Biology subjects

Shaikh, A.

Publications and source records attributed to Shaikh, A..

4 recordsLinked to original sources

bioRxiv2023

Acetyl transferase EP300 deficiency leads to chronic replication stress mediated by defective fork protection at stalled replication forks

Mutations in the epigenetic regulator and global transcriptional activator, E1A binding protein (EP300), is being increasingly reported in aggressive hematological malignancies including adult T-cell leukemia/lymphoma (ATLL). However, the mechanistic contribution of EP300 dysregulation to cancer initiation and progression are currently unknown. Independent inhibition of EP300 in human cells results in the differential expression of genes involved in regulating the cell cycle, DNA replication and DNA damage response. Nevertheless, specific function played by EP300 in DNA replication initiation, progression and replication fork integrity has not been studied. Here, using ATLL cells as a model to study EP300 deficiency and an p300-selective PROTAC degrader, degrader as a pharmacologic tool, we reveal that EP300-mutated cells display prolonged cell cycle kinetics, due to pronounced dysregulations in DNA replication dynamics leading to persistent genomic instability. Aberrant DNA replication in EP300-mutated cells is characterized by elevated replication origin firing due to increased replisome pausing genome-wide. We demonstrate that EP300 deficiency results in nucleolytic degradation of nascently synthesized DNA at stalled forks due to a prominent defect in fork stabilization and protection. This in turn results in the accumulation of single stranded DNA gaps at collapsed replication forks, in EP300-deficient cells. Inhibition of Mre11 nuclease rescues the ssDNA accumulation indicating a dysregulation in downstream mechanisms that restrain nuclease activity at stalled forks. Importantly, we find that the absence of EP300 results in decreased expression of BRCA2 protein expression and a dependency on POLD3-mediated error-prone replication restart mechanisms. The overall S-phase abnormalities observed lead to under-replicated DNA in G2/M that instigates mitotic DNA synthesis. This in turn is associated with mitotic segregation defects characterized by elevated micronuclei formation, accumulation of cytosolic DNA and transmission of unrepaired inherited DNA lesions in the subsequent G1-phase in EP300-deficient cells. We demonstrate that the DNA replication dynamics of EP300-mutated cells ATLL cells recapitulate features of BRCA-deficient cancers. Altogether these results suggest that mutations in EP300 cause chronic DNA replication stress and defective replication fork restart results in persistent genomic instability that underlie aggressive chemo-resistant tumorigenesis in humans.

cancer biology↗

bioRxiv2022

A Simple Model of Cortical Intraregional Metastability

Transient synchronization of bursting activity in neural networks, which occurs in patterns of metastable phase relationships between neurons, is a notable feature of network dynamics observed in vivo. However, the mechanisms that contribute to this dynamical complexity in neural circuits are not well understood. Local circuits in cortical regions consist of populations of neurons with diverse intrinsic oscillatory features. In this study, we numerically show that the phenomenon of transient synchronization, also referred to as metastability, emerges in an inhibitory neural population when the neurons intrinsic fast-spiking dynamics are appropriately modulated by slower inputs from an excitatory neural population. Using a compact model of a mesoscopic-scale network consisting of excitatory pyramidal and inhibitory fast-spiking neurons, our work demonstrates a relationship between the frequency of neural oscillations and the features of emergent metastability. In addition, a novel metric is formulated to characterize collective transitions in metastable networks. Finally, we discuss a blueprint to model the whole-brain resting-state dynamics using our scalable representation of intraregional network metastability.

neuroscience↗

bioRxiv2022

A pro-oxidant combination of resveratrol and copper down-regulates multiple biological hallmarks of ageing and neurodegeneration

Several hundred billion to a trillion cells die in the body every day, and cell-free chromatin particles (cfChPs) that are released from them enter into the extracellular compartments of the body, including into the circulation. We have earlier reported that cfChPs can readily enter into healthy cells to damage their DNA, activate apoptotic pathways and induce inflammatory cytokines. We hypothesized that repeated lifelong assault on healthy cells by cfChPs is the underlying cause of ageing, and that the ageing process could be retarded by deactivating cfChPs. The latter can be effected by oxygen radicals that are generated upon admixing the nutraceuticals resveratrol (R) and copper (Cu). Using confocal microscopy and antibodies against DNA and histone we detected copious presence of extra-cellular cfChPs in brain of ageing mice, and observed that these were deactivated / eradicated following prolong oral administration of small quantities of R-Cu. Deactivation / eradication of cfChPs was associated with down-regulation of several biological hallmarks of ageing in brain cells which included reduction in: 1) telomere attrition, 2) amyloid deposition, 3) DNA damage, 4) apoptosis, 5) inflammation, 6) senescence, 7) aneuploidy and 8) mitochondrial dysfunction. At a systemic level, R- Cu treatment led to significant reduction in blood levels of glucose, cholesterol and C-reactive protein. These results suggest that cfChPs may be global instigators of ageing and neurodegeneration, and that therapeutic use of R-Cu may help to retard the process of ageing.

neuroscience↗

bioRxiv2019

High-Throughput Functional Annotation of Natural Products by Integrated Activity Profiling

Determining mechanism of action (MOA) is one of the biggest challenges in natural products discovery. Here, we report a comprehensive platform that uses Similarity Network Fusion (SNF) to improve MOA predictions by integrating data from the cytological profiling high-content imaging platform and the gene expression platform FUSION, and pairs these data with untargeted metabolomics analysis for de novo bioactive compound discovery. The predictive value of the integrative approach was assessed using a library of target-annotated small molecules as benchmarks. Using Kolmogorov-Smirnov (KS) tests to compare in-class to out-of-class similarity, we found that SNF retains the ability to identify significant in-class similarity across a diverse set of target classes, and could also find target classes that were not detectable in either platform alone. This confirmed that integration of expression-based and image-based phenotypes can accurately report on MOA. Furthermore, we integrated untargeted metabolomics of complex natural product fractions with the SNF network to map biological signatures to specific metabolites. Three examples are presented where SNF coupled with metabolomics was used to directly functionally characterize natural products and accelerate identification of bioactive metabolites, including the discovery of the novel azoxy-containing biaryl compounds parkamycins A and B. Our results support SNF integration of multiple phenotypic screening approaches along with untargeted metabolomics as a powerful approach for advancing natural products drug discovery. Significance statementNew data-driven methods to aid in the discovery and biological characterization of natural products are necessary to advance the field. Assigning the mechanism of action (MOA) to novel bioactive compounds is an essential step in drug discovery and a major challenge in chemical biology. Despite technological advances in isolation, synthesis and screening strategies that make many bioactive substances readily available, in most cases their biological targets remain unknown. Additionally, a major bottleneck in natural products discovery efforts is de-replication of the large number of known compounds that predominate in crude extracts and fraction libraries. Advances in metabolomics has provided a better understanding of the constituents present in these libraries, but is not sufficient in itself to drive the discovery of novel biologically active metabolites. Here we describe an unbiased, data-driven strategy which integrates phenotypic screening with metabolomics into a single platform that provides rapid identification and functional annotation of natural products. This approach can be applied to any cohort of uncharacterized chemicals and represents a strategy that could significantly accelerate the process of drug discovery.

pharmacology and toxicology↗