl release 89: ENSG00000078061 – Ensembl, May 2017
^ ^a ^b ^c GRCm38: Ensembl release 89: ENSMUSG00000001127 – Ensembl, May 2017
^ "Human PubMed Reference:". National Center for Biotechnology Information, U.S. National Library of Medicine.
^ "Mouse PubMed Reference:". National Center for Biotechnology Information, U.S. National Library of Medicine.
^ "Entrez Gene: ARAF V-raf murine sarcoma 3611 viral oncogene homolog".
^ Mark GE, Seeley TW, Shows TB, Mountz JD (September 1986). "Pks, a raf-related sequence in humans". Proc. Natl. Acad. Sci. U.S.A. 83 (17): 6312–6. doi:10.1073/pnas.83.17.6312. PMC 386493. PMID 3529082.
^ Lee, J. E.; Beck, T. W.; Wojnowski, L.; Rapp, U. R. (1996-04-18). "Regulation of A-raf expression". Oncogene. 12 (8): 1669–1677. ISSN 0950-9232. PMID 8622887.
^ Baljuls, Angela; Mueller, Thomas; Drexler, Hannes C. A.; Hekman, Mirko; Rapp, Ulf R. (2007-09-07). "Unique N-region determines low basal activity and limited inducibility of A-RAF kinase: the role of N-region in the evolutionary divergence of RAF kinase function in vertebrates". The Journal of Biological Chemistry. 282 (36): 26575–26590. doi:10.1074/jbc.M702429200. ISSN 0021-9258. PMID 17613527.
^ Mercer, Kathryn; Giblett, Susan; Oakden, Anthony; Brown, Jane; Marais, Richard; Pritchard, Catrin (2005-04-25). "A-Raf and Raf-1 work together to influence transient ERK phosphorylation and Gl/S cell cycle progression". Oncogene. 24 (33): 5207–5217. doi:10.1038/sj.onc.1208707. ISSN 0950-9232. PMID 15856007.
^ Matallanas, David; Birtwistle, Marc; Romano, David; Zebisch, Armin; Rauch, Jens; Kriegsheim, Alexander von; Kolch, Walter (2011-03-01). "Raf Family Kinases Old Dogs Have Learned New Tricks". Genes & Cancer. 2 (3): 232–260. doi:10.1177/1947601911407323. ISSN 1947-6019. PMC 3128629. PMID 21779496.
^ Rauch, Jens; O'Neill, Eric; Mack, Brigitte; Matthias, Christoph; Munz, Markus; Kolch, Walter; Gires, Olivier (2010-02-15). "Heterogeneous Nuclear Ribonucleoprotein H Blocks MST2-Mediated Apoptosis in Cancer Cells by Regulating a-raf Transcription". Cancer Research. 70 (4): 1679–1688. doi:10.1158/0008-5472.CAN-09-2740. ISSN 0008-5472. PMC 2880479. PMID 20145135.
^ Christofk, Heather R.; Vander Heiden, Matthew G.; Harris, Marian H.; Ramanathan, Arvind; Gerszten, Robert E.; Wei, Ru; Fleming, Mark D.; Schreiber, Stuart L.; Cantley, Lewis C. (2008-03-13). "The M2 splice isoform of pyruvate kinase is important for cancer metabolism and tumour growth". Nature. 452 (7184): 230–233. doi:10.1038/nature06734. ISSN 0028-0836. PMID 18337823. S2CID 16111842.
^ Mazurek, Sybille; Drexler, Hannes C. A.; Troppmair, Jakob; Eigenbrodt, Erich; Rapp, Ulf R. (2007-11-01). "Regulation of Pyruvate Kinase Type M2 by A-Raf: A Possible Glycolytic Stop or Go Mechanism". Anticancer Research. 27 (6B): 3963–3971. ISSN 0250-7005. PMID 18225557.
^ Nekhoroshkova, Elena; Albert, Stefan; Becker, Matthias; Rapp, Ulf R. (2009-02-27). "A-RAF Kinase Functions in ARF6 Regulated Endocytic Membrane Traffic". PLOS ONE. 4 (2): e4647. doi:10.1371/journal.pone.0004647. ISSN 1932-6203. PMC 2645234. PMID 19247477.
^ ^a ^b ^c ^d ^e Yuryev A, Wennogle LP (February 2003). "Novel raf kinase protein-protein interactions found by an exhaustive yeast two-hybrid analysis". Genomics. 81 (2): 112–25. doi:10.1016/S0888-7543(02)00008-3. PMID 12620389.
^ Yin XL, Chen S, Yan J, Hu Y, Gu JX (February 2002). "Identification of interaction between MEK2 and A-Raf-1". Biochim. Biophys. Acta. 1589 (1): 71–6. doi:10.1016/S0167-4889(01)00188-4. PMID 11909642.
^ ^a ^b ^c Yuryev A, Ono M, Goff SA, Macaluso F, Wennogle LP (July 2000). "Isoform-Specific Localization of A-RAF in Mitochondria". Mol. Cell. Biol. 20 (13): 4870–8. doi:10.1128/MCB.20.13.4870-4878.2000. PMC 85938. PMID 10848612.
^ Yin XL, Chen S, Gu JX (February 2002). "Identification of TH1 as an interaction partner of A-Raf kinase". Mol. Cell. Biochem. 231 (1–2): 69–74. doi:10.1023/A:1014437024129. PMID 11952167. S2CID 19362635.

External links

Human ARAF genome location and ARAF gene details page in the UCSC Genome Browser.
PDBe-KB provides an overview of all the structure information available in the PDB for Human Serine/threonine-protein kinase A-Raf