Stereocilia morphogenesis and maintenance through regulation of actin stability

McGrath, Jamis; Roy, Pallabi; Perrin, Benjamin J.

doi:10.1016/j.semcdb.2016.08.017

Cited by 66 publications

(66 citation statements)

References 87 publications

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“…Thoenes et al [30] carried out genome-wide linkage analysis and whole exome sequencing, identifying a co-segregating heterozygous frameshift mutation in OSBPL2, which truncates the encoded protein. Immunohistochemistry in mouse cochlea by using a commercial ORP2 antibody suggested the presence of ORP2 protein in the inner and outer hair cell stereocilia, structures which strongly depend on F-actin [46]. Similar observations were reported in a large Chinese family by Xing et al [45], who also found a frameshift mutation in OSBPL2 co-segregating with the ADNSHL phenotype.…”

Section: Mutations In Osbpl2 Are Associated With Hereditary Nonsyndrosupporting

confidence: 78%

OSBP-related protein 2 (ORP2): Unraveling its functions in cellular lipid/carbohydrate metabolism, signaling and F-actin regulation

Olkkonen

Koponen

Arora

2019

The Journal of Steroid Biochemistry and Molecular Biology

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Oxysterol-binding protein (OSBP)-related proteins (ORPs) constitute a family of intracellular lipid-binding/ transport proteins (LTPs) in eukaryotes. They typically have a modular structure comprising a lipid-binding domain and membrane targeting determinants, being thus suited for function at membrane contact sites. Among the mammalian ORPs, ORP2/OSBPL2 is the only member that only exists as a 'short' variant lacking a membrane-targeting pleckstrin homology domain. ORP2 is expressed ubiquitously and has been assigned a multitude of functions. Its OSBP-related domain binds cholesterol, oxysterols, and phosphoinositides, and its overexpression enhances cellular cholesterol efflux. Consistently, the latest observations suggest a function of ORP2 in cholesterol transport to the plasma membrane (PM) in exchange for phosphatidylinositol 4,5-bisphosphate (PI4,5P 2), with significant impacts on the concentrations of PM cholesterol and PI4,5P 2. On the other hand, ORP2 localizes at the surface of cytoplasmic lipid droplets (LDs) and at endoplasmic-reticulum-LD contact sites, and its depletion modifies cellular triglyceride (TG) metabolism. Study in an adrenocortical cell line further suggested a function of ORP2 in the synthesis of steroid hormones. Our recent knockout of ORP2 in human hepatoma cells revealed its function in hepatocellular PI3K/Akt signaling, glucose and triglyceride metabolism, as well as in actin cytoskeletal regulation, cell adhesion, migration and proliferation. ORP2 was shown to interact physically with F-actin regulators such as DIAPH1, ARHGAP12, SEPT9 and MLC12, as well as with IQGAP1 and the Cdc37-Hsp90 chaperone complex controlling the activity of Akt. Interestingly, mutations in OSBPL2 encoding ORP2 are associated with autosomal dominant non-syndromic hearing loss, and the protein was found to localize in cochlear hair cell stereocilia. The functions assigned to ORP2 suggest that this protein, in concert with other LTPs, controls the subcellular distribution of cholesterol in various cell types and steroid hormone synthesis in adrenocortical cells. However, it also impacts cellular TG and carbohydrate metabolism and F-actin-dependent functions, revealing a bewildering spectrum of activities.

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Section: Mutations In Osbpl2 Are Associated With Hereditary Nonsyndrosupporting

confidence: 78%

OSBP-related protein 2 (ORP2): Unraveling its functions in cellular lipid/carbohydrate metabolism, signaling and F-actin regulation

Olkkonen

Koponen

Arora

2019

The Journal of Steroid Biochemistry and Molecular Biology

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“…We find it likely that the present observations relate to the localization of ORP2 in the stereocilia of cochlear cells and the documented role of its mutations in autosomal dominant nonsyndromic hearing loss (11,12). Our data suggest that the function of ORP2 involves regulation of F-actin, which forms a key structural element of stereocilia (65). Consistently, mutations in DIAPH1, a physical interaction partner of ORP2 and a regulator of actin dynamics, were identified as a cause of similar nonsyndromic hearing loss (66)(67)(68).…”

