Rapid turnover rate of phosphoinositides at the front of migrating MDCK cells.
ABSTRACT Phosphoinositides (PtdInss) play key roles in cell polarization and motility. With a series of biosensors based on Förster resonance energy transfer, we examined the distribution and metabolism of PtdInss and diacylglycerol (DAG) in stochastically migrating Madin-Darby canine kidney (MDCK) cells. The concentrations of phosphatidylinositol (4,5)-bisphosphate, phosphatidylinositol (3,4,5)-trisphosphate (PIP(3)), phosphatidylinositol (3,4)-bisphosphate, and DAG were higher at the plasma membrane in the front of the cell than at the plasma membrane of the rear of the cell. The difference in the concentrations of PtdInss was estimated to be less than twofold between the front and rear of the migrating MDCK cells. To decode the spatial activities of PtdIns metabolic enzymes from the obtained concentration maps of PtdInss, we developed a one-dimensional reaction diffusion model of PtdIns metabolism. In this model, the activities of phosphatidylinositol monophosphate 5-kinase, phosphatidylinositol 3-kinase, phospholipase C, and PIP(3) 5-phosphatases were higher at the plasma membrane of the front than at the plasma membrane of the rear of the cell. This result suggests that, although the difference in the steady-state level of PtdInss is less than twofold, PtdInss were more rapidly turned over at the front than the rear of the migrating MDCK cells.
Article: An essential role for the SHIP2-dependent negative feedback loop in neuritogenesis of nerve growth factor-stimulated PC12 cells.[show abstract] [hide abstract]
ABSTRACT: The local accumulation of phosphatidylinositol (3,4,5) trisphosphate (PIP(3)) and resulting activation of Rac1/Cdc42 play a critical role in nerve growth factor (NGF)-induced neurite outgrowth. To further explore the mechanism, we visualized PIP(3), phosphatidylinositol (3,4) bisphosphate, and Rac1/Cdc42 activities by fluorescence resonance energy transfer (FRET) imaging in NGF-stimulated PC12 cells. Based on the obtained FRET images, and with the help of in silico kinetic reaction model, we predicted that PI-5-phosphatase negatively regulates PIP(3) upon NGF stimulation. In agreement with this model, depletion of Src homology 2 domain-containing inositol polyphosphate 5-phosphatase 2 (SHIP2) markedly potentiated NGF-induced Rac1/Cdc42 activation and PIP(3) accumulation and considerably increased the number and the length of neurites in phosphate and tensin homologue-depleted PC12 cells. Further refinement of the computational model predicted Rac1 regulation of PI3-kinase and SHIP2, which was also validated experimentally. We propose that the SHIP2-mediated negative feedback on PIP(3) coordinately works with the PI3-kinase-mediated positive feedback to form an initial protrusive pattern and, later, to punctuate the PIP(3) accumulation to maintain proper neurite outgrowth.The Journal of Cell Biology 07/2007; 177(5):817-27. · 10.26 Impact Factor
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ABSTRACT: The incidence of lymphoproliferative disease is significantly higher in individuals who have congenital, acquired, or iatrogenically induced immunodeficiency. The immunodeficiency-associated lymphoproliferative disorders are clinically and pathologically heterogeneous, are of variable clonal composition, and vary according to the immunodeficiency syndrome. Nonetheless, they share several features, including frequent origination in or involvement of extranodal sites, diffuse aggressive histology, B-cell lineage derivation, association with the Epstein-Barr virus (EBV), and, often, rapid clinical progression. Reactive and atypical lymphoid hyperplasias and malignant lymphomas occur in association with congenital (primary) immunodeficiency. Post-transplantation lymphoproliferative disorders are often comprised of a polymorphic cell population, making it difficult to identify their benign or malignant nature by histopathologic criteria alone. Recent studies suggest that they are divisible into plasmacytic hyperplasias, polymorphic lymphoproliferative disorders, and malignant lymphomas. The plasmacytic hyperplasias are polyclonal and generally regress spontaneously following withdrawal of immunosuppression. The malignant lymphomas are monoclonal, possess a variety of genetic alterations, and generally progress despite aggressive therapy. The polymorphic lymphoproliferative disorders are also monoclonal but display variable clinical behavior, their progression apparently correlating with bcl-6 gene mutation. Non-Hodgkin's lymphoma (NHL) is the second most common AIDS-related neoplasm and an AIDS-defining illness. AIDS-related NHLs are divisible by anatomic site of origin into systemic (nodal/extra nodal), primary central nervous system, and body cavity-based (primary effusion) lymphomas; and by histopathology into Burkitt's and Burkitt's-like lymphoma, large cell lymphoma, and large cell immunoblastic (plasmacytoid) lymphoma More than 90% are monoclonal B-cell neoplasms. The primary effusion lymphomas contain the Kaposi's sarcoma-associated herpesvirus. Multiple molecular pathways appear to operate in AIDS lymphomagenesis and some may be preferentially associated with specific histopathologic categories or anatomic sites of origin. In conclusion, the immunodeficiency-associated lymphoproliferative disorders often represent a significant diagnostic problem requiring correlative analysis of the clinical behavior of the patient with the histopathology, immunophenotype, clonal composition, viral content, and genetic alterations of the lymphoproliferative disorder. They also represent an important biological model for studying the development and progression of lymphoid neoplasiaModern Pathology 03/1999; 12(2):200-17. · 4.79 Impact Factor