Effect of adenovirus E3/19K protein on cellular processes in the endoplasmic reticulum

• Main Author: Lomas, Cyprien
• Format: Others
• Language: English
• Published: 2009
• Online Access: http://hdl.handle.net/2429/10006

The human adenovirus has developed several methods to evade the immune system. One mechanism by which it accomplishes this involves the endoplasmic reticulum (ER) retained adenovirus E3/19K protein. This protein interferes with antigen presentation by binding and retaining Major Histocompatibility Complex Class I (MHC C1 I) proteins in the ER. E3/19K binds all human and all but one mouse MHC C1 I molecules tested to date. Differences in mouse MHC C1 I sequences were exploited to determine the structures involved in binding. Human 293 cells transfected with the mouse H-2 alleles K[sup d], K[sup b], K[sup k], D[sup d], D[sup b], L[sup d] were infected with adenovirus 2. It was found that MHC C1 I alleles could be grouped into three categories. The H-2 allelic proteins K[sup d] and K[sup b] were found to be binders; K[sup k] and D[sup d] non binders and D[sup b] and L[sup d] slow binders. Examination of a cell line transfected with the slow-binding H-2D[sup b] protein revealed that D[sup b] is expressed at a reduced level at the cell surface. To determine the cause of this, cells were subjected to conditions previously used to restore defective cell surface expression of MHC C1 I including culture at reduced temperature, addition of excess β₂m and exposure to gamma interferon. All these methods were unsuccessful in increasing cell surface expression of Db. Rather than being due to a missing co-factor or unstable conformation, the accumulation of the allelic proteins in the ER in this transfectant was due to an undetermined mechanism. Because E3/19K binding quickly stabilised a mature MHC C1 I conformation in the presence of tunicamycin it was suggested that it bound MHC C1 I like a chaperone. It was found that E3/19K binding to MHC C1 I did not block the association of endogenous ER resident chaperones calnexin and TAP. Peptide binding to the MHC C1 I-E3/19K complex could also occur. These experiments showed that E3/19K did not associate with MHC C1 I through the peptide binding groove and did not disrupt the interaction between the MHC C1 I and the processing machinery found in the ER, namely calnexin and TAP, and therefore does not retain MHC molecules by making them conformationally immature. This study shows E3/19K works independently of chaperones. E3/19K may be a tool to trap MHC C1 I - chaperone complexes at a specific point in their maturation. === Science, Faculty of === Zoology, Department of === Graduate