FYVE, RhoGEF and PH domain-containing protein 1 (FGD1) also known as faciogenital dysplasia 1 protein (FGDY), zinc finger FYVE domain-containing protein 3 (ZFYVE3), or Rho/Rac guanine nucleotide exchange factor FGD1 (Rho/Rac GEF) is a protein that in humans is encoded by the FGD1 gene that lies on the X chromosome. [5] Orthologs of the FGD1 gene are found in dog, cow, mouse, rat, and zebrafish, and also budding yeast and C. elegans . [6] It is a member of the FYVE, RhoGEF and PH domain containing family.
FGD1 is a guanine-nucleotide exchange factor (GEF) that can activate the Rho GTPase Cdc42. It localizes preferentially to the trans-Golgi network (TGN) of mammalian cells and regulates, for example, the secretory transport of bone-specific proteins from the Golgi complex. Thus Cdc42 and FGD1 regulate secretory membrane trafficking that occurs especially during bone growth and mineralization in humans. [7] FGD1 promotes nucleotide exchange on the GTPase Cdc42, a key player in the establishment of cell polarity in all eukaryotic cells. The GEF activity of FGD1, which activates Cdc42, is harbored in its DH domain and causes the formation of filopodia, enabling the cells to migrate. FGD1 also activates the c-Jun N-terminal kinase (JNK) signaling cascade, important in cell differentiation and apoptosis. [8] It also promotes the transition through G1 during the cell cycle and causes tumorgenic transformation of NIH/3T3 fibroblasts. [9] [10]
The FGD1 gene is located on the short arm of the X-chromosome and is essential for normal mammalian embryonic development. Mice embryos that carried experimentally introduced mutations in the FGD1 gene had skeletal abnormalities affecting bone size, cartilage growth, vertebrae formation and distal extremities. [8] These severe phenotypes are consistent with a lack of Cdc42 activity, as it controls membrane traffic as well as the organization of the actin cytoskeleton. [11] Mutations in the FGD1 gene that cause the production of non-functional proteins are responsible for the severe phenotype of the X-linked disorder faciogenital dysplasia (FGDY), also called Aarskog-Scott syndrome.
The mature human protein contains several characteristic motifs and domains that are involved in the protein's function. The 961 amino acid long protein has an approximate size of 106kDa. The N-terminal is a proline-rich stretch, predicted to encode two partially overlapping src homology 3 (SH3)-binding domains, stretches from amino acid 7 – 330, followed by a DH domain (DBL homology domain), which harbors the GEF enzymatic activity, and lies between the residue 373 – 561, then a first PH domain between residues 590 – 689, a FYVE zinc finger domain (named after the four proteins it was found in Fab1, YOTB, Vac1, and EEA1) between residues 730 – 790, and a second PH domain between residues 821 – 921. [12]
The DH domain is required for the activation of Cdc42, through the catalytic exchange of GDP with GTP on Cdc42, while the PH domains confer membrane binding. The prolin-rich domain interacts with cortactin and actin-binding protein 1. [7] [13] FYVE-finger domains are conserved through evolution and often involved in membrane trafficking (e.g. Vac1p, Vps27p, Fab1, Hrs-2). One class of these domains was shown to bind selectively to phosphatidylinositol 3-phosphate. PH domains are known to specifically bind to polyphosphoinositides and influence the enzymatic activity of the GEF they are located in. [14]
FGD1 activates Cdc42 by exchanging GDP bound to Cdc42 for GTP and regulates the recruitment of Cdc42 to Golgi membranes. Levels of both FGD1 and Cdc42 are enriched on the Golgi complex itself and their interdependence regulates the transport of cargo proteins from the Golgi. FGD1 and Cdc42 colocalize in the trans-Golgi network. FGD1 inhibition has an inhibitory effect on post-Golgi transport. [7] Another interaction partner of FGD1 is cortactin, which is directly bound by the proline-rich domain of FGD1. As cortactin is known to promote actin polymerization by the Arp2/3 complex, this interaction seems to promote actin assembly. [11]
FGD1 is also transiently associated with and required for the formation of membrane protrusions on invasive tumor cells. [13]
Human FGD1 is expressed predominantly in fetal tissues of brain and kidney, but also present in the heart and lung. It is hardly detectable in the corresponding adult tissues. FGD1 is expressed in areas of bone formation and post-natally in skeletal tissue, the perichondrium, joint capsule fibroblasts and resting chondrocytes. [5] [7]
Mutations in the FGD1 gene cause phenotypes associated with the X-linked recessively transmitted faciogential dysplasia (FGDY) also known as Aarskog-Scott syndrome, a human developmental disorder that can occur with neurological problems. [5]
The disease phenotypes are due to improper bone formation and is more often seen in males though the severity depends on age. Mutations in the FGD1 gene are randomly distributed in all the domains of the protein product, modifying the intracellular localization and/or the GEF catalytic activity of FGD1. [12] [15] [16] [17] Up to 2010 twenty distinct mutations have been reported, including three missense mutations (R402Q; S558W; K748E), four truncating mutations (Y530X; R656X; 806delC; 1620delC), one in-frame deletion (2020_2022delGAG) and the first reported splice site mutation (1935þ3A→C). [18]
Increased expression of FGD1 correlates with tumor aggressiveness in prostate and breast cancer, linking the protein to cancer progression. [13]
The Wiskott–Aldrich Syndrome protein (WASp) is a 502-amino acid protein expressed in cells of the hematopoietic system that in humans is encoded by the WAS gene. In the inactive state, WASp exists in an autoinhibited conformation with sequences near its C-terminus binding to a region near its N-terminus. Its activation is dependent upon CDC42 and PIP2 acting to disrupt this interaction, causing the WASp protein to 'open'. This exposes a domain near the WASp C-terminus that binds to and activates the Arp2/3 complex. Activated Arp2/3 nucleates new F-actin.
