{
  "abstract": "Background Phospholipase C gamma 1 (PLCG1) plays a pivotal role in transducing T cell receptor (TCR) signaling. PLCG1 is frequently mutated in T-cell lymphomas such as adult T-cell leukemia/lymphoma (ATLL). However, the pathogenic mechanisms and clinical significance of PLCG1 mutation in T-cell malignancies remain largely undefined. Methods and Results Leukemia-associated PLCG1 mutants (R48W, S345F, and D1165H) exhibited markedly enhanced LAT condensation compared to wild type in both biochemical reconstitution assays and Jurkat T cells, accompanied by increased downstream calcium influx and ERK phosphorylation following TCR stimulation. To investigate their pathological impact, we ectopically expressed wild-type or mutant PLCG1 in human primary T cells via lentiviral transduction. PLCG1 mutations promoted primary T cell activation and proliferation in the absence of TCR stimulation, indicative of a cell-autonomous activation phenotype. This phenotype was recapitulated in Hut78 cells, as evidenced by elevated ERK phosphorylation. Furthermore, PLCG1 mutations conferred a gain-of-function phenotype characterized by the formation of T cell aggregates in Hut78 cells. Co-culture assays revealed that these PLCG1 mutation-driven aggregates co-clustered with and activated neighboring wild-type Hut78 cells, suggesting a previously unrecognized mechanism of bystander intercellular T cell activation. This effect correlated with increased ICAM1 expression and was functionally linked to ICAM1-LFA-1-mediated intercellular signaling. Consistently, ERK phosphorylation was reduced in a dose-dependent manner upon treatment with an LFA-1 blocking antibody.Drug sensitivity assays in Hut78 cells identified that PLCG1 mutations confer significant resistance to the histone deacetylase (HDAC) inhibitor SAHA, as evidenced by increased cell viability and reduced apoptosis compared to wild type. Notably, co-treatment with the ERK inhibitor LY3214996 effectively reversed SAHA resistance induced by PLCG1 mutations. To elucidate the mechanism underlying hyperactive PLCG1 signaling, we performed RNA-seq analysis and pull-down mass spectrometry in Hut78 cells. PLCG1 mutations specifically induce expression of alpha smooth muscle actin and directly bind to actin filament. CRISPR-Cas9-mediated knockout of alpha smooth muscle actin significantly attenuated phosphorylation of mutant PLCG1, suggesting that the PLCG1-actin interaction contributes to its hyperactivation. Supporting these findings, bulk RNA-seq analysis of ATLL patient samples revealed elevated expression of both alpha smooth muscle actin and ICAM1 compared to healthy donors.Conclusions These findings provide mechanistic insights into hyperactive PLCG1 signaling in T-cell malignancies implicating both intracellular LAT-ERK axis and intercellular ICAM1-LFA-1-ERK axis. Our study highlights a potential combinatorial therapeutic strategy employing ERK inhibition to overcome resistance to HDAC inhibitors in cancers.",
  "authors": [
    {
      "affiliations": [
        "Yale University, New Haven, CT, USA"
      ],
      "name": "Longhui Zeng"
    },
    {
      "affiliations": [
        "Yale School of Medicine, New Haven, CT, USA"
      ],
      "name": "Xinyan Zhang"
    },
    {
      "affiliations": [
        "Yale School of Medicine, New Haven, CT, USA"
      ],
      "name": "Yiwei Xiong"
    },
    {
      "affiliations": [
        "Yale School of Medicine, New Haven, CT, USA"
      ],
      "name": "Kazuki Sato"
    },
    {
      "affiliations": [
        "The University of North Carolina at Chapel Hill, Chapel Hill, NC, USA"
      ],
      "name": "Nicole Hajicek"
    },
    {
      "affiliations": [
        "National Cancer Center Research Institute, Tokyo, Japan"
      ],
      "name": "Yasunori Kogure"
    },
    {
      "affiliations": [
        "National Cancer Center Research Institute, Tokyo, Japan",
        "Keio University School of Medicine, Tokyo, Japan"
      ],
      "name": "Keisuke Kataoka"
    },
    {
      "affiliations": [
        "Kyoto University, Kyoto, Japan",
        "Kindai University Faculty of Medicine, Osakasayama, Japan"
      ],
      "name": "Seishi Ogawa"
    },
    {
      "affiliations": [
        "The University of North Carolina at Chapel Hill, Chapel Hill, NC, USA"
      ],
      "name": "John Sondek"
    },
    {
      "affiliations": [
        "Yale School of Medicine, New Haven, CT, USA"
      ],
      "name": "Xiaolei Su"
    }
  ],
  "title": "783 Oncogenic PLCG1 drives aberrant intra- and intercellular T cell activation",
  "uid": "244be198-a172-5ada-8535-3b6730f06dbb"
}