Origin Firing Research Articles

Metabolic clogging of mannose triggers dNTP loss and genomic instability in human cancer cells.

Mannose has anticancer activity that inhibits cell proliferation and enhances the efficacy of chemotherapy. How mannose exerts its anticancer activity, however, remains poorly understood. Here, using genetically engineered human cancer cells that permit the precise control of mannose metabolic flux, we demonstrate that the large influx of mannose exceeding its metabolic capacity induced metabolic remodeling, leading to the generation of slow-cycling cells with limited deoxyribonucleoside triphosphates (dNTPs). This metabolic remodeling impaired dormant origin firing required to rescue stalled forks by cisplatin, thus exacerbating replication stress. Importantly, pharmacological inhibition of de novo dNTP biosynthesis was sufficient to retard cell cycle progression, sensitize cells to cisplatin, and inhibit dormant origin firing, suggesting dNTP loss-induced genomic instability as a central mechanism for the anticancer activity of mannose.

Forensic Examination of Post-Fire Damaged Electrical Conductors by Using X-Ray Radiographs

Structural fires globally have a catastrophic impact on loss of life, property damage, and socioeconomic factors. Forensic scientists, engineers, and/or fire investigators — often working together as fire investigation practitioners — are commonly tasked with determining both the area of fire origin and its cause. During the course of a fire investigation, a fire investigation practitioner may implement an origin determination methodology termed “arc mapping” or an “arc survey.” The correct application of an arc survey as a fire origin determination method is dependent on the fire investigation practitioner’s ability to distinguish and characterize features observed on post-fire damage electrical wiring and equipment. Experiments were conducted to generate a dataset of post-fire damaged electrical conductor artifacts. Generated artifacts were visually examined, compared, and characterized by X-ray examination. The research results produced a validated, novel, non-destructive methodology for utilizing X-ray imagery to reliably distinguish and characterize electrical conductor damage features for forensic investigations.

Chronic treatment with ATR and CHK1 inhibitors does not substantially increase the mutational burden of human cells

DNA replication stress (RS) entails the frequent slow down and arrest of replication forks by a variety of conditions that hinder accurate and processive genome duplication. Elevated RS leads to genome instability, replication catastrophe and eventually cell death. RS is particularly prevalent in cancer cells and its exacerbation to unsustainable levels by chemotherapeutic agents remains a cornerstone of cancer treatments. The adverse consequences of RS are normally prevented by the ATR and CHK1 checkpoint kinases that stabilize stressed forks, suppress origin firing and promote cell cycle arrest when replication is perturbed. Specific inhibitors of these kinases have been developed and shown to potentiate RS and cell death in multiple in vitro cancer settings. Ongoing clinical trials are now probing their efficacy against various cancer types, either as single agents or in combination with mainstay chemotherapeutics. Despite their promise as valuable additions to the anti-cancer pharmacopoeia, we still lack a genome-wide view of the potential mutagenicity of these new drugs. To investigate this question, we performed chronic long-term treatments of TP53-depleted human cancer cells with ATR and CHK1 inhibitors (ATRi, AZD6738/ceralasertib and CHK1i, MK8776/SCH-900776). ATR or CHK1 inhibition did not significantly increase the mutational burden of cells, nor generate specific mutational signatures. Indeed, no notable changes in the numbers of base substitutions, short insertions/deletions and larger scale rearrangements were observed despite induction of replication-associated DNA breaks during treatments. Interestingly, ATR inhibition did induce a slight increase in closely-spaced mutations, a feature previously attributed to translesion synthesis DNA polymerases. The results suggest that ATRi and CHK1i do not have substantial mutagenic effects in vitro when used as standalone agents.

