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Vasudevan, S.

Publications and source records attributed to Vasudevan, S..

25 records · Page 2Linked to original sources

Overcoming Resistance to BRAFV600E Inhibition in Melanoma by Deciphering and Targeting Personalized Protein Network Alterations

BRAFV600E melanoma patients, despite initially responding to the clinically prescribed anti-BRAFV600E therapy, often relapse and their tumors develop drug resistance. While it is widely accepted that these tumors are originally driven by the BRAFV600E mutation, they often eventually diverge and become supported by various signaling networks. Therefore, patient-specific altered signaling signatures should be deciphered and treated individually. In this study, we design individualized melanoma combination treatments based on personalized network alterations. Using an information-theoretic approach, we compute high-resolution patient-specific altered signaling signatures. These altered signaling signatures each consist of several co-expressed subnetworks, which should all be targeted to optimally inhibit the entire altered signaling flux. Based on these data, we design smart, personalized drug combinations, often consisting of FDA-approved drugs. We validate our approach in vitro and in vivo showing that individualized drug combinations that are rationally based on patient-specific altered signaling signatures are more efficient than the clinically used anti-BRAFV600E or BRAFV600E/MEK targeted therapy. Furthermore, these drug combinations are highly selective, as a drug combination efficient for one BRAFV600E tumor is significantly less efficient for another, and vice versa. The approach presented herein can be broadly applicable to aid clinicians to rationally design patient-specific anti-melanoma drug combinations.

systems biology↗

Circulating adiponectin mediates the association between omentin gene polymorphism and cardiometabolic health in Asian Indians

BackgroundPlasma omentin levels have been shown to be associated with circulating adiponectin concentrations and cardiometabolic disease-related outcomes. However, the findings have been inconsistent due to high level of confounding. In this study, we aim to examine the association of omentin gene polymorphism with plasma adiponectin levels and cardiometabolic health status using a genetic approach, which is less prone to confounding, and investigate whether these associations are modified by lifestyle factors such as diet and physical activity. MethodsThe study included 945 normal glucose tolerant and 941 unrelated individuals with type 2 diabetes randomly selected from the Chennai Urban Rural Epidemiology Study (CURES), in southern India. Study participants were further classified into cardiometabolically healthy and unhealthy, where cardiometabolically healthy were those without hypertension, diabetes, and dyslipidemia. Fasting serum adiponectin levels were measured by radioimmunoassay. The A326T (rs2274907) single nucleotide polymorphism (SNP) in the exon 4 of the omentin gene was screened by polymerase chain reaction-restriction fragment length polymorphism and direct sequencing. ResultsThe A allele of the omentin SNP was significantly associated with lower adiponectin concentrations after adjusting for age, sex, body mass index (BMI), waist circumference (WC) and cardiometabolic health status (p=1.90 x 10-47). There was also a significant association between circulating adiponectin concentrations and cardiometabolic health status after adjusting for age, sex, BMI, WC and Omentin SNP (p=7.47x10-10). However, after adjusting for age, sex, BMI, WC and adiponectin levels, the association of A allele with cardiometabolic health status disappeared (p=0.79) suggesting that adiponectin serves as a mediator of the association between omentin SNP and cardiometabolic health status. There were no significant interactions between the SNP and dietary factors on adiponectin levels and cardiometabolic health status (p>0.25, for all comparisons). ConclusionsOur findings show that adiponectin might function as a mechanistic link between omentin SNP and increased risk of cardiometabolic diseases independent of common and central obesity in this Asian Indian population. Further studies are required to confirm the molecular mechanisms involved in this triangular relationship between omentin gene, adiponectin and cardiometabolic diseases.

genetics↗

Crystal structures of full length DENV4 NS2B-NS3 reveal the dynamic interaction between NS2B and NS3 upon binding to protease inhibitors

Flavivirus is a genus of emerging and re-emerging arboviruses which include many significant human pathogens. Non-structural protein 3 (NS3), a multifunctional protein with N-terminal protease and C-terminal helicase, is essential in viral replication. The NS3 protease together with NS2B cofactor is an attractive antiviral target. A construct with an artificial glycine linker connecting the NS2B cofactor and NS3 protease has been used for structural, biochemical and drug-screening studies. The effect of this linker on dynamics and enzymatic activity of the protease was studied by several biochemical and NMR methods but the findings remained inconclusive. Here, we designed constructs of NS2B cofactor joined to full length DENV4 NS3 in three different manners, namely bNS2B47NS3 (bivalent), eNS2B47NS3(enzymatically cleavable) and gNS2B47NS3 (glycine-rich G4SG4 linker). We report the first crystal structures of linked and unlinked full-length NS2B-NS3 enzyme in its free state and also in complex with Bovine Pancreatic Trypsin Inhibitor (BPTI). These structures demonstrate that the NS2B-NS3 protease mainly adopts a closed conformation. BPTI binding is not essential to but favors the closed conformation by interacting with both NS2B and NS3. The artificial linker between NS2B and NS3 tends to induce the open conformation and interfere with the protease activity. This negative impact on the enzyme structure and function is restricted to the protease domain as the ATPase activities of these constructs are not affected.

biochemistry↗

Meiosis and Kinetochore genes are used by cancer cells as genome destabilizers and transformation catalysts

