Alternative titles; symbols
HGNC Approved Gene Symbol: INF2
SNOMEDCT: 722294004;
Cytogenetic location: 14q32.33 Genomic coordinates (GRCh38) : 14:104,681,133-104,722,535 (from NCBI)
| Location | Phenotype |
Phenotype MIM number |
Inheritance |
Phenotype mapping key |
|---|---|---|---|---|
| 14q32.33 | Charcot-Marie-Tooth disease, dominant intermediate E | 614455 | Autosomal dominant | 3 |
| Glomerulosclerosis, focal segmental, 5 | 613237 | 3 |
Actin filaments grow only when actin monomers have access to the fast-growing barbed end of the filament. The geometry of the filament network depends on the actions of the ARP2/3 complex (604221) and members of the formin family, such as INF2. The ARP2/3 complex binds to the sides of preexisting filaments and nucleates filaments whose barbed ends are quickly blocked by capping proteins, producing brush-like structures, such as those found at the leading edges of crawling cells. In contrast, formins bind to the barbed ends of growing filaments and protect them from capping, creating long filaments that can be cross-linked into bundles, such as those found in actin cables of yeast. Interaction of formins with actin barbed ends occurs through the formin homology-2 (FH2) domain. FH2 domains accelerate filament nucleation, move with the barbed end as the filament grows, and block capping of the barbed end by proteins such as gelsolin (GSN; 137350). The FH1 domain of formins binds to profilin (see 176610) and accelerates elongation from the FH2-bound barbed ends (Bindschadler and McGrath, 2004; Chhabra and Higgs, 2006).
By searching databases for FH2 domain sequences, Higgs and Peterson (2005) identified mouse and human INF2, a member of the inverted formin group. Inverted formins have an N-terminal FH2 domain rather than the C-terminal FH2 domain found in all other formins.
By database analysis and RT-PCR, Chhabra and Higgs (2006) cloned full-length mouse Inf2. The deduced 1,274-amino acid protein has an N-terminal diaphanous inhibitory domain (DID), followed by an FH1 domain, an FH2 domain, and a C-terminal diaphanous autoregulatory domain (DAD)/ WASP (300392) homology-2 (WH2) domain. Thus, Inf2 is not an inverted formin, but is most similar to diaphanous formins (e.g., DIAPH1; 602121), which are regulated by autoinhibition via DID-DAD interaction.
By immunohistochemical staining, Boyer et al. (2011) demonstrated robust IFN2 expression in peripheral nerve Schwann cells and light staining in some axons. INF2 was also expressed predominantly in podocytes in the kidney, as well as in some tubules, but not in vessels. INF2 colocalized with the myelin and lymphocyte protein (MAL; 188860) in human peripheral nerve and mouse Schwann cells, and with MAL2 (609684) in human podocytes. MAL was not present in glomeruli. In HeLa cells, INF2 showed perinuclear localization.
Gross (2025) mapped the INF2 gene to chromosome 14q32.33 based on an alignment of the INF2 sequence (GenBank BC006173) with the genomic sequence (GRCh38).
Using fluorescence microscopy to study the effects of various constructs containing domains of mouse Inf2 on actin elongation and nucleation, Chhabra and Higgs (2006) showed that Inf2 interacted with actin through a region C-terminal to the FH2 domain. This region, in combination with the FH2 domain, accelerated both polymerization and depolymerization of actin filaments. Depolymerization resulted from actin monomer-binding ability of the WH2 domain and a severing activity that depended on attachment of the FH2 domain to the C terminus. Phosphate inhibited both depolymerization and severing, suggesting that phosphate release from actin subunits in the filament triggers depolymerization. Mutation of the WH2 domain abrogated depolymerization.
Korobova et al. (2013) found that actin polymerization through endoplasmic reticulum (ER)-localized INF2 was required for efficient mitochondrial fission in mammalian cells. INF2 functioned upstream of DRP1 (603850). Actin filaments appeared to accumulate between mitochondria and INF2-enriched ER membranes at constriction sites. Thus, INF2-induced actin filaments may drive initial mitochondrial constriction, which allows DRP1-driven secondary constriction. Because INF2 mutations can lead to Charcot-Marie-Tooth disease (614455), Korobova et al. (2013) concluded that their results provided a potential cellular mechanism for this disease state.