A Case Study on the Effects of Weather Conditions on Forest Fire Propagation Parameters in the Malekroud Forest in Guilan, Iran

The present study investigates the effect of climatic parameters, such as air relative humidity and wind speed, on fire spread propagation indexes in the Malekroud Forest, Iran using the FARSITE simulator based on Rothermel’s original fire spread equation. Standard fuel models are used to calibrate the vegetation cover. Sorensen (SC) and kappa (κ) coefficients, as well as the Overestimation Index (OI), are used to estimate the simulation’s accuracy. The results confirm that using both ambient condition data and appropriate fuel models is crucial to reaching reasonable results in fire propagation simulations. The values of the Rate of Fire Spread (ROS), Flame Length (FML), and Fire Line Intensity (FLI) are reported for each particular scenario. The simulation results show that the Sorensen and Kappa coefficient for situations most similar to the real fire reached 0.82 and 0.80, respectively. The investigated fire’s severity is categorized as low-condition fire behavior. The simulation shows that fire propagation falls harshly in the case of air relative humidity by more than 72%, and we will not witness natural fire propagation on a large scale.

Firing of Replication Origins Is Disturbed by a CDK4/6 Inhibitor in a pRb-Independent Manner.

Over the last decade, CDK4/6 inhibitors (palbociclib, ribociclib and abemaciclib) have emerged as promising anticancer drugs. Numerous studies have demonstrated that CDK4/6 inhibitors efficiently block the pRb-E2F pathway and induce cell cycle arrest in pRb-proficient cells. Based on these studies, the inhibitors have been approved by the FDA for treatment of advanced hormonal receptor (HR) positive breast cancers in combination with hormonal therapy. However, some evidence has recently shown unexpected effects of the inhibitors, underlining a need to characterize the effects of CDK4/6 inhibitors beyond pRb. Our study demonstrates how palbociclib impairs origin firing in the DNA replication process in pRb-deficient cell lines. Strikingly, despite the absence of pRb, cells treated with palbociclib synthesize less DNA while showing no cell cycle arrest. Furthermore, this CDK4/6 inhibitor treatment disturbs the temporal program of DNA replication and reduces the density of replication forks. Cells treated with palbociclib show a defect in the loading of the Pre-initiation complex (Pre-IC) proteins on chromatin, indicating a reduced initiation of DNA replication. Our findings highlight hidden effects of palbociclib on the dynamics of DNA replication and of its cytotoxic consequences on cell viability in the absence of pRb. This study provides a potential therapeutic application of palbociclib in combination with other drugs to target genomic instability in pRB-deficient cancers.

The Adaptive Mechanisms and Checkpoint Responses to a Stressed DNA Replication Fork.

DNA replication is a tightly controlled process that ensures the faithful duplication of the genome. However, DNA damage arising from both endogenous and exogenous assaults gives rise to DNA replication stress associated with replication fork slowing or stalling. Therefore, protecting the stressed fork while prompting its recovery to complete DNA replication is critical for safeguarding genomic integrity and cell survival. Specifically, the plasticity of the replication fork in engaging distinct DNA damage tolerance mechanisms, including fork reversal, repriming, and translesion DNA synthesis, enables cells to overcome a variety of replication obstacles. Furthermore, stretches of single-stranded DNA generated upon fork stalling trigger the activation of the ATR kinase, which coordinates the cellular responses to replication stress by stabilizing the replication fork, promoting DNA repair, and controlling cell cycle and replication origin firing. Deregulation of the ATR checkpoint and aberrant levels of chronic replication stress is a common characteristic of cancer and a point of vulnerability being exploited in cancer therapy. Here, we discuss the various adaptive responses of a replication fork to replication stress and the roles of ATR signaling that bring fork stabilization mechanisms together. We also review how this knowledge is being harnessed for the development of checkpoint inhibitors to trigger the replication catastrophe of cancer cells.

ATR kinase supports normal proliferation in the early S phase by preventing replication resource exhaustion

The ATR kinase, which coordinates cellular responses to DNA replication stress, is also essential for the proliferation of normal unstressed cells. Although its role in the replication stress response is well defined, the mechanisms by which ATR supports normal cell proliferation remain elusive. Here, we show that ATR is dispensable for the viability of G0-arrested naïve B cells. However, upon cytokine-induced proliferation, Atr-deficient B cells initiate DNA replication efficiently, but by mid-S phase they display dNTP depletion, fork stalling, and replication failure. Nonetheless, productive DNA replication and dNTP levels can be restored in Atr-deficient cells by suppressing origin firing, such as partial inhibition of CDC7 and CDK1 kinase activities. Together, these findings indicate that ATR supports the proliferation of normal unstressed cells by tempering the pace of origin firing during the early S phase to avoid exhaustion of dNTPs and importantly also other replication factors.