Section: Discussionsupporting

confidence: 54%

Analysis of ORP2‐knockout hepatocytes uncovers a novel function in actin cytoskeletal regulation

et al. 2018

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ORP2 is implicated in cholesterol transport, triglyceride metabolism, and adrenocortical steroid hormone production. We addressed ORP2 function in hepatocytes by generating ORP2-knockout (KO) HuH7 cells by CRISPR-Cas9 gene editing, followed by analyses of transcriptome, F-actin morphology, migration, adhesion, and proliferation. RNA sequencing of ORP2-KO cells revealed >2-fold changes in 579 mRNAs. The Ingenuity Pathway Analysis (IPA) uncovered alterations in the following functional categories: cellular movement, cell-cell signaling and interaction, cellular development, cellular function and maintenance, cellular growth and proliferation, and cell morphology. Many pathways in these categories involved actin cytoskeleton, cell migration, adhesion, or proliferation. Analysis of the ORP2 interactome uncovered 109 putative new partners. Their IPA analysis revealed Ras homolog A (RhoA) signaling as the most significant pathway. Interactions of ORP2 with SEPT9, MLC12, and ARHGAP12 were validated by independent assays. ORP2-KO resulted in abnormal F-actin morphology characterized by impaired capacity to form lamellipodia, migration defect, and impaired adhesion and proliferation. Rescue of the migration phenotype and generation of typical cell surface morphology required an intact ORP2 phosphoinositide binding site, suggesting that ORP2 function involves phosphoinositide binding and transport. The results point at a novel function of ORP2 as a lipid-sensing regulator of the actin cytoskeleton, with impacts on hepatocellular migration, adhesion, and proliferation.-Kentala, H., Koponen, A., Kivelä, A. M., Andrews, R., Li, C., Zhou, Y., Olkkonen, V. M. Analysis of ORP2-knockout hepatocytes uncovers a novel function in actin cytoskeletal regulation.

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“…Looking now at the role of HOMER2 in stereocilia maintenance, stereocilia are actin-based protrusions on auditory and vestibular sensory cells that are required for hearing and balance. 33 As a key regulator of dynamic actin organization, CDC42 is required for stereociliogenesis in the immature cochlea and structural differentiation of auditory supporting cells. [34][35][36] In HeLa cells, overexpression of HOMER2 suppresses CDC42 inducing the formation of filopodia-like protrusions through its CBD domain (aa202-294).…”

Section: C840_841insc Variant Affects Subcellular Localization In mentioning

confidence: 99%

Whole exome sequencing identified a second pathogenic variant in HOMER2 for autosomal dominant non‐syndromic deafness

Wang

et al. 2018

Clinical Genetics

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Hearing loss is one of the most common sensory disorders worldwide, and about half of all occurrences are attributable to genetic factors. Here, we have identified a novel pathogenic variant in HOMER2 in a Chinese family with autosomal dominant, non-syndromic hearing loss. This is the second family reported globally with hearing loss caused by a variant in HOMER2. The pathogenic variant c.840_841insC in HOMER2 (NM_199330), segregating with the hearing-loss phenotype in the family, leads to a premature stop codon producing a truncated protein. The coiled-coil domain in the C-terminal of HOMER2 protein is essential for protein multimerization and HOMER2-CDC42 interaction. We compared the phenotypes in the two families and found that hearing impairment in this Chinese family was more severe. Furthermore, we found that the ability of this insertion mutant type HOMER2 (HOMER2 ) to multimerize decreased more significantly than wild-type HOMER2 (HOMER2 ) and the reported c.554G>C (NM_004839) mutant HOMER2. HOMER2 protein tended to be distributed in a diffuse manner, whereas HOMER2 and the reported mutant HOMER2 tended to cluster together. Our research provides a validating second family for variants in HOMER2 causing non-syndromic sensorineural hearing loss. HOMER2 homo-/hetero-multimerization might be the first step in exerting its normal function.

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Stereocilia morphogenesis and maintenance through regulation of actin stability

Cited by 66 publications

References 87 publications

OSBP-related protein 2 (ORP2): Unraveling its functions in cellular lipid/carbohydrate metabolism, signaling and F-actin regulation

OSBP-related protein 2 (ORP2): Unraveling its functions in cellular lipid/carbohydrate metabolism, signaling and F-actin regulation

Analysis of ORP2‐knockout hepatocytes uncovers a novel function in actin cytoskeletal regulation

Whole exome sequencing identified a second pathogenic variant in HOMER2 for autosomal dominant non‐syndromic deafness

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