Browsing by Author "Mao, Yuntao Steve"
Now showing 1 - 2 of 2
- Results Per Page
- Sort Options
Item Functions of Phosphatidylinositol 4-Phosphate 5 Kinases in Actin Cytoskeletal Regulation During Phagocytosis(2009-06-18) Mao, Yuntao Steve; Yin, Helen L.Phosphatidylinositol (4,5)-bisphosphate (PIP2) is a crucial signaling phosphoinositide at the plasma membrane (PM) which mediates a variety of biochemical activities and cellular functions. It is primarily synthesized by type I phosphatidylinositol 4-phosphate 5-kinases (PIP5Ks) through the phosphorylation on the D-5 position of the inositol ring of phatidylinositol 4-phosphate [PI(4)P]. Mammals have three PIP5K isoforms named a, b, and g (human isoform designation) which have a highly conserved central kinase homology domain and divergent amino and carboxyl terminal extensions. There is now extensive evidence suggesting that PIP5Ks have unique functions and regulations in many cellular processes which provide the key to understand how functionally, and possibly physically, segregated PIP2 pools are generated. The actin cytoskeleton is dynamically remodeled during Fcg receptor (FcgR)-mediated phagocytosis in a PIP2-dependent manner. I investigated the role of PIP5Kg and a isoforms, which synthesize PIP2, during phagocytosis. PIP5Kg-/- bone marrow-derived macrophages (BMM) have a highly polymerized actin cytoskeleton and are defective in attachment to IgG-opsonized particles and FcgR clustering. Delivery of exogenous PIP2 rescued these defects. PIP5Kg knockout BMM also have more RhoA and less Rac1 activation and pharmacological manipulations establish that they contribute to the abnormal phenotype. Likewise, depletion of PIP5Kg by RNA interference (RNAi) inhibits particle attachment. In contrast, PIP5Ka knockout or silencing has no effect on attachment but inhibits ingestion by decreasing Wiskott-Aldrich syndrome protein (WASP) activation and hence actin polymerization, in the nascent phagocytic cup. In addition, PIP5Kg but not a is transiently activated by spleen tyrosine kinase (Syk)-mediated phosphorylation. I propose that PIP5Kg acts upstream of Rac/Rho and that the differential regulation of PIP5Kg and a allows them to work in tandem to modulate the actin cytoskeleton during the attachment and ingestion phases of phagocytosis.Item Herp Reduces ER Calcium Content by Proteasomal Degradation of SERCA(2007-08-08) Mao, Yuntao Steve; Kodadek, Thomas J.Herp, an endoplasmic reticulum (ER) stress inducible protein, reduces ER Ca2+ content in neurons and prevents their apoptosis. An understanding of the mechanism by which Herp decreases ER Ca2+ content requires studies of Herp interacting proteins, which could be SERCA and the proteasome. Herp may recruit the proteasome from the cytosol to the ER membrane, thereby facilitating the ER associated degradation (ERAD) of SERCA. The proteasome recruitment and the subsequent degradation of SERCA reduce ER lumenal Ca2+ concentration and the Ca2+ release during ER stress which counteracts the activation of apoptosis. This proposal describes how to determine the mechanism through which Herp reduces ER Ca2+ content, how to test the proteasomal degradation of SERCA, how to illustrate the proteasome recruitment to the ER membrane, and how to demonstrate the interaction between Herp and SERCA. The work will provide a new regulatory link between ER stress and Ca2+ homeostasis. In addition, studies of the proteasomal degradation of SERCA will broaden our present understanding of the regulation of SERCA. Since dysregulation of Ca2+ homeostasis has been implicated in the pathophysiology of several neurodegenerative diseases like Alzheimer's and Huntington's, research focused on Herp may lead to insights regarding therapies for those.