Alternative titles; symbols
HGNC Approved Gene Symbol: MARCHF9
Cytogenetic location: 12q14.1 Genomic coordinates (GRCh38): 12:57,755,103-57,760,411 (from NCBI)
MARCH9 is a member of the MARCH family of membrane-bound E3 ubiquitin ligases (EC 6.3.2.19). MARCH enzymes add ubiquitin (see 191339) to target lysines in substrate proteins, thereby signaling their vesicular transport between membrane compartments. MARCH9 induces internalization of several membrane glycoproteins and directs them to the endosomal compartment (Bartee et al., 2004; Hoer et al., 2007).
Poxviruses and gamma-2 herpesviruses express ubiquitin ligases called K3 proteins that inhibit the surface expression of glycoproteins, including major histocompatibility complex (MHC) class I molecules (see 142800). By searching a database for sequences similar to the functional domains of viral K3 proteins, Bartee et al. (2004) identified 9 human MARCH proteins, including MARCH9. The deduced full-length MARCH9 protein contains a short N terminus, followed by a RING-CH domain and 2 transmembrane domains. It shares 90% identity with MARCH4 (608208) in the RING-CH and transmembrane domains. Bartee et al. (2004) also identified a MARCH9 variant that encodes a protein lacking the RING-CH domain. Real-time PCR analysis showed that both MARCH9 variants were expressed in all human tissues examined at variable levels.
Hoer et al. (2007) determined that the short MARCH9 variant, which they called MARCH9 RINGless, uses a transcription initiation site within intron 2 of the MARCH9 gene. The deduced protein contains the same 2 C-terminal transmembrane domains as full-length MARCH9, but it has a unique 57-amino acid N terminus that replaces the RING-CH domain. Epitope-tagged full-length MARCH9 colocalized with a lysosomal marker. When overexpressed, it also colocalized with the trans-Golgi network (TGN).
Using RT-PCR, De Gassart et al. (2008) detected robust MARCH9 expression in all human cells and cell lines examined, including immature and mature dendritic cells, HeLa and B-cell lines, and monocytes.
Using an in vitro ubiquitination assay, Bartee et al. (2004) found that the isolated RING-CH domain of MARCH9 could not function as an E3 ubiquitin ligase with any E2 ubiquitin-conjugating enzymes tested, including UBCH2 (UBE2H; 601082), UBCH3 (CDC34; 116948), UBCH5A (UBE2D1; 602961), UBCH6 (UBE2E1; 602916), and UBCH7 (UBE2L3; 603721). Following transfection into HeLa cells, full-length MARCH9 downregulated the surface expression of cotransfected CD4 (186940) and endogenous MHC I. Mutation analysis showed that the RING-CH domain of MARCH9 was essential for MHC I downregulation, and the MARCH9 isoform lacking the RING-CH domain did not downregulate MHC I surface expression. MHC I was internalized to lysosomes via multivesicular bodies, and inhibition of endosome acidification or expression of a dominant-negative VPS4 (see 609982) mutant abrogated MARCH9-induced MHC I internalization. Deletion of lysines in the tails of HLA-A2.1 (600642) and CD4 made these proteins resistant to MARCH9-induced degradation, suggesting that ubiquitination of these lysines is required for their uptake and degradation.
Hoer et al. (2007) found that overexpression of full-length MARCH9 downregulated the surface expression of ICAM1 (147840), a critical cell adhesion molecule, and MHC I in transfected HeLa and 293T cells. Downregulation of ICAM1 involved monoubiquitination of ICAM1 on a cytoplasmic lysine. Mutation analysis revealed that a critical aspartate within the transmembrane region of MARCH9 was required for recognition of MHC I molecules, but not ICAM1. The MARCH9 RINGless isoform stabilized full-length MARCH9 via heterodimerization, resulting in enhanced MARCH9-mediated MHC I and ICAM1 downregulation. Full-length MARCH9 was also able to homodimerize.
Hoer et al. (2007) determined that the MARCH9 gene contains 4 exons.
Hartz (2010) mapped the MARCH9 gene to chromosome 12q14.1 based on an alignment of the MARCH9 sequence (GenBank BC009489) with the genomic sequence (GRCh37).
Bartee, E., Mansouri, M., Nerenberg, B. T. H., Gouveia, K., Fruh, K. Downregulation of major histocompatibility complex class I by human ubiquitin ligases related to viral immune evasion proteins. J. Virology 78: 1109-1120, 2004. [PubMed: 14722266] [Full Text: https://doi.org/10.1128/jvi.78.3.1109-1120.2004]
De Gassart, A., Camosseto, V., Thibodeau, J., Ceppi, M., Catalan, N., Pierre, P., Gatti, E. MHC class II stabilization at the surface of human dendritic cells is the result of maturation-dependent MARCH I down-regulation. Proc. Nat. Acad. Sci. 105: 3491-3496, 2008. [PubMed: 18305173] [Full Text: https://doi.org/10.1073/pnas.0708874105]
Hartz, P. A. Personal Communication. Baltimore, Md. 3/29/2010.
Hoer, S., Smith, L., Lehner, P. J. MARCH-IX mediates ubiquitination and downregulation of ICAM-1. FEBS Lett. 581: 45-51, 2007. [PubMed: 17174307] [Full Text: https://doi.org/10.1016/j.febslet.2006.11.075]