Pinarbasi Degirmenci, N. | Search bioRxiv

bioRxiv2024

Chromatin-focused genetic and chemical screens identify BRPF1 as a targetable vulnerability in Taxol-resistant triple-negative breast cancer

Triple-negative breast cancer (TNBC) stands out as a particularly aggressive and frequently recurring form of breast cancer. Due to the absence of hormone receptors, the available treatment avenues are constrained, making chemotherapy the primary approach. Unfortunately, the development of resistance to chemotherapy poses a significant challenge, further restricting the already limited therapeutic alternatives for recurrent cases. Understanding the molecular basis of chemotherapy resistance in TNBC is pivotal for improving treatment outcomes. Here, we generated two different Taxol-resistant TNBC cell lines with a dose-escalation method to mimic chemotherapy resistance in vitro. These cells exhibited hallmark features of resistance, including reduced cell growth, altered morphology, and evasion of apoptosis. Transcriptome analysis uncovered elevated ABCB1 expression and multidrug-resistant phenotype in the resistant cells. To comprehensively investigate the key epigenetic regulators of Taxol resistance, we conducted chromatin-focused genetic and chemical screens and pinpointed Bromodomain and PHD Finger Containing 1 (BRPF1) as a novel regulator of Taxol resistance in TNBC cells. Knockout of BRPF1, the reader protein in the MOZ/MORF histone acetyl-transferase complex, but not the other complex members, sensitized resistant cells to Taxol. Additionally, BRPF1 inhibitors, PFI-4 and OF-1, in combination with Taxol significantly reduced cell viability. Transcriptome analysis upon BRPF1 loss or inhibition revealed a negative impact on ribosome biogenesis-related gene sets, resulting in a global decrease in protein translation in Taxol-resistant cells. Our ChIP-qPCR analysis demonstrated that active BRPF1 directly interacts with the ABCB1 promoter, enhancing its expression towards inducing a multidrug-resistant phenotype. Conversely, knockout or inhibition of BRPF1 leads to decreased ABCB1 expression. This dual mechanism critically sensitizes Taxol-resistant TNBC cells to chemotherapy. Our findings uncover a comprehensive molecular framework, highlighting the pivotal role of epigenetic reader protein BRPF1 in Taxol resistance and providing potential avenues for therapeutic intervention in TNBC.

cancer biology↗

bioRxiv2022

Chronically radiation-exposed survivor glioblastoma cells display poor response to Chk1 inhibition

Glioblastoma is the most common type of primary brain tumor with an aggressive clinical course, and one of the cornerstones in its treatment regimen is radiotherapy. However, tumor cells surviving after radiation is an indicator of treatment failure; therefore, better understanding of the molecular mechanisms regulating radiotherapy response is of utmost importance. In this study, we generated multiple clinically relevant irradiation exposed models, where we applied fractionated radiotherapy over a long period of time and selected irradiation-survivor (IR-Surv) glioblastoma cell populations. In these cells, we examined the transcriptomic alterations, cell cycle and growth rate changes as well as responses to secondary radiotherapy and DNA damage response (DDR) modulators. Accordingly, IR-Surv cells exhibited slower growth and partly retained their ability to resist secondary irradiation. Transcriptomic analysis revealed that IR-Surv cells upregulated the expression of DDR-related genes, such as CHK1, ATM, ATR, MGMT, and had better DNA repair capacity as an adaptive mechanism. Separately, we report IR-Surv cells to display downregulation of hypoxic signature and the lower induction of hypoxia target genes and not exhibiting the same level of hypoxia-induced changes with naive glioblastoma cells, as gauged by exposing cells to different hypoxia conditions. We also showed that Chk1 inhibition alone or in combination with irradiation significantly reduces cell viability in both naive and IR-Surv cells. However, IR-Surv cells were markedly less sensitive to Chk1 inhibition under hypoxic conditions. In conclusion, consistent with previous reports, we demonstrate the utility of combining DDR inhibitors and irradiation as a successful approach for both naive and IR-Surv glioblastoma cells as long as cells are refrained from hypoxic conditions. Thus, our findings with clinically relevant radiation survivor models will have future translational implications and benefit the optimization of combination therapies for glioblastoma patients.

cancer biology↗