A human-specific TNF-responsive promoter for Goodpasture antigen-binding protein

The Goodpasture antigen-binding protein, GPBP, is a serine/threonine kinase whose relative expression increases in autoimmune processes. Tumor necrosis factor (TNF) is a pro-inflammatory cytokine implicated in autoimmune pathogenesis. Here we show that COL4A3BP, the gene encoding GPBP, maps head-to-head with POLK, the gene encoding for DNA polymerase kappa (pol kappa), and shares with it a 140-bp promoter containing a Sp1 site, a TATA-like element, and a nuclear factor kappa B (NFkappaB)-like site. These three elements cooperate in the assembly of a bidirectional transcription complex containing abundant Sp1 and little NFkappaB that is more efficient in the POLK direction. Tumour necrosis factor cell induction is associated with Sp1 release, NFkappaB recruitment and assembly of a complex comparatively more efficient in the COL4A3BP direction. This is accomplished by competitive binding of Sp1 and NFkappaB to a DNA element encompassing a NFkappaB-like site that is pivotal for the 140-bp promoter to function. Consistently, a murine homologous DNA region, which contains the Sp1 site and the TATA-like element but is devoid of the NFkappaB-like site, does not show transcriptional activity in transient gene expression assays. Our findings identify a human-specific TNF-responsive transcriptional unit that locates GPBP in the signalling cascade of TNF and substantiates previous observations, which independently related TNF and GPBP with human autoimmunity.