DUB-1A, a novel deubiquitinating enzyme subfamily member, is polyubiquitinated and cytokine-inducible in B-lymphocytes

Recently, we isolated the Dub-2A gene, which encodes a novel murine deubiquitinating enzyme subfamily member, from a bacterial artificial chromosome library clone by PCR amplification with degenerate PCR primers for the Dub-2 cDNA (Baek, K.- H., Mondoux, M. A., Jaster, R., Fire-Levin E., and D'Andrea, A. D. ( 2001) Blood 98, 636 - 642). In this study, we analyzed two more clones from the library to isolate genes encoding other deubiquitinating enzymes. Dub-1A, which encodes the shortest member of the DUB subfamily of deubiquitinating enzymes so far, has been identified in both clones and characterized. Sequence analysis showed that Dub-1A encodes a 468-amino acid protein that has a molecular mass of similar to 51 kDa and that contains a putative catalytic domain (Cys, His, and Asp) conserved among DUB proteins. The amino acid sequence of DUB-1A is 84.5, 84.7, and 85.3% identical to those of DUB-1, DUB-2, and DUB-2A, respectively. Reverse transcription-PCR revealed that Dub-1A is expressed not only in B-lymphocytes in response to interleukin-3 stimulation, but also in T-lymphocytes, brain, heart, liver, lung, kidney, ovary, and spleen. This suggests that Dub-1A may play essential roles in each of these organs. In vivo and in vitro deubiquitinating enzyme assays showed that DUB-1A has functional deubiquitinating activity and that the 5'-flanking sequence of Dub-1A has a functional enhancer domain as shown in Dub-1 and Dub-2A. Interestingly, immunoblot analysis revealed that DUB-1A is polyubiquitinated, indicating that it is degraded through proteasome-mediated degradation. In the absence of JAK2, Dub-1A was expressed at a lower level. This suggests that DUB-1A functions downstream of JAK2 kinase in the interleukin-3 signaling pathway.