User:Barberm01/prex1

P-Rex1 (Phosphatidylinositol (3,4,5)-triphosphate-dependent Rac exchanger), is an enzyme (~185 kDa) involved in intracellular signalling networks. P-Rex1 is highly expressed in leukocytes and the brain and activates the small Guanosine triphosphate (GTP)-binding protein (G protein) Rac. P-Rex1 controls leukocyte function and neuronal morphology, contributes to the regulation of motor coordination, and promotes cancer metastasis. P-Rex1 was the first member of the P-Rex enzyme family to be described and belongs to the Dbl family of Guanine nucleotide exchange factors (GEFs).

{{Protbox
  |Name=P-Rex1
  |Photo=
  |Caption=
  |Gene=[[PREX1|57580]]
  |Gene_type=Protein coding
  |Protein_length=1659
  |Molecular_weight=185,000
  |Structure=
  |Type=Guanine nucleotide exchange factor (GEF)
  |Functions=Stabalises nucleotide free form of Rac GTPases
  |Domains=[[RhoGEF domain|DH]], [[Pleckstrin homology domain|PH]], DEP, [[PDZ domain]]
  |Motifs=
  |Alternative_products=
  |Catalytic_activity=
  |Cofactors=
  |Enzyme_regulation=Gβγ binding, PIP<sub>3</sub> production
  |Diseases=Overexpressed in some cancers<ref name="Qin_2009">{{cite journal | author =Qin J., Want B., Hoshino M., ''et al.'' | title = Upregulation of PIP<sub>3</sub>-dependent Rac exchanger 1 (P-Rex1) promotes prostrate cancer metastasis | journal = Oncogene | volume = 28 | issue = 16 | pages = 1853–1863 | year = 2009 | date = April 2009 | pmid = 19305425 | doi = 10.1038/onc.2009.30| pmc = 2672965 | url = | issn = }}</ref>
  |Pharmaceuticals=
  |Taxa= 
  |Cells=Nervous and haematopoietic
  |Location=Cytosol and plasma membrane
  |Names=PREX1, KIAA1415
  |Pathways=
  |Interactions=Gβγ, PIP<sub>3</sub>, mTOR<ref name="Hernández-Negrete_2007">{{cite journal | author =Hernández-Negrete I., Carretero-Ortega J., Rosenfeldt H., ''et al.'' | title = P-Rex1 Links Mammalian Target of Rapamycin Signaling to Rac Activation and Cell Migration | journal = J. Biol. Chem. | volume = 282 | issue = 32 | pages = 23708–23715 | year = 2007 | date = August 2007 | pmid = 17565979 | doi = 10.1074/jbc.M703771200| url = | issn =  | doi-access = free }}</ref>
  |Pages=
  |Review= 
}}

Discovery

P-Rex1 was purified from pig leukocyte cytosol in a screen for proteins mediating phosphatidylinositol (3,4,5)-triphosphate (PIP₃)-dependent activation of the Rho-family G protein (GTPase) Rac1. A cytosolic fraction corresponding to the major peak of PIP₃-sensitive Rac-GEF activity was purified to yield a preparation that contained a single pure protein which was identified using MALDI-TOF and N-terminal sequencing and named P-Rex1. The protein contains tandem DH/PH domains, typical of Dbl family GEFs, two DEP and two PDZ domains, and significant sequence similarity over its C-terminal half to Inositol Polyphosphate 4-Phosphatases.

Function and Activation

P-Rex1 contributes to cellular signalling events by activating the Rho-family G proteins Rac1 and Rac2 (with a preference for Rac2 in vivo. In their resting state G proteins are bound to Guanosine diphosphate (GDP) and their activation requires the dissociation of GDP and binding of GTP. P-Rex1 is assumed to act as a classical Dbl family GEF, which activates small G proteins by stabilising the nucleotide free form, allowing excess free cytosolic GTP to bind. P-Rex1 is directly activated by the lipid second messenger PIP₃, which is generated by phosphoinositide 3-kinase (PI3K), via it's PH domain, and was the first Rho GEF shown to be directly stimulated by the Gβγ subunits of heterotrimeric G proteins. P-Rex1 is maximally stimulated by Gβγ heterodimers containing Gβ_1-4 complexed with γ₂ while the Gα subunits G_s, G_i, G_q, G₁₂, and G₁₃ are unable to activate P-Rex1. The cAMP-dependent kinase Protein kinase A (PKA) phosphorylates P-Rex1 and negatively regulates it's PIP₃- and Gβγ-dependent GEF activity both in vitro and in vivo. Truncation of protein domains C-terminal to the catalytic DH/PH tandem leads to increased basal and stimulated GEF activity, suggesting some level of interaction between these domains and the catalytic core in the basal state of the enzyme.

