Emerging roles of bromodomain protein 4 in regulation of stem cell identity

Non-oncogene dependencies: Novel opportunities for cancer therapy

Targeting oncogene addictions have changed the history of subsets of malignancies and continues to represent an excellent therapeutic opportunity. Nonetheless, alternative strategies are required to treat malignancies driven by undruggable oncogenes or loss of tumor suppressor genes and to overcome drug resistance also occurring in cancers addicted to actionable drivers. The discovery of non-oncogene addiction (NOA) uncovered novel therapeutically exploitable "Achilles' heels". NOA refers to genes/pathways not oncogenic per sé but essential for the tumor cell growth/survival while dispensable for normal cells. The clinical success of several classes of conventional and molecular targeted agents can be ascribed to their impact on both tumor cell-associated intrinsic as well as microenvironment-related extrinsic NOA. The integration of genetic, computational and pharmacological high-throughput approaches led to the identification of an expanded repertoire of synthetic lethality interactions implicating NOA targets. Only a few of them have been translated into the clinics as most NOA vulnerabilities are not easily druggable or appealing targets. Nonetheless, their identification has provided in-depth knowledge of tumor pathobiology and suggested novel therapeutic opportunities. Here, we summarize conceptual framework of intrinsic and extrinsic NOA providing exploitable vulnerabilities. Conventional and emerging methodological approaches used to disclose NOA dependencies are reported together with their limits. We illustrate NOA paradigmatic and peculiar examples and outline the functional/mechanistic aspects, potential druggability and translational interest. Finally, we comment on difficulties in exploiting the NOA-generated knowledge to develop novel therapeutic approaches to be translated into the clinics and to fully harness the potential of clinically available drugs.

Hematopoiesis: a BETter understanding

Epigenetic modifications are known to be crucial for hematopoietic stem cell (HSC) differentiation, with the BET family member BRD4 playing a vital role in this as an epigenetic reader. In this issue of EMBO reports, Yang et al (2023) demonstrate that the absence of BRD4 leads to senescence in HSCs and hematopoietic progenitor cells (HPCs), affecting the expression of crucial genes involved in myeloid and erythroid development. These data suggest that BRD4 has a protective role in preserving histone tails, thereby sustaining normal HSC/HPC functions.

Downregulation of BRD4 attenuates high glucose-induced damage of trophoblast cells by inhibiting activation of AKT/mTOR pathway

It was elucidated that bromodomain-containing protein 4 (BRD4) has involvement with diabetic complication. However, the role and molecular mechanism of BRD4 in gestational diabetes mellitus (GDM) are still unclear. In this study, the mRNA and protein contents of BRD4 in placenta tissues of GDM patients and high glucose (HG)-induced HTR8/SVneo cells were detected by qRT-PCR and western blot assay. CCK-8, EdU staining, flow cytometry as well as western blot were applied for the appraisement of cell viability and apoptosis. Wound healing assay and transwell assay were conducted for the assessment of cell migration and invasion. Oxidative stress and inflammatory factors were detected. Additionally, the contents of AKT/mTOR pathway-related proteins were estimated applying western blot. It was discovered that BRD4 expression was ascended in tissues and HG-induced HTR8/SVneo cells. BRD4 downregulation cut down the contents of p-AKT and p-mTOR but had no effects on the total protein levels of AKT or mTOR in HG-induced HTR8/SVneo cells. BRD4 depletion promoted cell viability, enhanced proliferative capability, and reduced cell apoptotic level. Moreover, BRD4 depletion facilitated cell migrative and invasive capabilities, and repressed the oxidative stress as well as inflammatory damage in HG-induced HTR8/SVneo cells. The activation of Akt reversed the protective impacts of BRD4 depletion on HG-induced HTR8/SVneo cells. To sum up, BRD4 silencing may alleviate HG-induced HTR8/SVneo cell damage through the inhibition of the AKT/mTOR pathway.

