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This Article Full Text Full Text (PDF) Data Supplement All Versions of this Article: jimmunol.0901521v1 183/10/6500    most recent Alert me when this article is cited Alert me if a correction is posted Citation Map Services Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Request Permissions Google Scholar Articles by Jabbour, M. Articles by Lybarger, L. PubMed PubMed Citation Articles by Jabbour, M. Articles by Lybarger, L.

Discrete Domains of MARCH1 Mediate Its Localization, Functional Interactions, and Posttranscriptional Control of Expression¹

Maurice Jabbour,^* Erin M. Campbell, Hanna Fares, and Lonnie Lybarger^2*

^*Department of Immunobiology, Department of Molecular and Cellular Biology, and Department of Cell Biology and Anatomy, University of Arizona, Tucson, AZ 85724

Within APCs, ubiquitination regulates the trafficking of immune modulators such as MHC class II and CD86 (B7.2) molecules. MARCH1 (membrane-associated RING-CH), a newly identified ubiquitin E3 ligase expressed in APCs, ubiquitinates MHC class II, thereby reducing its surface expression. Following LPS-induced maturation of dendritic cells, MARCH1 mRNA is down-regulated and MHC class II is redistributed to the cell surface from endosomal compartments. Here, we show that MARCH1 expression is also regulated at the posttranscriptional level. In primary dendritic cell and APC cell lines of murine origin, MARCH1 had a half-life of <30 min. MARCH1 degradation appears to occur partly in lysosomes, since inhibiting lysosomal activity stabilized MARCH1. 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. Taken together, these data suggest that MARCH1 expression is regulated at a posttranscriptional level by trafficking within the endolysosomal pathway where MARCH1 is proteolyzed. 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 Ag presentation once APCs receive maturational signals.

The costs of publication of this article were defrayed in part by the payment of page charges. This article must therefore be hereby marked advertisement in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.

¹ This work was supported by grants from the National Institutes of Health (AI060723) and from the Arizona Biomedical Research Commission (8-123).

² Address correspondence and reprint requests to Dr. Lonnie Lybarger, Department of Cell Biology and Anatomy, University of Arizona, 1501 N. Campbell Avenue, LSN 444, Tucson, AZ 85724. E-mail address: lybarger{at}email.arizona.edu

³ Abbreviations used in this paper: DC, dendritic cell; Baf A, bafilomycin A; BMDC, bone marrow-derived dendritic cell; Cat, cathepsin; HA, hemagglutinin; IRES, internal ribosome entry site; MARCH1, membrane-associated RING-CH protein; RING, really interesting new gene; shRNA, small hairpin RNA.

⁴ The online version of this article contains supplemental material.