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A novel class of herpesvirus-encoded membrane-bound E3 ubiquitin ligases regulates endocytosis of proteins involved in immune recognition.

Coscoy L, Sanchez DJ, Ganem D - J. Cell Biol. (2001)

Bottom Line: Kaposi's sarcoma-associated herpesvirus encodes two transmembrane proteins (modulator of immune recognition [MIR]1 and MIR2) that downregulate cell surface molecules (MHC-I, B7.2, and ICAM-1) involved in the immune recognition of infected cells.This downregulation results from enhanced endocytosis and subsequent endolysosomal degradation of the target proteins.Thus, MIR2 defines a novel class of membrane-bound E3 Ub ligases that modulates the trafficking of host cell membrane proteins.

View Article: PubMed Central - PubMed

Affiliation: Howard Hughes Medical Institute and Department of Microbiology, University of California Medical Center, San Francisco, CA 94143, USA.

ABSTRACT
Kaposi's sarcoma-associated herpesvirus encodes two transmembrane proteins (modulator of immune recognition [MIR]1 and MIR2) that downregulate cell surface molecules (MHC-I, B7.2, and ICAM-1) involved in the immune recognition of infected cells. This downregulation results from enhanced endocytosis and subsequent endolysosomal degradation of the target proteins. Here, we show that expression of MIR1 and MIR2 leads to ubiquitination of the cytosolic tail of their target proteins and that ubiquitination is essential for their removal from the cell surface. MIR1 and MIR2 both contain cytosolic zinc fingers of the PHD subfamily, and these structures are required for this activity. In vitro, addition of a MIR2-glutathione S-transferase (GST) fusion protein to purified E1 and E2 enzymes leads to transfer of ubiquitin (Ub) to GST-containing targets in an ATP- and E2-dependent fashion; this reaction is abolished by mutation of the Zn-coordinating residues of the PHD domain. Thus, MIR2 defines a novel class of membrane-bound E3 Ub ligases that modulates the trafficking of host cell membrane proteins.

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A model for MIR2 function as an E3 Ub ligase. MIR2 TM domains mediate recognition of their target molecules TM regions in the plane of the membrane, whereas its cytosolic PHD domain recruits one or more E2 Ub-conjugating enzymes and brings them into proximity with the cytosolic tail of the target protein, facilitating the transfer of Ub to key lysine residues.
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fig8: A model for MIR2 function as an E3 Ub ligase. MIR2 TM domains mediate recognition of their target molecules TM regions in the plane of the membrane, whereas its cytosolic PHD domain recruits one or more E2 Ub-conjugating enzymes and brings them into proximity with the cytosolic tail of the target protein, facilitating the transfer of Ub to key lysine residues.

Mentions: The basis of this targeting function has been illuminated by experiments (Fig. 7; D. Sanchez et al, personal communication), implicating the TM and juxtamembrane regions of both target and effector chains in target selection. Based on these studies, we propose a model for how MIR-mediated ubiquitination might proceed (Fig. 8). In this model, the TM and juxtamembrane regions of MIR2 and its target chains mediate an interaction in the plane of the membrane; this juxtaposes the NH2-terminal PHD domain of MIR2 (with its associated E2) with the cytosolic tail of the target, thereby facilitating ubiquitination of its substrate lysine residues. How ubiquitination of the target promotes its endocytosis and endolysosomal degradation remains a matter for further study. In other systems, ubiquitination is known to affect both internalization and the delivery of endosomal contents to lysosomes (for review see Hicke, 2001a). The fact that coexpression of MIR2 with dynamin dominant negative mutants leads to accumulation of cell surface MHC-I (Coscoy and Ganem, 2000) suggests that MIR-induced ubiquitination likely targets at least the internalization step, but further work will be needed to determine if downstream events are also influenced by MIR2.


A novel class of herpesvirus-encoded membrane-bound E3 ubiquitin ligases regulates endocytosis of proteins involved in immune recognition.

Coscoy L, Sanchez DJ, Ganem D - J. Cell Biol. (2001)

A model for MIR2 function as an E3 Ub ligase. MIR2 TM domains mediate recognition of their target molecules TM regions in the plane of the membrane, whereas its cytosolic PHD domain recruits one or more E2 Ub-conjugating enzymes and brings them into proximity with the cytosolic tail of the target protein, facilitating the transfer of Ub to key lysine residues.
© Copyright Policy
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC2199318&req=5

fig8: A model for MIR2 function as an E3 Ub ligase. MIR2 TM domains mediate recognition of their target molecules TM regions in the plane of the membrane, whereas its cytosolic PHD domain recruits one or more E2 Ub-conjugating enzymes and brings them into proximity with the cytosolic tail of the target protein, facilitating the transfer of Ub to key lysine residues.
Mentions: The basis of this targeting function has been illuminated by experiments (Fig. 7; D. Sanchez et al, personal communication), implicating the TM and juxtamembrane regions of both target and effector chains in target selection. Based on these studies, we propose a model for how MIR-mediated ubiquitination might proceed (Fig. 8). In this model, the TM and juxtamembrane regions of MIR2 and its target chains mediate an interaction in the plane of the membrane; this juxtaposes the NH2-terminal PHD domain of MIR2 (with its associated E2) with the cytosolic tail of the target, thereby facilitating ubiquitination of its substrate lysine residues. How ubiquitination of the target promotes its endocytosis and endolysosomal degradation remains a matter for further study. In other systems, ubiquitination is known to affect both internalization and the delivery of endosomal contents to lysosomes (for review see Hicke, 2001a). The fact that coexpression of MIR2 with dynamin dominant negative mutants leads to accumulation of cell surface MHC-I (Coscoy and Ganem, 2000) suggests that MIR-induced ubiquitination likely targets at least the internalization step, but further work will be needed to determine if downstream events are also influenced by MIR2.

Bottom Line: Kaposi's sarcoma-associated herpesvirus encodes two transmembrane proteins (modulator of immune recognition [MIR]1 and MIR2) that downregulate cell surface molecules (MHC-I, B7.2, and ICAM-1) involved in the immune recognition of infected cells.This downregulation results from enhanced endocytosis and subsequent endolysosomal degradation of the target proteins.Thus, MIR2 defines a novel class of membrane-bound E3 Ub ligases that modulates the trafficking of host cell membrane proteins.

View Article: PubMed Central - PubMed

Affiliation: Howard Hughes Medical Institute and Department of Microbiology, University of California Medical Center, San Francisco, CA 94143, USA.

ABSTRACT
Kaposi's sarcoma-associated herpesvirus encodes two transmembrane proteins (modulator of immune recognition [MIR]1 and MIR2) that downregulate cell surface molecules (MHC-I, B7.2, and ICAM-1) involved in the immune recognition of infected cells. This downregulation results from enhanced endocytosis and subsequent endolysosomal degradation of the target proteins. Here, we show that expression of MIR1 and MIR2 leads to ubiquitination of the cytosolic tail of their target proteins and that ubiquitination is essential for their removal from the cell surface. MIR1 and MIR2 both contain cytosolic zinc fingers of the PHD subfamily, and these structures are required for this activity. In vitro, addition of a MIR2-glutathione S-transferase (GST) fusion protein to purified E1 and E2 enzymes leads to transfer of ubiquitin (Ub) to GST-containing targets in an ATP- and E2-dependent fashion; this reaction is abolished by mutation of the Zn-coordinating residues of the PHD domain. Thus, MIR2 defines a novel class of membrane-bound E3 Ub ligases that modulates the trafficking of host cell membrane proteins.

Show MeSH