B lymphocyte-restricted transcription of immunoglobulin heavy-chain (IgH) genes is specified by elements within the variable region (Va) promoter and the intronic enhancer (EIX). The gene encoding a protein that binds a VH promoter proximal site necessary for induced ix-heavy-chain transcription has been cloned. This B-cell specific protein, termed Bright (B cell regulator of IgH transcription), is found in both soluble and matrix insoluble nuclear fractions. Bright binds the minor groove of a restricted ATC sequence that is sufficient for nuclear matrix association. This sequence motif is present in previously described matrix-associating regions (MARs) proximal to the promoter and flanking EIX. Bright can activate Ela-driven transcription by binding these sites, but only when they occur in their natural context and in cell lines permissive for E~ activity. To bind DNA, Bright requires a novel tetramerization domain and a previously undescribed domain that shares identity with several proteins, including SWI1, a component of the SWI/SNF complex.
The SET and MYND Domain (SMYD) proteins comprise a unique family of multi-domain SET histone methyltransferases that are implicated in human cancer progression. Here we report an analysis of the crystal structure of the full length human SMYD3 in a complex with an analog of the S-adenosyl methionine (SAM) methyl donor cofactor. The structure revealed an overall compact architecture in which the “split-SET” domain adopts a canonical SET domain fold and closely assembles with a Zn-binding MYND domain and a C-terminal superhelical 9 α-helical bundle similar to that observed for the mouse SMYD1 structure. Together, these structurally interlocked domains impose a highly confined binding pocket for histone substrates, suggesting a regulated mechanism for its enzymatic activity. Our mutational and biochemical analyses confirm regulatory roles of the unique structural elements both inside and outside the core SET domain and establish a previously undetected preference for trimethylation of H4K20.
Although much has been learned about basal levels of immunoglobulin (Ig) transcription, the regulatory effects of cytokines and antigen (Ag) (23,36). Nuclear extracts prepared from B cells contain several different octamer-binding proteins, two of which are thought to be expressed only in B cells (33,34,40). In addition to the octamer sequence, several other sequences that contribute to basal VH transcription have been identified, some of which bind to the IgH enhancer that resides in the intron between the rearranged V-and constant-region coding sequences (3,4,6,13,15,20,28,30,35
The SMYD3 histone methyl transferase (HMTase) and the nuclear chaperone, HSP90, have been independently implicated as proto-oncogenes in several human malignancies. We show that a degenerate tetratricopeptide repeat (TPR)-like domain encoded in the SMYD3 C-terminal domain (CTD) mediates physical interaction with HSP90. We further demonstrate that the CTD of SMYD3 is essential for its basal HMTase activity and that the TPR-like structure is required for HSP90-enhanced enzyme activity. Loss of SMYD3-HSP90 interaction leads to SMYD3 mislocalization within the nucleus, thereby losing its chromatin association. This results in reduction of SMYD3-mediated cell proliferation and, potentially, impairment of SMYD3′s oncogenic activity. These results suggest a novel approach for blocking HSP90-driven malignancy in SMYD3-overexpressing cells with a reduced toxicity profile over current HSP90 inhibitors.
), we characterize B-cell-specific protein-DNA interactions at -500 and -200 bp upstream of the IL immunoglobulin heavy chain promoter whose abundances were increased by interleukin-5 plus antigen. Because of the high A+T/G+C ratio of these sequences and the consistent findings by others that enhancer-and promoterlike regions are often located near matrix-associated regions, we asked whether these sequences might also be involved in binding to the nuclear matrix. Indeed, DNA fragments containing the -500 binding site were bound by nuclear matrix proteins. Furthermore, UV cross-linking studies showed that the DNA binding site for interleukin-5-plus-antigen-inducible proteins could also bind to proteins solubilized from the nuclear matrix. Nuclear matrix-associated sequences have also been demonstrated on either side of the intronic immunoglobulin heavy chain enhancer. Our data suggest a topological model by which interactions among proteins bound to the promoter and distal enhancer sequences might occur.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.