Gamma Interferon-Dependent Transcriptional Memory via Relocalization of a Gene Locus to PML Nuclear Bodies▿ †

Memory of past cellular responses is an essential adaptation to repeating environmental stimuli. We addressed the question of whether gamma interferon (IFN-γ)-inducible transcription generates memory that sensitizes cells to a second stimulus. We have found that the major histocompatibility complex class II gene DRA is relocated to promyelocytic leukemia (PML) nuclear bodies upon induction with IFN-γ, and this topology is maintained long after transcription shut off. Concurrent interaction of PML protein with mixed-lineage leukemia generates a prolonged permissive chromatin state on the DRA gene characterized by high promoter histone H3 K4 dimethylation that facilitates rapid expression upon restimulation. We propose that the primary signal-induced transcription generates spatial and epigenetic memory that is maintained through several cell generations and endows the cell with increased responsiveness to future activation signals

CIITA regulates transcription onset via Ser5-phosphorylation of RNA Pol II

We describe the temporal order of recruitment of transcription factors, cofactors and basal transcriptional components and the consequent biochemical events that lead to activation of the major histocompatibility class II (MHCII) DRA gene transcription by IFN-γ. We found that the gene is ‘poised’ for activation since both the activators and a fraction of the basal transcriptional machinery are pre-assembled at the enhancer and promoter prior to IFN-γ treatment. The class II transactivator is synthesized following IFN-γ treatment and it is recruited to the enhanceosome leading to the subsequent recruitment of the CBP and GCN5 coactivators. This is followed by histone acetylation and recruitment of the SWI/SNF chromatin remodeling complex. CIITA also recruits the CDK7 and CDK9 kinases and enhances the ability of CDK7 to phosphorylate Pol II at Ser5 leading to initiation of mRNA synthesis. Thus, the gene-specific class II transactivator selects the target genes for expression by coordinating a multiple set of biochemical activities ranging from chromatin alterations and pre-initiation complex assembly to promoter clearance

Promyelocytic leukemia protein regulates angiogenesis and epithelial–mesenchymal transition to limit metastasis in MDA‐MB‐231 breast cancer cells

Promyelocytic leukemia protein (PML) modulates diverse cell functions that contribute to both tumor suppressor and pro‐oncogenic effects, depending on the cellular context. We show here that PML knockdown (KD) in MDA‐MB‐231, but not MCF7, breast cancer cells, prolonged stem‐cell‐like survival, and increased cell proliferation and migration, which is in line with gene‐enrichment results from their RNA sequencing analysis. Of note, increased migration was accompanied by higher levels of the epithelial–mesenchymal transition (EMT) regulator Twist‐related protein 2 (TWIST2). We showed here that PML binds to TWIST2 via its basic helix–loop–helix (bHLH) region and functionally interferes with the suppression of the epithelial target of TWIST2, CD24. In addition, PML ablation in MDA‐MB‐231 cells led to higher protein levels of hypoxia‐inducible factor 1‐alpha (HIF1a), resulting in a higher cell hypoxic response. Functionally, PML directly suppressed the induction of the HIF1a target gene vascular endothelial growth factor A (VEGFa). In line with these results, tumor xenografts of MDA‐MB‐231 PML‐KD cells had enhanced aggressive properties, including higher microvessel density, faster local growth, and higher metastatic ability, with a preference for lung. Collectively, PML suppresses the cancer aggressive behavior by multiple mechanisms that impede both the HIF–hypoxia–angiogenic and EMT pathways

The Temozolomide-Doxorubicin paradox in Glioblastoma in vitro-in silico preclinical drug-screening.

Acknowledgements: Authors would like to thank Eleftheria Parasiraki, Evangelos Liapis for all the help they provided, as well as Despina Tsoukatou for the expert technical assistance.Adjuvant Temozolomide is considered the front-line Glioblastoma chemotherapeutic treatment; yet not all patients respond. Latest trends in clinical trials usually refer to Doxorubicin; yet it can lead to severe side-effects if administered in high doses. While Glioblastoma prognosis remains poor, little is known about the combination of the two chemotherapeutics. Patient-derived spheroids were generated and treated with a range of Temozolomide/Doxorubicin concentrations either as monotherapy or in combination. Optical microscopy was used to monitor the growth pattern and cell death. Based on the monotherapy experiments, we developed a probabilistic mathematical framework in order to describe the drug-induced effect at the single-cell level and simulate drug doses in combination assuming probabilistic independence. Doxorubicin was found to be effective in doses even four orders of magnitude less than Temozolomide in monotherapy. The combination therapy doses tested in vitro were able to lead to irreversible growth inhibition at doses where monotherapy resulted in relapse. In our simulations, we assumed both drugs are anti-mitotic; Temozolomide has a growth-arrest effect, while Doxorubicin is able to cumulatively cause necrosis. Interestingly, under no mechanistic synergy assumption, the in silico predictions underestimate the in vitro results. In silico models allow the exploration of a variety of potential underlying hypotheses. The simulated-biological discrepancy at certain doses indicates a supra-additive response when both drugs are combined. Our results suggest a Temozolomide-Doxorubicin dual chemotherapeutic scheme to both disable proliferation and increase cytotoxicity against Glioblastoma

The Temozolomide–Doxorubicin paradox in Glioblastoma in vitro–in silico preclinical drug-screening

Abstract Adjuvant Temozolomide is considered the front-line Glioblastoma chemotherapeutic treatment; yet not all patients respond. Latest trends in clinical trials usually refer to Doxorubicin; yet it can lead to severe side-effects if administered in high doses. While Glioblastoma prognosis remains poor, little is known about the combination of the two chemotherapeutics. Patient-derived spheroids were generated and treated with a range of Temozolomide/Doxorubicin concentrations either as monotherapy or in combination. Optical microscopy was used to monitor the growth pattern and cell death. Based on the monotherapy experiments, we developed a probabilistic mathematical framework in order to describe the drug-induced effect at the single-cell level and simulate drug doses in combination assuming probabilistic independence. Doxorubicin was found to be effective in doses even four orders of magnitude less than Temozolomide in monotherapy. The combination therapy doses tested in vitro were able to lead to irreversible growth inhibition at doses where monotherapy resulted in relapse. In our simulations, we assumed both drugs are anti-mitotic; Temozolomide has a growth-arrest effect, while Doxorubicin is able to cumulatively cause necrosis. Interestingly, under no mechanistic synergy assumption, the in silico predictions underestimate the in vitro results. In silico models allow the exploration of a variety of potential underlying hypotheses. The simulated-biological discrepancy at certain doses indicates a supra-additive response when both drugs are combined. Our results suggest a Temozolomide–Doxorubicin dual chemotherapeutic scheme to both disable proliferation and increase cytotoxicity against Glioblastoma