The β2-microglobulin-free heterodimerization of rhesus monkey MHC class I A with its normally spliced variant reduces the ubiquitin-dependent degradation of MHC class I A

• Published in: The Journal of immunology (1950) 2012-03, Vol.188 (5), p.2285-2296
• Main Authors: Dai, Zheng-Xi, Zhang, Gao-Hong, Zhang, Xi-He, Xia, Hou-Jun, Li, Shao-You, Zheng, Yong-Tang
• Format: Article
• Language: English
• Subjects: Alternative Splicing - genetics; Alternative Splicing - immunology; Animals; beta 2-Microglobulin - deficiency; beta 2-Microglobulin - genetics; beta 2-Microglobulin - metabolism; Disulfides - metabolism; Down-Regulation - genetics; Down-Regulation - immunology; Glycoproteins - genetics; Glycoproteins - metabolism; Histocompatibility Antigens Class I - genetics; Histocompatibility Antigens Class I - metabolism; Humans; K562 Cells; Macaca mulatta; Mice; Molecular Sequence Data; Mutagenesis, Site-Directed; Protein Isoforms - genetics; Protein Isoforms - metabolism; Protein Multimerization; Protein Processing, Post-Translational - genetics; Protein Processing, Post-Translational - immunology; Sequence Deletion - genetics; Sequence Deletion - immunology; Transfection; Ubiquitin - antagonists & inhibitors; Ubiquitin - metabolism; Ubiquitin - physiology
• ISSN: 0022-1767; 1550-6606
• DOI: 10.4049/jimmunol.1100665

The MHC class I (MHC I) molecules play a pivotal role in the regulation of immune responses by presenting antigenic peptides to CTLs and by regulating cytolytic activities of NK cells. In this article, we show that MHC I A in rhesus macaques can be alternatively spliced, generating a novel MHC I A isoform (termed "MHC I A-sv1") devoid of α(3) domain. Despite the absence of β2-microglobulin (β2m), the MHC I A-sv1 proteins reached the cell surface of K562-transfected cells as endoglycosidase H-sensitive glycoproteins that could form disulfide-bonded homodimers. Cycloheximide-based protein chase experiments showed that the MHC I A-sv1 proteins were more stable than the full-length MHC I A in transiently or stably transfected cell lines. Of particular interest, our studies demonstrated that MHC I A-sv1 could form β2m-free heterodimers with its full-length protein in mammalian cells. The formation of heterodimers was accompanied by a reduction in full-length MHC I A ubiquitination and consequent stabilization of the protein. Taken together, these results demonstrated that MHC I A-sv1 and MHC I A can form a novel heterodimeric complex as a result of the displacement of β2m and illustrated the relevance of regulated MHC I A protein degradation in the β2m-free heterodimerization-dependent control, which may have some implications for the MHC I A splice variant in the fine tuning of classical MHC I A/TCR and MHC I A/killer cell Ig-like receptor interactions.