TY - JOUR T1 - Methionine uptake via the SLC43A2 transporter is essential for regulatory T-cell survival. JF - Life Sci Alliance Y1 - 2022 A1 - Saini, Neetu A1 - Naaz, Afsana A1 - Metur, Shree Padma A1 - Gahlot, Pinki A1 - Walvekar, Adhish A1 - Dutta, Anupam A1 - Davathamizhan, Umamaheswari A1 - Sarin, Apurva A1 - Laxman, Sunil KW - Interleukin-2 KW - Methionine KW - Racemethionine KW - Solute Carrier Proteins KW - T-Lymphocytes, Regulatory AB -

Cell death, survival, or growth decisions in T-cell subsets depend on interplay between cytokine-dependent and metabolic processes. The metabolic requirements of T-regulatory cells (Tregs) for their survival and how these are satisfied remain unclear. Herein, we identified a necessary requirement of methionine uptake and usage for Tregs survival upon IL-2 deprivation. Activated Tregs have high methionine uptake and usage to S-adenosyl methionine, and this uptake is essential for Tregs survival in conditions of IL-2 deprivation. We identify a solute carrier protein SLC43A2 transporter, regulated in a Notch1-dependent manner that is necessary for this methionine uptake and Tregs viability. Collectively, we uncover a specifically regulated mechanism of methionine import in Tregs that is required for cells to adapt to cytokine withdrawal. We highlight the need for methionine availability and metabolism in contextually regulating cell death in this immunosuppressive population of T cells.

VL - 5 IS - 12 ER - TY - JOUR T1 - Sirtuin1 meditated modification of Notch1 intracellular domain regulates nucleolar localization and activation of distinct signaling cascades. JF - Front Cell Dev Biol Y1 - 2022 A1 - Saini, Neetu A1 - Bheeshmachar, Geetha A1 - Sarin, Apurva AB -

Notch signaling is involved in cell fate decisions in the development and maintenance of tissue homeostasis. Spatial regulation of the Notch1 intracellular domain (NIC1), has been shown to underpin signaling outcomes mediated by this receptor. We recently reported a putative Nucleolar Localization Sequence (NoLS) in NIC1. Here we investigate if the putative NoLS identified in NIC1 regulates localization in the nucleolus and anti-apoptotic activity. Confocal imaging of live cells expressing NIC1 or forms modified by deletion or site-directed mutagenesis established that the putative NoLS in NIC1 is required for nucleolar localization and regulated by the deacetylase Sirtuin1. Subsequent analysis of anti-apoptotic activity revealed signaling cascades linked to nucleolar localization. For this, etoposide and 4-Nitroquinoline 1-oxide, an inhibitor of topoisomerase-II and a UV mimetic drug respectively, were used as prototypic triggers of genomic damage in a mammalian cell line. While NIC1 blocked apoptosis regardless of its localization to the nucleoplasm or nucleolus, modifications of NIC1 which promoted localization to the nucleolus triggered a dependence on the nucleolar proteins fibrillarin and nucleolin for anti-apoptotic activity. Further, cells co-expressing NIC1 and Sirtuin1 (but not its catalytically inactive form), confirmed both spatial regulation and the switch to dependence on the nucleolar proteins. Finally, site-directed mutagenesis showed that the NoLS lysine residues are targets of Sirtuin1 activity. NIC1 mediated transcription is not similarly regulated. Thus, NIC1 localization to the nucleolus is regulated by Sirtuin1 modification of the lysine residues in NoLS and triggers a distinct signaling cascade involving nucleolar intermediates for anti-apoptotic activity.

VL - 10 ER - TY - JOUR T1 - Genomic characterization and epidemiology of an emerging SARS-CoV-2 variant in Delhi, India. JF - Science Y1 - 2021 A1 - Dhar, Mahesh S A1 - Marwal, Robin A1 - Vs, Radhakrishnan A1 - Ponnusamy, Kalaiarasan A1 - Jolly, Bani A1 - Bhoyar, Rahul C A1 - Sardana, Viren A1 - Naushin, Salwa A1 - Rophina, Mercy A1 - Mellan, Thomas A A1 - Mishra, Swapnil A1 - Whittaker, Charles A1 - Fatihi, Saman A1 - Datta, Meena A1 - Singh, Priyanka A1 - Sharma, Uma A1 - Ujjainiya, Rajat A1 - Bhatheja, Nitin A1 - Divakar, Mohit Kumar A1 - Singh, Manoj K A1 - Imran, Mohamed A1 - Senthivel, Vigneshwar A1 - Maurya, Ranjeet A1 - Jha, Neha A1 - Mehta, Priyanka A1 - A, Vivekanand A1 - Sharma, Pooja A1 - Vr, Arvinden A1 - Chaudhary, Urmila A1 - Soni, Namita A1 - Thukral, Lipi A1 - Flaxman, Seth A1 - Bhatt, Samir A1 - Pandey, Rajesh A1 - Dash, Debasis A1 - Faruq, Mohammed A1 - Lall, Hemlata A1 - Gogia, Hema A1 - Madan, Preeti A1 - Kulkarni, Sanket A1 - Chauhan, Himanshu A1 - Sengupta, Shantanu A1 - Kabra, Sandhya A1 - Gupta, Ravindra K A1 - Singh, Sujeet K A1 - Agrawal, Anurag A1 - Rakshit, Partha A1 - Nandicoori, Vinay A1 - Tallapaka, Karthik Bharadwaj A1 - Sowpati, Divya Tej A1 - Thangaraj, K A1 - Bashyam, Murali Dharan A1 - Dalal, Ashwin A1 - Sivasubbu, Sridhar A1 - Scaria, Vinod A1 - Parida, Ajay A1 - Raghav, Sunil K A1 - Prasad, Punit A1 - Sarin, Apurva A1 - Mayor, Satyajit A1 - Ramakrishnan, Uma A1 - Palakodeti, Dasaradhi A1 - Seshasayee, Aswin Sai Narain A1 - Bhat, Manoj A1 - Shouche, Yogesh A1 - Pillai, Ajay A1 - Dikid, Tanzin A1 - Das, Saumitra A1 - Maitra, Arindam A1 - Chinnaswamy, Sreedhar A1 - Biswas, Nidhan Kumar A1 - Desai, Anita Sudhir A1 - Pattabiraman, Chitra A1 - Manjunatha, M V A1 - Mani, Reeta S A1 - Arunachal Udupi, Gautam A1 - Abraham, Priya A1 - Atul, Potdar Varsha A1 - Cherian, Sarah S AB -

