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

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-kappaB were suppressed to an identical degree. The SUMO-4M (Met) variant is associated with type I diabetes mellitus susceptibility in families (p = 4.0 x 10(-4)), suggesting that it may be involved in the pathogenesis of type I diabetes.