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Infection and Immunity, February 2000, p. 861-870, Vol. 68, No. 2
Channing Laboratory1
and Division of Hematology,2
Department of Medicine, Brigham and Women's Hospital, and
Department of Biological Chemistry and Molecular
Pharmacology,3 Harvard Medical School,
Boston, Massachusetts 02115
Received 9 August 1999/Returned for modification 8 October
1999/Accepted 21 October 1999
The cystic fibrosis transmembrane conductance regulator (CFTR) is a
chloride ion channel that also serves as a receptor for entry of
Pseudomonas aeruginosa and Salmonella enterica
serovar Typhi into epithelial cells. To evaluate heterogeneity in CFTR protein expression in cultured cells and the effect of heterogeneity on
internalization of different P. aeruginosa and serovar
Typhi strains, we used two-color flow cytometry and confocal laser
microscopy to study bacterial uptake by Madin-Darby canine kidney
(MDCK) type I epithelial cells stably expressing a green fluorescent protein (GFP)-CFTR fusion construct (MDCK-GFP-CFTR cells). We found a
strong correlation between cell size and GFP-CFTR protein expression,
with 60 to 70% of cells expressing low levels of GFP-CFTR protein, 20 to 30% expressing intermediate levels, and <10% expressing high
levels. The cells were sorted into low-, intermediate-, or high-level
producers of CFTR protein; in vitro growth of each sorted population
yielded the same distribution of CFTR protein expression as that in the
original population. Cells expressing either low or high levels of CFTR
protein internalized bacteria poorly; maximal bacterial uptake occurred
in the cells expressing intermediate levels of CFTR protein. Treatment
of MDCK cells with sodium butyrate markedly enhanced the production of
CFTR protein without increasing cell size; butyrate treatment also
increased the proportion of cells with internalized bacteria. However,
there were fewer bacteria per butyrate-treated cell and, for P. aeruginosa, there was an overall decrease in the total level of
bacterial uptake. The most highly ingested bacterial strains were
internalized by fewer total MDCK-GFP-CFTR cells, indicating
preferential bacterial uptake by a minority of epithelial cells within
a given culture. Confocal fluorescence microscopy showed that P. aeruginosa and serovar Typhi induced cytoplasmic accumulation of
CFTR protein close to the plasma membrane where the bacteria were
adherent. These results show that within a population of MDCK-GFP-CFTR
cells, there are cells with markedly different abilities to ingest
bacteria via CFTR, the majority of the P. aeruginosa and
serovar Typhi cells are ingested by the one-fourth to one-third of the
cells that exhibit an intermediate size and level of CFTR protein
expression, and overexpression of the CFTR receptor does not increase
total bacterial uptake but rather allows more epithelial cells to
ingest fewer total bacteria.
0019-9567/00/$04.00+0
Copyright © 2000, American Society for Microbiology. All rights reserved.
Impact of Heterogeneity within Cultured Cells on Bacterial
Invasion: Analysis of Pseudomonas aeruginosa and
Salmonella enterica Serovar Typhi Entry into MDCK cells by
Using a Green Fluorescent Protein-Labelled Cystic Fibrosis
Transmembrane Conductance Regulator Receptor

*
Corresponding author. Mailing address: Channing
Laboratory, 181 Longwood Ave., Boston, MA 02115. Phone: (617) 525-2269. Fax: (617) 731-1541. E-mail: gpier{at}channing.harvard.edu.
Present address: Faculty of Pharmacy, Dept. of Pharmaceutical
Microbiology, Istanbul University, 34452 Beyazit-Istanbul, Turkey.
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