Aarskog–Scott syndrome is a rare disease inherited as X-linked and characterized by short stature, facial abnormalities, skeletal and genital anomalies. This condition mainly affects males, although females may have mild features of the syndrome.
Inositol polyphosphate 5-phosphatase OCRL-1, also known as Lowe oculocerebrorenal syndrome protein, is an enzyme encoded by the OCRL gene located on the X chromosome in humans.
The Rho family of GTPases is a family of small signaling G proteins, and is a subfamily of the Ras superfamily. The members of the Rho GTPase family have been shown to regulate many aspects of intracellular actin dynamics, and are found in all eukaryotic kingdoms, including yeasts and some plants. Three members of the family have been studied in detail: Cdc42, Rac1, and RhoA. All G proteins are "molecular switches", and Rho proteins play a role in organelle development, cytoskeletal dynamics, cell movement, and other common cellular functions.
Cell division control protein 42 homolog, also known as Cdc42, is a protein involved in regulation of the cell cycle. It was originally identified in S. cerevisiae (yeast) as a mediator of cell division, and is now known to influence a variety of signaling events and cellular processes in a variety of organisms from yeast to mammals.
FYVE, RhoGEF and PH domain containing (FGD) is a gene family consisting of:
RhoGEF domain describes two distinct structural domains with guanine nucleotide exchange factor (GEF) activity to regulate small GTPases in the Rho family. Rho small GTPases are inactive when bound to GDP but active when bound to GTP; RhoGEF domains in proteins are able to promote GDP release and GTP binding to activate specific Rho family members, including RhoA, Rac1 and Cdc42.
Rho guanine nucleotide exchange factor 1 is a protein that in humans is encoded by the ARHGEF1 gene. This protein is also called RhoGEF1 or p115-RhoGEF.
Rho guanine nucleotide exchange factor 11 is a protein that in humans is encoded by the ARHGEF11 gene. This protein is also called RhoGEF11 or PDZ-RhoGEF.
RhoG is a small monomeric GTP-binding protein, and is an important component of many intracellular signalling pathways. It is a member of the Rac subfamily of the Rho family of small G proteins and is encoded by the gene RHOG.
Dock7, also known as Zir2, is a large protein involved in intracellular signalling networks. It is a member of the DOCK-C subfamily of the DOCK family of guanine nucleotide exchange factors (GEFs) which function as activators of small G proteins. Dock7 activates isoforms of the small G protein Rac.
FYVE, RhoGEF and PH domain-containing protein 3 is a protein that in humans is encoded by the FGD3 gene.
FYVE, RhoGEF and PH domain-containing protein 4 is a protein that in humans is encoded by the FGD4 gene.
Dock9, also known as Zizimin1, is a large protein involved in intracellular signalling networks. It is a member of the DOCK-D subfamily of the DOCK family of guanine nucleotide exchange factors that function as activators of small G proteins. Dock9 activates the small G protein Cdc42.
Cingulin-like protein 1, also known as paracingulin or junction-associated-coiled-coil protein (JACOP), is a protein which is encoded by the CGNL1 gene.
Clostridium difficile toxin A (TcdA) is a toxin generated by Clostridioides difficile, formerly known as Clostridium difficile. It is similar to Clostridium difficile Toxin B. The toxins are the main virulence factors produced by the gram positive, anaerobic, Clostridioides difficile bacteria. The toxins function by damaging the intestinal mucosa and cause the symptoms of C. difficile infection, including pseudomembranous colitis.
FYVE, RhoGEF and PH domain-containing protein 2 (FGD2), also known as zinc finger FYVE domain-containing protein 4 (ZFYVE4), is a protein that in humans is encoded by the FGD2 gene.
The Rho GTPase activating protein 31 is encoded in humans by the ARHGAP31 gene. It is a Cdc42/Rac1 GTPase regulator.
Rho GTPase activating protein 21 is a protein that in humans is encoded by the ARHGAP21 gene.
Pleckstrin homology domain containing, family G member 2 (PLEKHG2) is a protein that in humans is encoded by the PLEKHG2 gene. It is sometimes written as ARHGEF42, FLJ00018.