Publications by authors named "Geethu E Thomas"

5 Publications

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A genome-wide CRISPR/Cas9 screen in acute myeloid leukemia cells identifies regulators of TAK-243 sensitivity.

JCI Insight 2021 Mar 8;6(5). Epub 2021 Mar 8.

Princess Margaret Cancer Centre, University Health Network, Toronto, Ontario, Canada.

TAK-243 is a first-in-class inhibitor of ubiquitin-like modifier activating enzyme 1 that catalyzes ubiquitin activation, the first step in the ubiquitylation cascade. Based on its preclinical efficacy and tolerability, TAK-243 has been advanced to phase I clinical trials in advanced malignancies. Nonetheless, the determinants of TAK-243 sensitivity remain largely unknown. Here, we conducted a genome-wide CRISPR/Cas9 knockout screen in acute myeloid leukemia (AML) cells in the presence of TAK-243 to identify genes essential for TAK-243 action. We identified BEN domain-containing protein 3 (BEND3), a transcriptional repressor and a regulator of chromatin organization, as the top gene whose knockout confers resistance to TAK-243 in vitro and in vivo. Knockout of BEND3 dampened TAK-243 effects on ubiquitylation, proteotoxic stress, and DNA damage response. BEND3 knockout upregulated the ATP-binding cassette efflux transporter breast cancer resistance protein (BCRP; ABCG2) and reduced the intracellular levelsof TAK-243. TAK-243 sensitivity correlated with BCRP expression in cancer cell lines of different origins. Moreover, chemical inhibition and genetic knockdown of BCRP sensitized intrinsically resistant high-BCRP cells to TAK-243. Thus, our data demonstrate that BEND3 regulates the expression of BCRP for which TAK-243 is a substrate. Moreover, BCRP expression could serve as a predictor of TAK-243 sensitivity.
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http://dx.doi.org/10.1172/jci.insight.141518DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC8021101PMC
March 2021

Transduction of Primary AML Cells with Lentiviral Vector for Study or Engraftment.

STAR Protoc 2020 Dec 25;1(3):100163. Epub 2020 Nov 25.

Princess Margaret Cancer Centre, University Health Network, Room 8-706, 101 College St., Toronto, ON M5G1L7, USA.

We describe a method to silence genes in primary acute myeloid leukemia cells by transducing them with shRNA in lentiviral vectors. The transduction of primary non-adherent cells is particularly challenging. The protocol will aid in performing such experiments and is particularly helpful to prepare cells for engraftment studies. Use of a special medium supplemented with cytokines preserves the viability of the leukemic stem cells and their ability to engraft the marrow of immune-deficient mice. For complete details on the use and execution of this protocol, please refer to Singh et al. (2020).
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http://dx.doi.org/10.1016/j.xpro.2020.100163DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7757357PMC
December 2020

Disrupting Mitochondrial Copper Distribution Inhibits Leukemic Stem Cell Self-Renewal.

Cell Stem Cell 2020 06 15;26(6):926-937.e10. Epub 2020 May 15.

Princess Margaret Cancer Centre, University Health Network, Toronto, ON, Canada. Electronic address:

Leukemic stem cells (LSCs) rely on oxidative metabolism and are differentially sensitive to targeting mitochondrial pathways, which spares normal hematopoietic cells. A subset of mitochondrial proteins is folded in the intermembrane space via the mitochondrial intermembrane assembly (MIA) pathway. We found increased mRNA expression of MIA pathway substrates in acute myeloid leukemia (AML) stem cells. Therefore, we evaluated the effects of inhibiting this pathway in AML. Genetic and chemical inhibition of ALR reduces AML growth and viability, disrupts LSC self-renewal, and induces their differentiation. ALR inhibition preferentially decreases its substrate COX17, a mitochondrial copper chaperone, and knockdown of COX17 phenocopies ALR loss. Inhibiting ALR and COX17 increases mitochondrial copper levels which in turn inhibit S-adenosylhomocysteine hydrolase (SAHH) and lower levels of S-adenosylmethionine (SAM), DNA methylation, and chromatin accessibility to lower LSC viability. These results provide insight into mechanisms through which mitochondrial copper controls epigenetic status and viability of LSCs.
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http://dx.doi.org/10.1016/j.stem.2020.04.010DOI Listing
June 2020

Analyses between Reproductive Behavior, Genetic Diversity and Responsiveness in spp. Reveal an Adaptive Significance for Hemiclonality.