P-Rex1 exists mainly in the cytosol but translocates to the cell membrane in response to chemoattractant receptor activation and PIP₃- and Gβγ stimulation. PKA activity, which inactivates P-Rex1 GEF activity, can also inhibit this translocation. In addition to a negative effect on P-Rex1 GEF activity, the C-terminal domains also serve to keep the protein sequestered in the cytosol. A truncated form of P-Rex1, containing only the tandem DH/PH domains has a higher level of association with the plasma membrane. PIP₃ and Gβγ stimulation can increase the membrane association of this P-Rex1 mutant, suggesting that these tandem domains are sufficient for membrane translocation. Membrane-derived P-Rex1 has higher basal activity than cytosolic P-Rex1..

Cellular functions regulated by P-Rex1

Role in leukocyte function

P-Rex1 controls neutrophil migration towards sites of inflammation and generation of reactive oxygen species (ROS or superoxide).

P-Rex1 functions to activate Rac2 (and to a lesser extent Rac1) in response to chemoattractant stimulation of GPCRs. Mouse neutrophils that lack P-Rex1 mount an impared NADPH-dependent ROS response to LPS priming and fMLP or C5a stimulation. Similarly, the recruitment of neutrophils to sites of inflammation is severely impaired in mice that lack P-Rex1. Isolated P-Rex1-deficient neutrophils migrate with slightly reduced speed but can orientate themselves in a chemotactic gradient.

In macrophages, P-Rex1 regulates Rac1 activation and chemotaxis. Macrophages that lack P-Rex1 were deficient for ROS production after C5a stimulation and showed decreased Rac1 activation in experiments similar to those described above for neutrophils.

Role in neurons

P-Rex1 is expressed in a range of cells associated with the nervous system and it's expression changes throughout the stages of mouse brain development. In neuronal cell culture studies P-Rex1 has been shown to regulate al migration and neurite differentiation. Furthermore, transfection experiments with dominant-negative P-Rex1-constructs show that P-Rex1 can regulate neuronal migration in the developing mouse nervous system.

Interactions

Gβγ, PIP₃, mTOR, PTEN.

Further reading

• Weiner O. D. (June 2002). "Rac activation: P-Rex1 - a convergence point for PIP(3) and Gbetagamma?". Curr. Biol. 12 (12): R429-31. doi:10.1016/s0960-9822(02)00917-x. PMC 2819105. PMID 12123595.{{cite journal}}: CS1 maint: date and year (link)
• Dinauer M. C. (January 2003). "Regulation of neutrophil function by Rac GTPases". Curr. Opin. Hematol. 10 (1): 8–15. doi:10.1097/00062752-200301000-00003. PMID 12483106.{{cite journal}}: CS1 maint: date and year (link)
• Hill K. and Welch H. C. E. (2006). "Purification of P-Rex1 from Neutrophils and Nucleotide Exchange Assay". Regulators and Effectors of Small GTPases: Rho Family. Methods in Enzymology. Vol. 406. pp. 406:26–41. doi:10.1016/S0076-6879(06)06003-4. ISBN 9780121828110. PMID 16472647.
• Urano D., Nakata A., Mizuno N.; et al. (August 2008). "Domain-domain interaction of P-Rex1 is essential for the activation and inhibition by G protein betagamma subunits and PKA". Cell Signal. 20 (8): 1545–1554. doi:10.1016/j.cellsig.2008.04.009. PMID 18514484. {{cite journal}}: Explicit use of et al. in: |author= (help)CS1 maint: date and year (link) CS1 maint: multiple names: authors list (link)