Cancer-associated fibroblasts promote the stemness of CD24+ liver cells via paracrine signaling

Cancer stem cells (CSCs), which support tumor progress in hepatocellular carcinoma (HCC) developed in fibrotic or cirrhotic livers, are regulated by the tumor microenvironment. Cancer-associated fibroblasts (CAFs) are the major component of the tumor stroma in HCC; however, the mechanisms by which CAFs contribute to stemness maintenance remain largely unknown. Here, we found that the expression of CD24 was high in HCC tissues compared with adjacent normal liver tissues, and positively correlated with the poor prognosis and α-SMA expression in CAFs. CD24+ cells isolated from HCC cell lines exhibited stemness properties of self-renewal, chemotherapy resistance, metastasis, and tumorigenicity in NOD/SCID mice. Moreover, CAF-derived HGF and IL6 enhanced the stemness properties of CD24+ cells via activating STAT3 Tyr705 phosphorylation. Blockade of HGF/c-Met or IL6/IL6R signaling significantly abolished the effect of CAFs on stemness properties, which compromised the activation of STAT3 pathway in CD24+ cells. Meanwhile, knockdown of STAT3 in CD24+ cells notably attenuated CAF-induced stemness characteristics of CD24+ cells. Furthermore, in HCC patients, higher expression of phospho-STAT3 was also demonstrated to be positively correlated with poor clinical outcomes. In summary, HGF and IL6 secreted by CAFs promoted the stemness properties of CD24+ cells through the phosphorylation of STAT3 signaling, and targeting the paracrine pathways may provide a new therapeutic strategy for HCC. KEY MESSAGES: CD24, identified as a marker for HCC CSCs, was positively correlated with the poor prognosis and α-SMA expression in CAFs. CAFs promoted self-renewal, chemotherapy resistance, metastasis, and tumorigenicity of CD24+ HCC cells. HGF and IL6 secreted by CAFs promoted the stemness properties of CD24+ HCC cells through the phosphorylation of STAT3.