Thierry Lerouge

NSD1 is essential for early post-implantation development and has a catalytically active SET domain

The nuclear receptor‐binding SET domain‐containing protein (NSD1) belongs to an emerging family of proteins, which have all been implicated in human malignancy. To gain insight into the biological functions of NSD1, we have generated NSD1‐deficient mice by gene disruption. Homozygous mutant NSD1 embryos, which initiate mesoderm formation, display a high incidence of apoptosis and fail to complete gastrulation, indicating that NSD1 is a developmental regulatory protein that exerts function(s) essential for early post‐implantation development. We have also examined the enzymatic potential of NSD1 and found that its SET domain possesses intrinsic histone methyltransferase activity with specificity for Lys36 of histone H3 (H3‐K36) and Lys20 of histone H4 (H4‐K20).

Two distinct nuclear receptor interaction domains in NSD1, a novel SET protein that exhibits characteristics of both corepressors and coactivators

NSD1, a novel 2588 amino acid mouse nuclear protein that interacts directly with the ligand‐binding domain (LBD) of several nuclear receptors (NRs), has been identified and characterized. NSD1 contains a SET domain and multiple PHD fingers. In addition to these conserved domains found in both positive and negative Drosophila chromosomal regulators, NSD1 contains two distinct NR interaction domains, NID−L and NID+L, that exhibit binding properties of NIDs found in NR corepressors and coactivators, respectively. NID−L, but not NID+L, interacts with the unliganded LBDs of retinoic acid receptors (RAR) and thyroid hormone receptors (TR), and this interaction is severely impaired by mutations in the LBD α‐helix 1 that prevent binding of corepressors and transcriptional silencing by apo‐NRs. NID+L, but not NID−L, interacts with the liganded LBDs of RAR, TR, retinoid X receptor (RXR), and estrogen receptor (ER), and this interaction is abrogated by mutations in the LBD α‐helix 12 that prevent binding of coactivators of the ligand‐induced transcriptional activation function AF‐2. A novel variant (FxxLL) of the NR box motif (LxxLL) is present in NID+L and is required for the binding of NSD1 to holo‐LBDs. Interestingly, NSD1 contains separate repression and activation domains. Thus, NSD1 may define a novel class of bifunctional transcriptional intermediary factors playing distinct roles in both the presence and absence of ligand.

Selective interaction between the chromatin-remodeling factor BRG1 and the heterochromatin-associated protein HP1α

Mammalian heterochromatin protein 1 (HP1) α, HP1β and HP1γ are closely related non‐histone chromosomal proteins that function in gene silencing, presumably by organizing higher order chromatin structures. Here, we show by co‐immunoprecipitation that HP1α, but neither HP1β nor HP1γ, forms a complex with the BRG1 chromatin‐remodeling factor in HeLa cells. In vitro, BRG1 interacts directly and preferentially with HP1α. The region conferring this preferential binding has been mapped to residues 106–180 of the HP1α C‐terminal chromoshadow domain. Using site‐directed mutagenesis, we have identified three amino acid residues I113, A114 and C133 in HP1α (K, P and S in HP1β and HP1γ) that are essential for the selective interaction of HP1α with BRG1. Interestingly, these residues were also shown to be critical for the silencing activity of HP1α. Taken together, these results demonstrate that mammalian HP1 proteins are biochemically distinct and suggest an entirely novel function for BRG1 in modulating HP1α‐containing heterochromatic structures.

Nizp1, a novel multitype zinc finger protein that interacts with the NSD1 histone lysine methyltransferase through a unique C2HR motif.

ABSTRACT Haploinsufficiency of the NSD1 gene is a hallmark of Sotos syndrome, and rearrangements of this gene by translocation can cause acute myeloid leukemia. The NSD1 gene product is a SET-domain histone lysine methyltransferase that has previously been shown to interact with nuclear receptors. We describe here a novel NSD1-interacting protein, Nizp1, that contains a SCAN box, a KRAB-A domain, and four consensus C2H2-type zinc fingers preceded by a unique finger derivative, referred to herein as the C2HR motif. The C2HR motif functions to mediate protein-protein interaction with the cysteine-rich (C5HCH) domain of NSD1 in a Zn(II)-dependent fashion, and when tethered to RNA polymerase II promoters, represses transcription in an NSD1-dependent manner. Mutations of the cysteine or histidine residues in the C2HR motif abolish the interaction of Nizp1 with NSD1 and compromise the ability of Nizp1 to repress transcription. Interestingly, converting the C2HR motif into a canonical C2H2 zinc finger has a similar effect. Thus, Nizp1 contains a novel type of zinc finger motif that functions as a docking site for NSD1 and is more than just a degenerate evolutionary remnant of a C2H2 motif.