Biology subjects

Viswanathan, P.

Publications and source records attributed to Viswanathan, P..

7 recordsLinked to original sources

bioRxiv2024

The Mitochondrial Ubiquitin Ligase MARCHF5 Cooperates with MCL1 to Inhibit Apoptosis in KSHV-Transformed Primary Effusion Lymphoma Cell Lines

Kaposis sarcoma-associated herpesvirus (KSHV) causes several malignancies in people with HIV including Kaposis sarcoma and primary effusion lymphoma (PEL). We have previously shown that PEL cell lines require myeloid cell leukemia-1 (MCL1) to inhibit apoptosis. MCL1 is an oncogene that is amplified in cancers and causes resistance to chemotherapy regimens. MCL1 is thus an attractive target for drug development. The emerging clinical relevance and therapeutic potential of MCL1 motivated us to study the roles of this oncogene in PEL in depth. Using a systems biology approach, we uncovered an unexpected genetic interaction between MCL1 and MARCHF5 indicating that they function in the same pathway. MARCHF5 is an E3 ubiquitin ligase most known for regulating mitochondrial homeostasis and antiviral signaling, but not apoptosis. We thus investigated how MCL1 and MARCHF5 cooperate to promote PEL cell survival. CRISPR knockout (KO) of MARCHF5 in PEL cell lines resulted in a significant increase in apoptosis despite the presence of MCL1. The anti-apoptotic function of MARCHF5 was dependent on its E3 ligase and dimerization activities. Loss of MARCHF5 or inhibition of the 26S proteasome furthermore stabilized the MCL1 antagonist NOXA without affecting levels of MCL1. Interestingly, NOXA KO provides a fitness advantage to PEL cells suggesting that NOXA is the pro-apoptotic signal that necessitates the anti-apoptotic activities of MCL1 and MARCHF5. Finally, endogenous reciprocal co-immunoprecipitation experiments show that MARCHF5 and NOXA are found in the same protein complex. Our findings thus provide the mechanistic link that underlies the genetic interaction between MCL1 and MARCHF5. We propose that MARCHF5 induces the degradation of the MCL1 antagonist NOXA thus reinforcing the pro-survival role of MCL1 in these tumor cells. This newly appreciated interaction of the MCL1 and MARCHF5 oncogenes may be useful to improve the design of combination therapies for KSHV malignancies.

cancer biology↗

bioRxiv2022

Expression Ratios of the Anti-Apoptotic BCL2 Family Members Dictate the Selective Addiction of KSHV-Transformed Primary Effusion Lymphoma Cell Lines to MCL1

Kaposis sarcoma-associated herpesvirus (KSHV) causes several malignancies in people living with HIV, including primary effusion lymphoma (PEL). PEL cell lines exhibit oncogene addictions to both viral and cellular genes. Using CRISPR screens, we previously identified cellular oncogene addictions in PEL cell lines, including MCL1. MCL1 is a member of the BCL2 family, which functions to prevent intrinsic apoptosis and has been implicated in several cancers. Despite the overlapping functions of the BCL2 family members, PEL cells are only dependent on MCL1 suggesting that MCL1 may have non-redundant functions. To investigate why PEL cells exhibit selective addiction to MCL1, we inactivated the intrinsic apoptosis pathway by engineering BAX/BAK1 double knockout cells. In this context, PEL cells become resistant to MCL1 knockdown or MCL1 inactivation by the MCL1 inhibitor S63845, indicating that the main function of MCL1 in PEL cells is to prevent BAX/BAK1-mediated apoptosis. The selective requirement to MCL1 is due to MCL1 being expressed in excess over the BCL2 family. Ectopic expression of several BCL2 family proteins, as well as the KSHV BCL2 homolog, significantly decreased basal caspase 3/7 activity and buffered against staurosporine-induced apoptosis. Finally, over-expressed BCL2 family members can functionally substitute for MCL1, when it is inhibited by S63845. Together our data indicate that the expression levels of the BCL2 family likely explain why PEL tumor cells are highly addicted to MCL1. Importantly, our results suggest that caution should be taken when considering MCL1i as a monotherapy regimen for PEL, because resistance can easily develop. IMPORTANCEPrimary effusion lymphoma (PEL) is caused by Kaposis sarcoma-associated herpesvirus. We previously showed that PEL cell lines require the anti-apoptotic protein MCL1 for survival, but not the other BCL2 family proteins. This selective dependence to MCL1 is unexpected as the BCL2 family functions similarly in preventing intrinsic apoptosis. Recently, new roles for MCL1 not shared with the BCL2 family have emerged. Here, we show that non-canonical functions of MCL1 are unlikely essential. Instead, MCL1 mainly functions to prevent apoptosis. The specific requirement to MCL1 is due to MCL1 being expressed in excess over the BCL2 family. Consistent with this model, shifting these expression ratios changes the requirement away from MCL1 and towards the dominant BCL2 family gene. Together, our results indicate that although MCL1 is an attractive chemotherapeutic target to treat PEL, careful consideration must be taken as resistance to MCL1-specific inhibitors easily develops through BCL2 family overexpression.

microbiology↗

bioRxiv2020

Initial insights into the genetic epidemiology of SARS-CoV-2 isolates from Kerala suggest local spread from limited introductions

