Cell fate and metabolic reprogramming of tumor-initiating stem-like cells

Background & Aims: Tumor-initiating stem-like cells (TICs) are defective in maintaining asymmetric cell division and responsible for tumor recurrence. Stem cell markers such as Nanog have been implicated in various cancer, but whether they are functionally contributing to cancer pathogenesis has remained unclear. Novel NOTCH/NUMB-interacting protein, TBC1D15, is overexpressed and contributes to p53 degradation in TICs. Aims are to identify NANOG- or TBC1D15-mediated oncogenic mechanisms and to test tumorigenic roles. Methods: We determined novel targets of NANOG in tumor-initiating cells (TICs) from patient and mouse-models of hepatocellular carcinoma (HCC) using genome-wide NANOG-binding site analysis (ChIP-seq) and how Nanog is regulated at the transcriptional to promote oncogenesis and self-renewal in TICs. TBC1D15 interacting proteins were searched by large-scale immunoaffinity purification and LC-MS analysis. We examined HCC development in alcohol Western diet (AWD)-fed HCV NS5A Tg mice with hepatocyte-specific TBC1D15 deficiency or hepatocyte-specific expression of non-phosphorylatable NUMB mutations (non-p-NUMB). Results: Silencing NANOG inhibits tumor development in HCC mouse-models and genesis of TICs. NANOG binds genes of oxidative phosphorylation and b-oxidation in mitochondria. Silencing NANOG promotes oxidative phosphorylation and b-oxidation, indicating that NANOG is a suppressor of mitochondria-mediated energy production. We identified NuMA1, RANGAP1 and NOTCH1-4 as TBC1D15-interacting proteins. TBC1D15-NuMA1 association impaired NuMA1-LAN interaction which is essential for an asymmetric division machinery, thereby promoting TIC self-renewal. TBC1D15-NOTCH1 interaction activated and stabilized NOTCH1 and NOTCH1 Intracellular Domain (N1ICD) which in turn upregulated transcription of Nanog essential for TICs. Conclusions: These results suggest that NANOG-mediated metabolic reprogramming through suppression of mitochondria function in both experimental and clinical HCC downstream of TLR4/ NANOG generates TICs and drives liver tumorigenesis. TBC1D15 and p-NUMB are required for liver tumor development in vivo