HGNC Approved Gene Symbol: INPP5E
SNOMEDCT: 715628009;
Cytogenetic location: 9q34.3 Genomic coordinates (GRCh38): 9:136,428,619-136,439,845 (from NCBI)
| Location | Phenotype |
Phenotype MIM number |
Inheritance |
Phenotype mapping key |
|---|---|---|---|---|
| 9q34.3 | Impaired intellectual development, truncal obesity, retinal dystrophy, and micropenis syndrome | 610156 | Autosomal recessive | 3 |
| Joubert syndrome 1 | 213300 | Autosomal recessive | 3 |
Inositol polyphosphate-5-phosphatases, such as INPP5E, cleave the 5-position phosphate from soluble inositol phosphates or inositol phospholipids. Members of this large family of enzymes are classified into 4 groups based on their substrate specificity. INPP5E belongs to group IV based on its preference for phosphatidylinositol 3,4,5-trisphosphate (PtdIns(3,4,5)P3) (Kisseleva et al., 2000).
By searching an EST database for genes encoding the essential domains of inositol polyphosphate-5-phosphatases, followed by screening and 5-prime RACE of a human fetal brain cDNA library, Kisseleva et al. (2000) cloned INPP5E. The deduced 644-amino acid protein contains an N-terminal proline-rich domain with 13 PxxP motifs, followed by a putative immunoreceptor activation motif (ITAM) domain, 2 critical 5-phosphatase domains, and a putative C-terminal farnesylation signal. Kisseleva et al. (2000) also identified a splice variant that encodes a protein lacking a 34-amino acid sequence covering the putative ITAM domain. Northern blot analysis detected a major transcript of 3.6 kb in all tissues examined, with highest expression in brain, heart, spleen, pancreas, and testis. Additional transcripts of 4.9 and 9.5 kb were also detected, predominantly in testis. Northern blot analysis of mouse tissues showed highest expression in testis, heart, and brain. Western blot analysis detected INPP5E at an apparent molecular mass of 68 kD in human brain, but not in liver, spleen, or kidney. In mouse, highest protein expression was in brain, heart, and testis, with lower expression in thymus and lung, and very little expression in kidney, spleen, and liver.
Kong et al. (2000) cloned mouse Inpp5e. Northern blot analysis detected highest Inpp5e expression in mouse testis and a mouse spermatocyte cell line. Lower expression was detected in mouse brain and in rat glioma and neuroteratocarcinoma cell lines. In situ hybridization detected Inpp5e in pachytene and diplotene spermatocytes of testis and in neurons throughout the brain, including cerebral cortex, hippocampus, diencephalon, brainstem, and cerebellum. Immunohistochemical analysis detected Inpp5e associated with the trans-Golgi, and proteinase K digestion showed that it was oriented on the cytoplasmic face of microsome membranes. Western blot analysis detected Inpp5e at an apparent molecular mass of 72 kD in adult mouse testis and brain and in mouse spermatocyte and teratocarcinoma cell lines, but not in other tissues and cell lines examined.
By immunohistochemical analysis of a human retinal pigment epithelial cell line, Bielas et al. (2009) localized INPP5E predominantly to the ciliary axoneme. In mitotically active cells, INPP5E showed cytoplasmic localization. Inpp5e colocalized with fluorescence-tagged centrin-2 (CETN2; 300006), a marker for the base of cilia, in transgenic mice. In renal collecting tubules, Inpp5e-positive cilia projected into the lumen, and in most neuroblasts of the cerebellar internal granule layer, Inpp5e-positive cilia projected into the parenchyma. Inpp5e localized to the region adjacent to the basal body and connecting cilium in photoreceptor cells of the retina.
Using scanning and transmission electron microscopy, Jacoby et al. (2009) showed that Inpp5e localized to the axoneme of primary cilia in ciliated mouse embryonic fibroblasts.
Kisseleva et al. (2000) showed that purified human INPP5E expressed in insect cells readily hydrolyzed PtdIns(3,4,5)P3 to PtdIns(3,4)P2 in a time- and concentration-dependent manner. It did not hydrolyze soluble inositol phosphate or other inositol lipids. Altering the detergent composition of the assay permitted INPP5E-mediated hydrolysis of PtdIns(4,5)P2 to PtdIns(4)P.
Kong et al. (2000) showed that mouse Inpp5e converted PtdIns(3,4,5) P3 to PtdIns(3,4)P2 following expression in COS-7 cells. It also hydrolyzed PtdIns(3,5)P2 to PtdIns(3)P, but it did not use any other inositol phospholipid.
