Tomofusa Fukuyama

Target gene context influences the transcriptional requirement for the KAT3 family of CBP and p300 histone acetyltransferases.

One general principle of gene regulation is that DNA-binding transcription factors modulate transcription by recruiting cofactors that modify histones and chromatin structure. A second implicit principle is that a particular cofactor is necessary at all the target genes where the cofactor is recruited. Increasingly, these principles do not appear to be absolute, as experimentally defined relationships between transcription, cofactors, and chromatin modification grow in complexity. The KAT3 histone acetyltransferases CREB binding protein (CBP) and p300 have at least 400 interacting protein partners, thereby acting as hubs in gene regulatory networks. Studies using mutant primary cells indicate that the occurrence of CBP and p300 at any given target gene sometimes correlates with, rather than dictates transcription. This suggests that there are unexpected levels of redundancy between CBP/p300 and other unrelated coactivators, or that CBP/p300 recruitment may sometimes be coincidental. A transcription factor may therefore recruit the same group of coactivators as part of its “toolbox,” but it is the characteristics of the individual target gene that determines which coactivation “tools” are required for its transcription.

Conditional knockout mice reveal distinct functions for the global transcriptional coactivators CBP and p300 in T-cell development.

ABSTRACT The global transcriptional coactivators CREB-binding protein (CBP) and the closely related p300 interact with over 312 proteins, making them among the most heavily connected hubs in the known mammalian protein-protein interactome. It is largely uncertain, however, if these interactions are important in specific cell lineages of adult animals, as homozygous null mutations in either CBP or p300 result in early embryonic lethality in mice. Here we describe a Cre/LoxP conditional p300 null allele (p300 flox ) that allows for the temporal and tissue-specific inactivation of p300. We used mice carrying p300 flox and a CBP conditional knockout allele (CBP flox ) in conjunction with an Lck-Cre transgene to delete CBP and p300 starting at the CD4− CD8− double-negative thymocyte stage of T-cell development. Loss of either p300 or CBP led to a decrease in CD4+ CD8+ double-positive thymocytes, but an increase in the percentage of CD8+ single-positive thymocytes seen in CBP mutant mice was not observed in p300 mutants. T cells completely lacking both CBP and p300 did not develop normally and were nonexistent or very rare in the periphery, however. T cells lacking CBP or p300 had reduced tumor necrosis factor alpha gene expression in response to phorbol ester and ionophore, while signal-responsive gene expression in CBP- or p300-deficient macrophages was largely intact. Thus, CBP and p300 each supply a surprising degree of redundant coactivation capacity in T cells and macrophages, although each gene has also unique properties in thymocyte development.

Histone acetyltransferase CBP is vital to demarcate conventional and innate CD8+ T-cell development.

ABSTRACT Defining the chromatin modifications and transcriptional mechanisms that direct the development of different T-cell lineages is a major challenge in immunology. The transcriptional coactivators CREB binding protein (CBP) and the closely related p300, which comprise the KAT3 family of histone/protein lysine acetyltransferases, interact with over 50 T-lymphocyte-essential transcriptional regulators. We show here that CBP, but not p300, modulates the thymic development of conventional adaptive T cells versus those having unconventional innate functions. Conditional inactivation of CBP in the thymus yielded CD8 single-positive (SP) thymocytes with an effector-, memory-, or innate-like T-cell phenotype. In this regard, CD8 SP thymocytes in CBP mutant mice were phenotypically similar to those reported for Itk and Rlk protein tyrosine kinase mutants, including the increased expression of the T-cell master regulatory transcription factor eomesodermin (Eomes) and the interleukin-2 and -15 receptor beta chain (CD122) and an enhanced ability to rapidly produce gamma interferon. CBP was required for the expression of the Itk-dependent genes Egr2, Egr3, and Il2, suggesting that CBP helps mediate Itk-responsive transcription. CBP therefore defines a nuclear component of the signaling pathways that demarcate the development of innate and adaptive naïve CD8+ T cells in the thymus.

Genetic interaction between mutations in c-Myb and the KIX domains of CBP and p300 affects multiple blood cell lineages and influences both gene activation and repression.

