Exosomal circHIF1A derived from hypoxic-induced carcinoma-associated fibroblasts promotes hepatocellular carcinoma cell malignant phenotypes and immune escape.

ABSTRACT

Hypoxia is a hallmark of solid tumors. Cancer-associated fibroblasts (CAFs) are an important component of the tumor microenvironment, and CAF-derived exosomes are involved in cancer genesis and progression. Here, this work investigated the role and mechanism of exosomal circHIF1A derived from hypoxia-induced CAFs in hepatocellular carcinoma (HCC) tumorigenesis. CAFs isolated from fresh HCC tissues were incubated in normoxia or hypoxia condition (N/CAFs or H/CAFs), and then the exosomes from N/CAFs or H/CAFs were isolated for functional analysis. Cell proliferation, migration and invasion were analyzed by cell counting kit-8, colony formation, and transwell assays. Immune evasion was evaluated by measuring the cytotoxicity and viability of CD8+T cells. qRT-PCR and western blotting analyses were used for the level measurement of genes and proteins. The binding between Hu antigen R (HuR) and circHIF1A or Programmed death ligand 1 (PD-L1) was analyzed by RNA immunoprecipitation assay. Functionally, we found that CAFs, especially CAFs under hypoxic stress (H/CAFs), promoted the proliferation, migration, invasion and EMT progression in HCC cells, as well as induced immune escape by suppressing CD8+T cell cytotoxicity and activity in an exosome-dependent manner. H/CAFs-derived exosomes showed highly expressed circHIF1A, and could secrete circHIF1A into HCC cells via exosomes. The oncogenic effects of H/CAFs-secreted exosomes were abolished by circHIF1A knockdown. Mechanistically, circHIF1A interacted with HuR to stabilize PD-L1 expression in HCC cells. Meanwhile, circHIF1A silencing suppressed HCC cell proliferation, mobility and immune escape by regulating PD-L1 expression. In all, exosomal circHIF1A derived from hypoxic-induced CAFs promoted the proliferation, migration, invasion, EMT progression and immune escape in HCC cells by up-regulating PD-L1 expression in a HuR-dependent manner.