Functional Interaction of BRCA1 and CREBBP in Murine Hematopoiesis

Small-molecule CBP/p300 histone acetyltransferase inhibition mobilizes leukocytes from the bone marrow via the endocrine stress response

Mutations of the CBP/p300 histone acetyltransferase (HAT) domain can be linked to leukemic transformation in humans, suggestive of a checkpoint of leukocyte compartment sizes. Here, we examined the impact of reversible inhibition of this domain by the small-molecule A485. We found that A485 triggered acute and transient mobilization of leukocytes from the bone marrow into the blood. Leukocyte mobilization by A485 was equally potent as, but mechanistically distinct from, granulocyte colony-stimulating factor (G-CSF), which allowed for additive neutrophil mobilization when both compounds were combined. These effects were maintained in models of leukopenia and conferred augmented host defenses. Mechanistically, activation of the hypothalamus-pituitary-adrenal gland (HPA) axis by A485 relayed shifts in leukocyte distribution through corticotropin-releasing hormone receptor 1 (CRHR1) and adrenocorticotropic hormone (ACTH), but independently of glucocorticoids. Our findings identify a strategy for rapid expansion of the blood leukocyte compartment via a neuroendocrine loop, with implications for the treatment of human pathologies.

The Role of CREBBP/EP300 and Its Therapeutic Implications in Hematological Malignancies

Disordered histone acetylation has emerged as a key mechanism in promoting hematological malignancies. CREB-binding protein (CREBBP) and E1A-binding protein P300 (EP300) are two key acetyltransferases and transcriptional cofactors that regulate gene expression by regulating the acetylation levels of histone proteins and non-histone proteins. CREBBP/EP300 dysregulation and CREBBP/EP300-containing complexes are critical for the initiation, progression, and chemoresistance of hematological malignancies. CREBBP/EP300 also participate in tumor immune responses by regulating the differentiation and function of multiple immune cells. Currently, CREBBP/EP300 are attractive targets for drug development and are increasingly used as favorable tools in preclinical studies of hematological malignancies. In this review, we summarize the role of CREBBP/EP300 in normal hematopoiesis and highlight the pathogenic mechanisms of CREBBP/EP300 in hematological malignancies. Moreover, the research basis and potential future therapeutic implications of related inhibitors were also discussed from several aspects. This review represents an in-depth insight into the physiological and pathological significance of CREBBP/EP300 in hematology.

BRCA1 and TP53 codeficiency causes a PARP inhibitor-sensitive erythroproliferative neoplasm

Mutations in the BRCA1 tumor suppressor gene, such as 5382insC (BRCA1insC), give carriers an increased risk for breast, ovarian, prostate, and pancreatic cancers. We have previously reported that, in mice, Brca1 deficiency in the hematopoietic system leads to pancytopenia and, as a result, early lethality. We explored the cellular consequences of Brca1-null and BRCA1insC alleles in combination with Trp53 deficiency in the murine hematopoietic system. We found that Brca1 and Trp53 codeficiency led to a highly penetrant erythroproliferative disorder that is characterized by hepatosplenomegaly and by expanded megakaryocyte erythroid progenitor (MEP) and immature erythroid blast populations. The expanded erythroid progenitor populations in both BM and spleen had the capacity to transmit the disease into secondary mouse recipients, suggesting that Brca1 and Trp53 codeficiency provides a murine model of hematopoietic neoplasia. This Brca1/Trp53 model replicated Poly (ADP-ribose) polymerase (PARP) inhibitor olaparib sensitivity seen in existing Brca1/Trp53 breast cancer models and had the benefits of monitoring disease progression and drug responses via peripheral blood analyses without sacrificing experimental animals. In addition, this erythroid neoplasia developed much faster than murine breast cancer, allowing for increased efficiency of future preclinical studies.

BRCA1 Antibodies Matter

Breast cancer susceptibility gene 1 (BRCA1) encodes a tumor suppressor that is frequently mutated in familial breast and ovarian cancer patients. BRCA1 functions in multiple important cellular processes including DNA damage repair, cell cycle checkpoint activation, protein ubiquitination, chromatin remodeling, transcriptional regulation, as well as R-loop formation and apoptosis. A large number of BRCA1 antibodies have been generated and become commercially available over the past three decades, however, many commercial antibodies are poorly characterized and, when widely used, led to unreliable data. In search of reliable and specific BRCA1 antibodies (Abs), particularly antibodies recognizing mouse BRCA1, we performed a rigorous validation of a number of commercially available anti-BRCA1 antibodies, using proper controls in a panel of validation applications, including Western blot (WB), immunoprecipitation (IP), immunoprecipitation-mass spectrometry (IP-MS), chromatin immunoprecipitation (ChIP) and immunofluorescence (IF). Furthermore, we assessed the specificity of these antibodies to detect mouse BRCA1 protein through the use of testis tissue and mouse embryonic fibroblasts (MEFs) from Brca1^+/+ and Brca1^Δ11/Δ11 mice. We find that Ab1, D-9, 07-434 (for recognizing human BRCA1) and 287.17, 440621, BR-64 (for recognizing mouse BRCA1) are specific with high quality performance in the indicated assays. We share these results here with the goal of helping the community combat the common challenges associated with anti-BRCA1 antibody specificity and reproducibility and, hopefully, better understanding BRCA1 functions at cellular and tissue levels.