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Inhibition of intracellular transport of B cell antigen receptor complexes by Kaposi's sarcoma-associated herpesvirus K1.

Lee BS, Alvarez X, Ishido S, Lackner AA, Jung JU - J. Exp. Med. (2000)

Bottom Line: The NH(2)-terminal region of K1 specifically interacts with the mu chains of BCR complexes, and this interaction retains BCR complexes in the endoplasmic reticulum, preventing their intracellular transport to the cell surface.Thus, KSHV K1 resembles Igalpha and Igbeta in its ability to induce signaling and to interact with mu chains of the BCR.However, unlike Igalpha and Igbeta, which interact with mu chains to direct BCR complexes to the cell surface, K1 interacts with mu chains to block the intracellular transport of BCR complexes to the cell surface.

View Article: PubMed Central - PubMed

Affiliation: Department of Microbiology and Molecular Genetics, New England Regional Primate Research Center, Harvard Medical School, Southborough, Massachusetts 01772, USA.

ABSTRACT
The B cell antigen receptor (BCR) is a large complex that consists of a disulfide-linked tetramer of two transmembrane heavy (mu) chains and two light (lambda or kappa) chains in association with a heterodimer of Igalpha and Igbeta. Kaposi's sarcoma-associated herpesvirus (KSHV) encodes a transforming protein called K1, which has structural and functional similarity to Igalpha and Igbeta. We demonstrate that K1 downregulates the expression of BCR complexes on the surface. The NH(2)-terminal region of K1 specifically interacts with the mu chains of BCR complexes, and this interaction retains BCR complexes in the endoplasmic reticulum, preventing their intracellular transport to the cell surface. Thus, KSHV K1 resembles Igalpha and Igbeta in its ability to induce signaling and to interact with mu chains of the BCR. However, unlike Igalpha and Igbeta, which interact with mu chains to direct BCR complexes to the cell surface, K1 interacts with mu chains to block the intracellular transport of BCR complexes to the cell surface. These results demonstrate a unique feature of the K1 transforming protein, which may confer virus-infected cells with a long-term survival advantage.

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Localization of IgM. BJAB/babe (BJAB) cells and BJAB/K1 cells were fixed and colabeled with anti-μ antibody (αμ) together with anticalnexin (αcalnexin) or anti–Golgi compartment 58K (αGolgi 58K) antibody. The μ chain was detected with a secondary antibody conjugated with Alexa 568 (red). Calnexin for ER localization and 58K for Golgi compartment localization were detected with a secondary antibody conjugated with Alexa 488 (green). Yellow color at merged images indicates colocalization of the red and green labels. The data were reproduced in two independent experiments.
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Figure 6: Localization of IgM. BJAB/babe (BJAB) cells and BJAB/K1 cells were fixed and colabeled with anti-μ antibody (αμ) together with anticalnexin (αcalnexin) or anti–Golgi compartment 58K (αGolgi 58K) antibody. The μ chain was detected with a secondary antibody conjugated with Alexa 568 (red). Calnexin for ER localization and 58K for Golgi compartment localization were detected with a secondary antibody conjugated with Alexa 488 (green). Yellow color at merged images indicates colocalization of the red and green labels. The data were reproduced in two independent experiments.

Mentions: We investigated whether K1 expression also affected intracellular localization of BCR components. BJAB and BJAB/K1 cells were stained with antibodies specific for Igα, Igβ, or μ chains, followed by reaction with Alexa 568–conjugated secondary antibody (red). Confocal microscopy of the immunostained cells showed that the localization of μ chains was significantly affected by K1 expression. μ chains were primarily localized in the plasma membrane in control BJAB cells (Fig. 5 A). In contrast, they were predominantly localized at the perinuclear region in BJAB/K1 cells (Fig. 5 A). Because this perinuclear staining pattern is similar to that obtained when the ER is visualized, we further defined the localization of μ chains, using Alexa 488–conjugated (green) Con A for ER-specific staining or BODIPY C5FL-ceramide for Golgi compartment–specific staining. Confocal microscopy showed that μ chains in K1-expressing cells were primarily localized in the ER but not in the Golgi compartment (Fig. 5 A). When an anticalnexin antibody for ER localization 7 and an anti–Golgi compartment 58K antibody for Golgi compartment localization 25 were used for immunofluorescence tests, essentially the same results were obtained (Fig. 6). Similar to μ chains, Igα and Igβ were predominantly localized in the ER in BJAB/K1 cells, whereas they were present in both the plasma membrane and the ER in BJAB cells (Fig. 5b and Fig. c). In addition, confocal microscopy with several different antibodies showed a lower level of Igβ detection in BJAB/K1 cells than in BJAB cells (Fig. 5 C). These results demonstrated that K1 expression led to the retention of BCR subunits in the ER.