Neural network and kinetic modelling of human genome replication reveal replication origin locations and strengths.

In human and other metazoans, the determinants of replication origin location and strength are still elusive. Origins are licensed in G1 phase and fired in S phase of the cell cycle, respectively. It is debated which of these two temporally separate steps determines origin efficiency. Experiments can independently profile mean replication timing (MRT) and replication fork directionality (RFD) genome-wide. Such profiles contain information on multiple origins' properties and on fork speed. Due to possible origin inactivation by passive replication, however, observed and intrinsic origin efficiencies can markedly differ. Thus, there is a need for methods to infer intrinsic from observed origin efficiency, which is context-dependent. Here, we show that MRT and RFD data are highly consistent with each other but contain information at different spatial scales. Using neural networks, we infer an origin licensing landscape that, when inserted in an appropriate simulation framework, jointly predicts MRT and RFD data with unprecedented precision and underlies the importance of dispersive origin firing. We furthermore uncover an analytical formula that predicts intrinsic from observed origin efficiency combined with MRT data. Comparison of inferred intrinsic origin efficiencies with experimental profiles of licensed origins (ORC, MCM) and actual initiation events (Bubble-seq, SNS-seq, OK-seq, ORM) show that intrinsic origin efficiency is not solely determined by licensing efficiency. Thus, human replication origin efficiency is set at both the origin licensing and firing steps.

PTBP1 enforces ATR-CHK1 signaling determining the potency of CDC7 inhibitors

CDC7 kinase is crucial for DNA replication initiation and fork processing. CDC7 inhibition mildly activates the ATR pathway, which further limits origin firing; however, to date the relationship between CDC7 and ATR remains controversial. We show that CDC7 and ATR inhibitors are either synergistic or antagonistic depending on the degree of inhibition of each individual kinase. We find that Polypyrimidine Tract Binding Protein 1 (PTBP1) is important for ATR activity in response to CDC7 inhibition and genotoxic agents. Compromised PTBP1 expression makes cells defective in RPA recruitment, genomically unstable, and resistant to CDC7 inhibitors. PTBP1 deficiency affects the expression and splicing of many genes indicating a multifactorial impact on drug response. We find that an exon skipping event in RAD51AP1 contributes to checkpoint deficiency in PTBP1-deficient cells. These results identify PTBP1 as a key factor in replication stress response and define how ATR activity modulates the activity of CDC7 inhibitors.

