Role of BRD4 in Normal Hematopoiesis and Hematopoietic Stem Cell Biology

BRD4 在正常造血和造血干细胞生物学中的作用

• 批准号: 10741506
• 负责人: Feng-Chun Yang
• 金额: $ 7.91万
• 依托单位: UNIVERSITY OF TEXAS HLTH SCIENCE CENTER
• 依托单位国家: 美国
• 财政年份: 2021
• 资助国家: 美国
• 起止时间: 2021-12-01 至 2024-11-30
• 项目状态: 已结题
• 来源: https://reporter.nih.gov/project-details/10741506
• 关键词: Acetylation; Active Sites; Acute Myelocytic Leukemia; Affect; Apoptosis; BRD2 gene; Behavior; Binding; Biology; Bromodomain; Bromodomains and extra-terminal domain inhibitor; C-terminal; CD34 gene; Cell Cycle Progression; Cell Lineage; Cell Survival; Cell physiology; Cells; Chromatin; Chromatin Structure; Clinical Trials; Complex; Data; Development; Disease; Exhibits; Fibrosis; Frequencies; Gene Expression; Gene Targeting; Genes; Genetic Crosses; Genetic Transcription; Genomics; Goals; Hematologic Neoplasms; Hematology; Hematopoiesis; Hematopoietic; Hematopoietic Neoplasms; Hematopoietic System; Hematopoietic stem cells; Heterozygote; Histone Acetylation; Histones; Human; Impairment; In Vitro; Induction of Apoptosis; Inflammatory; Injections; Knock-out; Knockout Mice; Knowledge; Lysine; MYC gene; Malignant - descriptor; Malignant Neoplasms; Maps; Mediating; Mitotic Cell Cycle; Molecular; Mus; Myeloproliferative disease; Output; Pathogenesis; Population; Positive Transcriptional Elongation Factor B; Protein Family; Proteins; RNA Polymerase II; Regulation; Role; Solid; Solid Neoplasm; Tail; Testing; Thrombocytopenia; Toxic effect; Transcription Elongation; Transgenic Mice; Transgenic Organisms; clinically significant; cyclin T1; genome-wide; histone acetyltransferase; histone modification; in vivo; knock-down; leukemic transformation; member; mouse model; nuclease; overexpression; recruit; single-cell RNA sequencing; small molecule; small molecule inhibitor; stem cell biology; stem cell function; transcriptome; transgene expression; tumor

Bromodomain-containing protein 4 (BRD4) is a member of the BET (bromodomain and extra terminal domain) family proteins that also include BRD2, BRD3, and BRDT. BRD4 facilitates the initiation and elongation of transcription by binding to acetylated lysine residues of histone tails to promote the recruitment of the RNA polymerase II complex to sites of active transcription. Since BRD4 is required for MYC oncogene expression, BRD4 inhibition represents an attractive strategy to target MYC-dependent cancers via small-molecule inhibitors. BRD4 is over-expression in both solid tumors and myeloid malignancies, including acute myeloid leukemia (AML). BET inhibitors (BETi) have been shown to have efficacy against various types of tumors, especially MYC-driven cancers. Despite robust studies of BRD4 in solid tumors, the role of BRD4 in normal hematopoiesis and the impact of BRD4 overexpression on the pathogenesis of hematological malignancies remain largely unknown. Filling this critical gap of knowledge is the primary goal of this 3-year SHINE application. In the current project, we aim to determine the roles of BRD4 in hematopoietic stem/progenitor cells (HSC/HPCs) function and explore whether Brd4 overexpression affects HSC/HPC cell fate and leukemic transformation. Using a conditional Brd4 knock- out (Mx1Cre;Brd4f/f) mouse model, we found that while heterozygous deletion of Brd4 in mice did not cause noticeable changes in hematopoiesis, homozygous deletion of Brd4 in the hematopoietic system quickly diminished HSC/HPCs and pan lineage cells due to the induction of apoptosis. Therefore, the conditional Brd4 knock-out mouse model alone is not suitable for studying the hidden role of BRD4 in HSC/HPC functions. We thus generated several Brd4 transgenic (Tg) mouse lines with different levels of BRD4 transgene expression (ranging from 25% to 200%). Our preliminary data showed that overexpression of BRD4 (Brd4200%Tg) in hematopoietic cells altered HSC/HPC pools in vivo and increased HSC/HPC replating potential in vitro. Interestingly, re-expression of a lower level of BRD4 in Brd4Δ/Δ BMMNCs (Brd4Δ/Δ;Brd425%Tg) significantly increased the cell survival and the frequencies of CFU-Cs. We hypothesize that a hypomorph BRD4 mouse model (Mx1Cre;Brd4f/f;Brd425%Tg), by expressing a protectable level of BRD4 in hematopoiesis which allow for HSC/HPC survival, would suit better for evaluating the hidden role of BRD4 in HSC/HPC functions. We will also examine whether BETi affect normal hematopoiesis in mice. Furthermore, we will decipher how BRD4 regulates the HSC/HPCs functions by assessing genome-wide BRD4, P-TEFb, Pol-II, H3K27ac, and H3K122ac occupancies in HSC/HPCs and correlating with the gene expression outputs. These studies are timely and fundamentally crucial for filling an essential and critical gap of knowledge towards uncovering the hidden roles of BRD4 in normal and malignant hematopoiesis, thus fill a critical gap in knowledge on Brd4 in hematopoiesis and BETi for the treatment of hematopoietic malignancies.

含溴结构域蛋白4 （BRD4）是溴结构域和额外末端结构域的一个成员。