Ubiquitin ligase TRUSS augments the expression of interleukin-10 via proteasomal processing of NF-κB1/p105 to NF-κB/p50

The NF-κB/Rel family of transcription factors that play critical roles in a variety of cellular processes. Their production in the cell and physiological activation are tightly regulated. The proteasomal processing of inactive NF-κB1/p105 to active p50, with an anti-inflammatory role, is not well characterized. Here we show that ubiquitin ligase TRUSS is a mediator of transcriptional activation of anti-inflammatory cytokine IL-10 gene. Enforced expression of TRUSS led to enhanced IL-10 expression that could be inhibited in the presence of chemical inhibitors of NF-κB [BAY11-7082] and PI3K/Akt [LY249002] or after p65 overexpression. p50 was actively recruited on IL10 promoter in the presence of TRUSS but competed by p65 for binding. TRUSS facilitated the ubiquitination of NF-κB1/p105 and promoted its proteolytic processing to generate excess of p50. Our immune-histochemical studies confirmed enhanced expression of p105/p50 in the human HCC tumors. Further, the hepatic tumors of HCC patient as well as transgenic mice showed decreased levels of p50 as well as TRUSS and accumulation of p105. Thus, enhanced expression of IL-10 gene in the presence of TRUSS and regulation of NF-κB1/p105 processing could be an important regulatory mechanism for inflammatory response and tumorgenic transformation.