Focal Segmental Glomerulosclerosis 5
In 2 large families segregating autosomal dominant focal segmental glomerulosclerosis mapping to chromosome 14q32 (FSGS5; 613237), Brown et al. (2010) sequenced 15 candidate genes and identified heterozygous missense mutations in the INF2 gene in both families that segregated with disease (610982.0001 and 610982.0002, respectively). Sequencing of the INF2 gene in 91 unrelated individuals with familial FSGS revealed 9 additional families with heterozygous mutations in the INF2 gene that segregated with disease (see, e.g., 610982.0003-610982.0005). Brown et al. (2010) noted that all 9 of the disease-segregating substitutions are located at conserved residues within the DID (diaphanous-inhibitory domain) region of INF2, with 7 residing in close proximity to each other in exon 4 of the gene. Studies in transfected podocytes demonstrated alterations in the subcellular localization of INF2 and the pattern of distribution of the associated F-actin with mutant forms of INF2 compared to wildtype, as well as less prominent actin filament bundles on electron micrographs.
Dominant Intermediate Charcot-Marie-Tooth Disease E with Focal Segmental Glomerulosclerosis
In 12 (75%) of 16 index patients with dominant intermediate Charcot-Marie-Tooth disease E (CMTDIE; 614455) with focal segmental glomerulosclerosis (FSGS), Boyer et al. (2011) identified 9 novel heterozygous mutations in the INF2 gene (see, e.g., 610982.0006-610982.0011). All mutations were located in exons 2 and 3, which encode the diaphanous inhibitory domain (DID), and most of them were between nucleotides 300 and 500 in the second and third armadillo repeats. These mutations were located in distinct areas from those associated with isolated FSGS5, most of which are located downstream of nucleotide 500 in the fourth armadillo repeat domain. The 12 index patients with INF2 mutations reported by Boyer et al. (2011) presented with proteinuria at a median age of 18 years (range, 10-21 years), and 11 developed end-stage renal disease at a median age of 21 years (range, 12-47 years). Renal biopsies showed FSGS. The median age at onset of neurologic dysfunction was 13 years (range, 5-28 years), and all had distal muscle atrophy and weakness affecting the lower limbs. Some had upper limb involvement as well. Neurophysiologic studies and sural nerve biopsies indicated an intermediate form of CMT. Four patients also had mild to moderate sensorineural hearing loss. INF2 mutations were not found in 50 patients with CMT without renal involvement. In vitro functional expression studies by Boyer et al. (2011) showed that mutant INF2 was abnormally dispersed throughout the cytoplasm, resulting in a broader cytoplasmic distribution of MAL. Cells expressing mutant INF2 exhibited less cortical actin and a reduced number of long actin stress fibers compared to wildtype, suggesting a disorganized microtubule network. Finally, INF2 mutants showed an enhanced interaction with CDC42 (116952), an actin-regulating Rho-GTPase known to interact with the INF2 DID domain, resulting in altered intracellular localization of CDC42. Boyer et al. (2011) concluded that mutant INF2 disrupts actin dynamics in peripheral Schwann cells, leading to disturbed myelin formation and maintenance and resulting in CMT.
Subramanian et al. (2024) found that knockin mice heterozygous for the FSGS-associated arg218-to-gln (R218Q; 610982.0002) mutation in the DID of Inf2 developed kidney disease, whereas mice heterozygous for Inf2 knockout did not, indicating that Inf2-mediated kidney disease occurred due to gain-of-function effects of mutant Inf2. Analysis with podocytes showed that mutation in the DID of Inf2 conferred a gain-of-function effect by altering the localization of wildtype Inf2 and Inf2 actin-polymerizing activity, leading to activity at abnormal sites. RNA sequencing analysis identified cellular processes that were altered by the gain-of-function effect of mutant Inf2, and mutant mouse podocytes displayed altered cell adhesion and mitochondrial morphology. Moreover, kidney organoid-derived podocytes from a patient with an INF2 mutation recapitulated the mouse disease phenotype.
In affected members of 2 large Canadian families segregating autosomal dominant focal segmental glomerulosclerosis (FSGS5; 613237), Brown et al. (2010) identified a heterozygous alteration in exon 4 of the INF2 gene, resulting in a ser186-to-pro (S186P) substitution at a conserved residue within the autoinhibitory DID region. Transfection studies in cultured podocytes showed a slightly more diffuse distribution of INF2 with a more vermiform appearance than wildtype, and less prominent stress fibers and cortical actin compared to wildtype. The mutation was not found in 282 controls. Age at diagnosis in the 2 families ranged from 12 years to 67 years; 12 of 28 affected individuals developed end-stage renal disease, with age of onset ranging from 20 years to 67 years.
