title: Localization of intracellular Ca2+ stores in HeLa cells during infection with Chlamydia trachomatis.
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.
authors.affiliation: Divisions of Medical Microbiology and Clinical Microbiology, Faculty of Health Sciences, Linköping University, S-581 85 Linköping, Sweden. meytham.majeed@mme.liu.se
authors.forename: M
authors.initials: M
authors.lastname: Majeed
authors.forename: K H
authors.initials: KH
authors.lastname: Krause
authors.forename: R A
authors.initials: RA
authors.lastname: Clark
authors.forename: E
authors.initials: E
authors.lastname: Kihlström
authors.forename: O
authors.initials: O
authors.lastname: Stendahl
mesh_terms: D000255:Adenosine Triphosphate / Q000494:pharmacology; D000918:Antibody Specificity; D002118:Calcium / Q000378:metabolism*; D015220:Calcium Channels / Q000276:immunology / Q000378:metabolism; D002135:Calcium-Binding Proteins / Q000276:immunology / Q000378:metabolism; D000252:Calcium-Transporting ATPases / Q000037:antagonists & inhibitors / Q000276:immunology / Q000378:metabolism; D037282:Calreticulin; D002690:Chlamydia Infections / Q000378:metabolism* / Q000382:microbiology; D002692:Chlamydia trachomatis / Q000378:metabolism / Q000472:pathogenicity; D002701:Chloramphenicol / Q000494:pharmacology; D004640:Emetine / Q000494:pharmacology; D004705:Endocytosis / Q000502:physiology; D005455:Fluorescent Antibody Technique; D006367:HeLa Cells; D006801:Humans; D053496:Inositol 1,4,5-Trisphosphate Receptors; D007424:Intracellular Fluid / Q000378:metabolism*; D018832:Molecular Chaperones / Q000276:immunology / Q000378:metabolism; D018160:Receptors, Cytoplasmic and Nuclear / Q000276:immunology / Q000378:metabolism; D012261:Ribonucleoproteins / Q000276:immunology / Q000378:metabolism; D012519:Sarcoplasmic Reticulum / Q000201:enzymology; D019284:Thapsigargin / Q000494:pharmacology; D013997:Time Factors
chemical_list: D015220:Calcium Channels; D002135:Calcium-Binding Proteins; D037282:Calreticulin; C506926:ITPR1 protein, human; C506927:ITPR2 protein, human; D053496:Inositol 1,4,5-Trisphosphate Receptors; D018832:Molecular Chaperones; D018160:Receptors, Cytoplasmic and Nuclear; D012261:Ribonucleoproteins; D002701:Chloramphenicol; D019284:Thapsigargin; D000255:Adenosine Triphosphate; D000252:Calcium-Transporting ATPases; D002118:Calcium; D004640:Emetine