Newly Discovered Viral E3 Ligase pK3 Induces Endoplasmic Reticulum-associated Degradation of Class I Major Histocompatibility Proteins and Their Membrane-bound Chaperones

Herr, Roger A.; Wang, Xiaoli; Loh, Joy; Virgin, Herbert W.; Hansen, Ted H.

doi:10.1074/jbc.m111.325340

Cited by 14 publications

(14 citation statements)

References 57 publications

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“…In contrast to K5, K3 activity was restricted to the later stages of lytic replication. While a positionally conserved homologue of K3 can be found in several other gammaherpesvirus genomes (100,(107)(108)(109), the presence of more than one vMARCH gene is a unique feature of KSHV. As for some other gammaherpesvirus genes (100,110), it has been suggested that K5 may have originated from a gene duplication event (22).…”

Section: Discussionmentioning

confidence: 99%

Kaposi's Sarcoma-Associated Herpesvirus K3 and K5 Ubiquitin E3 Ligases Have Stage-Specific Immune Evasion Roles during Lytic Replication

Brulois

Tóth

Wong

et al. 2014

J Virol

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The downregulation of immune synapse components such as major histocompatibility complex class I (MHC-I) and ICAM-1 is a common viral immune evasion strategy that protects infected cells from targeted elimination by cytolytic effector functions of the immune system. Kaposi's sarcoma-associated herpesvirus (KSHV) encodes two membrane-bound ubiquitin E3 ligases, called K3 and K5, which share the ability to induce internalization and degradation of MHC-I molecules. Although individual functions of K3 and K5 outside the viral genome are well characterized, their roles during the KSHV life cycle are still unclear. In this study, we individually introduced the amino acid-coding sequences of K3 or K5 into a ⌬K3 ⌬K5 recombinant virus, at either original or interchanged genomic positions. Recombinants harboring coding sequences within the K5 locus showed higher K3 and K5 protein expression levels and more rapid surface receptor downregulation than cognate recombinants in which coding sequences were introduced into the K3 locus. To identify infected cells undergoing K3-mediated downregulation of MHC-I, we employed a novel reporter virus, called red-green-blue-BAC16 (RGB-BAC16), which was engineered to harbor three fluorescent protein expression cassettes: EF1␣-monomeric red fluorescent protein 1 (mRFP1), polyadenylated nuclear RNA promoter (pPAN)-enhanced green fluorescent protein (EGFP), and pK8.1-monomeric blue fluorescent protein (tagBFP), marking latent, immediate early, and late viral gene expression, respectively. Analysis of RGB-derived K3 and K5 deletion mutants showed that while the K5-mediated downregulation of MHC-I was concomitant with pPAN induction, the reduction of MHC-I surface expression by K3 was evident in cells that were enriched for pPAN-driven EGFP high and pK8.1-driven blue fluorescent proteinpositive (BFP ؉ ) populations. These data support the notion that immunoreceptor downregulation occurs by a sequential process wherein K5 is critical during the immediately early phase and K3 plays a significant role during later stages. IMPORTANCEAlthough the roles of K3 and K5 outside the viral genome are well characterized, the function of these proteins in the context of the KSHV life cycle has remained unclear, particularly in the case of K3. This study examined the relative contributions of K3 and K5 to the downregulation of MHC-I during the lytic replication of KSHV. We show that while K5 acts immediately upon entry into the lytic phase, K3-mediated downregulation of MHC-I was evident during later stages of lytic replication. The identification of distinctly timed K3 and K5 activities significantly advances our understanding of KSHV-mediated immune evasion. Crucial to this study was the development of a novel recombinant KSHV, called RGB-BAC16, which facilitated the delineation of stage-specific phenotypes.

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Section: Discussionmentioning

confidence: 99%

Kaposi's Sarcoma-Associated Herpesvirus K3 and K5 Ubiquitin E3 Ligases Have Stage-Specific Immune Evasion Roles during Lytic Replication

Brulois

Tóth

Wong

et al. 2014

J Virol

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“…One problem is that this evidence for DRiPs was indirect and the drop in presentation observed after inhibiting protein synthesis could have been due to effects on other processes, such as a depletion of a limiting component of the class I pathway or a compensatory cellular response. Among other possibilities, MHC class I presentation clearly requires synthesis of MHC heavy and light chain and depletion of these nascent molecules leads to the degradation of TAP1 and tapasin (30), which are necessary for loading peptides onto class I molecules. Also in support of this possibility, inhibition of protein synthesis was found to block the cross presentation of exogenous antigens (9,31), which obviously does not require antigen synthesis.…”

Section: Discussionmentioning

confidence: 99%

Using intein catalysis to probe the origin of major histocompatibility complex class I-presented peptides

Farfán-Arribas

Stern

Rock

2012

Proc. Natl. Acad. Sci. U.S.A.

