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Analysis of occludin trafficking, demonstrating continuous endocytosis, degradation, recycling and biosynthetic secretory trafficking.

ABSTRACT: Tight junctions (TJs) link adjacent cells and are critical for maintenance of apical-basolateral polarity in epithelial monolayers. The TJ protein occludin functions in disparate processes, including wound healing and Hepatitis C Virus infection. Little is known about steady-state occludin trafficking into and out of the plasma membrane. Therefore, we determined the mechanisms responsible for occludin turnover in confluent Madin-Darby canine kidney (MDCK) epithelial monolayers. Using various biotin-based trafficking assays we observed continuous and rapid endocytosis of plasma membrane localised occludin (the majority internalised within 30 minutes). By 120 minutes a significant reduction in internalised occludin was observed. Inhibition of lysosomal function attenuated the reduction in occludin signal post-endocytosis and promoted co-localisation with the late endocytic system. Using a similar method we demonstrated that ?20% of internalised occludin was transported back to the cell surface. Consistent with these findings, significant co-localisation between internalised occludin and recycling endosomal compartments was observed. We then quantified the extent to which occludin synthesis and transport to the plasma membrane contributes to plasma membrane occludin homeostasis, identifying inhibition of protein synthesis led to decreased plasma membrane localised occludin. Significant co-localisation between occludin and the biosynthetic secretory pathway was demonstrated. Thus, under steady-state conditions occludin undergoes turnover via a continuous cycle of endocytosis, recycling and degradation, with degradation compensated for by biosynthetic exocytic trafficking. We developed a mathematical model to describe the endocytosis, recycling and degradation of occludin, utilising experimental data to provide quantitative estimates for the rates of these processes.

SUBMITTER: Fletcher SJ

PROVIDER: S-EPMC4244031 | biostudies-literature | 2014

REPOSITORIES: biostudies-literature

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Analysis of occludin trafficking, demonstrating continuous endocytosis, degradation, recycling and biosynthetic secretory trafficking.

Fletcher Sarah J SJ Iqbal Mudassar M Jabbari Sara S Stekel Dov D Rappoport Joshua Z JZ

PloS one 20141125 11

Tight junctions (TJs) link adjacent cells and are critical for maintenance of apical-basolateral polarity in epithelial monolayers. The TJ protein occludin functions in disparate processes, including wound healing and Hepatitis C Virus infection. Little is known about steady-state occludin trafficking into and out of the plasma membrane. Therefore, we determined the mechanisms responsible for occludin turnover in confluent Madin-Darby canine kidney (MDCK) epithelial monolayers. Using various bio ...[more]

PMID: 25422932

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Project description:The chemokine receptor CCR5 is a cofactor for the entry of R5 tropic strains of human immunodeficiency viruses (HIV)-1 and -2 and simian immunodeficiency virus. Cells susceptible to infection by these viruses can be protected by treatment with the CCR5 ligands regulated on activation, normal T cell expressed and secreted (RANTES), MIP-1alpha, and MIP-1beta. A major component of the mechanism through which chemokines protect cells from HIV infection is by inducing endocytosis of the chemokine receptor. Aminooxypentane (AOP)-RANTES, an NH(2)-terminal modified form of RANTES, is a potent inhibitor of infection by R5 HIV strains. AOP-RANTES efficiently downmodulates the cell surface expression of CCR5 and, in contrast with RANTES, appears to prevent recycling of CCR5 to the cell surface. Here, we investigate the cellular basis of this effect. Using CHO cells expressing human CCR5, we show that both RANTES and AOP-RANTES induce rapid internalization of CCR5. In the absence of ligand, CCR5 shows constitutive turnover with a half-time of 6-9 h. Addition of RANTES or AOP-RANTES has little effect on the rate of CCR5 turnover. Immunofluorescence and immunoelectron microscopy show that most of the CCR5 internalized after RANTES or AOP-RANTES treatment accumulates in small membrane-bound vesicles and tubules clustered in the perinuclear region of the cell. Colocalization with transferrin receptors in the same clusters of vesicles indicates that CCR5 accumulates in recycling endosomes. After the removal of RANTES, internalized CCR5 recycles to the cell surface and is sensitive to further rounds of RANTES-induced endocytosis. In contrast, after the removal of AOP-RANTES, most CCR5 remains intracellular. We show that these CCR5 molecules do recycle to the cell surface, with kinetics equivalent to those of receptors in RANTES-treated cells. However, these recycled CCR5 molecules are rapidly reinternalized. Our results indicate that AOP-RANTES-induced changes in CCR5 alter the steady-state distribution of the receptor and provide the first evidence for G protein-coupled receptor trafficking through the recycling endosome compartment.

Dataset Information

Analysis of occludin trafficking, demonstrating continuous endocytosis, degradation, recycling and biosynthetic secretory trafficking.

Publications

Analysis of occludin trafficking, demonstrating continuous endocytosis, degradation, recycling and biosynthetic secretory trafficking.

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