@article {716,
	title = {Caveolin-2 associates with intracellular chlamydial inclusions independently of caveolin-1.},
	journal = {BMC Infect Dis},
	volume = {4},
	year = {2004},
	month = {2004 Jul 22},
	pages = {23},
	abstract = {BACKGROUND: Lipid raft domains form in plasma membranes of eukaryotic cells by the tight packing of glycosphingolipids and cholesterol. Caveolae are invaginated structures that form in lipid raft domains when the protein caveolin-1 is expressed. The Chlamydiaceae are obligate intracellular bacterial pathogens that replicate entirely within inclusions that develop from the phagocytic vacuoles in which they enter. We recently found that host cell caveolin-1 is associated with the intracellular vacuoles and inclusions of some chlamydial strains and species, and that entry of those strains depends on intact lipid raft domains. Caveolin-2 is another member of the caveolin family of proteins that is present in caveolae, but of unknown function.

METHODS: We utilized a caveolin-1 negative/caveolin-2 positive FRT cell line and laser confocal immunofluorescence techniques to visualize the colocalization of caveolin-2 with the chlamydial inclusions.

RESULTS: We show here that in infected HeLa cells, caveolin-2, as well as caveolin-1, colocalizes with inclusions of C. pneumoniae (Cp), C. caviae (GPIC), and C. trachomatis serovars E, F and K. In addition, caveolin-2 also associates with C. trachomatis serovars A, B and C, although caveolin-1 did not colocalize with these organisms. Moreover, caveolin-2 appears to be specifically, or indirectly, associated with the pathogens at the inclusion membranes. Using caveolin-1 deficient FRT cells, we show that although caveolin-2 normally is not transported out of the Golgi in the absence of caveolin-1, it nevertheless colocalizes with chlamydial inclusions in these cells. However, our results also show that caveolin-2 did not colocalize with UV-irradiated Chlamydia in FRT cells, suggesting that in these caveolin-1 negative cells, pathogen viability and very likely pathogen gene expression are necessary for the acquisition of caveolin-2 from the Golgi.

CONCLUSION: Caveolin-2 associates with the chlamydial inclusion independently of caveolin-1. The function of caveolin-2, either in the uninfected cell or in the chlamydial developmental cycle, remains to be elucidated. Nevertheless, this second caveolin protein can now be added to the small number of host proteins that are associated with the inclusions of this obligate intracellular pathogen.},
	keywords = {Animals, Blotting, Western, Caveolin 1, Caveolin 2, Caveolins, Cells, Cultured, Chlamydia, Fluorescent Antibody Technique, Golgi Apparatus, Guinea Pigs, HeLa Cells, Humans, Mice, Microscopy, Confocal, Rats, Vacuoles, Virulence},
	issn = {1471-2334},
	doi = {10.1186/1471-2334-4-23},
	author = {Webley, Wilmore C and Norkin, Leonard C and Stuart, Elizabeth S}
}
@article {715,
	title = {Lipid rafts, caveolae, caveolin-1, and entry by Chlamydiae into host cells.},
	journal = {Exp Cell Res},
	volume = {287},
	year = {2003},
	month = {2003 Jul 1},
	pages = {67-78},
	abstract = {Obligate intracellular bacterial pathogens of the genus Chlamydia are reported to enter host cells by both clathrin-dependent and clathrin-independent processes. C. trachomatis serovar K recently was shown to enter cells via caveolae-like lipid raft domains. We asked here how widespread raft-mediated entry might be among the Chlamydia. We show that C. pneumoniae, an important cause of respiratory infections in humans that additionally is associated with cardiovascular disease, and C. psittaci, an important pathogen in domestic mammals and birds that also infects humans, each enter host cells via cholesterol-rich lipid raft microdomains. Further, we show that C. trachomatis serovars E and F also use these domains to enter host cells. The involvement of these membrane domains in the entry of these organisms was indicated by the sensitivity of their entry to the raft-disrupting agents Nystatin and filipin, and by their intracellular association with caveolin-1, a 22-kDa protein associated with the formation of caveolae in rafts. In contrast, caveolin-marked lipid raft domains do not mediate entry of C. trachomatis serovars A, 36B, and C, nor of LGV serovar L2 and MoPn. Finally, we show that entry of each of these chlamydial strains is independent of cellular expression of caveolin-1. Thus, entry via the Nystatin and filipin-sensitive pathway is dependent on lipid rafts containing cholesterol, rather than invaginated caveolae per se.},
