Alternative titles; symbols
HGNC Approved Gene Symbol: ARHGAP24
Cytogenetic location: 4q21.23-q21.3 Genomic coordinates (GRCh38): 4:85,475,150-86,002,666 (from NCBI)
ARHGAPs, such as ARHGAP24, encode negative regulators of Rho GTPases (see ARHA, 165390), which are implicated in actin remodeling, cell polarity, and cell migration (Katoh and Katoh, 2004).
By searching an EST database for sequences similar to ARHGAP22 (610585), Katoh and Katoh (2004) identified ARHGAP24. The deduced 748-amino acid protein has an N-terminal pleckstrin homology (PH) domain, followed by a RhoGAP domain and a C-terminal coiled-coil domain.
Using a PCR-based subtraction hybridization approach to identify genes upregulated during capillary tube formation in human umbilical vein endothelial cells (HUVECs), followed by database analysis and PCR of an endothelial cell cDNA library, Su et al. (2004) cloned ARHGAP24, which they called p73. The predicted p73 protein contains 655 amino acids and has a calculated molecular mass of 73 kD. Northern blot analysis detected a 4.5-kb transcript in HUVECs, and virtual Northern blot analysis of various cell lines showed high p73 expression restricted to HUVECs and vascular smooth muscle cells. Using quantitative RT-PCR, Su et al. (2004) found that the ratio of p73 expression in HUVECs over the median expression in 5 other primary tissues correlated with the ratio obtained with the endothelial marker CD31 (PECAM1; 173445), suggesting that p73 is expressed specifically in endothelial cells.
By database analysis, Lavelin and Geiger (2005) identified ARHGAP24, which they called RCGAP72. The deduced 655-amino acid protein has a calculated molecular mass of 72 kD and shares 87% amino acid identity its mouse homolog. Northern blot analysis detected variable expression of Rcgap72 in all mouse tissues examined, with highest expression in kidney. Northern and Western blot analyses of several human cell lines detected RCGAP72 expression in HeLa cells and a nonsmall cell lung carcinoma cell line only. Western blot analysis of HeLa cells revealed an 80-kD RCGAP72 protein. Immunofluorescence microscopy of transfected mouse fibroblasts showed fluorescence-tagged RCGAP72 associated with actin stress fibers. In canine kidney cells, it colocalized primarily along alpha-actinin (see ACTN1; 102575)-containing adherens junctions and in the nucleus.
Using the C terminus of FLNA (300017) in a yeast 2-hybrid screen of a spleen cDNA library, Ohta et al. (2006) cloned ARHGAP24, which they called FILGAP. The deduced 748-amino acid protein has a calculated molecular mass of 84 kD. Ohta et al. (2006) determined that the p73 (Su et al., 2004)/RCGAP72 (Lavelin and Geiger, 2005) protein is encoded by a splice variant and lacks the PH domain of the full-length FILGAP protein. Northern blot analysis detected transcripts of 3.0 and 4.0 kb in most tissues examined, with highest expression in kidney, and FILGAP was widely expressed in human cell lines.
By Western blot analysis, Akilesh et al. (2011) found highest expression of Arhgap24 in mouse kidney. RT-PCR and confocal imaging of mouse glomeruli and isolated podocytes in culture detected highest Arhgap24 mRNA and protein expression in highly differentiated podocytes. Arhgap24 was specifically expressed in podocyte focal adhesions.
Su et al. (2004) found that p73 cloned from HUVECs showed GTPase activity to RHO, but not to RAC (RAC1; 602048) or CDC42 (116952). p73 was upregulated in endothelial cells growing in a 3-dimensional (3D) matrix, but not in cells growing on a 2D surface. Knockdown of p73 in endothelial cells by antisense p73 or small interfering RNA reduced cell migration, proliferation, and capillary tube formation in 3D gels. A p73 mutant lacking GAP activity caused similar results, and antisense p73 inhibited blood vessel migration in a mouse model of angiogenesis. Su et al. (2004) concluded that p73 is a vascular cell-specific GAP important in modulation of angiogenesis.
Lavelin and Geiger (2005) found that the levels of active RAC1 and CDC42 were significantly reduced in HeLa cells overexpressing RCGAP72, whereas the level of RHOA-GTP was not affected. Overexpression of RCGAP72 in rat fibroblasts induced cell rounding with partial or complete disruption of actin stress fibers and formation of membrane ruffles, lamellipodia, and filopodia. Mutation analysis indicated that cytoskeletal localization of RCGAP72 and its interaction with RAC1 and/or CDC42 were essential for disruption of stress fibers. In contrast, induction of filopodia depended on the GAP activity of RCGAP72 irrespective of cytoskeletal localization.
By mutation analysis, Ohta et al. (2006) determined that the coiled-coil domain of FILGAP interacted with the C-terminal repeats of FLNA. FLNA binding targeted FILGAP to sites of membrane protrusion in mammalian cell lines, where FILGAP mediated ROCK (see ROCK1; 601702)-dependent downregulation of RAC activity and suppressed leading lamellar formation. Overexpression of FILGAP induced numerous blebs around the cell periphery, and phosphorylation of FILGAP by ROCK was required for FILGAP-mediated bleb formation.
