Oculocerebral renal syndrome of Lowe (OCRL or Lowe syndrome), a severe X-linked congenital disorder characterized by congenital cataracts and glaucoma, mental retardation and kidney dysfunction, is caused by mutations in the OCRL gene. OCRL is a phosphoinositide 5-phosphatase that interacts with small GTPases and is involved in intracellular trafficking. Despite extensive studies, it is unclear how OCRL mutations result in a myriad of phenotypes found in Lowe syndrome. Our results show that OCRL localizes to the primary cilium of retinal pigment epithelial cells, fibroblasts and kidney tubular cells. Lowe syndrome-associated mutations in OCRL result in shortened cilia and this phenotype can be rescued by the introduction of wild-type OCRL; in vivo, knockdown of ocrl in zebrafish embryos results in defective cilia formation in Kupffer vesicles and cilia-dependent phenotypes. Cumulatively, our data provide evidence for a role of OCRL in cilia maintenance and suggest the involvement of ciliary dysfunction in the manifestation of Lowe syndrome.

Lowe syndrome is a rare X-linked congenital disease that presents with congenital cataracts and glaucoma, as well as renal and cerebral dysfunction. OCRL, an inositol polyphosphate 5-phosphatase, is mutated in Lowe syndrome. We previously showed that OCRL is involved in vesicular trafficking to the primary cilium. Primary cilia are sensory organelles on the surface of eukaryotic cells that mediate mechanotransduction in the kidney, brain, and bone. However, their potential role in the trabecular meshwork (TM) in the eye, which regulates intraocular pressure, is unknown. Here, we show that TM cells, which are defective in glaucoma, have primary cilia that are critical for response to pressure changes. Primary cilia in TM cells shorten in response to fluid flow and elevated hydrostatic pressure, and promote increased transcription of TNF-α, TGF-β, and GLI1 genes. Furthermore, OCRL is found to be required for primary cilia to respond to pressure stimulation. The interaction of OCRL with transient receptor potential vanilloid 4 (TRPV4), a ciliary mechanosensory channel, suggests that OCRL may act through regulation of this channel. A novel disease-causing OCRL allele prevents TRPV4-mediated calcium signaling. In addition, TRPV4 agonist GSK 1016790A treatment reduced intraocular pressure in mice; TRPV4 knockout animals exhibited elevated intraocular pressure and shortened cilia. Thus, mechanotransduction by primary cilia in TM cells is implicated in how the eye senses pressure changes and highlights OCRL and TRPV4 as attractive therapeutic targets for the treatment of glaucoma. Implications of OCRL and TRPV4 in primary cilia function may also shed light on mechanosensation in other organ systems.

Abstract. MicroRNAs (miRNAs) have been implicated in the maintenance of the cancer stem cell (CSC) phenotype via their ability to affect expression of genes and proteins that regulate cell proliferation and/or cell death. Thus, identification of CSC-related miRNAs would provide information for a better understanding of CSCs. Here, we compared the miRNA profiles of CD133 + and CD133 -primary hepatocellular carcinoma (HCC) subpopulations and found upregulation of 5 miRNAs in CD133 -subpopulations, including hsa-miR-150, which may be involved in maintenance of the CD133 + liver CSC phenotype. We also show that miR-150 interacts with the 3'UTR of c-Myb mRNA and overexpression of miR-150 downregulates c-Myb protein levels. Furthermore, overexpression of miR-150 lead to a significant reduction of CD133 + cells, accompanied by significant inhibition of cell growth and tumorsphere formation. In addition, overexpression of miR-150 induces cell cycle arrest and apoptosis in CD133 + cells. Consistent with the outcome of cell cycle arrest and cell apoptosis, Western blotting results demonstrate that the cell cycle regulator cyclin D1 and cell survival regulator Bcl-2 are decreased in cells transfected with miR-150. Collectively, our findings demonstrate for the first time that miR-150 may be involved in liver CSC self-renewal, potentially via modulation of the downstream target c-Myb.

Lowe syndrome is a rare X-linked disorder characterized by bilateral congenital cataracts and glaucoma, mental retardation, and proximal renal tubular dysfunction. Mutations in OCRL, an inositol polyphosphate 5-phosphatase that dephosphorylates PI(4,5)P, cause Lowe syndrome. Previously we showed that OCRL localizes to the primary cilium, which has a distinct membrane phospholipid composition, but disruption of phosphoinositides in the ciliary membrane is poorly understood. Here, we demonstrate that cilia from Lowe syndrome patient fibroblasts exhibit increased levels of PI(4,5)P and decreased levels of PI4P. In particular, subcellular distribution of PI(4,5)P build-up was observed at the transition zone. Accumulation of ciliary PI(4,5)P was pronounced in mouse embryonic fibroblasts (MEFs) derived from Lowe syndrome mouse model as well as in -null MEFs, which was reversed by reintroduction of OCRL. Similarly, expression of wild-type OCRL reversed the elevated PI(4,5)P in Lowe patient cells. Accumulation of sonic hedgehog protein in response to hedgehog agonist was decreased in MEFs derived from a Lowe syndrome mouse model. Together, our findings show for the first time an abnormality in ciliary phosphoinositides of both human and mouse cell models of Lowe syndrome.