Inhibition of intracellular transport of B cell antigen receptor complexes by Kaposi's sarcoma-associated herpesvirus K1.

Lee BS, Alvarez X, Ishido S, Lackner AA, Jung JU - J. Exp. Med. (2000)

Localization of IgM. BJAB/babe (BJAB) cells and BJAB/K1 cells were fixed and colabeled with anti-μ antibody (αμ) together with anticalnexin (αcalnexin) or anti–Golgi compartment 58K (αGolgi 58K) antibody. The μ chain was detected with a secondary antibody conjugated with Alexa 568 (red). Calnexin for ER localization and 58K for Golgi compartment localization were detected with a secondary antibody conjugated with Alexa 488 (green). Yellow color at merged images indicates colocalization of the red and green labels. The data were reproduced in two independent experiments.
© Copyright Policy
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC1887702&req=5

Figure 6: Localization of IgM. BJAB/babe (BJAB) cells and BJAB/K1 cells were fixed and colabeled with anti-μ antibody (αμ) together with anticalnexin (αcalnexin) or anti–Golgi compartment 58K (αGolgi 58K) antibody. The μ chain was detected with a secondary antibody conjugated with Alexa 568 (red). Calnexin for ER localization and 58K for Golgi compartment localization were detected with a secondary antibody conjugated with Alexa 488 (green). Yellow color at merged images indicates colocalization of the red and green labels. The data were reproduced in two independent experiments.
Mentions: We investigated whether K1 expression also affected intracellular localization of BCR components. BJAB and BJAB/K1 cells were stained with antibodies specific for Igα, Igβ, or μ chains, followed by reaction with Alexa 568–conjugated secondary antibody (red). Confocal microscopy of the immunostained cells showed that the localization of μ chains was significantly affected by K1 expression. μ chains were primarily localized in the plasma membrane in control BJAB cells (Fig. 5 A). In contrast, they were predominantly localized at the perinuclear region in BJAB/K1 cells (Fig. 5 A). Because this perinuclear staining pattern is similar to that obtained when the ER is visualized, we further defined the localization of μ chains, using Alexa 488–conjugated (green) Con A for ER-specific staining or BODIPY C5FL-ceramide for Golgi compartment–specific staining. Confocal microscopy showed that μ chains in K1-expressing cells were primarily localized in the ER but not in the Golgi compartment (Fig. 5 A). When an anticalnexin antibody for ER localization 7 and an anti–Golgi compartment 58K antibody for Golgi compartment localization 25 were used for immunofluorescence tests, essentially the same results were obtained (Fig. 6). Similar to μ chains, Igα and Igβ were predominantly localized in the ER in BJAB/K1 cells, whereas they were present in both the plasma membrane and the ER in BJAB cells (Fig. 5b and Fig. c). In addition, confocal microscopy with several different antibodies showed a lower level of Igβ detection in BJAB/K1 cells than in BJAB cells (Fig. 5 C). These results demonstrated that K1 expression led to the retention of BCR subunits in the ER.

Bottom Line: The NH(2)-terminal region of K1 specifically interacts with the mu chains of BCR complexes, and this interaction retains BCR complexes in the endoplasmic reticulum, preventing their intracellular transport to the cell surface.Thus, KSHV K1 resembles Igalpha and Igbeta in its ability to induce signaling and to interact with mu chains of the BCR.However, unlike Igalpha and Igbeta, which interact with mu chains to direct BCR complexes to the cell surface, K1 interacts with mu chains to block the intracellular transport of BCR complexes to the cell surface.

View Article: PubMed Central - PubMed

Affiliation: Department of Microbiology and Molecular Genetics, New England Regional Primate Research Center, Harvard Medical School, Southborough, Massachusetts 01772, USA.

ABSTRACT
The B cell antigen receptor (BCR) is a large complex that consists of a disulfide-linked tetramer of two transmembrane heavy (mu) chains and two light (lambda or kappa) chains in association with a heterodimer of Igalpha and Igbeta. Kaposi's sarcoma-associated herpesvirus (KSHV) encodes a transforming protein called K1, which has structural and functional similarity to Igalpha and Igbeta. We demonstrate that K1 downregulates the expression of BCR complexes on the surface. The NH(2)-terminal region of K1 specifically interacts with the mu chains of BCR complexes, and this interaction retains BCR complexes in the endoplasmic reticulum, preventing their intracellular transport to the cell surface. Thus, KSHV K1 resembles Igalpha and Igbeta in its ability to induce signaling and to interact with mu chains of the BCR. However, unlike Igalpha and Igbeta, which interact with mu chains to direct BCR complexes to the cell surface, K1 interacts with mu chains to block the intracellular transport of BCR complexes to the cell surface. These results demonstrate a unique feature of the K1 transforming protein, which may confer virus-infected cells with a long-term survival advantage.

Show MeSH
Related in: MedlinePlus