Biomedical subjects

Michael R Harris

Publications and source records attributed to Michael R Harris.

4 recordsLinked to original sources

PubMed2005

Requirements for the selective degradation of endoplasmic reticulum-resident major histocompatibility complex class I proteins by the viral immune evasion molecule mK3.

Recent studies suggest that certain viral proteins co-opt endoplasmic reticulum (ER) degradation pathways to prevent the surface display of major histocompatibility complex class I molecules to the immune system. A novel example of such a molecule is the mK3 protein of gammaherpesvirus 68. mK3 belongs to an extensive family of structurally similar viral and cellular proteins that function as ubiquitin ligases using a conserved RING-CH domain. In the specific case of mK3, it selectively targets the rapid degradation of nascent class I heavy chains in the ER while they are associated with the class I peptide-loading complex (PLC). We present here evidence that the PLC imposes a relative proximity and/or orientation on the RING-CH domain of mK3 that is required for it to specifically target class I molecules for degradation. Furthermore, we demonstrate that full assembly of class I molecules with peptide is not a prerequisite for mK3-mediated degradation. Surprisingly, although the cytosolic tail of class I is required for rapid mK3-mediated degradation, we observed that a class I mutant lacking lysine residues in its cytosolic tail was ubiquitinated and degraded in the presence of mK3 in a manner indistinguishable from wild-type class I molecules. These findings are consistent with a "partial dislocation" model for turnover of ER proteins and define some common features of ER degradation pathways initiated by structurally distinct herpesvirus proteins.

Animals↗

PubMed2004

Model for the interaction of gammaherpesvirus 68 RING-CH finger protein mK3 with major histocompatibility complex class I and the peptide-loading complex.

The mK3 protein of gammaherpesvirus 68 and the kK5 protein of Kaposi's sarcoma-associated herpesvirus are members of a family of structurally related viral immune evasion molecules that all possess a RING-CH domain with ubiquitin ligase activity. These proteins modulate the expression of major histocompatibility complex class I molecules (mK3 and kK5) as well as other molecules like ICAM-1 and B7.2 (kK5). Previously, mK3 was shown to ubiquitinate nascent class I molecules, resulting in their rapid degradation, and this process was found to be dependent on TAP and tapasin, endoplasmic reticulum molecules involved in class I assembly. Here, we demonstrate that in murine cells, kK5 does not affect class I expression but does downregulate human B7.2 molecules in a TAP/tapasin-independent manner. These differences in substrate specificity and TAP/tapasin dependence between mK3 and kK5 permitted us, using chimeric molecules, to map the sites of mK3 interaction with TAP/tapasin and to determine the requirements for substrate recognition by mK3. Our findings indicate that mK3 interacts with TAP1 and -2 via their C-terminal domains and with class I molecules via their N-terminal domains. Furthermore, by orienting the RING-CH domain of mK3 appropriately with respect to class I, mK3 binding to TAP/tapasin, rather than the presence of unique sequences in class I, appears to be the primary determinant of substrate specificity.

ATP Binding Cassette Transporter, Subfamily B, Mem↗

PubMed2003

Virus subversion of the MHC class I peptide-loading complex.

Many viral proteins modulate class I expression, yet, in general, their mechanisms of specific class I recognition are poorly understood. The mK3 protein of gamma(2)-Herpesvirus 68 targets the degradation of nascent class I molecules via the ubiquitin/proteasome pathway. Here, we identify cellular components of the MHC class I assembly machinery, TAP and tapasin, that are required for mK3 function. mK3 failed to regulate class I in TAP- or tapasin-deficient cells, and mK3 interacted with TAP/tapasin, even in the absence of class I. Expression of mK3 resulted in the ubiquitination of TAP/tapasin-associated class I, and mutants of class I incapable of TAP/tapasin interaction were unaffected by mK3. Thus, mK3 subverts TAP/tapasin to specifically target class I molecules for destruction.

ATP Binding Cassette Transporter, Subfamily B, Mem↗

PubMed2002

Physical association of the K3 protein of gamma-2 herpesvirus 68 with major histocompatibility complex class I molecules with impaired peptide and beta(2)-microglobulin assembly.

To persist in the presence of an active immune system, viruses encode proteins that decrease expression of major histocompatibility complex class I molecules by using a variety of mechanisms. For example, murine gamma-2 herpesvirus 68 expresses the K3 protein, which causes the rapid turnover of nascent class I molecules. In this report we show that certain mouse class I alleles are more susceptible than others to K3-mediated down regulation. Prior to their rapid degradation, class I molecules in K3-expressing cells exhibit impaired assembly with beta(2)-microglobulin. Furthermore, K3 is detected predominantly in association with class I molecules lacking assembly with high-affinity peptides, including class I molecules associated with the peptide loading complex TAP/tapasin/calreticulin. The detection of K3 with class I assembly intermediates raises the possibility that molecular chaperones involved in class I assembly are involved in K3-mediated class I regulation.

Animals↗