Lipid desaturation-associated endoplasmic reticulum stress regulates MYCN gene expression in hepatocellular carcinoma cells

Abstract

Hepatocellular carcinoma (HCC) is the second leading cause of cancer-related deaths worldwide due to its high rate of recurrence, in part because of cancer stem cell (CSC)-dependent "field cancerization". Recently, we identified that the oncogene v-myc avian myelocytomatosis viral oncogene neuroblastoma derived homolog (MYCN) marked CSC-like subpopulations in heterogeneous HCC and served as a therapeutic target and prognostic marker for HCC. In this study, we explored the molecular basis of upregulated MYCN gene expression in HCC cells. Liquid chromatograph time-of-flight mass spectrometry-based metabolome analysis demonstrated that the content of unsaturated fatty acids was increased in MYCN high expression (MYCN high ) CSC-like HCC cells. Inhibition of lipid desaturation using either the chemical inhibitor or siRNA/shRNA against stearoyl-CoA desaturase-1 (SCD1) suppressed cell proliferation as well as MYCN gene expression in MYCN high HCC cells, grown as both monolayer and spheres. Further mechanistic study using RNA-seq based transcriptome analysis revealed that endoplasmic reticulum (ER) stress related signaling networks such as endocannabinoid cancer inhibition pathway were under the control of SCD1 in MYCN high HCC cells. Furthermore, the expression of ER stress-inducible transcription suppressor cyclic AMP-dependent transcription factor (ATF3) was downregulated in MYCN high CSC-like HCC cells and CSC-rich spheroids, which was upregulated by inhibition of lipid desaturation or treatment with acyclic retinoid (ACR). Lipid profiling using NMR spectroscopy revealed that the ACR dramatically reduced the content of unsaturated fatty acids in HCC cells. The chemical inducer of ER stress inhibited MYCN gene expression, while the chemical inhibitor of ER stress or knockdown of ATF3 gene expression partially rescued the suppression of MYCN gene expression by ACR in MYCN high HCC cells. These data suggested that lipid desaturation-mediated ER stress signaling regulates MYCN gene expression in HCC cells and serves as a promising therapeutic target for the treatment and prevention of HCC.

Immunotherapy for targeting cancer stem cells in hepatocellular carcinoma

“…Related studies also have verified that there is a close link between NASH and CSCs in HCC. Qin and colleagues demonstrated that neuroblastoma derived homolog (MYCN) high expression (MYCN high ) CSC-like HCC cells have more unsaturated fatty acids, and lipid desaturation-mediated endoplasmic reticulum (ER) stress signaling regulates the expression of MYCN gene in HCC CSCs 68 . Chong et al .…”

Beyond the Warburg Effect: N-Myc Contributes to Metabolic Reprogramming in Cancer Cells

“…Qin et al (55) reported that signaling networks that regulate ER stress, characterized by the endocannabinoid cancer inhibition pathway, are regulated by stearoyl-CoA desaturase-1 (SCD1) in hepatic tumor-initiating cells with high N-Myc expression. SCD1 is a rate-limiting enzyme which contributes to the synthesis of monounsaturated fatty acids.…”

Molecular Mechanisms of MYCN Dysregulation in Cancers

“…Moreover, N-MYC regulates PLAGL2 transcription through five N-MYC-binding E-boxes in the PLAGL2 promoter region, forming a positively regulatory loop between the two transcription factors, which is crucial for expression of each other in neuroblastoma tumors ( 90 ). Lipid desaturation-associated endoplasmic reticulum (ER) stress inhibits MYCN expression via upregulating the transcriptional repressor ATF3 in hepatocellular carcinoma cells ( 91 ). Since these transcription factors including SP1, E2F2, and PLAGL2 are involved in the regulation of MYCN expression, they mediate the effects of metabolic change and pharmacological treatment on MYCN expression and MYCN -driven tumors ( 92 ).…”

“…Loss of E2F binding or suppression of PLAGL2 expression mediates the negative regulation of MYCN expression by retinoic acid ( 89 , 90 ). Acyclic retinoid dampens MYCN gene expression and suppresses cell proliferation of MYCN -overexpressed hepatocellular carcinoma cells, at least in part by ER stress-induced ATF3 signaling pathway ( 91 ).…”