Molecular mechanisms of transcriptional control by Sp2
Biochemistry
Cell Biology
Final Report Abstract
Sp2 is an essential ubiquitously expressed transcription factor which occupies proximal promoters of highly expressed genes. Sp2 is closely related to the transcription factors Sp1 and Sp3, which all share three consecutive C2H2-type zinc fingers near their C-terminus, glutamine-rich domains, and two highly conserved short sequence motifs, the so-called Spbox close to the N-terminus and the button head box (Btd-box) preceding the first zinc finger. In previous ChIP-seq experiments, we found that Sp1 and Sp3 bind to a common set of sites distinct from Sp2 bound regions. Significantly, unlike Sp1 and Sp3, Sp2 does not require its DNA binding domain for genomic binding and it occupies target promoters independently of whether they contain a cognate DNA-binding motif. Hence the genomic targeting mechanism of Sp2 is strikingly different from Sp1 and Sp3. How Sp2 achieves recognition of its targets was unknown. In this project we set out to gain further insights into the genomic targeting mechanism of Sp2. ChIP-exo sequencing revealed genomic binding of Sp2 to a composite motif where a recognition sequence for TALE homeoproteins and a recognition sequence for the trimeric histone-fold domain protein Nf-y are separated by exactly eleven base pairs. We identified a complex consisting of the TALE homeoprotein Prep1, its interaction partner Pbx1, and Nf-y as the major partners in Sp2-promoter interaction. Dimeric Pbx1:Prep1 together with Nf-y recruits Sp2 to co-occupied regulatory elements. In turn, Sp2 potentiates binding of Pbx1:Prep1 and Nf-y. We also found that the Sp-box, a short sequence motif located close to the N-terminus of Sp2, is crucial for Sp2´s function as a cofactor. Finally, biochemical analysis revealed that Sp2 interacts directly with DNA-bound Pbx1:Prep1-Nf-y through its most N- terminal domain. Together, this study revealed a mechanism by which the DNA bindingindependent action of the transcription factor Sp2 potentiates genomic loading of Pbx1:Prep1 and Nf-y to composite motifs present in many promoters of highly expressed genes.
Publications
- (2012). Genome-wide localization and expression profiling establish Sp2 as a sequence-specific transcription factor regulating vitally important genes. Nucleic Acids Res. 40, 7844-7857
Terrados, G., Finkernagel, F., Stielow, B., Sadic, D., Neubert, J., Herdt, O., Krause, M., Scharfe, M., Jarek, M., and Suske, G.
(See online at https://doi.org/10.1093/nar/gks544) - (2015). Zinc finger independent genome-wide binding of Sp2 potentiates recruitment of histone-fold protein Nf-y distinguishing it from Sp1 and Sp3. PLOS Genet.11, e1005102
Völkel, S., Stielow, B., Finkernagel, F., Stiewe, T., Nist, A., and Suske, G.
(See online at https://doi.org/10.1371/journal.pgen.1005102) - (2017). NF-Y and SP transcription factors - New insights in a long-standing liaison. Biochim. Biophys. Acta 1860, 590-597
Suske, G.
(See online at https://doi.org/10.1016/j.bbagrm.2016.08.011) - (2018), Transcription factor Sp2 potentiates binding of the TALE homeoproteins Pbx1:Prep1 and the histone-fold domain protein Nf-y to composite genomic sites. J. Biol. Chem.
Völkel, S., Stielow B, Finkernagel F, Berger, D., Stiewe T, Nist A, Suske G.
(See online at https://doi.org/10.1074/jbc.RA118.005341)