THE ACCURACY OF GILILAWA DARAT WILDFIRE SPREAD ESTIMATION USING BURN SEVERITY AND WRF-SFIRE MODEL

In this research, the origin of the wildfire area is assessed by using the potential of burn severity and the WRF-SFIRE model. This research focuses on the mountainous savanna region, by taking the case of the Gililawa Darat wildfire event. The most accurate index among Sentinel-2B optical burn severity indices, i.e. dNBR, MIRBI, dMIRBI, CSI, dCSI, NDVI, dNDVI, EVI, and dEVI and among Landsat-8 OLI/TIRS thermal and mixed burn severity indices, i.e. LST, dLST, LST/EVI, and d(LST/EVI) was used to map the areas with low burn severity, an indication generally found at origin area. A series of fire spread simulation from these areas was conducted using WRF-SFIRE to assess the accuracy of each simulation in reproducing the burned area. The burn severity accuracy assessment showed that dNBR and dCSI indices had the highest value of Overall Accuracy and Kappa Hat Coefficient, i.e. 91.67% and 0.889 (almost perfect agreement). However, dNBR was the most suitable index for mapping burn severity in the region due to its goodness-of-fit measure for linear regression model with the R-squared value of 0.7856. The assessment of thermal and mixed burn severity indices based on Landsat-8 OLI/TIRS resulted in LST, LST/EVI, and d(LST/EVI) gained the same overall accuracy of 58.33% and Kappa Hat Coefficient of 0.444 indicating moderate agreement, whereas dLST performed poorer than these indices. However, it is not recommended to use these burn severity indices in the region due to the nonlinearity of severity level with the index value. According to WRF-SFIRE simulations result, it was found that fire ignition started from low burn severity area coordinates which have a distance of 0 to 334 metres from the origin area resulting in fire area witan h overall accuracy value range from 77.04% to 81.90% and Kappa Hat Coefficient value range from 0.536 to 0.626. The simulation from the origin area resulted in an overall accuracy of 81.57%, a Kappa hat coefficient of 0.613, underestimated burned area ratio of 0.08, overestimated burned area ratio of 0.23, and a backing fire perimeter difference ratio of 0.4 to the reference.
 Keywords: wildfire; Gililawa Darat; wildfire spread; burn severity; WRF-SFIRE, fire origin area

THE DYNAMICS OF LANDSCAPE FIRES IS IN UKRAINE AND EKOLOGO-EKONOMIC CONSEQUENCES OF THEIR ORIGIN

In the article the geoecological aspects of emergency situations are examined related to the landscape fires, their negative influence on an environment. Information is analysed about the dynamics of amount of origin of landscape fires, areas overcame a fire and to the inflicted harm for period 2007-2011 on territory of Ukraine. It is expedient to utillize materials of the presented researches for forming of base of the consequences given in relation to scales at the emergency situations of technogenic and natural character, related to the landscape fires.

Fault diagnosis of reciprocating machinery based on improved MEEMD-SqueezeNet

Reciprocating machinery structure is complex, and its signal is nonlinear and nonstationary. Because of the complex working environment, the signal usually contains noise interference. Modified Ensemble Empirical Mode Decomposition(MEEMD) reduces residual noise by introducing permutation entropy. But it directly eliminates components larger than the threshold, which may lose the effective information of the original signal. Deep learning models can solve nonlinear problems. But with the number of network layers increases, it increases the number of parameters, resulting in long model training time. Based on the above analysis, this paper proposes a fault diagnosis of reciprocating machinery based on improved MEEMD-SqueezeNet. By introducing multi-scale permutation entropy to replace the original single-scale permutation entropy, the calculated entropy contains more scale information. Singular value decomposition (SVD) is carried out to denoise the signal larger than the threshold to retain more effective information in the original signal. Convert the noise reduced 1D time series to 2D images by Gram Angle Field(GAF) to preserve the temporal correlation of 1D vibration data. Combined with the idea of Inception series model, an InFire module is proposed to replace the original Fire model of SqueezeNet. Use the improved SqueezeNet to extract features from the generated 2D images, and finally input the softmax classifier for classification to obtain fault diagnosis results. The simulation experiment and noise reduction comparison experiment prove that the improved MEEMD method proposed in this paper can effectively achieve signal noise reduction and improve the overall average accuracy of diagnosis from 89.49% to 94.35%. The fault classification comparison experiments prove that the accuracy of improved SqueezeNet is basically the same as that of VGG19. Compared with SqueezeNet, the accuracy of improved Squeezenet is improved by 1.77%, and the number of model parameters is reduced by nearly 29.4%. In terms of training time, it is proved that the training time of the improved SqueezeNet is basically the same as that of SqueezeNet, accounting for only one-third of the training time of VGG19. The improved SqueezeNet not only ensures lower training time, but also improves the accuracy of SqueezeNet. The above experimental results show that the proposed method reduces the model training time and improves the fault diagnosis accuracy of reciprocating machinery.

Emerging strategies for cancer therapy by ATR inhibitors.

