TGF-β1 Induced SOX18 Elevation Promotes Hepatocellular Carcinoma Progression and Metastasis through Transcriptionally Upregulating PD-L1 and CXCL12.

BACKGROUND AND AIMS: Hepatocellular carcinoma (HCC) is characterized by an immune-suppressive microenvironment, which contributes to tumor progression, metastasis and immunotherapy resistance. Identification of HCC-intrinsic factors regulating immunosuppressive microenvironment is urgently needed. Here, we aimed to elucidate the role of SYR-Related High-Mobility Group Box 18 (SOX18) in inducing immunosuppression and to validate novel combination strategies for SOX18-mediated HCC progression and metastasis.

METHODS: The role of SOX18 in HCC was investigated in orthotopic allografts and diethylinitrosamine/carbon tetrachloride (DEN/CCl4 ) induced spontaneous models by using murine cell lines, adeno-associated virus 8 and hepatocyte-specific knockin and knockout mice. The immune cellular composition in HCC microenvironment was evaluated by flow cytometry and immunofluorescence.

RESULTS: SOX18 overexpression promoted the infiltration of tumor-associated macrophages (TAMs) and regulatory T cells (Tregs) while diminishing cytotoxic T cells to facilitate HCC progression and metastasis in cell-derived allografts and chemically-induced HCC models. Mechanistically, transforming growth factor-beta 1 (TGF-β1) upregulated SOX18 expression by activating the Smad2/3 complex. SOX18 transactivated chemokine (C-X-C motif) ligand 12 and programmed death ligand 1 (PD-L1) to induce the immunosuppressive microenvironment. CXCL12 knockdown significantly attenuated SOX18-induced TAMs and Tregs accumulation and HCC dissemination. Antagonism of CXCR4, the cognate receptor of CXCL12, or selective knockout of CXCR4 in TAMs or Tregs likewise abolished SOX18-mediated effects. TGFβR1 inhibitor Vactosertib or CXCR4 inhibitor AMD3100 in combination with anti-PD-L1 dramatically inhibited SOX18-mediated HCC progression and metastasis.

CONCLUSIONS: SOX18 promoted the accumulation of immunosuppressive TAMs and Tregs in microenvironment by transactivating CXCL12 and PD-L1. CXCR4 inhibitor or TGFβR1 inhibitor in synergy with anti-PD-L1 represented a promising combination strategy to suppress HCC progression and metastasis.