Investigation of the molecular mechanism of the putative histone reader function of the NSD histone methyltransferase family.
Final Report Abstract
The polycomb repressive complex 2 (PRC2) plays an important role to regulate the transcription of a large number of genes, by creating the repressive H3K27me3 histone methylation mark. Not surprisingly, aberrant function of PRC2 is linked to human diseases, especially cancer. Despite growing recognition of the role of PRC2 in diseases, little is known about its regulation in vivo. In particular, how precisely PRC2 is recruited to its target genes in normal versus diseases states remains poorly understood. Proteins associated with PRC2 have been implicated to be important for its recruitment as well as for the fine-tuning of the function of PRC2. The main goal of this project was/is to decipher the function of the PRC2 associated protein PHF19 and its biological role. Importantly, in humans a short isoform of PHF19 exists (PHF19S), which lacks the C-terminal part of PHF19 but possess two potential histone reader domains. I wanted to address if those isoforms might possess distinct biological functions. Following discoveries were made: 1) Both PHF19 isoforms and possesses a H3K36me3 binding Tudor domain. 2) Only the full length PHF19 protein but not the short isoform interacts with PRC2. 3) The interaction with PRC2 is facilitated via a C-terminal chromo-like domain, which is not present in the short isoform. 4) The chromo-like domain has a so far undescribed secondary structure. 5) In human neuroblastom cells the two isoforms appear to have opposite functions. PHF19S enhances proliferation and prevents differentiation, while the long isoform enhances proliferation. 6) The balance of both isoforms is regulated by retinoic acid. 7) Microarray experiments support that PHF19S and PHF19L regulate common target genes in an opposite manner. In summary, these results suggest that PHF19S could function as a dominant negative version of PHF19 by competing for the same histone tail binding site. Since PHF19S was found upregulated in multiple cancer types, small molecule inhibitor, which prevents the binding of PHF19S to its target, might therefore be suitable to treat human cancer. In addition, C17orf96 has been found as a so far hardly characterized PRC2 associated protein. Following discoveries regarding C17orf96 were made: 1) C17orf96 is an intrinsically unstructured and nuclear protein with no obvious domain. 2) C17orf96 is mainly expressed in embryonic tissues and in the adult brain. 3) C17orf96 forms at least two distinct complexes. a) A complex consisting of at least C17orf96, Elongin B and Elongin C, but not containing members of PRC2; b) C17orf96 in complex with PRC2. 4) C17orf96 interact with PRC2 via is C-terminal unstructured end 5) C17orf96 interacts directly with Elongin B/C via its N-terminal domain, as well as with separate BC- Box, which is common for Elongin B/C interacting proteins. In sum, C17orf96 and Elongin B/C probably play an important role to precisely regulate the function of PRC2. During these projects, I also have developed a complex purification work-flow which allows me to obtain high quality protein complexes on a regular basis.
Publications
- Phf19 links methylated Lys36 of histone H3 to regulation of Polycomb activity. Nat Struct Mol Biol. 2012 Dec;19(12):1257-65
Ballaré C, Lange M, Lapinaite A, Martin GM, Morey L, Pascual G, Liefke R, Simon B, Shi Y, Gozani O, Carlomagno T, Benitah SA, Di Croce L
(See online at https://doi.org/10.1038/nsmb.2434)