In affected members of a large family segregating autosomal dominant focal segmental glomerulosclerosis (FSGS5; 613237), Brown et al. (2010) identified a heterozygous alteration in exon 4 of the INF2 gene, resulting in an arg218-to-gln (R218Q) substitution at a conserved residue within the DID. Structural modeling revealed that the R218 residue lies close to the DAD-binding region of the DID, and transfection studies in cultured podocytes showed a finer, more diffuse distribution of INF2 and less prominent stress fibers and cortical actin with mutant compared to wildtype INF2. The mutation was not found in 682 control chromosomes. Age at diagnosis in this kindred ranged from 22 years to 45 years; 4 of 10 affected individuals developed end-stage renal disease, with age of onset ranging from 23 years to 30 years.
Subramanian et al. (2024) found that knockin mice heterozygous for the FSGS-associated arg218-to-gln (R218Q; 610982.0002) mutation in the DID of Inf2 developed kidney disease, whereas mice heterozygous for Inf2 knockout did not, indicating that Inf2-mediated kidney disease occurred due to gain-of-function effects of mutant Inf2. Analysis with podocytes showed that mutation in the DID of Inf2 conferred a gain-of-function effect by altering the localization of wildtype Inf2 and Inf2 actin-polymerizing activity, leading to activity at abnormal sites. RNA sequencing analysis identified cellular processes that were altered by the gain-of-function effect of mutant Inf2, and mutant mouse podocytes displayed altered cell adhesion and mitochondrial morphology.
In 2 African-American brothers with focal segmental glomerulosclerosis (FSGS5; 613237), Brown et al. (2010) identified a heterozygous alteration in exon 4 of the INF2 gene, resulting in an arg218-to-trp (R218W) substitution at a conserved residue within the autoinhibitory DID region. Structural modeling revealed that the R218 residue lies close to the DAD-binding region of the DID. The mutation was not found in 282 controls. The brothers were diagnosed at 27 and 33 years of age, respectively, and developed end-stage renal disease at 30 and 40 years of age, respectively. Their affected father was deceased.
In affected members of 2 large families segregating autosomal dominant focal segmental glomerulosclerosis (FSGS5; 613237), Brown et al. (2010) identified a heterozygous alteration in exon 4 of the INF2 gene, resulting in an arg214-to-his (R214H) substitution at a conserved residue within the autoinhibitory DID region. Structural modeling revealed that the R214 residue lies close to the DAD-binding region of the DID. The mutation was not found in 282 controls. Age at diagnosis in the 2 families ranged from 12 years to 72 years; 4 of 12 affected individuals developed end-stage renal disease, with age of onset ranging from 17 years to 60 years.
In a sister and brother with focal segmental glomerulosclerosis (FSGS5; 613237), Brown et al. (2010) identified a heterozygous alteration in exon 2 of the INF2 gene, resulting in a leu42-to-pro (L42P) substitution at a conserved residue within the autoinhibitory DID region. Their affected father was also heterozygous for the mutation, which was not found in 341 controls. Diagnosis in this family occurred between 11 to 13 years of age, and all 3 affected individuals developed end-stage renal disease by 13 to 14 years of age.
In a Caucasian Moroccan patient with dominant intermediate Charcot-Marie-Tooth disease E (CMTDIE; 614455) with focal segmental glomerulosclerosis, Boyer et al. (2011) identified a de novo heterozygous 310T-C transition in exon 2 of the INF2 gene, resulting in a cys104-to-arg (C104R) substitution in a highly conserved residue in the N-terminal diaphanous-inhibitory domain (DID). The mutation was not found in 670 control chromosomes. The same residue was mutated in another patient (C104F; 610982.0007) and in affected members of a family (C104W; 610982.0008).
In a Caucasian/African patient from the French West Indies with CMTDIE (614455), Boyer et al. (2011) identified a heterozygous 311G-T transversion in exon 2 of the INF2 gene, resulting in a cys104-to-phe (C104F) substitution in a highly conserved residue in the N-terminal DID domain. The mutation was not found in 670 control chromosomes. The same residue was mutated in another patient (C104R; 610982.0006) and in affected members of a family (C104W; 610982.0008).