DNA replication stress (RS) causes genomic instability and vulnerability in cancer cells. To counteract RS, cells have evolved various mechanisms involving the ATR kinase signaling pathway, which regulates origin firing, cell cycle checkpoints, and fork stabilization to secure the fidelity of replication. However, ATR signaling also alleviates RS to support cell survival by driving RS tolerance, thereby contributing to therapeutic resistance. Cancer cells harboring genetic mutations and other changes that disrupt normal DNA replication increase the risk of DNA damage and the levels of RS, conferring addiction to ATR activity for sustainable replication and susceptibility to therapeutic approaches using ATR inhibitors (ATRis). Therefore, clinical trials are currently being conducted to evaluate the efficacy of ATRis as monotherapies or in combination with other drugs and biomarkers. In this review, we discuss recent advances in the elucidation of the mechanisms by which ATR functions in the RS response and its therapeutic relevance when utilizing ATRis.

An adapted hourly Himawari-8 fire product for China: principle, methodology and verification

Abstract. Wildfires exert strong influences on the environment, ecology, economy and public security. However, the existing hourly Himawari-8 fire product produced by the Japan Meteorological Agency (JMA) presents large uncertainties and is not suitable for reliable real-time fire monitoring in China. To fill this gap, the National Satellite Meteorological Center (NSMC) proposed an adaptive hourly Himawari-8 fire product for China based on the original Himawari-8 source by employing a dynamical threshold for fire extraction and a database of ground thermal sources. According to the visually extracted reference and consistency check, we found that the NSMC-Himawari-8 fire product effectively removed a majority of false fire alarms included in the original Himawari-8 fire product. Based on a rare field-collected ground reference dataset, we evaluated the reliability of original Himawari-8 and NSMC-Himawari-8 fire products across China. The overall accuracy of the raw Himawari-8 fire product was 54 % and 59 % (not considering the omission errors), respectively. As a comparison, by identifying more real fire pixels and avoiding a majority of false fire alarms, the overall accuracy of the NSMC-Himawari-8 fire product was 80 % and 84 % (not considering the omission errors), respectively, making it an ideal source for improved real-time fire monitoring across China. This research also provides a useful reference for employing a local dataset of underlying surfaces and thermal sources to enhance the accuracy of global fire products in specific regions. The NSMC-Himawari-8 fire product can be downloaded at http://figshare.com (last access: 17 April 2023) with the following DOI: https://doi.org/10.6084/m9.figshare.21550248 (Chen et al., 2022a).

Replisome dysfunction upon inducible TIMELESS degradation synergizes with ATR inhibition to trigger replication catastrophe.

The structure of DNA replication forks is preserved by TIMELESS (TIM) in the fork protection complex (FPC) to support seamless fork progression. While the scaffolding role of the FPC to couple the replisome activity is much appreciated, the detailed mechanism whereby inherent replication fork damage is sensed and counteracted during DNA replication remains largely elusive. Here, we implemented an auxin-based degron system that rapidly triggers inducible proteolysis of TIM as a source of endogenous DNA replication stress and replisome dysfunction to dissect the signaling events that unfold at stalled forks. We demonstrate that acute TIM degradation activates the ATR-CHK1 checkpoint, whose inhibition culminates in replication catastrophe by single-stranded DNA accumulation and RPA exhaustion. Mechanistically, unrestrained replisome uncoupling, excessive origin firing, and aberrant reversed fork processing account for the synergistic fork instability. Simultaneous TIM loss and ATR inactivation triggers DNA-PK-dependent CHK1 activation, which is unexpectedly necessary for promoting fork breakage by MRE11 and catastrophic cell death. We propose that acute replisome dysfunction results in a hyper-dependency on ATR to activate local and global fork stabilization mechanisms to counteract irreversible fork collapse. Our study identifies TIM as a point of replication vulnerability in cancer that can be exploited with ATR inhibitors.