Humbert et al. (2012) found that mutations in the KRR or FDRELYL motifs near the C terminus of INPP5E disrupted ciliary targeting of INPP5E in transfected human RPE1 retinal pigment epithelium cells and mouse IMCD3 collecting duct cells. The C-terminal CaaX prenylation motif contributed to targeting of full-length prenylated INPP5E, but not soluble INPP5E, to cilia. Mass spectrometric analysis, followed by coimmunoprecipitation, mutation, and knockdown experiments, revealed that the phosphodiesterase PDE6D (602676), the ciliary protein CEP164 (614848), and the small GTPase ARL13B (608922) bound INPP5E and contributed to targeting of INPP5E to ciliary membranes. PDE6D bound the prenylated form of INPP5E, and the GTP-bound form of ARL13B interacted with an adjacent region of INPP5E. Overexpression of ARL13B promoted release of INPP5E from PDE6D. Knockdown of CEP164 or ARL13B reduced or eliminated ciliogenesis in RPE1 cells, whereas knockdown of PDE6D had little effect on ciliogenesis. Humbert et al. (2012) hypothesized that PDE6D, CEP164, and ARL13B mediate sequential steps in targeting INPP5E to ciliary membranes for cilia formation.
Jacoby et al. (2009) stated that the INPP5E gene maps to chromosome 9q34.3. Hartz (2009) determined that the INPP5E gene overlaps the PMPCA gene (613036) and is transcribed in the opposite direction.
Impaired Intellectual Development, Truncal Obesity, Retinal Dystrophy, and Micropenis Syndrome
In affected members of a family with impaired intellectual development, truncal obesity, retinal dystrophy, and micropenis syndrome (MORMS; 610156), Jacoby et al. (2009) identified a homozygous mutation (Q627X; 613037.0001) in the INPP5E gene. In vitro functional expression studies showed that the mutant protein had impaired localization in cilia and was unable to stabilize ciliary structures.
Joubert Syndrome 1
In affected members of 7 families with Joubert syndrome-1 (JBTS1; 213300), Bielas et al. (2009) identified 5 different homozygous mutations in the INPP5E gene (see, e.g., 613037.0002-613037.0005). Three families were from the United Arab Emirates, 1 from Turkey, 1 from Egypt, and 2 from Italy. All of the mutations were in the catalytic domain of the protein, and all mutant proteins showed decreased phosphatase activity. The findings implied a link between PtdIns signaling and ciliopathies.
Jacoby et al. (2009) found that Inpp5e deletion in mice led to embryonic and early postnatal death. All Inpp5e -/- mice showed bilateral anophthalmos, cystic kidneys, and delayed ossification of metacarpals and phalanges, and many showed postaxial hexadactyly, bifid sternum, cleft palate, and anencephaly or exencephaly. No defects in liver or respiratory cilium were detected. The lesions in Inpp5e -/- mice reflected the tissue distribution of Inpp5e expression during normal mouse embryogenesis. Inpp5e inactivation did not impair ciliary assembly in cultured mouse embryonic fibroblasts, but it destabilized pre-established cilia following activation of Pdgf receptor-alpha (PDGFRA; 173490) or other factors contained in serum. Blocking PI3 kinase (see PK3R1; 171833) activity or ciliary Pdgf (see 173430) signaling prevented ciliary instability.
In affected members of a family with impaired intellectual development, truncal obesity, retinal dystrophy, and micropenis syndrome (MORMS; 610156), Jacoby et al. (2009) identified a homozygous 1879C-T transition in the last exon of the INPP5E gene, resulting in a gln627-to-ter (Q627X) substitution. The mutation was predicted to cause premature termination of the protein with omission of the terminal 18 amino acids and loss of the highly conserved C-terminal CaaX domain. The mutation was not present in 200 ethnically matched controls. In vitro functional expression studies in ciliated human retinal pigment epithelial cells showed that wildtype INPP5E was evenly distributed along the cilial axoneme, whereas expression of the mutant protein was limited to one extremity of the cilium. The mutant protein was protein was also unable to interact with 14-3-3 proteins but retained its 5-phosphatase activity. The findings indicated that the mutant protein had decreased ability to stabilize the primary cilium, which is likely due to its defect in ciliary localization and protein interaction. Despite its normal enzymatic activity, mutant INPP5E expression outside of the cilium is clearly not sufficient for stabilization.
