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Abstract
The P53-destabilizing TBC1D15-NOTCH protein interaction promotes self-renewal of tumor-initiating stem-like cells (TICs); however, the mechanisms governing the regulation of this pathway have not been fully elucidated. Here, we show that TBC1D15 stabilizes NOTCH and c-JUN through blockade of E3 ligase and CDK8 recruitment to phosphodegron sequences. Chromatin immunoprecipitation (ChIP-seq) analysis was performed to determine whether TBC1D15-dependent NOTCH1 binding occurs in TICs or non-TICs. The TIC population was isolated to evaluate TBC1D15-dependent NOTCH1 stabilization mechanisms. The tumor incidence in hepatocyte-specific triple knockout (Alb::CreERT2;Tbc1d15Flox/Flox;Notch1Flox/Flox;Notch2Flox/Flox;HCV-NS5A) Transgenic (Tg) mice and wild-type mice was compared after being fed an alcohol-containing Western diet (WD) for 12 months. The NOTCH1-TBC1D15-FIS1 interaction resulted in recruitment of mitochondria to the perinuclear region. TBC1D15 bound to full-length NUMB and to NUMB isoform 5, which lacks three Ser phosphorylation sites, and relocalized NUMB5 to mitochondria. TBC1D15 binding to NOTCH1 blocked CDK8- and CDK19-mediated phosphorylation of the NOTCH1 PEST phosphodegron to block FBW7 recruitment to Thr-2512 of NOTCH1. ChIP-seq analysis revealed that TBC1D15 and NOTCH1 regulated the expression of genes involved in mitochondrial metabolism-related pathways required for the maintenance of TICs. TBC1D15 inhibited CDK8-mediated phosphorylation to stabilize NOTCH1 and protect it from degradation The NUMB-binding oncoprotein TBC1D15 rescued NOTCH1 from NUMB-mediated ubiquitin-dependent degradation and recruited NOTCH1 to the mitochondrial outer membrane for the generation and expansion of liver TICs. A NOTCH-TBC1D15 inhibitor was found to inhibit NOTCH-dependent pathways and exhibited potent therapeutic effects in PDX mouse models. This unique targeting of the NOTCH-TBC1D15 interaction not only normalized the perinuclear localization of mitochondria but also promoted potent cytotoxic effects against TICs to eradicate patient-derived xenografts through NOTCH-dependent pathways.
Mitochondrial recruitment: TBC1D15’s role in stabilising NOTCH1
Cancer development often involves a small reservoir of cells known as tumor-initiating stem-like cells, which are resistant to treatment and can lead to cancer recurrence. Despite their significance, identifying and targeting these cells remains a challenge. In this study, researchers focused on a protein called TBC1D15 (oncofetal protein), which interacts with another protein, NOTCH1, to influence TIC behavior. Using mouse models and human cell lines, the team investigated how TBC1D15 affects TICs and explored potential therapeutic strategies. The study revealed that TBC1D15 promotes the self-renewal and growth of TICs by interacting with NOTCH1 and affecting mitochondrial function. The researchers also identified small molecules that can disrupt the TBC1D15-NOTCH1 interaction, offering a new approach to target TICs in cancer treatment. The results showed that interfering with the TBC1D15-NOTCH1 interaction could reduce the growth of TICs and potentially improve cancer treatment outcomes.
This summary was initially drafted using artificial intelligence, then revised and fact-checked by the author.
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1 University of Southern California, Departments of Molecular Microbiology and Immunology, Los Angeles, USA (GRID:grid.42505.36) (ISNI:0000 0001 2156 6853)
2 University of Southern California, Viterbi School of Engineering, Los Angeles, USA (GRID:grid.42505.36) (ISNI:0000 0001 2156 6853)
3 International Centre for Genetic Engineering and Biotechnology, Trieste, Italy (GRID:grid.425196.d) (ISNI:0000 0004 1759 4810)
4 University of Trieste, Department of Life Sciences, Trieste, Italy (GRID:grid.5133.4) (ISNI:0000 0001 1941 4308); Area Science Park-Padriciano, International Centre for Genetic Engineering and Biotechnology (ICGEB), Trieste, Italy (GRID:grid.425196.d) (ISNI:0000 0004 1759 4810); The AIRC Institute of Molecular Oncology, IFOM ETS, Milan, Italy (GRID:grid.7678.e) (ISNI:0000 0004 1757 7797)
5 Saint Louis University, School of Medicine, St Louis, USA (GRID:grid.262962.b) (ISNI:0000 0004 1936 9342)
6 University of Southern California, Department of Pathology, Los Angeles, USA (GRID:grid.42505.36) (ISNI:0000 0001 2156 6853); Southern California Research Center for ALPD and Cirrhosis, Los Angeles, USA (GRID:grid.42505.36) (ISNI:0000 0001 2156 6853)
7 University of Southern California, Departments of Molecular Microbiology and Immunology, Los Angeles, USA (GRID:grid.42505.36) (ISNI:0000 0001 2156 6853); Southern California Research Center for ALPD and Cirrhosis, Los Angeles, USA (GRID:grid.42505.36) (ISNI:0000 0001 2156 6853)