Exosomal SLC16A1-AS1-induced M2 macrophages polarization facilitates hepatocellular carcinoma progression.

Macrophages are the most abundant alternative immune cells in the tumor microenvironment (TME). The cross-talk between macrophages and tumor cells provides an important shelter for the occurrence and development of tumors. As an important information transfer medium, exosomes play an important role in intercellular communication. Nonetheless, how exosomal lncRNAs coordinate the communication between tumor cells and immune cells in hepatocellular carcinoma (HCC) is incompletely understood. We found that HCC exosomes-derived antisense RNA of SLC16A1(SLC16A1-AS1) promoted the malignant progression of HCC by regulating macrophage M2-type polarization. Mechanistically, the HCC exosomal SLC16A1-AS1 enhanced mRNA stabilization of SLC16A1 in macrophage by promoting the interaction between 3' untranslated regions (3'UTR) of SLC16A1 mRNA and heterogeneous nuclear ribonucleoprotein A1 (HNRNPA1). As a lactate transporter, SLC16A1 accelerated lactate influx and then activated c-Raf/ERK signaling to induce M2 polarization of macrophages. Reciprocally, M2 macrophages secreted IL-6 to activate STAT3 and then induce METTL3 transcription in HCC cells, which increasing m6A methylation and stabilization of SLC16A1-AS1. In turn, the reciprocal SLC16A1-AS1/IL-6 signaling between HCC cells and M2 macrophages promoted the proliferation, invasion and glycolysis of HCC cells. Our study highlights that exosomal SLC16A1-AS1 acts as a signaling message that induces lactate-mediated M2 polarization of macrophages, and implies that SLC16A1-AS1 might be an applicable target for therapeutic treatment of HCC.