Анализ технических решений по противопожарной защите обычных лестничных клеток при реконструкции секционных жилых зданий

Introduction. Fire protection of stairwells plays a key role in ensuring human safety in residential buildings of sectional type, since a single stairwell blocked by fire makes it impossible to safely evacuate people from all apartments in a section and complicates the possibility of their rescue. Modern regulations exclude the possibility of gas-dynamic connection of apartments directly to stairwells by prohibiting evacuation from apartments directly to the stairwell in buildings higher than 3 floors. Since a considerable part of the existing housing stock in the country has such architectural solutions, in which apartments have access to stairwells directly, there is a need for a scientific analysis of the effectiveness of engineering solutions to ensure the necessary level of protection of usual stairwells during the reconstruction of buildings. The purpose of this article is to develop criteria and mathematical relationships for evaluating the effectiveness of engineering solutions for the protection of stairwells. Methods. Analytical and mathematical methods are used to assess the combined effect of the dynamics of changes in fire hazards in the stairwell and in apartments with the location of a rescued person, depending on the engineering solutions for the stairwell protection. Results. Theoretical provisions have been developed to estimate the influence of different engineering solutions to limit the spread of fire from a burning apartment to a stairwell and apartments on the other floors, taking into account the ventilation of the stairwell and the fire resistance of structures in relation to the problem of ensuring evacuation and saving people. The developed provisions have been approbated. Conclusions. On the basis of the researches criteria and mathematical relations have been worked out to estimate the efficiency of different engineering solutions to protect stairwells, based on the forecasts of dynamics of spread of fire hazards from a fire origin to the stairwell and apartments, taking into account window openings, fire resistance of constructions in comparison with the time intervals of evacuation and rescuing people.

Mistimed origin licensing and activation stabilize common fragile sites under tight DNA-replication checkpoint activation

Genome integrity requires replication to be completed before chromosome segregation. The DNA-replication checkpoint (DRC) contributes to this coordination by inhibiting CDK1, which delays mitotic onset. Under-replication of common fragile sites (CFSs), however, escapes surveillance, resulting in mitotic chromosome breaks. Here we asked whether loose DRC activation induced by modest stresses commonly used to destabilize CFSs could explain this leakage. We found that tightening DRC activation or CDK1 inhibition stabilizes CFSs in human cells. Repli-Seq and molecular combing analyses showed a burst of replication initiations implemented in mid S-phase across a subset of late-replicating sequences, including CFSs, while the bulk genome was unaffected. CFS rescue and extra-initiations required CDC6 and CDT1 availability in S-phase, implying that CDK1 inhibition permits mistimed origin licensing and firing. In addition to delaying mitotic onset, tight DRC activation therefore supports replication completion of late origin-poor domains at risk of under-replication, two complementary roles preserving genome stability.

DNA replication initiation factor RECQ4 possesses a role in antagonizing DNA replication initiation

Deletion of the conserved C-terminus of the Rothmund-Thomson syndrome helicase RECQ4 is highly tumorigenic. However, while the RECQ4 N-terminus is known to facilitate DNA replication initiation, the function of its C-terminus remains unclear. Using an unbiased proteomic approach, we identify an interaction between the RECQ4 N-terminus and the anaphase-promoting complex/cyclosome (APC/C) on human chromatin. We further show that this interaction stabilizes APC/C co-activator CDH1 and enhances APC/C-dependent degradation of the replication inhibitor Geminin, allowing replication factors to accumulate on chromatin. In contrast, the function is blocked by the RECQ4 C-terminus, which binds to protein inhibitors of APC/C. A cancer-prone, C-terminal-deleted RECQ4 mutation increases origin firing frequency, accelerates G1/S transition, and supports abnormally high DNA content. Our study reveals a role of the human RECQ4 C-terminus in antagonizing its N-terminus, thereby suppressing replication initiation, and this suppression is impaired by oncogenic mutations.

