Abstract
Deubiquitinating enzymes (DUBs) are important regulators of cell proliferation. Here we identified a functional deubiquitinating enzyme, ovarian tumor domain-containing 6B (OTUD-6B). Mutation of the conserved Cys residue abolished its deubiquitinating activity in vitro. Otud-6b expression was induced with cytokine stimulation in both mouse Ba/F3 cells and primary B lymphocytes followed a rapid decrease. This rapid decrease was partially facilitated by tristetraprolin (TTP) destabilization of Otud-6b mRNA through AU-rich motifs. Enforced expression of OTUD-6B in Ba/F3 cells could block cell proliferation by arresting cells in G1 phase. In addition, cyclin D2 level was down-regulated when OTUD-6B WT was overexpressed. Therefore, down-regulation of Otud-6b expression after prolonged cytokine stimulation may be required for cell proliferation in B lymphocytes.
Highlights
The ubiquitin-mediated proteolytic pathway is involved in multiple cellular processes including cell cycle regulation [1], transcriptional activation [2], and antigen presentation [3]
Microarray data have shown that many OTU family members were rapidly up-regulated or down-regulated in human esophageal epithelial cells and lymphocytes when stimulated by different cytokines, such as ovarian tumor domain containing 6B (OTUD-6B), a novel deubiquitinating enzymes (DUBs) of the OTU family members
RT-PCR results revealed that Otud-6b mRNA is expressed in various mouse tissues, including brain, heart, lung, kidney, ovary, spleen, and B lymphocytes (Figure 1B), which indicated that Otud-6b is probably a widely expressed housekeeping gene
Summary
The ubiquitin-mediated proteolytic pathway is involved in multiple cellular processes including cell cycle regulation [1], transcriptional activation [2], and antigen presentation [3]. The expression levels of those DUBs were sharply down-regulated following the fast induction and little is known about this fast down-regulation These four DUBs belong to the USP17 gene family, members of which form part of highly polymorphic tandem repeat sequences on mouse chromosome 7 [15]. OTUD-6B was originally named as CGI-77 and has deubiquitinating enzyme activity in vitro [16] It was up-regulated on human esophageal epithelial cells after interleukin-13 (IL-13) stimulation [17]. Granulocyte colony-stimulating factor (G-CSF) could effectively down-regulate OTUD-6B expression when human leukocytes were stimulated for 16 hours [19] These experiments showed that OTU family members were regulated by cytokines, little is known about the mechanism and function of such regulations
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