	keywords = {Anti-Bacterial Agents, Caveolae, Caveolin 1, Caveolins, Chlamydia, Chlamydia Infections, Cholesterol, Dose-Response Relationship, Drug, Eukaryotic Cells, Filipin, HeLa Cells, Host-Parasite Interactions, Humans, Membrane Microdomains, Nystatin, Species Specificity},
	issn = {0014-4827},
	author = {Stuart, Elizabeth S and Webley, Wilmore C and Norkin, Leonard C}
}
@article {712,
	title = {Association of caveolin with Chlamydia trachomatis inclusions at early and late stages of infection.},
	journal = {Exp Cell Res},
	volume = {266},
	year = {2001},
	month = {2001 Jun 10},
	pages = {229-38},
	abstract = {The mechanism by which the intracellular bacterial pathogen Chlamydia trachomatis enters eukaryotic cells is poorly understood. There are conflicting reports of entry occurring by clathrin-dependent and clathrin-independent processes. We report here that C. trachomatis serovar K enters HEp-2 and HeLa 229 epithelial cells and J-774A.1 mouse macrophage/monocyte cells via caveolin-containing sphingolipid and cholesterol-enriched raft microdomains in the host cell plasma membranes. First, filipin and nystatin, drugs that specifically disrupt raft function by cholesterol chelation, each impaired entry of C. trachomatis serovar K. In control experiments, filipin did not impair entry of the same organism by an antibody-mediated opsonic process, nor did it impair entry of BSA-coated microspheres. Second, the chlamydia-containing endocytic vesicles specifically reacted with antisera against the caveolae marker protein caveolin. These vesicles are known to become the inclusions in which parasite replication occurs. They avoid fusion with lysosomes and instead traffic to the Golgi region, where they intercept Golgi-derived vesicles that recycle sphingolipids and cholesterol to the plasma membrane. We also report that late-stage C. trachomatis inclusions continue to display high levels of caveolin, which they likely acquire from the exocytic Golgi vesicles. We suggest that the atypical raft-mediated entry process may have important consequences for the host-pathogen interaction well after entry has occurred. These consequences include enabling the chlamydial vesicle to avoid acidification and fusion with lysosomes, to traffic to the Golgi region, and to intercept sphingolipid-containing vesicles from the Golgi.},
	keywords = {Animals, Caveolin 1, Caveolins, Cell Line, Chlamydia trachomatis, Epithelium, Filipin, HeLa Cells, Humans, Inclusion Bodies, Macrophages, Membrane Microdomains, Mice, Nystatin, Phagosomes},
	issn = {0014-4827},
	doi = {10.1006/excr.2001.5202},
	author = {Norkin, L C and Wolfrom, S A and Stuart, E S}
}
@article {710,
	title = {Extracellular simian virus 40 transmits a signal that promotes virus enclosure within caveolae.},
	journal = {Exp Cell Res},
	volume = {246},
	year = {1999},
	month = {1999 Jan 10},
	pages = {83-90},
	abstract = {It was reported earlier that entry of simian virus 40 (SV40) into cells is promoted by a signal transmitted by the virus from the cell surface and that SV40 enters cells through caveolae. It is shown here that bound SV40 begins to partition into a caveolae-enriched Triton X-100-insoluble membrane fraction at 30 min postadsorption. Maximal levels of SV40 were seen in that fraction at 1 h. The sterol-binding agent nystatin, which selectively disrupts the cholesterol-enriched caveolae-containing membrane microdomain, selectively blocked the SV40-induced signal. This implies that the SV40 signal is transmitted from that membrane microdomain. The tyrosine kinase inhibitor genistein, which was earlier shown to block the SV40-induced signal and infectious entry, did not block the partitioning of SV40 into the detergent-insoluble membrane fraction. This shows that the signal is not required for the