Abstract P2-03-10: DNA replication licensing is associated with resistance to CDK4/6 inhibitors in ER-positive breast cancer

Abstract Background: The use of CDK4/6 inhibitors (CDK4/6i) has led to a remarkable progress in the treatment of advanced ER-positive (+) breast cancer (BC). The fact that both CDK4/6i and endocrine therapy (ET) target cell-cycle G1-S transition suggests some overlap of resistance mechanisms. However, clinical variability in response to CDK4/6i in patients progressing on ET suggests the involvement of additional or unique resistance mechanisms. Using bioinformatics analyses of clinical and preclinical data, we now identified genes involved in DNA replication licensing, in particular, excess MCM2 as a new mechanism of resistance to CDK4/6i. Methods: Gene expression data from the neoadjuvant NeoPalAna trial of the CDK4/6i palbociclib (Palbo) and the aromatase inhibitor (AI) anastrozole in ER+ BC was downloaded from Gene Expression Omnibus (GSE93204). Response to AI and Palbo was obtained using the published Ki67 immunohistochemistry data and cutoff on biopsies post treatment. Gene Set Enrichment Analysis comparing tumors with different sensitivity to AI vs. Palbo was performed using the Gene Ontology related to DNA replication, DNA repair, and DNA damage checkpoint. The DNA replication gene set was further sub-assigned by their selective role in origin licensing, firing, elongation, replication repair, and checkpoint regulation. A series of bioinformatics analyses was applied on five ER+/HER2-negative BC cell lines with gene expression and DepMap (from CCLE) and Palbo sensitivity data (from GDSC). Two ER+ BC cell models (MCF7 and T47D) and their estrogen deprivation (mimicking AIs)-resistant (EDR) derivatives were used for further studies including RNA-seq, Palbo sensitivity (data from PMID: 33536276), and chromatin fractionation assays. Results: We found that the DNA replication-associated gene set, comprising > 80% genes outside the Rb-loss gene signature, was significantly enriched in baseline biopsies of Palbo-resistant (PalboR) tumors from patients in the NeoPalAna trial. Of the DNA replication genes, the subset of genes involved in origin licensing were preferentially enriched in PalboR vs. AI-resistant tumors. Similarly, the enrichment of genes involved in replication initiation was also seen in ER+/HER2-negative BC cell lines with a decreased response to Palbo. Notably, these PalboR cell lines showed a reduced vitality to shRNA knockdown of the replication initiation genes compared to randomly selected other genes or the Rb-loss gene set. Based on the modeling of DepMap gene dependency score and Palbo sensitivity, we nominated minichromosome maintenance 2 (MCM2), the key origin licensing factor, as the top gene that is essential for PalboR cell survival. Additionally, using our previously reported MCF7-EDR and T47D-EDR cell models with increased or decreased sensitivity to Palbo compared to their parental lines, respectively, we observed a corresponding decrease or increase in the expression of origin licensing genes and MCM2 in EDR vs. parental lines. Decreased Palbo sensitivity in the EDR cells was associated with sustained MCM2 chromatin loading and reduced expression of genes including the cyclin-dependent kinase inhibitor p21. Ongoing studies investigate whether elevated MCM2 levels confer resistance to CDK4/6i by resolving replication stress. Conclusions: Our strategic bioinformatics analyses reveal that excess DNA replication licensing is associated with CDK4/6i resistance in clinical and preclinical settings upon resistance to estrogen deprivation. Among the replication initiation-associated genes, MCM2 plays a potential role in conferring CDK4/6i resistance via sustaining origin licensing and suppressing p21. Our study provides a new avenue via lens of replication licensing to explore novel mechanisms and therapeutic opportunities in CDK4/6i resistance. Citation Format: Sarmistha Nanda, Martin J. Shea, Rachel Schiff, C. Kent Osborne, Mothaffar Rimawi, Xiaoyong Fu. DNA replication licensing is associated with resistance to CDK4/6 inhibitors in ER-positive breast cancer [abstract]. In: Proceedings of the 2022 San Antonio Breast Cancer Symposium; 2022 Dec 6-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2023;83(5 Suppl):Abstract nr P2-03-10.

An Investigation of the Factors Affecting the Mechanical Smoke Extraction System for A Building with an Atrium

convective boundary layer or interface layer the building smoke rises from the originof fire due to its buoyancy [2].