Ehrlicher et al. (2011) identified the actin-binding protein filamin A (FLNA) as a central mechanotransduction element of the cytoskeleton, and reconstituted a minimal system consisting of actin filaments, FLNA, and 2 FLNA-binding partners: the cytoplasmic tail of beta-integrin (135630) and FILGAP. Integrins form an essential mechanical linkage between extracellular and intracellular environments, with beta-integrin tails connecting to the actin cytoskeleton by binding directly to filamin. FILGAP is an FLNA-binding GTPase-activating protein specific for RAC, which in vivo regulates cell spreading and bleb formation. Using fluorescence loss after photoconversion, Ehrlicher et al. (2011) demonstrated that both externally imposed bulk shear and myosin-II-driven forces differentially regulate the binding of these partners to FLNA. Consistent with structural predictions, strain increases beta-integrin binding to FLNA, whereas it causes FILGAP to dissociate from FLNA, providing a direct and specific molecular basis for cellular mechanotransduction. Ehrlicher et al. (2011) concluded that their results identified a molecular mechanotransduction element within the actin cytoskeleton, revealing that mechanical strain of key proteins regulates the binding of signaling molecules.
By microarray analysis, Akilesh et al. (2011) observed upregulated expression of Arhgap24 in immortalized differentiated mouse podocytes compared with undifferentiated controls. Knockdown of Arhgap24 via anti-Arhgap24 lentiviral infection increased membrane motility in fully differentiated podocytes in vitro and accelerated kinetics of wound closure in a scratch wound assay. Akilesh et al. (2011) concluded that ARHGAP24 functions in podocytes to inhibit RAC1- and CDC42-dependent membrane dynamics.
Katoh and Katoh (2004) determined that the ARHGAP24 gene contains at least 10 exons.
By genomic sequence analysis, Katoh and Katoh (2004) mapped the ARHGAP24 gene to chromosome 4q21. The region containing ARHGAP24 and that containing ARHGAP22 on chromosome 10q11 appear to be paralogous.
Associations Pending Confirmation
For discussion of a possible association between variation in the ARHGAP24 gene and focal segmental glomerulosclerosis (see, e.g., FSGS1, 603278), see 610586.0001.
This variant is classified as a variant of unknown significance because its contribution to focal segmental glomerulosclerosis (see, e.g., FSGS1, 603278) has not been confirmed.
In a Hispanic man, his mother, and his sister with FSGS, Akilesh et al. (2011) identified a heterozygous G-to-A transition in the ARHGAP24 gene, resulting in a gln158-to-arg (Q158R) substitution at a conserved residue close to the catalytic site in isoform 1 (Q65R in isoform 2). The variant was not found in over 900 control chromosomes. In vitro functional expression studies of the corresponding Q156R variant in the mouse gene in HEK293 cells showed that it impaired the GAP activity of Arhgap24; there was a marked increase in the level of active RAC1. Additional studies showed that the variant protein could homo- and heterodimerize with wildtype ARHGAP24, which may explain the dominant effect in this family. The proband had increased serum creatinine, and a biopsy at age 20 showed FSGS; his affected sister had biopsy-proven FSGS and end-stage kidney disease at age 12; their mother presented at a late stage and died of renal failure at age 29. The proband was 1 of 310 patients with biopsy-proven FSGS who underwent exon sequencing of the ARHGAP24 gene. Kniffin (2016) noted that the Q158R variant (rs112475438) was present in the ExAC database (February 19, 2016) in 1 individual of Latino descent who was homozygous for the variant, yielding a frequency of 0.003562.
Akilesh, S., Suleiman, H., Yu, H., Stander, M. C., Lavin, P., Gbadegesin, R., Antignac, C., Pollak, M., Kopp, J. B., Winn, M. P., Shaw, A. S. Arhgap24 inactivates Rac1 in mouse podocytes, and a mutant form is associated with familial focal segmental glomerulosclerosis. J. Clin. Invest. 121: 4127-4137, 2011. [PubMed: 21911940] [Full Text: https://doi.org/10.1172/JCI46458]
Ehrlicher, A. J., Nakamura, F., Hartwig, J. H., Weitz, D. A., Stossel, T. P. Mechanical strain in actin networks regulates FilGAP and integrin binding to filamin A. Nature 478: 260-263, 2011. [PubMed: 21926999] [Full Text: https://doi.org/10.1038/nature10430]
Katoh, M., Katoh, M. Identification and characterization of ARHGAP24 and ARHGAP25 genes in silico. Int. J. Molec. Med. 14: 333-338, 2004. [PubMed: 15254788]
Kniffin, C. L. Personal Communication. Baltimore, Md. 3/11/2016.
Lavelin, I., Geiger, B. Characterization of a novel GTPase-activating protein associated with focal adhesions and the actin cytoskeleton. J. Biol. Chem. 280: 7178-7185, 2005. [PubMed: 15611138] [Full Text: https://doi.org/10.1074/jbc.M411990200]
Ohta, Y., Hartwig, J. H., Stossel, T. P. FilGAP, a Rho- and ROCK-regulated GAP for Rac binds filamin A to control actin remodelling. Nature Cell Biol. 8: 803-814, 2006. [PubMed: 16862148] [Full Text: https://doi.org/10.1038/ncb1437]
Su, Z.-J., Hahn, C. N., Goodall, G. J., Reck, N. M., Leske, A. F., Davy, A., Kremmidiotis, G., Vadas, M. A., Gamble, J. R. A vascular cell-restricted RhoGAP, p73RhoGAP, is a key regulator of angiogenesis. Proc. Nat. Acad. Sci. 101: 12212-12217, 2004. [PubMed: 15302923] [Full Text: https://doi.org/10.1073/pnas.0404631101]