TMEM147 aggravates the progression of HCC by modulating cholesterol homeostasis, suppressing ferroptosis, and promoting M2 polarization of TAMs

Abstract

Background: The endoplasmic reticulum (ER) regulates critical processes, including lipid synthesis, which can be affected by transmembrane proteins localized in the ER membrane. One of them, the transmembrane protein 147 (TMEM147) has been recently implicated for its role in hepatocellular carcinoma (HCC) tumorigenesis, though the mechanisms remain unclear. Here, we investigated the role of TMEM147 in HCC and its underlying mechanisms. Methods: Expression of TMEM147 was examined in human HCC and adjacent non-tumorous tissues using quantitative real-time polymerase chain reaction (qRT-PCR), western blotting, and immunohistochemistry. The effects of TMEM147 on HCC progression were investigated both in vitro and in vivo. Proteins interacting with TMEM147 were identified using RNAseq analysis, immunoprecipitation, and mass spectrometry analyses. Lipidomic analysis and enzyme-linked immunosorbent assay (ELISA) were employed to identify and analyze cholesterol and 27-hydroxycholesterol (27HC) contents. Comprehensive experimental methods were used to demonstrate ferroptosis in HCC cells. The fatty acid content of macrophages affected by TMEM147 was quantified using ELISA. Macrophage phenotypes were determined using various assays, such as immunofluorescence assay and flow cytometry analysis. Results: TMEM147 mRNA and protein levels were upregulated in HCC, and increased TMEM147 expression was associated with poor survival. TMEM147 promoted tumor cell proliferation and metastasis in vitro and in vivo. It was found to interact with the key sterol reductase DHCR7, which affected cellular cholesterol homeostasis and increased extracellular 27HC levels in HCC. TMEM147 promoted the expression of DHCR7 by enhancing the activity of the transcription factor, STAT2. 27HC upregulated the expression of glutathione peroxidase 4 in HCC, leading to ferroptosis resistance and promotion of HCC proliferation. HCC cell-derived 27HC activated PPARγ signaling and enhanced lipid metabolism in macrophages, thereby activating M2 polarization, and then promoted the invasion and migration of HCC. Conclusions: Our results indicated that TMEM147 confers ferroptosis resistance and M2 macrophage polarization, which are mainly dependent on the upregulation of cellular cholesterol homeostasis and 27HC secretion, leading to cancer growth and metastasis. Our findings suggest that the TMEM147/STAT2/DHCR7/27HC axis in the tumor microenvironment may serve as a promising therapeutic target for HCC.