Proteins containing the evolutionarily conserved SET domain are involved in regulation of eukaryotic gene expression and chromatin structure through their histone lysine methyltransferase (HMTase) activity. The Drosophila SU(VAR)3-9 protein and related proteins of other organisms have been associated with gene repression and heterochromatinization. In Arabidopsis there are 10 SUVH and 5 SUVR genes encoding proteins similar to SU(VAR)3-9, and 4 SUVH proteins have been shown to control heterochromatic silencing by its HMTase activity and by directing DNA methylation. The SUVR proteins differ from the SUVH proteins in their domain structure, and we show that the closely related SUVR1, SUVR2 and SUVR4 proteins contain a novel domain at their N-terminus, and a SUVR specific region preceding the SET domain. Green fluorescent protein (GFP)-fusions of these SUVR proteins preferably localize to the nucleolus, suggesting involvement in regulation of rRNA expression, in contrast to other SET-domain proteins studied so far. A novel HMTase specificity was demonstrated for SUVR4, in that monomethylated histone H3K9 is its preferred substrate in vitro.

SPBP (Stromelysin-1 PDGF responsive element binding protein) is a ubiquitously expressed 220 kDa nuclear protein shown to enhance or repress the transcriptional activity of various transcription factors. A yeast two-hybrid screen, with the extended plant homeodomain (ePHD) of SPBP as bait, identified TopBP1 (topoisomerase II β-binding protein 1) as a candidate interaction partner of SPBP. TopBP1 has eight BRCA1 carboxy-terminal (BRCT) domains and is involved in DNA replication, DNA damage responses and in the regulation of gene expression. The interaction between SPBP and TopBP1 was confirmed in vitro and in vivo, and was found to be mediated by the ePHD domain of SPBP and the BRCT6 domain of TopBP1. Both SPBP and TopBP1 enhanced the transcriptional activity of Ets1 on the c-myc P1P2- and matrix metalloproteinase-3 (MMP3) promoters. Together they displayed a more than additive effect. Both proteins were associated with these promoters. The involvement of TopBP1 was dependent on the serine 1159 phosphorylation site, known to be important for transcriptional activation. Depletion of endogenous SPBP by siRNA treatment reduced MMP3 secretion by 50% in phorbol ester-stimulated human fibroblasts. Taken together, our results show that TopBP1 and SPBP interact physically and functionally to co-operate as co-activators of Ets1.

Transcriptional regulation requires co-ordinated action of transcription factors, co-activator complexes and general transcription factors to access specific loci in the dense chromatin structure. In the present study we demonstrate that the transcriptional co-regulator SPBP [stromelysin-1 PDGF (platelet-derived growth factor)-responsive element binding protein] contains two independent chromatin-binding domains, the SPBP-(1551-1666) region and the C-terminal extended PHD [ePHD/ADD (extended plant homeodomain/ATRX-DNMT3-DNMT3L)] domain. The region 1551-1666 is a novel core nucleosome-interaction domain located adjacent to the AT-hook motif in the DNA-binding domain. This novel nucleosome-binding region is critically important for proper localization of SPBP in the cell nucleus. The ePHD/ADD domain associates with nucleosomes in a histone tail-dependent manner, and has significant impact on the dynamic interaction between SPBP and chromatin. Furthermore, SPBP and its homologue RAI1 (retinoic-acid-inducible protein 1), are strongly enriched on chromatin in interphase HeLa cells, and both proteins display low nuclear mobility. RAI1 contains a region with homology to the novel nucleosome-binding region SPBP-(1551-1666) and an ePHD/ADD domain with ability to bind nucleosomes. These results indicate that the transcriptional co-regulator SPBP and its homologue RAI1 implicated in Smith-Magenis syndrome and Potocki-Lupski syndrome both belong to the expanding family of chromatin-binding proteins containing several domains involved in specific chromatin interactions.

TNF-α -238 or -308 GA/AA genotypes in patients with AS are associated with signs of less severe disease. Serum TNF-α is, however, undetectable in two-thirds of patients with AS and is not influenced by TNF-α promoter genotype or TNFi therapy. These data suggest a more significant role for TNF-α at local sites of inflammation in AS than through systemic effects.

The androgen receptor (AR) has a central role in development and maintenance of the male reproductive system and in the etiology of prostate cancer. The transcription factor Pax6 has recently been reported to act as a repressor of AR and to be hypermethylated in prostate cancer cells. SPBP is a transcriptional regulator that previously has been shown to enhance the activity of Pax6. In this study we have identified SPBP to act as a transcriptional coactivator of AR. We also show that Pax6 inhibits SPBP-mediated enhancement of AR activity on the AR target gene probasin promoter, a repression that was partly reversed by increased expression of SPBP. Enhanced expression of Pax6 reduced the amount of SPBP associated with the probasin promoter when assayed by ChIP in HeLa cells. We mapped the interaction between both AR and SPBP, and AR and Pax6 to the DNA-binding domains of the involved proteins. Further binding studies revealed that Pax6 and SPBP compete for binding to AR. These results suggest that Pax6 represses AR activity by displacing and/or inhibiting recruitment of coactivators to AR target promoters. Understanding the mechanism for inhibition of AR coactivators can give rise to molecular targeted drugs for treatment of prostate cancer.