Details

Autor(en) / Beteiligte

• Jabbour, Maurice E

Titel

Regulation and function of MARCH1: Modulation of immunity through ubiquitination

Ort / Verlag

ProQuest Dissertations & Theses

Erscheinungsjahr

2010

Link zum Volltext

• ProQuest

Quelle

ProQuest Dissertations & Theses A&I

Beschreibungen/Notizen

• The activation of the immune system, particularly adaptive immunity, in response to a pathogen (e.g. viruses) relies on complex network of cell interactions including those between lymphocytes (T cells) and dendritic cells (DC). In its simplest form, the DC-mediated activation of T cells is dependent on 1) binding of antigen presenting molecules (MHC class I and class II) and their peptides to the T cell receptor and 2) interaction between costimulatory molecules (CD80 and CD86) on DC and their receptors on T cells. Together these signaling events induce an optimal T cell-dependent immune response. Viruses, including herpesviruses and poxviruses, using evolutionarily conserved ubiquitin E3 ligases, appropriate cellular ubiquitin pathways for targeting immune molecules (CD86 or MHC), thereby evading the immune response. The notion that two evolutionarily divergent virus families share conserved ubiquitin E3 ligases suggested that viruses have acquired these enzymes from the host. Indeed, a set of cellular ubiquitin E3 ligases, termed membrane-associated RING-CH1 proteins (MARCH), was identified in mammalian genomes. Unlike their viral orthologs, cellular E3 ligases including MARCH proteins have regulatory functions in various cellular processes and, therefore, must be tightly controlled to prevent inadvertent effects to the host. Interestingly, due to its lymphoid-restricted expression and targeting of CD86 and MHC class II levels, MARCH1 is potentially critical for the function of DC. Furthermore, since DC are essential players in the regulation of the immune response (as evident by immune deficiencies observed following ablation of DC), MARCH1 should play a critical role in immunity. Therefore, the work presented in this thesis explores the regulation and function of MARCH1 in DC. Initial studies have shown that MARCH1-deficient DC have increased surface expression of MHC II and CD86, thereby suggesting that MARCH1 is a negative regulator of antigen presentation. Accordingly, De Gassart et al. shown that the increase in MHC II levels is correlated with a decrease in the mRNA levels of MARCH1 in response to DC maturation signals. However, MARCH1 protein levels were significantly decreased within 4-hrs of DC maturation, which cannot be accounted solely by a transcriptional regulation mechanism. In fact, our first study indicates an additional posttranscriptional level of MARCH1 regulation. In addition, we show that lysosomal function is critical for MARCH1 expression and stability, though not exclusively. This post-transcriptional regulation is needed to allow for the rapid decrease in MARCH1 protein levels leading to an increase in expression of MHC class II and CD86 in response to DC maturation. In a separate study, we examine the regulation of CD86 biogenesis by MARCH1 and using a structure-function approach, substrate and enzyme determinants, critical for sensitivity to MARCH1 were mapped. We show that the presence of lysines in the cytosolic tail of MARCH1 substrates and optimal transmembrane interactions as being critical determinants for MARCH1-mediated sensitivity. In addition, our data indicate that MARCH1, like its viral orthologs, can regulate the expression of multiple unrelated substrates using yet-to-be-identified accessory (adaptor) molecules. Finally, preliminary data suggest an additional level of MARCH1 regulation, which is the regulation of its E3 ligase function following ligand-induced DC maturation. Overall, data presented in this work highlight new findings on the regulation of an important cellular E3 ligase, MARCH1, which is emerging as a critical factor for the biology of DC as well as immunity. One major contribution of this work is the identification of stability determinants that are important for MARCH1 regulation and potentially DC function. 1RING – Really Interesting New Gene RING-CH domain is a variant of the RING domain present in many cellular E3 ligases.