Delhi, the national capital of India, has experienced multiple SARS-CoV-2 outbreaks in 2020 and reached population seropositivity of over 50% by 2021. During April 2021, the city became overwhelmed by COVID-19 cases and fatalities, as a new variant B.1.617.2 (Delta) replaced B.1.1.7 (Alpha). A Bayesian model explains the growth advantage of Delta through a combination of increased transmissibility and reduced sensitivity to immune responses generated against earlier variants (median estimates; ×1.5-fold, 20% reduction). Seropositivity of an employee and family cohort increased from 42% to 87.5% between March and July 2021, with 27% reinfections, as judged by increased antibody concentration after a previous decline. The likely high transmissibility and partial evasion of immunity by the Delta variant contributed to an overwhelming surge in Delhi.

ER - TY - JOUR T1 - Spatial regulation and generation of diversity in signaling pathways. JF - J Biosci Y1 - 2021 A1 - Saini, Neetu A1 - Sarin, Apurva AB -

Signaling pathways orchestrate diverse cellular outcomes in the same tissue, spatially and temporally. These interactions, which are played out in micro-environments within cells and involve a relatively small number of core pathways, are the key to the development and function of multi-cellular organisms. How these outcomes are regulated has prompted interest in intracellular mechanisms that build diversity in signaling outcomes. This review specifically addresses spatial positioning of molecules as a means of enabling interactions and novel outcomes of signaling cascades. Using the Notch and Ras pathways as exemplars, we describe mechanisms that contribute to diverse signaling outcomes.

VL - 46 ER - TY - JOUR T1 - Nucleolar localization of the Notch4 intracellular domain underpins its regulation of the cellular response to genotoxic stressors. JF - Cell Death Discov Y1 - 2020 A1 - Saini, Neetu A1 - Sarin, Apurva AB -

Cell survival is one of the many cellular processes regulated by Notch family of proteins. A comparison of human breast cancer cell lines, which differ in the levels of endogenous Notch4, implicated the protein in regulating susceptibility to apoptosis triggered by genomic damage. In agreement with this observation, increased susceptibility to genotoxic damage was observed following siRNA ablations of Notch4 in two breast cancer cell lines. Further, overexpressing Notch4 intracellular domain (NIC4) tagged to GFP (NIC4-GFP), protected cells from apoptosis triggered by genotoxic drugs. In cells immune-stained for endogenous Notch4, protein was detected in the nucleolus and nucleoplasm, which was also confirmed by the co-localization of NIC4-GFP with RFP-tagged nucleolar proteins in breast cancer cells or the unrelated HEK cell line. Linking functional outcomes to nucleolar localization, NIC4-GFP protection from apoptosis, required the nucleolar proteins Nucleolin and Fibrillarin. Consistently, immunoprecipitation analysis revealed associations between nucleolar proteins-Nucleolin and Nucleophosmin-and Notch4. Microscopy-based biophysical analysis of live cells showed that nucleolar and nucleoplasmic pools of NIC4-GFP are mobile, with some sequestration of nucleolar NIC4-GFP pools. A nucleolar excluded form, NIC4_3RA-GFP, generated by site-directed mutagenesis of the nucleolar localization sequence in NIC4, could not protect from apoptosis triggered by genotoxic stressors. However, transcriptional activity or protection from apoptosis triggered by endoplasmic stress was comparable in cells expressing NIC4_3RA-GFP or NIC4-GFP. Together, the data show that nucleolar localization of NIC4 is critical for the regulation of genomic damage and may be uncoupled from its activities in the nucleoplasm. This study identifies intrinsic features of NIC4 that regulate signaling outcomes activated by the receptor by controlling its spatial localization.

VL - 6 ER - TY - JOUR T1 - Notch1 regulated autophagy controls survival and suppressor activity of activated murine T-regulatory cells. JF - Elife Y1 - 2016 A1 - Marcel, Nimi A1 - Sarin, Apurva AB -

Cell survival is one of several processes regulated by the Notch pathway in mammalian cells. Here we report functional outcomes of non-nuclear Notch signaling to activate autophagy, a conserved cellular response to nutrient stress, regulating survival in murine natural T-regulatory cells (Tregs), an immune subset controlling tolerance and inflammation. Induction of autophagy required ligand-dependent, Notch intracellular domain (NIC) activity, which controlled mitochondrial organization and survival of activated Tregs. Consistently, NIC immune-precipitated Beclin and Atg14, constituents of the autophagy initiation complex. Further, ectopic expression of an effector of autophagy (Atg3) or recombinant NIC tagged to a nuclear export signal (NIC-NES), restored autophagy and suppressor function in Notch1(-/-) Tregs. Furthermore, Notch1 deficiency in the Treg lineage resulted in immune hyperactivity, implicating Notch activity in Treg homeostasis. Notch1 integration with autophagy, revealed in these experiments, holds implications for Notch regulated cell-fate decisions governing differentiation.

VL - 5 ER -