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All vertebrate nucleated cells generate peptides from their expressed gene products and then display them at the cell surface bound to MHC class I molecules. This allows CD8 + T cells to detect and eliminate abnormal cells that are synthesizing foreign proteins, e.g., from viruses or mutations. To permit the immune system to more uniformly monitor a cell's proteins, regardless of their half-life or location, it has been thought that the products of rapid degradation of the mistakes of protein synthesis (defective ribosomal products, DRiPs) preferentially contribute to the class I-presented peptides. However, using intein catalysis to generate peptide sequences exclusively by posttranslational splicing of mature proteins, we show here that presented peptides can be generated from fully folded and functional proteins. Remarkably, the presentation of peptides from two model mature proteins is just as efficient as from newly synthesized proteins subject to errors in translation or folding. These results indicate that for the constructs we have analyzed, DRiPs are not a more efficient source of class I peptides for antigen presentation than the turnover of mature functional proteins. Accordingly, our data suggest that one of the major ways the immune system evaluates the health of cells is by monitoring the breakdown products of the proteome.

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“…If the constitutive ERAD activity is insufficient, folding-defective polypeptides may remain in the ER lumen thereby eventually interfering with protein biogenesis and secretion upon, as one example, persistent sequestration of folding chaperones (41,140,141). In contrast, excessive ERAD activity would drastically reduce the time allocated to nascent chains for maturation, thus causing loss-of-function phenotypes and diseases (19,34,35,(38)(39)(40)(142)(143)(144)(145)(146)(147)(148)(149).…”

Section: Regulation Of the Erad Activitymentioning

confidence: 99%

Specificity and Regulation of the Endoplasmic Reticulum‐Associated Degradation Machinery

Merulla

Fasana

Soldà

et al. 2013

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The endoplasmic reticulum-associated degradation (ERAD) machinery selects native and misfolded polypeptides for dislocation across the ER membrane and proteasomal degradation. Regulated degradation of native proteins is an important aspect of cell physiology. For example, it contributes to the control of lipid biosynthesis, calcium homeostasis and ERAD capacity by setting the turnover rate of crucial regulators of these pathways. In contrast, degradation of native proteins has pathologic relevance when caused by viral or bacterial infections, or when it occurs as a consequence of dysregulated ERAD activity. The efficient disposal of misfolded proteins prevents toxic depositions and persistent sequestration of molecular chaperones that could induce cellular stress and perturb maintenance of cellular proteostasis. In the first section of this review, we survey the available literature on mechanisms of selection of native and non-native proteins for degradation from the ER and on how pathogens hijack them. In the second section, we highlight the mechanisms of ERAD activity adaptation to changes in the ER environment with a particular emphasis on the post-translational regulatory mechanisms collectively defined as ERAD tuning. The cellular proteome is mostly synthesized by cytosolic ribosomes to operate in the cytosol and, upon appropriate targeting, in various intracellular organelles or in the extracellular space. Cellular compartments where protein folding occurs [e.g. the cytosol, mitochondria, the endoplasmic reticulum (ER)] contain two classes of non-native polypeptides: (i) newly synthesized polypeptide chains that must be assisted by folding chaperones and enzymes to attain the native mono-or oligomeric structure; (ii) terminally misfolded conformers that must efficiently be degraded to prevent the formation of toxic deposits and the persistent sequestration of chaperones that could eventually inhibit the cellular protein folding capacity and elicit stress (1-3) ( Figure 1A). The distinction between the two classes of non-native chains, one to be preserved, the second to be cleared from the folding compartment, is not an easy task for the cellular quality control machineries. Selection for disposal might be a stochastic process: the longer the persistency of structural defects in the ER, the greater is the probability to be selected for destruction. Therefore, mutations that delay folding may channel the polypeptide into destructive pathways, even if they do not compromise the function of the mutated protein.In the ER, non-native, but also native proteins might be selected for degradation by components of the endoplasmic reticulum-associated degradation (ERAD) machinery that deliver them at dislocation sites embedded in the ER membrane. Dislocation sites consist of a multitude of luminal and membrane-bound specialized ER-resident proteins as well as a number of cytosolic factors insuring dislocation across the ER membrane, poly-ubiquitylation and disposal of ERAD substrates by 26S proteasomes (Specificity of...

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Newly Discovered Viral E3 Ligase pK3 Induces Endoplasmic Reticulum-associated Degradation of Class I Major Histocompatibility Proteins and Their Membrane-bound Chaperones

Cited by 14 publications

References 57 publications

Kaposi's Sarcoma-Associated Herpesvirus K3 and K5 Ubiquitin E3 Ligases Have Stage-Specific Immune Evasion Roles during Lytic Replication

Kaposi's Sarcoma-Associated Herpesvirus K3 and K5 Ubiquitin E3 Ligases Have Stage-Specific Immune Evasion Roles during Lytic Replication

Using intein catalysis to probe the origin of major histocompatibility complex class I-presented peptides

Specificity and Regulation of the Endoplasmic Reticulum‐Associated Degradation Machinery

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