The C-terminal SET domains of ALL-1 and TRITHORAX interact with the INI1 and SNR1 proteins, components of the SWI/SNF complex

Abstract

The ALL-1 gene was discovered by virtue of its involvement in human acute leukemia. Its Drosophila homolog trithorax (trx) is a member of the trx-Polycomb gene family, which maintains correct spatial expression of the Antennapedia and bithorax complexes during embryogenesis. The C-terminal SET domain of ALL-1 and TRITHORAX (TRX) is a 150-aa motif, highly conserved during evolution. We performed yeast two hybrid screening of Drosophila cDNA library and detected interaction between a TRX polypeptide spanning SET and the SNR1 protein. SNR1 is a product of snr1, which is classified as a trx group gene. We found parallel interaction in yeast between the SET domain of ALL-1 and the human homolog of SNR1, INI1 (hSNF5). These results were confirmed by in vitro binding studies and by demonstrating coimmunoprecipitation of the proteins from cultured cells and͞or transgenic f lies. Epitope-tagged SNR1 was detected at discrete sites on larval salivary gland polytene chromosomes, and these sites colocalized with around one-half of TRX binding sites. Because SNR1 and INI1 are constituents of the SWI͞SNF complex, which acts to remodel chromatin and consequently to activate transcription, the interactions we observed suggest a mechanism by which the SWI͞SNF complex is recruited to ALL-1͞trx targets through physical interactions between the C-terminal domains of ALL-1 and TRX and INI1͞SNR1.The ALL-1 gene is involved in human acute leukemia, in particular infant and secondary leukemia, through chromosome translocations or partial tandem duplications (1-3). The chromosome translocations result in expression of chimeric proteins composed of the N-terminal Ϸ1,300 residues of ALL-1 linked to a C-terminal polypeptide encoded by any (Ͼ25) of the partner genes. The gene duplications produce altered (longer) ALL-1 proteins. ALL-1 is the human homolog of Drosophila trx (4). The latter is a member of the trithorax group (trx-G) gene family that together with the Polycomb group (Pc-G) genes act to control expression of the Antennapedia and bithorax homeotic gene complexes determining segment identify in Drosophila (ref. 5 and reviewed in refs. 6 and 7). Expression or silencing of the homeotic genes (HOM) is established by the gap and pair-rule genes at the cellular blastoderm stage. This determined state is maintained during subsequent development by the collective action of the trx-G and Pc-G genes, which function as transcriptional activators and repressors, respectively. trx-G͞Pc-G genes act through specific response elements present within their target genes (8,9). This activity is evidenced by the physical localization of the protein products of several trx-G͞Pc-G genes, including trx and Pc, to multiple sites (presumed to be the response elements in target genes) on salivary gland polytene chromosomes of third star larvae (refs. 10-13 and references therein).Converging lines of evidence suggest that trx-G and Pc-G genes act by establishing open and repressive chromatin states, respectively. A striking feature is the similarity...

Crosstalk between leukemia-associated proteins MOZ and MLL regulates HOX gene expression in human cord blood CD34+ cells

“…Histone acetylation and histone H3K4 methylation are predominant modifications associated with gene activation, whereas histone H3K9 methylation is correlated with gene repression. The H3K4 methyltransferase MLL was found to interact with the HAT CBP (Ernst et al, 2001), as well as the SWI/SNF chromatin-remodeling complex (Rozenblatt-Rosen et al, 1998), to activate the transcription of targets genes. An MLL supercomplex appears to function at the level of promoters.…”

MLL: How complex does it get?

“…One of them is the MLL SET domain itself, showing the ability to homo-dimerize [Rozovskaia et al, 2000]. Another protein that interacts with the carboxyl-terminus of MLL is hSNF5, a member of the SWI/SNF protein complex that functions in chromatin remodeling [Rozenblatt-Rosen et al, 1998]. Binding of MLL to chromatin-associated proteins supports the idea that wild-type MLL regulates target gene expression at the level of chromatin through interactions with other transcriptional regulators.…”

Self-association of the SET domains of human ALL-1 and of Drosophila TRITHORAX and ASH1 proteins

“…This highly conserved sequence is present in proteins implicated in transcriptional activation as well as in proteins associated with silencing (Jenuwein et al, 1998). A substantial e ort has been recently invested by us (Rozenblatt-Rosen et al, 1998) and others (Cui et al, 1998;Cardoso et al, 1998) in attempts to ®nd protein(s) interacting with metazoan SET domains. In parallel, studies in yeast demonstrated that the S. cerevisiae SET 1 protein interacts through the SET motif with the checkpoint MEC3 protein involved in DNA repair and telomere function (Corda et al, 1999).…”

“…Applying yeast two hybrid methodology as well as other techniques, we have shown that the SET domains of ALL-1 and its Drosophila homologue TRX interact with human INI1 and its Drosophila homologue SNR1, respectively (Rozenblatt-Rosen et al, 1998). SNR1 is encoded by a trithorax-group gene.…”