SUMMARY Mutations in human GRXCR2, which encodes a protein of undetermined function, cause hearing loss by unknown mechanisms. We found that mouse GRXCR2 localizes to the base of the stereocilia, which are actin-based mechanosensing organelles in cochlear hair cells that convert sound-induced vibrations into electrical signals. The stereocilia base also contains taperin, another protein of unknown function required for human hearing. We show that taperin and GRXCR2 form a complex and that taperin is diffused throughout the stereocilia length in Grxcr2-deficient hair cells. Stereocilia lacking GRXCR2 are longer than normal and disorganized due to the mislocalization of taperin, which could modulate the actin cytoskeleton in stereocilia. Remarkably, reducing taperin expression levels could rescue the morphological defects of stereocilia and restore the hearing of Grxcr2-deficient mice. Thus, our findings suggest that GRXCR2 is critical for the morphogenesis of stereocilia and auditory perception by restricting taperin to the stereocilia base.

Clonal hematopoiesis of indeterminate potential (CHIP) increases with age and is associated with increased risks of hematological malignancies. While TP53 mutations have been identified in CHIP, the molecular mechanisms by which mutant p53 promotes hematopoietic stem and progenitor cell (HSPC) expansion are largely unknown. Here we discover that mutant p53 confers a competitive advantage to HSPCs following transplantation and promotes HSPC expansion after radiation-induced stress. Mechanistically, mutant p53 interacts with EZH2 and enhances its association with the chromatin, thereby increasing the levels of H3K27me3 in genes regulating HSPC self-renewal and differentiation. Furthermore, genetic and pharmacological inhibition of EZH2 decreases the repopulating potential of p53 mutant HSPCs. Thus, we uncover an epigenetic mechanism by which mutant p53 drives clonal hematopoiesis. Our work will likely establish epigenetic regulator EZH2 as a novel therapeutic target for preventing CHIP progression and treating hematological malignancies with TP53 mutations.

Inositol phosphatases are important regulators of cell signaling, polarity, and vesicular trafficking. Mutations in OCRL, an inositol polyphosphate 5-phosphatase, result in Oculocerebrorenal syndrome of Lowe, an X-linked recessive disorder that presents with congenital cataracts, glaucoma, renal dysfunction and mental retardation. INPP5B is a paralog of OCRL and shares similar structural domains. The roles of OCRL and INPP5B in the development of cataracts and glaucoma are not understood. Using ocular tissues, this study finds low levels of INPP5B present in human trabecular meshwork but high levels in murine trabecular meshwork. In contrast, OCRL is localized in the trabecular meshwork and Schlemm’s canal endothelial cells in both human and murine eyes. In cultured human retinal pigmented epithelial cells, INPP5B was observed in the primary cilia. A functional role for INPP5B is revealed by defects in cilia formation in cells with silenced expression of INPP5B. This is further supported by the defective cilia formation in zebrafish Kupffer’s vesicles and in cilia-dependent melanosome transport assays in inpp5b morphants. Taken together, this study indicates that OCRL and INPP5B are differentially expressed in the human and murine eyes, and play compensatory roles in cilia development.

c Oncogene-induced senescence is a stable proliferative arrest that serves as a tumor-suppressing defense mechanism. p38 mitogen-activated protein kinase (MAPK) has been implicated in oncogene-induced senescence and tumor suppression. However, the specific role of each of the four p38 isoforms in oncogene-induced senescence is not fully understood. Here, we demonstrate that p38␦ mediates oncogene-induced senescence through a p53-and p16INK4A -independent mechanism. Instead, evidence suggests a link between p38␦ and the DNA damage pathways. Moreover, we have discovered a novel mechanism that enhances the expression of p38␦ during senescence. In this mechanism, oncogenic ras induces the Raf-1-MEK-extracellular signal-regulated kinase (ERK) pathway, which, in turn, activates the AP-1 and Ets transcription factors that are bound to the p38␦ promoter, leading to increased transcription of p38␦. These findings indicate that induction of the prosenescent function of p38␦ by oncogenic ras is achieved through 2 mechanisms, transcriptional activation by the Raf-1-MEK-ERK-AP-1/Ets pathway, which increases the cellular concentration of the p38␦ protein, and posttranslational modification by MKK3/6, which stimulates the enzymatic activity of p38␦. In addition, these studies identify the AP-1 and Ets transcription factors as novel signaling components in the senescence-inducing pathway.A lthough aberrant activation of Ras is associated with human tumors, activated ras in early-passage primary human and rodent cells causes permanent growth arrest known as oncogeneinduced senescence (OIS) (1-4). Like apoptosis, OIS is a tumorsuppressing defense mechanism, the disruption of which leads to tumorigenesis (5-10).Multiple signaling intermediates have been identified that play critical roles in the pathways mediating oncogene-induced senescence. The ability of ras to induce senescence depends on activation of the Raf-MEK-extracellular signal-regulated kinase (ERK) mitogen-activated protein kinase (MAPK) pathway (4, 11) and is accompanied by upregulation of p16 INK4A , p53, p14/p19 ARF , and p21 WAF1 (3, 12) and silencing of E2F target genes (13). We previously showed that ras-induced senescence relies on activation of p38, a MAPK previously identified as a major mediator of inflammation and stress responses (14). p38 and its upstream MAPK kinases MKK3 and MKK6 are activated by oncogenic ras as a result of persistent MEK/ERK activation in senescent cells. Constitutive activation of p38 causes premature senescence, whereas inhibition of p38 prevents ras-induced senescence (14). Consistent with the important role of p38 in oncogene-induced senescence and tumor suppression, targeted deletion of p38␣ or PRAK, a downstream substrate kinase of p38, accelerates cancer development in mouse models (10,15,16).p38 MAK has four mammalian isoforms, ␣, ␤, ␦, and ␥, which are encoded by different genes and differ in tissue-specific expression, substrate spectrum, and affinity for upstream MAPK activators (17-23). Our previous data indicated that p38...