Coronavirus disease 2019 (COVID-19) rapidly spread from a city in China to almost every country in the world, affecting millions of individuals. Genomic approaches have been extensively used to understand the evolution and epidemiology of SARS-CoV-2 across the world. Kerala is a unique state in India well connected with the rest of the world through a large number of expatriates, trade, and tourism. The first case of COVID-19 in India was reported in Kerala in January 2020, during the initial days of the pandemic. The rapid increase in the COVID-19 cases in the state of Kerala has necessitated the understanding of the genetic epidemiology of circulating virus, evolution, and mutations in SARS-CoV-2. We sequenced a total of 200 samples from patients at a tertiary hospital in Kerala using COVIDSeq protocol at a mean coverage of 7,755X. The analysis identified 166 unique high-quality variants encompassing 4 novel variants and 89 new variants identified for the first time in SARS-CoV-2 samples isolated from India. Phylogenetic and haplotype analysis revealed that the circulating population of the virus was dominated (94.6% of genomes) by three distinct introductions followed by local spread, apart from identifying polytomies suggesting recent outbreaks. The genomes formed a monophyletic distribution exclusively mapping to the A2a clade. Further analysis of the functional variants revealed two variants in the S gene of the virus reportedly associated with increased infectivity and 5 variants that mapped to five primer/probe binding sites that could potentially compromise the efficacy of RT-PCR detection. To the best of our knowledge, this is the first and most comprehensive report of genetic epidemiology and evolution of SARS-CoV-2 isolates from Kerala.

genomics↗

bioRxiv2018

Preservation of cellular nano-architecture by the process of chemical fixation for nanopathology

Transformation in chromatin organization is one of the most universal markers of carcinogenesis. Microscale chromatin alterations have been a staple of histopathological diagnosis of neoplasia, and nanoscale alterations have emerged as a promising marker for cancer prognostication and the detection of predysplastic changes. While numerous methods have been developed to detect these alterations, most methods for sample preparation remain largely validated via conventional microscopy, and have not been examined with nanoscale sensitive imaging techniques. For these nanoscale sensitive techniques to become standard of care screening tools, new histological protocols must be developed that preserve nanoscale information. Partial Wave Spectroscopic (PWS) microscopy has recently emerged as a novel imaging technique sensitive to length scales ranging between 20 and 200 nanometers. As a label-free, high-throughput, and non-invasive imaging technique, PWS microscopy offers many advantages for risk stratification of early cancer, and is an ideal tool to quantify structural information during sample preparation. Therefore, in this work we applied PWS microscopy to systematically evaluate the effects of cytological preparation on the nanoscales changes of chromatin using two cell line models: Hela cells differentially treated with daunorubicin and TP53 differentially mutated ovarian carcinoma cells. Notably, we show that existing cytological preparation can be modified in order to maintain clinically relevant nanoscopic differences, paving the way for the emerging field of nanopathology.

biophysics↗

bioRxiv2017

A random-matrix theory of the number sense

Number sense, a spontaneous ability to process approximate numbers, has been documented in human adults, infants and newborns, and many other animals. Species as distant as monkeys and crows exhibit number-selective neuronal activity. How number sense can emerge in the absence of learning or fine tuning is currently unknown. We introduce a random matrix theory of self-organised neural states where numbers are coded by vectors of activation across multiple units, and where the vector codes for successive integers are obtained through multiplication by a fixed but random matrix. This cortical implementation of the \"von Mises\" algorithm explains many otherwise disconnected observations ranging from neural tuning curves in monkeys to looking times in neonates and cortical numerotopy in adults. The theory clarifies the origin of Weber-Fechners law and yields a novel and empirically validated prediction of multi-peak number neurons. Random matrices constitute a novel mechanism for the emergence of brain states coding for quantity.

neuroscience↗

bioRxiv2017

A protein phosphatase network controls temporal and spatial dynamics of differentiation commitment in human epidermis

Epidermal homeostasis depends on a balance between stem cell renewal and terminal differentiation. The transition between the two cell states, termed commitment, is poorly understood. Here we characterise commitment by integrating transcriptomic and proteomic data from disaggregated primary human keratinocytes held in suspension for up to 12h to induce differentiation. We find that cell detachment induces a network of protein phosphatases. The pro-commitment phosphatases - including DUSP6, PPTC7, PTPN1, PTPN13 and PPP3CA - promote differentiation by negatively regulating ERK MAPK and positively regulating AP1 transcription factors. Their activity is antagonised by concomitant upregulation of DUSP10. Boolean network modelling of phosphatase interactions identifies commitment as an inherently unstable biological switch between the stem and differentiated cell states. Furthermore, phosphatase expression is spatially regulated both in vivo and in vitro. We conclude that an auto-regulatory phosphatase network maintains epidermal homeostasis by controlling the onset and duration of commitment.

developmental biology↗

bioRxiv2017

A protein phosphatase network controls the temporal and spatial dynamics of differentiation commitment in human epidermis

Epidermal homeostasis depends on a balance between stem cell renewal and terminal differentiation1,2. While progress has been made in characterising the stem and differentiated cell compartments3, the transition between the two cell states, termed commitment4, is poorly understood. Here we characterise commitment by integrating transcriptomic and proteomic data from disaggregated primary human keratinocytes held in suspension for up to 12h. We have previously shown that commitment begins at approximately 4h and differentiation is initiated by 8h5. We find that cell detachment induces a network of protein phosphatases. The pro-commitment phosphatases - including DUSP6, PPTC7, PTPN1, PTPN13 and PPP3CA - promote terminal differentiation by negatively regulating ERK MAPK and positively regulating key API transcription factors. Their activity is antagonised by concomitant upregulation of the anti-commitment phosphatase DUSP10. The phosphatases form a dynamic network of transient positive and negative interactions, with DUSP6 predominating at commitment. Boolean network modelling identifies a mandatory switch between two stable states (stem cell and differentiated cell) via an unstable (committed) state. In addition phosphatase expression is spatially regulated relative to the location of stem cells, both in vivo and in response to topographical cues in vitro. We conclude that an auto-regulatory phosphatase network maintains epidermal homeostasis by controlling the onset and duration of commitment.

cell biology↗