Adult blood cell production or definitive hematopoiesis requires the transcription factor c-Myb. The closely related KAT3 histone acetyltransferases CBP (CREBBP) and p300 (EP300) bind c-Myb through their KIX domains and mice homozygous for a p300 KIX domain mutation exhibit multiple blood defects. Perplexingly, mice homozygous for the same KIX domain mutation in CBP have normal blood. Here we test the hypothesis that the CBP KIX domain contributes subordinately to hematopoiesis via a genetic interaction with c-Myb. We assessed hematopoiesis in mice bearing compound mutations of c-Myb and/or the KIX domains of CBP and p300, and measured the effect of KIX domain mutations on c-Myb-dependent gene expression. We found that in the context of a p300 KIX mutation, the CBP KIX domain mutation affects platelets, B cells, T cells, and red cells. Gene interaction (epistasis) analysis provides mechanistic evidence that blood defects in KIX mutant mice are consistent with reduced c-Myb and KIX interaction. Lastly, we demonstrated that the CBP and p300 KIX domains contribute to both c-Myb-dependent gene activation and repression. Together these results suggest that the KIX domains of CBP, and especially p300, are principal mediators of c-Myb-dependent gene activation and repression that is required for definitive hematopoiesis.

A mouse model reveals that Mfsd2a is critical for unfolded protein response upon exposure to tunicamycin

Major facilitator superfamily domain containing 2a (Mfsd2a) is a member of the major facilitator superfamily. Mfsd2a functions as a transporter for docosahexaenoic acid and also plays a role in the unfolded protein response (UPR) upon tunicamycin (TM) exposure. UPR is involved in the pathogenesis of various human diseases. TM and thapsigargin are representative experimental reagents that induce UPR. To elucidate the detailed function of Mfsd2a in UPR in vivo, we generated Mfsd2a-deficient mice and investigated the role of Mfsd2a during UPR induced by TM or thapsigargin. Phenotypically, Mfsd2a-deficient mice were small and short-lived. No gross anatomical abnormalities in Mfsd2a-deficient mice compared with the wild-type mice were exhibited. Embryonic fibroblasts derived from Mfsd2a-null mice failed to show induction of GRP78 and DDIT3 expressions upon TM exposure but not upon Tg exposure. This phenomenon could not be overcome despite the exposure under high TM concentration. Reconstitution of Mfsd2a in Mfsd2a-null MEF showed hypersensitivity to TM. Furthermore, we examined the physiological role of Mfsd2a against TM using an in vivo mouse model. DDIT3 induction by TM was drastically attenuated in both the liver and brain of Mfsd2a-deficient mice. These results reveal that Mfsd2a plays a critical role in UPR upon TM exposure.

T-Cells Null for the MED23 Subunit of Mediator Express Decreased Levels of KLF2 and Inefficiently Populate the Peripheral Lymphoid Organs

MED23, a subunit of the Mediator coactivator complex, is important for the expression of a subset of MAPK/ERK pathway-responsive genes, the constituents of which vary between cell types for reasons that are not completely clear. MAPK/ERK pathway-dependent processes are essential for T-cell development and function, but whether MED23 has a role in this context is unknown. We generated Med23 conditional knockout mice and induced Med23 deletion in early T-cell development using the lineage specific Lck-Cre transgene. While the total cell number and distribution of cell populations in the thymuses of Med23flox/flox;Lck-Cre mice were essentially normal, MED23 null T-cells failed to efficiently populate the peripheral lymphoid organs. MED23 null thymocytes displayed decreased expression of the MAPK/ERK-responsive genes Egr1, Egr2, as well as of the membrane glycoprotein Cd52 (CAMPATH-1). MED23 null CD4 single-positive thymocytes also showed decreased expression of KLF2 (LKLF), a T-cell master regulatory transcription factor. Indeed, similarities between the phenotypes of mice lacking MED23 or KLF2 in T-cells suggest that KLF2 deficiency in MED23 null T-cells is one of their key defects. Mechanistic experiments using MED23 null MEFs further suggest that MED23 is required for full activity of the MAPK-responsive transcription factor MEF2, which has previously been shown to mediate Klf2 expression. In summary, our data indicate that MED23 has critical roles in enabling T-cells to populate the peripheral lymphoid organs, possibly by potentiating MEF2-dependent expression of the T-cell transcription factor KLF2.