ARAF

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For other uses, see Araf (disambiguation).
ARAF
Protein ARAF PDB 1wxm.png
Available structures
PDB Ortholog search: PDBe RCSB
Identifiers
Aliases ARAF, A-Raf proto-oncogene, serine/threonine kinase, A-RAF, ARAF1, PKS2, RAFA1
External IDs MGI: 88065 HomoloGene: 1249 GeneCards: ARAF
RNA expression pattern
PBB GE ARAF 201895 at fs.png
More reference expression data
Orthologs
Species Human Mouse
Entrez
Ensembl
UniProt
RefSeq (mRNA)

NM_001256196
NM_001256197
NM_001654

NM_001159645
NM_009703

RefSeq (protein)

NP_001243125
NP_001243126
NP_001645
NP_001243125.1

NP_001153117.1
NP_033833.1
NP_001153117
NP_033833

Location (UCSC) Chr X: 47.56 – 47.57 Mb Chr X: 20.8 – 20.86 Mb
PubMed search [1] [2]
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.[3] A-Raf is a member of the Raf kinase family of serine/threonine-specific protein kinases.[4]

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.[5] 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.[6]

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.[7] Among the Ras kinase family, A-Raf has the lowest kinase activity towards MEK proteins in the Raf kinase family.[8] Thus, it is possible that A-Raf has other functions outside of 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. Interestingly enough, 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.[9] 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.[10] 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.[11]

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.[12]

Interactions[edit]

ARAF has been shown to interact with:

References[edit]

  1. ^ "Human PubMed Reference:". 
  2. ^ "Mouse PubMed Reference:". 
  3. ^ "Entrez Gene: ARAF V-raf murine sarcoma 3611 viral oncogene homolog". 
  4. ^ 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 386493Freely accessible. PMID 3529082. 
  5. ^ 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. 
  6. ^ 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. 
  7. ^ 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. 
  8. ^ 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 3128629Freely accessible. PMID 21779496. 
  9. ^ 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 2880479Freely accessible. PMID 20145135. 
  10. ^ 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. 
  11. ^ 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. 
  12. ^ 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 2645234Freely accessible. PMID 19247477. 
  13. ^ 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. 
  14. ^ 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. 
  15. ^ 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 85938Freely accessible. PMID 10848612. 
  16. ^ 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. 

External links[edit]

Further reading[edit]