CDK9 inhibitors in multiple myeloma: a review of progress and perspectives

Currently, multiple myeloma is not yet considered a curable disease. Despite the recent advances in therapy, the average patient lifespan is still unsatisfactory. Recently, CDK9 inhibitors emerged as a suitable agent to overcome resistance and prolong survival in patients with poor diagnoses. Downregulation of c-MYC, XIAP, Mcl-1 and restoration of p53 tumor-suppressive functions seems to play a key role in achieving clinical response. The applicability of the first generation of CDK9 inhibitors was limited due to relatively high toxicity, but the introduction of novel, highly selective drugs, seems to reduce the effects of off-target inhibition. CDK9 inhibitors were able to induce dose-dependent cytotoxicity in Doxorubicin-resistant, Lenalidomide-resistant and Bortezomib-resistant cell lines. They seem to be effective in cell lines with unfavorable prognostic factors, such as p53 deletion, t(4; 14) and t(14; 16). In preclinical trials, the application of CDK9 inhibitors led to tumor cells apoptosis, tumor growth inhibition and tumor mass reduction. Synergistic effects between CDK9 inhibitors and either Venetoclax, Bortezomib, Lenalidomide or Erlotinib have been proven and are awaiting verification in clinical trials. Although conclusions should be drawn with due care, obtained reports suggest that including CDK9 inhibitors into the current drug regimen may turn out to be beneficial, especially in poor prognosis patients.

CRYAB predicts clinical prognosis and is associated with immunocyte infiltration in colorectal cancer

Background

αB-Crystallin (CRYAB) is differentially expressed in various tumors. However, the correlation between CRYAB and immune cell infiltration in colorectal cancer (CRC) remains unclear.

Materials & Methods

Kaplan-Meier survival curves in The Cancer Genome Atlas (TCGA) were used to evaluate the relationship between CRYAB expression and both overall survival and progression-free survival. The relationships between CRYAB expression and infiltrating immune cells and their corresponding gene marker sets were examined using the TIMER database.

Results

The expression of CRYAB was lower in CRC tumor tissues than in normal tissues (P < 0.05). High CRYAB gene expression and high levels of CRYAB gene methylation were correlated with high-grade malignant tumors and more advanced tumor, nodes and metastasis (TNM) cancer stages. In addition, in colorectal cancer, there was a positive correlation between CRYAB expression and immune infiltrating cells including neutrophils, macrophages, CD8 + T cells, and CD4 + T cells, as well as immune-related genes including CD2, CD3D, and CD3E. Methylation sites such as cg13084335, cg15545878, cg13210534, and cg15318568 were positively correlated with low expression of CRYAB.

Conclusion

Because CRYAB likely plays an important role in immune cell infiltration, it may be a potential tumor-suppressor gene in CRC and a potential novel therapeutic target and predictive biomarker for colorectal cancer (CRC).

Emerging roles of bromodomain protein 4 in regulation of stem cell identity

Understanding the mechanism of fate decision and lineage commitment is the key step for developing novel stem cell applications in therapeutics. This process is coordinately regulated through systematic epigenetic reprogramming and concomitant changes in the transcriptional landscape of the stem cells. One of the bromo- and extra-terminal domain (BET) family member proteins, bromodomain protein 4 (BRD4), performs the role of epigenetic reader and modulates gene expression by recruiting other transcription factors and directly regulating RNA polymerase II elongation. Controlled gene regulation is the critical step in maintenance of stem cell potency and dysregulation may lead to tumor formation. As a key transcriptional factor and epigenetic regulator, BRD4 contributes to stem cell maintenance in several ways. Being a druggable target, BRD4 is an attractive candidate for exploiting its potential in stem cell therapeutics. Therefore, it is crucial to elucidate how BRD4, through its interplay with pluripotency transcriptional regulators, control lineage commitment in stem cells. Here, we systemically review the role of BRD4 in complex gene regulatory network during three specific states of stem cell transitions: cell differentiation, cell reprogramming and transdifferentiation. A thorough understanding of BRD4 mediated epigenetic regulation in the maintenance of stem cell potency will be helpful to strategically control stem cell fates in regenerative medicine.