Post-transcriptional regulation of MARCH1 expression (78.16)

Abstract

Abstract In antigen presenting cells (APC) ubiquitination regulates the trafficking of immune modulators (e.g. MHC II). MARCH1 (membrane-associated RING-CH), a newly identified ubiquitin E3 ligase expressed in APC, ubiquitinates MHC II and prevents efficient surface expression. Following LPS-induced maturation of dendritic cells (DC), MARCH1 mRNA is downregulated, permitting MHC II redistribution to the cell surface. Here, we show that MARCH1 expression is also regulated at the post-transcriptional level. In primary DC and APC cell lines, MARCH1 is degraded with a half-life of <30 min. MARCH1 degradation appears to occur mostly, if not exclusively, in lysosomes, since inhibiting lysosomal activity stabilized MARCH1 protein levels. Similar stabilization was observed when MARCH1-expressing cells were treated with cysteine protease inhibitors. Mutational analyses of MARCH1 defined discrete domains required for destabilization, proper localization, and functional interaction with substrates. Together, these data suggest that MARCH1 expression is regulated at a post-transcriptional level by trafficking to endocytic compartments where MARCH1 is proteolysed. The short half-life of MARCH1 permits very rapid changes in the levels of the protein in response to changes in the mRNA, resulting in efficient induction of MHC class II and CD86 once APC receive maturational signals. Supported by Arizona Biomedical Research Commission