translocation of SV40 to the detergent-insoluble membrane and is consistent with the finding that the signal is likely transmitted from that membrane microdomain. However, electron microscopy of the Triton X-100-insoluble membrane fraction showed that genistein caused SV40 particles to accumulate at the annuli or mouths of the caveolae. In contrast, most SV40 particles were found enclosed within caveolae in parallel samples from untreated control cells. Together, these results imply that SV40 initially binds to flat detergent-soluble membrane. The virus then translocates to a caveolae-containing detergent-insoluble membrane microdomain. From the flat portion of that membrane microdomain the virus induces a signal which promotes its entry into caveolae.},
	keywords = {Animals, Blotting, Northern, Blotting, Western, Caveolin 1, Caveolins, Cell Line, Cell Membrane, Cercopithecus aethiops, Cholesterol, Endocytosis, Genes, myc, Genistein, Kidney, Membrane Proteins, Microscopy, Electron, Nystatin, Octoxynol, Signal Transduction, Simian virus 40, Solubility},
	issn = {0014-4827},
	doi = {10.1006/excr.1998.4301},
	author = {Chen, Y and Norkin, L C}
}
@article {709,
	title = {MHC class I molecules are enriched in caveolae but do not enter with simian virus 40.},
	journal = {J Gen Virol},
	volume = {79 ( Pt 6)},
	year = {1998},
	month = {1998 Jun},
	pages = {1469-77},
	abstract = {Simian virus 40 (SV40) binds to MHC class I molecules anywhere on the cell surface and then enters through caveolae. The fate of class I molecules after SV40 binding is not known. Sensitivity of 125I-surface-labelled class I molecules to papain cleavage was used to distinguish internalized class I molecules from class I molecules remaining at the cell surface. Whereas the caveolae-enriched membrane microdomain was found to also be enriched for class I molecules, no internalized papain-resistant 125I-surface-labelled class I molecules could be detected at any time in either control cells or in cells preadsorbed with saturating amounts of SV40. Instead, 125I-surface-labelled class I molecules, as well as preadsorbed 125I-labelled anti-class I antibodies, accumulated in the medium, coincident with the turnover of class I molecules at the cell surface. The class I heavy chains that accumulated in the medium were truncated and their release was specifically prevented by the metalloprotease inhibitor 1,10-phenanthroline. Thus, whereas class I molecules mediate SV40 binding, they do not appear to mediate SV40 entry.},
	keywords = {Animals, Caveolin 1, Caveolins, Cell Line, Cell Membrane, Cercopithecus aethiops, Histocompatibility Antigens Class I, Humans, Membrane Proteins, Simian virus 40},
	issn = {0022-1317},
	author = {Anderson, H A and Chen, Y and Norkin, L C}
}
@article {708,
	title = {Bound simian virus 40 translocates to caveolin-enriched membrane domains, and its entry is inhibited by drugs that selectively disrupt caveolae.},
	journal = {Mol Biol Cell},
	volume = {7},
	year = {1996},
	month = {1996 Nov},
	pages = {1825-34},
	abstract = {Simian virus 40 (SV40) entry leading to infection occurred only after the virus was at the cell surface for 1.5 to 2 h. SV40 infectious entry was not sensitive to cytosol acidification, a treatment that blocks endocytosis via clathrin-coated vesicles. Instead, SV40 infectious entry was blocked by treating cells with the phorbol ester PMA or nystatin, which selectively disrupts caveolae. In control experiments, transferrin internalization was sensitive to cytosol acidification but was not sensitive to PMA or nystatin. Also, absorbed transferrin entered cells within minutes. Finally, bound SV40 translocated to caveolin-enriched membrane complexes isolated by a Triton X-100 insolubility protocol. Treatment with nystatin did not impair SV40 binding but did block the partitioning of virus into the caveolin-enriched complexes.},
	keywords = {Animals, Antigens, Polyomavirus Transforming, Caveolin 1, Caveolins, Cell Line, Cell Membrane, Coated Vesicles, Endocytosis, Membrane Proteins, Nystatin, Organelles, Simian virus 40, Tetradecanoylphorbol Acetate},
	issn = {1059-1524},
	author = {Anderson, H A and Chen, Y and Norkin, L C}
}
