A M55V Polymorphism in a Novel SUMO Gene (SUMO-4) Differentially Activates Heat Shock Transcription Factors and Is Associated with Susceptibility to Type I Diabetes Mellitus

Abstract

Three SUMO (small ubiquitin-related modifier) genes have been identified in humans, which tag proteins to modulate subcellular localization and/or enhance protein stability and activity. We report the identification of a novel intronless SUMO gene, SUMO-4, that encodes a 95-amino acid protein having an 86% amino acid homology with SUMO-2. In contrast to SUMO-2, which is highly expressed in all of the tissues examined, SUMO-4 mRNA was detected mainly in the kidney. A single nucleotide polymorphism was detected in SUMO-4, substituting a highly conserved methionine with a valine residue (M55V). In HepG2 (liver carcinoma) cells transiently transfected with SUMO-4 expression vectors, Met-55 was associated with the elevated levels of activated heat shock factor transcription factors as compared with Val-55, whereas the levels of NF-B were suppressed to an identical degree. The SUMO-4M (Met) variant is associated with type I diabetes mellitus susceptibility in families (p ‫؍‬ 4.0 ؋ 10 ؊4 ), suggesting that it may be involved in the pathogenesis of type I diabetes. SUMO-11 is involved in the post-translational modification of cellular proteins and regulates various cellular processes such as nuclear transport, oncogenesis, stress response, inflammation, and the response to viral infection (1). SUMO-1 is related to ubiquitin, and although both share only an 18% sequence homology, they have a similar three-dimensional structure (1). In contrast to ubiquitin, which tags proteins for degradation, SUMO-1 seems to enhance protein stability and modulate the subcellular localization. The list of mammalian proteins, which are known to be sumoylated, is growing continually and includes RAN GTPase-activating protein 1 (nuclear import) (2), IB␣ (NF-B inhibition) (3), c-Jun (transcription factor), p53 (tumor suppressor) (4), GLUT1 and GLUT4 (glucose transport) (5), heat shock transcription factors 1 and 2 (HSF1 and 2) (6, 7), and FAS/APO-1 (cell death domain/ apoptosis) (8).SUMO-1 is expressed initially as an inactive precursor of 101 amino acids. A C-terminal proteolytic event exposes two glycine residues at the C terminus that are involved in the formation of a peptide bond with the ⑀-amino group of a lysine residue of a target protein. The activating enzymes E1 (AOS1 and UBA2) and the conjugating enzyme E2 (UBC9) are required for sumoylation in vitro (1). In vivo, an additional enzyme E3 is required for efficient sumoylation (9). The E2 enzyme, UBC9, is specific for sumoylation, and recently, two additional SUMO family members have been identified based on the interaction with UBC9, SUMO-2, and SUMO-3 (10, 11). SUMO-1 shares a 48% identity with SUMO-2 and a 46% with SUMO-3. Very little is known regarding the functions of SUMO-2 and SUMO-3. However, SUMO-2 and SUMO-3 contain a consensus SUMO modification site (Fig. 1), which enables self-sumoylation and the formation of polymeric chains (11), in contrast to SUMO-1. Thus, SUMO-2 and SUMO-3 may have different roles in cellular functions.Here, we identify and characterize a novel fou...

Functional variants in SUMO4, TAB2, and NFκB and the risk of type 1 diabetes

“…For the putative causative variant 163A4G, Owerbach et al report increased transmission of the A allele to T1D affecteds while Guo et al observe increased transmission of the G allele; although of opposite polarity, both findings were significant. 18,24 While Guo et al reported increased NFkB transcriptional activity in association with the G allele, no significant allele specific variation in such activity was observed in a separate report by Bohren et al 25 While the predicted effects of variants in the TAB2/ SUMO4 locus on NFkB activity are mediated through biochemical interactions with other molecules, Karban et al 26 have described a functional insertion/deletion (indel) polymorphism that directly affects the expression of NFkB. The deletion allele at position À94 in the promoter of the NFKB1 gene displayed reduced binding of proteins from nuclear extracts of specific tissues in mobility shift assays and reduced transcription in luciferase assays compared to the insertion allele.…”

Regulation of the Ets-1 transcription factor by sumoylation and ubiquitinylation

“…Three different SUMO proteins (B11 kDa) were identified in mammalian cells: SUMO-1, SUMO-2 and SUMO-3, with SUMO-2 and SUMO-3 having very high sequence similarity (Hay, 2005). A tissue-specific SUMO-4 has also been recently identified, with sequence homology to SUMO-2/3 (Bohren et al, 2004). SUMO modification consists in the covalent attachment of SUMO to a lysine residue, that generally lies within the consensus motif j-K-x-D/E (Rodriguez et al, 2001;Sampson et al, 2001).…”

SUMO-1 Modification Alters ADAR1 Editing Activity

“…In vertebrates there are at least three additional proteins. SUMO-2 and SUMO-3 are ϳ45% identical to SUMO-1 (Saitoh and Hinchey, 2000), and SUMO-4 shows an 86% amino acid homology to SUMO-2 (Bohren et al, 2004). SUMO is conjugated to protein substrates via an ATP-dependent enzymatic pathway that is mechanistically similar to ubiquitination.…”