Browsing by Author "Malarkannan, Subramaniam"

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    Mirc11 Disrupts Inflammatory but Not Cytotoxic Responses of NK Cells
    (AACR, 2019-10) Nanbakhsh, Arash; Srinivasamani, Anupallavi; Holzhauer, Sandra; Riese, Matthew J.; Zheng, Yongwei; Wang, Demin; Burns, Robert; Reimer, Michael H.; Rao, Sridhar; Lemke, Angela; Tsaih, Shirng-Wern; Flister, Michael J.; Lao, Shunhua; Dahl, Richard; Thakar, Monica S.; Malarkannan, Subramaniam; Microbiology and Immunology, School of Medicine
    Natural killer (NK) cells generate proinflammatory cytokines that are required to contain infections and tumor growth. However, the posttranscriptional mechanisms that regulate NK cell functions are not fully understood. Here, we define the role of the microRNA cluster known as Mirc11 (which includes miRNA-23a, miRNA-24a, and miRNA-27a) in NK cell–mediated proinflammatory responses. Absence of Mirc11 did not alter the development or the antitumor cytotoxicity of NK cells. However, loss of Mirc11 reduced generation of proinflammatory factors in vitro and interferon-γ–dependent clearance of Listeria monocytogenes or B16F10 melanoma in vivo by NK cells. These functional changes resulted from Mirc11 silencing ubiquitin modifiers A20, Cbl-b, and Itch, allowing TRAF6-dependent activation of NF-κB and AP-1. Lack of Mirc11 caused increased translation of A20, Cbl-b, and Itch proteins, resulting in deubiquitylation of scaffolding K63 and addition of degradative K48 moieties on TRAF6. Collectively, our results describe a function of Mirc11 that regulates generation of proinflammatory cytokines from effector lymphocytes.
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    Rap1b facilitates NK cell functions via IQGAP1-mediated signalosomes
    (Rockefeller University Press, 2010-08-23) Awasthi, Aradhana; Samarakoon, Asanga; Chu, Haiyan; Kamalakannan, Rajasekaran; Quilliam, Lawrence A.; Chrzanowska-Wodnicka, Magdalena; White, Gilbert C., II; Malarkannan, Subramaniam; Biochemistry and Molecular Biology, School of Medicine
    Rap1 GTPases control immune synapse formation and signaling in lymphocytes. However, the precise molecular mechanism by which Rap1 regulates natural killer (NK) cell activation is not known. Using Rap1a or Rap1b knockout mice, we identify Rap1b as the major isoform in NK cells. Its absence significantly impaired LFA1 polarization, spreading, and microtubule organizing center (MTOC) formation in NK cells. Neither Rap1 isoform was essential for NK cytotoxicity. However, absence of Rap1b impaired NKG2D, Ly49D, and NCR1-mediated cytokine and chemokine production. Upon activation, Rap1b colocalized with the scaffolding protein IQGAP1. This interaction facilitated sequential phosphorylation of B-Raf, C-Raf, and ERK1/2 and helped IQGAP1 to form a large signalosome in the perinuclear region. These results reveal a previously unrecognized role for Rap1b in NK cell signaling and effector functions.