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Localization of intracellular Ca2+ stores in HeLa cells during infection with Chlamydia trachomatis

Majeed, M.
Clark, R. A.
Kihlstrom, E.
Stendahl, O.
Published in Journal of Cell Science. 1999, vol. 112, no. 1, p. 35-44
Abstract Chlamydia trachomatis elementary bodies (EBs) enter epithelial cells within membrane-bound endosomes that aggregate with each other in a calcium-regulated process, but avoid fusion with lysosomes. Annexin III but not I translocates to chlamydial aggregates and inclusions. In this study, we localize the intracellular Ca2+ stores during the course of infection by analyzing the distribution of three intracellular Ca2+ store proteins: calreticulin, type-1 inositol-1,4, 5-trisphosphate receptor (IP3-R), and Sarcoplasmic/Endoplasmic Reticulum Ca2+ ATPase type 2 (SERCA2) in HeLa cells infected with C. trachomatis serovar L2. In uninfected cells, immunofluorescence staining of the proteins showed a fine granular distributed pattern for all three proteins. After infection with C. trachomatis, calreticulin was found at the periphery of chlamydial aggregates and inclusions from 3 to 48 hours post-infection. In infected cells, SERCA2 was intimately associated with chlamydial inclusions after 3 and 24 hours, but not after 48 hours. Moreover, IP3-R was translocated to and colocalized with EB aggregates and chlamydial inclusions and had a distribution very similar to that of SERCA 2. After 24 hours incubation with chlamydiae, there was a local accumulation of [Ca2+]i (105+/-17 nM) in the proximity of chlamydial inclusions, compared to 50+/-13 nM in other parts of the cell cytoplasm. In the absence of extracellular Ca2+, this local accumulation of Ca2+ increased to 295+/-50 nM after adding 50 microM ATP, and to a similar extent after adding 100 nM thapsigargin (Tg). These data indicate that during infection of HeLa cells with chlamydiae, intracellular Ca2+ stores are redistributed, causing local accumulation of Ca2+ in the vicinity of chlamydial inclusions. These changes may trigger the association of certain proteins such as annexins with chlamydia-containing vesicles, and thereby regulation of membrane-membrane interaction during endosome aggregation and inclusion formation.
Keywords Adenosine Triphosphate/pharmacologyAntibody SpecificityCalcium/ metabolismCalcium Channels/immunology/metabolismCalcium-Binding Proteins/immunology/metabolismCalcium-Transporting ATPases/antagonists & inhibitors/immunology/metabolismCalreticulinChlamydia Infections/ metabolism/microbiologyChlamydia trachomatis/metabolism/pathogenicityChloramphenicol/pharmacologyEmetine/pharmacologyEndocytosis/physiologyFluorescent Antibody TechniqueHela CellsHumansInositol 1,4,5-Trisphosphate ReceptorsIntracellular Fluid/ metabolismMolecular Chaperones/immunology/metabolismReceptors, Cytoplasmic and Nuclear/immunology/metabolismRibonucleoproteins/immunology/metabolismSarcoplasmic Reticulum/enzymologyThapsigargin/pharmacologyTime Factors
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PMID: 9841902
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