In affected members of 2 unrelated consanguineous families from the United Arab Emirates with Joubert syndrome-1 (JBTS1; 213300), Bielas et al. (2009) identified a homozygous 1546C-T transition in exon 7 of the INPP5E gene, resulting in an arg515-to-trp (R515W) substitution in the catalytic domain of the protein. Molecular modeling placed the affected residue in the presumed binding pocket for the PtdIns substrate, and in vitro functional expression studies confirmed decreased phosphatase activity of the mutant protein.
In affected members of a consanguineous family from the United Arab Emirates with Joubert syndrome-1 (JBTS1; 213300), Bielas et al. (2009) identified a homozygous 1691G-A transition in exon 9 of the INPP5E gene, resulting in an arg563-to-his (R563H) substitution in the catalytic domain of the protein. In vitro functional expression studies confirmed decreased phosphatase activity of the mutant protein.
In 2 affected members of a consanguineous Turkish family with Joubert syndrome-1 (JBTS1; 213300), Bielas et al. (2009) identified a homozygous 1305G-A transition in exon 6 of the INPP5E gene, resulting in an arg435-to-gln (R435Q) substitution in the catalytic domain of the protein. Molecular modeling placed the affected residue in the presumed binding pocket for the PtdIns substrate, and in vitro functional expression studies confirmed decreased phosphatase activity of the mutant protein. Studies of patient fibroblasts showed more rapid ciliary disassembly in response to serum compared to wildtype.
In affected members of 2 consanguineous Italian families with Joubert syndrome-1 (JBTS1; 213300), Bielas et al. (2009) identified a homozygous 1132C-T transition in exon 4 of the INPP5E gene, resulting in an arg378-to-cys (R378C) substitution in the catalytic domain of the protein. Molecular modeling placed the affected residue in the presumed binding pocket for the PtdIns substrate, and in vitro functional expression studies confirmed decreased phosphatase activity of the mutant protein.
Bielas, S. L., Silhavy, J. L., Brancati, F., Kisseleva, M. V., Al-Gazali, L., Sztriha, L., Bayoumi, R. A., Zaki, M. S., Abdel-Aleem, A., Rosti, R. O., Kayserili, H., Swistun, D., and 13 others. Mutations in INPP5E, encoding inositol polyphosphate-5-phosphatase E, link phosphatidyl inositol signaling to the ciliopathies. Nature Genet. 41: 1032-1036, 2009. [PubMed: 19668216] [Full Text: https://doi.org/10.1038/ng.423]
Hartz, P. A. Personal Communication. Baltimore, Md. 9/28/2009.
Humbert, M. C., Weihbrecht, K., Searby, C. C., Li, Y., Pope, R. M., Sheffield, V. C., Seo, S. ARL13B, PDE6D, and CEP164 form a functional network for INPP5E targeting. Proc. Nat. Acad. Sci. 109: 19691-19696, 2012. [PubMed: 23150559] [Full Text: https://doi.org/10.1073/pnas.1210916109]
Jacoby, M., Cox, J. J., Gayral, S., Hampshire, D. J., Ayub, M., Blockmans, M., Pernot, E., Kisseleva, M. V., Compere, P., Schiffmann, S. N., Gergely, F., Riley, J. H., Perez-Morga, D., Woods, C. G., Schurmans, S. INPP5E mutations cause primary cilium signaling defects, ciliary instability and ciliopathies in human and mouse. Nature Genet. 41: 1027-1031, 2009. [PubMed: 19668215] [Full Text: https://doi.org/10.1038/ng.427]
Kisseleva, M. V., Wilson, M. P., Majerus, P. W. The isolation and characterization of a cDNA encoding phospholipid-specific inositol polyphosphate 5-phosphatase. J. Biol. Chem. 275: 20110-20116, 2000. [PubMed: 10764818] [Full Text: https://doi.org/10.1074/jbc.M910119199]
Kong, A. M., Speed, C. J., O'Malley, C. J., Layton, M. J., Meehan, T., Loveland, K. L., Cheema, S., Ooms, L. M., Mitchell, C. A. Cloning and characterization of a 72-kDa inositol-polyphosphate 5-phosphatase localized to the Golgi network. J. Biol. Chem. 275: 24052-24064, 2000. [PubMed: 10806194] [Full Text: https://doi.org/10.1074/jbc.M000874200]