Front Plant Sci 2016 20;7:1913. Epub 2016 Dec 20.

Plant Disease Biology and Biotechnology, Rajiv Gandhi Centre for Biotechnology Thiruvananthapuram, India.

Mode of reproduction is generally considered to have long-range evolutionary implications on population survival. Because sexual reproduction produces genetically diverse genotypes, this mode of reproduction is predicted to positively influence the success potential of offspring in evolutionary arms race with parasites (Red queen) whereas, without segregation and recombination, the obligate asexual multiplication may push a species into extinction due to the steady accumulation of deleterious mutations (Muller's ratchet). However, the extent of linearity between reproductive strategies, genetic diversity and population fitness, and the contributions of different breeding strategies to population fitness are yet to be understood clearly. Genus belonging to the pan-tropic family Zingiberaceae represents a good system to study contributions of different breeding behavior on genetic diversity and population fitness, as this genus comprises species with contrasting breeding systems. In this study, we analyzed breeding behavior, amplified fragment length polymorphism diversity and response to the soft-rot pathogen in 18 natural populations of three wild spp.: , and , together with the obligately asexual cultivated congener, ginger (). Ginger showed an exceptionally narrow genetic base, and adding to this, all the tested cultivars were uniformly susceptible to soft-rot. Concordant with the postulates of Muller's ratchet, the background selection may be continuously pushing ginger into the ancestral state, rendering it inefficient in host-pathogen coevolution. and populations were sexual and genetically diverse; however, contrary to Red Queen expectations, the populations were highly susceptible to soft-rot. showed a hemiclonal breeding behavior. The populations inhabiting forest understory were large and continuous, sexual and genetically diverse, but were susceptible, whereas populations inhabiting the revenue land were fragmented and monoclonal, but were resistant. It may be possible that, when genetic recombination becomes at a premium due to the genetic constraints imparted by habitat fragmentation or pathogen pressure, Z. zerumbet.
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http://dx.doi.org/10.3389/fpls.2016.01913DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5167741PMC
December 2016

EB1 regulates attachment of Ska1 with microtubules by forming extended structures on the microtubule lattice.

Nat Commun 2016 05 26;7:11665. Epub 2016 May 26.

School of Biology, Indian Institute of Science Education and Research Thiruvananthapuram, CET Campus, Thiruvananthapuram 695016, India.

Kinetochore couples chromosome movement to dynamic microtubules, a process that is fundamental to mitosis in all eukaryotes but poorly understood. In vertebrates, spindle-kinetochore-associated (Ska1-3) protein complex plays an important role in this process. However, the proteins that stabilize Ska-mediated kinetochore-microtubule attachment remain unknown. Here we show that microtubule plus-end tracking protein EB1 facilitates Ska localization on microtubules in vertebrate cells. EB1 depletion results in a significant reduction of Ska1 recruitment onto microtubules and defects in mitotic chromosome alignment, which is also reflected in computational modelling. Biochemical experiments reveal that EB1 interacts with Ska1, facilitates Ska1-microtubule attachment and together stabilizes microtubules. Structural studies reveal that EB1 either with Ska1 or Ska complex forms extended structures on microtubule lattice. Results indicate that EB1 promotes Ska association with K-fibres and facilitates kinetochore-microtubule attachment. They also implicate that in vertebrates, chromosome coupling to dynamic microtubules could be mediated through EB1-Ska extended structures.
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http://dx.doi.org/10.1038/ncomms11665DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4894954PMC
May 2016