In affected members of a Caucasian Canadian family with CMTDIE (614455) (Lemieux and Neemeh, 1967), Boyer et al. (2011) identified a heterozygous 312C-G transversion in exon 2 of the INF2 gene, resulting in a cys104-to-trp (C104W) substitution in a highly conserved residue in the N-terminal DID domain. The mutation was not found in 670 control chromosomes. The same residue was mutated in 2 other unrelated patients with sporadic disease (C104R, 610982.0006 and C104F, 610982.0007).
In 2 unrelated Caucasian patients from Portugal and France, respectively, with CMTDIE (614455), Boyer et al. (2011) identified a heterozygous 383T-C transition in exon 2 of the INF2 gene, resulting in a leu128-to-pro (L128P) substitution in a highly conserved residue in the N-terminal DID domain. The mutation was not found in 670 control chromosomes, and was confirmed to be de novo in 1 of the patients.
In affected members of a Caucasian French family with CMTDIE (614455), Boyer et al. (2011) identified a heterozygous 395T-C transition in exon 3 of the INF2 gene, resulting in a leu132-to-arg (L132R) substitution in a highly conserved residue in the N-terminal DID domain. The mutation was also identified in a patient with sporadic disease, but was not found in 670 control chromosomes.
In affected members of 2 Caucasian families with CMTDIE (614455), Boyer et al. (2011) identified a heterozygous 9-bp deletion (490_498del) in exon 3 of the INF2 gene, resulting in an in-frame deletion of 3 conserved residues (ala164-asp166). The mutation was not found in 670 control chromosomes.
Bindschadler, M., McGrath, J. L. Formin' new ideas about actin filament generation. Proc. Nat. Acad. Sci. 101: 14685-14686, 2004. [PubMed: 15466701] [Full Text: https://doi.org/10.1073/pnas.0406317101]
Boyer, O., Nevo, F., Plaisier, E., Funalot, B., Gribouval, O., Benoit, G., Cong, E. H., Arrondel, C., Tete, M.-J., Montjean, R., Richard, L., Karras, A., and 21 others. INF2 mutations in Charcot-Marie-Tooth disease with glomerulopathy. New Eng. J. Med. 365: 2377-2388, 2011. [PubMed: 22187985] [Full Text: https://doi.org/10.1056/NEJMoa1109122]
Brown, E. J., Schlondorff, J. S., Becker, D. J., Tsukaguchi, H., Uscinski, A. L., Higgs, H. N., Henderson, J. M., Pollak, M. R., Tonna, S. J. Mutations in the formin gene INF2 cause focal segmental glomerulosclerosis. Nature Genet. 42: 72-76, 2010. Note: Erratum: Nature Genet. 42: 361 only, 2010. [PubMed: 20023659] [Full Text: https://doi.org/10.1038/ng.505]
Chhabra, E. S., Higgs, H. N. INF2 is a WASP homology 2 motif-containing formin that severs actin filaments and accelerates both polymerization and depolymerization. J. Biol. Chem. 281: 26754-26767, 2006. [PubMed: 16818491] [Full Text: https://doi.org/10.1074/jbc.M604666200]
Gross, M. B. Personal Communication. Baltimore, Md. 1/3/2025.
Higgs, H. N., Peterson, K. J. Phylogenetic analysis of the formin homology 2 domain. Molec. Biol. Cell 16: 1-13, 2005. [PubMed: 15509653] [Full Text: https://doi.org/10.1091/mbc.e04-07-0565]
Korobova, F., Ramabhadran, V., Higgs, H. N. An actin-dependent step in mitochondrial fission mediated by the ER-associated formin INF2. Science 339: 464-467, 2013. [PubMed: 23349293] [Full Text: https://doi.org/10.1126/science.1228360]
Lemieux, G., Neemeh, J. A. Charcot-Marie-Tooth disease and nephritis. Canad. Med. Assoc. J. 97: 1193-1198, 1967. [PubMed: 6054293]
Subramanian, B., Williams, S., Karp, S., Hennino, M. F., Jacas, S., Lee, M., Riella, C. V., Alper, S. L., Higgs, H. N., Pollak, M. R. INF2 mutations cause kidney disease through a gain-of-function mechanism. Sci. Adv. 10: eadr1017, 2024. [PubMed: 39536114] [Full Text: https://doi.org/10.1126/sciadv.adr1017]