Cancer cells have an altered transcriptome which contributes to their altered behaviors compared to normal cells. Indeed, many tumors express high levels of genes participating in meiosis or kinetochore biology, but the role of this high expression has not been fully elucidated. In this study we explore the relationship between this overexpression and genome instability and transformation capabilities of cancer cells. For this, we obtained expression data from 5 different cancer types which were analyzed using computational information-theoretic analysis. We were able to show that highly expressed meiotic/kinetochore genes were enriched in the altered gene expression subnetworks characterizing unstable cancer types with high chromosome instability (CIN). However, altered subnetworks found in the cancers with low CIN did not include meiotic and kinetochore genes. Representative gene candidates, found by the analysis to be correlated with a CIN phenotype, were further explored by transfecting genomically-stable (HCT116) and unstable (MCF7) cancer cell lines with vectors overexpressing those genes. This overexpression resulted in an increase in the numbers of abnormal cell divisions and defective spindle formations and in increased transformation properties in stable cancer HCT116 cells. Interestingly, the same properties were less affected by the overexpressed genes in the unstable MCF7 cancer cells. Our results indicate that overexpression of both meiosis and kinetochore genes is capable of driving genomic instability and cancer progression.

cancer biology↗

JNK MAPK Regulates IFN-Stimulated Genes and Cell Adhesion in Chemoresistant, Quiescent Leukemic Cells

Cancer cells survive environmental stresses including DNA damage-inducing chemotherapy by entering cellular quiescence (G0). In our previous study, to elucidate how G0 leukemic cells become resistant to chemotherapy, we profiled them at the transcriptome, translatome and proteome levels. We interrogated these datasets and find that IFN-stimulated genes are enhanced in our G0 models of leukemic cells induced by chemotherapy or serum-starvation. Mechanistically, upon induction of G0, STAT1 is phosphorylated on tyrosine 701, leading to transcription of IFN-stimulated genes. Importantly, our data reveal that activation of JNK and p38 MAPK is integral to STAT1 phosphorylation and expression of IFN-stimulated genes. Pharmacological inhibition of JNK or p38 MAPK greatly reduced expression of IFN-stimulated genes as well as STAT1 phosphorylation, revealing a JNK-STAT1 pathway that regulates IFN-stimulated genes. We find that the JNK-STAT1 pathway enhances adherence of G0 leukemic cells. Consistently, inhibition of the JNK-STAT1 pathway dramatically reduced the number of adherent G0 cells. STAT1 is transiently phosphorylated within 24 hours of chemotherapy, leading to transcriptional expression of IFN-stimulated genes. Subsequently, translational regulation attenuates their expression in G0 leukemic cells. These studies uncover translational and transcriptional regulation of IFN-stimulated genes by a JNK-STAT1 pathway that enhances cell adhesion in G0 leukemic cells.

immunology↗

Gene Sets Analysis using Network Patterns

High throughput assays allow researchers to identify sets of genes related to experimental conditions or phenotypes of interest. These gene sets are frequently subjected to functional interpretation using databases of gene annotations. Recent approaches have extended this approach to also consider networks of gene-gene relationships and interactions when attempting to characterize properties of a gene set. We present here a supervised learning algorithm for gene set analysis, called GeneSet MAPR, that for the first time explicitly considers the patterns of direct as well as indirect relationships present in the network to quantify gene-gene similarities and then report shared properties of the gene set. Our extensive evaluations show that GeneSet MAPR performs better than other network-based methods for the task of identifying genes related to a given gene set, enabling more reliable functional characterizations of the gene set. When applied to the set of response-associated genes from a triple negative breast cancer study, GeneSet MAPR uncovers gene families such as claudins, kallikreins, and collagen type alpha chains related to patients response to treatment, and which are not uncovered with traditional analysis.

systems biology↗

A post-transcriptional program of chemoresistance by AU-rich elements/TTP in cancer quiescence

BackgroundQuiescence (G0) is a transient, cell cycle-arrested state. By entering G0, cancer cells survive unfavorable conditions such as chemotherapy and cause relapse. While G0 cells have been studied at the transcriptome level, how post-transcriptional regulation contributes to their chemoresistance remains unknown.\n\nResultsWe induced chemoresistant and quiescent (G0) leukemic cells by serum-starvation or chemotherapy treatment. To study post-transcriptional regulation in G0 leukemic cells, we systematically analyzed their transcriptome, translatome, and proteome. We find that our resistant G0 cells recapitulate gene expression profiles of in vivo chemoresistant leukemic and G0 models. In G0 cells, canonical translation initiation is inhibited; yet we find that inflammatory genes are highly translated, indicating alternative post-transcriptional regulation. Importantly, AU-rich elements (AREs) are significantly enriched in the up-regulated G0 translatome and transcriptome. Mechanistically, we find the stress-responsive p38 MAPK-MK2 signaling pathway stabilizes ARE mRNAs by phosphorylation and inactivation of mRNA decay factor, tristetraprolin (TTP) in G0. This permits expression of ARE-bearing TNF and DUSP1 that promote chemoresistance. Conversely, inhibition of TTP phophorylation by p38 MAPK inhibitors and non-phosphorylatable TTP mutant decreases ARE mRNAs and sensitizes leukemic cells to chemotherapy. Furthermore, co-inhibiting p38 MAPK and TNF--prior to or along with chemotherapy--substantially reduced chemoresistance in primary leukemic cells ex vivo and in vivo.\n\nConclusionsThese studies uncover post-transcriptional regulation underlying chemoresistance in leukemia. Our data reveal the p38 MAPK-MK2-TTP axis as a key regulator of expression of ARE bearing mRNAs that promote chemoresistance. By disrupting this pathway, we developed an effective combination therapy against chemosurvival.

cancer biology↗