This entry consists of AFF (AF4/FMR2) family of proteins which includes AFF1-AFF4 and the Drosophila protein Lilliputian [1-4]. Lilliputian acts in cytoskeleton regulation, segmentation and morphogenesis [2]. All AFF proteins are localised in the cell nucleus and are involved in regulation of gene expression. They are scaffold proteins that mediate the multisubunit super-elongation complex (SEC) assembly [1-4]. This entry represents the C-terminal homology domain (CHD, also known as C-terminal signature sequence), highly conserved among its members. This domain mediates the formation of an AFF4 homodimer or an AFF1-AFF4 heterodimer [4]. This domain is essential for AFF4 interaction with Transcription Start Site (TSS)-associated histone H3K27 whose acetylation signals SEC to regulate transcriptional elongation of the ESR1 gene [4]. Depletion of AFF4 reduces expression of ESR1, and, consequently inhibits breast cancer cell growth [4]. These proteins have been linked to human diseases such as acute lymphoblastic leukaemia and FRAXE [5].

1: Lilliputian: an AF4/FMR2-related protein that controls cell identity and cell growth. Wittwer F, van der Straten A, Keleman K, Dickson BJ, Hafen E; Development 2001;128:791-800. PMID:11171403

2: Transcriptional regulation of cytoskeletal functions and segmentation by a novel maternal pair-rule gene, lilliputian. Tang AH, Neufeld TP, Rubin GM, Muller HA; Development 2001;128:801-813. PMID:11171404

3: Structure of the super-elongation complex subunit AFF4 C-terminal homology domain reveals requirements for AFF homo- and heterodimerization. Chen Y, Cramer P; J Biol Chem. 2019;294:10663-10673. PMID:31147444

4: Acetylation of histone H3K27 signals the transcriptional elongation for estrogen receptor alpha. Gao Y, Chen L, Han Y, Wu F, Yang WS, Zhang Z, Huo T, Zhu Y, Yu C, Kim H, Lee M, Tang Z, Phillips K, He B, Jung SY, Song Y, Zhu B, Xu RM, Feng Q; Commun Biol. 2020;3:165. PMID:32265480

5: Functional characterization of the AFF (AF4/FMR2) family of RNA-binding proteins: insights into the molecular pathology of FRAXE intellectual disability. Melko M, Douguet D, Bensaid M, Zongaro S, Verheggen C, Gecz J, Bardoni B; Hum Mol Genet. 2011;20:1873-1885. PMID:21330300